J/30 Class Association Forums J/30 Forum The Boat, Sails and Equipment Backstay adjuster mod.

The ability to depower or flatten the main via backstay may have been a bit over-optimistic concept. but then the original traveller track was choked. This was designs from 30 years ago. 16 true may have been one of those edge points for moving into a #2 which was a required sail 30 years ago. Some of us like the #2 a lot over 15. I think it is perhaps a 145+?

Flattening the main was not a problem, mostly I would have liked more backstay to help reduce the headstay sag as we were definitely at the top end of the #1. The upside is that the J/30 is a Freightliner uphill in those conditions_.

A balanced rudder would help, no question about that. Unfortunately in our PHRF region rudder modifications get hit fairly aggressively.

reducing head stay sag ... something completely different ... Bill has a theory that backstay tension does not help reduce a lot of headstay sag. and in testing with roller furling sags In think he is right ...
has something to do with fractionals.

Correct Vic - jib halyard tension is the best, as backstay just rakes back the top of the mast and depowers the main. You can also shorten the headstay turnbuckle in heavy air to help balance the boat.

From my experience, and that includes some time I spent with QSDG working on ILC 40's with load cells up to an including some more recent time spent on TP 52's and most recently with Alan Andrews working on the Andrews 28 project at the Whidbey Island Race Week, it would not be accurate on a swept spreader fractional rig to suggest that headstay say on a properly tuned rig cannot be significantly adjusted by the backstay.

That is not to suggest that other considerations such as halyard tension, headstay length, rig tension/tunning and mainsheet tension are not also factors in this case but I would not overlook how a properly tuned rig with an effective backstay system can help in heavy airs.

That said I would also submit that jib halyard tension would have a more dramatic effect on sag on a furling equipped boat then one with a foil, for obvious reasons.

Headstay sag is a function of its length, diameter of the wire and tention. Shortening the headstay an inch or two won't much affect head stay tention but, as Bill points out, move the mast forward - which will move the CoE to help balance. On the J/30, backstay tention will only marginally help headstay sag as most of the force of tentioning goes toward bending the mast. Some have even argued that bending the mast causes the center portion of the mast to move forward, thus inducing more headstay sag. My conclusion is that I don't get any noticable improvement in headstay sag from increased backstay tention.

As for depowering the main, backstay tention will flatten the top 1/3 of the sail and open up the leach. Enough backstay tention will actually invert the top of the main. The right compbination of traveller adjustment and backstay tention will go a long way toward balancing the helm. A de-powered main and a balanced helm are a lot faster than an overpowered J/30 and make it a lot more comfortable to drive.
And as an FYI, while I can't speak to current Dacron sail design, the original Dacron mains came with a flattening reef about 6-8" up the leach. The old rule of thumb was for 16k of wind and above - strap in the flattening reef. The flattening reef pretty much took care of the bottom of the sail - the backstay took care of the top. A blade for a main, traveller down, full crew on the rail - the old mantra was "which number 1 are we putting up today?" (as in; the old blown out #1 or the new - let's save it for important races #1)

Ultimately headstay sag is controlled by tension on the headstay_.more tension helps to minimize and negate sag. The backstay can help to add to the tension on that backstay, however there are also rig tuning ideas that can help to further maximize the abilities of the backstay adjustment.

Specifically on a swept fractional rig if you set the uppers and lowers to equal tension then you will minimize the mast bend and create a stiffer mast overall_.a stiffer mast will help to ensure that more load is transferred to the headstay as opposed to mast bend_that is not to suggest that the mast will not still bend, it will, only to a lesser degree.

If any of you are in doubt next time you have your foil or furling extrusion removed attach a professional model Loos Gauge directly to your headstay and watch the different headstay tensions you can achieve with the backstay applied at 50%, 70% and then maximum. You can also leave the backstay adjuster applied at miximum and relax the lowers and you will see that indeed headstay tensions does in fact change much as your mast bend characteristics will also change.

I oncet had a conversation with a guy named Baird... a pretty good J/24 sailor in his day. He pretty much confirmed what LakeSailor said... the lowers effect how stiff the mast is. If you have a stiff mast, then backstay does indeed effect headstay sag pretty dramatically.

When it's blowing here on Loch Mich, we'll crank on uppers, and lowers are about the same tension.

Interesting ... just returned from making my uppers and lowers both 35 for regatta this weekend ... roller furling here is saggy and this was an experiment to see if I can get some sag out by evening tension on lowers ... with above info that mast is more likely to stiffen and help sag with backstay ... nice.