What engines for this boat?

Question

I have a ex wooden lifeboat, (open) 37 foot long by some 10.5 wide, I want put a diesel engine in her and, if possible achieve a speed of around 12-15 knots, It must be a diesel engine, at presnt she weigns in around 4 ton, by the time I have finshed putting a superstructure and steering house up front etc leaving around 12-15 feet open at the stern, I figure she will come in around 6 ton. So! is this speed achievable with such a boat

or am I stuck at 5-7 knots which is what I believe she was originally built for , but they didnt have the power stuff in 1938 we have now. Any assistance would be appreciated as I know nowt about powering boats, at the moment she has a single s***w shaft housing.

Answer 1

OMDZ!!!!!

I love HELLO magazine too!

Answer 2

You have a displacement hull which means the design speed will be 1.34 x Sqrt( waterline)  

if your waterline is 30' then you have a hull speed of 7 kts.

you can push it higher, but the fuel consumption goes up exponentially.

so displaceing 6 tons at 6 knts you'll need about 200 hp.  you can run slightly less and only need about 2/3 of that for efficiency.

since the most efficient Diesels use about 0.35 lb/hr/hp expect 7.2 gal/hr consumption.

if you throttle back to 100 hp y our consumption falls to 3.5 gph but the speed falls only to about 5 knots.

these are  just rough estimates Ive collected over the years and use for comparison purposes only.

wer

Answer 3

Get over 100 hp.  Cummins, Perkins/Westerbeke, Volvo, Yanmar..

Answer 4

I don't know if you will get that speed from that hull shape. You could pick up a GM 6-71 or 6V53 and drop it in. They can put out tons of power (200-485) and run forever. But they weigh a ton. Or you could get a more modern Cummins 6BT and have from 210 to 370 hp and the engine weighs less. The 210 is really under stressed and will last a long time. Cat has engines like the Cummins and a Cat 3208 ranges from 210 to 435hp, there are tons of them around. I would stay with an engine at the lower hp range. You will not benefit from the higher hp and the lower hp engine will last longer. Look at

www.boatdiesel.com and you might find some good deals on used engines.

Answer 5

Yamaha makes a lightweight engine, it is expensive, about $20,000/ that will give you 5-7 knots. with the type of hull you have that is about as good as you can expect. putting more power will not do any better and you run the risk of damage to the hull.