So the drives are 1:1 and the trans is 1:1? So are the props huge then?
I not a math guy, but I was figuring a BBC spinning 6k rpm through a 1.5 drive is spinning a prop 4500 rpm. Depending on HP, torque, and weight will determine the pitch of the prop. Lets just say it's spinning a 23p prop to achieve 60mph. These Cigs typically max out at 55-60 from what I've read. So with a disel running max rpm through a 1:1 drive and trans they are spinning their prop at only 2500-3000 rpm. Am I figuring this right??

Thisisstank - that black and red one is the boat we're looking at.

The weight of the diesels is half of a BBC. So we're cutting about 2000 lbs out of the ass end of this thing. Is this gonna work or bad idea??

Not going to work with 1:1 drives. Will need 1.6's to get a 468 to push that boat.

I'm almost positive the owner of that boat is a member on OSO.

I don't think pulling the weight out of the stern will really affect the CG that much because they're just so damn heavy!!

You in the Ventura /so cal area? I'm 5 miles from where that boat is sitting. Just saw it's still in Ventura.

Not because of gear ratio.

Going from a 1.5 to a 1.0 (no other changes) would require a much smaller pitch prop.

This is why many very fast I/O's change from 1.5 to 1.36" . They need more pitch but can't get it or fit it, so they drop the gear ratio so they can run a more available (able to fit) smaller pitch.

Reducing the ratio gives you more prop speed. Pitch x prop shaft rpm (per engine rpm) = how far you go per shaft revolution.

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Use cars for example. 3:08's vs 4:11's. Say 1:1 trans final ratio for easy understanding.

If you drive at 6000 engine rpm with the 3:08's. And then same rpm with the 4:11's, which is going to have a much higher mph ? The 3:08's will cause a much higher mph. The higher mph of course has faster wheel speed.

SB thanks for clearing that up for me. I actually had it backwards in my head.

Did they have 3208s originally?

https://marine.cat.com/cda/files/101...Propulsion.pdf

Supercharged 468s would get the job done with 1.5s.

250s on 468s would work well and not cost a fortune to build.

Well that was a bust. Drove 7 hours with a trailer and a fist full of dough to find the boat was not really as expected. So we made the best of Long Beach and came home with an empty trailer.

Sorry to hear that. Boats now in long beach eh?

What was the issues with it?

The front deck has deep stress cracks in every 90°angle the entire length. There were signs in the cabin that there had been standing water in for awhile. Bulk head between anchor locker and vbirth was rotting, wet mud was in there too. Every interior panel in the cabin was starting to come unglued from all the moisture. It had potential, but not what we were looking for. Basically rub rail up would need crack repair and paint. All new interior below. Props were wasted. All the wires in the engine compartment were cut to remove engines. To be honest the space layout for a 41' boat with almost a 10' beam left some to be desired. Oh and a huge crack in fiberglass wall separating the cabin to the head. Toilet was busted and not hooked up. I could keep going. Is advertised as drop your motors in and go. I suppose you could.