Thinking Outside The Box 101

It appears that canting keels and buckets of cash have made monos faster. Not a big deal considering how relatively slow they were before.

So how about the next steps? Start with some of the things that make CBTF slow.

1. The strut and the ballast move through the water, which must be slower than moving through air.
2. The ballast is in the water, which makes it effectively lighter than if it was in the air.
3. It requires a large amount of machinery to move it from side to side, which is dead weight.
4. The ballast strut is short for rules, draft and strength reasons so the ballast has to be heavier than otherwise.
5. The ballast and strut have to be dragged downwind, when all of it is not required.
6. The boat still heels, making the sails and steering foils less efficient
7. It is absurdly expensive, making for very conservative development.

First stage was to attach the top of the strut to tracks running from gunwhale to gunwhale under the boat. see fig 1 The tracks are rebated into the hull and covered when not in use. Drawback: If the boat is tacked accidentally, or the breeze drops it capsizes to 90 degrees.

Second stage was to enlarge the bulb and partially fill it with air to achieve neutral buoyancy. Wouldn't float, wouldn't sink, meets the 10 degree rule and the self righting rule. At rest, the waterline is the top of the bulb fig 2. If the boat heels , the bulb lifts out of the water and you have the full weight of the lead trying to right the boat. Breeze drops and you are ok, but tack accidentally, and you still capsize as the bulb is neutrally buoyant .

Third stage was to increase the air volume, so that the buoyancy of the keel was equal to it's weight. Fig 3. That is, it floated with only the lead filled portion in the water. Then, as soon as the boat heeled, the weight would come into play, but if it tacked inadvertently, the buoyancy of the bulb would keep the boat upright, with the same amount of righting moment that it had on the other tack.

Appears to be legal under the Open 60 rules. Maybe the mini rules (their rules page is in French) and the IRC rules as well. The Volvo rules place the keel amidships, but a variation would work for them. Would a large bulb skimming the surface be less drag than a strut and small lead bulb through the water? Probably. Would it be worth all the hassles? Maybe on a class with all the complexities of an Open 60 (canting keels and rigs, outriggers, water ballast etc). Then again, maybe not.

However, replace the lead with water and drain (not pump) some or all of the water out for downwind/light air sailing, you effectively eliminate the the weight of the ballast as well as the water drag of the bulb and strut. This would definitely be quicker Depending on how silly you were, the air could be partially replaced by water for heavy air sailing, which would also definitely be quicker.

For serious speed advantage, make the strut telescope and reduce the size of the bulb. (fig 4) For measuring and while tacking and gybing , it would be 14' long, and vertical under the hull. For maximum power, it would be maybe 36' to windward, 3' diameter, 14' long and containing half a ton of water. This is roughly the same righting moment as an Open 60 with 14' draft and a 2.75 ton lead bulb on a one ton strut. The differences are 1) the weird boat develops this rm at 3 degrees of heel, not 30, 2) it weighs 6-7 tonnes instead of 9, 3) it is dragging the strut and most of the bulb through air, not water.

As the attachment points and the strut are clear of the water, they can be larger, lighter and less stressed than the canting keel.

Telescoping, pumping and location around the hull would be altered as the boat heeled. Not a whole lot more work than the current CBTF/water ballast boats require. Could be done without engines much easier than the canters as well. Could even be controlled by computer to keep it just skimming the surface.

It fulfills the 10 degree heel rule, the draft restrictions and self rights from upside down. Leeway and steering are still handled by a rudder and a daggerboard. Only one of each is required as the boat will develop max righting moment at very low heel angles.

Regards,
Rob Denney