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Old 25-09-2008, 07:19   #1
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Behind the mast furling

I come from an aviation background. It would seem to me that a lot of features on sailboats are reactions to various racing rules. If a cruiser did not give a flip about race-derived sail limits then maybe some things that we all accept as givens should be reevaluated. So here goes:
  • If one was to install behind-the-mast mainsail furling would the slot between the leading edge of the sail (the luff, for the cantankerous old pure sailors) and the mast itself act as a leading edge slot and increase the lift, (er, power) of the sail?
  • Since the furling sail would not have battens and a lot of roach and would be free flying, the boom could be lighter and longer on a sloop. Would that move the center of effort so far back that we would have to add a bowsprit to move the jib forward?

I realize that I am a heretic that should be burned at the stake for questioning the way it has always been done! Show me the error of my ways. Explain it so that even an airplane pilot can gain understanding of the mysteries of the sail.
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Old 25-09-2008, 08:46   #2
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Behind the mast add on for in mast furling is a cheap solution that adds nearly as many problems as it solves.

both behind mast and in mast do not prevent full length vertical battens, and these with a loose footed main will provide a reasonable sail shape.

boom will need to be just as strong as before as the kcicker is still a vital part of the sail shape, and thus a loose footed sail actually requires a stronger boom than a captive footed sail, where the stress is shared more evenly along the boom.

Behind mast (and to a lesser extent the in-mast) will naturally reduce the overall sail area, as you loose a bit under the clew. You can recover some of this by increasing the roach, but that shifts the effort higher up the sail, which combined with the extra weight of the behind mast unit, will have an impact on stability and solidity of the boat.

a vertical batten system makes a big difference to sail shape, but can increase the possibility of jams when reefing from 1st reef to second reef position (or equivalent). This can be avoided by always shacking out a reef before reefing further.

Most jams in these systems are caused by trying to cut a badly worn and baggy older sail down into something suitable for in-mast reeefing, or by ignoring the one or two simple requirements for use such as boom and kicker positions.

I had a behind mast system for several years and liked it for its simplicity of use, especially when singlehanded. However when Gludy was asking for advice, I recommended that he looked instead at in-boom systems, as a lot of the problems of the in-mast, are solved using this. But an in-boom is not really suitable for a boat with a low boom.

You have to weigh up the advantages and disadvantages of each.
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Old 25-09-2008, 09:00   #3
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Talbot

I was thinking of going to a behind the mast main with out battens. I pretty much single-hand my 46ft.cat. Because of her quick motion sometimes on seas. I would like to eliminate going to the mast to reef, and have a greater variety of reefing than just 3-4 points.

Soon I will be doing the Pacific, and would like to make it easier, and safer to reef. It's a long way all the way across.
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Old 25-09-2008, 09:17   #4
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I was thinking of going to a behind the mast main with out battens. I pretty much single-hand my 46ft.cat. Because of her quick motion sometimes on seas. I would like to eliminate going to the mast to reef, and have a greater variety of reefing than just 3-4 points.
Soon I will be doing the Pacific, and would like to make it easier, and safer to reef. It's a long way all the way across.
Strongly recommend you look at the leisurefurl in-boom system, or slightly cheaper, the profurl system. There was quite a long discussion on this on one of gludys threads, if the moderators have not removed it.
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Old 25-09-2008, 09:22   #5
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I looked at inboom furling, and it was an arm, and a leg expensive. I looked 2 years ago, but I will look again. Maybe cost has dropped? They wanted 15k with an electric winch to raise the main.
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Old 25-09-2008, 09:26   #6
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The fear of a jammed vertical roller furling main is to me very worrisome. At least when rolling the main on the boom you have the ability to get the thing down if the S### hits the fan.

But like almost everything else discussed here you have to be the one to judge the cost/benefit that is best for you.

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Talbot

I was thinking of going to a behind the mast main with out battens. I pretty much single-hand my 46ft.cat. Because of her quick motion sometimes on seas. I would like to eliminate going to the mast to reef, and have a greater variety of reefing than just 3-4 points.

Soon I will be doing the Pacific, and would like to make it easier, and safer to reef. It's a long way all the way across.
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Old 25-09-2008, 10:31   #7
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I cannot speak about such a large sail as my experience is of rather more economy scale boating. There was not a lot in it between a new mast, and a new boom when I looked. I would not consider an add on at all for a boat of your size.

If you dont need an electric winch to raise the existing main, why would you need one for the in-boom system? Granted it would remove a lot of the hassle out of raising the sale, and simplify the choice of who goes up the mast!
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Old 25-09-2008, 10:37   #8
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Have a look at the Facnor system from Charleston Spar, www.charlstonspar.com. It uses a tube up the back of the mast in which the sail rolls round a mandrel, just like in-mast, very neat and the best I have seen. You are right about gadgets filtering down from racing boats, the same as in car racing, and one of the worst things are battens in cruising sails. If you are worried about jamming or reefing have a proper furling sail made without battens and concave roach, you will have no problems after you become used to rolling it in and out.
My son in law is an airline pilot and canít stand the slowness and inefficiency of a cruising sailboat, where the idea is not to be pressed to time, but to travel safely and in maximum comfort.
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Old 25-09-2008, 11:37   #9
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The fear of a jammed vertical roller furling main is to me very worrisome. At least when rolling the main on the boom you have the ability to get the thing down if the S### hits the fan.

But like almost everything else discussed here you have to be the one to judge the cost/benefit that is best for you.
This, jamming, is my main concern, but as of yet I have not had any sort of problem with the headsails. People say I will lose effeciency, and I understand this. The previous owner averaged 8 knots crossing the Atlantic without pushing the boat.

I averaged 4 knots over 40000 miles on my previous boat. Losing 10% seems minute after that sail.....lolololol My gut feeling says stick with the slab reefing. After being throw from the previous boat while at the mast. My brain says roller the main.....lolololol
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Old 25-09-2008, 11:42   #10
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Head foil roller furling is pretty much bullet proof. The problem you have with the in mast furlers is clearance. Lots of people use them and love them but to me the potential for problem is there when you really don't want it.

The performance hit you take is caused by the hollow you must cut in the leech so it rolls up. I would imagine you have a substantial roach so you could loose half your sail area?
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Old 25-09-2008, 12:07   #11
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No roach, and I would be going with behind the mast. Not in the mast
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Old 25-09-2008, 12:15   #12
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No roach, and I would be going with behind the mast. Not in the mast
If that is your decision, I am sure you have good reasons for it, but I would not make the same decision. Proper inmast - possibly, but not an add-on unit.
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Old 25-09-2008, 13:14   #13
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I used to fly a Stinson 108-3 with wing slots only at the outboard portion of the wings. The slots allowed the plane to fly at higher angles of attack without the outboard tips stalling. Slots increase the coefficient of lift of the wing about 40%. Since sails are low speed airfoils I thought that slots would increase the coefficient of lift and make up some of the losses that the sail might suffer from the furling. In order to get the aerodynamic benefit the furling needs to leave a gap of several inches behind the mast.
As far as fouling the whole thing is identical to headsail furling and suffers some of the same disadvantages.
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Old 25-09-2008, 13:16   #14
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If that is your decision, I am sure you have good reasons for it, but I would not make the same decision. Proper inmast - possibly, but not an add-on unit.
Would you share your thinking with me? As for the reason no add-on.
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Old 25-09-2008, 13:31   #15
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A mast that has been designed for an in-mast system is not significantly heavier nor larger than a normal mast, as most of the differences are inside. Fur thermore it is designed from the start to be able to handle the loads impo sed by that system,

The behind mast system adds significant weight to the mast and adds that weight all the way up to the top. Thus adding to the loads on the rigging. The design is compromised by being added to the back of the mast - this can nearly double the side profile of the mast , and in a big blow would be of serious concern.

The behind mast bit reduces sail area by the size of that extrusion, plus the length under the foot of the sail to the clew. I wont make any percentage claims because it would only be a wag anyway.

The loose foot and design of the sail prohibits any ability to gather fresh water in extremis. (for example the profurl in boom has a spigot at the front of the boom to connect a hose for this purpose).

I Know the leisure furl is expensive, and at 45ft you are into the largest size boom from most of the in-boom makers other than superyacht specialists. I would be looking at prices from profurl, or working out how to introduce single line reefing controlled from the cockpit.
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