Mast rake Versus Mast bend

Posted on by

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.

MAST RAKE:

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

 

Safety at Sea Seminars for 2015

Posted on by

Cooper’s “Save the Dates” for winter 2015 Updated 06 NOV 2014

 

There are at two Safety at Sea seminars in the North East scheduled for early 2015. The first one, at Mystic Seaport does NOT have ISAF endorsement. It is rather a seminar focusing on the coastal and nearshore sailor. It is a long day, but the content is fantastic. I visited last year and the place was sold out. There are  plenty of breaks, copious amounts of coffee and lunch.

This years seminar is to be a reprise plus you get me presenting too.

07 February 2015: Saturday

Mystic Seaport: 0800: 1600. A one-day Safety at Sea seminar with a number of topics covered, including sails (by of course yours truly) this seminar focuses on inshore and near coastal sailors. I was at this year’s one and it was sold out and very highly regarded by attendees.

MYSTIC seminar does NOT qualify as an ISAF SAS

21-22 March 2015. Sat & Sun

At UMASS Boston. 0700-1800 This seminar, or an equivalent ISAF certified course, is mandatory for Marion Bermuda and all offshore races including the 2016 Newport to Bermuda Race.

This seminar is hosted by the Marion to Bermuda race in conjunction with the Marblehead to Halifax Race Organizing Authority. This seminar does qualify for the ISAF crew SAS certificate from US sailing. This certificate is required generally for at least 30% of crews in offshore races, more air less anywhere. So even if you are not planning on doing either of these races in your own boat, having this certificate is a “PLUS’ in the event you look for crew spots on the races.

It is a two day seminar. Class the first day with break-out sessions. On Sunday there are dedicated sessions including first aid, in the water life raft instruction, (bring your swimmers) and weather presented by the very knowledgeable Frank Bohlen who has a great ability to make a complex science understandable to normal people. The entry fee is worth it just for this seminar.

BOSTON seminar DOES qualify for ISAF certification.

As always if you have any questions you know where to find me.

Cheers

Coop

Newport to Bermuda Race 2016: Part one

Posted on by

 

An inside staysail suitable for setting of small sails is a requirement of the Newport to Bermuda race. Any offshore race actually

An inside staysail suitable for setting of small sails is a requirement of the Newport to Bermuda race. Any offshore race actually

Yeah yeah, I know, some of the boats are not even back home after the 2014 event but, it is never too early to start planning.

And anyway, last week I received an email from a fellow who wanted counsel on putting together a campaign for the 2016 Newport Bermuda race. We met for a burger and beer and had a great time going over the various elements comprising a successful campaign. IT should be noted that at the moment he does not have a boat suitable for this race. After writing the Spindrift post yesterday, I thought it might be interesting to compare my notes from this meeting with what the Spindrift guys might be thinking about.

For this fellow I came up with, in no particular, just as I thought of them:

A boat suitable for the raced AND ones which the Race committee will permit to enter.

While not used in "normal" yacht races, the physical testing of a boats stability is normal in the open classes, as evidenced here by the pull down test for a 6.5 meter Mini-Transat boat. FOr the Newport to Bermuda race, the Organizing Authority refers to a boats rating certificates and imposes regulations on stability from that data.

While not used in “normal” yacht races, the physical testing of a boats stability is normal in the open classes, as evidenced here by the pull down test for a 6.5 meter Mini-Transat boat. For the Newport to Bermuda race, the Organizing Authority refers to a boats rating certificates and imposes regulations on stability from that data.

The Racing rules of Sailing AND the particular rules of the Newport to Bermuda race.

Preparation of the boat, going over all the systems, upgrading or paring them as necessary
Management of the whole project INCLUDING returning from Bermuda…
Delegation of tasks and areas of responsibility—Sailboat racing is a management exercise as much as a sail boat race.
Strategies for developing the boat, the systems and the crew—Proposed crew is light on for offshore experience into an integrated team. Coaching practice theory and other class room work as it were.
Safety at Sea education—both formal, the usual weekend seminars in the Spring and more intuitive, experiential sort
Weather, (including Gulf Stream) learning about and then decision making during the race.

The ability to capture weather information and the skill to interoperate it is a key element in any ocean race these days with the latter being the more difficult.

The ability to capture weather information and the skill to interoperate it is a key element in any ocean race these days with the latter being the more difficult.

Rigging and sails AND related components of crew co-ordination for setting, changing, lowering sails and the techniques, where each person is for what maneuver
Food—What, how prepared, what kind, where stowed, how served and what to eat when the wx. goes to pieces.

Cooking facilities are mandatory

The care and feeding of the boat’s most important resource and asset is essential

Health of the crew. Overall physical ability to cope with 3-6 days at sea. Meds, issues like Diabetes, seasickness for just couple of issues
And related Medical expertise, what to do when something happens to one of the crew
Logistics, paperwork—passports, race entry paperwork etc.: Back office stuff.
Electronics, related to performance and to Navigation.
Navigation and related disciplines of the position of the boat relative to the Gulf Stream, the expected weather and the competition.
The foregoing is a reasonable overview of what needs to be managed for a 40 foot mono-hull, sailed by Corinthian sailors in a 600-mile race 2 years from now.
In the next few posts I will break down these by number and elaborate a little on just what is needed.

 

OFFSHORE SAILING: Spindrift Racing and SEAMANSHIP: The three legs of….

Posted on by

What are the THREE most important things to consider when contemplating a voyage?

Planning, Preparation, regardless of your Experience.

The kind of sailing contemplated by the sailors described in the second half of this post can go nowhere without using all three legs of the seamanship stool: Planning, Preparation and Experience.

In Newport a couple of weeks ago I counted the following classes of boats:

Team Alvimedica, US ENTRY IN THE VOR  who were out Friday, doing the Around the Island Race as part of the NYYC annual regatta.

US entry in the 2014/15 Volvo Ocean Race

US entry in the 2014/15 Volvo Ocean Race during their Naming Ceremony

There were various High Test boats, like the TP 542 Interlodge, Bella Mente, Rambler and others in town for the Bermuda Race.

A TP 52 out practicing on Narragansett Bay prior to the NYYC Annual regatta

The TP 52 Interlodge out practicing on Narragansett Bay prior to the NYYC Annual regatta

Daily half a dozen Etchells arrive in advance of their worlds.

There was a record turn out for the NYYC annual regatta (Regatta Number 160)

There were two different Around Jamestown Island speed records broken, one on the Mastrand 32 Cat and one in the large mono hull category (Bella Mente in fact)….Phew…

A few of the Class 40’s in town for The Atlantic Cup are on moorings or in the Shipyard patiently waiting for the Bermuda race.

One of half a dozen Class 40's in town for The Atlantic Cup

Dragon, one of half a dozen Class 40’s in town for the Atlantic Cup seen here competing in the second to last race of the inshore series.

Another C40, Bodacious Dream, was coming in from a Circumnavigation.

Then there was the Clagett Memorial Clinic and Regatta, (one of the key regattas for sailors not as physically capable as many of us)

There were  kids arriving for a few days of coaching in the Booke Gonzales clinic for up and coming winners.

Oh, and the usual beer can, Shields, J-24 & sport boat racing on Monday, Tuesday, Wednesday, Thursday nights and just so much more. In lots of sailing ports one can get lots of boats, but in my experience that are all of a similar species at any given time. Only in Newport can one get such a wide swath of sailing boats for different uses all at the same time. AND frankly this is kind of a slow year with only 3 world championships this year….Where else do you get that?

OK, NOW reference my second sentence, above:

ALL of the boats ands sailors in attendance for anyone of these events have the first two characteristics in common, regardless of the level of their third.

Sitting quietly in the midst of all this sailing energy there is one boat making hardly a ruffle where she is moored at the west end of the docks at the Newport Shipyard. This boat is the absolute epitome of preparation and planning

The boat in question is a 40-meter LOA (131 feet) trimaran.

Rarely do American Sailors get close to the elite of the French ocean racing scene, unless in France. This boat came to us and is seen here at the Newport Shipyard

Rarely do American sailors get close to the elite of the French ocean racing scene, unless of course that travel to France. This boat came to us and is seen here at the Newport Shipyard. Spindrift Racing are waiting for a “weather window” of suitable characteristics to give them a shot at breaking the all time and absolute Trans-Atlantic sailing speed record west to east, from Ambrose light to The Lizard in SW England

I speak of course of Spindrift Racing, the former Banque Populaire under whose colors she set the current absolute Transat-Atlantic speed record from Ambrose to the Lizard in 3 days 15 hours and change, including a 24-hour run record of 905 miles, which is averaging a small dollop of spray south of 33 knots. Moored as she is away from the cluster of huge (tall) spars with which the bulk of the 40 meter cruising yachts at the shipyard are rigged there is, to the practiced eye, an incongruity to her spar as seen from out on the lower bay. It is thick, as in like a wing mast yet not so tall. The wing section is not so long, perhaps a meter and a bit fore and aft. The entire spar has been modified for this record. The Spindrift team cut some large number of feet, I want to say 20 feet off the top and re-did the sails since, as Banque Populaire the last time, her crew sailed almost all the way with a reef in I am told.

The current owners and crew are of course waiting for that much discussed and worried over piece of equipment “essential” to setting and/or breaking Trans-Atlantic sailing records today, the “Weather Window”. According to the chap I was chatting with on Wednesday, said window is still a minimum 10 days out, so the crew was flying home to France (where else?). It is hard to absorb the scope of this boat from pictures but I try.

Standing next to Spindrift Racing, one’s mind is readily boggled by just how massive this boat is.

When simply looking at a picture of Spindrift it is not possible to gauge the scope or the scale of this boat.

When simply looking at a picture of Spindrift it is not possible to gauge the scope or the scale of this boat.

For starters the lashings for the cap shrouds are 25 mmm spectra  based on being roughly half the diameter of my water bottle.

Compare the size of my water bottle, roughly 2.5" wide and 9 inches tall with the lashings for the side stays.

Compare the size of my water bottle, roughly 2.0 inches wide and 9 inches tall with the lashings for the side stays.

One can commonly can stand on the dock and get a good idea of the on-deck workings of a boat. NOT so with this one whose working area/cockpit is perhaps 10 feet up on the air. This, “flight deck”  one is tempted to call it, has all the sail controls and is contained inside a hemisphere the arc of which is outlined by the mainsheet traveler. The outboard ends of the traveler are fixed to the aft cross beam about half way between the side of the main hull to the inside edge of the Ama (the name of the outside hulls on a Tri) on each cross beam. The traveler describes an arc around the stern and lands on the corresponding point on the opposite cross beam. I asked one of the crew about the loads on the mainsheet when the boat was fully loaded….About 15 tonnes he remarked.

A glimpse onto the flight deck

A glimpse onto the flight deck

The bulk of this working area is trampoline netting. There are two wheels of not particularly large diameter connected by, and operating through, large motorcycle chain, roughly from a 1000 cc Super bike I’d reckon.

Spindrift

Spindrift giving a good impression of a slumbering Giant or Sea Monster, just waiting to be unleashed

Inside this platform live both the crew waiting on benches under the spray cowlings. OF the 13 crew members to be sailing aboard, three do not stand watches leaving two watches of 5 hands apiece.  On the Flight Deck there are,  well as the primary winches with their grinder pedestals, sailing instruments, misc. winches, control lines and the steering wheels and a p air of large suitcase shaped heavy material canvas bags. Their purpose I was told is to stow the tails of the various lines. The mainsheet is EIGHT to ONE and one end of it probably goes to a long hydraulic piston in the boom, unless they have removed it in the chase to make the boat lighter for this record attempt. The traveler is atop the radius at the back of the work platform and so the traveler adjusts the angle to the wind and the mainsheet adjusts the twist.

This image may give an idea of the size of things on this boat. These are merely the traveler blocks and my starboard paw for reference.

This image may give an idea of the size of things on this boat. These are merely the traveler blocks and my starboard paw for reference.

On Wednesday I took some pictures from the causeway adjacent to the Shipyard, the best place to actually see “down” onto the boat albeit giving up 50 yards of proximity.

There were a few guys working on the boat and I captured this picture of one of the guys standing on the dock next to her. You have to really look for him, which is remarkable because he is a stand out dressed in team uniform black and is standing on a largely light colored dock. For another reference, the white boat on the other side of the dock is a 75 foot cruising boat

It took me a few minutes to find the image with the crew member standing on the dock, so small is he relative to the boat.

It took me a few minutes to find the image with the crew member standing on the dock, so small is he relative to the boat. The white boat is 75 feet LOA.

Alongside the reduction in the mast height & weight (and the sail track and sail weight) in other weight savings, Tim Carrie, the only non-French part of the team and in charge of the considerable logistics support this caper requires, rattled off a long list of things they have done:

Taken the engine out, one dagger board The one on the starboard side) removed and the hole plugged up, shortening the port one and reducing it’s weight by 40% plus the reduction in mast height and a few other modifications which escaped me.

Reflect if you will on sailing this boat. To average 33 knots, one is sailing at or over 40 knots basically all the time.  Next time you are bored grab a mate with a pick up truck, rig up some safety lines or similar mechanism in the back and have yer mate drive down an empty road on Sunday morning, at say 45-50 miles per hour with you hanging on while standing on the truck bed. To really get the effect, do it when in the midst of a downpour

Then do it for 3 days, with only 13 mates.

IF you were to be steering Spindrift at 40 knots, this is where you would be standing. The B&G meters are about 80 feet away

If you WERE to be steering Spindrift at 40 knots, this is where you would be standing. The B&G meters are about 80 feet away

What are the two things that these guys are doing that ANY sailor can do, regardless of their own EXPERIENCE, the passage to be undertaken or the boat aboard which they will undertake it?

PLANNING

AND

PREPARATION.

It is absolutely just not possible to take on an exercise of this magnitude without planning of the highest order and the finest mesh. The good news is there is nothing special about planning and preparation for going sailing it just needs to be done.

Code Zero Spinnakers

Posted on by

Some thoughts on sail design:

With particular attention “pointing” ability

Especially with respect to Code Zero sails

This essay is in direct response to a statement from another sailmaker to a customer that “a laminated material will point higher” compared to the heavy nylon I was proposing.This is an altogether a too broad a statement.

The type of fabric from which a sail is made is not at the top of the list when contemplating sail shape. Certainly building say a heavy jib of too light a material is not going to be effective but bear in mild also shape is only one aspect of a sail. Apart from “the shape” sails need to consider the following criteria, in no particular order.

Cost, durability, ease of handling, response to hard handling (aka tear strength) range of utility, (wind speed and angle), stowage issues are some of theses criteria.

A code zero is a unique sail in that in most cases it needs to rate like a spinnaker but to work like a genoa. That is it is intended to be used in light air when the boat wants to go up wind and for want ever reason, the “normal headsails” on the boat are not as effective as a “code zero” thus the response about pointing. Years ago such sails might have been referred to as cheater sails

The original code zeros were invented over 20 years ago for the Volvo Ocean Race. Due to the sail limitation rules and the lack of a normal overlapping genoas, Paul Cayard’s team fell upon the idea of having a sail that was designated a “spinnaker” but used as a headsail. They beefed up the boat to take the high loads generated by the tight luff that this sail needed. Fast forward to about 10-15 years ago and similar sails started making their appearances on the domestic recreational race course. Since they had to measure as a spinnaker, which is a girth* issue, all the girth was in the leech, rather like the roach on a mainsail. The other issue with such sails on furlers is the tremendous loads required to set up the luff of the sail so the sail would actually roll around the luff. The boats or the masts that Corinthian sailors sail were just not built for such loads.

About 8 years ago, Hood developed a version of this cheater headsail that was able to set and handled like a normal spinnaker, and was measured as one. This sail did not need a furler, tight luff rope and related costs, was made from Nylon yet could sail as close as 40 degrees apparent.

These sails fit the use profile of the non-professional sailor: They were inexpensive-nylon is cheaper than laminated materials, especially the more recent ones designated code zero materials, they were easy to handle-Just like a normal kite, took up a pretty small space, and considering the infrequence with which they are used this is appreciated by weekend racers. And a particularly appreciated aspect of nylon sails is their relative tear resistance compared to the very light film sails from which code zeros are built. Also nylon is much more resistance to damage from flex, read flogging than Mylar film, a detail if you are to be caught out in a squall somewhere.

With respect to the statement above, a review of design issues is in order.

The pointing ability of a sail is a function of at least two details: the draft of the sail and the entry angle. The draft is of course the fullness of the sail, technically the chord depth. And this depth changes vertically up the sail too. Consider for a moment a conventional spinnaker. If it is full, you can only head up so much in any kind of luffing match with it in pole-on-the-head-stay conditions, close reaching. This is why boats have a flatter reaching spinnaker. Same idea applies to the zero it is flatter again than a regular spinnaker, but fuller than a headsail.

The entry angle is a bit less obvious. This is the angle between the chord line and the angle of the very front couple of inches of the luff of the sail. A narrower angle here means the boat can point higher BUT it also requires that the boat be more accurately steered in order to keep in the groove. If the boat falls out of the groove as when a wave passes, the boat will slow down & the trim needs to be adjusted and the boat brought up to speed again. It is not uncommon for one-design boats to have different shaped headsails for use in flat, moderate of choppy waters. The choppier the waters the wider the angle of attack needs to be so the boat can be steered around waves with out stalling. Stalling is the “falling out of the groove” feeling.

With a sail like a code zero, intended to be used by most production cruiser racers generally in under ten knots true, a wider angle of attack is to be preferred. This is to accommodate the wide variety of conditions that such boats generally sail in.

The loads on a sail diminish dramatically as soon as the sheets are started even a small amount. For instance the load between a spinnaker trimmed hard enough to develop a crease between the tack and clew, as when trying to keep it full in really light air, diminishes quickly when the sail is eased to where the crease vanishes. That is why you may need someone to crank the sail to get it to that stage, but ease it a foot or so and the trimmer can trim by hand.

Going back to the sentence above about building a heavy weather jib from light fabrics, one enters the realm of properties of the fabrics in question: Nylon and code zero fabrics. The latter are a sandwich similar to composite boat building in that there are several layers and glue.

By far and away the vast majority by area of a code zero fabric is Mylar film. Bear in mind that the fabric has two sides, so the Mylar film is 50% of the total fabric in area. This film is half a mil thick. For comparison, a normal laminated sail might be .75 of a mil Mylar for a light air headsail for a 35 foot boat up to say 2 mil Mylar in sails on a bigger boat. It is pretty rare to get thicker film than that because such fabric becomes a real bear to handle.

Next in area is the other 50% of the sail fabric which is very thin deniers (small, tiny in fact yarns) woven polyester that is not shrunk. This is glued onto one side of the fabric.

Finally we get to the strong fibers. These fibers, called tows are glued in between the film and the taffeta. They are described by their denier. This is how thick they are, roughly like half inch line is thicker than quarter inch but thinker than five eighth. 50 denier is what light nylon sails are woven from, 1100 is a thick denier. Most fabrics operate in the 300-900 denier, as a broad statement. Reading the data from one of the major cloth suppliers in the US, their second to lightest material is made as follow:

Half a mil of film:

A tow (cloth speak for a “bundle” of fibers-Visually a tow will look like a thick piece of string) of 1140 denier aramid fiber, gold in color, set on half inch centers on the zero axis. The zero axis is parallel with the length of the roll.

There is a flat X shaped 750 denier tow of an aramid called Technora, this is black

There is a taffeta on the other side of the film.

There is a glue line holding the lot together.

To review

This material is 2.1 oz

This code zero fabric is close to two times the cost per yard than 1.5 oz Nylon.

It is about 30% more expensive per yard than grand prix nylon.

It is about half as stretchy on the zero axis as a comparable nylon

The film on this fabric is only half a mil-Not a strength consideration but a handling and durability question:

Durability is a factor in the sense of dragging the sail over life lines, across stuff on the deck, by the rigging turn buckles with cotter pins just starting to poke thru the electric tape, meat hooks on the halyards of the mast, and around down below. And as noted if caught out in building breeze and it spends time flogging, this (flexing) will degrade the film more than any overloading will do. At any rate most sailmakers to day will make the clew so the ring fails before the sails blows up.

This video is of a Hood Code Zero on a J-105. I was sailing this boat from Newport to Fishers Island alone. In this circumstance we are actually beam reaching, not going to go up wind. I have used this same sail in 25-30 knots true sailing at 90 apparent double handed from Block Island to Greenport in a race. We won because we had a sail we co old set that was right for the conditions.