Friday, February 16, 2007

Cutting Rudder and Skeg Lashing Notches

This is one of four notched areas in the aft edge of the skeg. These notches are 80mm long. The purpose is to allow clearance for the lashing cord used in the Wharram rudder lashing method, while minimizing the gap between the trailing edge of the skeg and leading edge of the rudder. A large gap would create turbulance at speed.

The sliding miter table on the table saw makes it easy to cut these notches accurately. The depth of the cut is specified at 2.5 mm. I'm cutting them slightly deeper to allow for a hardwood insert to be fitted into the notch where the bearing edge for the lashing lines will be formed.

The finished notches on the adjoining rudder and skeg assembly.

This is one of those tasks that is much easier done before the boat is built, but this efficiency is not suggested in the plans. I wanted to completely finish the lashing assembly while the skegs and rudders could be laid on a flat work bench and parts could be cut and drilled with the table saw and drill press.

I know firsthand from experience with my Hitia 17 and my Tiki 21 that this rudder lashing method works great. It is much smoother than conventional rudder hardware, and much cheaper too. My Tiki 21 was fitted with stainless steel gundgeons and pintles when I bought it, and I converted it back to the Wharram method of lashing. Accurately drilling the holes for this lashing is difficult after the boat is built, as it is hard to drill a perpendicular hole by hand, especially as close together as these holes must be. Being able to place the mating edges of the skeg and rudder together on a flat surface makes it much easier to accurately mark these holes. I plan to drill them on the drill press, but first, there are many steps to take before I get to that point. For long term longevity in a wooden boat, it is essential to prevent moisture ingress into the core of the plywood. Any holes passing through the plywood are pathways for water to enter, and the only reliable way to keep it out is to first overdrill any such holes, then fill the larger holes with epoxy, and then drill the finished holes through this hardened epoxy so that the walls of the holes are solid epoxy and no wood edges are exposed. I'm taking it a step further with the rudder lashing holes and will explain this in the next post.

The notches shown in the photos above allow for a smooth, slightly rounded-over bearing surface for the lashing lines to come in contact with, on both the skeg and rudder. I cut these slightly deeper to allow for a thin hardwood insert to be epoxied in place. The hardwood will seal the plywood edges in the notch and again help prevent water entering the core under the lashings.

No comments: