Friday, February 16, 2007

Preparing Skegs for Drilling Rudder Lashings

Although it is possible to drill the rudder lashing holes directly through the plywood of the skegs and rudders, taking care to seal the holes with epoxy when the lashings are put in place, I don't want to take any chances with possible rot in these areas due to water eventually seeping in. This is especially important for the lower lashings that are below the waterline and where they are constantly submerged. Some builders of these designs have cut out large sections where the lashings go and placed hardened inserts of epoxy in the cutouts. I feel better about having some solid wood in the edges of the skegs and rudders, so I drew the lashing hole centerline 18mm back from the edge and cut a slot 12mm wide and as long as the lashing area, by first drilling the ends and then cutting between the two end holes with a jigsaw. The resulting slot, much larger than the needed holes, will be completely filled with a thickened epoxy mix, and after it has cured and has been sanded flush with the surfaces, the lashing holes will then be marked and drilled through this epoxy insert. This leaves no chance for water to get into the surrounding wood through the lashing holes. The sequence for creating these inserts is shown below:


First a line is drawn 18mm back from the edge of the skeg, directly behind each lashing notch described in the previous post. I then used a 1/2" Forstner bit in my drill press to drill a hole at dead center in the line, at each end of the notched area.

Two quick cuts between the holes with a jigsaw removes all the material in between, leaving a slot that is 1/2" wide, centered 3/4" (18mm) back from the edge.

The resulting slot. There are four of these on each skeg, and I will cut adjacent ones on each mating rudder. edge.



The slots are filled with a thickened epoxy mixture that is about the consistancy of ketchup, so that it will self-level and completely fill the area. I first taped pieces of poly plastic to the other side of the slot to prevent the epoxy from running out. These large slots cannot be filled in one step, as the epoxy would get too hot if it were all poured in at once. This could cause it to expand and leave air pockets inside, so I'm doing the fill pours in stages, probably 3 or 4 separate steps, allowing at least partial curing in between. When these are finished, I'll cut the rudder slots and do the same, then sand all these surfaces, mark the exact lashing holes, and drill them out on the drill press. I know I'll thank myself for all this extra work when it comes time to hang the rudders on the finished hulls. And with a good quality Dacron line for the lashings, the rudder attachments won't need attention for years to come.

1 comment:

James Baldwin said...

Scott

The rope lashings worked well enough for the 51-foot Wharram Rapa Nui so they'll sure work on your boat. Here's links to the photos:

http://atomvoyages.com/images/Hans07kb68.jpg

http://atomvoyages.com/images/Hans08kb78.jpg


James
s/v Atom