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windward abilities of Bermuda vs Gaff rig.


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  #1 Guest_Ray Frechette jr_*

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Posted 22 October 2002 - 07:56 PM

OK, looking to delve into theoreticals here.

hy does a Bermuda rig point higher than a gaff rig? What are the physics at work that prove a high aspect rig points higher? And as a corrolary why does the gaff reach better than the Bermuda?

I have pondered a bit and the only thing I can come up with is that as wind strength is higher as you go up, apparent wind would shift aft as you go up as the vector of true direction vs boat wind would tend to bias torward true wind direction as you go up.

To that end, would a topsail on a gaff rig aid going to windward?

Anyone able to reccomend some readings to understand the theory here? Also interested in understanding better pro's and con's of Ketch rig, schooner rig vs Sloop.

I am interested in building a mid 30 foot Coastal Cruiser with some offshore abilities as well. I like the idea of having two masts for several reasons. Less reliance on winches, smaller sails, sail plan being split up making for easier sail transport from lockers to rig, setup easier, Less forces on sheets, redudndacy if you have problems with some aspect of rig, more options for balancing rig.

More romantic looking boat!!!

Some of the downsides I see are more complex rig, more blocks and tackle throughout boat. hence greater expense. Loss of space below decks due to extra mast. less windward ability, (though I 've read that nothing points higher than the iron jib which can be called into play as needed when convenient)

Any thoughts?

refent@prodigy.net

  #2 Guest_Simon_*

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Posted 22 October 2002 - 10:08 PM

My guess would be that the Bermuda rig is closer to a theoretical ideal wing shape, and hence performs better to windward, working as an aerofoil.

When reaching, the aerofoil characteristics are less important than just the fact that the sail is a kite, dragging the boat behind it. The gaff rig has a lower profile for the same area, so more of the force would go into forward propulsion as opposed to digging the bow of the boat down into the water.

scolaway@yahoo.com

  #3 Guest_Frank Hagan, Weekender, O_*

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Posted 22 October 2002 - 10:26 PM

Well, I've heard that a gaffer with a highly peaked mainsail (with the gaff nearly vertical) will point into the wind better than one where the gaff is out at about a 30 degree angle like on the Weekender. The physics? I don't know, but a highly peaked gaffer looks more like a bermuda sail in shape.

As to downwind performance, I would guess that the gaff sail's lower center of effort puts the power closer to the boat, so more power can be applied there than at the top of a stick high above the boat. But then, that's just a guess. :D



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  #4 Guest_Graeme"SNUPI bui_*

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Posted 23 October 2002 - 12:58 AM

BEEN THAT AN' DUN THET !!!

You're getting into the extremely complex & confusing area of airfoil definition i.e., high speed/low drag, high lift low aspect v/s low speed high lift / high aspect ratios !

Or to simplify the issue ....think about the aspect ratios of a WW2 Spitfire v/s a Piper J2 ...or and the aspect ratio of a F16 v/s modern sailplane.

Then ....... you get into a whole other world of airfoil shape for different purposed !

Michael Ludwig of the University of Illinois spent countless hours designing / wind tunnel testing the the extremely lightweight / effective airfoil shape and the high aspect ratio 100 ft + low speed high lift wing of NASA's Solar powered PATHFINDER !

I won't get into all the buzz I got into researching sail shapes & airfoils when designing SNUPI's sail / ROTATING AIRFOIL MAST over a period of time from January to the present, ( and still at it to a degree ), but if you want to start the brain twisting quest, start with aircraft wing aspect ratios, their various shapes or NASA # airfoils and uses,

Punch into a good search engine, "High aspect & low aspect wings " ......... Then search for, "high lift, low speed airfoils"

Take a look at the "NASA Pathfinder" sites on the web. Good Luck and keep the aspirin handy !

Graeme, Nova Scotia

Take a look at a Clarke airfoil,... I am using that design for the SNUPI's airfoil mast.

graeme.realtor@ns.sympatico.ca

  #5 Guest_Greg_*

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Posted 25 October 2002 - 11:21 AM

Well you guys must forgive me, but I think you need to look at the center of pressure effect or where the impact of the wind is on those two very different sail configurations. I thought I read that a Gaff Rig could not point up as high do to the vector result of the wind versus all that square yardage of sail the gaff carries....just a thought...

nvdwarrior@yahoo.com

  #6 Guest_Gordy Hill_*

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Posted 23 October 2002 - 05:39 AM

Oh, I just gotta put my two cents worth in!
The way I understand it, the gaff falls off to leeward, less on a more vertical one, but there's still a twist in the sail. If the lower part of your sail is trimmed properly the top will be luffing. You'll have to ease off a bit to fill the top of the sail...sometimes a big bit. How much you bare off is pretty much the difference between the gaff rig and the Bermuda. When going downwind the sail still wants to twist but it's not so critical. However, on both types the boom wants to lift and a cunningham (more stuff) is often used to address it.
My Core Sound 17 goes to windward remarkably well. Because the sprits bisect the angle of the clew the lower half of the sail acts like a cummingham. The masts are free-standing and the sprits, (like wishbones, but cheaper, lighter, and easier to make and rig) keep the sail shape just about perfect. I don't have stays, shrouds, turnbuckles, winches, halyards, or gooseneck.
Also, since the sprit doesn't want to lift like a boom, there's much less effort on the sheet. Since there is no rigging, I can let the sails go beyond center when running in heavy condictions. I can sail right onto a lee shore and let the sails go completely like two big flags.
There's no boom to duck. The sail just whooshes by during a tack or jibe. There's no headsail to tend. When I take someone with me there's not a damn thing for them to do 'cept mind the cooler.
I kinda like my Core Sound 17. If I built another one I might put a cabin on it.

This is a link to some pictures.

http://groups.msn.co...d17.msnw?Page=1

sirgordy@peoplepc.com

  #7 Guest_Budd Cochran_*

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Posted 25 October 2002 - 08:51 AM

Sorry about stirring up your curiosity. Mine runs 24/7/365.

Of course, the advantage of being curious is that it allows us to go thru life in a state of constant amazement.

Or is it confusion? :D

Budd

mr-d150@citlink.net

  #8 Guest_Graeme, SNUPI Builder_*

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Posted 23 October 2002 - 12:08 PM

The Clarke airfoil, and I'd have to go thru my notes to find the type, is symetrical. I printed the profile ( shape) and dimensions/ specs etc and worked from there. The wind tunnel specs as I recall were ideally suited ,(as a symetrical foil goes), for low speed lift. Combined with the rotation around the mast and the "softsail" flap, it seems to be the ticket.

If my lousey memory serves, I think it's one of a series used or copied ,by the Decathelon ( not the Citabria which was asymetrical) Years ago, flew 'em both & survived getting my airbatic rating !

Too bad the Maule Rocket's wing is so complicated,slots & flaps,there'd be "LIFT" unit ! I loved watching the 25 mph, hangin' on the prop, tail wheel departures and 50' landing roll outs !

Gotta go,(thanks Buddy), to the notes "File", commonly referred to as the "Misc. & anything box, that I wuz too lazy to properly file"!
I might have them in my box marked ~ "Notes from Peter Bell / Dynawing !"

You've got me curious NOW ! Oh well !

Graeme

graeme.realtor@ns.sympatico.ca

  #9 Guest_Budd Cochran_*

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Posted 23 October 2002 - 11:15 AM

If I remember correctly, the Clarke airfoils are incidence dependent because they are asymmetrical. They work better if the airflow comes in at an angle to the bottom of the wing. The older Piper Cubs used the Clarke "Y" airfoil for example.

I would think a symmetrical foil would be better suited, or am I way off track?

Budd

mr-d150@citlink.net

  #10 Guest_Frank Hagan, Weekender, O_*

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Posted 26 October 2002 - 11:14 AM

I think you're right to consider sail handling more important than pointing ability.

This is going to be heresy, but I think windward ability gets less important with a displacement-style cruiser. They are built heavy, and so many of the stories I read in sailing magazines have people mentioning motoring whenever they have to beat against the wind (Lin and Larry Pardy are the exceptions I think ... not sure they even have a motor on Sarafyn or whatever it is they are sailing now.) So the cruisers are much happier with 5.5 knots directly on course than they are with ANY pointing off-course.

How much slower is a gaffer on a race course than a bermuda, after beating to windward? A few minutes. For most cruisers, that amount of time isn't going to make much of a difference, as you usually plan your sails for the most advantageous wind anyway ... and that is not beating to windward. Its not uncommon for sailors to head out almost to Hawai'i, then tack back east toward San Francisco rather than beat up the coast of California. And that's in high-aspect bermuda rigs.

So you plan your journeys to be downwind most of the time, if you can, and that's where a gaffer has an advantage. I think pointing ability probably evens out everywhere except in a race.

After the first race which became the America's Cup, the Queen was told who won. She then asked who came in second, and the answer was "Your Majesty, there is no second." That's racing.

"Hey Frank, we fired up the blender and here's your margarita" is cruising if you're in second place. :D

fshagan@ev1.net

  #11 Guest_Frank Hagan, Weekender, O_*

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Posted 28 October 2002 - 11:05 PM

Great looking boats! Thanks for the link. Now I have somewhere else to look at pictures with boat-lust in my heart.

fshagan@ev1.net

  #12 Guest_Paul J [Aberdeen Wa]_*

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Posted 28 October 2002 - 06:42 AM

Check out this designer of cat ketches he has been designing them for 35 years. Big boats too.

Paul J

Tanton Yachts
paul@ultasail.com

  #13 Guest_Gordy Hill_*

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Posted 27 October 2002 - 08:45 PM

Actually, the first cat-ketch I remember was a Freedom 40 I encountered on Long Island Sound while I was sailing a 17 foot silhouette. Of course he blew buy me. That was in the early 70's. It had fully battened sails with free-standing masts and wishbones. I believe it was being sailed singlehanded and had no engine.

sirgordy@peoplepc.com

  #14 Guest_Frank Hagan, Weekender, O_*

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Posted 27 October 2002 - 08:19 PM

I know Graham of B&B Yachts likes the cat-ketch for sailing ease. How large can you get the rig? Graham's plans are for boats up to 22', but could you do a cat-ketch in a larger boat, say up to 35'?

With technology, there is a lot you can do with sail handling for larger boats. In boom furling, furlers on the jib or genoa, winches, powered windlass for the anchor, bow thrusters for easier docking, etc. So maybe the question begs the point for larger boats. I like the idea of the cat-ketch because at its core it is simple to operate, and that appeals to me.

fshagan@ev1.net

  #15 Guest_Gordy Hill_*

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Posted 27 October 2002 - 05:54 PM

Frank,
I don't want to sound like an evangelist, but I've become totally converted to the cat-ketch. Of course there are some truly wonderful boats with more conventional rigs. I don't know any sailboat that isn't wonderful on a broad reach on a warm sunny day, but I always have to get back to the ramp. To me, pointing is important. Tacking isn't my favorite point of sail. My boat next to a Weekender would probably mean one or two less trips back and forth the bay. Gotta admit they're cute little boats though.
I've always felt that light wind ability was more a function of sail area than rig. About the only thing worse than sitting out on a sloppy sea in really light wind with the boom slamming back and forth is sitting out on a sloppy sea in really light wind with the boom and gaff slamming back and forth.
Come on down to Orlando and play with my boat!

sirgordy@peoplepc.com

  #16 Guest_Frank Hagan, Weekender, O_*

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Posted 26 October 2002 - 08:28 PM

I like the cat-ketch rig also ... although I haven't sailed one. The descriptions sound like they might be the easiest rig to sail.

Most of us have experience just with a gaff rig and "standard" bermuda rig, so making all the comparisons are limited by our own experience. What I usually hear are discussions about the ability to point. I think Ray's on the right track in talking about ease of sail handling, reefing, etc. as being more important for a cruiser. Gaff rigs do add a halyard or two, especially if you want to rig a topsail. But light wind performance counts for something too (which I assume a fully battened roachy sail would excel at also).



fshagan@ev1.net

  #17 Guest_Gordy Hill_*

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Posted 26 October 2002 - 02:42 PM

A gaff is more trouble than it's worth. If you like the look, sail near other boats with gaffs and look at theirs. There is just no good reason for having a big chunk of wood dangling from a couple lines near the top of the mast.
If you want a boat that does well both on or off the wind, a cat-ketch (or cat-scooner) with freestanding masts and wishbones is just about impossible to beat. If you want a lower center of effort go with fully battened roachy sails. The battens will also make reefing much easier. I learned to sail with gaffs and cotton sails. I used to want a boat that was totally traditional. I'm beyond that now. I don't mind Dacron or Nylon or two-part epoxies or composite blocks. I prefer a boat that's very easy to sail and out performs most of the similar boats.

sirgordy@peoplepc.com

  #18 Guest_Ray Frechette jr_*

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Posted 26 October 2002 - 05:41 AM

In all honesty my interest has less to do witht he Weekender than with that gaff rigged Schooner I want to build and cruise during retirement.

Next couple of years is research time to determine if the sailing abilities, cost and effort means this is a feasible dream or not.

I so far like the gaff rig schooner over a ig marconi sloop as sail handling is far easier and you greatly reduce your need for mechanical aids to sail trim. reefing options and sail trim options are increased, adn it sure looks a whole lot nicer.

Windard abilites is a tradeoff.

refent@prodigy.net

  #19 Guest_Frank Hagan, Weekender, O_*

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Posted 25 October 2002 - 09:59 PM

You could rig running backstays on a Weekender ... you switch them after each tack, I think. The Weekender boom doesn't protrude that far past the cockpit, so it is possible. Still, what is all this about boat speed, windward abilities, etc.? If "getting there" were the issue, I wouldn't be in a sailboat! :D

fshagan@ev1.net

  #20 Guest_Ray Frechette jr_*

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Posted 25 October 2002 - 01:08 PM

Well I've been studying the archives at Woodenboat forum. Seems one if the big issues affecting windward ability of the gaff rig is Headsail sag from lack of a backstay.

So tighten up those aft shrouds, and snug up the forestay.

refent@prodigy.net




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