Masts/Rigs all you need to know

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General Gps & Speed Waves Foiling Gear Reviews Lost & Found WA NSW QLD SA VIC TAS

choco

4186 posts

choco

SA, 4186 posts

2 May 2007 5:29pm

Came across some info on masts and sails that everyone will find interesting.
www.peterman.dk/start-windsurfing-gb01.htm

decrepit

12885 posts

decrepit

WA, 12885 posts

2 May 2007 4:46pm

Thanks choco, very interesting, but I notice an error in this bit.

quote:

As to the action, the more sluggishness of a stiffer mast shall allow the sail to keep its profile/draft a bit longer (and result in acceleration and/or overpowering the sail), while a softer mast with higher reflex speed shall absorb the action (gust) by more quickly de-powering (flatten) the sail. In other words Neil Pryde probably hasn't invented a word or a characteristic ("speed reflex") that can replace the precise definition of "stiffness" - and it's consequently highly questionable if Neil Pryde has a scientific background for even considering cheating with the figures for the stiffness of the masts.

I'm sure it's wrong that a soft mast depowers the sail more in a gust.
When the mast bends downwind, the sail gets fuller and actually powers up!!!!
So a stiff mast powers up less in a gust, a soft mast powers up more.

hoop

1979 posts

hoop

1979 posts

2 May 2007 7:01pm

I always thought a softer mast would allow the sail to twist off more. The more the mast bends the flatter the sail becomes.

decrepit

12885 posts

decrepit

WA, 12885 posts

2 May 2007 7:09pm

That seems to be a very common misconception. (And now maybe we know were it's come from)
But you can demonstrate the principal for yourself.
It's more obvious with a wave sail, (non cambered anyway)

Rig it with a loose leach, lay it on the ground, get a mate to hold the mast foot down, then bend the tip of the mast downwards. You'll see the leach tightening, and the draft increasing.

hoop

1979 posts

hoop

1979 posts

2 May 2007 10:03pm

I reckon you're on your own there tiger.

fordyD

NSW

17 posts

fordyD

NSW, 17 posts

3 May 2007 10:54am

I think your only looking at it in 2d on the beach. Loaded up its different. Because while the leach looks tight there's actually twist in the 3rd dimension that allows the exhuast out the top.
The mast bends to the luff curve of the sail and releases the tension that causes the luff panel to bend into shape and increase the batten tension. Sails are optimised for upwind but with the outhaul loose downwind the effect is less.

Leech

1933 posts

Leech

WA, 1933 posts

3 May 2007 8:54am

My 5.2 rigs comfortably on both a 400 and 430 mast (430 top / 400 bottom recommended). I was under the impression that a softer mast made the sail more forgiving so on days where I was relying on its top end I would rig it on the 400.

What I found was that the mast's extra flexibility made the sail go all out of shape in the gusts and I lost the stability. It felt like I was trying to tame a wild animal.

Not sure if this is the same as decrepit's tight leech theory but from now on I stick to the 430. It's my "happy leech" theory.

decrepit

12885 posts

decrepit

WA, 12885 posts

3 May 2007 6:09pm

fordy, no not talking 2d on the beach.
I'm talking dynamic on the water, the push down on the mast tip experiment simulates the effect a gust has on the rig.
When the mast bends downwind, the luffcurve bend diminishes!!! So leach gets tighter, making sail power up. The only thing that allows sail to depower, in a gust is good sail design of the head section, (loose leach , batten stiffness and placement).

The other experiment you can do is pump the sail on the beach, watch what happens as you pump harder and harder, yes the sail gets more draft the more you pump.
Before the loose leach design, sails were a real handfull in gusts because of the way they powered up.

Longreef

NSW

49 posts

Longreef

NSW, 49 posts

4 May 2007 11:07am

Ok so if you've done any sailing on big yachts and put extra bend the mast with the back stay you will see the twist. The sail will have a slightly fuller look right down at the boom but a flater profile mid to upper. You can then adjust draft and leach tension by a combo of outhaul, vang and traveller posi if your reaching (no luxury like this on a sail board, so we use a comboof outhaul and downhaul to acheive the same and the angle of attack and apparent wind speeds are much finer so all over the sail is flatter and with more twist. If the sail twists off in a gust beyond it's max then of course the draft will move back as the sail released the tension caused by the mast wanting to be straight -- and this can be counteracted somewhat with outhaul. The draft only moves forward in the intitial stage when powering up against the outhaul tension.

kris59

QLD

142 posts

kris59

QLD, 142 posts

4 May 2007 11:13am

well said, it's much clearer to see when u have sailed big boats like me. the traveler makes a big difference

bay to bay this weekend yay

kris

decrepit

12885 posts

decrepit

WA, 12885 posts

4 May 2007 11:06am

Ben thinking about this, and for all you proper yacht sailors remember we're talking unstayed mast here!!

I see now where Fordy's coming from, he thinks the force on the sail bends the mast tip towards the clew, thus twisting off. This force must be there, but I think it's outweighed by the mast bending downwind.
Hardie and I are off to see our local expert, we'll see what he thinks.

MikeyS

VIC

1509 posts

MikeyS

VIC, 1509 posts

4 May 2007 1:55pm

quote:
This force must be there, but I think it's outweighed by the mast bending downwind.

Decrepit. In your opinion, what is forcing the mast tip to bend downwind?

hoop

1979 posts

hoop

1979 posts

4 May 2007 1:41pm

Skiff sails are the same ,bendier mast = earlier depoower. Wave sails are the same, softer mast earlier depower. I dont know how you think a stiffer mast is going to depower you earlier. Bit like saying more rocker in your board will make you go faster.

decrepit

12885 posts

decrepit

WA, 12885 posts

4 May 2007 1:44pm

Sorry guys, seems I'm wrong, our resident guru agrees that a softer mast spills gusts better, and he knows a hell of a lot more than me.

Although I'm still not quite sure of how it happens.

quote:
Originally posted by MikeyS

Decrepit. In your opinion, what is forcing the mast tip to bend downwind?

Well surely it's the wind, it's pushing the sail downwind. The sailor is counterbalancing this force with their weight pulling upwind. The unstayed mast above the boom, has to bend downwind.
But the bend in the mast is lower down, closer to the boom, pushing on the tip is just trying to simulate the wind force on the sail. If you look at any photo of a loaded sail side on, you'll see the effect.

decrepit

12885 posts

decrepit

WA, 12885 posts

4 May 2007 1:51pm

quote:
Originally posted by hoop

Skiff sails are the same ,bendier mast = earlier depoower. Wave sails are the same, softer mast earlier depower. I dont know how you think a stiffer mast is going to depower you earlier. Bit like saying more rocker in your board will make you go faster.

Aren't skiff sails stayed???? That's a whole different ball game.

And I didn't say stiffer sails help depowering, I just thought as they don't bend as much the power up effect is reduced.
Anyway, as I said, seems I'm wrong.

Apparently as far as I understand it now the initial mast bend downwind near the boom powers the sail up, but in a gust, the tip bends more and depowers the sail.
But must admit it's now become a bit muddy in this old head!!!

I've now put an adjustable top strap on my 5.3 so I can try a 460 and 430, to see what happens in practice.

Mark _australia

23695 posts

Mark _australia

WA, 23695 posts

4 May 2007 2:15pm

Sorry Decrep, it was all a bit of a useless argument anyway....What was mpre important: Peterman was referring to reflex response.... and how the manufacturer (some of us don't like) tries to use that as an excuse for their stiffness figures printed on the mast being wrong.

Oops I'm NP bashing again

decrepit

12885 posts

decrepit

WA, 12885 posts

4 May 2007 2:22pm

Well I was blaming them for spreading misinformation about what happens in gusts, but seems we can't hold that against them afterall

Mark _australia

23695 posts

Mark _australia

WA, 23695 posts

4 May 2007 2:30pm

So u were spreading misinformation, that they were speading misinformation?

Hey.. just realised how much that sounds like a Brucie Bewsift/Snowyguy/Ajoe/CupofJoe kinda post...........

decrepit

12885 posts

decrepit

WA, 12885 posts

4 May 2007 3:02pm

Noooooooo------------------

MikeyS

VIC

1509 posts

MikeyS

VIC, 1509 posts

4 May 2007 5:43pm

quote:
Originally posted by decrepit

Sorry guys, seems I'm wrong, our resident guru agrees that a softer mast spills gusts better, and he knows a hell of a lot more than me.

Although I'm still not quite sure of how it happens.

quote:
Originally posted by MikeyS

Decrepit. In your opinion, what is forcing the mast tip to bend downwind?

Well surely it's the wind, it's pushing the sail downwind. The sailor is counterbalancing this force with their weight pulling upwind. The unstayed mast above the boom, has to bend downwind.
But the bend in the mast is lower down, closer to the boom, pushing on the tip is just trying to simulate the wind force on the sail. If you look at any photo of a loaded sail side on, you'll see the effect.

Precisely! My understanding is that a softer mast will let the tip twist off more easily so that the angle of attack (and perhaps the draft also??) is reduced at the tip. A bit like sheeting out the top of your sail. A stiffer mast won't "sheet out" quite as much.

Interesting discussion though. I never realized that big boats tuned the flex in their masts with shroud and stay tension. Probably why as a kid I never got the old Mirror dinghy to go as fast as possible.

hoop

1979 posts

hoop

1979 posts

4 May 2007 6:37pm

Carbon yacht and skiff rigs work pretty much the same way sailboard rigs work. they bend evenly above and below the stays. What happens to the draft and leech tension is all the same when it's loaded up.

Sharky

6 posts

Sharky

6 posts

4 May 2007 8:34pm

Here's a futher hypothetical. Take it a given that a carbon mast would be more responsive than an epoxy mast. With two masts of the same size and ICMS, the Carbon reacts and returns to memory or stat more quickly. Would the slower movement of an epoxy allow for more power during a gust? You have a longer moment and more time with the sail out of shape or powered up. In other words, if you were rigging for a day with strong gusts, a carbon would be preferable, but if the gusts were weak and you wanted to put more power in your floppy head or loose leach wouldn't an epoxy mast do that for you?

decrepit

12885 posts

decrepit

WA, 12885 posts

4 May 2007 8:44pm

Do you mean carbon and fiberglass???
Not sure what resins are used, but I suspect all good quality masts are made from epoxy

Sharky

6 posts

Sharky

6 posts

4 May 2007 8:52pm

Yes, fiberglass. No carbon masts, made for their lack of expense and not used much anymore except by beginners.

decrepit

12885 posts

decrepit

WA, 12885 posts

4 May 2007 8:59pm

Think the problem would be finding an old fiberglass mast with the same bend characteristics. Think they were softer in the middle.

Sharky

6 posts

Sharky

6 posts

4 May 2007 10:07pm

Actually, I bought a modern one a couple of years ago. It's a 430 and it was made in a factory in Finland then. I also have a new 55% Carbon North which was made in the same factory. I'm planning on experimenting with them in this regard, but am curious about the theoretics.

elmo

8895 posts

elmo

WA, 8895 posts

4 May 2007 10:38pm

apart from 100% carbon masts all masts contain glass and or kevlar as reinforcing fibres.

The resin is epoxy rather than polyester

decrepit

12885 posts

decrepit

WA, 12885 posts

4 May 2007 10:57pm

quote:
Originally posted by Sharky

I'm planning on experimenting with them in this regard, but am curious about the theoretics.

Interesting, let us know what you find out.

elmo

8895 posts

elmo

WA, 8895 posts

4 May 2007 11:44pm

Sharkyguy

I also have a 510 Finish mast which is high glass content what make is yours?

Mark _australia

23695 posts

Mark _australia

WA, 23695 posts

5 May 2007 4:14am

Sharky: only 3 posts. New here huh? You wouldn't be "Sharkguy" who abused me a coupla days ago on email?? Otherwise knwon as cosmicharlie/snowyguy/tycoonguy/swiftsailor/beswift etc etc list goes on

nebbian

6277 posts

nebbian

WA, 6277 posts

5 May 2007 6:18am

Mark_Aus: That style rang alarm bells for me too...

I'm sure that a good bayesian filter could pick him out, just like they can pick spam reasonably well these days

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