USAMARINE Web Group - Captains' Corner Boatbuilding Tips

Building Fiberglass Shaft Logs (Revised 07/30/04)

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NEW! -- Actual images & sequence of installation! -- NEW!

This tip was written in response to a Bertram 31, but the basic discriptions and proceedures will apply to any boat...

The components are two heavy wall fiberglass shaft log tubes available from Lewis Marine in Miami, (fig # 9585). You will select two sizes. The smaller I.D. should be 1/2" larger than the diameter of your shaft. The larger will have an I.D. the same as the O.D of the smaller tube. Even if you have 1 3/8" shafts, you might want to go ahead and make your tubes to accept 1 1/2" shafts, just in case you or the next Steward wants to upgrade the shaft size to 1 1/2".

To build two shaft logs, you'll need 3 feet of the smaller & 3 feet of the larger.

Cut the small tubes at a 90 degree angle in the center. Cut the large tube into two 15" lengths. Epoxy the smaller tube into the larger so that one end is flush.

With the bronze shaft log removed and the hole enlarged to allow the tube to pass freely through, install and couple a shaft to the engine. Align the engine/shaft/strut. Remove the shaft from the coupling and slide on the fiberglass tubing.

Both ends of the large section of the tube should extend fully through the hull. The aft end should extend about 1/4" beyond the exterior of the hull.

Once you're happy with the fit, use small wedges to center the tube to the shaft. These wedges will remain in place throughout the process of glassing the tube into the hull.

When everything has cured fully, sand as necessary and fair it out on the exterior side at least.

If you are going to be using standard flax packing glands, you'll need to cut off the excess tube so that the opening is flush to the hull.

If you are using packless seals you can leave the tube projecting out on the 90 degree cut. As Tom Oakes pointed out to me on our initial meeting, that's just that much less rotational shaft drag on the wetted surface...

Lewis Marine 800.327.3792 -- figure number 9585 page 599 in the 2000 catalog.

Be sure to see the web page showing the actual process as done on Richard Eastman's B31...

Have fun! Feel free to download and print this page, but please don't use it on a website without linking it to

Capt Patrick McCrary

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