hello everyone im in desperate need of help i have a 27ft x 8.5ft planing hull all in weight of 2.3 ton with a 440hp yanmar diesel 2 speed trannie 1.3-1 and 1-1 with fixed surface drive.
The maximum rpm of the engine is 3300, i started of with a 17 x28 3 blade bronze prop with 75% blade area. It was doing 57 mph at 2700rpm in calm conditions and 60 with a chop. Then i changed to a 26 4-blade mercury, it was doing 60 in calm conditions and 64 in a chop and pulling 3000rpm. Then i changed to a 25 3-blade bronze doing 60 in calm conditions and 64 in a chop also at 3000rpm.
Then i tried a 23 3-blade bronze and it still would only do 60 in a chop still 3000rpm. It doesnt seem to want to go faster than 60!!! or over 3000rpm!!!!
I know getting air under the hull will get more speed but is there any way i can modify the hull so that it will run faster in the calm? and get more rpm?

Any help would be greatly appreciated
Look forward to hearing your ideas.
Any questions ask away!

Regards,
Gerard

I kind of surprised that you couldn't get away using a larger prop on that torque monster. Unfortunetly diesel power is relatively new in the Perfomance Power Boat relm. Try calling BTM marine in FLA. Bill has done a bunch of work with diesel's. He may have some good info. Good luck

What do you expect from the boat?????

The 64mph top speed sounds about right to me with 440hp in a 4600lb 27' V bottom.

Exactly what hull is this???? What deadrise????

I'm not sure you can expect much more than 3000 rpm from a diesel engine, or 64 mph from the boat. I'm with Griff, it sounds like you're getting good numbers for the set up. If you want to go faster, it may be time for a different boat.

Or another turbo!!!

i was told that the 440 yanmar needs to be running no less than 3300 rpm or it will start dropping valves they need to be reved but i cant get it to go over that or else the speed will start to drop . maby it is the hull it is a fletcher zingaro

Yanmars like higher RPM's than other diesels. If my memory is correct I think your goal is to run them 3300-3400 at WOT.

Is the engine new? What RPM does it run unloaded? I think spec unloaded is almost 3,500. Are you sure the RPM gauge is working properly?

Based on your speeds and RPM's I tend to think you have a faulty tach. I would check that before doing anything else.

To get more air under the hull you might be able to use a set of rocker plates to get some bow lift.

the engine and trannie is brand new. and the taco seems fine it revs to its maximum in its first gear no problem boat on the plane in a couple of seconds but as soon as i hit the second gear it drops from 3500 down to 2600 then back up to 3000 as soon as it gets settled in

Gerard, a "planing hull" is a little vague. What boat is this? Some hulls just are not designed for high speeds.

Michael

European manufacturer. See post 6.