Can you tell us in what direction the boom flexes ?

Of what material is the current boom ?

My current analysis is two fold.

First where does the flexing come from ? With the boom fitted to the mainbeam there is absolutely no reason to have the boom under compression. On beach cats the boom is under compression to actively rotate the mast but clearly this is not the case with your setup. In effect you can just release the car on the underside of the boom as fixing it is absolutely pointless. The car on top holding the sail still needs to be fixed to set the draft in the bottom of the sail, however this loading should be nowhere near the level that is required to bend the boom under compression. And if it is then your boom has a serious design flaw; one that is not to difficult to solve. But more about this if this is truly the case, which I really don't believe.

I think the boom is flexing downwards because your forces don't line up well. If your leech car is much to the rear of your mainsheet car (on boom) then these loads create a bending moment that acts all along your boom. A first quick fix is to fit a slide to your tack corner of your sail and hold that corner close to the mast. It appears a couple of centrimeters can be won that way on the total misalignment of maybe 15 centrimeters. This is already a 15 % improvement.

Is it possible that you load up the boom and sail and give us a picture of the flexing boom. For I suspect the solution is really simple and easily homemade for 100 bucks.

If the misalignment of the boom cars are the reason for the flexing then what you want in the way of weight is a non-prismatic boom. Meaning one that is not constant in its crosssection. This means additional weight can be won with respect to a straight carbon section. Not too mention alot of money.

Pretty much the advantage of carbon is that it is twice as stiff for a given weight as aluminium. Aluminium and other metals are pretty much equal in their stiffness/weight ratio's. Forget about glass laminate as the has a worse ratio between stiffness and/weight then aluminium. This carbon advantage is ONLY attractive when a designer is seriously limited in the volume AND weight he can accept for a given element. If either one of these is NOT limited then their is no reason to spend more money on carbon as a simple adjustment of the design will result in exactly the same performance.

Homebuilding a boom for your boat can be as simple as getting cutting out some ply sides (non-prismatic) and just gluing two strips of aluminium to the top and bottom, closing of the box. For weight reduction you could cut large holes in the sides as was done at the rear of your current boom. At the point of the cars you'll just glue in a piece of solid wood (between the ply sides).

The advantage of this setup is that flat alu strips can easily be bend to follow the non-prismatic shapes you have cut in the sides. The ply sides are only there to stabilize the alu strips that take all of the load. Of course the alu strips can be replaced by carbon if you really want but alu strips is a simple way of quickly getting results by an amateur. The advantage of ply is that it is MUCH lighter then carbon laminate. Think 2.3 times lighter and don't underestimate the load baring properties of ply. In effect ply is nothing more then a naturally produced carbon based fibre matrix. Glues or screws are easily available to fit the box together. This much lighter ply can possibly allow you to homebuild an equally performing boom for less weight then a constant section carbon boom and for less cost. Professionally made custom non-prismatic booms are far too expensive to even consider.

Like I always say. Carbon is for lazy engineers.

Wouter