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W17 trimaran – Under Spinnaker

In this video, the wind is down in the 6-8k range, but on a reach, she’s still able to slice through the water at wind speed. The asymmetrical works from about 70 deg off the wind to fully downwind, as the boat is wide enough to wing it out without a boom, even if this position is rarely used on a multihull. Helps to slacken the forward edge (luff) as you go closer to the wind, to avoid it curling in and collapsing the sail.

There’s a short piece of video included taken from the windward ama, that offers a side view of the main hull. This is particularly interesting as it shows the bow truly ‘slicing’ the water instead of wasting energy throwing it to the side. The clarity of the water below the waterline allowing one to clearly see the hull underwater, is proof of this. (My design approach here is that for a required underwater volume (buoyancy), it’s better to go down lower but keep the sides more vertical – in a deep U rather than a V). This way, a larger proportion of the required volume is underwater where the wavemaking resistance is less (a la submarine**) … and the wave at the surface is permitted to easily ride up and down and is therefore not absorbing energy being thrown out to the sides, as wider and more flared monohulls typically do. The easy flow and low resistance is apparent.

**  Just to clarify for those interested.  While a submerged submarine also experiences residuary resistance, this is due to a varying pressure wave along its length, caused by it's basic form (nose entry, length to diameter, tail shape etc) moving water particles aside, and, also in no small part, to the form resistance of fins and control surfaces.  But compared to a surface vessel, this part of the total resistance will still be 'relatively' low, with close to 80% of the total resistance coming from surface friction ..  a percentage only likely on a surface vessel at very low (or very high) speeds.