USAMARINE Web Group - Captains' Corner Boatbuilding Tips

Relocation of Struts and Alignment - (Bertram 31)

I have found it desireable to adjust the strut alignment on the Bertram 31 so that the shafts can be removed without dropping the rudders. This is an entirely optional modification, and it will also include a re-alignment of the shaft alley.

As always, setting the shafts to be true with the struts & shaft alleys is the first job. Engines are always aligned to the shafts, never the reverse.

Remove the struts and remove any shims that may be in place, remounting the shafts directly to the hull. It's totally optional, but if you want, the rotational position of the strut can be altered slightly to allow you pass the shaft outboard of the rudders without dropping the rudders.

The way to go about that adjustment is to fill all of the strut boltholes except the forward inboard hole. Remove the shaft logs, bolt the strut into place in the one remaining hole and jig a support to hold the strut up and against the hull.

Insert the shaft about half way into the strut tube & outboard of the rudder blade. Clamp the shaft to the rudder with a 1/2" shim between the shaft and rudder. Don't worry about vertical alignment of the shaft at this point.

With this setup, re-drill the other 5 strut mounting holes and add the other 3 corner bolts. Remove the temporary support from beneath the strut.

At this point you might want consider replacing your bronze bolted up shaft alley with fiberglassed shaft tubes. (see: Building Fiberglass Shaft Logs)

If you elect to keep the cast alleys, follow the procedure below.

Move the shaft fully into place through the un-bolted shaft alley. Make up a jig to support the transmission end of the shaft and reposition the shaft so that it is very close alignment with the strut tube.

Once the shaft is parallel to, and turns smoothly in the strut tube, move the shaft alley into alignment with the shaft and in contact with the hull. You will see that your alley boltholes no longer align with the hull holes. Re-drill several of the holes to act as a guide point. Remove the shaft & shaft alley.

From the underside of the hull, mark your newly drilled boltholes. From the inside of the hull, grind down the fiberglass around the shaft hole to a taper leaving a knife edged hole. This taper should flair out about 4" all the way around the shaft hole.

A piece of 1/4" - 1/2" plywood cut large enough to cover all holes and covered with wax paper is placed against the underside of the hull and wedged into place, thereby blocking off all of the holes from the inside. (see: hole scarfing as was done on Rich Eastman's B31.)

Re-glass the inside of the hull, bringing the surface back to flush with the original thickness of the hull. Use epoxy only, not polyester resin...

Once the patch has cured, re-drill the new alignment holes, (the ones that you drilled earlier & marked for identification on the under side of the hull), remove the plywood from under the hull. Set the shaft alley in place and insert bolts into the drilled holes. Re-drill the remaining holes.

Using the shaft alley, make a paper pattern that includes the shaft opening. Align the pattern with your hull hole and transfer the new shaft opening to be cut out.

Back under the hull, grind the area of the shaft alley inside of & touching the new holes to be about 1/16" onto the hull, (below flush). Add one layer of 12 oz fiberglass, making sure that the glass stops about 1/4" short of going all the way to the edges of the depression.

Fair over the external patch with epoxy thickened with high-density filler.

Cut out your new shaft hole and re-install the shaft alley. Put the shaft back through the strut tube & shaft alley to its proper placement. Using wooden wedges around the inside of the shaft alley, (where the packing gland hole attaches), align the shaft to be dead center in the opening.

Whether you go with the fiberglass alleys or used your original bronze casting, your engine will now need to be aligned to the shaft...

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

Capt Patrick McCrary

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