25 Bertram Express with outboard splash

[Howesounder]

Put the Bertram in the water today with its single 250 HP Yamaha outboard, with 50 HP kicker. 17" propeller on the Yamaha and it leapt out of the water. No tach working, so a bit of a seat of the pants report. Did not go flat out, but let it rev out a bit. It never hit the rev limiter, and did 34 knots. At my design cruise speed of 20 knots, the Yamaha sounded really relaxed. At 23-24 knots you could hear it starting to work. With the Honda 50 kicker running nearly flat out it did only 7 knots, but the prop was for a speed boat, and that will need to get changed out for a much flatter prop.

Super delighted with this package, thanks for your help everyone. I now have a working boat for summer, and will slowly start the above the waterline work.

Steve

[Navatech]

Good job!...

[Tony Meola]

Congratulations.

Now it is time to enjoy the fruits of your labor.

[CamB25]

That's terrific! I hope you enjoy the ride!

Any way you can post a picture or two? You can send them to me and I'll post if you like.

Cam

[Howesounder]

Thanks for the offer, I shot a short video from the dock when my buddy went by at the design speed of 20 knots, and I will send that along in a PM. I did some math last night and thought I would see if you folk would like to shoot holes in it:

The boat did 20 knots at just below 3500 rpm. Fuel bun at that rpm, is 7 gph.

I own a Suzuki df150 and 25 hp tohatsu four stroke. If I use that engine package as a main and aux, I will loose 150 lbs off the back of the boat. The Suzuki burns 7 gallons per hour at 4500 rpm, and the engine is pretty happy at that rpm. If all I want is a 20 knot cruise, it seems that the hp that you get at a 7gpm burn is enough for this boat to do 20 knots. If that's true, the very low hours Suzuki 150 will power the boat just fine for my speed of 20 knots. Suspect that full speed will become 26.6 knots and that's ok with me......Shoot that full of holes? (Suzuki has a lower gear ratio and that will help as it swings a bigger prop, and the 250 Yamaha has 3100 hours so is not really a long term engine for this boat anayways)

Steve

[CamB25]

Are your assumptions based on ideal conditions? no wind, tide, etc? You might need that extra horsepower to get you out of trouble one day.

[captbone]

Grin. Great news. Looking forward to pictures and video.

[Pete Fallon]

Howesounde,
Try using a Mercury Mirage prop on that Yamaha, I used to have luck running Merc props on Yamahas back when I was building boats, e got a lot more speed and seemed to handle better .
Pete Fallon

[Howesounder]

Added more fuel, anchor, and some gear and:

Took the boat out for a longer ride yesterday. Still no tachometer as the electronics are a shambles, but I did put the hammer down on flat water against about 12 knots of wind, and the boat did 37 knots without playing around with the trim. The rev limiter did not kick in, but from my feel, I suspect we were at or just beyond 6000 rpm. This would make my 20 knot rpm about 3250. We got into a bit of boat waves and small seas, and noticed a few things.

The propeller lost grip a few times when we went through big waves, and quickly gained grip again, this at 22 knots. Assuming this is because the standard shaft Yamaha is a wee bit short, as the boat was set up for twins, and each of those would have been relatively longer as they were not on the centreline where the hull is deeper, and the single Yamaha is. Hopeing a Davis plate hydrofoil will help with this?

The 14 knot minimum planing speed I quoted was not the case. The wake is absurd with a huge rooster at that speed, and the boat seems to need more like 16-18 as a minimum reliable planing speed, and even at 16 is ready to fall off. This is a bit high, and I would like to think in bigger water, I could slow down and have a reliable planing speed of 14-16. Again thinking a Hydrofoil, or Davis plate will help lower my lowest reliable planing speed? (I used one on a little 14 foot 4 winns jet boat I converted to a 25 hp outboard. It too had a very high minimum planing speed of about 16 knots. I used a Davis plate, and it now is on a strong plane by 11 knots, top speed being 21 knots, and top speed is unaffected by the Davis plate as the plate is just clear of the water over 19 knots.

So I have the Yamaha 250 as low as it can go in the water already. The prop looses traction even when I gas it to go from say 18, to 26 knots. When I give it the gas the engine revs up just like the clutch is slipping on a car, then a few moments later you hear the Revs drop, and the boat start to accelerate as the prop gains grip. As above also lost traction a few times in bigger following seas and going over big wakes. Trimmed fully down and the problem almost disappeared, but trimmed up gives a bit more speed.

One last thought. One of the reasons the boat sort of falls off the plane so easy is that there is not as much torque available at that low engine speed. I have a 17 inch prop on it, and I am wondering if I might get a prop shop to pound out another inch to make it a 16" pitch. This would bring up the revs, and lower the top speed, (I will never use anyways) but add torque where I need it no?

Steve

[CamB25]

Steve,

Sounds like your engine is mounted way too high. Are you using a 25" shaft engine on a bracket? can't remember your set up. 1" up for every 12" of set back has been quoted as the general rule of thumb. Get the engine lower or farther aft, or better - use a 30" engine. I think you can convert the 25" shaft to a 30" shaft pretty easily if you can source the parts.

16-18 mph is probably the minimum planning speed for the hull. This is controlled by physics - relationship between the shape of the boat and the water with respect to speed. I think the engine power is irrelevant. At what speed does the interaction between the hull and water create lift and decrease the boat's draft? This will be the transition between displacement and plane. I think you need to fix your engine's relationship to the hull and water before you worry about plane speed or wakes.

Pat, Capt Bone, or others on the board may have some better information.

[Yannis]

You're setting 20 knots as your ideal cruising speed, when your boat lifts at 18 or so.

It should not present a problem when the sea is calm and there are no wakes or other issues.
It is therefore irrelevant, in this case, to discuss 150 or 250 since both engines can do the obvious.
I would set a slightly higher cruising speed though, as I think 18 is too close to 20 and you risk falling back into the hole if you're not on top of it.

The engine choice starts being meaningful when the sea is not ideal.
In this case you'll have to be doing two things simultaneously, that is, play with the throttle so as to keep a speed that is comfortable with the sea conditions, AND, is almost always above the 18 knot mark. Otherwise you're back into the hole.
On the other hand, you can't go all that faster, because you'll end up with a smashed chin.
So, what's important is the acceleration that will allow you to cruise close to 18 and when need be to fly to 22, until you drop back again. If that engine cannot do this, or can do it with pain, then its better to choose another engine.

Of course, I agree that your mounting is way too high. I should try to arrange this issue before I make any engine choice. How do you think you can better brake a shaft?

[Rocket]

Great progress Steve, congratulations! I am not sure why you are so dead set on the 20 knot cruise, the 25 hull is more efficient when it is up on the inner lift strakes, your fuel economy in terms of MPG will be much better at 25 Knots than at 20. I find the sweet spot on my 25 was more like 28 Knots. This hull does not punish you financially for a slightly faster cruise, in fact it rewards you with better economy. The ride is still soft and comfortable at the higher speeds and the handling becomes much nicer, you skip over smaller wakes rather than pounding. You do have to be more vigilant about debris in the water, although if it is small debris on a tideline, I have found that if you cut an arc through the tideline the "V" pushes the floating debris away from the prop. The only bad hit that I have had is with a submerged log that must have been 6 to 8" under water.

I hear your concerns about the planning speed but you will find that the boat is much softer in big seas, particularly beam and following seas than most 25 footers, so you will find it is very comfortable to cruise at 20, even into a fairly nasty head sea, if you have to slow down to 14 due to conditions, your fuel burn will be so nasty that you will want to slow down to 7 knots and be in full displacement mode.

Ditto with the others that you want a spacer to put your prop in deeper.

Get out and enjoy it before making too many prop changes etc...You may find you are trying to solve problems that don't exist.

[Howesounder]

Thanks all, I took it out today and finally had some bigger water to try it in. The slippage is just not an issue if I keep the engine told down, so I tried getting to a speed, then trimming up to see how much speed I was loosing by staying trimmed down. Results seem strange. At 20 knots it don't make a lick of difference. At 26 it only raised my speed about 1 knot, yet at those speeds I had no issue with slipping in waves or wakes. Seems like it only happens when trimmed up, and at lower speeds, so Rod, you may be right, this may turn out to be a non issue.

Did like 24 knots as a cruise speed better. Boat just feels more on rails at that speed verses 20, so I get that. In general though, it costs to go fast, and I am just trying to keep the cruise to a speed I can mentally afford.

So this boat according to the P.O. Did 50 mph (43.5 knots) wide open with a pair of 225 to stroke mercs. Now with a single 250 it will do 37 knots. Pretty expensive price to do an extra 6.5 knots.

Rod, I sent you a couple of videos on email. Tried to PM Cam, but could not load the vids to that.

[captbone]

Great news.

Look into bay manufacturing for a 5 inch spacer kit. It will get your prop down deeper while also allowing you to raise the powerhead up higher since you can then move up holes.

I do highly recommend the Doel fin planning aid since it does give you stern lift when the engine is trimmed down. The ideal prop in my opinion would be a 16 pitch Enertia. Much better prop.

I used to run on plan often at 14mph at 3000rpm. I tucked the engine and dropped the tabs. I ran like that alot because it was quiet and also my engine would sound an alarm above 3000 rpm sometimes so I just stayed there.

You can improve your performance with Doel find, prop and 30inch outboard.

[Michael]

I agree with 25 plus knots being the best cruise speed in B25. That is where I normally cruise at unless the weather is too snotty. Regarding the engine ventilating - it sounds like it is only just a little too high, so perhaps some prop work to make the prop work in at this higher level would be the cheapest and easiest option. If you are already reving to 6000rpm, I do not think going down in pitch will be a good idea as rpm will increase even further. Talk to a prop guy and see what he can recommend.

[Howesounder]

Thanks for that Michael. I had it out in some real snotty stuff today and the ventilation was not an issue. Big waves from some outflow winds, and I went through them at 24-26 knots. Nice dry boat!

I know the idea of underproping a boat is counter intuitive, but the 16" pitch would just unload the motor further, and bring the tourque curve back for me at slower planing speeds. It will slow down my top end, and the thing might even hit the rev limiter, but since I am not going to be running at above 30 knots, it's all good. An engine will be happy to rev slightly higher, and therefore be less loaded at all rpms. Thinking a 16 along with a hydrofoil will also help with the ventilation. My 20 knot rpm was 3250, so with a 16 this would go up to 3450. A spacer might be the best long term solution, but I want to do that on the final engine I choose for the boat. This one has 3100 hours, and I only bought it because it was only 3500 bucks with all controls and a 17" SS prop. The idea was to get something on the boat, and see how this single engine and auxiliary works on the Bertram. While perhaps not my first choice, I do have a newish Suzuki DF150 that needs a home, and I am just not sure I want to head out for big water adventures with this 3100 hour Yamaha. Does run well......and I have heard some people getting 6000 hours from the 250f Yamaha's?. I will leave it on for the summer I think.

Steve

[Howesounder]

Now understand why my minimum planing speed seemed to have changed from that first 40 minute ride to the next. Missed a small hole on the outboard bracket, and the bilge pump inside the pod bracket failed. Pod was full of water on second and third rides. Boat is now back to doing a rather sluggish plane at14 knots, healthy flat wake plane at 18, and a slightly higher top speed of 39 knots.

Steve

[Howesounder]

Another update.

Spent some time in rough water, steep 3-4 footers, and yes I could blast over them but quite a pounding at 20-26 knots. Not something I would want to subject myself to for long. So I tried to slow down and the prop would ventilate, but the pounding at 14 knots was much more agreeable. But the boat was on and off plane, and a pain in the arse to keep at any speed below 20.

Installed the most cheap and cheerful hydrofoil I could find (sting ray) and the boat will now chug along with a reasonable wake at right down to 12 knots with a decent looking wake. At 14, it looks very good, and it is happy to sit at any speed I choose above 12, where before it could easily fall off plane. The prop does not ventilate even when in a steep turn, and before the foil, it ventilated at moderate turns. At above 20 knots the sting ray is fully out of the water by about 2-3 inches

So will get that 5 inch extension and use some of that available height to lower the leg about 3 inches, and the other 2 inches to get the power head a bit higher out of the water?

Lastly, is this a east coast, west cost deal on waves? I consider myself a pretty intrepid guy, and the spine compressing, tooth rattling,eardrum shocking pounding I was taking was to me, just sort of insane. East coast waves a longer pattern? Y'all seem to want this boat to do 24-26 knots through the snot, and I tried it, but what a beating! Tried nose up and nose down without a big difference, and ended up at about 14 to 16 knots being best. Did I just get old, and no one told me?

Steve

[captbone]

Great news. Glad to hear she will stay on a plane at lower speed.

I agree with you on the ride. People talk about cruising at higher speeds and I never was able to really boogy with her due offshore conditions. 2.5 ratio LOA/Beam is pretty wide for high speeds in steep chop. 18mph-20mph was my normal cruise in chop. Anything faster and she would slam. One of my reasons that I think anything more than a 300hp outboard is a waste on a 25bertram.

Please post some pictures.

[Tony Meola]

Bob lilco is the best one to answer this since he used to race. You actually need to get on top of the wave and steer the boat do you skip from wave to wave.

Don't ask how to read the waves. Something I struggle with.

[Howesounder]

Trying a picture here. Movie next

Steve

[Howesounder]

[Howesounder]

[Joseph Fikentscher]

Looks good running!

[CamB25]

I love the video! I didn't realize you had a bracket, the 25" shaft looks pretty close.

[Bo Toepfer]

I would enjoy seeing the video, and I did not see a link in the thread. Also did you have the engine bracket made , I am wondering if the Bracket Mfg. have the B 25 template?

[CaptPatrick]

Video: http://s1077.photobucket.com/user/howso ... g.mp4.html

[Bruce]

To me it looks like the ob cavitation plate is above the hull bottom if I picture that correctly.

If your gonna run like that you might think about a cleaver style prop.

[captbone]

Great video. Armstrong has the template for the 25 Bertram bracket all set. You can call them and they will have it on file.

The video shows why the ride is a little harsh. You run bow proud which makes for a very dry ride but since the waves are impacting midship, it does not cut as nice. My OB Bertram did the same thing. It was the driest 25ft boat running like that. Dropping the tabs will allow the forefoot to cut better but you give the dry ride and some performance. It's a trade off.

[Bo Toepfer]

very nice thanks

[Howesounder]

Thanks for all of the thoughtful comments people. Yes the cav plate/engine is too high, and I really need a 30 inch engine. I will add a spacer once I settle on a particular engine. I just don't want to invest in a 3100 hour Yamaha, but may well look around for a 30" one with less hours?

The boat goes a few knots faster bow high, but once it gets snotty, I do let the bow drop, and yes it tends to cleave the waves a bit better bow down.

Mine is a G bracket? And was meant for a pair of 25" outboards, as where I hey ride is relatively deeper in the water off the centreline.

Never thought of a surface piercing type prop, as the engine is only a bit too high, and I think the surface prop would drown. I did wonder if the 4 or 5 blade props might allow to to get away with this slightly high setup, as they are smaller in diameter, so would by design and diameter, be less likely to gulp air. When the boat is doing 20 knots the cav plate is solidly on the water. At 24 knots the cave plate is 1.5 inches above the water, but the ventilation never happens above 22 knots. It is at 16-22 knots where is looses grip over waves or in following seas. I got a recommendation above to use a Merc prop, but they are very expensive to "buy and try" I had a 5 blade and 4 blade on other boats and they were truly stump pullers compared to the three blades I had used, and certainly helped my 19 foot aluminum centre consul that I converted to an outboard with a long pod, from an I/O this boat had a bad habit of loosing grip in a sharp turn (as does this 25) and the 4 blade prop fixed that as well as reducing minimum planing speed.

Yes on the dry ride! What an great attribute here in the cooler Pacific Northwest.

Steve

[Howesounder]

Did a measured run last weekend, and filled up again last night. I am burning just over 10 gph @ 23 knots. I was hoping for 7 but expect that this will improve with the 4 blade, and 19-20 knots.

Did 51 NM and used 31 gallons of fuel so 1.6 gallons per mile?

Steve