SLIT SEAMS Part B2 IOM Class Rule Change Proposals.

[Robert Hales]

COMMENTS ON PART B2 of 2005 IOM class RULE CHANGE PROPOSALS.

2 August 2005

I have no objection to the concept of shaping sails by the use of "slits". I can however see a number of issues resulting from these new rules as they presently stand.

1. Is there a maximum number of "slits" permitted?

2. Is the length of the "slits" regulated?

3. I assume the "slits" will be reinforced by a "cover" or "reinforcement" strip. Is this strip regulated by the existing rule for flutter patches or
would reinforcement within the seam width (15mm) be permitted?

In summary my first impression is that this rule, as it stands, would allow
one to make a sail with any number of seams (ie panels) with the only
restriction being that the luff should be continuous.

Far from this resulting in an easy way of making a "home made" sail, it
could result in complicated sails of many panels.

I think there should be a limit on the number and size of "slits" that can
be used on a single part sail. I suggest three slits on a main and two slits
on a headsail, no longer than (??) mm.

An alternative suggestion might be to change the wording of G.3.1(a)(2) and (3) to:

(2) The body of the sail shall consist of the same ply throughout comprising not more than four parts and not more than three seams.

(3) Seams and/or their extension shall not deviate more than 10mm from a straight line between luff and leech.

The definition of a seam does include a seam closing a "slit". A mainsail could therefore be of one part but with up to three "slit" type seams. Since the "slits" would be effectively replacing the more conventional overlap seams (and defined as seams) there would be no reason to limit their length or even define a "slit" type seam.

A "slit" seam will probably require reinforcement. This could be achieved by adding (if necessary) the item under secondary reinforcement and a modification to the Seam width item:

Secondary Reinforcement:
from nearest sail corner measurement point……………….125 mm
for flutter patches………………………………………………………….. 50 mm
at luff fittings, luff slides and/or luff openings………………. 20 mm

At a seam

Tabling width………………………………………………………………………..........……15 mm
Seam width including seam secondary reinforcement………………….. 15 mm

The Headsail rules would also be modified in a similar way.

The only effect these rule modifications would have on the existing sails is to allow a "standard" overlap seam to be reinforced. This would seem to be appropriate to retain parity between the overlap and slit methods of making seams.

In this way there is no need to define or even mention a "slit" seam, a term which is not covered in the ERS.

There could be an interpretation confirming that a slit seam is a seam if it was felt that it was necessary.


What do you think?

In the end it may not be worth the trouble!

Robert Hales
Technical Officer
Australian Radio Yachting Association Inc.

[Chairman]

I can however see a number of issues resulting from these new rules as they presently stand.

Hi Robert

Your thoughtful comments are appreciated.

1. Is there a maximum number of "slits" permitted?
2. Is the length of the "slits" regulated?
3. I assume the "slits" will be reinforced by a "cover" or "reinforcement" strip.

My unofficial reading (smile) is no, no, and no.

In summary my first impression is that this rule, as it stands, would allow one to make a sail with any number of seams (ie panels) with the only restriction being that the luff should be continuous.

An excellent summary. But, ah, the word "panel" is not a good one, because it is close to suggesting the sail might be panelled, ie made up of "parts". The sail shall be one panel or part only. And, the word "seam" similarly is to be avoided, because *seam* is a ERS defined term, and the intention is not to permit a *seam* of any kind.

Far from this resulting in an easy way of making a "home made" sail, it could result in complicated sails of many panels.

I don't think this particularly matters, does it? Allowing a hull to be made of wood could result in a pretty complicated hull, but I don't think this means the idea is flawed. This is not an "either/or" situation. A sail with one slit is indeed an easy way to introduce shape, of course it is, and two, three or even four slits is similarly easy. We'd probably need to get over 10 slits before the costs became comparable to a four-panelled seamed sail.

I think there should be a limit on the number and size of "slits" that can be used on a single part sail. I suggest three slits on a main and two slits on a headsail, no longer than (??) mm.

Yes, there is something to be said for limiting the number. I don't think it is necessary to limit the length at all.

The definition of a seam does include a seam closing a "slit".

I'm not sure. The ERS definition of a *seam* is pretty restrictive.

Since the "slits" would be effectively replacing the more conventional overlap seams there would be no reason to limit their length or even define a "slit" type seam.

Exactly.

A "slit" seam will probably require reinforcement.

I'm not sure. My unofficial view is that the slit can be joined using any of the construction methods mentioned in G3.2, but that reinforcement should not be permitted for the slit as such.

[spaldi01]

Robert has highlight some very interesting issues and I am quite frankly amazed after reading through his issues that the proposal is been considered. Making sails using slits would appear to allow a sail maker to make a suite of sails that would be superior to the standard panelled sails. Roberts suggestions to the rule changes appear to be very sensible but could result in existing sails will being modified or replaced if for example reinforcing conventional seams proves advantageous.

I’m surprised that there have not been more responses to his post because the slit proposal would appear to offer a definite competitive advantage which contrasts with the debate that continues surrounding pigmented resins, black glass, carbon fibre and texalium which in my opinion don’t offer any competitive advantages.


Chris

[Nigel]

Chris,

as Lester has mentioned, any reinforcement of the slit joins (seams) is regulated / prohibited by the class rules, thus making the this construction inferior to the panelled sails we all use today.
The main problem being, the stability at the begining or end (how ever you see it) of the slit where the missing reinforcement might result in the sail material tearing.

[Roy Thompson]

a definite competitive advantage

Exactly how do you see it as being so much of an competitive advantage? (or is that a sailmakers secret?)
On a construction point of view, have you tried the slit method? I have - on some non-IOM sails, and it's not so easy as panelled sails to get right in my humble opinion.

[spaldi01]

I think that I may have gone off at a tangent! I have never made any sails using slits but as I read the proposal it appears that a slit could extend from the leech to say 1mm from the luff and as many slits could be inserted as one wants. A slit of this type would be hard to distinguish from a seam. However the number of seams is limited so greater control a sail shape and a competitive advantage could in theory be introduced with slits. From a practicality point of view the gluing of this slit would be impossible and I wrongly assumed that slit sails would be able to have the slit glued by using single side tape placed along the slit. This would stiffen the sail from leach to luff and introduce another possible advantage over standard sails. I now realise that the slits have to be glued using methods already defined by the rules. This would appear to only allow slits to be positioned at the batten locations so that the batten can be used to reinforce the slit join. I think it may however be wise to limit the number and size of slits just in case somebody develops a method of joining slits where they do not need to be reinforced using battens or flutter patches.

Chris