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post #47 of Old 03-15-2013
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Re: my boat dances on a ball

Originally Posted by Bene505 View Post
I think it's because the attachment point is more forward. By way of an absurd example, if we all had anchor rollers at the end of a 50 foot bowsprit, none of us would dance at anchor. The extra distance lets the tension from the anchor pull the nose into the wind better.

Just a guess. It might be more of an oscillation frequency thing.

Very true, there are some similar dynamically unstable 'ratios' involved with simple trailers towed behind vehicles ... when the towbar is less than about 3 times the length of the trailer tire width such trailers become very 'whippy'; ditto when automotive front suspensions have forward facing axle control arms the shorter the control arms the higher the frequency of oscilation; also, 'tail dragger' landing gear on aircraft are more dynamically unstable than 'tricycle' gear.

And, there are additional oscillation instabilities in the vertical direction that become more aggressive when the trailer towbars arent strictly 'horizontal' between the two ........ and thats probably why using an anchoring bridle which holds the pendent or the rode to 'as low as possible' seems to help dampen out most 'swings'. Probably a good reason to use less stretchy dacron polyester rope rodes than the more common nylon or even 'much heavier' nylon to lessen the 'elasticity' of rodes and attachments if you have a 'swing problem'.

Once you introduce any sort of 'spring' to a mechanical system, whether flexing metal, elastic rope, a chain that forms a catenary, etc. you can surely and usually expect some sort of slow vibratory oscillations to develop. Such almost suggests the usage of wire cable or long 'rods' for mooring and anchoring.

Last edited by RichH; 03-15-2013 at 11:00 AM.
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