Tuesday, February 20, 2007

More Sternpost Details

I didn't do any work on the boat over the weekend or Monday, but I was back at it again today,working on the preparations to the sternposts and rudders as described in my last post. The epoxy fills in the drilled out slots I made in the sternposts last week turned out great. This mixture of wood flour and silica has cured rock-hard and will provide a solid, waterproof section for the small holes that will be drilled for the lashing line. I sanded these smooth today to remove excess epoxy buildup, but they will have to have one more application of thickened epoxy for the final fairing before they are ready to be glassed over and then drilled. I went ahead today and drilled out the matching slots in the rudders, and started the filling process in those this afternoon. When filling a large cavity such as these with epoxy, you can't just pour it all in in one batch, as large amounts of mixed epoxy concentrated this way will get very hot in the reaction process and could literally boil over, leaving air pockets and voids in the filling. To make these fills, I first coat the inside surfaces of the cut-outs with clear, unthickened epoxy, then fill a small amount and allow that to partially cure before mixing more epoxy to fill some more. To completely fill these holes has taken three separate applications with curing time in between.

With the rudder slots cut and the first batch of epoxy filling in them, I turned my attention back to the sternposts and began making hardwood inserts to glue into the notches I cut last week in the trailing edges. These notches, as described in my previous post are simply clearance notches with a rounded over surface to allow the lashing lines to bear against them without chafe. Rather than just round over the cut edge of the plywood, I wanted to seal and protect the plywood by cutting the notches a fraction deeper and then laminating in these inserts. I made the inserts of solid mahogany, first by cutting a piece of stock the exact thickness of the plywood, then using a roundover bit in the router to radius the edges, then slicing off a thin strip with the table saw, and cutting these strips to the exact length to fit each notch.

The hardwood inserts are shown here, adjacent to the notches they will be glued into

Here the inserts are glued into place. After the epoxy cures, they will be further shaped with a nice rounded edge on each side, then the whole area will be glassed over before the lashing holes are drilled. After the boat is built, the fiberglass sheathing on the hull will also cover all exposed areas of the sternposts and skegs with an additional layer of protection.


kim whitmyre said...

Excellent work on the stems, Scott. I like your variation on the epoxy blocks: looks like good thinking to me.


Scott B. Williams said...

Thanks Kim,

These extra steps take a bit of time but I feel they will definately be worthwhile in the longterm for reduced maintenance and increased longevity of the boat.