Bob Drive Propulsion

[tom kane]

Has anyone tried this type of propulsion for shallow water boating.You could not get a cheaper design.And it can be built by anyone. It can run as surface drive or sub-surface drive. A few design changes can easily up-grade this drive to something realy flash. The design was made available freely to under developed countries. A couple of weeks work woul give a great drive using a bit of innovation and modern technology.

[dand0_4]

Tom, interesting design. I am currently building a drive very similar to your pivotal drive, but I am stuck on the shaft seal for a trimmable system. What do you use? I greatly appreciate your help. Thanks Dan

[gonzo]

I've seen a design where the engine is in a cradle that pivots with the shaft. It is less complicated with no alignment problems or the need for a complicated thrust bearing system.

[tom kane]

You can use any type of sealing syatem.I used tetrafluorethylene "Teflon". In my design the motor does not move,it is the same as a conventional inboard drive except provisions are made for the shaft to move freely from horizontal to 20 degree down,or from side to side if wanted.It can run as surface drive or down to 20 degrees.Everything is soft rubber mounted.There is no restriction of size or HP. The picture shows one of the torque tube models i used which is all water lubed with Silversheen bearing material and it lasted all the life time of the drive used in shallow water work.You must completely understand the geometery of universal joints.

[dand0_4]

Thanks so much for the replies. Gonzo, I really dont want to try and pivot a 350 chevy and turbo 400 trans. Tom, I am still confused. Do I need to use a torque tube or is there a way to seal a bare shaft and still be trimmable? I have a regular gland with teflon packing but I am concerned that it will rub on the shaft when I trim it, also I am having trouble locating a suitable bellows. I have seen drawings, pictures of your drive and understand the principles just not the shaft seal parts. Thank you , Dan

[gonzo]

What are you using for thrust bearing and brackets?

[dand0_4]

Let me try and describe my current setup. 350 chevy, turbo 400 trans, slip yoke of trans is supported by large flange/thrust bearing mounted to stringers,then into u-joint connected to shaft which runs out transom to trimmable cutlass bearing and rudder. I have a way to seal it but it is somewhat complicated. Tom Kanes design in pictures I saw seemed to be a simple bellows and seal, much simpler. I like to keep things as simple as possible. But I may be missing something from the pictures, and a torque tube may be required. Thanks

[Frosty]

You are treading close to patent laws there.

http://www.powervent.com/

[gonzo]

It is simpler to not have u-joints, and tilt the whole thing. If the tilt is at the motor mounts, the setup will be balanced.

[Frosty]

Originally Posted by gonzo

It is simpler to not have u-joints, and tilt the whole thing. If the tilt is at the motor mounts, the setup will be balanced.

That would be the ubiquitous Thai long tail.

[gonzo]

I hate when you are right

[dand0_4]

Frosty, I have looked at all the commercial systems and I know mine is similar to some, but this is a one off for myself so I dont think Im violating any laws. Gonzo, I thought of this at first but my engine/ trans is about 6 feet long so balance and engine height would be tough. I have been experiimenting for several years with supercupped props on my outboard and I have been able to run the bottom of the prop blades even with the bottom of my hull with no tunnel. I have run my boat across sand bars and mud flats with only 4 inches of water. The tunnel boats down here can do it, but I can do it without a tunnel. I also have a custom water intake system that is totally weedless and is even with the bottom of my transom. It is a Bobs machine remote water pickup with a livewell screen installed. Works much better than the low water pickups on the lower units which suck up mud and grass. Anyway, I digress. The u joint allows me to trim up slightly for hole shot and then trim to get a straight shaft angle at an acceptable prop height relative to the bottom of the hull on plane.

[gonzo]

So the prop is working on the wake which is higher than the bottom of the boat at the transom, right?

[dand0_4]

correct, with the extra cupping it is able to run in surfacing mode. You can tell this as the through prop exhaust actually comes up out of the water

[powerabout]

Will that be using a single u joint????