Balancing the boat with more chain.

[GordMay]

Greetings and welcome aboard the CF, Old Dave.

Originally Posted by colemj

... A light end boat will hobby-horse with considerably less amplitude, but at higher frequency, while a heavy end boat can hobby-horse with an amplitude great enough to take water over the bows and up the stern ...

Indeed.

[GrahamHO]

Originally Posted by skipmac

Mass in motion has inertia, more mass has more inertia.

So as the bow rises to a wave the weight in the bow accelerates upwards, builds inertia, wave passes but bow continues moving upwards until gravity overcomes the inertia and the bow starts moving down again. Acceleration of gravity without the buoyancy of the water the bow drops and accelerates. Bow hits trough but the inertia of the weight pushes the bow down into the water until the buoyancy overcomes the inertia, bow starts to rise again.

Inertia is the mass times the square of the distance to the center of rotation so moving mass farther from the center of the boat increases the inertia a lot.

Add weight in the stern and it compliments this process.

If anyone can be bothered with the physics, it's called the "polar moment of inertia". It's the same reason old rear engine VW Beetles would go off a wet road tail first. (and I believe the Porsche 911 but I haven driven one)
A dumbbell has a high polar moment of inertia if you try to twist it and a shot put ball has a low polar moment of inertia if you twist it in your hand.
Weight in the ends is dumb...bell.

[skipgundlach]

☺ I learn something new every day.

Reading this thread, I see that hobbyhorsing is a slow, continuous sine wave if effort is exerted on the ends.

I'd thought it to be a fast sine wave motion. I personally would find that more uncomfortable, but, then, I have one of the former (or at least I presume I do, as much weight as we have on both ends of our 44,000 pounds)...

[a64pilot]

Im in the same position, and do not have any choice but to weight the bow, however as I don't yet have a windlass mounted, it, it's battery and chain I think will "fix" my trim.
It's a displacement thing obviously, to drop the stern 6" takes a lot of weight as the stern is so wide, you have to displace a whole lot of water to get that 6" drop, but to drop the bow 6" due to it's much lower surface area isn't going to take all that much weight.

Lots of "stuff" you really have to put on the stern, davits, Solar panels, RIB, in my case a generator pretty much can't go forward.


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[GrahamHO]

Originally Posted by a64pilot

Im in the same position, and do not have any choice but to weight the bow, however as I don't yet have a windlass mounted, it, it's battery and chain I think will "fix" my trim.
It's a displacement thing obviously, to drop the stern 6" takes a lot of weight as the stern is so wide, you have to displace a whole lot of water to get that 6" drop, but to drop the bow 6" due to it's much lower surface area isn't going to take all that much weight.

Lots of "stuff" you really have to put on the stern, davits, Solar panels, RIB, in my case a generator pretty much can't go forward.


Sent from my iPad using Cruisers Sailing Forum

Which is why some yachts have their lead ballast fitted with more weight towards the front of the keel.