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Mast rake: explain please! |
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NHRC 
Posting king 
Joined: 13 Dec 13 Location: Lymington Online Status: Offline Posts: 102 |
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 Topic: Mast rake: explain please!Posted: 03 Dec 14 at 1:10pm |
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Moving one pin stop would make minimal rake difference.
Consider the shrouds shorten by 65mm from upright to full rake. 1 pin stop is 10mm at most |
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Oatsandbeans
Far too distracted from work 
Joined: 19 Sep 05 Location: United Kingdom Online Status: Offline Posts: 382 |
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Posted: 03 Dec 14 at 2:26pm |
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Moving one pin on the shrouds in itself may make only a small difference in rake but it does effect the rig tension significantly, so in order to get the rig tension back to your baseline setting you need to adjust the jib luff more than you have on the shrouds -this will have a significant effect on the rake. ( in some ways it is better to think of the shrouds as defining the rig tension, and the jib luff defining the rake, although we all know that you adjust the rig tension with the jib luff not the shrouds- if you get where I'm coming from!)
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RS400atC
Really should get out more 
Joined: 04 Dec 08 Online Status: Offline Posts: 3011 |
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Posted: 03 Dec 14 at 7:11pm |
Most people think in terms of setting the shroud postion, then pulling on jb halyard to whatever rig tension you want. (or you are prepared to inflict on your boat?) On a 400, you'd probably set the deck level ram after the shrouds, or you might leave it, because you happen to want more bend when you want more rake anyway. And it helps the mast not to invert with the kite up. The amount of rake change in the 400 is small, as you're stuck with the same shroud setting upwind and down. Merlins on the face of it move the rake a serious amount, but effectively take some of back by trimming the bow down more uphill. Anyway, my point was, even if the sail shape stays constant, and whether or not you move the clr around with trim or moving the plate, rake is good upwind, and more rake is better in more wind. I don't think we'll get a coherent 'why' on this, we didn't last time or the time before. But think about planes, those intended for faster air speed tend to have the wings swept back. |
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NHRC
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Joined: 13 Dec 13 Location: Lymington Online Status: Offline Posts: 102 |
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Posted: 03 Dec 14 at 7:27pm |
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With most dinghies and skiffs Rake is roughly a 3.5:1 ratio between shroud and forestay.
You adjust shroud length by 10mm you need to adjust your forestay length by 35mm to get rake without increasing or de-creasing your rig tension as a factor. This depends on the angle of your forestay, foredeck length and height of your shrouds but I would be surprised if this factors incrementally different between classes that you would see that ratio change by more than a few 0.01's. Edited by NHRC - 03 Dec 14 at 7:36pm |
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Vronny
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Joined: 31 Mar 08 Location: United Kingdom Online Status: Offline Posts: 121 |
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Posted: 03 Dec 14 at 7:39pm |
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Just curious . . . and definitely not trying to be critical or nasty in any way! . . . do the D-Zero and RS Aero have means to adjust mast rake?
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Null
Really should get out more
Joined: 11 May 14 Online Status: Offline Posts: 745 |
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Posted: 03 Dec 14 at 7:47pm |
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D zero does vroony, we can adjust mast heal position and rake via chocking of the mast gate. So we can achieve a form of mast rake in two different ways. Still early days to work out what's fast, I am experimenting different setups. I have found flipping the mast heal in 15-20 knotts is blisteringly quick upwind. But not as fast (obviously) in about 10 knotts.
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Vronny
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Joined: 31 Mar 08 Location: United Kingdom Online Status: Offline Posts: 121 |
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Posted: 03 Dec 14 at 7:51pm |
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Is that the same sort of mast heel flipping thing that the D-Ones have?
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Daniel Holman
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Joined: 17 Nov 08 Online Status: Offline Posts: 997 |
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Posted: 03 Dec 14 at 7:55pm |
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Yep its the same part as the D One!
Somebody asked why people don't rake all the time if its so great. In aerodynamics, a swept aerofoil cannot derive as large a lift coefficient as an upright one, so when not overpowered you get more "bite" from an upright rig. As for raking, big long old subject that could fill best part of a book. It is fast in the wind in most stuff. 49ers don't do it as fixed length forestay I believe. Not many i14s do it as if you pull a string you lose 10 boat lengths minimum, and you can have a set that works over a very broad range. |
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craiggo
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Joined: 01 Apr 04 Location: United Kingdom Online Status: Offline Posts: 1810 |
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Posted: 03 Dec 14 at 8:12pm |
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Just logged in, read the question regarding why doesn't rake work all the time, and by the time I get to the last post low and behold the forums dinghy design expert has beaten me to it. Thank Dan ;)
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blaze720
Really should get out more
Joined: 28 Sep 05 Location: United Kingdom Online Status: Offline Posts: 1635 |
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Posted: 03 Dec 14 at 8:46pm |
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The Blaze has always run with a fair amount of rake..... add too much and you don't go faster but you will eventually face handling problems ! Adjustable mast rake has a small following still having been more popular 5 years ago ... but the stayed rig is very adjustable / adaptable anyway using just cunningham and kicker. The relationship and interplay with centreboard is a related factor.. and like many similar classes we do adjust the centre lateral resistance particularly in higher winds. Offwind it is standard practice to set with half or even less plate .. upwind full down or just a few degrees of rake.
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