Lowers? Diamonds?
Printed From: Yachts and Yachting Online
Category: Dinghy classes
Forum Name: Dinghy development
Forum Discription: The latest moves in the dinghy market
URL: http://www.yachtsandyachting.com/forum/forum_posts.asp?TID=3399
Printed Date: 19 Aug 25 at 6:42am
Software Version: Web Wiz Forums 9.665y - http://www.webwizforums.com
Topic: Lowers? Diamonds?
Posted By: Smight at BBSC
Subject: Lowers? Diamonds?
Date Posted: 16 Sep 07 at 6:25pm
|
What do they do? How do they do it? ------------- RS600 988 |
Replies:
Posted By: JimC
Date Posted: 16 Sep 07 at 6:47pm
|
Lowers stop the forward load from the boom/kicking strap bending the bottom of the mast.
Diamond stays are an alternate to spreaders for keepig the mid mast straight. Normally the spreaders are in line with the mast so they control side bend only, but sometimes (Tornado Cats I think are an example). The big advantage of diamonds is that they are independant of the load in the shrouds, so the mast doesn't go floppy when the crew gets on the wire. The big disadvantage is that there are two wires up the mast each side instead of one, so more drag and more weight aloft. |
Posted By: tgruitt
Date Posted: 16 Sep 07 at 6:48pm
|
Lowers control mast bend in the bottom section of the mast near the gooseneck, (this obviously affects the top of the mast a bit too) and stops sideways bend too if they are pulled on tight. Diamonds control mast bend in the middle to top section by adjusting their tension, this means you can sail with good prebend which is not completely controlled by the shroud tension. The diamonds also support the mast sideways too, especially with the kite up. I think I have got this right, any corrections?? Edit: I seem to have been beaten to it, not too far wrong from what the Oracle has written. ------------- Needs to sail more... |
Posted By: Wave Rider
Date Posted: 16 Sep 07 at 6:48pm
|
Beat me to it
------------- -[Franko]- Chew Valley Lake Sailing Club RS600 933 |
Posted By: Splosh
Date Posted: 16 Sep 07 at 6:48pm
|
Lowers and dimonds are put on trapeeze boats to stop the mast bending in the wrong places when someones on the wire. When one of our lowers snapped on our old 4k you could clearly see the differnce it was making. Splosh ------------- RS300 - 346 :D |
Posted By: Smight at BBSC
Date Posted: 16 Sep 07 at 7:08pm
|
Cheers guys but what does it ultimatly do to the sail(s)
------------- RS600 988 |
Posted By: tgruitt
Date Posted: 16 Sep 07 at 7:26pm
|
Gives more or less power by controlling stiffness and bend in different sections. To increase power pull on lowers to straighten mast, to give more bend and less power let off the lowers.
------------- Needs to sail more... |
Posted By: JimC
Date Posted: 16 Sep 07 at 7:29pm
|
If you have a boat set up for lowers and sail off without them on what you notice is that the bottom mast bends alarmingly to windward. You can't get any decent kicker tension so the leech flop offs, and the bottom of the sail is flattened off and depowered due to the overbend... So basically no power.
Shall I leave diamonds/spreaders to someone else? |
Posted By: tgruitt
Date Posted: 16 Sep 07 at 7:30pm
|
Jim go for it, I don't have enough experience of diamonds to comment...
------------- Needs to sail more... |
Posted By: Chew my RS
Date Posted: 17 Sep 07 at 6:49am
|
http://www.landenberger-sailing.com/spip.php?article22 - http://www.landenberger-sailing.com/spip.php?article22 diamond tuning ------------- http://www.sailns14.org - http://www.sailns14.org - The ultimate family raceboat now available in the UK |
Posted By: JimC
Date 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... |
Posted By: Smight at BBSC
Date 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 ------------- RS600 988 |
Posted By: JimC
Date Posted: 17 Sep 07 at 4:48pm
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. |
Posted By: Smight at BBSC
Date Posted: 17 Sep 07 at 6:16pm
|
Thanks very much ------------- RS600 988 |
Posted By: Ross
Date 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. http://imageshack.us">  ------------- Ross If you can't carry it, don't sail it! |
Posted By: JimC
Date Posted: 17 Sep 07 at 7:34pm
|
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. |
Posted By: Ross
Date Posted: 17 Sep 07 at 7:46pm
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 If you can't carry it, don't sail it! |
Posted By: Granite
Date Posted: 17 Sep 07 at 8:01pm
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 |
Posted By: JimC
Date Posted: 17 Sep 07 at 8:28pm
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...
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... |
Posted By: Ross
Date 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 If you can't carry it, don't sail it! |
Posted By: JimC
Date Posted: 17 Sep 07 at 9:53pm
You need to put that in perspective : you're not buying a 27 year old boat and expecting to win the Champs I hope, and in any case boat speed is irrelevant until you are staying upright round the track in 90% of your races. This was early 90s. I don't know what's happened with rigs since. Personally I think it was one lousy set of sails. I don't propose to name the sailmaker, but they were not 97 rules sized sails. I wouldn't worry about it - honestly! I'll send you a pic showing the offending rig... |
Posted By: I luv Wight
Date Posted: 17 Sep 07 at 10:13pm
|
Yeah but the rs600 rig was a compromise because of the perceived need to reef the sail - by shrinking the mast.
The diamonds mean that it is simple to reduce mast height by just removing the bottom, and shortening the shrouds. However, proper control over mast bend is lost. The 600 rig is based on moth rigs of the late 80's, but reverts to the bad points of the moth rigs of the mid 80's. Moth rig development in the 80's saw the boom being attached at the bottom of the mast, thus removing kicker induced lower mast bend. This was a problem in the magnum 6 era, with the nast bend being huge at the bottom. with a straight topmast, making it difficult to depower. magnum 8 and axeman onwards, the lower mast bend is independent of the kicker, which only affect the upper mast and flattening of the top of the sail. But the 600 has the old-fashioned style horrid lower mast bend, but straight mast and full sail at the top, making it much more difficult than it could be. re cherubs, the now normal double spreader rigs and lowers allow the use of light masts, that are stiff enough, flex nicely to allow auto depowering, support the 2 trapezes, big kites, and don't invert. The wires hold the mast in a bent shape, so the sail shape stays similar until it gets windy, then the top flattens, twists and depowers in a low drag fashion. Matching the luff curves and mast bend and prebend is tricky, but when it works it's fast! ------------- " rel="nofollow - http://www.bloodaxeboats.co.uk" rel="nofollow - http://www.bloodaxeboats.co.uk Andy P foiling Int Moth GBR3467 Freedom 21 Codling |
Posted By: Ross
Date Posted: 17 Sep 07 at 10:31pm
Not looking to win any national championships in this boat. It's a learning boat and after a few seasons I'll look into either upgrading it to an 05' rules rig (a massive project!), or sell her on and get a new boat. Currently using using Batt sails, like the ones in the picture you sent me. ------------- Ross If you can't carry it, don't sail it! |
Posted By: Smight at BBSC
Date Posted: 18 Sep 07 at 10:12am
|
Post the picture ross ------------- RS600 988 |
Posted By: Ross
Date Posted: 18 Sep 07 at 11:08pm
|
Original http://imageshack.us">  This picture is the best picture I have that shows the current rig and sail shape. I'll take some pictures of the whole rig at the weekend. http://imageshack.us">  ------------- Ross If you can't carry it, don't sail it! |
Posted By: Smight at BBSC
Date Posted: 19 Sep 07 at 1:22pm
|
She's looks in great condition from the pics but it might be a different story up close as i have found with some cherubs ------------- RS600 988 |
Posted By: mike ellis
Date Posted: 19 Sep 07 at 6:49pm
|
one word, DOWNHAUL! ------------- 600 732, will call it Sticks and Stones when i get round to it. Also International 14, 1318 |
Posted By: JimC
Date Posted: 19 Sep 07 at 8:23pm
Nope, its a fundamental feature of the 600 rig. Its not really an issue for the 600 owner, because the sail is cut for the way it bends, and they are all the same of course, but with lowers the boat would be a tad faster and the rig a tad more controllable. |
Posted By: Smight at BBSC
Date Posted: 19 Sep 07 at 9:06pm
|
would lowers stop the mast rotating? ------------- RS600 988 |