an Uncle Al attempt at keeping it simple
|Aim: All the numbers are merely a guideline to serve the one and only aim of getting your mainsail to set approximately the way your sailmaker designed it to work most efficiently. It's like baking a cake, I guess. If the recipe says 10 minutes at 350F, that's a good start but you still have to taste the cake to confirm that those numbers are right for your oven. Too many sailors get all the numbers right and figure they've done all that needs doing. The most important thing, the "taste test", is that your main should set at a good angle to the wind and have a shape that is not (overly) distorted from what your sailmaker had in mind when he created his work of art.|
|Angle: There are two mast angles to consider
|Desired result:||How to get there:||Rationale:|
|Mast does not lean to one side||
that a vertical mast athwartships must work better than one leaning to
one side where the rig angle would have to be wrong on at least one
Apart from all else, the effect of the spreaders would be skewed if the mast were leaning to one side.
The mast should be permanently chocked such that it is centred athwartships in its deck hole with no appreciable play. This reduces sideways bend and keeps the jib sheet from getting wedged between mast and deck during tacks.
|mast raked slightly aft||
the recommended numbers gives better pointing but worse performance
while the reverse is true for forward rake. Like most extremes, this is
not desired since, on balance, the overall performance suffers, e.g.
lose more off the wind with extreme aft rake than you can hope to gain
by the better pointing upwind.
The 23' 5-7" rake distance gives the best potential to go fast on all points of sail.
bend > Sail
shape: Your average Wayfarer racing main is designed on the
that your mast will be relatively straight athwartships (i.e. no lean
windward or leeward) but will have about 2-3" of fore and aft mast bend
at spreader height. Your main will work to best effect when these
are more or less fulfilled, i.e. its luff entry will be neither too
nor too flat and as a result, the leech (of a properly sheeted main, of
course!) will be neither to tight nor too loose.
The factor that controls mast bend tendencies is the spreaders. Totally free-swinging spreaders would angle aft to permit the shrouds to assume a straight line between the hounds and the chainplate as the rig comes under tension. But the spreader is slightly longer than the spreader-less distance between shroud and mast. Thus, rig tension will push the spreader into the mast which in turn moves out of the way as increasing rig tension forces the shroud into a straight line. Since the mast is fixed at the hounds and at or near deck level, only the middle of the mast at spreader height moves forward and we get bend.
In light airs, such spreader-promoted bend is desirable, since other factors that cause/increase mast bend, i.e. mainsheet tension and vang, cannot come into play. However, as the wind increases, the mast quickly becomes too easy to bend. A mast with too much bend results in an underpowered main (overly flattened) that will not point well since excessive sail flattening also loosens the leech. Even when the boat is badly overpowered, you don't want to bend the mast so much that, despite applying lots of cunningham, you still get large creases from mid-mast towards the clew. This loosens your leech too much and you will not point as well as someone who bends the mast a bit less and rags the main a bit more to keep the boat flat.
To help maintain adequate leech tension, you must make the mast harder to bend. This is achieved by progressively reducing the aft angle of the spreaders (i.e. moving the tips forward) as the wind strength increases. Moving the spreader tips forward (equal amounts on both sides, of course!) means that the shrouds are deflected forward of the straight line from the hounds to the chain plate. As rig tension is increased, the shroud tries to assume a straight line but can only do this by pulling the spreader tip aft. Since the spreader tip is attached to the spreader which in turn is attached to the mast by the spreader bracket, the result is an aft pull on the mast at spreader height that is more or less proportional to how far forward the spreaders tips have moved. The mast will still bend in a breeze due to mainsheet tension (upwind) and vang tension but the main leech now has to work harder to achieve this bend since it's fighting the spreader effect. Ergo, better leech tension!!
|no windward/leeward bend||spreader length (mast wall to tip): 20 - 20½"||This length has been shown to do the job of keeping the mast from bending off to leeward just nicely.|
|suitable fore/aft bend||spreader
to tip distance) medium wind: 38" with both spreaders angled aft an
amount. Distance between tips decreases as spreaders are angled further
aft. Spreaders are never angled forward of the mast!
If you do not have adjustable spreaders, it's not a real performance drag except in a major blow, so don't let it ruin your sailing. But if you're serious about racing, adjustable spreaders should rank high on your list of priorities!
to be a
good distance to give suitable mast bend for most mains on most masts
a nice medium breeze where, close-hauled, both of you are sitting on
high side but using little or no vang since you are not yet overpowered.
Most racers also chock the front of their mast at deck level in medium breezes when they want to increase sail power by decreasing bend near deck level.
tip to tip distance can be < 38"
|In lighter airs, the 38" distance can be reduced to facilitate mast bend, although we rarely do this unless we anticipate a long beat in steadily light airs.|
tip to tip distance can be > 38"
|Once the boat becomes significantly overpowered, it tends to pay to increase distance between the tips to more than 38", i.e. spreader tips further forward, especially if you find that adding lots of vang is putting major creases in your main that can't be removed by using lots of main cunningham.|
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