Tuesday, 25 September 2012

Back from a break - Mast started

I have had a little break, putting the frames up went much quicker than I thought and had to order more wood for the chines.  This is all 25mm x 20mm, but I now have to scarf/join them all together so I end up with 34 pieces each around 8m long before I can start fitting them to the frames.  That part has me a bit worried, the build guide says take your time because the hull will show the bumps if you don't.  

So I decided to make something else instead.  Ordered some Oregon Pine, some spotted gum hardwood and away I went.  The main section of the mast was ordered and delivered, a 100mm diameter, 3mm wall thickness tube of marine alloy 6500mm long.  It weighs 16kg, and is easily carried by myself, and makes the whole thing a lot easier to build.

The top and bottom pieces are hollow to save weight.  For example, to make the bottom get two pieces of 120mm x 40mm and sandwich two 40mm x 40mm pieces each side leaving the centre 40mm x 40mm space empty.  For the top you use 100mm x 30mm. 

But you need to add strength in places and to cap the top and bottom.  This requires extra 40mmx 40mm pieces in the otherwise empty middle.  The top and bottom, and where important strength is required you add 40mm x 40mm pieces, 400mm long for mast fittings and the mast pivot at the bottom.  The end result is two semi hollow boxes, the bottom 120mm square and the top 100mm square.

Overall length of the mast is 9800mm which is longer than my shed.  

Below is the base of the bottom piece, that will have a pivot fitted and go into the tabernacle (800mm high metal mast support on deck):

And showing the length.

And after final shaping.  I cut down the upper section to fit inside the alloy tube, it is 1200mm to the flat surface the tube will rest on.  The outside hardwood pieces (small) are vertical legs for the boom support (see later photos).

The top wooden piece is 2400mm long, 300mm of that to go inside the tube.  There are two positions for rigging hardware, so it maintains the 100mm width for strength for the first 800mm.  However I planed large sections off the corners to end up with a hexagon shape, I was too lazy to go for a circle and the added benefit I see is a flat surface to bolt the rigging fittings through both sides.  The final 1300mm tapers from a 100mm wide hexagon to a 70mm square

I was adding internal plugs for the top and bottom, and supports at each of the two rigging places so I decided to make some adjustments.

As I needed to run wiring down the mast, I planed a corner off each of the inserts to leave a space for this.  

I also cut the tops of each insert on an angle down to the gap, thinking that any water that gets in through the mast top or rigging bolts will run down and eventually out where the bottom of the pipe meets the wooden base where the electrical wire will run.

Below is the view down from the top.

 Epoxy it all together:

 With the mast top platform sitting on it.

A bit of sanding on the inserts to get them sliding into the tube and then on to finish the boom support.  Below is 3 layers of 9mm ply that will be screwed to the small hardwood uprights shown earlier.


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