[MHml] Multihulls Digest, Vol 29, Issue 11

[Rob Denney]

Something is wrong here. I seriously doubt you can buy materials to build a multihull of 50 feet with 12500 US  in materials. When I built my tri, some years ago the cost of the ceder alone was 6000 US. Carbon,core and resin would excede the aforementioned figures.

Rich

G'day,

True, the cost of carbon, core and resin for your tri would exceed $12,500.  

Assuming it is more or less conventional, the tri probably has:

More surface area than the 44 sq m/473 sq', including bulkheads and bunk on the proa.  It probably weighs a bit more than the 500 kgs/1,120 pounds of the proa in race ready trim as well.  

Much higher loads due to the forestay, shrouds and mainsheet all being attached to the extremities of the boat and trying to lift them while pushing the mast through the middle of the hull.  This set up needs the entire boat to be very strong, and consequently heavy.  The proa with it's unstayed single sail rig has all the rig, steering and leeway reducing loads within the middle third of one hull. This is built very strong, the rest of the boat "only" needs to keep the water out.

An extra hull and beams (the windward ones) which are not doing much at any given time.

Maybe 6 sails and  6 bunks (one of each on the proa, and both are small), sheet tracks, traveller, daggerboard/centreboard/fixed keel, motor and mount, kitchen sink, floorboards, head, plumbing, electric gadgets, winches,  bolts and screws holding things on, skin fittings and a well faired and painted finish inside and out  (none of any of these on the proa).  

100m/120 yds of standing rigging, turnbuckles, chain plates and spreaders. The proa mast is self supporting and only 12m/40' long.  

200m/240 yds of running rigging to trim the sails.  The proa has one halyard (very light as there is a simple halyard lock), a main sheet, a luff downhaul and a snotter on the wishbone boom.  Each are 4:1 purchases with a simple cleat.  No jammers or other expensive/heavy means of holding ropes.

Carbon varies enormously in price and availability at present, but by buying large quantities and selling the surplus, I occasionally get it at a good price.  The core is Polycore, a plastic honeycomb with a scrim on each face.  It is very resilient and it is possible to get an excellent bond (far better than to foam) without vacuum.  It weighs the same as H80 foam and costs less than half as much.  

Your scepticism is justified, but if you want to build one of these boats, that is the price at which I will supply the materials, assuming I can get some more carbon.  

regards,

Rob

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