Coyote II design - what do I do with all that shaft?

[Clifton Brittain]

I now have the hull in the back yard, the engine and propeller chosen, and I am looking at the lofting and I see that the shaft is going to be too long to go into the boat from the front (and would require removal of the engine and much of the interior).

What are my options here? A two-piece drive shaft? How is a shaft connected to the transmission? I assumed a plate matching the transmission output was welded onto the shaft, but that precludes bringing the shaft in/out through the shaft log, doesn't it?

Help!

[videoguy]

CB Most boats have a flang on the end of the shaft
held in place with a key way and a setscrew.AS far as puting the shaft in can you jack up the aft end of the boat and also dig out a trench for the shaft to get clearence to slide the shaft in.... smile.gif Phil

[Keith Wilson]

Hi Cliff - It was definitely an experience schlepping your hull from Urban Boatbuilders to your backyard - All things considered, it went pretty smoothly. It's going to be a very cool boat when it's done.

Anyway, although I'm not an expert in powerboat drive trains by any means, the normal method is a flange attached to the forward end of the shaft, generally by a keyway and set screws, that bolts to the flange on the output shaft of the transmission. Remember that all the axial thrust of the prop goes through that coupling unless there's a separate thrust bearing; that's the only thing that drives the boat. The flange-type shaft coupling is rigid, so accurate alignment of the motor flange and the shaft flange, done by adjusting the motor mounts, is critical. Here's a flange coupling:

http://www.tadiesels.com/images/borg_warner-psc-type1-dim.gif

There are also various types of flexible couplings that can go between the motor and the shaft. Some can handle axial loads, some have a separate thrust bearing that bolts to a floor timber or something, some have a pair of universal joints that handle lots of misalignment. Here's a flexible couping that handles axial load:

http://www.pyiinc.com/images/rdmarine/flexshaftcoupling.jpg

And another with a separate thrust bearing and U-joints:

http://www.python-drive.com/pictures/python/p60-k-picture.jpg

It seems a good idea to me to isolate the vibrating motor from the rigidly-mounted shaft; it would at least allow softer motor mounts, but again I'm no expert. Perhaps some of those here who know more about powerboats could help. What's the kind of motor and shaft diameter you're using?

[ 09-26-2003, 04:45 PM: Message edited by: Keith Wilson ]

[Clifton Brittain]

Thanks for the help, guys. I now know how long to order the shaft. I did anticipate that the shaft would be rigidly mounted and the engine on flexible mounts.

The flexible joint also makes sense to me.

The lofting process is making all these problems more evident and more importantly, more yielding of solutions. It must have been a pretty smart guy that invented lofting.

Thanks again for your help.

[Keith Wilson]

I've got a copy of the Glen-L book on inboard engine installations which you can borrow if you like. It's not a great book, but would probably be helpful. Send me a private message and I can drop it by the next time I'm in the neighborhood.