Jib counter-weight

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John Thomson asked me about the jib counter-weight.  I scratched my head and scraped the following paragraphs together.

As I understand it, the counter-weight is needed in light air to allow the jib to goose-wing on the run, and to set well on a reach.  If there is no chance of light air, you don't need the counter-weight.  If there is even the slightest chance of the wind dying for a while, you'll get killed without a counter-weight.

Most skippers set up their counter-weight to balance the jib boom.  That is, they hold the hull horizontally (lie it on the floor), and set the counter-weight so that the jib boom aligns with the centre line no matter which side the hull is resting on.  That is tricky, in that the boom almost always favours one side over another.  It has something to do with the topping lift attachment point on the jibstay, and any twist in the jibstay.

Some skippers set up the counter-weight so that it doesn't quite counter-balance the boom -- so the boom always tends to sag towards the centre line.  One of their theories is that they can then "throw" the boat into a gybe, and the weight and momentum of the boom will swing the jib over as required.

Me, I set up the counter-weight so that it slightly over-balances the boom.  I have to watch out that it doesn't extend beyond the bows here; that'll take the boat out of measurement.  With this setup, the jib is always pulling very lightly against the sheet, no matter what the wind.  My theory is that this gives me positive control over the jib at all times.

Another thought on the counterweight is that its size and projection from the boom will depend on your jib pivot offset, and the boom material.  I have found that running a 15% pivot offset, instead of the more usual 20% to 25% on an IOM, and using a non-arrow shaft (ie non-lightweight) boom, I could not get the boom (legally) balanced with the heaviest counterweight I had, 35 grams...  These were drifting conditions, so reducing the pivot offset to 20% wasn't a problem.  But it is time to reconsider whether I should not be using an arrow-shaft boom.

If your fellow-skippers are leaving their counter-weights off, you will want to be confident that their boats still measure.  If I took my 25 gm counter-weight off, I'd have an illegal boat immediately, about 20 gm under weight...


2023 Lester Gilbert