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Phils Rig School continued...
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winging it View Drop Down
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Posts: 3958 		Post Options Post Options   Quote winging it Quote  Post ReplyReply Direct Link To This Post Topic: Phils Rig School continued...
    Posted: 26 Nov 09 at 5:59pm
Originally posted by grimupnorth

Must control . . . desire to post point by point
rebuttals all night . . . medication wearing off . . .
resistance breaking down . . . must persevere . . .

Sorry where was I

Oh yes. The point about deck vs gate is not the strength
of the structure under the mast, but whether the mast is
fixed only at its heel (=deck stepped)- free to bend all
the way up its length unless controlled by lowers /
strut; or fixed at its heel and at another point higher
up (=gate stepped, if I've got the right terminology) -
not free to bend in the lower section, although
adjustable by mast ram / chocks / whatever.

Old skool desk stepped mast - Enterprise
Old skool gate stepped mast - GP14
New skool desk stepped mast - almost any cat or 'stand
on' skiffy-shaped dinghy
New skool gate stepped - take your pick from the others


Yes: the contender is deck stepped but has lowers enabling you to control the bend.  My 'classic (ancient)' phantom is also deck stepped, but built before lowers came along and the bend is uncontrollable.  Combined with a very bendy needlespar rig, very short spreaders and a flat cut sail and the thing is a nightmare.
the same, but different...

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blaze720 View Drop Down
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Posts: 1635 		Post Options Post Options   Quote blaze720 Quote  Post ReplyReply Direct Link To This Post Posted: 26 Nov 09 at 6:32pm
Rule 1 - Do not feed !
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chrisg View Drop Down
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Posts: 893 		Post Options Post Options   Quote chrisg Quote  Post ReplyReply Direct Link To This Post Posted: 26 Nov 09 at 6:34pm
Ok how about a stumped rig....

The 12's (and im sure there are other classes that do too) have a solid stump built in to the boat. The mast sits on top of this stump. However, the boom also attaches to the solid stump of the hull, not the mast. This removals all of the kicker loads from the mast. This seems like a good idea to me.

In the pic below you can see where the mast starts as its a different colour just above the boom. The mast has a nice even curve all the way up too:
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Posts: 476 		Post Options Post Options   Quote Granite Quote  Post ReplyReply Direct Link To This Post Posted: 26 Nov 09 at 7:04pm
When going upwind in underpowered conditions the tip of the mast in the 12 rig will not fall off to leeward as it will be held straight side to side by the cap shrouds.

Once over powered the application of some downhaul and kicker will bend the mast, flattening the sail, effectively loosening the caps allowing the mast to fall off to leeward, also depowering.
If it doesn't break it's too heavy; if it does it wasn't built right
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Posts: 8956 		Post Options Post Options   Quote Rupert Quote  Post ReplyReply Direct Link To This Post Posted: 26 Nov 09 at 7:28pm

How do you control mast rake on a stumped mast? There must be a method, but I'm stumped if I can see it...

Don't windsurfers effectively have a deck stepped mast?!
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G.R.F. View Drop Down
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Posts: 4028 		Post Options Post Options   Quote G.R.F. Quote  Post ReplyReply Direct Link To This Post Posted: 26 Nov 09 at 7:29pm
That sounds like a good idea, and what I'd certainly consider, except I
want the base of the mast to be able
to slide back and forward.

So, lets get back to this hyperthetical two part mast.

Now the outer has to be rigid stiff and super light so it jut doesn't move,
all the bending gets done by the
inner.

So I hear you thinking how? How heavy might it be and how could it be
done..

Have a photo for this one, it's not our application, but I did speak to the
guy that builds this stuff and he did
say he'd be interested in building masts for boats..

So it's called Iso Truss, a weave of carbon kevlar, half the weight than
carbon in any given application, with
the strength of steel, but 9% of it's equivalent weight.



Hyperthetical don't forget I'm not proposing anything, just trying to
stretch the imagination out side of the
box here...

There are
lots of hi tech things going
on in the world.

At the very least Featherweight boom I thought...

Edited by G.R.F.
https://www.ease-distribution.com/
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Noah View Drop Down
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Posts: 611 		Post Options Post Options   Quote Noah Quote  Post ReplyReply Direct Link To This Post Posted: 26 Nov 09 at 7:41pm
Grumph, now please ask the guy who built the Iso Truss (not that I'd want that in my strides!) how he would make it strong enough with a slot in the back for the sail to poke out from. Surely the strength in any structure of this type is in its basically cylindrical form...

Ask the Cherub boys & girls if it is remotely feasible to build a carbon tube with sufficient strength without making it either a) of enormous diameter or b) of great sidewall thickness or c) both.

Masts have evolved the way they have for a reason - 'cos its effective - at a reasonable cost.


Edited by Noah
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G.R.F. View Drop Down
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Posts: 4028 		Post Options Post Options   Quote G.R.F. Quote  Post ReplyReply Direct Link To This Post Posted: 26 Nov 09 at 7:54pm
The stuff is woven that way for that particular structure, nothing to stop it
being woven some other way.

It wouldn't be the bit that carried the sail, the sail would be on a
conventional carrier. The "truss" would/could be the outer, kind of an
extension to the 'stump' idea only much taller.

Doh, this all needs drawing up...



Edited by G.R.F.
https://www.ease-distribution.com/
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Skiffybob View Drop Down
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Posts: 842 		Post Options Post Options   Quote Skiffybob Quote  Post ReplyReply Direct Link To This Post Posted: 26 Nov 09 at 8:03pm

There are a number of good reasons why 12fters use stumped masts, which are:-

1./ No rules resticting what you can or can't do

2./ It adds more weight into the boat and makes the masts (which are not weighed with the boat) shorter and hence lighter.

3./ All the forward kicker loads are transferred directly into the boat. The reduces the stress on the mast, allowing it to be lighter, and means that when you apply kicker, you don't push the mast forwards at goosenck level, flatterning the main. So we can shut the leech whilst keeping the fulness that we want.

3./ It doesn't put lateral stresses on the hull, as a keel-stepped mast will as it passes through the gate.

4./ As said above, it allows us to completely control the mast shape in all conditions and it also allows the mast to be raked by a quick adjustment to the main shrouds and the D2s.

5./ We don't need lower shrouds as you don't need to worry about controlling the mast at the gooseneck.

Hope that helps.
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Posts: 102 		Post Options Post Options   Quote Flick-Flock Quote  Post ReplyReply Direct Link To This Post Posted: 26 Nov 09 at 8:06pm
I wonder what a mast made completely of that iso truss stuff would do to the flow around the sail good or bad?

My moneys on bad because the airflow wouldn't split very well. But like you say, thats not a problem with your double mast thingy, but it could still screw up the air flow, or cause some windage at the least.

Their bikes look rather strange
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