Waiting For More Plywood

I'm still waiting to hear about the next batch of 5mm plywood; the mill suggested February 4th as a possibility but I'm not holding my breath. In the meantime I set about making the outer part of the stem.

This outer stem is 75mm wide and 80mm thick at the maximum point but it tapers towards the sheer. I decided to laminate it out of 10 x 8mm thick strips but these would be difficult to bend and would probably break. So I built a steam box and read about steam bending timber. It sounds straightforward and making the steam box was. Using it was easy too, just put the wood in and cook it at 100C for an hour per inch of thickness. I expected that the wood would bend fairly easily while it was hot but...... Here's what I found out:

• The timber cools and stiffens up very quickly so you have to bend it and clamp it in a matter of seconds,
• The outside of the bend must be supported by a flexible strap to help prevent the fibres breaking away where the grain runs out.
• A strong fixed former is needed to withstand the force involved. It has to be fixed so it doesn't move about when you heave on it.
• It is difficult to do single handed, holding the bend in place and putting clamps in place needs 3 (or more) hands.
• Each laminate would have to be bent individually because 2 or more would need more force to bend than one person (ie me) could apply. This would be tedious and would take several days.

Here's a photo of some of my test pieces; there were quite a few more!

I think my problems were: the test pieces were all too dry because it gets very hot in the shed (up to 40C), they were not carefully selected (the grain should be straight with no run outs where it has to bend), they might have been too thick (about 10mm), maybe they were not a good choice of timber.

Having spent about 3 days learning about steam bending I decided to Build up the outer skeg from solid pieces glued together in 4 layers. This is the same method that I used for the inside part of the stem. It is quick and easy. Here is the finished result which only took a couple of days to make. There are 4 layers of 19mm thick timber each made up of 3 pieces. The joints in each layer are staggered so that each joint lies against 3 layers without a joint. The gap between the hull and the stem at the upper left is the hooked scarf joint where the stem joins the keel. There is more work to do after the hull is finished and before the stem is glued in place.

I started building up the skeg but before I could do that I needed to know the size of the hole for the stern tube and to decide on that I needed to know the diameter of the propeller shaft and that depends on the propeller, etc, etc. This brought me to a standstill because there are too many variables. I muddled around for a while trying to work out what was needed. Eventually I managed to contact and meet a marine engineer (that took several days because it's a) holiday time and b) he was then working elsewhere on a boat) who cleared up all these issues in a few minutes. He said: use an off the shelf fibre glass tube because it is cheaper than buying the materials to make your own and is probably better quality, use an off the shelf "cutless" or "cutlass" bearing which is made to fit the tube, use a 1" diameter propeller shaft because the vast majority of propellers in the sizes I am interested in have a 1" taper bore (a smaller shaft would be strong enough but ground round 316 stainless steel smaller than 1" has to be made to order and is therefore very expensive).

So the outside diameter of the tube is 1.75" but he suggests making the hole a bit bigger to allow some wiggle room to get the tube and propeller shaft correctly aligned. Once the tube is lined up the space around it in the hole is filled up with epoxy "bog".

Here is the start of my built up skeg. There are 2 pieces at the moment, above and below the hole for the tube, The skeg is almost 100mm thick where the tube goes through and 75mm thick above and below that. I made it in 2 halves so that I could rout out a channel about 12mm square exactly along the middle of the join. I also routed out 2 grooves towards the edges of the join for splines to be inserted to locate the joint. Then I clamped the 2 halves together and ran a 16mm diameter drill through the hole.

You can see that the skeg has to be built up more to reach the bottom of the keel that will run the length of the hull. Once that is done I will glued the joint around the hole. Believe it or not but I ran out of timber the day before the Australia Day long weekend!

When the hull it complete the skeg and keel will be fitted in place and the 16mm hole used as a pilot hole to drill the rest of the way through the hull. Then a block has to be fitted inside the keel where the stern tube comes through and this will be glued in place when its location is known. The 16mm hole will be extended through this block. Finally the pilot hole will be opened up in stages using long drills and a boring bar until it is big enough (almost 2") for the stern tube. I have a selection of drills up to 1" and will make up an extension to work through what will be a hole almost a metre long. From 1" up I will make up a boring bar with an adjustable cutter because drills over 1" are expensive and of limited future use.