Surface drive for v6 ford

[jamesp2k]

Heres what im up against...

I have a rocca 600 sports boat (20 ft weighs about a ton and a half) a knackered old omc leg and a good ford v6 engine my idea is to go surface drive rather than leg. To make it more intresting im going to try and make the drive myself. any advice on design or anything aka gearbox type, prop size/pitch and anything else like that.

Look foward to some help

James

[CDK]

Look at Lancing Marine surface drives (LM-14). Their catalog shows a drawing with dimensions. A very simple construction, once you've obtained the material, you can weld it together in a weekend.
If you're a good welder you could construct it all from stainless steel.
The only expensive parts are a gearbox and a prop.

[jamesp2k]

Cheers for that, how would i work out the prop size and with that design would the boat not 'walk a bit'. oh what size shaf should i use same as the lancing spec?

[CDK]

Put that question to Mike Bellamy at Lancing Marine. He wrote me a few years ago that he is very satisfied with his twin LM14 cabin cruiser, using Ford puma diesel engines. He claimed a significant increase in performance compared to stern drives.

They designed the LM14 for engines like yours and can advise you which gear ratio to use. As far as I know they only offer one solid hub nibral 14" prop for this drive.

I decided to design my own tunnel drive system which still isn't performing like I hoped it would. You have to accept the noise and vibration that belong to surface piercing. I found it unacceptable but tried it with 3 blade props and was afraid everything would fall apart.
Last week there was a large RIB here with 5 blade props and 2" shafts: I didn't see any parts falling off, but it was quite noisy.

[jamesp2k]

I have now managed to source a borg warner 1:1 gearbox but am struggling to located a adapter plate to connect to my engine any ideas on sourcing a second hand one since like i said trying to keep cost down. One other thought i have had is do i need to fit a angled plate on the transom for when going astern to ensure that prop wash/thrust goes below the boat as opposed to hitting the stern.