Boring the Shaft Hole


Shaft hole drilling apparatus
Here’s the apparatus I use to drill the shaft hole.

At some point, if you’re going to build a boat, you’re going to have to put some holes in it.  It just doesn’t seem natural at first.  But it gets easier the more you do it.  Best to get it right the first time though.

Boring a hole for the propeller shaft at a 10 degree angle to the hull, right through the keel takes some preparation.  First, you have to know exactly where to put it.  I use the strut as a guide.  I bolt the strut to the bottom and use some bushings to center a drill bit extension through it to guide my drilling.  You can use your lofting to check all of this and mark the exact location of the entry and exit holes.

Two halves of the guide block laid side by side. You can see the router-cut groove in the top half. The pilot bit rests in the groove in the bottom half.
Two halves of the guide block laid next to one another. You can see the router-cut groove in the top half. The pilot bit rests in the groove in the bottom half.

Then I make up a guide block that I can screw to the bottom of the boat, with a 1/4 inch line bore that will guide my pilot bit precisely.  I mark it out and use a bullnose router bit to cut a groove in each half of the guide block.  Having a 10 inch long hole already in my guide block to keep my pilot bit on track, I bore a hole through the hull with a long pilot bit.

Pilot bit emerging inside the boat
I mark out where the pilot bit should emerge inside the boat. I missed by about 1/8 inch.

Then I use the strut with some bushings in the shaft hole and bore the pilot hole through the hull.  I’ve marked out where the bit should emerge inside the hull.

Assembled guide block
Assembled guide block in place.

Finally, I use the pilot bit as a mandrel in a hole saw of the proper diameter to start boring through the guide block to a depth of about 1 inch.  I back the hole saw out and replace it with a forstner bit to clean out the hole.  Then put the hole saw in and bore another 1 inch in.  It’s a painstaking process, but it gets me where I want to be.




Completed shaft hole with guide block
Here’s the completed shaft hole with the guide block.
View from inside the boat
Here’s the view from inside looking out through the completed hole.

6 Replies to “Boring the Shaft Hole”

  1. Nice job Tim. Great technique.
    Ive seen large diameter auger bits used in various other builds online with a pre cut hole in the guide block….but it looked a lot harder to control the larger diameter bit right through. Seemed risky to get the hole coming through in exactly the right place.
    The smaller pilothole approach you’ve used looks lot more controlled ????

    1. Exactly. Having about a foot of the hole pre-drilled through the guide block is the key to the accuracy of this method. The pilot bit emerged about 1/8 inch from where I expected it too. I was very happy with that.

  2. Looks complex Tim. I can imagine the relief you felt after the job was complete. Thank heaven it wasn’t a twin-screw design!

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