Jeff,

I may be wrong but I do believe you're making the same error Neal is?
Aspect Sail Ratio is Chord distance compared to distance from luff to
leech measured horizontally. I don't understand how you're getting that
from the line drawing?

I can't e-mail you but you can use my addy to reply off line if you'd
like?

Ole Thom

Thom Stewart wrote:
Jeff,

I may be wrong but I do believe you're making the same error Neal is?
Aspect Sail Ratio is Chord distance compared to distance from luff to
leech measured horizontally. I don't understand how you're getting that
from the line drawing?

I can't e-mail you but you can use my addy to reply off line if you'd
like?

Ole Thom


Sorry Thom, the aspect ratio of a sail, as used by sailors, is the luff
to foot ratio. More properly, however, its the height squared divided
by the sail area. This number will be half what is normally given for a
triangular sail, but then increases as the roach is increased.

The wing sail of Spitfire has a luff to foot ratio of over 3 to 1, but
since it is nearly rectangular, its effective aspect ratio is much
higher than that of a triangular sail.

Is it possible you're thinking of the Camber Ratio, the depth of the
maximum draft over the luff to leech length?

Wow,
Just had a Hell-a-ish power dip (outage) lost the whole reply I was
writing to you Jeff, I'll try again

Jeff I was taught that mast height and boom length were used in " Rig
aspect ratio" & Chord (Chamber) & horizontal distance from Luff to Leech
were used to rate "Sail Aspect Ratio"

The reason I was given, so I wouldn't forget was; You can change Sail
Ratio on the Same Rig Ratio.

It may be Semantics. How 'bout we get some comments from the group. I'd
be interested in Doug's thoughts, We know Neal's but let him fire-away.

Ole Thom

While we are on the subject;

What are the advantages of the gaff rig and the advantages of the
Marconi?

The gaff is the better shaped sail for delivering force from the wind
but the disadvantage is the gaff, which provides excess weight aloft. It
also give more driving force with less heeling

The Marconi has less weight aloft because of no gaff but needs to go up
higher to control the shape of the working part of the sail. This extra
height increases heeling force

When we figure Rig Ratio the marconi will always be a "Higher Ratio" rig
by the nature of its shape.

A Gaff will always have a "Lower Ratio" rig because of the Gaff, around
3/4 to 2 /1 due to the shape, As efficent as the marconi but by
necessity has to be kept low because of the weight of the gaff.

Now on "Spitfire" they increased the height by using battens instead off
a gaff boom to decrease the heeling force and added another sail abaft
the other mast.

A much more efficent set-up with less heeling pressure.

Good Nite,
Ole Thom

Thom Stewart wrote:
While we are on the subject;

What are the advantages of the gaff rig and the advantages of the
Marconi?

The gaff is the better shaped sail for delivering force from the wind
but the disadvantage is the gaff, which provides excess weight aloft. It
also give more driving force with less heeling

The gaff also exerts less stress on the hull, and when you want to take
it down, it comes down easily & quickly. One of the disadvantages is
that the gaff tends to twist more.


The Marconi has less weight aloft because of no gaff but needs to go up
higher to control the shape of the working part of the sail. This extra
height increases heeling force

When we figure Rig Ratio the marconi will always be a "Higher Ratio" rig
by the nature of its shape.

A Gaff will always have a "Lower Ratio" rig because of the Gaff, around
3/4 to 2 /1 due to the shape, As efficent as the marconi but by
necessity has to be kept low because of the weight of the gaff.

Oh, I dunno, there are some pretty low aspect marconi rigs around...
some are called "leg o' mutton" rigs... and some high aspect gaffers.
L.Francis Herreshoff designed a number of relatively high aspect gaff
rigs, with short single-halyard gaffs.



Now on "Spitfire" they increased the height by using battens instead off
a gaff boom to decrease the heeling force and added another sail abaft
the other mast.

A much more efficent set-up with less heeling pressure.

The modern sails with the top two or three battens full-length and the
lower battens short is a nice practical & efficient sail.

Fresh Breezes- Doug King

"Thom Stewart" wrote

Now on "Spitfire" they increased the height by using battens instead off
a gaff boom to decrease the heeling force and added another sail abaft
the other mast.

Sorry old chap, but on a tandem rig one mast is not abaft the other.
They are side by side.

As for battens increasing the height of the sails, you gotta be kidding.
The purpose of battens is to shape and flatten the sail and to
facilitate less twist in the leech.

CN

What ever, you are correct Neal.
Would "Two Mast, Broad Abeam" be better?

Ole Thom

Neal,

The upper battens on "SPITFIRE" go upward. You are right in that they
reduce twist. In this case Twist to the horizontal.

Neal, I sail full battens and I can induce twist as well as you can and
keep the Roach section in shape as it twists.

That is what battens are for, to maintain sail shape.

Hope its warm by you. To cold here to get the aroma of a good fart.

Ole Thom