In mast furling mains - the good, bad and ugly

Kiwi Clipper

Member
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57
"Naturally you will be able to learn to optimize your boat, whith it's own characteristics." True, but maybe not so true. Especially to weather a 35 foot cruising boat (30'wl) being sailed to its optimum might sail lets say at anywhere from 27-35 degrees into the wind, apparent and maybe achieve 6.5 knots speed. To weather a roller furling main can greatly reduce that potential because it's not possible to shape the sail to get that performance. The guy ends up losing interest because he can't make his boat go.

 

Alaris

Super Anarchist
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695
Annapolis
If you get a furling main it will not be possible to learn to optimize boat and sail performance because the vertical battens will create bumps that interfere with laminar flow of air over the lee side of the sail.
The modern vertical batten sails are built with thin battens between the layers of the sail to reduce exactly this effect.
 

Cruisin Loser

Super Anarchist
2. Chafe going in and out of the slot. There's a lot of drag through these slots. The batten pockets stand proud of the rest of the leech, and will take the brunt of the abuse.
We treated our main with Sailcote and had teflon tape on both edges of the mainmast slot. Never had a problem until our last Bermuda race with her when some highly edumacated racing sailors were playing with it while I was off watch. Someone got me up and I 'splained it again to the guys with multiple, advanced science degrees and fancy sailing CVs.
 

accnick

Super Anarchist
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2,559
The modern vertical batten sails are built with thin battens between the layers of the sail to reduce exactly this effect.
Having sailed offshore quite a bit on an Oyster 53 with this vertical batten arrangement, they do work, to some extent. You can definitely build a better main with these than without them, provided the sailmaker knows what he/she is doing.

It also helps to have the sailmaker show you how to get the best out of an in-mast reefed main, as trimming it properly is not necessarily intuitive compared to a conventional main.

Gary LeDuc of Quantum built the one on the Oyster, and once we understood how to trim it properly, it proved to be a much better sail than I thought it would be when first stepping onto the boat.
 

slug zitski

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If you must drop a battened mainsail for common maintence like tell tales , or a leech line your are tangling with a monster
it can take days for the right wind condition that allow hoisting .

avoid these batten monsters
 
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Tylo

Member
208
117
Sweden
Vertical battens are great if your sailmaker has experience with them.

In my experience the downsides are that the angle the battens are furled at is critical which means they must be a) properly installed on the sail and b) be furled properly and the same way every time. As an example, I've heard of some mast-furling boats having issues with their vertical battens if the drag/load on the outhaul wasn't kept under control while furling, since it could cause the bottom of the sail to furl tighter than the top meaning the battens were no longer aligned with the mandrel in the mast.

My experience is that there is usually a good amount of room inside the mast for the battens, it's the slot that may cause some issues since sail+batten pocket+batten can create quite a thick section of sail to pull in and out of the slot. Make sure your sailmaker measures this carefully.

With regards to the type of batten I would highly recommend using stiff rectangular battens as opposed to the run-of-the-mill, cheaper, round pultruded battens which seem to feature on most cheaper in-mast furling mains. The round battens don't resist compression forces nearly as well and just "S" in the batten pocket, causing the roach to collapse and the sail to look awful. Normally you could upsize the round batten to compensate for this but in the case of in-mast furlers that would cause issues with the aforementioned slot in the mast. RBS and Bluestreak are good examples of high quality battens depending on where you are in the world.

Vertical battens means you can get away from a hollow/concave roach which in turn gives you a lot more sail area (like 15-20% more depending on the sail design and batten layout) in a place where it matters a lot (high up) and a much more aerodynamically efficient sail. These things greatly benefit the light air performance of the sail.

That being said, many long-distance cruisers swear by non-battened furling mains for their simplicity and reliability. They appreciate having one less thing that could go wrong and aren't too worried about losing the sail area mentioned above.
 

slug zitski

Super Anarchist
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Vertical battens are great if your sailmaker has experience with them.

In my experience the downsides are that the angle the battens are furled at is critical which means they must be a) properly installed on the sail and b) be furled properly and the same way every time. As an example, I've heard of some mast-furling boats having issues with their vertical battens if the drag/load on the outhaul wasn't kept under control while furling, since it could cause the bottom of the sail to furl tighter than the top meaning the battens were no longer aligned with the mandrel in the mast.

My experience is that there is usually a good amount of room inside the mast for the battens, it's the slot that may cause some issues since sail+batten pocket+batten can create quite a thick section of sail to pull in and out of the slot. Make sure your sailmaker measures this carefully.

With regards to the type of batten I would highly recommend using stiff rectangular battens as opposed to the run-of-the-mill, cheaper, round pultruded battens which seem to feature on most cheaper in-mast furling mains. The round battens don't resist compression forces nearly as well and just "S" in the batten pocket, causing the roach to collapse and the sail to look awful. Normally you could upsize the round batten to compensate for this but in the case of in-mast furlers that would cause issues with the aforementioned slot in the mast. RBS and Bluestreak are good examples of high quality battens depending on where you are in the world.

Vertical battens means you can get away from a hollow/concave roach which in turn gives you a lot more sail area (like 15-20% more depending on the sail design and batten layout) in a place where it matters a lot (high up) and a much more aerodynamically efficient sail. These things greatly benefit the light air performance of the sail.

That being said, many long-distance cruisers swear by non-battened furling mains for their simplicity and reliability. They appreciate having one less thing that could go wrong and aren't too worried about losing the sail area mentioned above.
In sailing there is the tortoise and the hare

the performance difference between full battens and no battens is small…reliability and ease of use are everything

the tortoise always wins
 

slug zitski

Super Anarchist
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Sailmakers…salesman..gone wild with the clients money….

F57C5B63-5C10-4C07-9F44-37EDFCE1628B.png
 

kinardly

Super Anarchist
Think I’ll stick with a flaking system, Dutchman or lazy jacks. Boat I’ve offered on has the latter, last boat had the former. They all have compromises, just have to pick my personal poison.
 

Panoramix

Super Anarchist
Roach is highly over-rated. Open up the wallet and spring for a fresh joint.
On a well cut mainsail, it lets you manage power by just modulating sheet tension to twist/untwist the sail.
The effect is not so important on a triangular main. I am lust talking of main with oreefing systems, not too sure if that applies to furling mains which seem very hard to trim judging by the ugly sail shapes often seen!
 

longy

Overlord of Anarchy
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San Diego
A in-mast mainsail has the same trimming techniques as a 'normal' mainsail. Results vary as most in mast mainsails are cheap, blown out bags.
 

Bagheera

Member
190
297
Alaska
Based on a lot of offshore miles on a lot of differrent kind of boats as well as a few years of working as a sailmaker/sail designer for North. I'd prefer the newer in-boom furling mains over in-mast furling any day of the week.

The older in-boom furling systems certainly had their issues, but in the modern hi-end systems they have been pretty much all resolved. The pro's for inboom over in-mast are easier sail handling, in case of a jam your sail can always come down, no extra weight aloft, lower cost, installing and removing sail can be done in pretty much any weather, sail shape is much nicer and last but not least, there is less wear on the mainsail.
 

slug zitski

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Based on a lot of offshore miles on a lot of differrent kind of boats as well as a few years of working as a sailmaker/sail designer for North. I'd prefer the newer in-boom furling mains over in-mast furling any day of the week.

The older in-boom furling systems certainly had their issues, but in the modern hi-end systems they have been pretty much all resolved. The pro's for inboom over in-mast are easier sail handling, in case of a jam your sail can always come down, no extra weight aloft, lower cost, installing and removing sail can be done in pretty much any weather, sail shape is much nicer and last but not least, there is less wear on the mainsail.
Luff tape And Full battens are the issue


batten compression erodes the luff and tape ..it could happen in one day if the wind goes soft and the sea state cause the sail to start talking

not good for offshore work .

and few small sail lofts have the floor space to attach a new luff tape

I once had to bring the mainsail to a grassy field so that the sail could be pulled over a machine

inshore day sailing or racer cruisers stuff is ok

for inshore stuff the defect is that the sail is rolled onto the boom mandrel …when the sail gets soaked it’s very hard for this horizontal roll of sail to dry out …mold, mildew

looks bad fast

6C865B75-2B75-4A15-B575-A25A3FEB9DBA.png
 

Bagheera

Member
190
297
Alaska
batten compression erodes the luff and tape ..it could happen in one day if the wind goes soft and the sea state cause the sail to start talking

not good for offshore work .
Than they used the wrong luff tape and batten ends. The last boat that I sailed on with in-boom furling had around 35.000 miles on the main. Mostly in the North Atlantic including a winter crossing. It has never been off the boom during those miles.

I am fully aware of the issues that you mention, but it is almost always due to poor workmanship or wrong choice of materials by the sailmaker. That is no different than excessive wear on the batten ends and batten joints in an in-mast furling system.
 

slug zitski

Super Anarchist
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Than they used the wrong luff tape and batten ends. The last boat that I sailed on with in-boom furling had around 35.000 miles on the main. Mostly in the North Atlantic including a winter crossing. It has never been off the boom during those miles.

I am fully aware of the issues that you mention, but it is almost always due to poor workmanship or wrong choice of materials by the sailmaker. That is no different than excessive wear on the batten ends and batten joints in an in-mast furling system.
What ever you say

I’ve been sailing with those booms for 25 years

the fIrst detail to go is the luff tape stitching in the vicinity of the batten end

I’ve spent hours in a bosuns chair restricting hoisted sail luffs ..very tedious and you need a flat calm day

on the last boat we had an automatic hoist counter so that the sailmaker could be alerted to…restitch time

another thing to consider is the mandrel loading when you are deep. Reefed …kind like having the mainsheet attach to the middle of the boom as opposed to the end …flex and leech chafe
 


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