pakrat - 22 June 2014 02:26 AM

The problem is to change the buoyancy characteristics of the ‘new stern’ after a shunt. A more buoyant stern will dampen hobby horsing by canceling out the teeter totter motion around the center of buoyancy.

In Robert’s sketch just above your entry (#29), the stern does have additional buyancy—due to the planing surface becoming immersed. It also provides planing lift at higher speeds, strongly damping pitch.

If we have the means to add water ballast to the ama, why not pump a couple dozen liters into a tank at the extreme bow? The extra weight would keep us from gaining any actual buoyancy, but the inertia should help prevent the teeter totter.

This is generally considered a bad idea. Consider the increased inertia of the water at the ends of the boat. Yes, you will decrease the frequency of the pitching, but you will increase its magnitude, driving the bow into every wave. Almost always, it makes most sense to concentrate the masses as near to the pitch centroid as possible.

Dave

Thank you Dave.

You say: “Yes, you will decrease the frequency of the pitching, but you will increase its magnitude, driving the bow into every wave.”

The bow is going to pitch higher, but shouldn’t flotation/buoyancy keep it from burying into the face of the on coming wave? Thus dampening the pitch before magnitude/amplitude becomes that big of an issue.

I gotta agree that sticking extra mass at the extreme ends of the craft is generally a dumb idea, my thought was that it would be quicker and simpler to trim the bow higher than to add temporary flotation aft.

Thanks for paying attention to the ramblings of an ignorant newby.