Main Bulkhead Work

I have been trying to do several small projects in parallel.   One of the recent projects are the main bulkheads that are at both ends of the main cabin.   These stations have reinforcing planks where the aka cross beams will bolt through the hull.

The unfinished area in the middle gets cut out of the companionway after the bulkhead is in the hull. Until then, it is an extra bracing support.

The bulkheads are large enough that they came from two pieces of plywood.  After gluing the puzzle joints, I have coated both sides with three layers of epoxy.  The epoxy then got sanded back as smooth as I could get it, so it is now ready for final finishing.

The reinforcing planks will get epoxied to the bulkheads before being placed on the strongback.  The planks were shaped from templates that I had made a few months back.  I recently dry-fitted them to the bulkheads with screws through the back.  This allowed me to get the alignment correct and bore holes for the aka bolts.  The screw holes will get filled with epoxy later.   They will mar the less visible surface of the bulkhead a bit.   The screws will be used to accurately locate the planks when they are slick with glue and to help with clamping.

I left the epoxy coating off of the gluing surface of the bulkheads.  This will give an area for a primary wood to wood bond.  Probably not that critical, but it can't hurt.

The hole through the bulkhead gets a similar treatment to the akas.  A G10 tube is inserted and then there is a 75mm cplate washer that the bolt will tighten against.

Task time: 20 hours

Total project time: 331 hours

Boring Beam Mounting Holes

The Akas are attached to the main bulkheads with 18mm bolts.  The bolts are carried through the beam holes with a 20mm (3/4 inch) G10 tube liner.  I needed to bore the holes through the solid interior of the beams before the first layer of carbon cloth.  CNCed holes are marked on the plywood sides and I did not want to lose the reference marks under the cloth.

This is one of those seemingly simple tasks that takes a lot of pondering and worry.  The holes must be perpendicular to the beam all the way through and be accurately located so that they will mate properly with the bulkheads.

All kinds of little issues arise for consideration:

- How do you level an 18 foot beam with one end across a drill press table?

- There is not enough throw on the drill press without shifting the tables and re-leveling in the middle of a hole.

- How do you drill an accurate hole without using a drill press?

- The forstner bit is not long enough.

- The forstner bit extension does not fit a metric forstner bit correctly.

- The collar on the bit extension does not fit down into the  hole.

Finally found a drill stand for a hand drill, but would it be accurate enough?

G10 (Garolite) Tube

Setup that allowed a hole "almost" deep enough.  It would not reach the last millimeter, but the point of the bit went through for reference.

A 3/4 inch hole that has been sanded slightly with a dowel covered with sandpaper.  The 3/4 inch tube fits snugly through most of the hole.  There is a little extra room at the top where the original hole in the plywood is slightly bigger (2mm), but the tube is squared in all directions.

All you can say when you drill that first hole and it is OK is whew.

Task time: 2 hours

Total project time: 311 hours