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  <1 234
Author
redback View Drop Down
Really should get out more
Really should get out more
Avatar

Joined: 16 Mar 04
Location: Tunbridge Wells
Online Status: Offline
Posts: 1502
Post Options Post Options   Quote redback Quote  Post ReplyReply Direct Link To This Post Posted: 27 Dec 10 at 5:16pm
I sail a 4000 and the rake makes a huge difference to the power of the rig.  I've experimented with easing lowers, sliding the fair leads back and altering the strop length.  They can all decrease power but nothing works quite as well as mast rake.  

One hole downwards on the shrouds makes the boat so much easier to handle in a really strong winds but you very thoroughly lose a lot of power and its a real disaster if the wind is marginal.  Unless its survival I generally go for half a hole and maybe move the fairleads back a click.

Now I'm a great theorist but I can't explain this.  Sure it opens the jib leach but so do the fair leads.  It eases the lowers but I do this anyway in strong winds.  As for rig height it must reduce it by about 1cm which I'd say is insignificant.

I can't explain it but it works a treat and I recall it worked nicely on the 800 that I crewed.  If anybody can find a good reason why this is so I'd love to hear it but I've heard nothing convincing yet, however it does work beautifully.
Back to Top
Garry View Drop Down
Really should get out more
Really should get out more
Avatar

Joined: 18 Apr 04
Location: United Kingdom
Online Status: Offline
Posts: 536
Post Options Post Options   Quote Garry Quote  Post ReplyReply Direct Link To This Post Posted: 27 Dec 10 at 5:23pm
IMHO, If you change nothing else raking the mast back 1 full hole increases the bend considerably = flatter sail.
Garry

Lark 2252, Contender 298

www.cuckoos.eclipse.co.uk
Back to Top
Skiffybob View Drop Down
Really should get out more
Really should get out more
Avatar

Joined: 04 Dec 06
Location: United Kingdom
Online Status: Offline
Posts: 842
Post Options Post Options   Quote Skiffybob Quote  Post ReplyReply Direct Link To This Post Posted: 27 Dec 10 at 7:03pm

As a starting-point, you need to think of your jib and main as a single foil with a slot in it. The jib essentially provides a lot of the powr for the main, and they need to work in harmony to get the best from them.

By raking the mast, you increase the slot and push the slot effect further down the main, hence reducing the venturi effect on the back of the main an making the power eer so slightly lower down. This has an enormous effect on the power that the main creates. It allow you to keep your critical angle of attack on the jib, and also lets you keep some leech tension on the main (for stability), whereas moving the job cars back opens the slot bu also ruins your pointing. Easing the barber-haulers (if you have them) has a similar effect, although not as great it can be done on the water.
 
It also have a really bigeffect on the weight distribution, and takes a lot of weight and inertia away from the bow, meaning that you can stand/sit further forwards and drive the boat hard without it mining.
 
Sail a short, over-powered boat for a while, and you'll learn all about it...
12ft Skiff - Gordon Keeble and the Furry Fly-by
AC - GBR271 - Whoosh
B49 - Island Alchemy
Back to Top
redback View Drop Down
Really should get out more
Really should get out more
Avatar

Joined: 16 Mar 04
Location: Tunbridge Wells
Online Status: Offline
Posts: 1502
Post Options Post Options   Quote redback Quote  Post ReplyReply Direct Link To This Post Posted: 24 Jan 11 at 6:34pm
Skiffybob - you may be right but I understand the rake angle has a large effect on Contenders and they don't have a foresail.  I'm afraid I'm not convinced about the weight distribution argument since we are only talking about moving the mast head a few inches for and aft.

However as I have said before it works.
Back to Top
NickA View Drop Down
Really should get out more
Really should get out more
Avatar

Joined: 30 Mar 05
Location: United Kingdom
Online Status: Offline
Posts: 712
Post Options Post Options   Quote NickA Quote  Post ReplyReply Direct Link To This Post Posted: 25 Jan 11 at 8:33pm
Don't contenders just go faster with more rake in pretty much all conditions?  I think they rake as much as they can whilst still being able to get under the boom!  Contenderers please confirm.  Plus in stronger winds you might raise the centre board .. which pushes it's centre of effort back - so the mast rakes back to place the sail COE back over the board's.

On the two boats I sail:

The Javelin has a tall very bendy mast, a huge jib and a swivelling centre board.  Rake makes a massive difference.  In about F4 a 24'10" rake can become un-manageable, whilst a 24'8" rake is fast as we can keep the boat flat with the boom centred (and hence leech well in).  I think the depowering comes from a wider slot and a shorter mast - but also we might pop the centre board up a tad and unless we rake the mast back to match the boat ceases to point properly.

The V3000 has a short stiff mast, a small / medium jib with no / little overlap and a near vertical dagger board that generally stays full down regardless.  Rake makes a bit of difference to power and quite a lot to pointing ability, but it isn't life and death.  I usually single hand it with lots of rake ... but mostly 'cause it looks kinda cool Cool
3604 ...lapse of reason
Javelin 558
Back to Top
Garry View Drop Down
Really should get out more
Really should get out more
Avatar

Joined: 18 Apr 04
Location: United Kingdom
Online Status: Offline
Posts: 536
Post Options Post Options   Quote Garry Quote  Post ReplyReply Direct Link To This Post Posted: 25 Jan 11 at 8:48pm
Contenders = as much rake as you can handle and still get under the boom.
Garry

Lark 2252, Contender 298

www.cuckoos.eclipse.co.uk
Back to Top
tim grasse View Drop Down
Newbie
Newbie


Joined: 01 Feb 10
Location: United Kingdom
Online Status: Offline
Posts: 34
Post Options Post Options   Quote tim grasse Quote  Post ReplyReply Direct Link To This Post Posted: 25 Jan 11 at 11:25pm

From what I gather in higher winds the hull starts to plane and the lateral resistance of the bow is decreased so the centre of lateral resistance is moved aft. To compensate for this you rake back the rig to keep the centre of effort above the centre of resistance so the bat is balanced and sails better.

Back to Top
17mika View Drop Down
Groupie
Groupie


Joined: 03 Nov 06
Location: Italy
Online Status: Offline
Posts: 52
Post Options Post Options   Quote 17mika Quote  Post ReplyReply Direct Link To This Post Posted: 29 Jun 11 at 4:43pm
Originally posted by tim grasse

From what I gather in higher winds the hull starts to plane and the lateral resistance of the bow is decreased so the centre of lateral resistance is moved aft. To compensate for this you rake back the rig to keep the centre of effort above the centre of resistance so the bat is balanced and sails better.

 
Sorry to highline an old discussion. I pretty much agree with this point in the 4k case upwind, toghether with the opening of the slot.
 
Thing I have never properly understood in the 4k is why a raked mast in low/medium breeze is ridicously bad upwind in terms of height (and not only speed). All times I went out with a raked mast and wind didn't go up as expected, even when I adjusted the lowers for the wind, upwind i felt everyone else like would go 5 degrees higher than me.
 
Looking also at this discussion, it may be a combination of too much wheather helm to counterbalance with the tiller + jib leech opened up too much. Or something else?
 


Edited by 17mika - 29 Jun 11 at 4:53pm
Back to Top
x1testpilot View Drop Down
Posting king
Posting king
Avatar

Joined: 11 Feb 11
Location: Ealing
Online Status: Offline
Posts: 175
Post Options Post Options   Quote x1testpilot Quote  Post ReplyReply Direct Link To This Post Posted: 30 Jun 11 at 3:24pm
In I14's a few years ago the rake became the main control (continuous systems led to the gunwale ere common) to adjust for wind strength. Since then things have changed a bit, but the raking theory really worked.

Rake was adjusted so much that a "flattener" had to be applied to the main leech to lift the boom so you could get under it.

If all else is kept the same raking will open up the jib leech (twist off at the top as the sheeting angle is effectively changed. The shrouds angles + the lowers (or mast ram) would do less to keep the mast straight, so it would bend and flatten the (luff of the) main. These also open the slot.

A little extra Cunningham and or uppers would twist off the top a bit more.

Centre of effort as mentioned above.

I have heard argument that some lift is generated, but I'm not convinced.


In the X1 we rely on the automatic flexing of the topmast / square-top and add Cunningham to increase this in wind. It is even possible to play the Cunningham instead of the mainsheet. The effect is very marked - pulling rapidly ion the Cunningham can alarm the helm! We do ajust rake on the day but so far not by much at all.
I like to take pictures of sailing, but I'd rather be sailing!
LCSC.org.uk
Xdinghies.com/ X0 & X1
Back to Top
 Post Reply Post Reply Page  <1 234

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