To stop pitching, no not horseshoes. - SailNet Community
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post #1 of 20 Old 02-04-2015 Thread Starter
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To stop pitching, no not horseshoes.

It has been suggested on other sites that if a 40 odd foot boat is pitching in an anchorage, this might be reduced by hanging a bag of rocks off the stern and possibly the bow also.
Just off the top of my head, I would guess that this bag would need to weigh a thousand pounds or more to have much effect, if any.
Can one of you really, really smart engineering types on here chime in with a bit of fact based information on this, please. Thank you.

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post #2 of 20 Old 02-04-2015
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Re: To stop pitching, no not horseshoes.

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It has been suggested on other sites that if a 40 odd foot boat is pitching in an anchorage, this might be reduced by hanging a bag of rocks off the stern and possibly the bow also.
Oh my.

I don't think weight would help. After all, we try to reduce weight in the ends to reduce pitching moment. You could talk me into a bucket that provides resistance to motion without significant weight.
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post #3 of 20 Old 02-04-2015
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Re: To stop pitching, no not horseshoes.

Auspicious,

Please do not try to discredit this hypothesis. I would very much enjoy being at anchor watching people tote a thousand pounds of rocks in their dinghies in the sort of conditions likely to create unpleasant pitching.
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post #4 of 20 Old 02-04-2015
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Re: To stop pitching, no not horseshoes.

In order to reduce the pitching movement of the boat you need to re-arrange your load distribution, placing proportionately more weight aft. Think of it as a hobbyhorse, where a fat guy sits in the back.

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post #5 of 20 Old 02-04-2015
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Re: To stop pitching, no not horseshoes.

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Think of it as a hobbyhorse, where a fat guy sits in the back.
Well I certainly solved this problem then... I am the fat guy always sitting in the back, although hardly a 40 footer.
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post #6 of 20 Old 02-04-2015
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Re: To stop pitching, no not horseshoes.

Adding a thousand pounds of rocks to one of the ends will increase both the period and the amplitude of the pitching.

Whatcha need to help stop the pitching is either a 'flopper stopper' or a 'paravane' ... and with no rocks required.
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post #7 of 20 Old 02-04-2015
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Re: To stop pitching, no not horseshoes.

The idea is not as bad as some of you want it to be. Those active in sailing some 3-4 decades ago may remember that about the same theory was quoted when pitching was to heavy during sailing - the cure was said to put something heavy (as a crew member) at the crosstrees in the mast.
And it worked - sometimes.

When pitching heavily there is a resonance, caused by wind, waves and the boat, mainly its moment of inertia. The moment of inertia can be changed be re-distribute weights on the boat, which might move the boat out of resonance with the waves & wind.
To this one should also note that the moment of inertia is proportional to the mass (weight) * r*r where r is the distance between the centre and the centre of the weight (google Steiners theorem if you want to know more). Thus ... distance is more important than weight, the further out the more moment of inertia is changed.

No 1000 pound is needed to make this change on a 40 ft boat. It is often perfectly enough with some few 100 pounds ... conclusion is given, eeh?

Now, all this is nice. In reality sea waves are not of one frequency, but have a wide distribution (a wide normal distribution if anything). In order to really avoid resonance effects, moment of inertia should be changed rather dramatically. So, these few 100 pounds, could they be kind enough to move up to the top of the mast?

OK, if all this works out well, what happens then when wind changes? Oh, new possibilities for resonances!

There are other methods, actually. But weights work, in theory and practice.

/J
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post #8 of 20 Old 02-04-2015
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Re: To stop pitching, no not horseshoes.

Reducing the distance the bow rises up, will lessen its fall.
So in cabin weight should go forward even if it lightens the stern. The stern never has a pitching problem.
You may want to try hanging an empty, wide lipped bucket ,from the bow chain. Place it up to 3' from the bow to avoid contact, and low enough that the bucket never rises above the sea during the pitch up. It should dampen the initial pitch.

Last edited by sony2000; 02-04-2015 at 02:42 PM.
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post #9 of 20 Old 02-04-2015
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Re: To stop pitching, no not horseshoes.

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Whatcha need to help stop the pitching is either a 'flopper stopper' or a 'paravane' ... and with no rocks required.
These are used to dampen the roll while anchored, but I guess you could rig a bowsprit (if you don't have one already) and hang it from the bow.

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post #10 of 20 Old 02-04-2015
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Re: To stop pitching, no not horseshoes.

Usually I would change anchorages,Just saying.
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