New Posts New Posts RSS Feed: So what's with mast rake?
  FAQ FAQ  Forum Search   Register Register  Login Login

So what's with mast rake?

 Post Reply Post Reply Page  <1234>
Author
Fearfull View Drop Down
Newbie
Newbie


Joined: 20 Mar 09
Location: United Kingdom
Online Status: Offline
Posts: 11
Post Options Post Options   Quote Fearfull Quote  Post ReplyReply Direct Link To This Post Posted: 26 Oct 10 at 3:29pm
Originally posted by blueboy

If I have a main that is not backwinding, then I ease it in a puff so the luff starts to backwind, the CoE moves aft. If I have (or expect) persistent backwinding, then I want to depower the rig and one of the things I'll do is rake.

Now where we came in was the argument that a reason to rake was the assertion (which I reject) that's it is because CoE moves forward as breeze increases.


Just one of the reasons though.
Back to Top
blueboy View Drop Down
Really should get out more
Really should get out more


Joined: 27 Aug 10
Online Status: Offline
Posts: 511
Post Options Post Options   Quote blueboy Quote  Post ReplyReply Direct Link To This Post Posted: 26 Oct 10 at 3:36pm
Oh yes there must be reasons! Wish I knew them is all. Rake works.
Back to Top
getafix View Drop Down
Really should get out more
Really should get out more
Avatar

Joined: 28 Mar 06
Location: United Kingdom
Online Status: Offline
Posts: 2123
Post Options Post Options   Quote getafix Quote  Post ReplyReply Direct Link To This Post 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
Back to Top
ellistine View Drop Down
Really should get out more
Really should get out more
Avatar

Joined: 06 Mar 08
Online Status: Offline
Posts: 762
Post Options Post Options   Quote ellistine Quote  Post ReplyReply Direct Link To This Post 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.
Back to Top
getafix View Drop Down
Really should get out more
Really should get out more
Avatar

Joined: 28 Mar 06
Location: United Kingdom
Online Status: Offline
Posts: 2123
Post Options Post Options   Quote getafix Quote  Post ReplyReply Direct Link To This Post Posted: 26 Oct 10 at 4:56pm
Originally posted by ellistine

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.


in that case, lets all hope we get a pro on here to give us their 'read' on it!
Back to Top
Fearfull View Drop Down
Newbie
Newbie


Joined: 20 Mar 09
Location: United Kingdom
Online Status: Offline
Posts: 11
Post Options Post Options   Quote Fearfull Quote  Post ReplyReply Direct Link To This Post Posted: 26 Oct 10 at 5:06pm
Originally posted by ellistine

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.


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.
Back to Top
ellistine View Drop Down
Really should get out more
Really should get out more
Avatar

Joined: 06 Mar 08
Online Status: Offline
Posts: 762
Post Options Post Options   Quote ellistine Quote  Post ReplyReply Direct Link To This Post Posted: 26 Oct 10 at 5:13pm
Originally posted by Fearfull

Originally posted by ellistine

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.


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.
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
Back to Top
ellistine View Drop Down
Really should get out more
Really should get out more
Avatar

Joined: 06 Mar 08
Online Status: Offline
Posts: 762
Post Options Post Options   Quote ellistine Quote  Post ReplyReply Direct Link To This Post 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
Back to Top
timeintheboat View Drop Down
Really should get out more
Really should get out more


Joined: 01 Feb 07
Location: United Kingdom
Online Status: Offline
Posts: 615
Post Options Post Options   Quote timeintheboat Quote  Post ReplyReply Direct Link To This Post 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?
Like some other things - sailing is more enjoyable when you do it with someone else
Back to Top
getafix View Drop Down
Really should get out more
Really should get out more
Avatar

Joined: 28 Mar 06
Location: United Kingdom
Online Status: Offline
Posts: 2123
Post Options Post Options   Quote getafix Quote  Post ReplyReply Direct Link To This Post Posted: 27 Oct 10 at 12:58pm
Originally posted by timeintheboat

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?


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 Confused 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.
Back to Top
 Post Reply Post Reply Page  <1234>

Forum Jump Forum Permissions View Drop Down

Bulletin Board Software by Web Wiz Forums® version 9.665y
Copyright ©2001-2010 Web Wiz
Change your personal settings, or read our privacy policy