bowsprit

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joeh

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i am in the process of fabricating a bowsprit to fly my asymmetric. question is what is the minimum length extending out from bow to allow for chute to pass easily between forestay and luff when gybing? also is a 2 cm diameter tubing ( alu or SS) robust enough ( restriction due to bow fitting ) ? boat is an old 30 footer. thks for any comments .

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I'm no expert but have had a few Bowsprit boats. In practice the issue is about pulling a certain amount of crumpled nylon through a slot, and the things that jam are the knots where the sheets join the clew (a single sheet folded in the middle minimises this).

The important thing with bowsprit length is, I believe, the ability to push the Tack further forward and therefore provide a larger gap between the mast and the leading edge of the chute so that it can get maximum air. If you push it too far out in front then you will introduce Lee-helm when Reaching.

Given that the sail will be pretty large, I would say that a 2cm pole would have to protrude a very short distance from the chain-plate or anchor roler in order to retain the structural integrity needed (any further and it would bend in half at the first puff of wind.

If the pole is going to be very short then there is no point in having one, and you may as well fix a block to the chain-plate and attach the Tack to a guy which is run through the block, so that you can ease it higher or lower as the wind dictates. This way you can also ease it before gybing so that there is room to pass before the forestay.

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From your description it would appear that the bowsprit will be taking all the sideways and upwards loading. I would be surprised if even thickwall tubed SS would take that loading at the size of tube you are discussing

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thks simon
i have already been using the bow tack arrangement for awhile . i am trying this bowsprit thing due to my singlehanded racing requirements. the one thing of concern is the pivoting/ leveraged upward load on the bow roller fitting. if the sprit folds thats ok but i would not want the stem fitting yanked out and lose my forestay and consequently the mast. however the sprit i plan extends 4 feet aft of bow fitting on deck to counter load. anyhow the best way is to test it out in light air 1st.

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Definitely give it a go. The benefit from pushing the Tack out is quite marked. I have tried sliding the pole back in on the J120 and it knocks a knot or so off when reaching at 9.5 knots. Good luck.

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With my MPS I find it much better to gybe the kite outside, rather than inside - the bowsprit will improve the slot, but still won't help inside gybing that much.

If you are fabricating an item that will be stayed (both down with a bobstay, and with port and starboard lines) then I'd imagine you'd want something in the order of 50mm x 2mm wall alloy tube, just to take the compressive loads. If it's unstayed, then 60 to 80mm carbon tube would be the go, assuming you're aiming on a 500mm or so projection, and extending back on the deck with max load at the stemhead. Have a look at a local sports boat flying asymetrics, and see what they use - even 16 foot skiffs here have 50mm plus carbon tube prodders for their asyms.

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