Monday, February 11, 2013

John Z's new Moth--Building the mast tube

Picking up from the last post, here we see that John has installed some of the permanent bulkheads and support framing for the stern deck.

This post documents the construction of the mast tube for the semi-free standing rig which John plans to use in this boat.  Here, he is using a piece of conduit slightly larger in diameter than the mast as a form for the tube.  He first wrapped the conduit with wax paper and plastic sheeting to prevent the carbon cloth from bonding to the conduit and then scotch taped the end of the dry cloth to the plastic film before wetting out the cloth.

Next, he rolls the carbon cloth, plus a piece of peel ply tightly around the pipe. John lets the epoxy resin kick off without the benefit of a vacuum bag.  Experience has taught him that the vacuum bag tends to leave nasty longitudinal wrinkles which detract from the strength of the finished tube.

After the epoxy resin has cured, John removed the tube from the conduit form and sliced it in half lengthwise.  The reason for this is that John wants to be able to change the rake of the mast.  The oval spacer will permit the required range of fore and aft movement at the deck partner.  The mast will rotate in the tube and rake will be controlled via block and tackle connected to the bow stay of the semi-free standing (no side shrouds) rig.

The keel end of the mast tube is replaced over the piece of conduit while the wood spacer controls the shape of the tube at the top end.  The mast tube was made larger than required to allow the wood spacer to be cut off with the excess after the side walls have been added.

With one side wall finished, John removes the peel ply and repeats the process on the remaining side to complete the rough tube.

The finished mast tube before trimming to the required height.

The temporary bulkhead called for in the Mistral plans must be removed so that the mast tube can be properly located.  Here John takes off the bevels to fit a temporary brace which will prevent the bow of the hull from twisting after the bulkhead has been removed.
Bevels also must be captured so that the keel support for the bottom of the mast tube can be fabricated.
The mast tube trial fitted in the boat.  Yes, it is a bit crooked due to the bottom of the tube being rough.  Trimming carbon fiber is very hard on saw blades.  John recommends using a diamond cutting wheel on a dremel tool instead.  He uses a wheel from this source:

Another look at the hull with the newly fabricated mast tube temporarily in place.


  1. Now that was a question I needed answering. thank you both.

  2. Hello, good to see people still having fun with one of dads old designs.
    Vince Chester

  3. Hello, good to see people still having fun with one of dads old designs.
    Vince Chester

  4. Hello Vince: I assume Derek is your father? Is he still alive? If so I'd love to contact him.

    Best regards,

  5. Hello George, yes Derek is my dad - he lives on the Isle of Wight and I'm afraid he is worse than me with IT. I'm sure he would love to have a chat about boats and cars as he is restricted to what he can do nowadays.

    1. Vince: Could you email me at: That way you could share your dad's snail mail address privately. I'd then send him a letter. Additionally I have a sailing friend (currently living in Florida) who hails from the IoW and returns home from time to time. Recently we lost another IoW Moth builder when Bill McCutcheon (he built many Shelley designed Moths in the early 1960s) passed away about a year ago.