Outboard Power

[AlansToy]

Please can somebody advise or suggest where i can get imformation on the following questions regarding this boat.
The boat is a Bennetti Falcon Royale 36,it is 2800kgs in weight only7'-6" beam and is a deep V with no engins or legs fitted.Originally it had 2No 5.7 V8 petrols with legs. Year of boat is about 1988
I have a Yamaha 250 hpdi Vmax Engine which i can mount on set back(jack plates)

1 Would this engine be ok.
2 What sort of speed could be expected.
3 Where would be the best place for propeller selection be.
4 What approx fuel MPG

The boat is to be used just for fun and a bit of cruising and be able to be fast enough to pull a wakeboard.
Thanks in advance any help will be appriecated Alan

[Pericles]

What power did the two V8s develop?

IIRC, you aren't too far from http://www.lancingmarine.com/. Why not consider their jet drive so as to prevent damage when cruising the south coast? Sell the o/b and bung in a diesel. You'd be lucky to get 2 mpg with the Yamaha and at £4-67 per gallon the boat will not be going out too much. Lancing also sell a neat surface piercing drive. Otherwise see http://www.coastalrides.com/ in New Romney.

Pericles

[Jango]

If the total Displacement, with fuel and Driver is 2800kg, max speed will be about 30 mph. Pericles is correct about Fuel economy - not that great, but probably alot better than twin 5.7,s.

Give me the numbers - Engine max RPM and gear ratio and also varify weight and I'll provide Prop size.

Jango

[AlansToy]

Thanks for the replys i was going to put a diesel engine and surface drives in the boat but trying too find a suitable engine at a good price and not having time to do the required work i thought this option was easier and quicker as summer is just around the corner.What i am after achieving is a boat suitable for a few passengers and some fun wakeboarding so if it will do 30 mph this will be ok. As for the fuel mpg the amount of nice days we have in the summer suitable for boating is not really a issue, you can't put a price on leisure as they say and its still a lot cheaper than buying a large wakeboard boat that will also take a few friends.
I do not know what power the V8s were but was told about 190 each, as one engine had already been removed and the other one was not complete and the legs had been removed that is why i took this route.

The Yamaha Is 250hp rated at propeller @ 5500 RPM
RPM range is 5000 - 6000
The engine will be mounted on 8" setback plates and the swim platform will have to be removed to allow fitting.
Gear Ratio is 1.75:1
Weight of engine is 245Kgs
The weight of Boat now is 2800kgs without any engines or legs
The waterline length of boat is approx 28 feet x 7'-6" beam that was when it was fitted with the twin 5.7 V8s and legs.
Thanks again for your quick responce Alan

[Pericles]

Bolt it on and see what occurs. What's the worst that could happen? Make sure you have valid insurance.

See u at sea.

Pericles

[Jango]

Adding 245 kg for motor, plus Driver and Fuel, another 250 kg, total Minimum displacement is 3300 kg.

Max Speed at 3300 Kg and 250 H P is 27+ mph or 24 kts. As load (people or wakeboard) is added speed will decrease slightly.

Recommended prop is a 15 1/4 x 11 or possibly 10 with Heavy loading ( min. prop D.A.R. 55% )

[AlansToy]

Many Thanks Jango for the imformation would it be the same if the set back plates were bigger than the eight inches that i had stated as with eight inches i will not be to tilt engine because of failing the transom.
How will i work out the height of cavatation plate in relation to bottom of boat is ther some data somwere that says for example twelve inches back requires five inches up.
Regards Alan

[Jango]

It shouldn't matter how far back you position the motor. Just be sure, your mounting is strong enough to withstand both the motor weight and thrust.

I would use an adjustable "Jack Plate" starting with the Motor cavatation plate, even or slightly below the boat bottom.
You can thus move the motor up and find the proper position during Sea trials. See:

http://www.iboats.com/Jack_Plates_an...view_id.217141

Hope this helps, Jango

[AlansToy]

Many thanks Jango i will let you know the outcome in due coarse i will fabricate Gill bracket with a mechanical Jack plate
Regards Alan