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Old 11-10-2010, 07:14 AM   #1
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Hi,

we are shopping for a new mainsail and we want to try an extra large roach that would extend over the backstay to beef up our sail area and also to get all those interesting perks that seem to come with the extra roach. Our main source of information about these sails comes from the Cruising Encyclopedia by Dashews.

Do you have such a sail and if so what are your experiences, good or bad? Can you offer any tips before we have it made?

Our boat is 31', 4.2 tonnes displacement, original mainsail little over 20m2.

The basic idea is:

- Dacron 8oz

- Full battens and loose foot (sic)

- Three reefs

- 1st reef allows tacking without hitting the backstay

UK Hasley in Hong Kong seems like the right choice in SE Asia.

Many thanks for any comments

Petr
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Old 11-10-2010, 10:46 AM   #2
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Hello Petr,

You haven't really told us why you want to do this? How will you stop the main fouling the backstay when you come about?

Have you spoken to Neil Pryde or Lee Sails? I have a large fully battened main on a catamaran - it cost an arm and 2 legs just for the hardware.

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Old 11-10-2010, 11:27 AM   #3
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Richard,

main reason is to get more sail area (sorry I'm not a native English speaker, I thought that "beef up our sail area" means exactly that).

Also lacking any personal experience with such a sail, I can only repeat what I've read (and heard from an owner of such a sail on a monohull):

- backstay can be covered by something like the spiral eletrical wrap or something similar

- the spots on the battens that overlap the backstay are reinforced

- S. Dashew specifically mentions that the sail actually clears the backstay in breeze, softer battens help this

- in light air, one swings the boom faster to achieve the same effect

- naturally all the above mentioned only helps a bit, the sail will frequently hit the backstay

- 1st reef will effectively be 100% (or near that) of the original sail area so when frequent tacking is expected, we reef down

The rough quote that we got from UK seems reasonable, after all we have a small boat and if the sails pushes us faster and we heel less, it should be worth it.

Is Neal Pride or Lee Sails better than UK? Basically we are thinking about UK mostly because we already have a sail from them.

Many thanks
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Old 11-11-2010, 12:09 AM   #4
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Quote:
Originally Posted by klubko View Post

- naturally all the above mentioned only helps a bit, the sail will frequently hit the backstay

- 1st reef will effectively be 100% (or near that) of the original sail area so when frequent tacking is expected, we reef down

The rough quote that we got from UK seems reasonable, after all we have a small boat and if the sails pushes us faster and we heel less, it should be worth it.

Is Neal Pride or Lee Sails better than UK? Basically we are thinking about UK mostly because we already have a sail from them.

Many thanks
Hi Petr,

The Hallberg-Rassy 31 is recognised as a very good sail boat, with a hull speed of around 7 knots. Does yours have a backstay that is adjusted with a 4 or 5 part tackle?

The idea of replacing the existing sail with a fully battened sail with an extra large roach that would foul the backstay frequently, needs very careful consideration. Nothing wrong with a fully battened sail that is designed to fit within the triangle formed by the backstay/mast/boom - Except that in addition to the battens, the sail itself requires additional reinforcement, Roller Bearing Slides, it also may be necessary to replace the Mast-track. If the new main has a significant increase in size compared to the original then the forestay, shrouds and spreaders may also need "beefing-up" (if the rigging is already 20 years old - it should be surveyed by a rigger).

If Quote "the 1st reef will effectively be 100% (or near that) of the original sail area" then surely this first reef will do nothing to de-power the main's effect on heeling?

Sanders Sails have made fully battened mains for the Hallberg-Rassy 31 - here is their website C L I C K It might be worthwhile contacting them.

I mentioned Neil Pryde 1) because he is based in Hong Kong and 2) because he has vast experience in designing and making fully battened mains for his own boat "Hi-Fidelity"
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Old 11-11-2010, 12:36 AM   #5
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Many thanks for your commetns.

Ours is 1974 Monsun, not the new 31. The backstay naturally has an adjuster. The rigging has been surveyed by us. It showed signs of aging, cracked and bent swages, rot in the swadges, being probably 15 year old (no clear info, the first owner passed away, and the intermediate owner having no clue at all) so we replaced it last year with 7mm (instead of the old 6mm).

The sail certainly needs reinforcement and extra protection, viz the list I've mentioned.

There will be batten slides for sure. The question of roller bearing cars came up, but other sources suggest that for sail of our size, it probably won't be necessary. I will leave this to the sailmaker and decide accordingly.

As for the heeling: this might sound rather unintuitive, but the experts say that the big roach, i.e. more sail are in the upper portion of the sail in fact reduced heeling. The reasoning seems correct and particularly the experience of users seems like a good evidence that this is indeed a case. Again, I have no personal experience with this.

Where have you found that the Sanders made such a sail for HR 31 (still you probably mean the new model, right?). I couldn't find anything on the website.

Thanks for pointing out Neil Pryde. I will ask them for a quote and consult. I haven't realized (well, forgot) they are in HK (as well as in Taiwan, actually).
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Old 11-11-2010, 02:30 AM   #6
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Petr,

You boat (http://www.hallberg-rassy.com/monsun/monsun.shtml) is a lovely design.

Assume you are doing this for light air performance? If so, have you just considered having a nylon light air mainsail designed and sewn up for your boat instead? The concept being that you drop the main onto the boom and run up your light air main (loose footed) when needed. When the winds come up, easily stow away the light sail and bring back up your main.

When I look at the design, there appears to be room for a longer boom (more sail in the foot, which is more powerful, btw) but any roach up high will certainly give a bit o interference. You also don't have a gallows with that boat, thus, how will you deal with the topping lift?

Finally, if you're really interested in a lot of roach, than you should be properly set up for it (IMHO) with running backstays on each side of the boat and nix the fixed backstay. That is just my opinion but it seems the right thing to do. If you cannot manage runners then perhaps other options besides excessive roach would be better.

Good luck!
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Old 11-11-2010, 02:47 AM   #7
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Quote:
Originally Posted by klubko View Post

As for the heeling: but the experts say that the big roach, i.e. more sail are in the upper portion of the sail in fact reduced heeling.
Puzzled by the contention that the 'experts, claim for reducing heel by having a "large roach"

The standard method of reducing excessive heel on a monohull is by easing the mainsheet combined with adjusting the vang (kicker) or moving the mainsheet traveller.

Having a large roach in the upper section of a size that fouls the backstay - without increasing ballast or weight of the counter balancing keel - will allow the boat to actually heel more than is safe.

One can be sure that the original sail plan of the Hallberg-Rassy 31 Monson was designed so as to take in the size/shape/weight of the counter balancing keel and other ballast. The 2 forces must be complementary
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Old 11-11-2010, 03:15 AM   #8
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Richard,

I can be only citing "the experts" I don't want to toss big names around here to support my argument (in fact, it's not my argument at all, it's theirs, I am only looking for fist hand experience with such a sail on monohulls), but this is what I've learned from Cruising Encyclopedia by S. Dashew (who backs his own experiments done together with D. Neri by John Letcher) and in similar words by a cruiser we've met in Malaysia who has such a sail and claims to be aeronautical engineer:

Quote:

In six cases I’ve been directly involved with, hollow-leech mainsails have been replaced with full-batten conventionally roached sails. The 10-percent increase in sail area has been, as expected, beneficial.

But more surprising have been the other results: significantly less heel while going faster, with reduced weather helm. Counterintuitive as the preceding statement may seem, there is sound basis in theory.

When I asked John Letcher, a highly experienced aero/hydrodynamicist about our observed results, he wasn’t at all surprised. “Induced drag is inversely proportional to span (luff length) squared, divided by sail area. The closer you can get to an elliptical tip shape, the better off you’re going to be.”

And of course, what we’d observed with the added roach area was an effective step toward an elliptical tip shape. I asked John just how much better the drag might be. “The difference between a sail built to IOR maximum dimensions and a hollow-leech sail could be as much as 40 percent,” he told me. This is even more important on a cruising boat, with its relatively inefficient (compared to a racing boat) hull and fins. Peter Schwenn at Design Systems added that “the extra area, up high, works better because the wind is stronger aloft. And even though the center of effort in the sail is higher and there’s more area, the reduction in induced drag could result in less heel.” (Dashew, 1998, pp. 95-96)
This has been written in 90s. I am sure there's more thorough understanding now. After all the big racing machines have exactly that, i.e. a lot of sail higher up.

I don't want to go extreme with this by no means, but at the same time, if the I get more speed together with less heel, I am willing to put up with little more maintenance and perhaps more tricky sail handling.

And as for the design of Monsun. Naturally you are right. But considering that it was designed in the 70s and that in the 90s the effect of the big roach seemed surprising, I think the sail plan might be redrawn. The counter-argument for the increase of ballast and draft is the "reduced heel".

To redbopeep:

We haven't really thought about nylon mainsail. I have to admit, I haven't seen anyone use it, but I haven't seen all that much On the other hand I've see a person with big roach sail and he was very pleased with it. Surely, we want to get more air light performace (not that it would be too bad now, the boat being quite slim, sails truly well) .

It would certainly be easier on the sail with runners, but it seems to work rather fine even with fixed backstay.
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Old 11-11-2010, 03:53 AM   #9
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In the quote by Dashew "In six cases I’ve been directly involved with, hollow-leech mainsails have been replaced with full-batten conventionally roached sails. The 10-percent increase in sail area has been, as expected, beneficial."

True, the above would be correct - however, Dashew is not talking about replacing the Monson's mainsail with a main that has a roach, that is so large that 'the sail will frequently hit the backstay'

He specifically speaks of 'conventionally roached' - not the roached mains that are seen on latter day Multihulls and planing Monos.
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Old 11-11-2010, 03:59 AM   #10
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sorry, the quote is a little misleading, because the argument follows previous discussion about hollow leech sail. It ends, later in the chapter from which I quotes with discussion about nearly 700mm overlap of the backstay. I don't mean to be argumentative, but it's really about big roaches extending over the backstay.
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Old 11-11-2010, 04:45 AM   #11
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Petr,

I understand your desire to improve the handling of your boat - including getting to a destination a little faster.

Could you confirm what type of mainsail furling that your Monson has? Some that I have seen furl the main by rotating the boom by winding a handle at the mast - this arrangement does not allow for the most efficient main sail, its shape is designed so that it rolls flat on the boom as it rotates. The Monson's tiller and Mainsheet track and controls limit the options that one has, certainly the boom could be extended but retain the present position of where the mainsheet attaches to the boom. If you go for a fully battened main sail - may I suggest that it is designed to keep the roach's leech a few centimeters forward of the back stay.Consider Harken batcars. Consider additional ballast in the form of lead ingots. Consider a stacking system to take the sail when reefing or dropping the sail.
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Old 11-11-2010, 04:51 AM   #12
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OK...What is the goal? I really and truly don't think you'll achieve less heeling by employing more roach. But, is heeling less than you presently heel one of your goals? More heeling certainly brings about more leeway which we can all do without. Or, are you just doing the "in theory xxx" thought process for your own boat?

If you wish light air performance--considering a light air mainsail in nylon,

If you wish to reduce heel by taking advantage of the sail twist that you can induce in a fully battened sail with a lot of roach, then you really need the rigging to support your goals. Having the sail interfere with the fixed backstay totally is screwy in terms of meeting these goals. It would seem that you'd have to have full batten at the appropriate (high) height AND that you'd have to have a means of de-powering the sail high while allowing it to develop good lift low. That means enough TWIST that the center of effort of the sail is significantly lowered. So, rather than simply letting out the sheet a bit and depowering the entire sail you'd be sheeting in tight and using vang/preventer down low and then maximizing leech curve perhaps by tightening up the topping lift. Then you might have less heel because you've lowered the center of effort of the sail. Or, it just might be a totally screwed up inefficient way of managing the mainsail
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Old 11-11-2010, 04:53 AM   #13
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Richard,

actually we enjoy being at sea. So these considerations are really not about making faster passages

Some Monsuns indeed have a furling boom, but we have slab reefing.I forgot to reply to redbopeep about the boom length. This something we don't consider at all.

We are still gathering information about the big roach. In the end we might just get as big a roach as possible as long as it stays under the backstay. But there's some additional support for the extra roach in the discussions on setsail.com. So we are still pondering...
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Old 11-11-2010, 05:12 AM   #14
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redbopeep,

The above cited people say it indeed reduces heel. You don't think it does. I have hardly anything to add, perhaps another quote:

Quote:

The mainsail in the upper left drawing [big overlapping roach] has 17 percent more sail area than the non-overlapping main

in the drawing to the right. The induced drag of the left sail will be lower due to its more efficient tip shape. This means less weather helm and less heeling, even though there is more sail area up high and aft of the center of lift of your keel. While this may sound counterintuitive, we can tell you from a lot of real-world experience that things do indeed work this way. (page 101)
You ask me about the goal. We hope to be able to go cruising quite soon and hopefully do it for few years, so we want a versatile sail, as large as possible, while being able to use it as long as possible. There will be extra maintenance, I know. But again, the advantages the seem to come with such a sail, seem quite considerable.

Some people that have followed Dashew's example, seem to be happy with it as well, viz. setsail.com

But I take your worries to heart and consult in detail with a sailmaker. I am nevertheless still looking for more first hand experience. As you point out, I am of course doing thougt experiments, what else can I do?
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