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Old 07-03-2012, 04:30   #1
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A-Frame for a Mast?

Has anyone any info about this mast configuration? SMG boast phenonmal speeds without a boom and i am wondering about the actual configuration of the sails lowering and hoisting them .... seems a bit vague on info but agreed, interesting!
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Old 07-03-2012, 04:39   #2
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Re: A frame for a mast?

Another vessel

http://www.cruisersforum.com/forums/...ran-70486.html
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Old 07-03-2012, 06:31   #3
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Re: A frame for a mast?

I don't know about the A-mast in particular, other than the old AquaCat beachcats had them.

I do know about boomless rigs, having one myself, and yes, they're fast. Mr Randy Smyth is a believer, you don't have to take my word for it.
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Old 07-03-2012, 09:57   #4
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Re: A frame for a mast?

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Originally Posted by niel12 View Post
Has anyone any info about this mast configuration? SMG boast phenonmal speeds without a boom and i am wondering about the actual configuration of the sails lowering and hoisting them .... seems a bit vague on info but agreed, interesting!
No lowering or hoisting, all sails furl. Can't get any easier than that.
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Old 07-03-2012, 12:41   #5
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Re: A frame for a mast?

Sure make a guy wish he had invested better LOL Love the idea of the all furling sails !! a guy could sail till he was 90 with rig like that !!LOL just dreaming !!
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Old 07-03-2012, 13:30   #6
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Re: A frame for a mast?

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Sure make a guy wish he had invested better LOL Love the idea of the all furling sails !! a guy could sail till he was 90 with rig like that !!LOL just dreaming !!
Bob, I hear you loud and clear. The SMG 50 is currently for sale, and even at the newly reduced price of $524,000, would require me to sell my home (which I planned to anyway) plus my vacation residence that I was going to keep when too old to cruise (we have a topic on this that you and I have participated) and would require most of my cruising kitty to pull off. So I guess I'll allow "Number One" to be owned by a second owner before I become the 3rd. lol

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Old 08-03-2012, 10:41   #7
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Re: A frame for a mast?

With a bit of research you will find dozens of A-frame mast systems. You might also find a few yard-queens in the less expensive marinas all around. Were they anywhere close to the performance and ease of use claimed, there would be more of them in the water than sitting on sagging jack stands.
The issues, in descending order are weight aloft, windage, design and construction issues, and weirdness. The last is of course a plus to some observers.
The espoused advantages are a presumed disadvantage in the aerodynamics of a mast, the need to be headed into the wind to reef, the need for a horizontal Guillotine otherwise called a boom, and the boring slavery of convention.
One of the most respected researchers in sail aerodynamics, Howard I Chapelle, is often quoted as saying that a mast reduces the power of a sail by 30%. That is questionable, and does not address solutions like unstayed masts and rotating masts. Nor does it agree with the use of wing-sails in ultra high performance vessels. I suspect that were this number proven to be much lower, A lot of unsuccessful attempts might never have been attempted!
There is still some appeal in the concept, (in my case where it would reduce the weight and complexity of the main bulkhead in a catamaran) if the problems of weight, windage and bare pole drag could be addressed. WW I fighters found advantage in streamlined struts. Airfoil shaped aluminum extrusions were found on almost every aircraft built in the postwar Biplane era. I vote for a streamlined A-frame cross-section.
Tall, thin masts are held in column by multiple spreaders and a spiderweb of rod and wire diamond triangulations. They all sing in a brisk wind. Where does the energy for the music come from? Drag. I would vote for a very carefully engineered carbon fiber leg held rigid by internal webbing. If needed, it could be a bit fatter in the middle, and both legs should rotate.
Booms are a hazard. So are redheads and motorcycles. Live with it. They make to most common sailing task, tacking, SO much easier, and its nice that sails can fall into such an orderly pile on top of a boom. I vote to keep booms. A conveniently controlled boom brake on the main and jib-boom would be icing on the hot dog. Yum. [an acquired taste, like catamarans.]
I don't like vertical furling sails on larger boats. They are heavy, require a winch to furl making it painstakingly slow and incredibly dangerous as the wind whips the sail violently, inflicting injury to the crew or possibly a fatal blow to the head by a barber-haul block left loose. You are reefing because the wind is picking up, right? A well trained main drops into a lazybag in seconds.
So, you may rightfully ask, if both legs rotate, what's happening at the top of the "A"? It's all loosy-goosey, right? And thats where you put a bunch of delicate stuff. How do you keep that orderly? I don't know. You figure it out and tell me. Inquiring minds want to know.....
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Old 08-03-2012, 11:14   #8
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Re: A frame for a mast?

You got that right Bob !! have to take a Big Loan on my great Grand kids and sell everything else to be the 4th owner on that one ! I will just buy a couple of powerd winchs LOL and show Connie where the button is !! all taken care of on my Motor Sailor !!
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Old 08-03-2012, 11:44   #9
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Re: A frame for a mast?

Niel12, have a look at this thread:

WishBone Sailing Rig - Boat Design Forums

Also show some good pictures there of A-frame boats.
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Old 08-03-2012, 11:51   #10
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Re: A frame for a mast?

Sandy Dougherty hits it right on the head! The analysis of A-frame rigs is absolutely correct, and here is my experience to validate that statement. In the 90's I sailed with friends of mine on a 49 foot A-frame, deep keel, narrow beam "cutter"; i.e. it had a furling yankee jib and a furling genoa forestays'l. No mainsail. The boat was almost a metre boat in shape. The A-frame was mounted at about station 9, and tilted forward so the mast head (apex of the frames) was over about station 4. She had a complex system of back stays to the transom using a pair of aft-facing spreaders. I can summarize the results.

Cons: too much weight aloft; weird windage issues (docking, running, heaving to); very high rig cost with the custom hardware required; poor performance on all points of sail and winds with the exception listed in the "pros"; there was no way to add sail area for downwind courses; reefing was limited to one sail or the other coming down; lee helm developed too easily; and I would not begin to address the engineering issues and stresses on the hull and rig.

Pros: the genoa forestays'l cleared the a-frame nicely with no chafe, great speed when close reaching in a good breeze; all roller furling made for a quick dousing of the sails.

Not a recommended approach in my opinion. If I were to get creative with rigs, I'd take the free-standing carbon spar approach. Cat ketch, cat schooner, or just a very modern una rig.
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Old 08-03-2012, 12:18   #11
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Re: A frame for a mast?

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In the 90's I sailed with friends of mine on a 49 foot A-frame, deep keel, narrow beam "cutter"; i.e. it had a furling yankee jib and a furling genoa forestays'l. No mainsail.

Was that Nimrod?
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Old 08-03-2012, 12:19   #12
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Re: A-Frame for a Mast?

Here's one on YW. Note that the hull says composite but I recall it being out of steel. 22 tons displacement reinforces my recollection.
2006 Gulyas Custom Galethea Sail Boat For Sale - www.yachtworld.com
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Old 08-03-2012, 12:21   #13
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Re: A-Frame for a Mast?

I think in the late 80's early 90's one of the "big names" did a one-off concept boat with all sorts of high tech new ideas in it. I don't recall the name, but think it did have an a-frame mast and no shrouds and this was supposed to be a Big Thing. But, there was no great followup and no great change in masts and rigs.

Could be, like Hunter losing the keel on Thursday's Child (?) the entire boat was something the makers wanted to move on past.
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Old 08-03-2012, 12:26   #14
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Re: A-Frame for a Mast?

Adelie - It was indeed 'Nimrod'. A very unusual boat, well built, and quite striking. But the rig was flawed, I have to say. The SA/Disp ratio was clearly too low.
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Old 08-03-2012, 14:28   #15
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Re: A-Frame for a Mast?

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I think in the late 80's early 90's one of the "big names" did a one-off concept boat with all sorts of high tech new ideas in it. I don't recall the name, but think it did have an a-frame mast and no shrouds and this was supposed to be a Big Thing. But, there was no great followup and no great change in masts and rigs.

Could be, like Hunter losing the keel on Thursday's Child (?) the entire boat was something the makers wanted to move on past.
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