Wharram Builders and Friends
Small Cats, Hitias, Maui, Melanésia etc...
Hitia 17- Alternative Construction Techniques
I'm currently in the process of building my Hitia 17, but I'm a little out of sequence, since I need to clear some projects from my shop before I can commence construction of the hulls.
Most of my deviations from the plans are driven by areas where my experience tell me there are better altenatives in either materials or techniques to those given in the plans. While I understand the plans are intended for someone to construct a Wharram with the minimum of experience or tools, you may want to consider where there are alternatives available. You need to decide whether the alternatives discussed are beyond your skill level or tooling available.
Even though I have access to larger machinery, it isn't always the best solution, especially if I have to factor in scheduling and travel time. For example, I originally planned for a friend of mine, with access to a CNC router, to cut the six pieces of plywood needed for the crossbeam webs. This would be a perfect example of the appropriate technology since the pieces must be identical in size and curvature. Too much trouble, so I ended up pattern routing the pieces in my own shop and learned in the process that I could produce the level of accuracy needed.
First item I'd like to discuss is the construction of the mast. The method given in the plans, while simplistic in approach, is difficult to assemble and not of the strongest possible construction. My approach is to use the birdsmouth technique that will yield a stronger and lighter version than what is in the plans. Various discussions of the technique can be found online and revolve around either a "rule of thumb" or an actual formula based upon empirical testing.
For a 3.5" diameter mast, the rule of thumb says 0.4 x 3.5"- 1.4" for the width of the stave, and 0.2 x 3.5"- .7" for the thickness of the stave. If you use Douglas Fir, the thickness factor can be 0.15 which yields a thickness of .525". I elected to go to the conservative side and chose the thicker option even though I'm using Douglas Fir. This will yield a 3.5" diameter mast with 95% of the cross sectional area of the JWD design and without the mass of epoxy fillets on the inside. The mast will be self jigging in glueup and will be MUCH easier to ensure it's straight.
Any thoughts?
Omar M. Rashash
Any time you propose to differ from what the designer recommends you must keep two things in mind. First, the change must be equal to or stronger than what the designer originally intended. Second, it should either reduce labor, for the same result, or if labor is increased, it is reflected in a better fit and finish than what was originally intended.
My recommended change in the glassing schedule meets both of these requirements:
This picture probably gives a better idea of what it actually ends up looking like:
The general rule of thumb for working with glass is to apply smaller pieces over large ones, which leaves you a stair step to fair, and you won't cut through the glass.
BTW, I know some people have done this, but don't glass the hulls until the decks have been attached. The hulls will not hold their proper shape until the decks are attached. It is possible to glass a twist into the hulls without the decks attached.
Nov 1, 2013
Rune M. Christensen
I see.
Thank you for the explanation and sketch. It makes sense :)
Nov 1, 2013
Rune M. Christensen
Hi Omar
I am getting near mast construction for my Hitia. I will use your birds-mouth design. So one question: It looks like you glued the mast in one step (not 2 halves), how did you then glue in the mast - foot, top and sheaves? It must be hard to get a good glue joint when these parts is inserted in the already joined mast?
Also, im having a hard time deciding if I should go for the sprit og gaff rig (have bought plans for gaff). Im leaning towards the gaff but the sprit seems simpler both in building and assembly on the beach.
I know you went for the gaff rig. What, in you opinion is the good reasons for doing so?
Rune
Mar 20, 2014