Join Date: Feb 2000
Location: Annapolis, Md
Thanked 195 Times in 159 Posts
Rep Power: 10
Re: Pros and cons of steel sailboats
My understanding of the weight up the mast was that it was allowed to swing through a reasonably wide angle. The concept was that it acted like a counter balancing pendulum, similar to the counterbalance weights on radio towers and tall street light poles.
Like most things the right amount of roll moment of inertia is a matter of doing things in a reasonable manner. The current thinking seems to be that if you end up with too much roll moment of inertia that will take the boat out of phase with the waves and so the kenetic rolling loads will be larger resulting in an over swing (continuing to roll past the point that the same boat with a lower roll moment of intertia might roll to), similar to excitation roll.
The problem of overswing is further exacerbated when the weight is up high, raising the vertical center of gravity and reducing the boat's tendancy to right itself.
I am always amazed at the sheer amount of attention paid to the likelihood of a capasize. There is a huge pile of factors at work such that its hard to have a one size fits all general rule. Take the debate about deep keels in big waves. In theory the surface of the wave is moving faster than its core. This creates a sheer which wants to rotate the boat, and the deeper the keel, the more sheer it is likely to experience. But most deep keels are also short chord and so stall easily, and that since the sheer forces are at a steep angle, the deep keel is also likely to stall and produce less side force. But even the reduced force is likely to heel the boat, but as the boat heels, it reaches a point where the keel has less penetration in the wave and so the force is further reduced, that is unless the boat starts to slide sidewards on the wave face in which case the velocity of the boat will add to the force the boat experiences and since a shallower keel is more likely to slide, its velocity is greater, and therefore the unit force is likely to be greater, and since a longer chord length keel does not stall as easily it is also more likely to produce a greater rotational force.
In other words, the specifics of the boat's shape and its loading, the wave height and ist shape matter more than theoretical advantages and disadvantages.
To view links or images in signatures your post count must be 10 or greater. You currently have 0 posts.
Curmudgeon at Large- and rhinestone in the rough, sailing my Farr 11.6 on the Chesapeake Bay
Last edited by Jeff_H; 10-31-2013 at 10:29 PM.