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So what's with mast rake?

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ellistine View Drop Down
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Post Options Post Options   Quote ellistine Quote  Post ReplyReply Direct Link To This Post Topic: So what's with mast rake?
    Posted: 24 Oct 10 at 9:19pm
It's one of those things that I've just accepted. The tuning guide says we should have a more upright mast in the light conditions and a more raked back mast when it's windy. I can see why an upright mast might help in the lighter conditions but what's the thinking behind raking the mast back when it's windy? What are we trying to achieve?

All I know is today our mast was raked back further than it's ever been (partly from stepping the mast in a hurry and not rechecking the pins) and with the wind in the upper teens we were stonking along. Properly planing up wind and even won the race both on the water and on corrected and that's never happened!
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G.R.F. View Drop Down
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Post Options Post Options   Quote G.R.F. Quote  Post ReplyReply Direct Link To This Post Posted: 24 Oct 10 at 9:42pm
Well I think its probably the same reason as in windsurfing, which is that in increasing wind, the centre of effort of the sail moves aft so raking the rig back re-addresses the balance over the Centre of Lateral resistance, it also depowers the rig a tad.

With boats that can retract their centreboard, that is also  a reason to rake the rig back.

Also in strong wind the sail isn't always sheeted in as far, so the entire rig isn't in play, raking it back keeps the c of e over c of lr balanced, probably more important on single handers.
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Post Options Post Options   Quote JimC Quote  Post ReplyReply Direct Link To This Post Posted: 24 Oct 10 at 11:17pm
To be quite honest the more I think about it the less I understand it... There are all sorts of things going on on a conventional dinghy from jib sheeting angle to the effect of the spreaders. I have a hunch that CLR is the least of it, but could easily be wrong.
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Post Options Post Options   Quote blueboy Quote  Post ReplyReply Direct Link To This Post Posted: 25 Oct 10 at 6:14am
Originally posted by JimC

To be quite honest the more I think about it the less I understand it...


Yep. I've never read a convincing explanation as to why raking a rig depowers it. All I know is that it works.
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Post Options Post Options   Quote blueboy Quote  Post ReplyReply Direct Link To This Post Posted: 25 Oct 10 at 6:19am
Originally posted by G.R.F.

Well I think its probably the same reason as in windsurfing, which is that in increasing wind, the centre of effort of the sail moves aft so raking the rig back re-addresses the balance over the Centre of Lateral resistance, it also depowers the rig a tad.

With boats that can retract their centreboard, that is also  a reason to rake the rig back.


The trouble with that theory is that keelboats also increase rake in stronger breeze. Also Merlins, for example, rake the rig long before they start raising the board.

Also in strong wind the sail isn't always sheeted in as far, so the entire rig isn't in play, raking it back keeps the c of e over c of lr balanced, probably more important on single handers.


That's 100% the wrong way around. If you ease the main-sheet, the luff depowers earlier than the leech. Therefore CoE moves back, so to restore balance you'd decrease rake, not increase it.
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Post Options Post Options   Quote Fearfull Quote  Post ReplyReply Direct Link To This Post Posted: 25 Oct 10 at 4:44pm
I have always thought there are two main reasons why I rake:
1. Center of effort of the sail moves forward as breeze increases, especially as the leech is doing less and less, so I rake to move this back to where it was.
2. As I rake the angle the shrouds are at makes the mast bend more. This is more noticable in rigs with raked spreaders.

3. Less tendancy to nose dive!

Third is a bonus reason.
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Post Options Post Options   Quote lynn1221 Quote  Post ReplyReply Direct Link To This Post Posted: 26 Oct 10 at 10:34am
All I know is today our mast was raked back further than it's ever been (partly from stepping the mast in a hurry and not rechecking the pins) and with the wind in the upper teens we were stonking along. Properly planing up wind and even won the race both on the water and on corrected and that's never happened!
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Post Options Post Options   Quote tgruitt Quote  Post ReplyReply Direct Link To This Post Posted: 26 Oct 10 at 11:08am


RAKE!
Needs to sail more...
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Post Options Post Options   Quote ifoxwell Quote  Post ReplyReply Direct Link To This Post Posted: 26 Oct 10 at 11:24am
Originally posted by JimC

To be quite honest the more I think about it the less I understand it... There are all sorts of things going on on a conventional dinghy from jib sheeting angle to the effect of the spreaders. I have a hunch that CLR is the least of it, but could easily be wrong.

I tend to agree I've always thought that the most significant factor is that raking the rig lets it all breath better, jib slot opens up, spreaders let the mast bend more etc etc.

The flaw in this theory however is that raking still works for a single sail, unstayed rig... so basically what i'm saying is that I don't have a clue either!

Ian
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Post Options Post Options   Quote blueboy Quote  Post ReplyReply Direct Link To This Post Posted: 26 Oct 10 at 12:52pm
Originally posted by Fearfull

I have always thought there are two main reasons why I rake:
1. Center of effort of the sail moves forward as breeze increases, especially as the leech is doing less and less, so I rake to move this back to where it was.


But the leech doesn't do (relatively) less. The luff does less as you either feather (jib) or ease the mainsheet while vang-sheeting.

2. As I rake the angle the shrouds are at makes the mast bend more. This is more noticable in rigs with raked spreaders.[/QUOTE]

But plenty of boats can adjust bend separately from rake e.g. with lowers, ram or backstay. Yet they all rake to depower as well as increasing mast bend.

I don't have an alternative explanation to put forward and I know rake works. I just don't buy these explanations. 
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