Hey all. I’m pretty much a newbie to this sailing stuff, but had a thought that matbe someone could run with. What about using mercury switches/or something similar to control your moveable ballast or your canting keel? This would take a little tinkering, but I think it could be very effective, eliminating the need to manage another control. I know you could use a gyro, but this is just another idea, and you wouldn’t need an additional channel for the gyro. Additionally, you wouldn’t have to manage the control of another function.
If you do this (and it has been done by at least one member of this group) you miss out on some of the advantages of a canting keel system.
Namely, you loose the ability to roll tack your boat by uncanting the keel just before you tack. You also loose the ability to heel the boat to windward to help wing the jib when sailing downwind.
You also open yourself up to some nasty feedback loops. You will either want to have a substantial “dead spot” between the two switches so that the boat does not go into uncontrolled (underdamped) oscillations or you will need to add damping to your control cicuit.
Most of the time, if the wind is moderate or stronger, you are going to pin the keel to windward when sailing upwind, and want it pretty much centered downwind. So you are not going to be spending that much time “controlling” the keel. You will simply switch sides each time you tack. So the overhead of controlling it yourself is not that great. And I think the advantages make it worth controling it actively rather than passively. Plus it adds a level of fun and skill…
Just my $0.02
Will
PS for a catamaran you would want sliding rack ballast rather than a movable keel. In order to prevent a swim you would need very fast servos. The Cat is not going to heel at all (to activate the system) until you are flying a hull. At that point, you are very near the point of flipping. At which point the system is going to need to throw the weight to windward until the boat comes back down again. If it was a gust, then you will be stuck with the weight to windward when you do not want it there… And you would still have to depower whenever you started flying a hull when the rack was pinned to windward. So again, I would opt for active control.
Appreciate the comments Will. I just had the idea and was curious. It will be sometime before I have the cash to do much experimenting, but it doesn’t mean that my mind should shut down right?! Maybe this would be helpful to those interested in building planing skiffs with moveable ballast, since it doesn’t sound helpful for canting keel and cats…
ha ha ha, you can still easily roll the boat to windward downwind which helps with sailing downwind anyway. mate, you reckon you dont have enough cash, i did it on a tight budget, the most expensive thing was the radio gear, i dont use a servo for canting the keel because they aren’t strong enough. but trust me, its hard work the way i have down it.
I see said the blind man to the crippled nudist who put his hands in his pockets & promptly walked away.
how much pressure would a canting keel exhert max. on a hull?
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It is easy to calculate. If you assume that the keel is horizontal, that is the maximum moment that it will exert on the hull. Take the bulb weight tomes the moment arm and that is the torque at the pivot point that needs to be reacted by the hull structure. This is a worst case scenario, but it will set your limit load.
There are two ways to take advantage of a canting keel. One is to keep the rig the same and reduce the keel weight. The other is to keep the keel weight the same and be able to carry more sail area. The canting keel generates more righting moment for a given amount of keel ballast than a fixed keel (for a given boat heel), so it really depends on how you use that potential.
On my canting mast US1M, I am using a smaller keel bulb than most guys are sailing with and keeping the maximum sail area. So the loads on the hull will not be any higher than a typical US1M (since those loads are the result of the sail area). Since the canting mast is free standing (no sidestays), I am working very hard to integrate the mast support structure into the keel box. That way, the heling moment induced by the sails goes straight into the keel and my hull structure does not carry much (if any) of the heeling loads.
It is easy to calculate. If you assume that the keel is horizontal, that is the maximum moment that it will exert on the hull. Take the bulb weight tomes the moment arm and that is the torque at the pivot point that needs to be reacted by the hull structure. This is a worst case scenario, but it will set your limit load.
i know we calculated it at the maximum cant, which wasnt horizontal, but it was complicated because you also have to calculate the arm & everything, worked out that there is about 11kg of torque for my keel which weighs bout 1kg.
I see said the blind man to the crippled nudist who put his hands in his pockets & promptly walked away.