Tag Archives: sail performance

sail cloth, sail fibers, sail making

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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.

Cheers

Coop

 

Mast bend and mainsail shape

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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.

 

 

 

Mast rake Versus Mast bend

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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

 

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

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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

OR

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.

 

Full Length Battens: 2b. In mast furling

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A reader on LinkedIn posted a response-comment-observation regarding FLB and conventional battens  with respect to in-mast furling so I will add this essay as a small side bar. My apologies I do not have many pictures for this subject, so you will have to read it, not look at it…

The question posed by this fellow is this:

And then there is the roller furling main! New experience for me as I have always sailed a traditional main (with battens). Very difficult to get used to looking at my main with the foot not fixed to the boom. My sail does have battens but the one nearest the head had to be removed to allow for the sail to be completely furled within the mast. I have been told that battens are not really needed in the furling main but started showing up because there was a “demand” for them. i like to convenience, especially when single handling, but………..would appreciate comments.

First a bit of background/History:

Most of us know that the original in-mast furling was invented and brought to market by Ted Hood, sometime in maybe the early 1970’s. They were unique at the time, had the Hood Cache and were almost the default spar on a long list of various sized Little Harbor yachts and then later other yachts particularly bigger ones, up to 80 footers which were big then.

Compared to the current crop of in mast furling spars, the Hood spars were really easy to work with from a sailmaker’s perspective. Not the least because they were designed by a sailmaker rather than a mast maker. There are two primary reasons related to this ease: The cavity into which the sail rolled was large.  Second, the slot through which the sail passed was wide, perhaps an inch or more. Boat for boat both these items were larger than the same parts on spars today.

Between the time of the Hood Spars introduction and the early/mid 1980’s Hood was the 800 Lb Gorilla: There was Hood Sailmakers and Hood Yacht Systems with the latter incorporating the Sto-Away masts and later on an in-boom furling arrangement  for a time plus the Hood Sea Furl furler, another virtual monopoly-No Harken, Profurl, Schaefer, Facnor, Furlex. There were a couple of older makes of furling (not reefing) head stays, one by Hyde and another by Stearns but they were not designed for using the headsail reefed. There was a particular part of the Hood Sea Furl Systems that made this viable. Regardless, if you wanted an in mast furling spar you went to Ted.

But things change. Hood sailmakers was sold in 1986, which is when I went to work for the new owner but Ted kept Hood Yacht Systems and brought it with him from Marblehead/Little harbor to Melville in Portsmouth RI.

Over time other mast makers began copying the Hood Spar, but of course they needed to be among other things, cheaper than the original (Hood Spar) in order to get a foot in the door. Anyway we now fast forward to the 21’st. C. Hood Yacht Spars was sold to the UK distributor of Hood Spars who sold it to another UK spar company who eventually went broke. Hood Yacht SYSTEMS, largely the furler’s, remains in business based in Florida and is a division of POMPANETTE. Roughly parallel with this progression many spar makers who used to do production aluminum spars have switched over to carbon and so today there are three remaining heavy weights in the production aluminum spar (In–mast furling) business:

Z spars, Charleston Spars/SparCraft both French and Selden, Swedish.

And on the edges of the In-mast terrain there are, or used to be, a couple of products you can bolt on to the back of the existing spar and some folks have taken a normal headsail furler and attached that to their spar with custom parts.

With respect to the sentence in the fellows remarks above, on “demand”, sailmakers (and cloth guys too) are forever trying to do something that will set them apart from other sailmakers. Battens, full and leech, for in-mast furling sails is a classic example of this. I am pretty sure that a Hood Franchise in Sweden invented both the batten idea and the necessary mechanics and sail designs to make it all work. Hood in the US marketed them as Vertech Mainsails and promoted, as does every one, the idea of more roach as opposed to the standard battenless sto-main with leech hollow, like a headsail.

Very broadly speaking, as viewed from my perch at Hood Sails for 15 years, there has been since the 1980’s an increase in people coming to sailing who did not grow up with it and so have a different seamanship background than say my generation who was sailing from age naught. Thus people buying boats (as well as a lot of others) were attracted to the idea of doing everything from the cockpit, so the in-mast furler’s, are now more common again than for a while. Without doubt the ability to “get the sail out and be sailing in one minute” or variations on same are pitch’s that do not quite fill the air at boat shows but is close.

Remember though there are two primary differences between the present in-mast spars and the original Hood Spars and they are the internal diameter of the cavity-Where the sail rolls up and the width of the slot through which the sail enters and leaves this cavity.

For all sorts of reasons the newer masts are smaller on the inside and the slot is much narrower than a Hood spar. Since the customer has a specific boat with a specific mast sailmakers are obliged to come up with ways of making their sails fit what the owner has, at a price they can sell them for while making money and having them work with sufficient success that the owner can use it, maybe enjoy it and so may return for other sails.

So, to the sails:

There are three flavors of in-mast furling mainsails: No battens, partial battens and full length battens. The latter are inserted vertically into the sail from the foot. These battens are usually in sections so they can be connected in some way. The ones we used at Hood, screwed together with custom fabricated terminals. The length of the sections, at least in the US, is determined by the maximum length UPS will carry so they can be shipped economically compared to shipping”regular” of FLB by truck.

With regard to sails, we know that the corners of a sail are reinforced with layers of fabric, the so called corner patches. The bigger the sail the larger, in area, are the patches. They are also thicker-more layers of material laid into the corner. This latter issue has a direct impact on the process of getting the sail in and out of the spar. The short answer is that for the current range of production spars the patches need to be thinner than they should be. This has a direct impact on the life, the shape retention life, of a sail because the corners distribute the loads into the body of the sail, less distribution surface, more load.

This thickness issues plays out with battens too. Let me first mention a couple of points about battens. As a general rule a batten’s length ought to be long enough so that 1/3 is “outside” the straight line between head and clew and 2/3 are inside. So the “inner” 2/3 is holding the outer third in place. This gets to be more critical the larger the roach-Hence full length battens in the first place.

This batten length calculus is relatively easy to meet in a conventional mainsail. It becomes a bit trickier with an in-mast sail. This is because when the batten is vertical, the batten needs to be a lot longer overall, in order to meet the desired ratio of batten inside versus outside the straight line. When the batten is longer it needs to be stiffer to achieve the desired effect. Given a same material, say polyester fiberglass, a pretty common material for battens, then a stiffer batten is thicker than a batten doing the same job on a conventional sail which will be shorter.

Still with me?

Then there is the batten pocket: It adds thickness to the sail. Typically the batten pocket is a couple of layers of material of the same weight as the sail’s cloth.  The pocket has a pleat in it so the there is volume inside the pocket to accept the batten and there is some kind of mechanism to keep the batten in the sail. Velcro is a favorite these days as are folded over flaps with lashings as well. This construction is often as thick, or thicker, than the corners AND it is on the leech so all the battens, all four or five of them must be able to roll inside the mast….

All of the above is of course at reasonable hazard of chafe. The pockets where they go in and out of the slot. The sail skin itself is liable to chafe when being rolled in or out in any condition apart from head to wind. The chafe issue applies to all flavors of in-mast furling sails: plain or with battens. On the full battens, where the connections are, they are a tad wider than the neighboring batten material so when the sail is passing the edges of the slot, there is chafe at each of the perhaps dozen or so connections.

Re-read the remark in the original question above where the owner had to have the top batten removed so the sail would get into the spar. This means I hope that the attending sailmaker had to re-fair the leech too otherwise the “local roach” at that batten would either wave around in the wind or be pulled into a curl by the leech line. Any way I digress…

Now connect the particulars of a sail so designed and built with the newer masts with smaller cavities and narrow slots. The end result is that sailmakers need to make the sails “thinner” in order to fit into the spar. Plus the batten’s are thicker and there is added thickness for the batten pocket assembly.On more than one occasion a prospect was unable to purchase a battened in-mast sail for his boat, at least from us, because when I looked into the particulars of the mast he had and the boat (so I could spec. the sail appropriately) comparing the width of the slot to the thickness of the battens and related structure, there was barely enough wiggle room and this was without the sail skin or the pockets.  I can recall one spar I was looking at, from one of three makers cited above and the slot was quoted as being only 16 mm wide, perhaps 9/16″. The battens, the pocket and sail was close to 12 or 13 mm.

The same problems or issues occur too with full length vertical battens only there is the additional complication of having to install the battens in the sail with the sail fully unrolled. Think about this for a minute…Would you willingly unroll (or hoist) your mainsail at the dock in the marina and let it flap around for the time it took to get the battens in? Perhaps not. This drill is required though with the full length battens in order to get the batten (s) into the sail. For instance on a Little Harbor 46 footer with in fact a Hood Spar, so it was actually pretty easy to operate the sail once the battens were in the sail, it would take me 45 minutes to an hour to assemble the battens get the sail into the spar and the battens into the sail. And it could only be done either on a calm morning or with only a light air wafting across the boat from the direction in which the bow was pointed.

All of this would make one think that the in mast furling system is not possible to manufacture and sell which is patented not the case. Rather I am presenting some of the issues that go on behind the curtain. For the sail these are:

Thinner or lighter base material, smaller patching both in area and in total weight in the patch and thinner battens and/ or pockets.

So, I hope this has offered some food for thought as well as a bit of a glance around “behind the curtain” into what goes on in the minds of, and discussions of, sail makers, their reps and designers.

I’ll get back to “regular” full length battens-soon.