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lug sail

Posted: Mon October 18th, 2010, 7:14 pm
by gh 192
I will rig the GH31 with a free standing mast and a lug sail.
I need to know the section of the mast, which will be 10 meters high, from the keel.
want to build it in wood, hollow, the sail will be around 50 square meters.
thanks so much.

Re: lug sail

Posted: Wed December 8th, 2010, 11:51 am
by Fiddler's Green
This is a good one, one wonders why you would like to do this. The Bermudan cutter rig is a proven rig. I suppose if the sail centre of effort is the same, it would work, but the extra weight aloft might have to be compensated with extra ballast.

Maybe the Old Gaffers might be able to assist.

A sail maker might help if you are going to buy his sails.... The Junk Rig guys get Sunbird sails to design their rigs....

Let us know how you get on. It will be the first!


Re: lug sail

Posted: Thu January 20th, 2011, 8:32 pm
by gh 192
i am a sailmaker and just need the data to build the mast.
i,ve been sailing many years with a lug sail and find it excellent, simple and quite eficient.
junk rig is too complicated, too many "strings", blocks, battens and the only advantage is the easy way to down sail, just ease halyard, while lug sail, been set free between tack and peak, need a hand at the mast to avoid sail flying away.
mast will be ligthter than a marconi rig with all rigging, so it,s not necesary to increase ballast.
i am old, and i don,t want anymore winches and sheets work at each tack!!
i also believe than one big sail is better than 2 medium ones. for free winds, lug sail is wonderfull!!
no rig, short mast, less wind heeling you.
anyway, i still looking for the rig size to build the mast, i intend to set at the samson post place.
thanks very much for your reply!!
(excuse my english, which isn't my first language!!)
p.s. have a look at the beautifull ketch Roxanne, from Nigel Irens..a dream to me!!

Re: lug sail

Posted: Thu January 20th, 2011, 8:44 pm
by Fiddler's Green
Hello julio,

The only thing I can suggest is to look at the information in the sales leaflets we have printed on the Gallery, here is a link to the page,

It gives sail areas and you can scale up the drawings easily enogh.

do send in some pictures once you have it rigged!


Re: lug sail

Posted: Sun February 6th, 2011, 9:58 am
by Kevan

I was considering converting a Bermuda rig to a Ketch rig and in my research on the internet I stumbled across a suite of old Excel based executable files that design circular mast sections based on your input height etc. I see a note on the bottom of the dialog box that they use Skenes's and Baader's heuristic. You could purchase a copy of Skenes's and do it by hand or perhaps these files can do the job.

They were developed by Robert Tyrell and as far as I can see they are neither supported (don't run on Windows 7, but do on XP) nor guaranteed. With respect to sections, I would think the Waterwitch would have a slightly higher righting moment than the GH due to the boxier shape. It is however a foot or so shorter. Irrespective you could purchase a copy of the WW drawings from EOG and use the ketch rig as a guide.

If you wish a copy and can't find them on the net, I am happy to email them. Just send me a Private Message with an address. Cheers


Re: lug sail

Posted: Tue February 8th, 2011, 2:57 pm
by JamesH
I would caution against using a stayed rig dimensions for an unstayed rig.
When a rig is un-stayed the loads in tension are much greater in than the loads on an stayed mast in compression as in an stayed mast since the rigging turns the load into a compression force down though the mast.

Also the coachroof /deck needs to be greatly strengthened to take the loads

Skene's Elements of Yacht Design gives a very simply (if somewhat vague) formula for a solid spruce mast:-

P = Wind Preassure = sq. feet of sail area * 1.5

L = Length of mast in INCHES

Safety Factor = 1.5 for small boats up to 3.5 for large catboats with gaff rigs

15,700 = pi * fiber stress of spruce, which is 5,000

Diameter (inches) = Cube Root of (16 * P * L * safety factor/15,700)

You can substitute other suitable woods for Spruce in the equation if you know the fiber stress.

It would take a bit more work to convert this equation to a hollow mast. Skene's just deals with hollow masts in the context of stayed masts."

To convert to a hollow mast use the 2 moment of area of the mast to calcuate the diameter required.

Yours James

Re: lug sail

Posted: Fri July 15th, 2011, 11:17 am
by gh 192
many thanks for your replys, hope i can make it work!!

Re: lug sail

Posted: Sun July 24th, 2011, 9:29 pm
by GHM
Hi Julio,

I don’t know if this will be of any help but, when I was building |Golden Hinds, I got estimates for (aluminium) spars from almost everyone in the UK and I was staggered as to how much they differed. I came to the conclusion that even the “professionals” were not very scientific about the design and, generally, just used the nearest standard section they had. The difference in weight and stiffness between the two extremes was about double. This was confirmed when I asked some if they could make the mast a little stronger and the usually replied that “the next standard section is…..”. I’m not convinced they did, or even could, do a precise stress analysis. And even if they could, you still have to decide when, and how you are prepared for it to fail. In other words, you can opt for a lightweight mast for racing which will fail sooner that a heavier, but stronger mast for cruising the World and Cape Horn.

Having said that, I had an order which specified a hollow wooden mast (sloop rig) and discovered a father and son business operating from a (large) floating barge in Bristol. The came up with the specification and built a beautiful spar at a very reasonable cost. At the moment I cant find their name and I don’t know whether they would advise you for home construction, but they did advertise regularly in Classic Boat.

You also mentioned ketch rig. I haven't sailed on a GH ketch but I have heard that the few that were built didn't sail as well as the sloop ??

Hope this may help. Good luck anyway.