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The 25 Bertram Project (Making the Power and Drive Line Decisions)

Making the decisions about any major project is always the hardest part for me. There always seem to be too many opinions, too many engines to choose from, too many design options, etc. The planning phase to a boat project needs to take 2 major elements into consideration. The rest will work itself out.

First is money. We all wish this was not a consideration but for most of us it is. Decide how much money you can put into the boat right up front, keep in mind that you don't have to be sitting on that pile of cash but rather have an estimate of the cash you will need to come up with over the time frame that the project will take to complete. At times my last boat project would sit for months waiting on cash, but hey there's always sanding, painting, etc. to keep you busy while the funds are low.

Second is skill level. Accurately access your own skill level. Can you completely gut a boat and start from scratch? Have you ever built anything of this magnitude from scratch? How's your tooling inventory? Do you have adequate space to handle something like this? Is this boat project all about fishing or is it about enjoying building the boat itself? If it's all about fishing, go find a decent boat in running condition and go fishing! The final question you should ask yourself is do you have the WILL to execute and complete the project?

Many of my decisions about building my 25 Bertram center around cash on hand for such frivolities as boats. But...if I can't do it right, I won't do it at all. I have built several boat in my life and it's a hobby that I love. The entire process is addictive to me...planning, finding the stuff, buying new stuff, fitting it all together and enjoying the finished product. But cash is definitely an issue around my house and most of the guys I run with.

Note on Drive Line Selection...

Most people that you are going to run across have pre-existing opinions about particular boats, engines, etc. 90% of boaters that you will discuss something like this with will NOT take the time to actually investigate the weights, COB, COG, etc. They just spit out their view and argue if yours differs. I have learned the hard way that to argue with someone that has no basis for their opinion is stupid and I rarely engage in this activity anymore. Hulls, engines, engine placement, etc. are not rocket science, but rather only very basic math, common sense and maintaining an over all view of the vessel, as a whole. Do your home work and go with what the math says will work. This is not a license to be an idiot. Be diligent in your research and if something that you "want" to do does not add up, don't do it! BUT, don't do it because YOU have determined that it will not work.


The power train was really never a problem for me to figure out. I really like in-line inboard boats. They are without argument the most dependable drive train that you can put into a boat, well a jet is extremely simple and very reliable but major bucks in a boat this size, and jets don't like heavy slow hulls from what I read. Here's where the problems came in to play for me on the Bertram 25. I became involved in the on line discussion boards operated by the Bertram fanatics and a few seemed to believe the hull could handle a single in-line inboard. Most believed the hull required a V-drive or stern drive to achieve the correct trim. I really dislike stern drives, you just can't leave them in the water without major headaches and a small piece of fishing line can take one out. Besides they tend not to live very long with higher horsepower diesels. Yes stern drives are more efficient and faster but I believe if not maintained carefully they become the achilles heal of any 25 Bertram.

Go with the V-drive and everyone knows it will work, be on the safe side. The problem for me is that I would like to avoid a V-drive boat if possible. Too many angles for me to get wrong, in some cases difficult shaft and stuffing box access. I think the V-drives are an excellent choice if they are set up correctly and provide the same durability as an in-line. Back to the skill level assessment, I lack the experience to do this work with confidence and having confidence in your boat offshore is essential.

The nagging issue...there is a 22 ft SeaRay which is another Raymond C Hunt hull that I modified that originally came equipped as a stern drive and I converted it to an in-line (not knowing any better at the time )and it worked great. Every time I would began to dismiss the in-line option based on "expert" opinions I would remember my SeaRay project. So I decided to go against the grain and do a little research myself.

I contacted Raymond C Hunt & Assoc. (The original Bertram hull design group) and posed a couple of simple questions; Where is the center of buoyancy (CB) on the Bertram 25 hull? and where is the center of gravity? Their answer; "the center of buoyancy is 10 ft forward of the stern cap and the center of gravity is slightly forward of that" So off to the SeaRay I went with the tape measure. The center of the in-line V8 engine measured 8 1/2 ft from the transom. So why wouldn't the Bertram 25 work as well? It will. My humble opinion is in fact; it is actually impossible to create a forward or bow down trim by placing any engine aft of the CB. The only way this can be done is if the weight forward of the CB exceeded the weight aft of the CB.

I have and will continue to reference David Pascoe's articles and opinions. With that said, one of the elements that I have taken away from his boat reviews is how well V bottom inboard boats perform with the engines placed just aft of the COB. He claims that these boats are better balanced, tend not to bow rise badly going onto plane and also believes that this engine placement provides a softer landing. You can read his reviews on various boats on his website;  http://www.yachtsurvey.com/ The Blackfin 29 & 32 are designed very similar to the Bertram hulls and place the engines just aft of the CB. This would explain the offshore ride that my reconfigured 22 SeaRay had, very soft landing and well balanced (I got lucky...it could have been a disaster!)

A friend from the  25 Bertram board sent me some shots of his B25 project in the water w/o an engine and the same boat in the water with a Cummins 6BTA, V-drive and 800lbs of water filled drums. The interesting thing that I took away from studying the photos is that the problem with the hulls for in-line installations is not that the boat does not have adequate amidships volume to handle the engine, but rather the aft or stern volume of the hull is huge and could overwhelm the boats trim if not accounted for. This boat is being set up with the engine well aft of the COB. No gamble here, should provide a great ride.

Take a look at some of the photos James Graham sent me relating to weight, hull volume and trim. These pictures were extremely valuable to me in helping me make my decisions about the re-power project....thanks again James.



Top left photo is an empty hull. All other photos are with a Cummins 6BTA, V-drive and (2) 55 gallon drums full of water installed.

If you look carefully you can see the boat's chine's are not even to the water line with well over 2,200 lbs sitting in the boat. That's a wide, buoyant hull by any standards. I'm not certain, but I believe the drums to be very near the CB based on their location as relates to the hump, or rise in the gunwale combing. Basically as James was verifying that his V-drive would sit correctly and that this engine placement would provide the correct trim he was inadvertently also verifying my design ideas. Essentially the combined weight of the Cummins 6BTA and the full drums equal the weight and engine placement of a CAT 3208. Still plenty of hull volume left.

Here's a couple more shots of James exceeding nice 6BTA Cummins V-Drive 25 Bertram under construction. For more photos of James project click on [James Graham's B25]


I prefer heavy boats. They are slower and use more fuel but they ride better and personally make for an easier day in the Gulf. I'm not as young as I once was and in no big hurry. At this point in my life I'll take a smooth ride over speed any day. There is no doubt that the boat James is building is going to be fast by Bertram 25 standards. 315 HP of Turbo-charged Cummins diesel in a Bertram 25 is going to fly. James enlisted Tony Athens of Seaboard Marine to assist in this conversion. Tony is well know for his expertise with re-powers and specifically with V-drive installations. Although we have differing opinions from time to time on various web boards I have great respect for Tony's opinion's and work. This project is about as clean of an engine installation as you will find anywhere. First class.

To avoid a prop pocket, i.e. chopping up a perfectly good vintage Bertram hull and gambling with hydrodynamics you have little or no choice but run a V-Drive in these hulls, you simply can't get the engine far enough aft in a straight shaft application and clear the required prop size.

Special thanks also go out to Kelly Small off the Bertram 25 board for putting up with all my questions and providing me with lots of measurements from the "Queen of Hearts"...a beautiful example of a Fly Bridge Bertram 25 Sport fisher equipped with twin V8 V-drives. Photo below left is Kelly's "Queen of Hearts" Note the shaft penetration location and the stern volume, these boats require V-drives if you don't want to modify the hull.

Now the issue of excess stern volume needs to be taken into consideration. The stern volume issue actually begins to take care of itself when you start laying out the geometry of engine placement, shaft angle and prop size. In order to place the engine aft of the COB and swing an 18"- 20" prop you have no options but to incorporate a small, shallow prop pocket into the hull. The pocket serves a dual purpose; First, it locates the shaft higher into the hull, thus making the shaft to gear connection further aft in the hull and effectively allows you to place the nose of the engine at, or aft of the COB. Without incorporating a shallow pocket this conversion is not possible. This keeps all engine and drive train weight aft of the COB. Second, it removes some of the stern buoyancy by reducing aft hull volume. I estimate that the pocket I will be incorporating into the hull will remove between 150-200 lbs of buoyancy. This will be verified once the pocket comes off the plug/mold. Not a great deal on a hull of this size but helpful in my case. (more on prop pocket design later)

In a very simplified explanation of marine design as relates to a boat trim, it is not unlike a teeter-totter that you might find on a school playground. Consider the fulcrum, or center of the teeter-totter as the hull's COB. The further the weight is away from the fulcrum the more dramatic the effect it has on the boat's trim. So, if you place a light engine near the COB the effect on trimming the hull into a stern down attitude is minimal. If you place a heavier engine near the COB the desired effect of stern down attitude, or trim is easier to accomplish. With the lighter engine placed near the CB, it's too close to the fulcrum to provide the required leverage to "push" the hull's stern downward. In my opinion if you are going to design an in-line drive system on a Bertram 25 the engine needs to be one of the heavier versions, or diesel. A gas V8 is relatively light by comparison and has a more difficult time creating the desired reaction at the stern of the boat.  If you want to run a light weight engine I suggest that you take the route that Bertram took and set the drive system up as a V-drive, this way you aren't gambling away your hard earned dollars.


The topic of creating the proper trim in boats of this size seems to develop into arguments often. I believe this debate in most cases is unnecessary. I say this because a 25ft deep V boat can deal with "out of trim" conditions better than you may think. Unless of course this condition is severe. In boats of this size the equipment, fuel, personnel, etc. can be moved around to correct mild poor trim conditions. I would not advocate designing any boat with questionable trim conditions but in some cases you just have to "put stuff where it will fit". A case in point for boats that may not appear correct but are extremely successful are the now famous 28 & 29 Topaz hulls.

These boats are considered some of the all-time greats in the under 30ft big game getter category, and they basically came from Topaz out of trim. Seems strange that a boat would come from a small, high quality builder out of trim? I have no evidence of this condition in these boats other than observations and logic. Basically the original Topaz hulls appear to require a full tank of fuel to provide the correct trim. This is not uncommon with larger commercial vessels. Empty tanks can send the stern of a 120ft crew boat boat sky high. In a perfect world a designer want's the vessel to be trimmed correctly under ALL conditions...but as with all vessel design it is basically one compromise after another.

Take a look at some photos of 28 & 29 Topaz's. Some of the pictures (I assume) are with the tanks full and some are with empty tanks. Notice anything?



Why does a boat of Topaz quality appear to be so effected by the weight of the fuel and/or people on board? Poor design? NO. It' because the designers placed more emphasis on cockpit space and the intended use, than they did on "no-load" trim. To facilitate a huge fishing cockpit the engines are positioned considerably forward by 28 & 29ft boat standards. This dictates that the fuel and passenger weight be considered in the ballast/COB/COG calculations. Ask yourself a few questions; Where will your guest be located while they are fishing? Under what fuel condition will you spend most of you time? Where will your ice chest be located?  By the way, the 29 Topaz is one of my all-time favorite boats and had I found one in the right price range this site would have been about rebuilding a 29 Topaz!

In some cases designing a vessels trim to be correct when the vessel is empty of passengers and equipment can produce unpleasant results when the vessel is actually used as intended!

The point here is to be realistic and examine "how" the boat will be used. If most of your trips will include three or four 200+lb fisherman, all jumping around in the aft cockpit it's a real good idea to account for this condition! The Topaz works great for that reason. Load her down with fuel, ice and fishing buddies and she comes right into trim, plus you have a huge cockpit! Most guys that own 25 Bertram's with twin IO's will tell you that when you put a couple of guys in the cockpit for a day of fishing offshore...it's a REAL good idea to have plugs in the cockpit drains! Now you tell me, who was smarter, Topaz or Bertram? I found 2 plugs hanging on the stern cleats, near the drains in my boat when I picked it up....let's see, I wonder what these are for?

If you end up a bit "bow down" with no one onboard, you will more than likely be trimmed correctly with the addition of all your fishing buddies in the aft cockpit....actually fishing!


1) Keep the engine aft of the CB, use the CB as the locator for the engines nose and work backward from there. 2) Use a heavy engine, 1,400 to 2,200 lbs. 3) Incorporate a small prop pocket into the hull. 4) Place all other heavy items aft of the engine. 5) Add "a little" weight to the transom if needed to achieve proper trim, additional transom coring, glass, etc. Note: "If" the boat needs additional transom weight, do so in such a manner that will increase the hull's strength, or function. By function I am referring to oversized batteries, etc. Not many boats that venture offshore can have too much electricity on board. Don't just stick concrete in the stern! Based on owners postings there are many IO version Bertram 25's out there that have added weight into the bow areas, this leads me to believe that the boats tend to run bow light with the stern mounted engines. When I tore my boat apart I found several bags of concret in the forward bow, I would guess the boat ran bow proud and the PO was tryiing to get some weight forward of the COB. Only time will tell but I believe this weight distribution will provide an excellent riding boat and that additional weight in the stern will not be required.

ENGINE SELECTION (Gas or Diesel)...

In a perfect world I would set the boat up with twin diesel inboards (wouldn't we all)....but cash and today fuel economy play a big role. I have a few friends that can drop $1,000 bucks at the fuel dock...but not many. Basically I realized I could have a single diesel or twin gas engines. After running a single gas inboard for the past five years I really didn't have an issue with single engine boats. There are advantages and disadvantages as to how many engines are on board your boat. Many boaters can't live with a single engine application in the open ocean. It freaks them out not to have spare everything. Then there are some guys that get freaked out by having 150 gallons of gas on board (like me). However if the single engine is gas, then a small kicker outboard is an option for offshore excursions. This is not an option with diesel because there are no diesel outboards to speak of.

Photo on the left is the 350 Chevy with Twin Disc marine gear in the SeaRay during construction. (not enough for the Bert)

If the decision is based on money and fuel economy I think I'll have to take the single diesel. If money is your bottom line than a good RTO big block gassers are a dime-a-dozen and by far the most cost effective in any boat of this size.

Every time someone fires up a cigar on my SeaRay I would get nervous and if I can't even smoke a cigar on my boat I don't want the thing. Single diesel is definitely my first choice....I'm a coward when it comes to fire at sea. This risk could be mitigated by designing the under deck space in such a manner that the fuel tanks are located in sealed compartments and 100% isolated from the engine. The engine bay area should be kept to a minimal size to reduce vapor volumes. Properly designing the space could reduce the risk to basically the same level as a boat running outboards.

A single big block inboard gasser would be OK in the 25 Bertram, maybe. Fuel consumption could be high and cruise would be faster with the diesel, requiring more fuel be carried on board. Other gas options that I believe could work (in-line) in the 25 Bertram hull based on my research include; twin V6 4.3 Chevy, twin I-4 3.0 Chevy. But diesel tops the list.

The single gas option actually creates a weight problem...it's too light! If your moving the engine to just aft of the COB than the engine needs to be heavy. Most V8 gasoline marine power packages weight in between 950- 1000lbs. Very light for a single mid-mounted engine in the 25 Bertram's hull. This would take a little though to keep the hull in trim.

Planning for the future...

If your going to install a gasoline engine the one thing that you MUST do is design the boat's space, fuel tanks, etc around a diesel conversion at a later date (you know you may want to) The cost at the construction stage is basically zero vs a major investment later. You should always build based on BIG diesel and if a good deal comes along later the installation will be an easy drop in. Here's the list of must-do's to make the boat diesel friendly:

1) Fuel tanks for diesels require a fitting for the return fuel from the engine.

2) The exhaust should be sized for the anticipated diesel requirements (diesel's require larger exhaust runs)

3) The air induction routes should be sized for the horsepower diesel you may install, again, diesel's require more air. (rule is .5cu inches for every 1 hp of diesel engine)

4) Pay close attention to the engine stringer spacing. It's easy to put an engine into stringers that are too wide but impossible to put an engine between stringers that are too narrow.

5) The raw water thru hull inlet and associated hose should be sized for the larger diesel engines, the gas engine won't care if it's too big! Set the boat up with a 2" raw water inlet, you want find a diesel that needs more water than 2".

6) The engine cowling, make sure your new diesel will fit when the right deal comes along. This may waste a little cockpit space but you don't want to be forced into hacking up your pretty fiberglass work....unless you NEVER plan on switching to diesel.

Here's a good article by David Pascoe that lays out some thoughts on the option; Gas or Diesel. http://www.yachtsurvey.com/GasNdiesel.htm (basically Pascoe says that boats in the under 10,000lb class should be gas) or you can read my opinions on the aspects of "useable horsepower" [Click Here] I disagree with Pascoe on this one. But this is just a bias toward diesel engines, his logic is actually sounder!


Now which diesel should I buy if I go the diesel route? Now that's a debate that you can spend countless hours on line trying to figure out. It appears that there are as many opinions about diesel engines as there are about car makes and models. So, I guess I need to revert to one of the initial issues...money. Once I received a few quotes on various engines it became obvious to me that I'm in the recon or low hour surplus market.

I'll start with a weight and horsepower budget to establish a base line from which to begin the evaluations on used/recon diesel engine selection. The base line that I will use for the weight was established by Bertram. I'll select the heaviest engine package that Bertram provided the 25 with and try to stay around that number. The heaviest power package offered by Bertram on the 25 was the twin V8 gas V-drive set up. Based on first hand information gleaned from the 25bertram.com board this package weighs around 2,400 lbs. There is some debate over this weight but it makes sense to me. The package was a Chrysler V8, old style log manifolds, Borg Warner reduction gear plus V-drives. If you do a little research on the weight of each of these components you won't have a problem coming up with 1,200 lbs per engine/gear package. Heavy for the 25 Bertram, but it is a 10ft beam boat and has proven over they years that it can handle the weight well. Basically "wall to wall" engines.

Photo left is the twin Chrysler V8, V-drive engine package that came in approximately 200 of the 25 Bertram's. That's a lot of iron to pack into a 25 ft boat, heavy pair of engines no doubt. A tribute to the hull's capacity. This particular engine/gear package exceeds 2,200lbs.

All boats have a weight budget. See: [WEIGHT BUDGET] The budget consist of everything, including the hull and is determined by the amount of buoyancy available. The weight of the hull can't realistically be changed, so for this project I will focus on 2 areas. First is the engine weight. Second is the cap, or super-structure weight. The cap of the 25 Bertram's came in several configurations. The boat's came from Bertram as Cabin Cruisers, designated Express, hard tops, open Sports and fly bridge versions. My boat will be configured as an open cockpit boat, read; "light". So, in conclusion for my weight budget I can actually accommodate a heavier engine package than the 2,400 lbs discussed because the hull can actually handle another 700 - 1000 lbs of cap weight....that will not be present. The over-all major component weight budget for this project is 3,460 lbs. See: [WEIGHT BUDGET]

Now, if the engine is light than the bonus weight comes in the form of payload. If the engine is heavy their is no bonus payload, but the boat will still be within the acceptable limits established by Bertram.

Photo on the right is the engine bay of Kelly Small's "Queen of Hearts". Twin 350 Chevy's are a bit lighter than the original Chryslers. Very clean installation. At 325 hp per engine this 25 Bertram is capable of 40 knots.

With an engine weight budget established at 2,400 lbs let's move on to the power requirements. I used the calculator software on boatdiesel.com to establish that around 250 hp would be considered a minimum for my goals and anything over 330 hp would be wasted, unless we're talking about one of the new generation diesels. The common rail, electronic engines coming on the market change several equations. These engines produce a tremendous amount of HP per/lb of engine. As I have stated before, there's no reason to set up these boats up for WOT speeds in excess of 40 knots. The hulls simply are not designed for high speeds....BUT if you can have a single diesel that "cruises" at 30+kts and still provides good fuel economy, go for it.

Onto the Diesel Options...

I've spent a bit of time researching diesel engine design, longevity, maintenance and fuel consumption. There are a few "givens" for diesel engines. First, the more cubic inches that you use to make a given horsepower, the longer the engine can live. Second, if the engine can make the required power without  turbo-charging or after-coolers the longer the engine will live. None turbo-charged engines are called naturally aspirated and typically given an "N" in the model number. "T" for turbo, "A" for after-cooler. So a 6BTA Cummins stands for "engine series 6B, turbo-charged, after-cooled. Same with a 3208TA CAT, 6V53T and so on.

Here's a link to another good reference article by David Pascoe explaining engine displacement size vs horsepower requirements; http://www.yachtsurvey.com/comparing_diesel_types.htm

The first options I will evaluate are the used, and recon diesel engines.


Ah the Cummins...I have always been a Cummins fan, I have one in my truck. The 5.9 liter (360 cu inches) 6BTA comes in horsepower ranges from 210 to 370. Making it the prime candidate from the power respective. The engine weights 1200-1,400 Lbs or so, another plus for my project. Some of my decision making factors to keep the cost down is finding an engine that meets the following criteria; 1) An engine model that has been in service a long time. 2) There are tens of thousands of them out there to choose from, i.e. they are, or were at one time popular. 3) The factory is still supporting the model with parts and service.  4) Local factory support must be excellent. So, I need 250-330 hp and a engine that weighs under 2,400 lbs. How about a CAT 3208T or a 6V53 Detroit....WHAT?

In the world of used and recon marine diesel engines the Cummins is the most desired package on the market. This really isn't rocket science, the Cummins is simply one of the lightest, strongest and most reliable engines on the water.  With that noted (by everyone who owns a boat) this makes the Cummins one of the more expensive options. The results of my research has been that a Cummins or a  CAT or Detroit of the same horsepower typically puts the Cummins somewhere between 30%-50% more expensive. Hey, the Cummins is lighter and therefore faster so why shouldn't it cost more?  It appears that the good deals out there on Cummins 6B's are in the 210 hp range...minimal for the Bertram 25 hull in my opinion, certainly not a prime candidate. A 210 hp single would be great on fuel but bad on speed. For only 210 hp a 6B would be taking up valuable real estate. 200-250 hp can be achieved with a 3 or 4 cyl engine and save a bunch of space.

The best deals out there on 6B Cummins that would run the 25 Bertram well are in the 250hp range. The 250hp is the 6BT, non-after cooled engine. This is the 6BT engine configuration that many consider a great compromise between power and longevity.

Photo on the right is Jame's 6BTA 315 hp Cummins, Chrome valve covers are a nice touch. No one can debate a "0" hour totally new Cummins that is sold as a "recon", as with this engine. These engines are a bargain if your buying new.

The Little Cummins...

The 3.9 liter (238 cu inches) 4B. A smaller version of the 6B, the 4B is a bit smallesh for the 25 Bertram. This little engines comes in hp ranges from 155 up to 250hp. That's a bunch of hp for a 4 cyl diesel engine. The 4B is basically the size of a small block gasser, with the usable output of a big block gasser. The little fellow weighs in around 850 lbs, less gear. The 4B "could" be considered in the 250hp version, but not really considered a stable engine at these power levels. To run a 238 cu in diesel at 250 hp is OK "if" the engine you keep the cooling system in top condition. Over heating this little guy could happen quickly. There have been reports of frequent injector failures on this engine, reportedly the latest OEM injector P/N has solved this problem.

 I believe the 4B would provide similar cruise speed performance to a big block gas engine...something in the 17-19 mph range. But the range would be incredible. The little engine could push the 25 Bertram hull in the lower 20's and deliver 5-7 gallon per hour burn rates. With 100 gallons of diesel on board the 4B could deliver a 375-400 mile range!....the down side is that it will be at a snails pace, with the little fellow straining. The 4B would be better suited in a twin engine configuration at the 155 hp rating in these hulls, which I believe would be just about the perfect power for a 25 Bertram.

A 250hp 4BTA would definitely be considered if the price is right. The 250hp variation has suffered it's share of injector problems but I would hope that the latest part numbers released by Cummins has solved this problem. Interior space and boat range would be great with a 4BTA 250hp.

Big Brother, 6C Series

The 6C. The 6C is the big brother to the 6B. Basically a larger version of the straight 6 cylinder design but with wet liners. (more on liners later) The 6C is within my weight budget for the project but really pushes the length issue. Provided mainly in 400 - 450 hp versions the 6C at 450 hp is too much power for the 25 Bertram (can a boat have too much power?). How can an engine that fits the boat be too much power? The answer is in the prop. 450hp worth of single diesel inboard power requires an enormous propeller and/or enormous pitch to take advantage of the engine's power. This translates into hull clearence issues and maybe an idle speed that is just too fast (due to the extreme pitch) The lower production numbers in marine trim take the 6C out of the prime candidate slot, and they aren't cheap. Not commonly found in the naturally aspirated configuration simply because the 6B fills those horse power requirements in most applications. From all indications the engine has a reputation for sipping fuel, so I would expect the burn & range to be similar to the 6B.

I believe the 6C could be the perfect combination for the 25 Bertram hull in 350hp configuration. Excess of power and the 2000lb engine would really smooth out the ride. The wet liners are a huge plus. Personally, the best find would be a 6CTA marine engine in need of a rebuild. Reason, 6Cs were fitting into practically every 18 wheeler on the road, so rotating parts for the engines are plentiful and cheap.. and it's a wet liner engine so typically heavy block machine work is not required.

Seems a bit odd to think about putting a good sized CAT, Detroit or Cummins C series engine in a 25 ft boat? But the math works out that these engines can work in this hull. I felt a little better about this as an option after I read an old CAT ad that references the 3208 as going into boats as small as 24 ft. Well there you go, it has been done before and they are proud of it. But if a good deal on a Cummins 6BTA comes along then I can have the best of both worlds, weigh and power.

Here are a few of the advantages of  V block engines, in this application; The V6 & V8 block designs are typically shorter than older similar horse powered I6's, making for more compact installations.... important for this project. The single engine boat cockpit means that space and/or maintenance will not be a big issue, unlike a twin installation. . These engines are extremely well proven, many seeing 10,000 plus hours of service. The engines are not expensive compared to other makes and models. At the time of this printing 325hp versions of the CAT 3208's were going for $10,000 in complete factory recon trim with a 2,000 hour warrantee. There were many 2,000-3,000 hour used engines going for between $5,000-$7,000. The Detroit's 53 series are even cheaper. You will have a tough time finding used Cummins 6B's in these $$$ ranges at this power level. The CAT uses over 600 cu inches to get to 325hp vs the Cummins at around 359 cu inches.

Photo above is a 25ft Blackfin, 8ft beam and single 210 hp CAT 3208N. If this 8ft beam boat can handle the weight of the 3208, the 10ft beam of the Bertram should be fine, assuming proper trim and balance can be achieved. The engine in this boat is located under the center console. The later 25 Blackfin boats utilized a prop pocket, the early versions did not. I bet this boat is a "Battering Ram" in a head sea. The 210hp version is not enough power for this boat IMHO. The 325hp 3208T would be a better choice here. BUT this factory equipped diesel 25ft boat does make the case that boats this size can handle 2000+ lb diesel engines.

These prices are much better than similar horse power Cummins 6BTA's...why? Well not so many people can use, or want an engine this heavy, at this power range. Put quite honestly there are much better engines out there today than and old CAT or Detroit. In any inboard application the wider V8 CAT eats up more cockpit space than an I6. The wide engines are also tougher to maintain in twins because access is not so good in these applications. And the bottom line is that one of the newer, lighter engines will produce a faster, easier to maintain boat. Boaters today crave speed, it drives 80% of their boat selection process. The key question today seems to be not how long will it last? or how does it handle a head sea?, but rather "how fast does it go?" A high cruise speed has become the Holy Grail of boating.


There are a few CAT options but from the recon or used markets the only models out there that I would consider would have to be the now famous 3208 or the 3116. 

The 3116...

"I thought those engines were crap". Not so, some of the 3116 series did suffered from what has come to be called "soft blocks" but a little research proves that the engines with the block problems are well documented by CAT among others. The serial numbers of the effected engines is publicized by Caterpillar and also posted on Boatdiesel.com boards. So, the 3116 can be considered a candidate..."IF" the serial numbers are checked carefully. Although basically any 3116 still running today will not have the bad blocks, they have long since gone to the bone yard.

Granted, the 3116 has a checked past, or does it? The engine actually has a very mixed reputation. Most owners report that they love the engines. This post from the Boatdiesel.com sorta sums it up "Although there were problems in the past with some, it seems to me that those few gave the engine a bad rap. I have a pair of 3116's 350 and love them with over 1700hrs."...or how about this one from the same board: "have a 1996 Cat 3116 with 9600 hours in my lobster boat".  I'm certain negative comments abound. The point is that there are plenty of happy owners of 3116's out there and that puts them in the potential bargain category.

So what to do? There are 2 ways to view the 3116. First avoid it and second get a great deal on one. The past issues with this engine make it a deal breaker on many boat sales and the resale on take-outs is really cheap. In my opinion there's a bargain in there somewhere. If you find a decent engine (crap shoot) then you have saved tons of money over the same weigh and HP 6B Cummins. The engines are said to be good for 3800-4000 hours. Of course this depends on many factors. The 300hp is said to be the best of the 3116 series and those in trawler service have a much better reputation than the "go-fast" sportfishing applications. So don't push one too hard and it may out live you.

Photo on the left shows a nice clean shot of a rebuilt 3116. Rebuilt by a CAT dealer, 350hp with a complete factory warrantee...for $13,000!!! VERY cheap by CAT standards.

These engines are basically the CAT answer to the Cummins 6B series. Very similar size and horsepower options. The 3116 is a couple of hundred pounds heavier, but who's counting 200 lbs on engine packages of this magnitude! The 3116 may be a little longer than the 6B's. The engine displaces 402cu inches so there is no shortage of muscle. The downside to these engines are the dry bores, I guess you can't have everything! also, the 3116 is a fairly current engine, and being a Caterpillar these are typically very expensive engines. Maybe a great deal will come along!

The internet forum boards seem to agree that these engines will live if not cruised too high. 2850 is max loaded, and most say 2200-2300 should be considered the cruise rpm range for these engines. This is why the trawlers with 3116 engines are happy campers...they cruise at 1800-1900.

3126 could be an option but there are really very few of these engines sitting around for sale. So I really haven't investigated the 3126 because of the small number of these engines in the used markets. The upside to any of the CAT's is smooth operation, not to much noise, plenty of power and long engine life.

The 3208...

The undisputed work horse of the older CAT's. This series engine came in various horsepower options ranging from 210 to 475. The 210 are naturals, everything above that is turbocharged. Most consider the 375hp as the perfect 3208. The 475hp was just trying to pull too much power from these engines and the service record at this power level ain't so great. Personally I like the 325hp 3208 because these engines have no after-cooler. No after-cooler means less maintenance and these engines will live a VERY long life at 325hp.

These "big-ole fat" engines are everywhere. Yacht owners the world over are yanking out perfectly good 3208's to get lighter, faster set ups. I have run across countless ads that read; "375hp 3208TA's low hours, engines in perfect condition, owner upgrading to higher horse power...$12,000 pair, will separate". If you spend much time looking around the used and recon boards I think you will agree that these engines are a real bargain at this time.

 Seems like a shame to let these great older engines just sit around and go to waste. In their day they were "the Cat's meow" (sorry I couldn't resist) and a primary choice for twin installations in the 31-45 ft range. Several Bertram 31's came from the factory with these engines. I "believe" the 25 year B31 "Silver Anniversary" editions came with 3208s. Without doubt, the 31's equipted with 3208s were the best riding 31s ever produced. I have once heard the term "battering ram" applied to these particular 31 Berts.

Image to the left of the 3208s are of the 375 hp variety, note the aftercoolers.

Remember the power requirements? an older, non electronic 375 hp is wasted in the 25 Bertram. If your going to run a 3208 look for a 325 hp version, it's going to burn less fuel and move you along plenty fast enough. That's right in the horse power range for a mechanical diesel in these hulls. As stated the natural version makes 210, not enough. No after-cooler is one less thing to maintain, and from what I have been told the sea water after-coolers on marine diesel engines requires routine care (disassemble & cleaning).

  LAST BUT NOT LEAST...The Detroits

During our conversations about the diesel engines James Grahm coined an accurate phrase for Detroit diesels, he said; "there's high tech, low tech and then there are Detroit's... which are NO tech"

The Plus of a Detroit is 3 million of them were made. The minus is noise, weight and emissions. 2 stroke Detroits have been out of production for several years compliments of the EPA. Apparently the Military did not get the memo because they are requiring MTU to maintain a parts supply!

The first "realistic" DD option....The 453.  The smallest engine that should be considered based on horsepower ratings alone. The 453 is a little guy with only 212 cubic inches and rated at 135hp. Based on what we have learned DD's 453 "should" be good for 225-250hp with injector changes and the addition of a turbo....but cooling capacity would more than likely be a problem and cooling capacity would need to be increased.. Weighting in at 1100-1300 lbs the 453N at 140 hp is really not an option, but the 453TI (turbocharger / inter-cooled) 210hp is a viable option. This may be one of the most economical "old school" diesel engines that could be installed into a 25 Bertram. The turbo is said to quiet down the Detroits considerably, in fact some say the reduction in noise is the main reason to run a turbo on a Detroit!

The 453 is the 4 cylinder 2 stroke that many older Bertram 31's run in the 140 hp trim. There is a fleet of (15) Bertram 31's in Panama at the Topic Star Lodge that all have a pair of 453 naturals. It's a great little engine and set up as a natural it will virtually live forever. A single 453N would not exactly burn up the water in a 25 Bertram but the fuel economy and durability would be excellent. The 453N would really be the "Slow boat to China" option. I think the heavy little Detroit at 140 hp would push the 25 Bertram along at 16-17 MPH...hammered! Ouch.

Pictured right is a 453N industrial version....."Old School" diesel power.

As noted earlier, a 453N DD in a 25 Bertram is a run forever engine, whether it's nursed along or run on the pin. I would expect 4-6 gallon per hour burn rates with a 453N. At 17-18 mph that's a 350+ mile range with 100 gallons of fuel! If your OK with a single diesel and your in no hurry, you've got yourself a little Canyon runner. Here's some real economy...run for 15 hours on $250 bucks worth of fuel!

With the 453TI 210hp I would anticipant 19-22 knot cruise speeds with a 25-26 knot WOT. This would be a very respectable combination of speed, durability and economy.

In marine trim the 453 is 30" wide, 36" tall and basically 40" long. That leaves plenty of cockpit space in the 10' beam 25 Bertram.

Photo on the left is a pair of 453's being removed from a Bertram 31after 40 years of service! Owner reported that one of the engines was rebuilt around 1600 hours prior to removing both for re-power to higher horsepower. The longevity of the old natural DD's is unbelievable, and so is the noise! Many Detroit fans say the reason that you install turbos onto Detroits to keep the noise down lol.


Here's a couple of shots of some marine 453N's / 140hp. I don't think the 140hp versions are strong enough for a 25 Bertram single. Both shown with Borg Warner 72C reduction marine transmissions ( not one of my favorite gears to say the least...18" long, ouch!)

471 Series

Like the 453N, the other 4 cyl, the 471 DD can't really be considered without a turbocharger because of the horsepower to weight ratio. Weighing in around 1800 lbs the 471 is a heavy chunk of iron for a 140 horses! Although these engines are everywhere and super cheap (because they came in trucks) they are heavy and tall. The 471TI is a different story. I have seen OEM Detroit literature rating the 471TI at 325 hp. Very respectable amount of power for the 1800lb weight. If your considering a 4 cyl Detroit go with one of the turbocharged versions, or turbo charge one yourself.

The 471TI 325hp is a stout beast and well within the weight limits of the Bertram 25, but height and length make this engine a tricky one. "IF" your boat is configured for the oddly tall 471 then it's a good choice, but don't expect to put this engine into any version of the 25 Bertram without MAJOR modifications. At 325hp and 2000lbs (with gear) it would certainly be a bull dozer with all the good qualities of the 71 inline series.

Engine on the left is a nice example of an industrial, or vehicle  471TI. They are only this clean right after the rebuild!



Heres a couple of pictures of the marine 471TA in 320 hp trim.


 What's required to add a turbo and 150+ hp?

As with most things Detroit, you can add a turbo to basically any of these engines and really boost your ponies. The basic difference between the natural engines and the turbo engine, is that require a different compression ratio, different liner port design, valves and blower seals. This can be accomplished with an "in-frame" over haul.. So, to convert a natural to a turbo you must install new pistons, turbo valves and turbo seals in the blower....no big deal if you are rebuilding anyway. But don't think you can buy a good running natural 53 series and bolt a turbo on it and go. Note: The 453 series requires a "turbo block", basically larger air ports and larger crank journals. These are rare. 71 series is much easier to convert.

BTW, turbos are cheap. They are abundant and easy to configure on these engines. Also, a water cooled, marine turbo is not required. These are known as "wet turbos". The standard non-jacketed turbo is known as a "hot turbo". Hot turbos are perfectly acceptable in marine service...BUT, you MUST install a high quality, custom fitting heat shield blanket to avoid fire at sea.

Another little DD Option???

Detroit made another little guy that will work as well. The 371 uses the same liners, pistons, heads and exhaust manifolds as the 6V71. So as with all things Detroit the engines output can be calculated based on know injector sizes and volumetric cylinder capacities. Basically the 371 is 1/2 the capacity of the 6V71, or 671 inline.

Photo on the left is an industrial version of the little 371.

The 371 is 213 cu inches, basically the same displacement as the 453. By applying a 6V71 formula to the engine it should be capable of 200+ horsepower! The 6V71TI came with twin turbos and was offered at 435hp. Logic and math work well with Detroits....hence the 200+ hp guess. Before you po-po this concept remember that Cummins sells the 238 cu inch 4BTA at 250hp. 1 hp p/cu inch is no stretch for a Detroit. This is getting interesting!

At this juncture a trip to the largest Detroit distributor in the world was in order. I can't name those guys on this site because the advice provided was off the record, unofficial and fairly radical!

So here's the scoop on the little 371's potential. YES, the little guy can make a bunch of horsepower....all day long. As noted, basically the 371 is 1/2 of a 671. The recommended build for the 371 is basically modeling the engine off of a J&T (Johnson & Towers marinizers) 671TI 450 or 485hp. This involves adding a turbocharger and intercooler, among a few other goodies such as turbo style valves, pistons and liners. The most interesting thing they told me was NOT to use the 17:1 turbo pistons? They recommended I use the 19:1 "natural" pistons on a turbocharged engine! Debatable.

Photo left is a J&T 485 hp, 671TI.

Photo on the right is a 371 and shows the common tail housing.


By adding the 17:1 pistons "some" believed the engine would be too difficult to start, there's just not enough compression and that combined with only 3 cylinders don't cut it. They said the engine would do just fine at 19:1 + turbocharger. But an intercooler is a MUST. One of the comments I will not forget was "you can't put too much air in a Detroit, but you can put too much HOT air in one" Other Detroit gurus say run the 17:1 turbo pistons....on 30 year old engines, you choose.

Photos below show a 371 that is used in commercial marine service as an auxiliary engine, i.e. pump or generator.

Here's the advantages over the 453 if you want to run a tiny displacement Detroit: The engine is "said" to be one of the smoothest Detroit built. Basically most of the inline 671 series components will bolt in or on the 371. That means pistons, rods, accessories, etc. In fact the aft tail housing and flywheel are interchangeable.

The downside? The engine weights in between 1350-1500lbs. That's a 200lb penalty over the 453. But the parts availability, durability and noise are worth 200lbs in my book. So I'll mark the 371 down as a very real possibility. Did I mention the 371 would be great in the wallet department. Good fuel burn numbers and really cheap parts. In a 25 Bertram the engine should burn 6.5-7.5 GPH, that translates into 3 miles per gallon, or a 300 mile range on 100 gallons of fuel. The 371 did come as primary propulsion engines in many large sailboats and also displacement yachts such as 50+ foot Hatteras MYs. The big down side is not so fast and not so great with heavy loads, figure on a 18kt cruise....23kts "on the pin"  and a light boat.

Here's a couple more shots of the 450+ hp 671TI's. It doesn't take much imagination to see this EXACT engine with only 3 or 4 cylinders.



Notably the most famous and well know of the 2,000 lb, 210-400hp Detroit diesel engines has got to be the 6V53T. The Detroit's, or DD's as many refer to them is by far the oldest design of the bunch and the 6V53 is smallest DD in the "V" series. This little engine has only 318 cubic inches. The engine was designed in the 1940's and was in production until the mid 1990's. That's a long production run by any standards. The DD's are different in many ways than the CAT or the Cummins but the main difference is that they are 2 stroke engines. This ultimately lead to their demise, the EPA emission standards for new engines just can't be met by the older 2 stroke design.

By the way: In the world of Detroit the engine series numbers stand for the number of cubic inches per cylinder. So a 6V53 basically means 53 cubic inches x 6 for a total of 318 cubic inches. Same with the 71 series.

The DD was the back bone of the USN and USCG for over 50 years. Virtually every vessel operated by the armed services ran DD's in one form or another. To this day their service record is unmatched. The original Higgins landing craft of WWII were equipped with Grey Marine 671's, the predecessor of the Detroit 671. There are more DD's in service world wide than any diesel engine ever built. How does that benefit a boater on a budget today? Surplus engines and parts are cheap, real cheap. The engines are still fully supported world wide and it's never a problem finding someone that can work on a DD, should you ever have to. Basically in any horsepower range the 6V53 was offered (besides 400) the little V6's will run forever. 10,000 - 20,000 hours is not uncommon for a 6V53...without ever taking the valve covers off. Seriously,15,000 hours is not uncommon for these engines with normal maintenance. The question is can you live with their manors (monster chain saw on steroids) for 15,000 hours!

  The image below left is a twin turbo 6V53 400hp version in a 31 Bertram FBC, offered for sale on the Bertram31.com board....$12,000 for the pair with gears. One of the things that makes maintenance and parts so cheap is that the engines were designed to be modular. Many of the parts that go on the 6V53 can also be found on other DD's. The industrial models are basically the same engines as the marine versions less marine accessories. So a generator, crane or bus engine is internally the same as the marine engines. Couple that with the extremely high production numbers of the DD's and you have real cheap and easy to find parts and service.

The 6V53's came in every size and shape vessel imaginable so finding them is no problem. In fact you will have no problem finding more of these engines that are just sitting around than any other diesel engine. I've seen 6V53's advertised as cheap as $2,500....running! Thousands of Sport fishing yachts were built around these little work horses and most are either still in service today or they have been yanked out in the quest for higher horsepower, lighter power options.

The rebuild factor. The DD's unlike the more modern 4 stroke designs in this size have "dry replaceable liners". What does that mean?, well it means that when you rebuild the engines you get new cylinder liners to go in the block. essentially they have brand new combustion packages with every rebuild. New liners, pistons, rings, main and rod bearings. No honed or over-bored cylinders on DD's. The blocks are also the heaviest castings of the group of engines I am considering.

Image on the right is an industrial 6V53 for sale on the internet. As mentioned these engines came in basically everything. Which earned them the nick name "bus motors" by many in the recreational boating crowd.

The 6V53 would work "OK" at the 225 hp level, or basically a "Natural". Turbo's would be required to move the 25 Bertram along at a good clip.

The Last DD' Option...

The 6V71N meets the weight, horsepower and over all length requirements...but it's TOO wide for the Mark II stringer system. If you intend to stay with the original fiberglass box stringers that came in the boat the 6V71N leaves no room for additional internal bulkheads or sound insulation. The stringer dimension is 48" inside-to-inside and the 6V71N is 44" wide. Add 3/4" glass over plywood on both sides, plus insulation and it's a zero clearance installation.

But as with all things DD there is a "mix-n-match" option. By mixing the parts around just a bit you can create a 37" wide 6V71N. The trick here is to use the exhaust manifolds that came on the 6V71T & 6V92T. These manifolds are designed to fit snug against the block, hence a narrow version of the 6V71. At 37" wide the 6V71N becomes an easy fit into the Mark II stringer system.

Photo left is a "donated" engine...that's correct, a free one. This 6V71N was given to me by a friend of mine. The engine was in an industrial air compressor and sitting around doing nothing for years. Tempting, but really better as "swapping fodder" for my Bertram project. Hey, I'll take it!

The 6V71 is 426 cu inches and will produce 287hp as a natural with N80 injectors at 2300 RPM.. That's enough to push the 25 Bertram along nicely if you don't mind the weight. Best deal here is that no turbo's or after-coolers are required to get the needed power, less to maintain and hopefully a life time engine, if you could put up with it's bad habits for a life time. 275hp with the N75 injectors is probably a better choice.

Estimated engine weight in marine trim with a down angle transmission is between 2,200 -2,400 lbs (nice smooth ride in a 25 Bertram)

I would anticipant based on various calculations that the 6V71N at 270hp should be capable of cruising a 25 Bertram in the low 20's with a sustainable top speed in the upper 20's. 30 knots is only a pipe dream with this engine in a 25 ft Bertram without a turbo and intercooler, add those and your in the 400hp category.

>>This 6V71N  ended up as "trading material" for another diesel<<

The current engine plan. SEE: [Going Modular]

Parts, Parts, Everywhere...

If your wondering why anyone would even consider running an old Detroit, here it is. As mentioned earlier there are literally millions of them in service. The images below right are pictures of just one of the DD bone yards I have located. This one is off the beaten path in South Louisiana. When I walked into this yard and told them what I wanted to accomplish, they said... "we got everything you need". After strolling around an acre of nothing but DD parts I had to agree.

Located in South Louisiana many of the engines in this yard were originally marine applications. These guy's are commercial industrial oriented people. Walking past some stainless steel exhaust risers one of them commented, "that's yacht stuff" and then stated "if you buy some parts from us...we'll throw in those risers, free" Fancy stuff is not the nature of these engines, running around the clock with little or no attention is.

BUT...my all time favorite shot is the image below. No less than 5 Detroit 8V71's that need a home. I can't even remember where in South Louisiana I was when I ran across this "Detroit Yard Sale".

The down sides to DD's....

Loud, smelly, nasty engines. Did I mention loud. The nature of the 2 stroke means that it is firing exactly twice as many times as a 4 stroke. twice as many combustion events = twice as much noise. The engines are prone to small irritating oil and coolant leaks, they tend to blench smoke and unspent fuel out of the exhaust, basically they are uncivilized. From what I am told the turbo versions are much quieter.

The Big Bonus with DD's...

One of the main differences in the Detroit and the Cummins or the CAT is the replaceable dry or wet liners. The Detroit's cylinder liner are considered "replaceable" because they are not integral to the block casting. The 53 & 92 series are wet liners and the 71 series is considered a dry liner. Basically they come right out and you drop in new ones when you rebuild the engines. The Cummins 6B and the CAT 3208s are both "dry bore" liner engines, so when the bore is shot basically the engine is shot. This has a huge impact on buying used engines. If you go in with the concept of buying a used engine and having it rebuilt, the Detroits or the 6C are actually the only ones out of the "old or recon" group that will end up with new bores. A bottom end rebuild kit for a 6V53 or 6V71 consisting of pistons, liners, rings, main and rod bearings will run you around $1,000, and everything's new again! This is why the Detroit fanatics say "there's no such thing as an old Detroit".

Note on liners...

Diesel engines are categorized by liner type; dry bore, dry replaceable and wet. This is a reference to the bores in the block that the pistons run in. A dry bore is integral to the block casting and the piston travels directly in the cast block bore. To rebuild a dry bore engine the block has to be over-bored by removing material from the block itself. A dry replaceable liner consist of a bored block that houses a replaceable liner. The liner resides in a block bore and is not exposed to coolant, but rather heat from combustion in the liner transfers into the block. In some cases the blocks are over-bored to accept new liners, but only if heat damage has occurred to the block. A wet liner means that the exterior of the liner once in the block is exposed to coolant and is sealed at the top and bottom of the liner. 

If you plan on running a DD here is what you can count on; a loud engine, a lot of engine room maintenance to keep things clean...maybe, a bit of smoke and smell, maybe, but you will also get an engine that for the most part will run forever with complete neglect. For many people there is  no equal to the Detroit Diesel in terms of reliability.

Conclusions for Diesel Options...

So in conclusion one of the Detroits or the CAT 3208T  wins by default if cash is the driver, with the Cummins 6BTA being the number one choice for speed. If ride quality is job 1 go with the CAT. At 1800-2,000 lbs the 3208T is an excellent choice, or the 3116 at 1500lbs. If money is top priority go with a Detroit. A secondary note that should influence your decision, ALWAYS select an engine that is well supported in OUR area. That should also be a serious factor in anyone's new or used engine selection. On the topic of local support the Detroit & CAT are the best supported in my area. I believe that's because I live in an industrial/oil field type region and there are tens of thousands of CATs and Detroits around here, running everything.

From a cockpit space and fuel economy perspective the main contenders would be the Detroit 453 and the Cummins 4B. The little Cummins is much lighter than the Detroit (about 500 lbs) but the durability is questionable at the 225+ hp range required to move the 25 Bertram. The little Cummins does have much better manners and would require less noise control. I think between these 2 engines I would feel more comfortable running one of the smaller Detroits, and that is based on durability.

Final note on Detroits, the 53 series are louder than the 71 series. Parts also much harder to find these days. However, MTU has recently announced that they will be supporting the 2 stroke Detroits well into the future. (press release in 2016)

The "Not" Considered Engines...


Yannies really can't be a factor here because there are just not enough used or recon Yanmars out there to put them in contention, all this aside they are reported to be good engines and most owners are happy campers except many of the unfortunate owners of a certain series of 6 cylinders. Many of these engines are trying to combine the valves with the pistons....always bad. But at the end of the day I just don't like lightweight, aluminum laden marine diesel engines, period. Time will not be a friend to the latest trend of aluminum engines.


Are not be considered for this project because of their service record and the high cost of parts. I'm really not a fan of ultra light weight, high RPM diesels in the first place. Here's a post from a D3 owner: "Again after about 50hrs use: D-3 190 engine stops" The larger Volvos are too heavy-per-hp.


Perkins and parts are reported to be getting hard to find. Durability is however, excellent and the little Perkins engines are good for a long, long time. If you have one, or someone gives you a deal you can't pass up, run it. If it's in good condition it will out last you.


There are none to be found in the used market. This is a new diesel to the marine market and there are very few in service, much less in the recon markets. Some reports are coming in on these engines that, well, don't sound so good. This one was recently posted on the boatdiesel.com board: "After 250 hours, one of the middle pistons off my Steyr 256 h 45 was burned completely." To go along with these reports, the OEM doesn't appear to be too excited to pony-up. IMHO, these engines are just another attempt at building a little, light weight, aluminum diesels. If the results are consistent with past similar attempts, these engines won't be around long. As with the Yannies...Time will not be a friend to the latest trend of aluminum engines.

The aluminum diesels remind me of manufactures versions of "inboard diesel outboards". Just because an engine burns diesel fuel, does not mean it will out live a gas engine of the same size and power.

FINALLY! The New Diesel Options...

It's not fair to the viewer's of my site NOT to talk about what is available today in the new diesel market.

I have always been a fan of "real diesel" engines. I define a real diesel as one made of IRON, and one designed to run at "diesel" rpms...like 2,200-3,000. Locked up in my "industrial" mind, I thought they were gone forever. After all, basically all you hear about on the recreational boaters blogs are the light weight, aluminum 4,000 rpm foreign units? Until recently I steered away from the newer stuff altogether (fear of change).

When I am wrong, I'm wrong.....some of the new diesel engines on the market today are incredible.

I attended the OTC (Offshore Technology Conference, Houston, TX) in May of 09 and man did my eyes get opened! I found myself staring at an all iron, 2600 rpm engine that was the size of a 6B Cummins and made 575hp!!!! and on top of that the fuel consumption curve was unbelievable. So how can I get excited about that much horsepower in a Bertram 25? Cruise speed and range. It's not that I would encourage anyone to install an engine in a B25 that would cause the boat to exceed a safe speed for the hull design, but if an engine can be installed that "cruises" the boat at 30+kts and NOT produce a WOT speed that the hull can't handle, and still provides incredible range? That's a no brainer for those with the means, or for those who just want the latest stuff.

Basically no iron diesel is going to push a 25B much over 40kts, so even 575hp is on the table when it's this small and slips fuel. These new engines have the ability to cruise your 25 Bertram at 30-35kts all day and use very little fuel doing it. Fuel is always a problem with these hulls because the stringer design takes up a lot of space under the decks, and the decks are low in relation to the hull itself.

The main concern of utilizing diesels of this magnitude is prop diameter. These engines will only need a 1:1, or 1:2 gear to keep the prop size down to a useable 20"-21". Using a wheel diameter this small, with this much power is under utilizing the capacity of these engines to push a boat.

The best part is that you have real iron in your boat and not a pot metal anode posing as an engine. I have narrowed down the new stuff to my favorite 4 new engines, 2 CAT's and 2 Cummins.

Lets start with CAT.

CAT has 2 current model engines that I believe would both be fantastic in a 25 Bertram single application. The C7 ACERT and the C9 ACERT. First, the smaller of the 2. The C7, which is actually not "much" smaller from a dimensional standpoint, it is lighter than the C9, but smaller, no.

Cat C7 ACERT 375 hp marine engineThe image on the left is the newest version of the C7.

These engines come in hp ranges from 255hp @ 2400 rpm  to 375hp @ 2600 rpm.

At 422 cu inches this is a big bore diesel. In fact, very close to the 426cu in of the original 3208. Of course in keeping with the current technology the C7 & C9 are both common rail and electronically controlled, as well as Tier II emission compliant.

The C7 is 48"L x 36"H x 36"W. That's no larger than a 6B Cummins and much smaller than the 6C. Moral of that story is this is NOT a physically large engine. The engine weights 1760 lbs, no light weight, but certainly well within the 25 Bertrams engine weight budget.

The C7 is a dry bore block. The reputation is good to date on the ACERT series, some claim this is the modern incarnation of the 3116 -3126 -C7 CAT, with a new fuel delivery system, electronics and Tier II compliance. Notable physical changes from it's predecessors is the expansion tank is now located on the side (makes the engine shorter) So if this is the "smaller" one...

The C9 is a monster in a small package. The C9 is a completely new CAT engine with wet liners. The C9 ACERT marine series comes in 2 basic hp configurations. 1 is considered a commercial rated engine (D series) 510hp at 2500 rpm and the other is off the charts at 575hp @ 2500 rpm. The C9 is 538 cu inches...och. The "D" rated 510 hp actually has "less" warrantee than the 575 hp. CAT C9 ACERT 575hp marine engineCAT claims this is due to the commercial designation. The D 510hp comes with a 1 year bumper-to-bumper and the 575hp has 2 years of CAT warranty. The reputation for this new series of CAT is outstanding. Considered a serious commercial grade diesel, the C9's are going into everything from trucks to bull dozers.

Image on the right is the monster beast C9 575hp.

The dimensions on the C9 are actually 1" shorter than the C7. The C9 is 47L x 38H x 38W. So, it's 1" shorter and 2" wider and taller. The engine weights in at 2,086lbs. Yes, when you add a gear this is all the engine you'll want to stuff in a single engine 25 Bertram. BUT, it will fit and it's not too heavy for the hull.

Either of these CATs would cruise your B25 in the 30+kt range. The C9 575hp would WOT the boat over 40kts. My favorite part of these engines is the lack of noise and the weight.

While "most" boaters consider light weight the holy grail of engines, I don't. Light boats will beat the crap out of you offshore, and "if" you can go fast, have great fuel economy...and a smooth ride, who needs light?

The new Cummins are equally hot!

I'll post some info on Cummins new options in coming days, I always "read up" on an engine and surf the reviews before I comment....coming soon.

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