Propshaft Diameter

[Das_Boot]

I am having a new engine fitted and have hit a snag.
My existing engine is a 36hp Volvo. I have a 12ton boat when loaded so want to go to at least 48 hp. The guy who came to survey the boat for the new engine 50hp Beta says that the prop shaft I have will be pushing the limits re. diameter.
I have no intentions of cutting the boat to pieces to fit a larger propshaft so should I look for a smaller engine. How critical is this issue, can anyone help.

 

[TheoSr]

Have a look at "propellor shafts" in http://www.vetus.nl/. The alloy specified is stronger than "normal" stainless, so the required diameter may well be less than it is now. Maybe you could have a shaft made locally out of the alloy specified by Vetus.
Good luck,
Theo.

 

[Mulge]

It costs to join, but the calculators on this site will allow you to at least look at different combinations.

http://boatdiesel.com/

 

[Ships_Cat]

Have you looked at the possibility of using a high strength stainless steel such as Aquamet, Aqualoy, etc (don't know the trade names of what is available in UK but any good stockest of shaft material will tell you)? Will be expensive.

John

 

[Das_Boot]

I have just checked the Vetus site I know that my shaft is a vetus I will check the paperwork. If it is the case my shaft should be 30% stronger than the diameter sugests therfore no problem.
Tnks for the help.

 

[boatmike]

What diameter is your existing shaft?

 

[Das_Boot]

I honestly dont know my engine is mounted inside the keel and is not mounted on an incline therefore the shaft is deep in the keel I have only greased it through the grease nipples and looked at it from a height.

Because I decided when I bought the boat to upgrade the engine I havent taken mutch notice but am learning fast that nothing is as simple as it first looked.

I will look at the paperwork tonite. I have a feeling it is a 1 inch Vetus.
It is counter intuitive to believe a 1 inch shaft might break. In my mind 1 inch of stainless steel could drive a jumbo jet.

 

[alahol2]

The Boat Data Book (Ian Nicholson) suggests, for 50BHP,
31mm @ 3000 max shaft rpm
35.5 @ 2000
39.5 @ 1500
45 @ 1000

 

[Guest]

Post deleted by danfoley

 

[Das_Boot]

Thanks for the help I will measure it this weekend. An engineer has told me that if your engine and prop are in-line ie there is no inclination, you can reduce the diameter of your prop shaft.
I cant measure it at the exit untill I pull the boat out of the water, I am definitely not getting in the water I prefer a decent into the abyss (bilge).
Anyway all shall be revealed this weekend.