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So what's with mast rake? |
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Fearfull
Newbie Joined: 20 Mar 09 Location: United Kingdom Online Status: Offline Posts: 11 |
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Topic: So what's with mast rake? Posted: 26 Oct 10 at 3:29pm |
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Just one of the reasons though. |
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blueboy
Really should get out more Joined: 27 Aug 10 Online Status: Offline Posts: 512 |
Post Options Quote Reply Posted: 26 Oct 10 at 3:36pm | |
Oh yes there must be reasons! Wish I knew them is all. Rake works.
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getafix
Really should get out more Joined: 28 Mar 06 Location: United Kingdom Online Status: Offline Posts: 2143 |
Post Options Quote Reply Posted: 26 Oct 10 at 4:27pm | |
I think the reason that rake depowers is that it moves the CofE down as well as changing the profile of the <wing(s)> sails which means;
less righting moment required = less turbulence around the foils and more speed generated by the power from the rig as power is more efficently transfered into motion = greater VMG Once, many years ago, we tried this on sailing school wayfarers, normally with their sloppy rigs and basic foils, large amounts of weather helm were present in any sort of blow, we raked the mast back and wound on the kicker and jury-rigged cunningham, result = neutral helm. the contrast was huge. Only thing I can compare it to is trying to bear away with the sails pinned in and boat heeled to leward versus bearing away with sails eased and the boat heeled to windward. To my <simple> mind the forces in play are similar, rig vs foils = turbulence & loss of speed, rig & foils working together = smoother tranference of power and greater speed hhhhhhhmmmm, sailmakers or similar pro's please feel free to tell me I'm wrong!! Edited by getafix - 26 Oct 10 at 4:35pm |
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ellistine
Really should get out more Joined: 06 Mar 08 Online Status: Offline Posts: 762 |
Post Options Quote Reply Posted: 26 Oct 10 at 4:47pm | |
That's the other odd thing. I would have thought a more raked mast would create more weather helm what with the CofE moving back and everything but the tiller was still really neutral. I've been quite conscious of weather helm after Paul Brotherton said the 4K rudder is too big and can really kill the speed if not balanced.
Perhaps lots of mast rake in lighter conditions would create weather helm? It's all very odd. I can see this turning into another one of those 'You Said' snippits in the Y&Y magazine.
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getafix
Really should get out more Joined: 28 Mar 06 Location: United Kingdom Online Status: Offline Posts: 2143 |
Post Options Quote Reply Posted: 26 Oct 10 at 4:56pm | |
in that case, lets all hope we get a pro on here to give us their 'read' on it! |
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Fearfull
Newbie Joined: 20 Mar 09 Location: United Kingdom Online Status: Offline Posts: 11 |
Post Options Quote Reply Posted: 26 Oct 10 at 5:06pm | |
I am still pretty convinced that when the main is fully depowered the CofE is further forward. Certainly on a high aspect ratio rig the sail above a line from the end of the boom to the top of the mast isn't doing a lot. |
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ellistine
Really should get out more Joined: 06 Mar 08 Online Status: Offline Posts: 762 |
Post Options Quote Reply Posted: 26 Oct 10 at 5:13pm | |
Which still fits. With a raked rig, if it's windy enough that the leach has given up and the CofE is forward then the weather helm will remain neutral. On the same raked rig, if the wind is light enough that the leach is still working then the CofE would be further back creating the potential for weather helm. All I know is I'd be useless on a Jury. I believe everybody's story!
Edited by ellistine - 26 Oct 10 at 5:15pm |
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ellistine
Really should get out more Joined: 06 Mar 08 Online Status: Offline Posts: 762 |
Post Options Quote Reply Posted: 26 Oct 10 at 5:19pm | |
Actually, thinking back to another 'story', we had a club member (who knows a thing or two) help us setup the boats when we first got them and he told us that if we're having to sail with the boom out beyond a certain point to start raking the rig so you can maintain the boom nearer to the center again. That would put the emphasis more on de-powering than balance.
Edited by ellistine - 26 Oct 10 at 5:20pm |
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timeintheboat
Really should get out more Joined: 01 Feb 07 Location: United Kingdom Online Status: Offline Posts: 615 |
Post Options Quote Reply Posted: 26 Oct 10 at 8:30pm | |
It is complicated and surely more so when the rake is achieved with either a stiff rig (a la Merlin photo) where the mast is raked but upright or a floppy rig. In the latter case more rake also means more fall-off laterally which I would have thought aids gust response.
Doesn't the modern Phantom have a floppy rake system and can offset the fall-off by tightening the lowers? |
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Like some other things - sailing is more enjoyable when you do it with someone else
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getafix
Really should get out more Joined: 28 Mar 06 Location: United Kingdom Online Status: Offline Posts: 2143 |
Post Options Quote Reply Posted: 27 Oct 10 at 12:58pm | |
The shroud & forestay tension and RAM/lowers won't be the main reason for the rake, the rake (to me) is the angle of the spar. After that, what you do with shroud, forestay and spreader angle will affect the deflection/bend of the spar and RAM/strut/lowers will impact on lower spar bend versus upper spar bend as well as have a bearing on sail shape (just as forestay tension) in combination with adjustable controls like halyards, cunningham and kicker. With spars having different bend characteristics, and some classes having 1, 2 or 3 sails hung off them, you'll see a divergence of rig tensions relative to each class, i.e Merlins may have more rig tension to control their relatively high aspect sails and resist the forces from the kite, while Blaze/Phantom will have 'sloppy' rigs as they don't need to worry about kites and have spar characteristics such that tensioning or loosening shrouds or forestay won't be neccessary to have the spar and sail work together the way the maker's intended. Although you need them 'on enough' to stop the mast jumping out of the foot! So what I'm thinking is that rake could be FIRST analysed seperately from those things as a factor and then after that as a secondary factor in as much as leech profiles will be effected by say kicker tension and rake, or jib luff profiles effected by both rake and jib lead/car position. |
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