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post #11 of 22 Old 01-28-2013
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Re: Can someone explain roach to me?

While increasing roach on an existing boat will increase sail are, that is not why modern designs are moving to high aspect, large roach designes. And really wind shear (wind further above the water is faster) has only a minimal effect.

The real answer is that the higher aspect a sail is the more efficient it is because it reduces tip vortexes, and maximized the lift generated by entire sail. This is why a number of classes that have maximum sail area restrictions on fixed height masts are also switching to a high aspect sail. This is the same reason that gliders have extremely long but narrow wings, you get a lot more lift out of the same surface area (read drag) with a long skinny foil than you do with a short stubby one.

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post #12 of 22 Old 01-29-2013
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Re: Can someone explain roach to me?

This is not completely about rules or strict aerodynamics. It is to compensate for a variety of shortfalls of a Bermuda rig. One of the short falls of a Bermuda sail on a mast (versus a wing sail), is that a very large percentage of the head of the sail operates in the disturbed air off coming of the mast. Another of the shortfalls of Bermuda mainsails (vs gaff mainsails) is that the gaff sail has more sail area up higher so it can work a little better when reaching in terms of greater drive for a given heeling moment.

Roach fairs out the air flow at the leach near the head of the sail, allows a greater sail area higher on the sail and which is further away from the mast, which then addresses both of these issues.

I would suggest that where practical, maximizing roach may actually make more sense on most cruising boats than race boats.

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post #13 of 22 Old 01-29-2013
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Re: Can someone explain roach to me?

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Originally Posted by Jeff_H View Post

I would suggest that where practical, maximizing roach may actually make more sense on most cruising boats than race boats.

Jeff
I agree wholeheartedly, but I must confess - I'm a bit surprised to hear a guy as 'racy' as you are, admit to that... (grin)

The resultant loss of roach area is one of the biggest downsides of in-mast furling on a cruising boat, for me...
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post #14 of 22 Old 01-29-2013
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Re: Can someone explain roach to me?

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Originally Posted by JonEisberg View Post
I agree wholeheartedly, but I must confess - I'm a bit surprised to hear a guy as 'racy' as you are, admit to that... (grin)

The resultant loss of roach area is one of the biggest downsides of in-mast furling on a cruising boat, for me...
What do you call this? Furling main with roach
I'm no big fan of furling mains but that problem has a solution.


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post #15 of 22 Old 01-29-2013
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Re: Can someone explain roach to me?

IMHO the purpose of roach is to make you spend lots of money on battens, cars, chafe protection and sailmaker repairs.

My mainsail was straight cut, no roach no battens no problems, ever - after 50K sea miles. The only drawback - I may have arrived perhaps a few hours later?

Another plus – a big one – you can reef on any point of sail.
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post #16 of 22 Old 01-29-2013
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Re: Can someone explain roach to me?

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Originally Posted by knuterikt View Post
What do you call this? Furling main with roach
I'm no big fan of furling mains but that problem has a solution.


Yes, I should have noted that, and it's probably a decent solution, given that H-R is now using it... One major advantage I can envision, seems it would allow a main of even greater roach to clear a backstay when tacking, than a sail with horizontal battens...



Still an extremely rare setup on this side of the Atlantic, however - I don't think I've ever actually seen vertical battens on a cruising boat yet over here... Do you know whether such battened mains can be retro-fitted to most existing rigs, or do they require a purpose-built spar with a wider slot? Some of the Hood Stowaway masts I've used, I can't imagine the slot being able to accommodate the additional bulk of battens, without a major modification...

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post #17 of 22 Old 01-29-2013
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Re: Can someone explain roach to me?

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I don't think I've ever actually seen vertical battens on a cruising boat yet over here
I saw them last year on a sail at the Easton, MD Evolution loft. It's not a great solution because it's very difficult to control the shape of the sail with vertical battens. As with anything, it's a compromise. Proper shape vs. the ease of in mast furling. IMO, it's a sailboat, so I opt for shape.

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post #18 of 22 Old 01-29-2013
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Re: Can someone explain roach to me?

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Originally Posted by JonEisberg View Post
Yes, I should have noted that, and it's probably a decent solution, given that H-R is now using it... One major advantage I can envision, seems it would allow a main of even greater roach to clear a backstay when tacking, than a sail with horizontal battens...



Still an extremely rare setup on this side of the Atlantic, however - I don't think I've ever actually seen vertical battens on a cruising boat yet over here... Do you know whether such battened mains can be retro-fitted to most existing rigs, or do they require a purpose-built spar with a wider slot? Some of the Hood Stowaway masts I've used, I can't imagine the slot being able to accommodate the additional bulk of battens, without a major modification...
The boat in the picture is a standard Bavaria 32 with furling mast.
I'm going to my sail maker soon - will try to remember asking him what the limitation's are
Here is a translation of what one owner wrote
Quote:
We were class winner in Færdern (One of the largest over night races in the world) and No. 2 over-all of all boats rounding at Mefjord!
So it seem's like Bavaria + Gran furling main is not so bad!
We received many comments during the ceremony, how can that be possible? What have you done with the boat? It is not possible to win with Bavaria, short keel and furling main when 90% of the race is tacking!
My only comment was: Talk with Henning at Gran if you are wondering what is possible.
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post #19 of 22 Old 01-29-2013 Thread Starter
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Re: Can someone explain roach to me?

The other solution to battens and mainsail furling is in-boom furling and horizontal battens.

I appreciate all the explanations so far about roachy heads of mainsails. Now what about further down? Seems like if we wanted more sail area down low, we'd all have longer booms right?

I'm thinking that there may be wisdom to the "first 2 battens full" and the rest partial, for a cruising main.

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post #20 of 22 Old 01-29-2013
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Re: Can someone explain roach to me?

Med,

A longer boom does two things. One helpful, one harmful.

First it increases sail area, this is good.

Second it reduces aspect ratio, this is bad.

A good designer must balance these things out when designing the rig. As well as a lot of other stuff like: running backs instead of a backstay, mast weight, mast taper, expected loads, boom length and traveler placement, ect...

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