Sail Re-tuning Kits - Update

[Pete1177]

Hi All,

Following on from Chris Blackburn's post in this forum (poor pointing/speed issues upwind) it's evident now that his issues arise from poor sail shape. It is well known that sails degrade with age for two main reasons - 1. The polyester braided bolt rope shrinks in proportion to how many times the rope is stretched (uphauled) and, 2. the sail cloth stretches so that the sail becomes 'baggy'. This has nothing to do with sail storage as such, but storing your sail in the boat over the season won't help. The bolt rope shrinkage appears to be the dominant mechanism as there doesn't appear to be much degradation in sail shape fore and aft, at least on my sails.

As the bolt rope shortens then it causes the sail draft to move aft - a similar mechanism to the draft moving forward as you use Cunningham. As the draft has moved aft then the power output of the sail is reduced. Also the luff tube starts to develop wrinkles. This can cause difficulty in raising and lowering the sail especially at the sail feeder. Worst case, you might find the luff tube catching on the sail feeder potentially tearing. At this point you need a new sail.

I have managed to obtain (courtesy of Nick Whiles at Girton) a brand new, unused Jeckells sail - the last of the 'old cloth' white sails manufactured in August 2017. I have used this as a 'reference' sail to measure dimensions and compare with my 3 Jeckells sails.

I am waiting for the 'design spec' of the sail from Hartley's via Gavin, but in the meantime I thought I would take some measurements.

Bolt rope shrinkage is clearly evident on my own sails, as is some stretch in the laminate. It seems that stretch is predominantly vertically with little dimensional change laterally across the sail.

The effect is a large amount of creasing at the luff and general 'bagginess' between the battens. I have mitigated the aft-wards draft by using tapered battens in all my sails. The bolt rope shrinkage needs to be fixed, so I intend to correct this soon and will publish a DIY guide on how to restore your old Jeckells sail sometime soon.

Sail #1: Jeckells 'old cloth' originally supplied with SN1177 (around 2016). Shrinkage at the luff around 130mm. This sail is my main 'club' sail and is used 80% of the time. I would consider this sail as nearing the end of it's life. I would never use it in a Championship or open event.

Sail #2: Jeckells 'old cloth' bought as a Championship sail for my old boat 1068 in 2015 and retained (Sail ID 689945). I use this sail occasionally at opens and the odd club event. It has been used probably about 30 times. Bolt rope shrinkage is about 60mm.

Sail #3: Jeckells 'new cloth' which is black mylar (sail ID 694154) purchased early 2018 when they first became available at £500. This has the same 'cut' as the old cloth sail so the size should be identical.I use this sail only at opens and events. Probably used only about 12 times. Bolt rope shrinkage is 100mm.

Early measurements appear to show that Sail #3 (newer black cloth) suffers more degradation than the older cloth. However this is a sample of just one sail. I am surprised to see this much shrinkage on this sail, especially with respect to the comments made in 2018 after the new sail cloth was introduced:

"The new cloth was selected as it was expected to have a longer lifespan than the previous cloth - this was a request of the Association given the increase in cost. Whilst the fabric is a similar "weight" the reinforced pattern should result in increased life expectancy."

So I'm going to correct the bolt rope problem on all 3 sails and with the tapered battens I should be able to re-tune sail power. After all, I only need 2% to gain 1 minute in a race. In a Championship event this would be enough to gain 20 places, all being equal.

Pete
SN1177

[Pete1177]

*** Update ***

I have taken my oldest Jeckells sail (#1) and done the repair. It took about 30 minutes in total and the lay of the sail looks much better. The measurements against the reference sail (an unused Jeckells sail) look spot on and I'll use this sail in racing this coming Sunday. Had it not been for the repair I think I would have ditched this sail, but now I think it's good for another couple of seasons. With the tapered battens forcing the correct draft, I'm expecting it to be as good as a new sail.

Here are the before and after pictures, both with battens installed. You can see the 'baggyness' in the sail in the 'before' picture as the excess cloth is bending the battens. The corrected sail shows much less excess baggyness so its draft will be spot on. There is no downhaul tension in these pictures.

Before Correction

1177 Old Before_small.jpg (121.62 KiB) Viewed 49007 times

After Correction

1177 Old Corrected_small.jpg (127.9 KiB) Viewed 49007 times

The corrected sail now is re-tuned as good as a new sail so I have saved myself £900 for a new sail. I left a tail of rope at the tack as I didn't want to let the bolt rope slide up the luff without any means of pulling it back down if I needed to.

The black mark shows the position now of the end of the original bolt rope - a 130mm correction.

IMG_0894_small.jpg (25.98 KiB) Viewed 49002 times

This is a simple repair with the right tools. I'll write a short article on how to do it in a future article once I've evaluated how this sail performs.

Pete
SN1177

[Steve1142]

Hi Pete
I checked my sail at the weekend and there is no spare bolt rope at all.
Will I still be able to attempt this repair?
Cheers
Steve 1142

[Pete1177]

Hi Steve,

Yes you can. It does irritate me that Jeckells crop the bolt rope so you don't have any spare. I did have a tail on 1068 (the one in Chris Blackburn's post as he now owns my old boat) but that sail only had about 70mm from memory - so it wouldn't be enough anyway.

I used a spare bit of braided polyester rope (say 6mm). It's not a bolt rope as such but standard braid with a filler core. You need to attach it (sew) to the bolt rope. You could get away with just letting the bolt rope slide up the luff tube then re-stitch (others have done this), but in my opinion I wouldn't want any sail luff without any filler as it might catch on the sail feeder and rip.

However. you do need the calibration measurements to find out how bad your sail is and you won't know how far to let the bolt rope go up the luff.

I'll put all this in an article which I'll try and write this week.

*** 14/09/2021 *** I've got 20m of bolt rope on order so I'll see if replacing the complete bolt rope is a feasible option, at the same time leaving a 150mm tail to cater for future shrinkage.

Pete

[Pete1177]

Following on from the quick sail repair, I have changed out the bolt rope in my oldest sail. This involves unpicking the stitching at the head and tack of the sail. The bolt rope I managed to get is a looser braid, quite stretchy, and not the original braid as sewn into the sail by Jeckells. I have asked Jeckells for a quote for the supply of the correct bolt rope.

Interestingly, if you look at the bolt rope in Chris Blackburn's post, you'll see it's the 3 braid polyester. I have obtained the same type as the replacement. My old sail uses a much tighter 12 braid polyester - so at some point between 2014 and 2016 Jeckells changed the specification to a different bolt rope. This may well have different shrink characteristics over time. This 12 strand braid has shrunk by 130mm over a 5m length. Although this is only 2.5%, which might not seem much, it is still very noticeable on the shape of the sail.

I managed to swap out the bolt rope this morning - not a particularly difficult job. The whole thing took about 45 minutes. I left 200mm of bolt rope as a bit of spare tail, so that if it shrinks in the future I can re-tune the sail back.

Below is the sail after completing the job. The sail looks good but it's clear that the sail cloth has relaxed a bit as the luff measurement is 20mm longer than the reference measurements. I did put some pre-stretch in the bolt rope prior to stitching. Of course the new bolt rope will quickly shrink as it settles in, so I don't see the extra length as a problem.

The picture shows the sail with battens installed. I've installed the lower 4 battens as tapered battens to help force a better wingfoil shape in the 'looser', slightly wrinkled laminate - the top batten is a standard untapered batten.

1177 (Old sail) with new Bolt Rope.jpg (108.29 KiB) Viewed 48930 times

Head stitching detail

IMG_0899.jpg (95.32 KiB) Viewed 48933 times

I'm going to test this sail tomorrow in 2 club races at Bowmoor (light winds forecast) and report back on how it performs.

Pete
SN1177

[Pete1177]

Test result:

I put the old corrected sail on for racing yesterday. Race 1 was very light and shifty winds, drifting at times - so not very decent winds for testing.

Race 2 in the afternoon gave us a decent breeze F1 to F2 at times. It was noticeable that my upwind speed had improved and I was faster than the one other Supernova on the water (sailed by a lighter helm of 67kgs - I am 78kgs), winning the race by a margin of 30 seconds or so. Downwind, he was marginally faster which maybe due to the lighter helm weight.

I did notice that the rig needed much less kicker than I used before (no other rig changes were made), although I did have to concentrate hard on the shifts and playing the kicker to get the right twist at the top of the sail in the variable winds. I think this is due to the sail camber. Older sails are much fuller in the camber. Also with more kicker, camber is increased, so maybe less kicker is needed in the corrected sail as the camber has been reduced to nearer optimum.

I am thinking of developing a kit so that those with older sails can correct them. This will contain detailed instructions as well as all the materials needed (bolt rope, thread, tools etc) for a DIY approach. A possible price point would be £20 to do 1 sail, with options for 2, 3 or 4 sails which would contain additional bolt rope.

Please let me know if you would be interested in this so that I can gauge if this is worth doing. If there's enough demand I will set to it.

Pete
SN1177

[Phil1187]

Hi Pete,
Very interesting article. One point - I'm not sure how you measure the amount of stretch. I would certainly be interested in the kit you are proposing.

[Steve1142]

Hi Pete

I would be interested in a kit.

Steve 1142

[kts]

Hi Pete,
I would be interested too.

Thanks
Karen 1131

[Pete1177]

I have contacted Jeckells regarding the bolt rope - apparently it is 3 ply polyester, so I'm not sure why I had 12 ply in my 2016 sail. While I was about it, I asked whether it was possible to buy sails directly from them. Unfortunately they can only be purchased from Hartleys, currently at £900 each.

So it makes a lot of economic sense to try and improve your existing sails. Now that I have the specification, I will order 200m of bolt rope to make up some service kits.

Here is the quick method to check your sails:

*** UPDATE 16/11/23 *** I deleted the following section as detailed instructions are now given with my sail tuning kits, which also contains the reference measurements. PM me if you are interested in a repair kit (£26.50 incl. P&P).

Measure as follows: +++DELETED SECTION+++

With a short bolt rope the luff won't match the luff curve of the mast, which is why you get creases in the luff. In correcting the sail, you need to match the curve of your sail to your particular mast. There is a particular way to do this to get accurate tuning which I will describe by way of instructions in my service kit.

I now have 20 meters of bolt rope as used by Jeckells on order. For the kits, I will order 200 meters (minimum quantity) at a much cheaper price elsewhere which will be enough for 40 sails. I will work out a service kit price in the next couple of weeks.

PS: I spent some of this week changing all my control lines to single colour (looks better) with slack take up blocks (Matt Biggs' rigging) and re-strung the bridle in 2.5mm Dyneema D12 to be fully adjustable with a range between 450 and 550mm. The nominal setting is 520mm on a Mark 2. The other change I made is to have it self-centering so that port and starboard are always the same, with one adjuster.

Pete
SN1177

[MarkR]

Pete,
Thanks for that, it's really useful. I got out to measure my sails this evening. I have an old (I think really old) Jeckells and an older tatty white sail I assume is a Banks.
The old Jeckells is 183mm short of the reference and the Banks 191mm short of the reference, both really big differences.
I always thought the Jeckells (which I use) was short, as the bottom of the sail sits well above the boom when first hoisted. Before sailing I have been stretching it by pulling down really hard on the downhaul for a few minutes, then it seems to fit better the length of the mast from the head to the boom. Can you think of any disadvantages to that?
It will certainly be interesting to add the missing 183mm bolt rope and see what difference it makes.
I suspect the long term answer is that I have to spend some money - and sail better of course!
At £900 per sail it would be great if Jeckells could find a kind of rope which maintains the dimensions better.
Mark

[Pete1177]

Mark,

I don't think pulling on the Cunningham hard will make any difference. The improvement will be temporary and the luff will re-tension fairly soon after. It might make the problem worse as the bolt rope shrinkage is a function of how often the rope is tensioned and relaxed, and its' diameter. Pulling on the Cunningham just increases the chances.

The bolt rope needs to have some elasticity. I think the shrinkage is down to the braided nature (a bit like Dyneema that shrinks under continual loading and unloading - the smaller diameters are worse). You could increase the diameter of the bolt rope but then it wouldn't fit the luff tube.

What we could do with sails made that have an extra 200mm of tail at the tack. Then it would be a relatively simple matter to rectify. If I was paying £900 for a sail then I would demand this.

Pete
SN1177

[Pete1177]

Here's an example taken from this year's inland championships at the windward mark.

SUPERS1.jpg (47.92 KiB) Viewed 48776 times

This isn't the front of the fleet. The two leading boats have rounded the mark onto a reach. The luff of both boats shows some creasing which might be too much kicker. Maybe they left the kicker on from the beat. SN1125 has a poor sail shape - the luff telltales are streaming nicely so no wind shadowing going on. SN1234 has a lot of luff creasing - you can see the large crescent-shaped crease. The wind has stalled in the bottom third of the sail as the luff telltale has dropped. The helm is sitting on port but the sail shape indicates starboard tack - maybe he just tacked in the zone on port (!!!) and hasn't popped the battens yet! The last boat coming into picture also has a lot of luff creases especially in the lower half of the sail.

Pete
SN1177

[MarkR]

Pete,

Great, many thanks.
Please put me down for the bolt rope fixing kit if you get enough takers.

Mark

[MatthewS]

I'd be up for a kit too! Thanks