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Lowers? Diamonds?
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JimC View Drop Down
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    Posted: 17 Sep 07 at 3:07pm
Diamonds are confusing because they work in three different ways. On an overotating mast, like Cats, the cat ref is good. On a non rotating mast like a Laser 2, then they work quitte differently. On a "rotate with the boom" mast like an RS600 they are different again. But in all cases the thing to do is to think about the effects of the bend the mast ends up with, not the wires themselves...
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Smight at BBSC View Drop Down
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Posts: 1129 		Post Options Post Options   Quote Smight at BBSC Quote  Post ReplyReply Direct Link To This Post Posted: 17 Sep 07 at 4:32pm
Well i was hopeing you'd explain it interms of the 600, it's slightly more relavant to me
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JimC View Drop Down
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Posts: 6662 		Post Options Post Options   Quote JimC Quote  Post ReplyReply Direct Link To This Post Posted: 17 Sep 07 at 4:48pm
Originally posted by Smight at BBSC

Well i was hopeing you'd explain it interms of the 600, it's slightly more relavant to me

I was hoping you wouldn't say that because that's the type I haven't actually owned... But its basically all about controlling mid mast sideways bend. The side loads from the sail will tend to bend the top of the mast to leeward so the mast between hounds and gooseneck will tend to bend to windward. This will open the leech and take fullness out of the middle of the sail. The diamonds restrict this bend, and keep the leech more solid. It also reduces top mast bend a little by straightening up the mast below the hounds.

The reason why (IMHO) diamonds are a much better choice than spreaders on the RS600 is that the effect of the diamonds is constant whether or not the crew is on the wire, whereas with spreaders it varies appreciably unless you have really extreme rig tension.

Edited by JimC
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Smight at BBSC View Drop Down
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Posts: 1129 		Post Options Post Options   Quote Smight at BBSC Quote  Post ReplyReply Direct Link To This Post Posted: 17 Sep 07 at 6:16pm

Thanks very much

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Ross View Drop Down
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Posts: 1163 		Post Options Post Options   Quote Ross Quote  Post ReplyReply Direct Link To This Post Posted: 17 Sep 07 at 6:57pm
Good topic. What does the strut that goes from the fordeck to the mast do? Fireballs use them as well as my (soon to be mine, 4 days!) Cherub.
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JimC View Drop Down
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That does much the same thing as the lowers. Most lowers are angled back, but on Flat Stanley they are at right angles to the centreline, which is much better as it means that you can change the prebend without compromising on the sideways movement restriction.

On Stanley the lowers want to be about twice as tight as you can manage! You really need to pull that lashing on really hard, and then some more, but of course end up with the tension the same both sides so the mast is straight sideways.

The prod then controls the amount of prebend on the mast. The way she used to be set up then the settings went sonething like this:-
Drifter - moderate prebend to take some of the curve out of the sails
F1.5 to overpowered - prod heavily loaded, set up to keep the mast dead straight between the foot and the spreaders at least.
Well overpowered - let a bit of prebend back in to take some power out of the rig.
The rig tension also needs to be dramatic. Guy Lewington used to pull it on by having Alex swing on the end of the Spinnaker pole (9 foot back then) which was hooked up to the kite halyard and if he really heaved it was just about possible to shackle on the jib. This probably equated to at least 400lbs down the shrouds. However if the rig now has caps and checks all this has changed... I haven't seen the boat since 1992 I don't think.

You need to match the prebend to the mast... Funnily enough Flat Stanley was never the same after Guy bought some new sails about 1990 to replace the mouse eaten Caws sails he'd had since 1984... Up to then she would match Bistros, but after that nowhere!

Complete culture shock to see the boat looking smart... That boat really needs to be looked after: she has the best open handicap racing record of any boat in any class through the 1980s.

Edited by JimC
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Ross View Drop Down
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Posts: 1163 		Post Options Post Options   Quote Ross Quote  Post ReplyReply Direct Link To This Post Posted: 17 Sep 07 at 7:46pm
Originally posted by JimC

That does much the same thing as the lowers. Most lowers are angled back, but on Flat Stanley they are at right angles to the centreline, which is much better as it means that you can change the prebend without compromising on the sideways movement restriction.

On Stanley the lowers want to be about twice as tight as you can manage! You really need to pull that lashing on really hard, and then some more, but of course end up with the tension the same both sides so the mast is straight sideways.

The prod then controls the amount of prebend on the mast. The way she used to be set up then the settings went sonething like this:-
Drifter - moderate prebend to take some of the curve out of the sails
F1.5 to overpowered - prod heavily loaded, set up to keep the mast dead straight between the foot and the spreaders at least.
Well overpowered - let a bit of prebend back in to take some power out of the rig.
The rig tension also needs to be dramatic. Guy Lewington used to pull it on by having Alex swing on the end of the Spinnaker pole (9 foot back then) which was hooked up to the kite halyard and if he really heaved it was just about possible to shackle on the jib. This probably equated to at least 400lbs down the shrouds. However if the rig now has caps and checks all this has changed... I haven't seen the boat since 1992 I don't think.

You need to match the prebend to the mast... Funnily enough Flat Stanley was never the same after Guy bought some new sails about 1990 to replace the mouse eaten Caws sails he'd had since 1984... Up to then she would match Bistros, but after that nowhere!

Complete culture shock to see the boat looking smart... That boat really needs to be looked after: she has the best open handicap racing record of any boat in any class through the 1980s.


Thanks! How do you know so much about Flat Stanley?

What do you mean by:
 "Funnily enough Flat Stanley was never the same after Guy bought some new sails about 1990 to replace the mouse eaten Caws sails he'd had since 1984... Up to then she would match Bistros, but after that nowhere!"
Ross
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Posts: 476 		Post Options Post Options   Quote Granite Quote  Post ReplyReply Direct Link To This Post Posted: 17 Sep 07 at 8:01pm

Originally posted by Ross

Good topic. What does the strut that goes from the fordeck to the mast do? Fireballs use them as well as my (soon to be mine, 4 days!) Cherub.





The other thing the strut does is stop the mast from inverting down wind with the spiniker up.

A high hoist point with no cap shrouds and particularly with a traditional spiniker pole pushing back was liable to make the mast fold back at the bottom.
If it doesn't break it's too heavy; if it does it wasn't built right
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JimC View Drop Down
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Posts: 6662 		Post Options Post Options   Quote JimC Quote  Post ReplyReply Direct Link To This Post Posted: 17 Sep 07 at 8:28pm
Originally posted by Ross

Thanks! How do you know so much about Flat Stanley?

Seen her transom disappear into the distance in front of me on rather a lot of occasions, raced level with her quite a bit more when I got my Bistro, knew Guy as well as anyone else in the fleet and better than most...

Originally posted by Ross

What do you mean by: "Funnily enough Flat Stanley was never the same after Guy bought some
new sails..."

Just that. The new rags resulted in a catastrophic reduction in boat speed. Never seen anything quite like it.

Oh, and Phil's point about the prod stopping the mast inverting is very well made. It was crucial with pole kites because you had a massive load pushing aft with the pole. Those unwise enough to put the pole fittings higher than the gooseneck instead of immediately opposite and no prod tended to have the mast go over the front before very long...

Edited by JimC
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Ross View Drop Down
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Posts: 1163 		Post Options Post Options   Quote Ross Quote  Post ReplyReply Direct Link To This Post Posted: 17 Sep 07 at 8:44pm
Has the boat speed been sorted out? New sails and new sail shapes mean other things have to change, so some experimenting will be needed I think.
Ross
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