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I am building a 16 foot gentlemans racer with a 4.3 Merc and a 72c velevet drive. I do not have the space to in the engine compartment to get enough angle to exit the boat bottom, has anyone used a cv or u joint mounted directly to the transmission to provide additional angle, I need approx. 9 degrees. Thnk you

I can't comment on a CV joint - no experience except with VW Beetle transaxles...

I do know that you cannot use a single u-joint. They have to be used in pairs, preferably one at each end of the shaft , and these have to be set at 90-degree offset to each other. This is because a u-joint creates axial motion (along the length of the rotational center line) as it deflects from 0-0 alignment. The more angle in the u-joint, the more axial motion. The opposite half of the pair absorbs the motion because of its 90-degree offset and sends it back with the next 90 degrees of rotation. This is also why it is best to halve the total angular deflection between the two u-joints of the pair - balanced oscillation. Essentially, as the shaft rotates it makes two oscillation cycles in a longitudinal direction. With only one-half of a u-joint pair, severe vibration will result.

Someone else offer a diatribe on CV joints...

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Paul Miller in Memphis, TN
"Yeah, I had lunch with him last week at the Cracker Barrel out on I-40."

Can you provide us with more info about your boat and engine installation ?? Is the gear ratio 1:1 or is this a reduction unit ? Strut drop, shaft angle, and propeller diameter would also help. Is the lack of space in the engine compartment a hatch clearance issue ??

Note that as shaft speeds increase, the maximum universal joint operating angles of 3.5 degrees can be significantly reduced e.g. 3.5° @ 3500 shaft RPM, 2.75° @ 4000 shaft RPM, 2.2° @ 5000 shaft RPM. (See Universal Joint Alignment Procedure For Passenger Cars).

Robert Hankins posted some photos of his TINY MIGHT in Customer Photos. He's coupled a CV joint to the flywheel of a 120 HP Honda Civic engine. Adapting to the transmission output flange should be straightforward but more space will be required to mount a thrust bearing cage and CV joint. Steep angles will lead to u-joint longevity issues and possible failure resulting in damage to the boat and/or passengers.

TINY MIGHT by Bob Hankins, Fresno, CA (7-05)

An Aqua Drive system may work but they're expensive and I haven't seen any reference to maximum angle. Here's a link to their Price List. Better be sitting down before clicking that link ...

A better option would be to use an inline 8° down-angle transmission such as a ZF 45A, ZF 63A, PCM 40A or Velvet Drive Liberty Series transmission. Refer to our Transmission Page for specs and suppliers.

If all else fails, a flywheel-forward engine with Velvet Drive C71 transmission is the ticket if space is at a premium. Click here to see a shaft layout diagram for a 15 foot boat. Engine CG is 70" from the transom and the shaft angle is 13.5°.

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Paul Kane
Kane Custom Boats Ltd.
Chelsea, Quebec

Building the Glen-L Hot Rod : http://www.kanecustomboats.com

Glen-L Boat Video Directory : http://www.kanecustomboats.com/pages/vi ... ctory.html

That tiny might drive is NOT a "cv" joint, it's a double carden. A "cv" typical in an automotive application is some variation of a rzeppa coupling.

You don't want a rzeppa in a drive shaft. Even more you absolutely don't want a rzeppa coupling on any thing that is unrestrained, and spinning between your legs.

A rzeppa applies the load to the small contact area of 4-8 steel balls. The joint IS going to brinell in short order. I recall seeing an engineering paper on the load pressure of a typical rzeppa "CV" in an automotive axle, the loading was carried over a contact area of a few hundredths of an inch. In an automotive drive line they are a necessity to avoid the speed changes typical of carden joints, and they have the ability to operate smoothly at angles well beyond the range of a carden joint. But that those advantages are completely irrelevant in a boat drive line.

One would think a joint sufficient for propelling a car would be fine for a boat, but you gotta remember at 150 Mph a typical 15" tire is only turning mid 1800 rpm range. Not the 4500 Rpm your engine is turning in a boat. For that matter, to hit near 5000rpm, the Cv in a car drive axel would have to be moving the 15" tire equipped car to around 400mph. Just how long do you think that would hold out? A joint designed for 2K rpm and relatively light loading is never going to survive 100% of the engine's power at 5-grand for sustained periods. In a car, when have you ever had the drive line loaded with 100% of the engine for sustained periods of time (and it didn't involve flashing red & blue lights in the rear view mirror - Or is that just me? Anyone?)

a rzeppa relies on vector changes to properly lubricate themselves. Once they are running in a fixed angle application the joint does not receive enough movement to properly exchange lubricant. Using a fibrous grease will help, but they are expensive, and not readily available. If yo have a marine application that has a drive angle that would necessitate a CV, something is rigged wrong.

A moderately sized double carden (H-joint to the jet boat crowd) easily handles 500+ Hp, and 5K+ rpm for sustained periods. The loading is dispersed across an actual contact area many times greater than a CV, A carden dissipates heat so much better than a Cv. Still not convinced? go check out some of the jeep forums for people dumping the rzeppa joint drive shafts for double cardens after the umpteenth (however many that is) failure.

Maintaining a double carden involves a few pumps of pretty much any #2 grease. Proper replacement of lube in a cv is a pain in the, er... well, you know. If the worst happens and the joint fails, a carden typically gives you plenty of warning, clanking, banging, and even smoking as the grease cooks out. I have seen more than a few double cardens with the cross chewing it's way through the yoke after the bearings were ground out, and the caps worn through. Cv's tend to just fall apart, and be completely useless with zero warning. Got a paddle?

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Some plan to stroll through Saint Peter's Gates, I plan to go through them at 150mph... backwards... in a screaming ball of flame, with a glimmer belt wrapped around my head, and a NOx button in my hand.

Very interesting and well put Caber...thanks!


I really hadn't thought about those points, and would have just thought about the basic...."well it works for cars",etc.

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