Why does boat sail on the mooring?

[hullcurves]

My Caliber 28 sails back and forth on the mooring. It has a fin keel and spade rudder. It does have somewhat higher topsides than, say, a Bristol. Is it the topsides, is it the underbody?

Is there a solution? A riding sail? Something else? If you have a riding sail, any suggestions on using it?

Thanks for any help you can offer.

hullcurves@gmail.com

[sailingdog]

Hullcurves-

There's a good explanation for this over on the Don Jordan website. You can find it here.

Basically, it has to do with the fact that you've got a fin keel and that the aerodynamic point of resistance (the mast) is somewhat ahead of the hydro-dynamic point of resistance (some where between the keel and rudder). This leads the boat to swing from side to side.

A riding sail would work. You could also try anchoring from the stern, as suggested in Don Jordan's article.

[Idiens]

Mine snuggles up to the bouy, even against a slight breeze and a current. Impossible I say, defies the laws of physics, etc.. My boat doesn't know that, so does it anyway. I resort to hanging a bucket over the stern.

I'm going to try SD's tip about anchoring stern first, but I sleep in the aft cabin, so that may be not such a useful idea.

[Faster]

Riding sails will "gentrify" the swinging about, but may not eliminate it. Still, they will greatly reduce the shock load on your rode/tackle as the boat doesn't fetch up so hard on the limits of the swing.

Stern anchoring sounds interesting, but with so many boats now providing aft cabin sleeping arrangements, the "chuckling" of waves and ripples under the counter could be quite noisy.

[bobwebster]

Originally Posted by Faster

Riding sails ... will greatly reduce the shock load on your rode/tackle as the boat doesn't fetch up so hard on the limits of the swing.

Funny you should mention that. I was anchored off Molokai last week with wind gusting over 35 knots. I was in 10-15 feet of water, with about 75 feet of chain out, in a Catana 52. I normally have more chain out, but this was a little tight (for me).

I thought it was jerking kind of hard as the boat was swinging back and forth, but the anchor held well and the bridle wasn't coming loose, chafing, smoking, or anything bad. Then, the next morning, I found this when I unclipped the bridle from the chain (the shackle, not the quarter).



The solution? A bigger shackle, of course!

The boat doesn't seem to swing back and forth as much with more anchor chain out. And catamarans seem to swing more than monohulls, even with anchor bridles.