Main-less rig

brian eiland said:

..... a LOT of discussions of A-frame type rigs.
http://www.boatdesign.net/forums/boat-design/wishbone-sailing-rig-1999-3.html

I just went back thru that discussion thread looking at all the posting for details that have been experimented with. I made some notes of postings I wanted to remember and/or look at a second time. Perhaps I should publish those notes?

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brian eiland said:

So here I present some variations of the mast-aft rig configured with a wishbone/bipod mast column. There is a wide based version, and a narrow based one. And with each of these there are two different spreader arrangements that affect the very important cap shroud angle. Modern mast and rigging materials could very well make these unusual rigs a viable entity

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catsketcher said:

Hello all

My two cents on the mainless rig as I see this dicussion heading

- the bi-pole rig has one very severe engineering compromise it must cope with. It has to do with the compression loading on the rig.

The basics of compression loading are worked out using a formula called Eulers (say Oilers) column buckling formula. It takes into account the length and the cross sectional area of the column in the following way

P(critical load) = Pi Squared x EI/L squared

E is the Youngs modulus of the material and
I is the second moment of area of the section
L is length

Increasing the E or stiffness helps buckling resistance in a linear way. Twice as stiff gives twice as much buckling resistance BUT
Calculating I is tricky and basically it goes up exponentially (measured in the fourth power) as you increase the size of the section. A section only slightly larger can have twice the buckling resistance of smaller section.

The result of all this is that it will always be lighter, cheaper and less windage to support a compression load in a single compression member - one mast. Bipole rigs will have to be heavier than a single mast and weight up high is a no-no as well as increased windage. At least in all the cruising cats I know of there have been no issues with the main box beam. It is very easy to reverse engineer what works and fit this in with the accommodation so getting away from a single mast form an engineering standpoint is not necessary.

As to the stay behind the mast. I have seen this done with two cranes hanging out the back of the mast - really bad idea. It was on my mums cat and if I did the stay up tight then the mast would threaten to come down as it was heavily loading up the back of the mast. It also was a dog to windward. She got a normal fully battened main and the boat sailed much better.

I think it is a really good idea to have a rig that works super well to windward. In the 5 trips north I have done it is always a little hard to get south. On the Ozzie east coast you wait until the northerlies come. Just a couple of hundred miles south they are getting northelies but up at Cairns or Lizard island you still get southerlies. We have often used the good windward performance of our cat (and previous tri) to get south when the trades have eased and gone slightly east. Once south we have better chance of getting tailwinds. My wife prefers sailing to windward on our cat (as long as we can lay the course) So I would counsel a careful overview of the positive aspects of the normal sloop rig. I certainly enjoy my windward sailing and have not enjoyed sailing on cats where this ability has been compromised.
cheers

Phil Thompson

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Built by Multimarine, ‘Artemis’ is a fully wheelchair accessible sailing boat, set for circumnavigation and exploration. Her design incorporates a number of innovations including the radical sail configuration, aimed at enabling singlehanded sailing from the wheelchair and much, much more.

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Spiv said:

A-Frame Etchells

I just found this article I thought I'd lost.
It was printed in Yachting World in 2000; in about 2001 I wrote to the inventor and he said he was rigging a 40' cat with his system, he had a web site with some pictures, but it eventually disappeared from cyberspace.

Some interesting points from the article:

• Designer Bill Dixon and engineers High Modulus had an input
• (Contrary to unstayed masts),[FONT=&quot]"With the A-frame system the main loads are kept within the A-frame structure and are not transferred into the hull in the form of high bending moments about the deck. The result is that we can build a surprisingly light but robust structure."[/FONT]
• The masts sit on the original chainplates and can be raked simply to obtain good balance.
• Once you adjust the sails for the wind speed, you just let the 'boom??' swing to maintain the best angle of attack.

Has anybody heard of Mark Wagner?
Did he really patent his rig?

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Spiv said:

Hi Perry,
the only reason to have a wing mast is to have it rotating into the wind.
In that case the sail has to be fully attached to the trailing adge and become part of the airfoil.
Same as in beach cats, it does work.
I had a rotating wing mast in my 12m cat and I could fill the difference in rotating it into the wind.

However, my gripe with the mainsail has only partially to do with the mast.
There are the reasons I will not have one again:

1. you must hoist it into the wind
2. you cannot furl it a little or a lot, but must take a reef at a time.
3. unless you are really a wiz when you need to reef:
4. 
   
   1. you will need help
   2. must head into the wind with the jib flapping wildly
5. if you are running and the wind picks up you can get in trouble very quickly
6. you need to be carefull when jibing
7. boom, preventer, downwhaul, boom lift, lazy jacks, battens, boom bag, zip.....

I am sure I can think of more if I want to!

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Spiv said:

Hi Brian,
thank you for keeping this thread alive.

Like the owner of the Catana 471 quoted above I use headsails as much as possible.

After two years of owning my Salina and 6 months of full time liveaboard, my dislike for my square top, fully battened 'you beaut' mainsails has steadily grown, here are the reasons:

1. it takes 4 strong people to fully hoist it by hand.
2. on my own I can only lift 1/3, then it is a winch job.
3. I need to go head-to or close to headwind for the whole operation, often in the wrong direction.
4. in light winds or DDW I have to use a preventer and shift it at any tack/jybe.
5. I have to contend with the battens getting stuck in the lazy jacks
6. the boom lift line too tight if close hauled,
7. the shrouds cutting into the main on broad reaches
8. the boom shading my solar panels, especially at anchor.
9. and my pet hate is taking reefs.

I could think of more, but lets say that my Genoa is a charm to unfurl on my own, in any directions and any windspeed, I keep it up to 30kn, then I furl it a bit, it works from 35 to 180 degrees and never tries to bash me or push me overboard.

The best thing is that I don't think twice if I want to furl or unfurl it in the middle of the night when my wife is asleep...... I love it.


So, my plan is to sell the main and the boom and put a big furling 'main'?? behind the mast, like some of those Turkish Goulets I mentioned before, then I will not be afraid of having two sail up in the middle of a dark night....


Now, I can hear the armchair sailors and the racing fans say "you'r mad, you'll loose so many knots" etc etc, well, that statement is still to be proven, I have records of my boat performances and will put it to the test.
However, for all the reasons above "I don't care!"

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Spiv said:

Lots of boomless rigs

I am in Turkey and when I visited the port of Fethiye, I could not believe my eyes: Hundreds of boats with the best cruising rigs!!!

They are mostly Schooners, but some are Ketch rigged.
In this port, contrary to some other I have been, it seems they hate booms and standard mainsails, so they fitted a furling sail behind their masts.

Also twin parallel, furling headsails and believe it or not furling mizzens.

Brian and many of us have been promoters of parallel headsails for their greater efficiency.
All those furlers give you a practically infinite sail trimming capacity AND, at any wind angle!

Schooner or Ketch, I am not so sure what's more efficient, but I think the Schooner looks better and you could probably tension the headstays more.

A free beer for anybody that can find an easier rig for a cruiser!

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