Stern tube design considerations

[ldigas]

Are there any good texts out there (or any alternative source of information you can think of) that deals with stern tube design, and what to take into consideration when doing so?

I'm particularly interested in various solutions, and what are the choosing factors that decide what solution will be applied? Also, the choice of bearings ...

This is a little vague topic, I know ... it is such on purpose, but I believe you understand what I'm asking in general.

[gonzo]

There isn't much to it. As long as the shaft fits in, the tube is fine. The only function of the stern tube is to keep water out.

[tom kane]

If you are smart you will fit your water glands and seals as high as possible above water level if possible.If they are low on the keelson water pressure is greater so a leak is guaranteed when the boat is at anchor.

[CaptBill]

Call me crazy but some strong neodymium motor magnets epoxied around a shaft with a squirt of ferrofluid may turn out to be the ultimate bearing assembly. You could have a reservior of a couple ounces of ferrofluid and change the bearings with a few twists of a dial. or a mini-greasegun type tool. No moving parts, nothing to break, and the ultimate bearing (zero-friction) plus zero play/dampening etc. also can energize the magnets for a variable strength setup. Oh yeah, it's totally waterproof to, like a fluid o-ring that forms into a bearing simply by the magnetic force .

[Frosty]

There should be no bearing in the stern tub unless your engines are bolted to the hull. If they are on flexible mountings then your stern tube and seal needs to accomadate that movement.

If you must have a bearing due to shaft length then some flexi drive must be used. Then you will need a thrust bearing. Simple it is not.

[CDK]

This is a thread I started in the summer of 2007:
Why are all prop shafts water lubricated?

I learned a lot from the replies, actually built and installed two oil filled stern tubes with integrated thrust bearings. They are in use for nearly 5 years now: the oil level is still unchanged.