Bob Drive Propulsion

[powerabout]

Originally Posted by tom kane

Image shows conventional set up in boats since Adam and you are saying this set up is wrong and will not work this is the same mis-information I encountered when patenting the pivotal drive. Hence the reason the patent was successful. An unexpected result from a combination of components.

If the drive will run as in the diagrams it will also run in any other position Up, down,left,or right.

I'm not saying it wont work but the link I posted ( and there a bizillion others) is how 2 u joints need to operate to survive.
Low horsepower low speed you would get away with it no doubt
I imagine the fact that you cant buy that style drive off the shelf is because no manufacturer would do it.

They do sell a cv joints though
and now also thompson joints http://www.thompsoncouplings.com/

[tom kane]

Thank you for your constructive comments and I can appreciate the understanding of anyone,regarding the mechanical geometry of U/V joints accepting what has been accepted practice of experts and the diagrams shown are from professionals.

The U/V joints as fitted in a boat are only under load when the propeller is in water but otherwise just rotate when the prop is lifted up,but not in a steerable drive if the prop is under water.

For a Pivotal Drive to function the self aligning thrust bearing must be shifted as close as possible to the rear U/V joint to make more movement available.

I was told by experts that a pivotal Drive would not work and I expected maybe to only run the drive lowered,but soon found out that it was very practical and had many advantages and that the experts only knew what they had experience with and conventional practice.

It is hard to believe that the millions of people who have played with these components have not realized that it is possible to run U/V joints in other configurations and moving between different angles within limitations.

Proving a mechanical device`s longevity or workability is like trying to prove the existence or otherwise of god when experts can not agree or simply don`t know.

There are many ways to design a trimmable drive,cheaply or with great expense depending on the needs of the boat owner.

The image shows a Spicer off-the-shelf U/V Marine setup which has been used since 1950`s in a pivotal drive and has never yet been serviced other than greasing and is still in top condition. Thank`s for your interest.

[powerabout]

well said,
they have built them tough

[tom kane]

In this image of a conventional truck transmission you would put a propeller where the U/V joints on the axle are. The prop would be on an angle so angle of drive plates on U/V`s does not matter.

In a boat the motor would be set at 10 degrees angle so the prop shaft would have a total angle of 20 degrees or more if you wanted it.

You can run and lift a propeller shaft set up as in the diagrams as fitted to a boat but the lifting angle useable would be small,as you shift the pivot point further up the shaft up to the the center point of the U/V joints the lifting angle increases. That point is where Inboard/outboard U/V joints are run.

[powerabout]

looks correct, the angle of the centre point and the diff are the same i.e. same plane, when the axle goes up with suspension travel the 2 angles will reduce but be the same so their rotational vibration will cancel each other out ( provided the yokes are aligned as your previous picture showed)
The drive into the middle joint is say parallel to the ground and so would the propshaft into the propellor
same as the other drawing I posted

[orb353]

Tom, do you have any up close pictures of the pivotal drive installed on your boat? I agree, it can work. Most of pictures you have of the boat look pretty old. Can you take a few newer close ups of the transom and prop shaft and such. Thanks

[tom kane]

I sold up every thing I could BEFORE the recession hit. I have many pictures of my project through the years which may help you although any competent Marine Engineer should be able to build you what you need or at least draw up some plans.Because I am still developing the project I can not Legally show new development work other than some basics.There are many ways to use the principle of a Pivotal Drive or Trimmable drive which makes it difficult to have a Standard model.

[tom kane]

A quick diagram shows one way to make a simple Pivotal drive using standard parts.
Twin U/V joint and sliding spline.Self aligning thrust bearing with collet to lock on to prop shaft.
A choice of seals to seal torque tube. A stainless steel torque tube with skeg to lift drive when going aground.A choice of outboard prop bearing mountings. A CV joint rubber cover to seal torque tube to stainless steel slot cover.

When boat is on a trailer the drive is up and when the boat is launched the drive drops down,just start up and drive away and the drive looks after itself and no need to do any thing unless you want to lock the drive in the up position or run in surface piercing mode.
The rudder travels with the torque tube up and down. All supports for drive can be soft rubber mounted

[orb353]

Tom,
I like the diagram in the first picture. That is basically what I had intended to build, something similar to that. Also check out the disappearing drive, same concept. Critical speeds for Semi-Planing

[tom kane]

The disappearing propeller concept as I understand it has the U/V joint running in water. Having all the crucial working parts all inside the hull should be preferable.

[tom kane]

Sea Spray Magazine September 1973 Introducing the Pivotal Drive.

[tom kane]

I do not know of a propulsion that can cope with so many different conditions of boating than this Pivotal Drive and you can build it as tough as you need and it works the same as a conventional shaft drive installation so no worries about if it works or not.