bertram31.com

What high hp engines will fit in a 31, 400 hp and higher?

Alex,

Do not exceed 330 hp in the B31. You don't have enought hull/prop clearance for proper loading of a higher hp engine. That's assuming, of course, that you're talking about diesel...

The two main choices are Yanmar and Cummins. Volvo, Perkins, Cat, and others have been used.

Alex,

Your money, your boat. The post I made earlier this week of the one with the outboards is evidence of that. But heres the real deal.

The Bertram 31 is a classic, and it is not designed for 40 knots. Build and run the boat within its design intent and limits and you will likely be happy.

Patrick is right, as he has a LOT of experience from which to speak. Can it be done? Yes. Prop pockets, etc are all really necessary.

But if you want to go fast, buy a go fast, not a B31. So ask yourself what you are trying to accomplish and why. And get ready for all the opinionated folks like me. But reality is a 40 year old B31 ain't the right boat for 400 hp engines. Ok?

Good.

Dug

Now, that all being said, I look forward to seeing how crazy you go.

:)

Dug wrote:Now, that all being said, I look forward to seeing how crazy you go.

:)

Many around here are "motor heads" (including this greasemonkey) but the truth is as you stated in your previous post… The Bertram 31 (and other Berty's from that era) are classical boats and were not designed for speed...

alex n wrote:What high hp engines will fit in a 31, 400 hp and higher?

What you could fit physically fit is one thing… Heck, you could even fit a couple of jet turbines and have a combined HP of 1,500-2,000 HP… What would actually work is another matter altogether… Please keep in mind that, for example, the Bertram 42 (which was at 39,000 Lb max weight at least twice as heavy at the Bertram 31) was equipped with engines in the area of 400 HP…

If you want to go fast get a go fast boat… Personally, I would feel uncomfortable pushing a Bertram 31 above 30 something knots…

Believe me I get it. Look, when I repowered, I put a set of 240 hp Yanmars in. I cruise all day long at 23-24 knots, burning 11 gph. Much of the time I can't actually keep up that speed because its just too bumpy. I will break the boat, stuff in the boat, etc. Its reality. If you live somewhere where it is glass smooth ALL THE TIME it might be worth it, but then what the heck do you want a B31 for? you can put a set of 400 plus hp engines in her, and have no room to access for service, and kill the boat and the stuff inside or never run her near the engines potential, its a waste. yes, that's my opinion, based on 15 plus years of watching others do it. I have a buddy who has a 31 who insisted in putting in cummins 370's or something like that, and he has me by 2 knots. Oh boy, oh boy! dumbass... He spent all kinds of $$$ reinforcing this, and strengthening that, and so on. He yammers about props and shaft angle and all that other bullshit. Hey, why did you think you needed those engines is my question. Power in reserve? You are running diesels, not gas. They have a sweet spot, and that's where you want to run them. Its where you get peak efficiency. Isnt that what you want and why you are putting in the diesels in the first place? Look in the mirror and be honest with yourself. Done.

I was thinking that it would be nice to be able to run 36 knots or so when conditions allow. How fast did the original 31 go that was raced?

The b31s raced by Bertram back in the 60s were gas powered and may, at times, have reached as much as 32 kt. Most probably averaged around 28 kt...

From Need For Speed

There are two primary factors that limit the upper power options for the B31.

Most importantly, in my opinion, is that the hull design allows the boat to plane at a relatively slow speed, beginning around 13 kt, but is limited, in terms of safety, to around 34 kt. Above that speed the B31 becomes progressively unstable. At 40 kt I consider the B31 to be dangerously unpredictable as it is literally balancing on the four inner most lifting strakes with the chines well clear of the water. It takes very little effort to loose that balance and fall off to one side or the other. A gust of wind, a crossing wake, a bit too much rudder, a change in current direction, or a shift in load can all lead to an abrupt change to the planning attitude. When that happens at above 35 kt, there is the potential for the chine to grab water and almost instantly, and dramatically, change the direction of the boat.

This has happened and is NOT just theory....

The other factor, is proper loading of the engine. The more horse power a marine engine develops, the larger the diameter and pitch of the prop has to be to utilize that power effectively and efficiently. With the stock shaft angle of 15º and the standard strut configuration, a 20" diameter wheel is a safe diameter. 21" is the maximum diameter without modifying the hull and struts. Above 320 hp, the necessary prop diameter can't be fitted under the stock hull/strut configuration. A 21" diameter wheel could be fitted without modifications, but the pitch would have to be so great that trolling/idling speeds would be excessive.

Everything has it's limitations. Just because we might lust to exceed those limitations doesn't make them go away....

The need for speed is perhaps OK, but only under the proper conditions, personal abilities, and equipment. You can't shoot the moon riding a bottle rocket.

I have 370 cummins in my 31 and with how I overbuilt the boat I have no concerns with getting squirrelly at high speeds. I also have a heavy custom cabin and full tower. I didn't build her to go fast, I built her to take a beating and shrug it off. I couldn't pass up the engines built by my dad's friend who worked for cummins northeast. Wouldn't change a thing, the bigger sixs make the 31 ride much different than the four cylinders. BH

Had 250 6bs on my somewhat stock Fbc, she pinned at 29 on a good day, stable, ran 25 at 2400 , was happy at 2200 at 22 kts.long runs at sea were that 2200. Go faster maybe ,but speed is for gomers with Bimini 41s with 3 350s and really nice gold chains. Seachele II is a 1979 38 with 300 hr 450 diamonds. I know it's a Napier hull like my old 28, rides kind of the same,but is happy at 22 and hit the pins at 27.5kts. Not bad for the old girl. Speed is for guys with gold chains, I lived in Miami.

I want speed because in the northeast we run 75 miles each way , to and from the fishing grounds, no gold chains here but I am Italian and say "how you doin " a lot . But honestly 370 hp would be nice to have if you need it, like for example to make the inlet by weigh in time in a tournament.

I am at this point playing with the idea. I currently have a 36 jersey cape with 480 hp volvos. It runs 32 on the pins, and is a beatiful boat, total refit in 06 , even made my own fighting chair that is as good or better than release or bluewater chairs. The 31 has a history and provenance that is alluring. Like many on this site I just want to build and fish one, it's in my future. Thanks for the input, I have already learned so much just touring the website

Then there is the issue of shaft angle.. as the HP increases the shaft angle results in the stern rising and the bow digging in.. how do you think that would effect control?

alex n wrote:I want speed because in the northeast we run 75 miles each way , to and from the fishing grounds, no gold chains here but I am Italian and say "how you doin " a lot . But honestly 370 hp would be nice to have if you need it, like for example to make the inlet by weigh in time in a tournament.

Alex

I run out of NJ. Yes it would be nice to run at that spead running the Canyons. But ask JP. He probably puts the most Canyon time in outside of Brewster who just stays out for Days. But JP will tell you, he can rarely cruise at 28 knots, and he has the 315 Cummins. When I repowered a couple of years ago, the diesel shop I purchased my engines off of said, remember it is only a 30 foot boat. So you get to race across the bay every day, but when you hit the inlet that is not going to happen.

You know what, he is right.

What area of the northeast do you operate your boat out of? I operate out of fire island inlet and travel about 72miles to canyon so I built my boat for maximum fuel economy and take a beating while captain remain coftable. Actually economy and speed run hand and hand.i have 315hp cummins and attain same economy as 240 hp Yanmars with a hell of a lot more weight in the ass to keep her staple in rough seas.i can run 30 kns.cruise but super economy is 28knts .wot speed use to 36 knots plus but idle speed is impractical so I deproped to run about 33 knot . there is extensive work you would have to do .Trust me 28/30 is all you want to attain on a normal day in the the northeast ,yes you could run 36 knots but you would use quite a bit of fuel.

Alex,
What the hell are you thinking, those e-cigs going to your brain?

You just go patch up that engine and get your girl back in the water. If you want to come for a ride on a shitty day to get the notions of going smaller out of your head jump on in.

If you really want to redo one I'd look at the QSB at 305hp, you'll see close to 36kts and burn less fuel then the mechanical 330's, be quieter and relatively smoke free.

One of the things I used to hear often coming from those who were repowering from gas to diesel is that they wanted bigger hp to provide power in reserve. I am not hearing that from anyone here, however I want to drop in the mechanics perspective from those who work on my boat. And trust me, I am open to other input from those who know more than I. And I consider that to be most.

With a diesel engine, it has a sweet spot. That rpm range is where the engines are happiest. They run most efficiently, they run the most cleanly, etc. If you are consistently running outside that sweet spot, you will likely not be as happy, and neither will the engines.

So if you want to run 24 knots consistently, you want to pick the engines in such a way as to that being the speed the boat runs when the engines are in the rpm sweet spot range.

Gas engines are not quite the same and power in reserve is a very good approach.

Correct me if I am wrong? And All of the makes of engine, especially Yanmar and Cummins are great engines. Your choice may well be dictated by your quality of service. I love Cummins and see nothing wrong with them. But in the Mystic area, Yanmar has much more support. I knew who I wanted to work on my boat, and they did and do not work on Cummins. So there you go.

Dug

JP,
Just playing around with ideas at this point, I'm keeping the boat I have now for a long time, just trying to learn as much as I can about the 31s

Well you came to the right place,this board has some great folks on it. You'll learn a bunch about these boats here, it was the first place I came when we started, everyone has been great.

I run to the canyon when it is flat out on the way out or back maybe 5-7 times a year at 29.8 knts. For a 31 that's smoking fast at cruise. Most all the time I beat my way out there at 23-27 knts. I have the Yanmar 315s. Many times it is so snotty I'm down to 10-13knts. Like already said; If you want to go fast get a go fast boat. But when it gets very rough and the waves are huge I will be laughing as I blow by you in your go fast boat that does not go fast in 5-8 footers. Just my 2 cents.

alex n wrote:I am at this point playing with the idea. I currently have a 36 jersey cape with 480 hp volvos. It runs 32 on the pins, and is a beatiful boat, total refit in 06 , even made my own fighting chair that is as good or better than release or bluewater chairs. The 31 has a history and provenance that is alluring. Like many on this site I just want to build and fish one, it's in my future. Thanks for the input, I have already learned so much just touring the website

Your not kidding Alex that's a beauty! Welcome aboard!

Bob H. wrote:I have 370 cummins in my 31 and with how I overbuilt the boat I have no concerns with getting squirrelly at high speeds. I also have a heavy custom cabin and full tower. I didn't build her to go fast, I built her to take a beating and shrug it off. I couldn't pass up the engines built by my dad's friend who worked for cummins northeast. Wouldn't change a thing, the bigger sixs make the 31 ride much different than the four cylinders. BH

Bob, what do you think of your 370's? I priced the 330's and 370's and there the same price, i was told the only difference is tuning and the rating is at 3000 rpm's. I'm ready to take the plunge. I fish Poormans Canyon to the Norfolk (70-120 NM) in the pursuit of White marlin so every knot i can get i will take on the cruise home there were many days I ran home at 30-31knots with my Yanmars. That being said I was never able to go out more then 27 Knots.

My 240hp Volvo diesel flybridge B31 was fairly heavy. I'd cruise easy at 22kts and high cruise it at 24kts with top end at 29kts with 18x 22 4 blades on her. Many trips to the edge (and running out of CT I had easy 93nm before I hit 100 fathoms. I sold the boat in 2007 and last year I picked up a 26 Pursuit CC with low hours and in pristine condition. Her low cruise is 28kts, cruise is 34kts and top end is 46kts. At 28kts I am burning 11GPH total and I carry 150. Yes, there are weather days that I could go in my B31 that I would be just plain stupid to try in the Pursuit. However, as life has gotten significantly too busy for me, if I am lucky I will get to the canyons 2 trips in 2014 -- and I will pick my days, pray that the weather holds up and hook it up for the run home. And probably after 45 minutes of rattling my fillings I will back it down to 20kts and get home in the same amount of time as I would have in the B31 -- just not as comfortably.

But, the purpose of the center console is I am mostly a 2 man crew these days, so bass fishing and even sharking are a lot easier on a center console.

Let the flogging begin.

Tom

TailhookTom wrote:Let the flogging begin.

I see no reason for any flogging… Boats are just a means to an end… A tool for a job if you wish… For some the "job" is to cruise around with the family, for others it's diving, for others it's offshore fishing… And even among those examples there's lot's of variation…

However, like with tools and jobs, there's more often then not several tools that will do the job… Some better then others… The tool one selects has as much to do with cost and availability as its utility… I like to do all of the above "jobs", considering my "crew" (Admiral, 2 grown sons and 2 preteen daughters) a sportfisher of a medium large size is the best all around tool… For somebody else it will be a smaller sportfisher or a CC…

Different strokes and so forth…

TailhookTom wrote: Let the flogging begin.

Tom

The 31 is a great boat, perhaps the best boat ever built...

But its not the best at everything nor the boat for everyone.

Jimmy, I LOVE my Cummins 370s, if your running a stock 31 fly bridge I'd go with the 330s, I've been on JPs Chimera and she runs great, like Brewster said most of the time you can't run that fast anyhow. My 31 is heavy, heck I used 60 gallons of epoxy during the rehab, I carry 300 gallons of fuel, generator, tower, custom cabin enclosure. My normal cruise right now is 25-26 knots and I don't have my props dialed in yet. The boat loves to get up on top and just runs right through stuff key is to stay on top. I moved most everything back 3-6" engines fuel tanks, got Capt Pats big rudders, ass end stays planted. I don't have but 120 hours on her this summer next season will be the offshore test for Resolute..will keep you posted..BH

Gent's

This thread has me really thinking about the old 3208T's I have in my 1983 38 Convertible II
What would be a good replacement for the motors in this boat.

Have had her now 20 years, and thinking it would be better to repower, than go out and get into another boat.

Kevin, just ran my 79 38 convertible to Islamorada from Stuart, full of fuel and water cruise at 21 kts at 2100, on the pins 27.5 at 2700. Slightly under propped. 450 c series diamond cummins. Lots of room in the engine room get the remans. Bill call me at 7722406146

JP Dalik wrote:Alex,
What the hell are you thinking, those e-cigs going to your brain?

You just go patch up that engine and get your girl back in the water. If you want to come for a ride on a shitty day to get the notions of going smaller out of your head jump on in.

If you really want to redo one I'd look at the QSB at 305hp, you'll see close to 36kts and burn less fuel then the mechanical 330's, be quieter and relatively smoke free.

Those QSBs sound like a nice fit for the boat, I'm guessing they're big money?

very dumb question !

Gert

Peter,
Any of the new computer diesels are costly which is why the reman mechanical program is still a good deal.
Frankly unless your living on the boat running it daily and keeping track of exact fuel usage to the drop a casual user will never realize the difference between the electronic and mechanical engines

The other alternative I have been seeing lately mostly on the Yanmar side since the 6lp and 4lh are gone is buying a whole boat just for the engines, yanking them and selling the hull for a repower project. I know a few who got decent deals doing it this way.

I repowered an Egg Harbor one time with a pair of Volvos I pulled out of a burnt to the deck SF.
Nasty smelly job, but the engines were low hours and nothing on them burned.

Just a note for everyone.

This type of thread has come up numerous times. I've seen 31's do over 40 knots(gas boat) so they can go fast to a point.

BUT, having repowered so many styles and size boats (leaving out go fast style boats for now) matching an engine, gear, prop combo to take advantage of the power curve and hp output of an engine in a boat is important.

Why put a 400hp pair of diesels in a 31 if even with prop pockets your available cruse is going to be in the mid to high 30 knot range. Why spend the money on that power if it can not be leveraged? It makes no sense when for less hp and money you can get good safe performance that you can use.

The notion that the engines are working less so they will last longer is nothing more than silly thinking. If you load the engine to factory rpm recommendations and loading, they will do just fine and give you good service.
Engines need proper loading to burn fuel at proper cylinder temps to keep from carboning up. Its just a fact.

Can't tell you how many rag sailors in the effort to save fuel and wear and tear on the engines choked up the exhaust with carbon like butter does to your arteries.

The largest engines in the 31 I ever agreed to do was a pair of 330 QSB's when they first came out.
The boat had prop pockets and with a stripped hull, no interior at all top end was 36 knots but even with the pockets idle speed was stupid fast.

If one wants to go fast in a 31, gas is the only way to go, diesels need too much prop loading even at 1.5:1.


There's always someone who wants to put a 429 cobra jet into a 70 Pinto. Its part of being in the testosterone family.
With enough money anything can be accomplished, (well really nothing gov't related) but remember having a wife with 76 DDD's is more like a freak show than a useful play toy.

Bruce:

In other support for your comment on benefit of mechanical versus electronic engines == many years ago while fishing in The Big Rock, there was a significant lightening storm that passed over the marina (the sit in the middle of the boat and pray to God you have clean underwear to change into after kind of storm). Needless to say, one of the lightening strikes managed to make the big cat diesel in our boat an idle only motor as the computer went burp -- happened to 3 other boats on the same dock -- the only boat that up and ran that next morning was the 892 powered -- and I mean an OLD mechanical 892 boat. The rest of us had to wait for the Geek Squad to show up with their laptops and assure our cat that her 880hp were fine.

Tom

Been there, done that Tom.

And guess what to the surprise of many owners, warrantee doesn't cover lightning strikes. While insurance does, many have high deductibles to afford the premiums.

Last electronic lightning strike I did the owner had a 30k deductible on a 600k boat. The bad computers, controls and one replacement injection pump along with labor ran just under 30k. His wife went back to work to pay me on time payments cause they ran out of money on the last 6k final bill.

He never thought about the consequences of lightning and electronic. I further informed him that between each of the 6 engine computers, controls and engine sensors if everything had died it would have ran over 60k.

This on engines with 75 hours run time.

Pm me if youre looking for a hull...

Bruce:

Amazing how many people try to bargain on their insurance and have cutrate policies -- we saw it on Sandy -- several of our neighbors ended up selling their beach houses as they had policies that were half the price of mine -- and covered 1/4 of the value.

Tom

I know I'm a bit late but thought I'd share a read on the 6BTA mechanical and differences between it and QSB common rail. I thought it to be interesting on oiling under the skirts for cooling/more rpm.


Paul Foulston, a boatdiesel forum Cummins moderator from the UK was on the engineering design team @ Cummins. He's retired now but "stays in touch" with the engineering innards @ Cummins.

Paul Foulston: Bill, There is actually very little common about the block B Vs QSB. However lets get down to some basics. The plain old B loved to scream with no ill effects as the Dodge Ram guys know, in fact it loves to spin around 3200 all day where there no hint of crank activitity at all. Bearing in mind that the B crank does not run into trouble until 4200 rpm, other than a torsional grumble at 2700 rpm bottom end is incredibly robust and torsional free. If you ever get to lay a Yanmar LY crank on the floor alongside a B the 3,300 rpm Yanmar crank which looks like a bent pin and nobody questions it. QSB did not need anything doing to the bottom end up to 380 Hp. The big deal is heat. Power equals heat. Once over 350 Hp the old B block has difficulty getting the heat out of the piston crown. The 91 block refinements improved piston cooling. The 370B has had a small piston design change since it first came out to make it more tolerant to abuse. ISB base motor design recognised the need release more power out of 5.9 liters to match the capability of the bottom end. As I said power is heat. The radical and simple piston cooling nozzles in the main bearing saddle of the B were no longer up to the job. ISB was designed from the outset with ´J´ jet under piston cooling nozzles just under the bottom of the bore in order that the oil jet travel was far shorter and better targeted on the underside of the piston. New higher capacity lube pump and cooler came as part of the ISB. The whole ISB block was redesigned and has far greater tensile strength than B Storm block as well as noise reduction benefits. QSB marine was slow off the blocks, the original top rating of 380 was all about using the 370B cooling package, bear in mind QSB 380 is 375 proper Hp 370B is 355 proper Hp. Higher ratings had to wait for a more capable cooling package. Right out of the box ISB proved to be a potential powerhouse and Cummins subcontracted Ricardo to develop ISB for military ´funny´ applications and 500 Hp came straight out of the box. That was in 2001. However what was apparent was the need to get the fluids pumping around the engine and this work saw the capability of the four valve head to continue to follow at high rpm´s. The four valve head actually demonstrated a better valve control than the two valve B at high rpm, probably due to the lower inertia of the valves. QSB 425 came out with a large heat exchanger an even larger oil cooler, still 3000 rpm rated speed. However Cummins is ultra conservative and they developed a unique con rod with an even larger pin bore than a normal 5.9 which is already generous. I think the larger pin bore is borrowed from the 6.7. If you take the QSB 425 as a base platform and improve the coolant flows by spinning it faster the power grows accordingly. If you consider the 480 will have been signed off at 10% overfuel overspeed for 500 hours before anybody even considered letting it loose to the public you realise what the capability of the engine is. Although the 440/480 benefit from the more muscular rods of the QSB425 the part#´s are different even though they look identical, I suspect they a balanced assemblies. I have been very close to a pair of QSB´s in a raceboat running at 3600 rpm all season with calibrations of over 600 Hp at times. Yes an engine blew. Why too much oil, same old story, oil level becomes super critical at 3600 rpm, increased windage in the pan causes aeration of the lube oil and lube temperature rockets. Boat ran a race with 20 psi lube pressue at 3600 and 600+ Hp! and the crank held out but the block split around the area of main bearings, but it held together. Problem solved with CAREFUL calibration of oil pan. New engine sat at 60 psi at 3,600 at the end of a days racing without any issues after that. To sum up the 3400 rpm QSB certainly not a marginal product it is not the Cummins way. What limits the engine from developing even more power? Just the lube oil cooler design, you just cannot cram any more plates in there. Once Cummins have solved that one like they did with the piston cooling jets somebody will be asking all the same questions about some even higher rating.

I finally got around to looking up some stats from SEA RACE by John Crouse, a definitive book on ocean racing.

1961 GLASS MOPPIE with a pair of 280HP Chryslers averaged 42.5mph in the Miami-Nassau, a course of 184 miles.

1961 GLASS MOPPIE with a pair of 330HP Chryslers averaged 44 mph in the Around Long Island,a course of 280 miles.

1964 LUCKY MOPPIE with a pair of 380HP Daytonas averaged 46.9 mph in the Sam Griffith Memorial Race, a course of 186 miles.

1964 SURFIDER with a pair of 380HP Daytonas averaged 48.6 in the Cowes-Torquay, a course of 188 miles.

1964 LUCKY MOPPIE with Daytonas averaged 46.9 in the Viareggio-Bastia-Viareggio, a course of 186 miles.

By 1965 Bertram was running non-production hulls.

There were many other victories at lower speeds due to sea conditions.

Daytonas 400 motors were also installed in sportfishing boat, including Daytonas, Rybovichs, and Merritts. I don't know what block they were based on, but had twin turbos and claimed 380 HP @ 3800 RPM.

They also claimed turbos would kick in somewhere around 2200-2500 RPM.

And the flattest torque curve of any sub four hundred hp in the world . Starts at 2000 rpm and goes to 2800 rating flat so if you load the engine by way of a ridiculous cup in the props you can "back off" to 2050- 2150 rpm with a smile looking at EGT pyrometers .unheard of fuel economy and engines will last till the end of century ! I look at turbo's last week ,been running since 2006 and never maintenance .you could eat off the fan blades .when I get some time I will show you how a 31 Bertram sedan or Bahia mar will run 55mph all day as you try from sleeping at the wheel.a 31 Bertram hull with no shafts is capable of running about 85 mph with no changes just balance .actually has a stability advantage over go fast boats but slower top speed with same power due to wider beam.case in point vintage 31' cigarette bullet.the 31 Bertram is capable of around 85mph with perfect running attitude and far better recovery in larger waves then a go fast 8' beam boat. When I get time I will give you facts figures, and photo's no need to hide the secrets I am to old to start building these boats. Yes Jimmey G there is a Santa Claus if you have a need for speed . I will release facts,figures and know how with photo's .i truly suspect Bruce was holding back I know he knows.

Sorry, Bob, but that is hypothetical B.S.

A B31n the real world, not specifically modified for racing, the proven safe hull speed limit is around 34 kt / 39 mph.

Anyone trying to run a standard B31 over 34 kt is flirting with danger. Over 40 kt the flirting is over. Over 50 kt is a death wish.

And even stripped down and highly modified/reinforced, 85 mph? Ridiculous on anything other than paper.

Trust me capt Patrick I will show you right now I have some very important obligations .give me a day or so.the first clue is " not a conventional inboard shaft driven. However cannot have any structure on top for center of gravity, a no top Bahia mar or no front brim sedan will be the boat to use.
I have step up to give a proper burial to a veteran whom past away penniless.i rufused to have his put in " potters field"

I can tell you from personal experience a 31 with no mods other than just big power IS dicing with conditions. Our factory(I don't know how you could order this option bless Bertram for having them) 31 was a FBC and no effort went into "balancing" with the Ford Cobra 427 side oilers. These were true BIG blocks in every sense of the word with big power almost cubed even at that time which is also almost unheard of but Ford had a reason, to win races from the Cobra car. Anyway, our 31 did 45 mph and at that speed we had ( even me at only 13 and I was not scared of at the edge) white knuckles and only opened her up within the SF bay particularly Richardson bay were your out of the ocean's swell/forces. Even small wakes from little boats as we rocketed past seemed to upset the hull. I remember the hull being easily upset and maybe due to just stock config. but would do exactly what the Capt says and be a handful with "catching" even small waves and having to correct fast or your going a different direction. It was fun, kinda. But not! Plus you had the extra benefit of burning close to 60 gallons an hour at WOT. I'd imagine you would have to do a lot of mods to be comfy at hose speeds.

Remove it all and
Run surface drives.

Is it a 31 Bertram anymore...I'd say about as much of a 31 Bertram as that Outboard powered boat in Dugs post.

I know that with those old 454 350HP big blocks, when pinned, and she got on top, it was a little squirrly. Not dangerous but you feel she was balancing on very little hull. Form what I can tell, the 24 to 30 knot range is the hull's sweet spot for a good ride. I know with the diesels, moving from that 19 to 20 knot cruise up to 24/25 knots, the boat rides and handles so much better.

Plus Kudos to Capt Pat's rudders. Real big difference.

Ok .let's start out by saying once upon a time ,maybe eight years ago a new boat owner rented a premium dock space with a hydro lift I went to set him up." I had a 95 mph fishing boat built" oh boy this is going to bea great BS story!. The boat came in a week or so later and we pull this beauty off the trailer and put into water.this was a offshore race boat with half f-16. Canopy and real race stand up bolsters. A Kevlar lay up 32' catamaran by viper. Twin 480hp Yanmar big blocks with three speed gears and speed master out drives. After tweaking props we went out for testing.no problem trolling in first gear long story short 75 mph cruise and 104mph wot. Only four rod holders so we mounted two behind cross brace. Ok take foot out of mouth and be more open minded.the boat really was not that bad on fuel considering 75mph cruise in 2 to 4' waves.
Let's start our no BS 31'bertram that run all day in complete safety very coftable at 50knt..we purchase a 31' Bahia- mar no top fitted with small blocks for 15,000 we take to capt Patrick yard and gut the cockpit,remove engines, gears,shafts,shaft logs,structs,rudders,rudder boxes.next we remove all thru hulls.we then blast all paint off bottom and the captain repairs All holes everything sealed ,no structs,rudders nothing just a straked 31 hull with reverse chines for added safety ( but slightly slower) over 24 degree deep vee race hull.we remove tank and side panels and grind down any rough spots.now we add 1/4" lay up on transom with knee braces in corners and short ones off two center stringers to new transom.capt goes in shop to design two stand up bolsters with fold down seats and nice hand rail on back.bruce comes in and lays out supports for 3 Yanmars 315 hp each , exhaust is over the top out back.bruce checks X dimensions and layout .generator consideration are discussed with customer at this time.fuel tanks will go forward of engines about 5" from harmonic balances.paint bilge area and prepare for engine installation. Bruce installs engines and the capt designs new cockpit sole as well as rear platform over engines with hinged engine cover.this will continue here is the triple engine install from forward and rear view Benny is option.

Another view exhaust will be wrap on completion of installation.

Our 50 knot Bertram will continue. Capt need a break.

Oh boy!

The rounded keel alone makes it a dangerous hull at speed… a Napier, sharp keel is much more speed friendly.
Unless Bob is planning on chopping the aft keel and making a big-ass delta pad, or similar for the boat to ride on at speed, then it'll be very likely to chine walk.
When/if the walk gets bad enough, then one of the chines will grab- causing the the forward sharp entry to dig and the entire boat to do a violent 90 degree hook. No thanks.

No freakin' turbines!?!? I was so sure there were going to be turbines....
Dang.