Forestay sag

[MagicalArmchair]

I'm going to do a bit of rig tweaking and was taking a wander around the boat in a force three to see how everything was setting. It appears the cap shrouds and lowers need quite a lot of tightening, and I did also note quite a lot of sag in the forestay. Now, as I understand it, this isn't a bad thing in light airs as it powers the sail up more, I do have a backstay tensioner that was about 30% cranked down at the time, and looking at this article http://www.sailingworld.com/how-to/sag-speed the optimum sag photo is about where it was at? Leave the forestay alone do we think? Mast rake etc all looks good.

Also, is it a good idea to tighten the bottle screw on the the forestay with the sail on the roller furling gear?

 

[smth448]

With a furling forestay you will never get rid of sag. The genoa will have been cut to cater for a certain amount of sag. If you lay the sail out on a flat surface the luff should follow a very slight S shape witht he very bottom being convex and the top 2/3 being concave. This puts more fullness into the bottom of the sail where the sail is wider and flattens the top.
If you put too much tension on the forestay you could end up damaging your furler anyway.
I assume your rig is masthead and deck stepped so the forestay wil be tensioned directly by the tension on the backstay. If you think the forestay is sagging too much tighten the backstay.
As to the shrouds I assume you have a single spreader rig so the caps an lowers need to be reasonably tight to maintain the mast in column. The leeward ones should be just slack when going to windward in lightish airs (f2-3). With the boat in the marina sight up the back of the mast to make sure it is straight. Use a halyard to either side to make sure it is vertical and then try tightening up the caps a turn at a time to both sides until you reach the sort of tension you would like. Check for straightness again and repeat with the lowers.
Also, unless you have a boat built to withstand high rig tension you could end up doing nothing but compressing the deck under the mast if you wind on too much.

There are plenty of rig tuning guides out there. I used to have a very good one written by an expert from one of the major mast manufacturer but I lent it to someone.

 

[prv]

With a furling forestay you will never get rid of sag.

Why's that? You can have the same tension in it as with hanked-on sails, so why should it sag more? The side load is spread over the whole length of the foil rather than a series of hanks, but I can't see that that should make a difference. Are you thinking of the weight of the foil or something?

If you put too much tension on the forestay you could end up damaging your furler anyway.

How? The only part of it that sees any of the forestay tension is the stationary core in the middle of the drum, and on mine at least that's a fairly massive piece of machined stainless steel.

Pete

 

[BabaYaga]

I would think the advice in that article is very specific to the J24 and similar boats. For a Ballad type of rig I would start looking elsewhere, perhaps here:
http://www.seldenmast.com/files/595-540-E.pdf

 

[trapezeartist]

I would think the advice in that article is very specific to the J24 and similar boats. For a Ballad type of rig I would start looking elsewhere, perhaps here:
http://www.seldenmast.com/files/595-540-E.pdf

+1 for the "folding rule" method in the Selden guide. I used a 2m length of wood about 10x10mm and it was surprisingly accurate. The only downside compared with a Loos gauge is that you have to slacken the shrouds completely and then wind all the tension back on again. The other surprise to me was that my 6 year-old Bav 30 still had exactly the right tension (minus half a turn) even though it hadn't been touched since commissioning. (Flimsy, floppy AWBs, eh? )