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Longer Amas and Increased Beam?

Question:

Ron: I have a question for you Mike. Someone bought an 18-foot Sailbird like mine but it has been modified with longer amas, set to give 14' beam vs the original 11'. Will that help the boat be faster? Also, will sailing qualities be improved?

Answer:

Yes, it's almost certain that longer amas will speed up your boat. Think of it like this. Most of the time you're sailing as a cat on 2 hulls—yet one hull is much shorter! That is surely slowing you down as longer, slimmer hulls are inherently faster. (The greater drag can cause lee helm also.) I've long thought that having all 3 hulls the same length, made the most sense just considering speed, but this needs compromising to allow more space in the center hull and also to help the boat turn. Personally, I like to have amas about 90% of the center hull length though—that's what my W17 and W22 have.

Now, as far as increased beam is concerned. Spacing them out will also add significantly to the stability and enable one to accept more driving sail power and therefore be faster. But this will put more load on the mast and also a lot more load on the akas (beams) that may well need to be beefed up—or have waterstays added. Many would also consider that the wider boat is not as safe—especially for novices—as the narrower one; the reason given is that the amas on the narrower boat will be pushed under, giving an early warning of possible capsize and also allowing the resulting increased angle of heel to spill wind from the sails. The wider boat DOES require more vigilance and skill, but for others (like myself), the extra power and speed is worth that effort.

Sailing qualities will change a little but whether they are improved or not, will depend on how the boat handles at present. The boat will likely be a better sea‑boat and also more stable on a straight line but possibly a little harder to turn. The extra beam and increased ama length will likely make the boat drier but all these positive things can encourage a sailor to push the boat faster and the end price for that is a pitchpole, as the higher stability of the wider boat will better resist a normal athwart-ship capsize. So the price required is more vigilance, better skills and quicker reactions.

Mike


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