sail cloth, sail fibers, sail making


I am presenting a lecture seminar on the subject topic this Thursday, tomorrow, 16 Feb 2017 at Newport Yacht Club, Long Wharf in Newport. All are welcome.

This is the presentation overview and the things I will be discussing.

Fiber, fabric, film and fabrication

  • What does a sail have to do?
  • What is required to do this?
  • Background on fibers and their properties
  • Weaving 101
  • Mylar properties
  • Laminates
  • Laminated method
  • “String sails”
  • What’s next?
  • What does the weekend sailor make of this?

And thanks to Hood Sailmakers and Dimension Polyant for the cloth samples.

Hood Sailmakers is paving the way by sponsoring the drinks to the tune of the first $150 of drinks served.

This is the email flier that Roy Guay, my host for the evening and the Chairman of the Bermuda 1-2 distributed to the club’s membership.

On 16 February at 1830 the Newport Yacht Club is trying to start a Winter Lecture Series. Our own Joe Cooper will be giving a talk on Sailcloth and Sails: “Separating marketing from facts to get to Value: A discussion of Sailcloth and things to look for and why for various types of sailing. What does “Premium Dacron” really mean? Why every sail maker has “The world’s best sails” What’s the difference? Woven, Laminates, fibers, molded, not molded, a glossary and guide to sail-maker speak.”

If you are in the neighborhood drop on by. All are welcome.

Roy Guay
Offshore Chairman

Cooper in action at a seminar in California last year.

Cooper in action at a seminar in California last year.

Hope to see you there.




Mast bend and mainsail shape

Bending the mast is a fast and simple way of managing the power on your sail boat

As discussed here mast-rake and mast bend are two different aspects of mast “tune” that affect the boats balance and so feel and ultimately performance. This essay discusses mast BEND. There is an element of headsail shaping connected to mast bend but we will get to that in future posts.There are other tools in the mainsail shaping tool box, but this essay is about mast bend

The Basics:

More wind requires a flatter sail

Less wind prefers a fuller sail.

Mainsails have shaping both across the sail (broad seaming) and at the luff, known as Luff Curve

This “curve” is intimately connected with the characteristics of the mast, and so, of the boat. There are differences in the amount of luff curve required between masthead and fractional rigs, masts with spreaders in line–that is to say where the cap shrouds are perpendicular to the mast-Or with “swept back” spreaders, such as many newer boats have.

Some Definitions:

Chord: Is an imaginary line between the luff and the leech

Depth: (and draft, camber & shape-They are quite synonymous and generally used interchangeably by Sailmakers in their jargon) is that distance, perpendicular to the chord line, at which the sail’s surface is furthest away from the chord line.

In the sketch below:

The line ZZ is the chord line.

The portion “C” is the chord LENGTH on the sail.

The distance “a” is the chord DEPTH (draft camber shape…).

The distance “b” is the POSITION of the draft measured aft of the leading edge of the foil which is in this case to the right of the image. Thus a/c is the draft and b/c is it’s position.

Chord (length) draft and location of draft are all depicted in this image.

Chord (length) draft and location of draft are all depicted in this image.

Power: over and under (powered)

Power (force, energy …wind speed) is what gives the sensations you feel thru the wheel or tiller and via the heel angle of the boat. With headsails, managing the power is relatively easy: Too much power, then put up the small (er) one-Or more likely today either partially roll up the genoa or roll it up all the way and motor-sail.

Sail size and shape:

Having the right (sized) sails of the right shape for the conditions is, for those who prefer to sail for the sensations of how the boat feels thru the tiller/wheel, a key part of this sensation. Too much sail and/or sails that are too full makes the helm feel heavy and generates too much weather helm. In this condition the boat heels more than you want and always inclined to want to round up. This is of course unpleasant, occasionally quite noisy, slow and not infrequently intimidating for some on board.

The sensations of being underpowered are less dramatic, noisy, violent and so less intimidating.

Power on a sailing boat comes of course from the sails. Having the right shape in the sails is therefore key to getting the boat to “feel good” and sail well.

Managing the power

One tool in the box of adjustments available to sailors is adjusting the camber of the mainsail-What many folks refer to as the belly of the sail. Camber is the “depth” of a sail at a given point on the sail. (NB when we/you say the sail is blown out, usually this refers to the draft being further than 50% aft on the sail)

This picture shows me and a high school intern measuring the draft amount and location on a 420 mainsail strung up in the loft.

This picture shows me and a high school intern measuring the draft , the amount and its location on a 420 mainsail strung up in the loft.

The camber on any foil is expressed as an amount, at a location. So you might hear Sailmakers say something like…”it was 8% at 35% aft.” This means that what they were looking at was 8% of the fore and aft span (of the chord line) perpendicular from that line and that position was 35% aft, from the luff. Translated: the sail was 8% deep at 35% aft.

Another picture of working with Tristan discussing issues surrounding sail shape: Chord, draft position and so on.

Working with the intern and discussing issues surrounding sail shape: Chord, draft position and so on. This sail looks quite full because the mast is not bent.

So for example if the chord span (“c” above) was 10 feet and 8% of 10 feet is 9.6 inches so the sail surface was (“a” above) 9.6 inches away from the Chord line, and this point is (“b” above) 3 and a-half feet aft along the span from the leading edge.

So far so good?

Luff round

Now sails are not just triangular (Yes, mainsails have roach but many/most “cruising boat” sails have very little), the point is they are curved at the luff too. This is called, no surprise, “luff curve or luff round”. How much curve and at what position on the luff and how these points is determined are all components of the sail’s design.

On this J 30 main, the area of the sail to the left of the left hand tape is called  luff round. There is a lot of it on a J 30 because they have relatively bendy masts, especially above the hounds.

On this J-30 main, the area of the sail to the left of the left hand tape is called luff round. There is a lot of it on a J-30 because they have relatively bendy masts, especially above the hounds.

Luff round and mast bend are intimately connected. If the luff curve and the mast bend “match” is correct, you have a 6-speed stick shift gearbox. If the mainsail luff curve and the mast bend are not mated, pretty closely, then you have a 1953 shift on the column three speed with no fluid in the transmission, as it were. It is really critical and the more performance oriented the boat the more critical it becomes. AND this is why having a back stay adjuster (and knowing how and when to use it) is a great thing to know, if you like sailing your boat, as opposed to being on while it is sailing.

Sketch of a mainsail set on a straight mast

Sketch of a mainsail set on a straight mast

Briefly stated, when you bend the mast, you can flatten the mainsail. A flatter sail is to be preferred in more wind. Flatter sails reduce power in the sail, that is reducing load on the tiller/wheel. When you bend the mast, in windier conditions you will feel the helm go lighter, all other things being equal.

Mast bend flattens the mainsail

Mast bend flattens the mainsail. When the mast is straight …”straight mast” the sail is fuller. When the mast is bent, as at point “a”, the luff curve gets pulled forward and so flattens the sail.


Mast bend on the 12 meter Australlia ion 1980

Mast bend on the 12 meter Australlia in 1980. The defender, Freedom is to weather.

The picture above shows the 12 meters Australia and Freedom coming off the starting line in one of the 1980 races for the America’s Cup. The Australians had fabricated a fiberglass top to one of their spars that would bend much more dramatically than an aluminium one. The top of the mast was controllable, apart from the regular topmast backstay, by “jumpers” and “diamonds” all controlled by hydraulics in the mainsheet trimmers cockpit. It gave the boat the abiity to have more mainsail and the rounder shape to the top of the mast was more efficient. In under about 9 kts of wind we were faster than Freedom. We won one race and were in front by 20 minutes when the time limit expired.

The large roach not withstanding, study the luff on the let. IT has a degree of "luff curve". This will match the mast bend on the boat and so be used to de-power the sail.

The large roach not withstanding, study the luff on the left. It has a degree of “luff curve” about 6 inches to my eye. This will match the mast bend on the boat and so be used to de-power the sail.

If you do not have any mechanism to bend the mast, consider adding a way to do so. For almost all boats there are a variety of pretty simple solutions.  If you cannot find one or need help, contact me….It is not impossible that the money spent on such a set up will be good value with respect to making the boat more agreeable to sail in breeze and so less uncomfortable for all hands.




Safety at Sea seminar

On Saturday 07 Feb 2015 at the Safety at Sea seminar, produced by LandfallNavigation, I will be presenting a section on sails & sail fibers. This nearshore Safety at Sea seminar is being held at the Mystic Seaport in Ct. from 0800-1630

The following is a table of the basic properties, sailmakers are interested in, of the fibers currently used in making sails. In an earlier day, this information would be distributed at the event, but today, well it is here.

The information is from the North Sails website attributed to research by their cloth people

Polyester (Dacron)
Modulus (gr/denier) Tenacity (gr/denier) UV Resist. (mo. to 50% strength loss) Flex Loss (% in std. test) Cost ($/lb.) Uses
80 – 120 5 – 8 6 mo. 0% $2 Racing & Cruising Sailing
Pros: Tough, durable, inexpensive, many weights and finishes.
Cons: Relatively stretchy compared to aramids.
PEN (Pentex)
Modulus (gr/denier) Tenacity (gr/denier) UV Resist. (mo. to 50% strength loss) Flex Loss (% in std. test) Cost ($/lb.) Uses
250 10 5 mo. 5% $7 Club Racers & Cruisers
Pros: Fits between Polyester and Aramid in performance and cost.
Cons: Cannot be woven tightly, best used in laminates.
Kevlar 29 Twaron SM
Modulus (gr/denier) Tenacity (gr/denier) UV Resist. (mo. to 50% strength loss) Flex Loss (% in std. test) Cost ($/lb.) Uses
600 23 3 mo. 25% $15 Regatta Racing Sails
Pros: Light weight, low stretch.
Cons: Low flex and UV resistance.
Kevlar 49 Twaron HM
Modulus (gr/denier) Tenacity (gr/denier) UV Resist. (mo. to 50% strength loss) Flex Loss (% in std. test) Cost ($/lb.) Uses
940 24 3 mo. 28% $18+ Grand Prix Racing Sails
Pros: Light weight, very low stretch.
Cons: Low flex and UV resistance. Expensive.
Modulus (gr/denier) Tenacity (gr/denier) UV Resist. (mo. to 50% strength loss) Flex Loss (% in std. test) Cost ($/lb.) Uses
1200 – 2500 20 – 40 No effect 30 – 100% $15 – $100 Grand Prix Racing Sails
Pros: Very light, extremely low stretch, good UV resistance.
Cons: Brittle, low flex resistance.
PBO (Zylon)
Modulus (gr/denier) Tenacity (gr/denier) UV Resist. (mo. to 50% strength loss) Flex Loss (% in std. test) Cost ($/lb.) Uses
1600 36 1.5 mo. 30% $60 Grand Prix Racing Sails
Pros: Extremely low stretch and light weight.
Cons: Low flex and very low UV resistance. Expensive.
Spectra / Dyneema
Modulus (gr/denier) Tenacity (gr/denier) UV Resist. (mo. to 50% strength loss) Flex Loss (% in std. test) Cost ($/lb.) Uses
1100 34 7 mo. No effect $25 – $35 Premium Cruisers
Pros: Very strong and durable.
Cons: Creep limits racing applications.
LCP (Vectran)
Modulus (gr/denier) Tenacity (gr/denier) UV Resist. (mo. to 50% strength loss) Flex Loss (% in std. test) Cost ($/lb.) Uses
580 28 1.5 mo. No effect without UV $25 Premium Cruisers
Pros: Good flex when protected for UV.
Cons: Requires complete UV protections.
Modulus: Stretch resistance per weight. Higher is better for upwind sails.
Tenacity: Breaking strength per weight. Higher is better for sails.
UV Resistance: Strength loss in a standardized exposure test.
Flex Loss: Percent breaking strength lost in an industry standard 50 fold test.

Mast rake Versus Mast bend

Mast RAKE and mast BEND are two aspects of a boat’s sail plan and rigging used in making small adjustments to the mast, thus the performance, on a sailing boat. The two adjustments are quite different. These two words and attendent adjustments are frequently confused among weekend sailors. I will try to separate the two in this post.

Mast RAKE refers to the distance aft of perpendicular (to the waterline-Horizontal) the top of the mast is. It is used to fine-tune the boats balance and is generally not changed very often on cruising boats and perhaps never.

Mast BEND refers to applying tension to the backstay so that the mast bends to some degree. The amount of bend varies with the boat. BEND can be adjusted on the boat while sailing to change the sail shape and is adjusted depending on the wind speed.

I will address mast rake first.


Some background:

Sail boat designers need to make sure the boat will ‘balance’ when sailing. This means in practice that there will be the ‘right’ amount of pressure, or ‘helm’, on the tiller or wheel when sailing up wind in about 10-15 knots of true wind. This balance is created by the relative positions of two features of the boat’s design. The sail plan’s Center of Effort (CE) and the boat’s (the hull, keel and rudder) Center of Lateral Resistance (CLR). The center of effort of the sail plan is quite easy to determine.

In the picture below you will see three short pencil lines at the pointy end of the crayon. This is the position of the sails C of E that I drew for this exercise. If you look carefully you will see the Designers hand written note indicating HIS C of E on the sail plan, (and a note on the sail’s size in square feet) immediately under where I found the C of E.

the intersections of the pencil lines is the Center of Effort of this sail

The intersections of the pencil lines is the Center of Effort of this sail

The designer calculates the C of E by drawing three lines on the sail plan. They are drawn from the center of one edge of the triangle (the sail) to the opposite angle as seen in the image below.

Big picture of the the center of effort

Big picture of the the center of effort

Lines are struck from the mid-point of the boom to the head, from the mid-point of the mast to clew and the mid-point of the leech to the tack. Where the lines intersect is the C of E. This point is an integral part of the sail and ‘moves’ with the sail. So if for instance the fore stay is lengthened, the mast HEAD moves aft (increasing the rake) the C of E moves aft (creating more weather helm). The reverse reduces weather helm and if excessive, creates neutral or sometimes lee helm.

Mid point of boom.

Mid point of boom.

The C of E is found by striking a line from each sides of the triangle to the opposite corner. Above is the mid-point of the boom, to the head of the sail.

A line from the mid point of the mast to the clew

A line from the mid point of the mast to the clew

The picture above shows a line from the mast mid-point to the clew.

This line is from the leech mid point to the tack

And this line is from the leech mid-point to the tack

Sailmakers need to know the mast rake for a few reasons all to do with making sure the sail(s) fit the boat.

RAKE is determined in most boats, not dinghies (they use another way) by measuring the distance the masthead is AFT of vertical, that is perpendicular to the waterline. It is measured at the boom and described as “xx inches of rake”, at least among Sailmakers & Riggers. Generally it looks like this:

Mast rake measurement on a J-105 rig.

Mast rake measurement on a J-105 rig.

The ruler shown above is set perpendicular to the water line, (on the dwg,) and just touching the back of the mast at the masthead (see picture of mast head below). Sailmakers do this, on a sail plan by using the right angle triangle on the right and laying the ruler alongside the triangle so it touches the mast head while perpendicular to the LWL. You can see here the rake on the J-105 on the sail plan is considerable.

Mast rake view at the top of the rig

Mast rake view at the top of the rig

To measure the rake on the boat you basically set up a plum bob, so you will need the following. The main halyard; a weight—a one gallon jug of water, fuel or rum, or the canvas tool bag is fine and a measuring tool: a 6-foot Stanley tape is fine. Ideally this measurement is done on a windless or light air day where the boat is not bouncing around. It should take 5 minutes or less. It is dead easy to do alone but a mate is always good to have.

Attach the weight to the main halyard and hoist the halyard only a couple of feet so the weight is half way between the bottom of the boom and the cabin top. Let the halyard/weight come to rest. Where the halyard crosses the boom, measure forward to the aft face of the mast and note the distance. This is the rake:-“xx inches”. So in the picture below, the amount of rake is that distance between the forward side of the ruler and the  aft side of the mast,

VIew of the plum bob/main halyard across the boom

View of the plum bob/main halyard across the boom

I used a J-105 as an example here because they have a lot of rake so it is clear in these pictures. Most ‘cruising’ boat’s do not have this much rake.

On the other side of the coin, If there is almost no rake, less than say 2 inches on a 35-foot boat, this bears looking into. If there is a lot, more than say 12-15 inches on the same boat, again this bears research. In the former, you may relate this to the light feel in the helm. In the latter, it will be a large factor in the boat’s weather helm.

Sailmakers need to know how much rake is on a boat when designing sails for several reasons. On a practical note, three key ones are: so the boom does not hit the dodger or bimini or on some boats the mast gallows. How much rake a boat has is also an indicator as to how the boat is set up; rigged or tuned up if you like. To use the J-105 example, if I were sent a measurement sheet that showed 3 inches of rake on a J-105 that would set of alarm bells because it is way off base.

Rake information is needed for designing headsails too. The C of E of headsails is determined the same way as for a mainsail. Thus the amount of rake has an impact on where the clew is going to land. If one was to merely duplicate the three edge dimensions for one boat of a particular class onto a sistership, without checking the sistership’s rake, AND the sistership had a lot of rake, then the clew would be a lot lower and perhaps the sail would not be able to be sheeted to the installed genoa track. The reverse is true if there is a lot less rake, the genoa may want to sheet where there is no track–Seen that happen too.

These two scenarios are less of a problem on cruising boats but a detail that consumes a lot of checking-time on race boats where the track locations are very specific and the tracks are usually pretty short, to save weight of course.

Next up Mast Bend


Full Length Battens-2c: To FB, or not to FB


With apologies to you know who.

I have received another question and a related comment  from some readers on the LinkedIn forum “Sailing Network”. This  forum requires authorization but the  access is free once registered.

The question comes from Pippa who appears to be either the principal or a partner and is a RYA Yachtmaster Instructor (Sail) with Miramar Sailing School, Antigua

“I’ve been reading your comments and blog about Fully Battened Mainsails – I have a Jeanneau Sun Odyssey 40 which has sails that are probably the originals from 1996. The main is starting to look ‘tired’ and we have been considering getting a new sail with only leech battens – do you think this would be a retrograde step, or not make a significant difference to her performance? Obviously the current main being a bit out of shape won’t help, but will we regret not getting a replacement that is fully battened? Interested in your opinions!”

This is the comment from the same forum from a reader in San Francisco, DG Tilton-

“Get the full battens. I got about half a knot better in low winds. Most importantly, for students, better control in a jibe. The extra expense of new batten cars/slides for the mast was well worth the investment. The command of out haul for shape also improved performance as well. The difference between old and new is always an increase in speed. But the performance of my sail in 12 years is like new. I teach heavy weather sailing in SF Bay. Our typical winds of 25 kts to 35kt present dynamic conditions due to micro cells of wind vortex. Your lighter winds in Antigua make sail shape even more important. The difference is like releasing more energy for speed instead of drag.”

This is interesting because both correspondents seem to be in the sailing instruction business and both seem to sail in conditions of more than enough wind, most of the time.

I will point out here I am not writing to advocate for or against full battens. Each boat, owner, situation, skill and experience level, sailing plans and a sea-bag full of other factors influence any decision on a boat and the decision on FLB’s is no different.

These essays are to share what I have learned over a more than 15 years as a sailmaker sales rep. that is incorporated into over 50 years of sailing including roughly 40 in the marine trade.

As I read through the question and comment i received, I have the following questions for Pippa centered on her basic question to me:

Would getting a sail with FLB be a retrograde step OR make a significant difference to her performance?

Then the first thing is to go back to the first essay and review the discussion there in particular the part about performance increases after either:

Adding FLB to an old sail. Second is getting a NEW sail with FLB.

My question at the beginning of the first essay is:

Can the “increased performance” be attributed to the Full Battens, on the new sail


Does the “increased performance” stem from the fact that the sail is new and so has all the advantages of a new sail?

These include of course a new(er) shape, perhaps “better” (more stretch resistant-even Dacron) materials than the old one, perhaps larger area via more roach, I note that OEM sails are notoriously “small” with regard to roach and the materials used in such sails are not so great, a superior shape design if from a different sailmakeing firm and or designer or simply what has been learned over the intervening years since that sail was designed.

I am not aware of truly empirical evidence that full length battens on THE SAME SAIL, ON THE SAME (class of) BOAT improve the PERFORMANCE of the boat. And how are we defining performance? Faster, higher or both?

Issues to consider when trying to answer that question include:

  • Does a FLB mainsail make the boat so equipped sail faster and or higher-compared to the “old” sail with out FLB?.
  • In what wind speed?
  • In what sea conditions,
  • Steered by whom?
  • With or without a prepared and smooth bottom?
  • With the same amount of stuff, in the same place in the interior?
  • With the same headsail, in the same “shape” condition as when the old main was being used?
  • Same rig setting?, rake, backstay, mast prebend cap shroud tension?
  • Same weight on the rail?
  • Same helmsman?

These all play a part in a boat’s “performance” and are some of the particulars that sailmakers want to have in place before even consenting to go on a sail speed trial. Organizing and executing such testing with two boats is a right royal tedious business too,even at the top end of the sport and is full lots of small details that are very hard to uncover. For instance I once did a sail for a fellow with a free standing cat rig spar. After delivery he called to complain that he could not keep up with some of the boats at the rally/rendezvous he was attending. After about 6 hours of sailing, questioning, measuring, reviewing details of the design, I discovered that this fellow had a mast step that was in totally different place than other boats I had measured on the dock adjacent to him and that his spar was, for reasons unknown it was larger in diameter…..He did not even know it was larger.

I can attest from my own experiences that determining if one sail is faster (and or higher) than another is a very long drawn out process. This experience comes from two America’s Cup campaigns and lots of hours sailing along in a straight line with lots of smart and experienced sailors and sailmakers trying to make the boat go as fast as it can, then changing nothing else except the sail in question and repeating.

Thus even with an identical Sun Odyssey prepared as closely as possible to Pippa’s boat in order to be as equal when sailing along side each other; there are still many variables to be incorporated before the “increased performance” of the sail can be attributed to the sail having Full Length Battens.

Read again my remarks in an earlier post as to why,” if FLB are faster”, why then does the J105 class not all have FLB mainsails for instance? The 105’s have no rules regarding batten length. The paragraph is about half way down the post.

The next part of a decision to incorporate FLB into a new sail has to do with, as I wrote in the first essay,  value and encompasses things like:

  • Extra cost for the (addition of the) battens on the sail.
  • Issues of moving FLB around by carrier if necessary. Long, and skinny is expensive to ship even if it light in weight. I am thinking, Spares.
  • What are you going to use for luff hardware, at what cost and thus value? In my going for the cheaper option is not sound. This is especially so on a 40 footer, used (I am assuming) as an instruction boat with the attendant minimal seamanship (as distinct from hours or miles of sailing) experience of the students, one assumes, in an area with more than enough wind most of the time.
  • Considerations of maintenance, specifically chafe: The Sun Odyssey 40 has spreaders with some amount of sweep to them. When running down wind the battens, especially the top couple will bear on the standing rigging and chafe due to the hard spot where battens in the sail cross the standing rigging. The chafe will be harder than a sail with conventional battens.
  • The mechanism for securing the sails into the pockets-Perhaps not a great issue on a boat that may not stray far from home. Regardless reefing any sailing 25-30 knots of wind always flogs the sail and invites battens to spear out the leech end.
  • Stowing the sail on the boom. Here is one area that the FLB are or can be superior and perhaps add the value but only if combined with a slippery track arrangement and some kind of sail containment. The SO 40’s I looked at on the web all have some kind of boom bag and lazy jacks for the sail to be captured by and stowed in. Again more money.
  • The battens and pockets, cars and batten boxes all add weight. I have memories of a mainsail for a 40 footer weighting 50-60 lbs. Add another 15 pounds for all “the stuff” if the sail has a really low friction track and car system.
  • The added weight of the track and the now heavier sail all sticking up in the air will have an effect of some magnitude on the boats stability. Whether or not it is visible to the human eye depends on other variables.

I am not going to recommend or not FLB. As I say above my goal is to lay out what I see as the issues that by experience many folks do not consider in their interest in and experience with FLB.

In sum the question for Pippa to contemplate is:

“Is all this worth the extra capital cost and the maintenance cost compared to the Value you get from them?”

Value being subjective but of course including performance (it will be a new sail after all), possible increase in ease of handling the sail-if appropriate sail capture kit is incorporated into the boat, additional weight to hoist, a less “aggressive” flogging” of the sail when it is not trimmed. This is because the battens slow up the frequency of the individual flaps, to and fro that are the components parts of flogging.

Pippa, you asked for my opinion, well here it is (grins) Mr. Tilton says that  the “extra cost” is worth it but that is a decision you will have to make for yourself and your own circumstances.

Were I consulting with Pippa on this sail in my previous life, these would be the questions I would be putting to her.