CV Joint / Drive Shaft

[TeddyDiver]

Originally Posted by S/V Alchemy

I intend to labour a fair bit to get "zero degrees" dialled in. In other words, the engine at rest will be mated to the AquaDrive coupler as if it were a solid coupler.

That will actually wear out the CV coupling much faster. Some misalignment and the wear is distributed on a larger area during each revolution..
BR Teddy

[DeepFrz]

That will actually wear out the CV coupling much faster. Some misalignment and the wear is distributed on a larger area during each revolution..
BR Teddy

That is correct. A few degree misalignment is the best practice. You should be able to find the tolerances on line.

[S/V Alchemy]

That's not what I was told by the fellow who helped me, and who also has an Aquadrive in a similar steel boat.

It's not hard to achieve, however, if this is best practice. A quarter-turn on each motor mount would do the trick.

When it unfreezes I'll be finishing up the exhaust system. We'll soon see.

[exkma367]

I put the shaft in today. I need to get some accurate measurements for attachment of the thrust bearing to the hull. The rubber bushings are on order. I plan to use 3 inch channel upside down on the beds and 3.8 plate at the end of the channel to match the plane of the thrust bearing with the prop shaft centered.

[S/V Alchemy]

Wow, that's quite an offset. May I ask why you moved the engine so far forward?



If you want to see my installation last year, you may find it of interest:

The world encompassed: Propositioning, or getting a right shafting, Part 1

The world encompassed: Propositioning, or getting a right shafting, Part 2

The world encompassed: Launch approacheth

[exkma367]

I like your install. Our boat is a tartan 34c, The engine was originally located just forward of the companionway steps. Did not like having to step on, over or around it coming down the steps. I found another 34c, (custom made by the Tartan master carpenter) that moved the engine forward to the same location, but used a straight shaft. I would like to say was to balance the boat, but it is really just our preference. Ours is a two year, tear it all out and put it back together refit so we decided to make it our own. Thanks again for the pics of your install, looks bulletproof.

[Nicholson58]

Originally Posted by stillbuilding

Well, it is said that there are no stupid questions so here goes.
I have a Perkins 135HP pushing a 2.43:1 reduction gear to a 26" prop.
I would like thrust block and cv joint/flexible shaft connection. Looks like Python Drive, Aquadrive or Orion units. Which are fine but seems outrageously expensive for what is a very simple and old technology.

Is there any reason why I could not use a heavy duty auto CV joint/shaft which are sold for peanuts in comparison? I imagine there are autos which have torque and wear solutions far greater than needed for my little diesel.

The automotive CV joints typically do not have accommodation for a thrust bearing. They transmit torque and permit extreme angular off-set. I have an Aquadrive on my 115 HP Westerbeke; 2:1 transmission. It is between the 2:1 and the Hundested variable pitch blade control. The other issue is that the automotive units tend to be very long.

As a builder of drive shaft & transmission testing machines for various auto makers, I know you will have yet another hurdle to deal with. The metal is extremely hard & tough so cutting a shaft down and welding is next to impossible for the average guy & equipment.

I agree they are ridiculously expensive compared to automotive but the best course is the Marine designed unit.

If you do have space and can add a thrust block, automotive can certainly work. Be sure to take a spare in your inventory if you travel far from home.

[S/V Alchemy]

Originally Posted by exkma367

I like your install. Our boat is a tartan 34c, The engine was originally located just forward of the companionway steps. Did not like having to step on, over or around it coming down the steps. I found another 34c, (custom made by the Tartan master carpenter) that moved the engine forward to the same location, but used a straight shaft. I would like to say was to balance the boat, but it is really just our preference. Ours is a two year, tear it all out and put it back together refit so we decided to make it our own. Thanks again for the pics of your install, looks bulletproof.

Thanks. It's a custom boat so I've needed to work out all the details ahead of time...our situations are similar.

I would be interested to know if your engine needs a box in the saloon or if it fits below the floorboards (I haven't got a hull view of the Tartan 34C in front of me). I would be also interested to know how you have routed the exhaust and your anti-siphon solution.

[snbrooker]

The reliability of all the CV joint/ thrust bearing systems relys on NOT being aligned perfectly... but require at least 3 degrees mis alignment to last... Check with the OEM...



QUOTE
I intend to labour a fair bit to get "zero degrees" dialled in. In other words, the engine at rest will be mated to the AquaDrive coupler as if it were a solid coupler.

[a64pilot]

To understand why this slight misalignment is necessary, chuck a long piece of steel rod like a gas welding rod in a drill and spin it. It will wobble badly, but if you put a slight bend in it, it will run true.
I first discovered this when I put a sting by the tailrotor driveshaft of a Bell 206 helicopter, it had a slight bow in it and I couldn't understand why, as luck would have it we had a Bell tech rep there that I could ask becasue the book didn't address it at all.

[stillbuilding]

Originally Posted by a64pilot

To understand why this slight misalignment is necessary, chuck a long piece of steel rod like a gas welding rod in a drill and spin it. It will wobble badly, but if you put a slight bend in it, it will run true. I first discovered this when I put a sting by the tailrotor driveshaft of a Bell 206 helicopter, it had a slight bow in it and I couldn't understand why, as luck would have it we had a Bell tech rep there that I could ask becasue the book didn't address it at all.

Hey, that is interesting - have wondered why myself. Many engineers and mechanics have advised true alignment but manufacturers do not explain why the purposeful misalignment is required so i have been stumped for a rebuttal argument. Thanks.

[stillbuilding]

I did not have any trouble getting few degrees os misalignment in this installation!

[Nicholson58]

The reason it must have offset is to cause the bearings to rotate enough to exercise the grease, otherwise, the result will be dry races & false brinelling and accelerated wear with flat spots on the balls/rollers. The best offset is parallel rather than pure angular. Each joint with offset induces a slight sinusoidal speed oscillation. If two opposite joints with only parallel offset are assembled correctly the phase of the sinusoids will be opposite and equal so the result at the prop is constant speed. If there is substantial total angular offset there will be a rotational speed vibration at 2X the prop rpm. We are critically concerned with this on the dynamometers we build over 6000 HP. The vibration in the boat prop shaft can be felt and thrums the hull. On our dynos, the shafts may be 20 feet long and 40 inches in diameter. Small shaft CV and Cardan joint testing we do on machines running at 12,000 rpm can walk the machine across the floor.

BTW, unbalance forces increase with the square of the rpm so cutting speed a little bit drops an unbalanced load a lot.

[S/V Alchemy]

Well, I'm clearly going to have to explore this point further. As I noted previously, misalignment or even quite precisely dialled in misalignment, would not be hard to achieve.

But it's not what was recommended to me. Thanks for the comments.