SELF TACKING AND JYBING JIB BOOM
by Gustaf Fresk
Our Class Rule allows a jib with three battens in the leech provided the foot of the sail is 95% of J or shorter. This makes it possible to use a self-tacking jib without reducing the sail area too much. We have developed a system that uses a "jib-boom" which also replaces the whisker pole and makes boat handling a lot easier both up and downwind.
We place a shaft with plastic bearings, in the bow, at the same angle or slightly less than that of the fore stay (65-70 degrees) in order to fit the bent end of the jib boom. The back end of the boom will then follow the same arc as the clew of the jib (a little bit lower when in the middle). The bend (110-115 degrees) in the front of the boom will work as a vang which must be stiff and strong. The boom should be as long as possible, but still clear the front of the mast.
A traveler with a bent track and a 120 cm radius is placed right in front of the splash guard with a swiveled micro block which is mounted on the traveler car. It is important to make this arrangement as low as possible.
Below, is a description and pictures of my boat from 2002 that has some modifications since the first 1996 version.
The sheet (A) runs from the boom through the micro block on the traveler, forward to an exit block (H) in the deck then back under the deck to the cleat on the sheet bench. The other end of the sheet runs through an exit block into the boom and ties to a thin (3mm) Spectra line inside the boom that exits in the very front of the boom (A2) and runs back on one side to a lead block (G1) and a 3:1 purchase fine tune at the port side cleat.
The outhaul (B) runs from the clew of the jib through a hole at the very end of the boom, forward inside and out through a hole at the underside of the boom with a micro block tied to the end of it. A 2:1 purchase is attached to it under the front of the boom and then runs back through a lead block (G2) to the starboard side cleat (B2).
A line (C) to trim the angle of the jib when sailing upwind runs from the car through a hole in the middle of the deck. The jib twist is trimmed with the floating (not tied around the boom) outhaul and by changing the mast rake. I have a forestay wire sewn into the luff of the jib and a 6:1 purchase on the halyard/forestay that makes it possible to change the mast rake without affecting the luff tension.
An 8 mm shock chord (D) runs from one side at the back of the boom forward around a "roller" (F) and back to the other side of the boom to hold the boom out on the downwind leg (like some single-handed dinghies have). "Wings" (E), on either side at the front bend, make it possible to gybe the boom by pulling on a "gybing line" (I).
For more information contact Gustaf Fresk at g@fresk.pp.se
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