I came across this old post on the Boat Design Form a while ago:

http://www.boatdesign.net/forums/diy-ma ... 26281.html

I think this guy had a solid idea, he just didn't execute it very well. I've been fooling around with a couple of different ideas and I think his chain drive idea has merit. A lot of the longtails I see use universal joints which I think causes more power loss than some people might think. That's why I'd rather have a straight shaft than one with a direction change. The problem is mounting it-you either have to come up with a custom machined piece, buy one of the Thai kits, or the Backwater Swomp Lite. Using a chain drive would not only allow you to have a straight shaft with little power loss, you'd also be able to utilize different size sprockets and get some reduction for more torque. Most, if not all outboards have some kind of reduction whether it's 1.5:1, 2:1, etc... I see a lot of "high thrust" outboards at the lower end now (9.9, etc...) that are as much as 2.5:1. Obviously you'd lose some speed, but if you run a heavy boat to begin with, it might be a big help.

Here's a crude (very crude) drawing of what it would look like:



The guy on boat design had the PTO of his motor facing forward so he could use a regular outboard prop-flipping the PTO around to the rear will keep the rotation counter clockwise allowing you to use a regular longtail prop. I think in his case, using the regular outboard prop was a mistake since they're meant for different RPM ranges. He also used a centrifugal clutch so that he could have neutral, but he later said that it was engaging at too high an RPM. I would just use a regular sprocket so that the motor would always be in gear, like a regular longtail. I'd like to hear what others think of this idea. There is at least one Thai company, CLP, that does gear reduction boxes that come right off of the PTO and drive the shaft. One model even has reverse.

Here's what I'm thinking for the shaft-sprocket end:



Prop end:



As you can see I'm trying to figure out how to keep the shaft from sliding up and down in the housing. I thought about getting it threaded enough on the prop end so that I could run two jam nuts up near the pipe cap and snug them so the shaft couldn't slide up toward the motor. Not sure what to do about the sprocket end though.

Bolt your end yokes to both the PTO shaft and the drive shaft, it solves a lot of problems.

Reverse your pulleys to get a reduction not a multiplication.

You need a thrust bearing of some kind. There are lots of them out there. Two pieces of metal fail almost immediately.

Do a search on chain drives. I think that a ABX belt that slips a little bit on impact is the better deal. You will get back to the launch at least.

UJs are necessary if you want a major motor co. to warrant your motor.

Mark F. Cheney