stern tube installation

[fredrosse]

Looking at the drawing of the keel, just forward of the propeller (where the shaft goes thru the keel), how thick is this section? Does it have imbedded steel? Perhaps you can check with a magnet, (or best with x-ray, but forget that unless you have access and certified testers) An automotive engine magnaflux outfit may give steel outlines also. Another option is to drill small (1/8 inch) transverse holes thru the keel along the intended path of the stern tube, to find out what metal reinforcement might be burried under the plastic.

If this section of the keel is 2 inches thick or less, then I would probably cut the keel thru to hull, (cut about 1/2 inch above and 1/2 inch below the shaft position) and cut a hole about 2 inch diameter into the hull. Then fit a bronze stern tube, fastened to the opening with fiberglass cloth and epoxy. Perhaps reinforcing plates (about 6 in x 3 in) epoxied and thru bolted on each side of the keel.

I did a similar job on a fiberglass sailboat conversion to indoard propeller drive, and have some photos of this work. It has worked well for 5 years now, with several groundings in shallow water, although it is only a 14 foot boat.

[johnp]

here is a shot of the stern from inside and the keel. the keel is about 3-4" wide

[DetroiTug]

John,

Yes, that is totally different than what I was visualizing. That shouldn't be much trouble.

Just determine the height of the engine from the keel, prop location and then calculate the angle.

-Ron

[johnp]

Thanks, Should i use a regular bit and work my way upto 2 1/2" diameter? or is there something else to use ? i'll probably use a 1 1/4" shaft.

[johnp]

I was thinking the prop to be 17" or 18"d x 18"p, i thought the diameter was to control rpm. what's the relation to LWL? after your post i'm thinking 20"dx20"p? and turn her alittle slower.

[DetroiTug]

I mentioned the 20" as it seems that's rule of the thumb for these sized steamboats. 1" of diameter for each foot of water line length. It works for me, my boat has a 20' LWL and using a 20" X 20" prop seems to work perfect. I experimented with a 19 X 25 and it didn't work near as well. And square props, or close to it are readily available. Much easier to find than perhaps a 17 X 26 etc. From my calculations, it appears there is very little slippage on a large diameter prop. I'm seeing 7.5 mph @ 80 psi, with this engine that is about 5 hp (It's 10 hp at 150 psi). And too, this tug is less then sleek under the water line. Pretty beamy and pushes a big bow wave.

It appears you won't be drilling that far, however it is drilled shouldn't be too critical. Could probably just use a hole saw. Stop and chisel out the core and proceed. Would be cheaper than buying a bit that large.

That is a nice hull, looks like it will make a perfect steamer.

-Ron

[johnp]

Thanks so much Ron, i appreciate the education. I'm sure i will have more inquries.

John