stern tube installation

[johnp]

what is the besy way to drill the keel on a fiberglass boat, and at what angle so i can install a stern tube?

[fredrosse]

I think we would need to see an outboard profile drawing of the boat hull to best determine the shaft position. Can you post this?

[johnp]

Here it is.

[mtnman]

As a life boat wouldn't she already have a stern tube and wouldn't it already be at the optimum angle?

[johnp]

no stern tube, never had an engine in her.

[DetroiTug]

John,

That may have a stern tube that was covered up for that model. It appears that the keel is cut out for a prop, easy to conclude the makers have installed a tube as well. If not..

First thing to do is load the boat with some ballast to simulate the engine and boiler, put it in the water and mark out the actual water line.

Then get the boat setting upright on a flat surface, measure down from each gunwale and make sure it is level to the floor. Use a 4 X 8 piece of 1/2" MDF as a template. Cut it to fit the interior upper profile of the keel and then cut and fit it up tight to the outer vertical profile of the stern. That would establish a 2D keel plan to work with. Mark the actual water line on the template to determine prop shaft location as dictated by half the wheel diameter plus 2-3 inches away. Then on the same template determine where the engine shaft coupler will go and it's height from the keel. Knowing those two points they can be intersected with a line draw through both all the way across the pattern. From this pattern a drill be can be fashioned with a length 60% of the total distance to be drilled.

Affix the pattern to the boat approx 2" off the center line of the keel and 90 degrees to the floor. Set up a lamp or have an observer watch the drill shank and make sure it is in line with the scored line of the pattern. Looking from atop while drilling make sure the shank stays parallel with the pattern surface. Drill the remainder from inside the same way, have each hole meet in the middle. There may be some misalignment, bit it will be internal and not visible.

-Ron

[fredrosse]

Here is a sketch with a starting point for discussion. I have assumed the 20 ft waterline length, marked with the white heavy line. Keel draft aft is about 9 to 10 inches more than the draft forward. The propeller is 17 inch diameter, with about 4-1/2 degrees rise from the keel. A rudder skeg is probably a good idea. Looks like a nice hull for a reasonable steamer, some parts are not ideal, but close enough to make a real nice boat.

[johnp]

Thanks, that's what i can visualize in my mind but in a couple of weeks i'll have to get the drill out and mak it happen. i'm trying to think of away to start the drilling process and finish it ending up with a straight hole. maybe a long hollow tube with a bit on one end and a shank for the drill on the other. that way it won't wonder. i can put a angle degree gauge ont he drill and as long as i maintain my angle and stay swaure to the keel with some guides it should work? sorry for the elementry remarks but it's my first boat build let alone steam boat.

[DetroiTug]

John,

Trying to drill it straight thru from one side and have it come out on location would be virtually impossible. I would use a forstner type bit with a 1/2" cold drawn rod for a shank welded on. You're going to want to be able to steer at least starting out. Plus without some diametric relief behind the cutter it can easily get jammed in the hole deep in the work.

Keep in mind too, the prop needs to be larger for a steamboat, about 1" per foot of water line length in diameter. Not having a prop tube is probably a plus, because it would be for a smaller diameter prop for I/C engines. If the prop protrudes below the keel a bit, that's ok and normal for that type hull. They sell rudder straps that accommodate for that.

Back to drilling the hole, the method I described is about the simplest thing I can think of other than just gambling on the alignment. One could map the keel and hull X Y Z locations in to a cad program, then design some complicated fixture with guides etc. It would still rely on some variables and luck.

On Muzzleloaders we use a fixture to drill the tang screw that goes thru the barrel tang and in to the trigger mechanism below. It's a C-shaped fixture with a drill bushing in one side, that always drills to a pointer on the other side. Not sure something like that would be practical for this. A large fixture like that might work?? Imagine a large C-clamp and the drill goes through where the Acme screw is. Through a bushing that beeps the bit aimed at a point on the other side.

-Ron

[DetroiTug]

Looking at your drawing closer, if that internal line in the actual profile of the keel inside, that won't be any problem to drill. I thought it came up a lot higher that that.

-Ron