|SJ23 Tech Tip F06, (Updated 2002-12-10) Art Brown & Bob Schimmel|
Jib Deck Tracks.
|One of the reasons why I bought a San Juan 23
is because she can tack through 450 and track
straight in a lumpy seaway without loosing headway like my previous boat
with its ballasted
center board. Both are valuable performance assets when the homeward leg is
upwind! However, to get maximum upwind drive from the jib, the
sheeting angle must be correct, both fore/aft and athwart ship. A track
installed on the side deck ensures both. While the operating
manual suggests attaching the jib sheet block to the toe rail, I find
that too far outboard. If the track is long enough,
the forward end can be used for the storm jib and the aft end for a
110% or 135% jib. The 150% jib is sheeted to the cockpit track. However, I do release the jib sheet a tad to create for foil in the jib for lift. It helps the boat to go faster.
NOTE: "There are limits to increasing boat speed or arriving at your upwind destination sooner by pointing higher. A high performance keel boat can do this for one reason only, keel shape. The keel is a foil that generates lift as it "pulls" through the water. Total lift is a squared function of forward speed: double the speed, quadruple the lift. An SJ24 keel is much more efficient upwind with its high aspect ratio and deeper keel than an SJ23. The SJ23 has a keel stub so it can be trailer launched.
The trick to getting the most pointing performance out of the SJ23 is to drive the boat hard to maintain speed through the water, which allows the keel stub to generate more lift, which leads to less leeway. You can aim the boat as high as you want and sheet the beejeezus out of the jib, but on the SJ23 with the stumpy keel, compounded with the flat centerboard, the underwater foil just stalls, lift goes in the toilet, and the boat ends up going sideways.
I sheet my working jib to the rail, led from about the shrouds. For Genoa sheeting, I trim it so the leach is about a foot off the spreaders, or more. For comparison, I trim an SJ24 jib to ~(2-4)" off the spreader. The goal here is to drive the boat hard with an open slot to let the sail plan breathe, not stall out the keel, and minimize leeway. In addition, the SJ23 has relatively little rocker and sailing lower and fast means you don't pound into head seas, which stops an SJ23 dead. When in doubt, foot off. If you have speed through the water you have way more options to make something happen." Glen Moore.
You can determine the optimum sheet angle by drawing a straight line from the middle of the luff, through the clew to the deck. This position is usually good for mid range winds for the particular jib. Since you now have a "middle point" for the track you simply have to allow for about a foot either way to accommodate the fore and aft positions required for lighter or stronger winds. Do this for each of your jibs and you will quickly determine the position and overall length of the track. The SJ23 manual, Tech Tip H08, Sail Setting Guide, also has for suggestions on where to place the sheet for the optimum angle. Panache's track is equipped with Merriman doublewide block, so it is possible to change jib sheets on the go without releasing tension. Also, a single sheet slides easier through a double block when tacking. If you install a single block on the track then use a spring under it to keep it standing. This does several things: it keeps it from flopping against the gel coat, which is also quieter when sailing in the "doldrums", and keeps it standing which means the sheet will run through it easier.
DECK MOUNTING - The track on Panache (shown at right) is through bolted to the deck and the holes are sealed with epoxy to prevent wood rot. Sikaflex is used to keep the water out. A strip of tapered oak is installed on the ceiling to encase the nuts to prevent a nasty scrape on your skull. Wow, can that make you miserable! I can't remember how the track nuts on Banana Split (below left) are covered but I sure wish I had that full length to position the block exactly for each jib.
track on Banana Split (at left) was bent horizontally (along the difficult axis) to
follow the curve of the cabin. Forming the track horizontally is best
performed with a bender equipped with three wheels or rollers; two idlers
rollers on one side
opposing a third hydraulically loaded roller on the other side, between
the two rollers. As
the track is pushed and pulled between the three rollers, the force from
the middle roller bends the track in a smooth curve. There's art involved
in doing this job and it pays to have some experience. Benders of this type are available in
machine or aircraft maintenance shops. Sometimes you can find an
old guy who just happens to have one. "This happens more
often than you think. All you have to do is ask, with a coffee in
hand." The alternative technique is to create 'steps' in the
bend using a bench vice. However, a stepped bend looks crude
next to the smooth curve of the cabin as your eye can compare the parallel lines. In
the car may
jamb at a step. I've also seen long tracks consisting of two sections,
one added later.
SIDE MOUNTING - Besides the potential for water leaks and wood
rot in the deck core, the other problem with a deck mounted track is that the
sheet block is perfect for catching bare toes. (I hate that!). I
realize you shouldn't walk barefoot on deck, but there are times
when it's simply too hot to bother with shoes. In this case, sandals
are a good alternative. Make sure they are the type that are OK to get wet and stay on your
NOTE: Bending the metal track to conform to the shape of the fibreglass prevents stressing the glass. Bending can be accomplished over a sand bag, between three rollers or over an anvil.
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