The spar is now even stronger!
 

The spar is now even stronger!
 

"Thom Stewart" wrote in message
...

Wally, I'm very surprised at how many in this group have no knowledge of
what the main shelf is.

Thom,

Many of us are fairly new to sailing. I had no idea what a "shelf" was
before the recent discussions.

My main does not have a shelf .... and I'm fairly sure that most of the very
expensive laminated sails do not have one.


Regards


Donal
--

The spar is now even stronger!
 

Good Lord. More in compression due to the bend? Is that why the crack is
so wide at the bottom?

Cheers MC

Sidney Greenstreet wrote:
Simon's spar is even stronger because of the bend!

That's right, folks! The neutral axis for tension and compression due to
bending has been moved off center, when stressed, more of the boom is in
compression rather than tension. The mid center joint means nothing with
such a clever and knowledgeable repair!

Don't believe me eh? Well check on the design of bridges - why are the spans
arched? Why do arches work for concrete? Concrete or stone block? Why are
engineered beams arched? Press stressed arches are used extensively, they
put the material in the arch more into compression rather than tension. Only
a REAL sailor would know this!! (Look at the undersides of decks of old
wooden ships - it's all arched too!!!)

Once again, the Simple one baits and hooks you all! He has proven many a
time who the simple ones really are!

I hope Bobsprit didn't get heart pangs from posting his silly web pictures.
Good job Simon, as always!

The spar is now even stronger!
 

It collects rainwater.

Cheers MC

Wally wrote:

Thom Stewart wrote:


A Shelf Main is a free footed sail in all respects. The shelf provides
nothing to the TRIM


So, what is the shelf for? I can see what it is, but not what purpose it
serves.


--
Wally
www.makearatherlonglinkthattakesyounowhere.com
Things are always clearer in the cold, post-upload light.

The spar is now even stronger!
 

Joe,

About the shelved Main. Do I think it is better than the loose foted
sail?
Joe, I don't Know. I've been a fan of the Shelf for a lot of years and
I would be sailing one right now if I hadn't FU.

I don't like the standard sail, with the foot connected to the boom.
I've alway preferred free footed main and assumed they should be selved,

I didn't asked for it on this sail and was shocked when it wasn't there.
I called "NORTH" and they said it would be no problem to add one but
they suggested I try the sail as is. Saying they will add the shelf any
time.

Know what? I don't miss it at all.
Is it better? I don't know.

I can't hook it up to my rain catcher.

The jury is still out on that question.

Ole Thom

The spar is now even stronger!
 

My main does not have a shelf .... and I'm fairly sure that most of the very
expensive laminated sails do not have one.

I'll bet they do. I think most people on here are confusing any main that's
attached to the boom with cloth as having a shelf foot. Most mains just roll
down and into the boom. A shelf foot is an extra cost option that allows the
main to maintain it's airfoil shape all the way down to a point parallel to the
boom. The main is attached to the boom with a foot made of inexpensive soft
Dacron that extends horizontally out from the boom (when the outhaul is eased)
to meet the main forming a flat shelf hence the name shelf foot. When the
outhaul is on hard the shelf foot disapears folding up on itself. It basically
has all the advantages of a loose foot but keeps the sail attached to the boom
along it's entire length. A loose foot may give the sail a very little bit of
extra sail area. Most laminated sails have either a shelf foot or a loose foot
only because of the person buying that type of sail is looking for a little
extra performance. A laminated mylar sail will still use a Dacron shelf.
S/V Express 30 "Ringmaster"
Trains are a winter sport

The spar is now even stronger!
 

Thom Stewart wrote:

I'll give it a try. Wally, the shelf is made of a very stretchy
material made to fill the opening at the bottom of the main when the
sail is trimmed to have a deeper draft. The theory being that the
separation between the foot and the boom will be a cause for the air
to form a vortex and lower the efficiency of the main. It is supposed
to act like the fins on the tips of aircraft wings.

I see. Is it the vortex itself that reduces efficiency? I'm wondering if it
has something to do with a loss of pressure near the foot of the sail, due
to it spilling out of the bottom.


Now, since the foot of the main is of flexible material and the free
footed main can carry the trim to the very bottom of the sail ( Sails
with there foot attached to the boom actually lose their trim at the
bottom of the sail) The possibility of the Vortex was eliminated by
putting a very light material that wouldn't have enough force to
effect the curve of the foot of the sail but would send the vortex
off the back of the sail rather than under it.

Does the shelf 'inflate', so to speak?


The shelf had to be made a material that would pull even with the foot
of the main when the main was flat. If it didn't that would have cause
its' own eddies.

I hope I haven't screwed you up but maybe at least you will be able to
see that there isn't any force on the center of the boom that could be
considered support.

I didn't think it was there for support (the photo of Neal's shelf foot
shows that it isn't set up to do that), just wondered what it was for.


Wally, I'm very surprised at how many in this group have no knowledge
of what the main shelf is.

I read somewhere that it also helps in light wind.


--
Wally
www.makearatherlonglinkthattakesyounowhere.com
Things are always clearer in the cold, post-upload light.

The spar is now even stronger!
 

Actually, it takes energy to create a vortex. The gain in efficiency by
reducing the vortex is a decrease in apparent drag. Sometimes the methods
used to quench the vortex use more energy than the vortex itself.


"Wally" wrote in message
...
Thom Stewart wrote:

I'll give it a try. Wally, the shelf is made of a very stretchy
material made to fill the opening at the bottom of the main when the
sail is trimmed to have a deeper draft. The theory being that the
separation between the foot and the boom will be a cause for the air
to form a vortex and lower the efficiency of the main. It is supposed
to act like the fins on the tips of aircraft wings.

I see. Is it the vortex itself that reduces efficiency? I'm wondering if
it
has something to do with a loss of pressure near the foot of the sail, due
to it spilling out of the bottom.


Now, since the foot of the main is of flexible material and the free
footed main can carry the trim to the very bottom of the sail ( Sails
with there foot attached to the boom actually lose their trim at the
bottom of the sail) The possibility of the Vortex was eliminated by
putting a very light material that wouldn't have enough force to
effect the curve of the foot of the sail but would send the vortex
off the back of the sail rather than under it.

Does the shelf 'inflate', so to speak?


The shelf had to be made a material that would pull even with the foot
of the main when the main was flat. If it didn't that would have cause
its' own eddies.

I hope I haven't screwed you up but maybe at least you will be able to
see that there isn't any force on the center of the boom that could be
considered support.

I didn't think it was there for support (the photo of Neal's shelf foot
shows that it isn't set up to do that), just wondered what it was for.


Wally, I'm very surprised at how many in this group have no knowledge
of what the main shelf is.

I read somewhere that it also helps in light wind.


--
Wally
www.makearatherlonglinkthattakesyounowhere.com
Things are always clearer in the cold, post-upload light.