swinging spreaders

[mutt]

swinging spreaders:
Is there a full-proof way to set up swinging spreaders? I tried it on 3486 a couple of years ago but found that when the shrouds were on tight the spreader would swing forward an inch or so rather than lock back and push the mast forward.
As I understand it the spreader when locked on is supposed to push the mast forward and outwards (ie. away from the locked shroud) so it seems to me that the pressure held in the mast is released by unlocking the speader and dropping back to its neutral bend. (clear? - probably not). Thats what seems to be happening on 3486.
I've designed a nifty mechanical thing to swing the speader forward against the pull of a bit of elastic (which helps it swing back into lock) but I bet its not needed if the spreaders are set up properly. So any help you can give will save me ages in fiddling.
Cheers
Matt
 
 
 

[Jimbo41]

I wonder what would happen if you released the pressure on the windward shroud before jibing /tacking/sail moving over and then putting more tension on the swinging shroud? Would that release enough pressure on this shroud to enable it to fully lock again?
Jim. (I'd like to try it myself, since I don't have shroud tracks)

[mutt]

think I wouldn't like gybing with a sloppy rig. sounds dangerous to me. Also the crew has a lot to do already at make roundings.

[Phil Brown]

Not sure where the problem is from your description

P&B's tuning guide gives an explanation of the effects of spreader deflection and rig tension

http://www.pinbax.com/index.asp?selection=Science%20Behind%20Sails&subsect=3.%20Mast%20and%20Spreaders

Without any rig tension on, are your spreaders deflecting the shroud forward or aft? With the former, as you tighten the rig, the shroud tries to straighten and the mast is pulled back and vice versa either inducing or restricting mast bend.

One issue may be the mast step. If the mast rests on the front of the heel plug, as the rig is tensioned, the heel plug tries to sit square on the mast step and induces the mast to bend back. I know on my boat, the step is not square to the normal mast position and I can affect the mast bend by which part of heel plug is in contact with the step and it can look as if the spreaders are not doing their job. However, once the main is up, the forces on the sail push the mast forward and the spreaders then work as intended.

[James Taylor]

We have had new carbon rig 12 months ago and spent most of last year trying to get any prebend in the mast at a surtain point the spreaders stopped working without the sail up so after many chats with Kevin I  filed the front of the mast step of by a couple of mm and we are doing sooooooo much better can finally get prebend.
Hope this helps;D
 
James
N3402
And going big boat racing tonight ( I hope):-/

[mutt]

I've currently got the spreaders fixed and the mast does pre-bend as necessary. If I take out the restraining bolt the the spreader 'opens' and the mast looses prebend - though I'm not sure if this happens under sail. I think I'll give that a try next time I go out sailing.
ta
Matt

[Graham Bailey]

Mike Jackson eliminated the problem in the late 70's by not having any spreaders.  He took his minimalist approach a step further the following year when turned up with a boat that had no centreboard.  It just had a deep, canard-like stem and a large rudder blade.  The no-spreader rig was fast but the no-centreboard boat had a fundamental flaw - when he capsized there was nothing to stand on.