gaff ketch sail plan

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seasolutions

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hi all,

I'm currently restoring a thirty seven foot double ended sailing yacht, and am using the Christmas period to attempt to re draw the sail plan. when i brought her she came with all the bits for a gaff cutter rig, but was obviously un-balanced like this as the previous owner had fitted a very dodgy looking mizzen right at the back.

I know from the chain-plates in the hull that she's carried a ketch rig at some point in the past with a mizzen fitted at the forward end of the cockpit so I was planning to re-rig as a ketch with the mizzen reinstated at the front of the cockpit.

I am currently struggling to draw a sail plan that has a sensible distribution of canvas, a sensible lead of C of E over CLR, and which look's vaguely appropriate.

can anybody suggest some sensible numbers for;
total area?
distribution between mizzen / main / fore-triangle?
lead?
sensible ratio of foot / luff / head length for gaff sails?

sketch attached gives a total area of 85 sq m / 987 sq ft
lead 21%
split 37% / 47% / 16% fore-triangle / main / mizzen
main mast 11m (36') mizzen mast 6.7m (21')

any comments at all would be gratefully received, thanks
Deneb.jpg
 
Your sail plan looks to me as though your total ce is a bit far forward? perhaps look to extend the mizzen boom abaft the stern.

boat would also look better (if it is a true representation) with the bowsprit following the upward sweep of the sheerline.

Have you thought out how your ce/clr works out as you reef down? Beleza is rigged as a cutter rigged topsail schooner and its rare that we get the chance to fly our full suite of sails. I'd be tempted to work out what sails you'd regard as working sails and then work out your ce/clr from that, for instance you are showing the head sail as a high cut yankee type, but there are times when a 100% genoa might be better.

Hope my meanderings are of some help. There is a very good book called Sailpower which goes into great technical detail on various sail plans and getting the most out your sails, but unfortunately its on my boat so I cant get you the details.
 
Thanks for your comments, I think you may be right about the mizzen boom although i was hoping to avoid this as i wish to fit some wind vane self steering.

the bowsprit dose follow the sheerline, i have just been a bit lazy with the drawing :-)

is this http://www.amazon.co.uk/gp/product/0713667206/ref=olp_product_details?ie=UTF8&me=&seller= the book you recommended?

The reading I've done thus far seems to suggest that mizzens should be quite small;- principals of yacht design says 15% of total sail plan. dose anyone have experience with a large mizzen? dose it lead to lots of weather helm as the wind builds? i suppose it would have to be the first sail to be reefed in that case...

cheers :-)
 
I think you are right about not making the mizzen too big. I have sailed bermudan ketches of various sizes quite a lot and in most cases the mizzen was as you say the first sail to reef, in fact in one boat I think we kept the first reef in the mizzen most of the time.

If it was me I would think about seeing if a professional designer would sell you a few hours of consultancy to help you design an appropriate rig. Might be a couple of hundred pounds well spent?
 
Even though I have an AWB, I am very interested in the traditional double ender style as in Perry, et al. Just out of interest, what type of boat do you have?
 
please excuse the clutter on deck :-)

Sept08021.jpg


Named Deneb K, was built in Denmark in 1938, designed and built by Nielsen, similar to a Colin Archer, but finer ends. Unfortunately I know very little about her history beyond a few old photographs and Lloyd's list entries (earliest of which is 1951)

[ QUOTE ]
If it was me I would think about seeing if a professional designer would sell you a few hours of consultancy to help you design an appropriate rig. Might be a couple of hundred pounds well spent?

[/ QUOTE ]

Where's the fun in that? seriously tho, I fully intend to seek professional advice on rigging wire dimensions etc. before putting anything together.

My understanding is that sail balance is still something of a black art, so I was planning to draw something about right, assemble it as cheaply as possible, then go sailing and re-evaluate....
 
Just a speculative guess, but it looks like you drawn up your plans using Rhino? And secondly have you worked out you CLR yet? (If you don’t have any plans to work from you can roughly work it out along side with reasonable ease!)

I would have thought a CE lead of 21% a tad excessive, which could lead to a nasty dose of lee helm, if you’re not careful. (However you may be using a different method to me, as their are several!) I would have said a lead of 11-15% of L.W.L was nearer the mark.

Are you trying to work with existing mast steps? If so and if your drawings are correct, it could mean that the mizzen is blanketed while sailing on anything but a broad reach. The leech of the main is very close to the forward face of the mizzen mast, not leaving much space for the venturi affect to do its work!.

If you look at any of the modern ketches about, you’ll see the gap between mizzen and main is often quite large; this is so the mizzen is working in clean air and not the turbulent spillage of the main!
 
You have way too much lead and the trial and error method for dealing with this could be expensive in terms of re-positioning chain plates, mast base etc. Mizzen is too close to the main. You would split the sails up subject to the type of sailing you intend to do. We sail a long keel ketch and only use the mizzen off the wind or in a blow where the main is doused and the jib and mizzen are used. Aage Nielsen was a very talented designer and knew what he was doing, my guess is that the dwgs would still exist for this boat somewhere and that an original rig plan will reveal what the intention was. Do you have his book?
 
Thanks for the input,

questions first:
Yes i use rhino for CAD work,
Yes, I intend to use the existing mast steps as re-positioning them would be a very difficult, due to superstructure / bulkheads / machinery.
No, I don't have Nielsen's book, because my boat was designed by I different Nielsen, of whom i have been able to find no record (thus far, all tho if anyone out there knows anything.....)
Yes, I have worked out the CLR, the drawing above is taken from a half model of the boat, and rhino gave the center of area

interesting point regarding back winding of the mizzen, hadn't ocured to me but makes perfect sense.

I have drawn another sail plan using a larger mizzen, which brings the lead back to 13%, which I agree is a better starting point, however the resulting sail plan is split so that the mizzen main and fore triangle represent about a third of the total area each. further to KenMcCulloch's comments, I am concerned that this will make the boat difficult to sail, indeed If I make the main smaller as suggested, I almost have a schooner.....

finally, dose anyone have experience with very tall narrow gaff sails? I have heard good reports of Michael Kasten style rigs, but never first hand

mk2 sail plan, approx 1000 sq foot excluding top sails
untitled.jpg
 
Now just resite your mizzenmast aft by 1/4 boom length and extend boom of main by same amount and it will start to look better balanced.

I think your problem is the closeness of the two masts, perhaps that was why it was resited rearwards originally? Maybe it was a schooner rig originally with the mainmast aft in the location you show?
 
Just a few thoughts.....
As a gaff rig I don't think the closeness of the main to mizzen is an issue as you get a nice bit of twist in the sail, unlike a bermidian rig. On my own lugger on the sail plan the main overlaps the mizzen, but in practice its well clear and is no problem. To windward you would probably set your boom over the quarter anyway, not on the centerline.
Most headsails overlap one way or another.

Another factor to the amount of lead may be the beam of your boat and general stability. If she is narrow and a bit tender as she heels the drive from the sails will want to head her up and give you a bit of weather helm. For a beamy girl visa versa.

A big get-out card is your bowsprit. Its easy to make it longer and add more foretriangle later.

I think 1000sqft working sail for this boat is plenty. My own boat has 1100 to drive a 37' wl and 14' beam. We are not slow.
Add tops'ls, jib top, mizzen stays'l and you could be up to 1800 sqft ish. If she is about 14t then 71 sqft/ton should be ample for working sail.

A feathering prop will improve your light air performance more than anything.

Finally, it is a bit of a pain not to get it in the right cricket pitch first time, as sails ain't cheap!

finally finally, is that Burseldon, 'Home of the Old Gaffer' (take cover, incoming from East Coast.....)?
 
Sadly moving the mizzen mast aft a small amount isn't particle; the cockpit is quite narrow, putting the mast where you suggest would leave no room for crew, although i agree that it would be a good solution.

a mizzen mast has got to stand either where it is or within about 2' of the stern

I'm starting to wonder about a sloop rig with a very long boom, whilst I'm not keen on handling large sails short handed, there is some attraction in the simplicity. drawing below is just over 1000sq ft, with a 15% lead....
untitled1.jpg

not so happy with this, the numbers add up, but it doesn't look right to me, perhaps other people thing otherwise?

on sails incidentally, I have with the boat a substantial collection of sails, all of which are past there best, so will hack these about to experiment, than have a new suit made once I'm happy.

yes, I am Bursledon based.....
 
By the looks of it the main mast is a bit too far forward to make a simple cutter. As far as sail area goes, on a boat that size 1000 square foot of sail is pretty easy to handle. We have that sail area on our 35 footer and one person can set and take in all the sails with a bit of practice.

If you want a ketch rig then take a look at the sail plans for the Colin Archer rescue boats for a bit of inspiration. They were a quite under canvassed (understandable when they were intended to sail in storms rather than fine weather) but the balance was good. Nice thing about a ketch rig is that you can eliminate any weather helm by sheeting the mizzen in a bit harder. As has been said though, it would probably be worth, after you've decided on a sail plan, to take it to a proper designer just to crunch the numbers and check it over for you. T'would be a bitch of a thing to get wrong.
 
Well, FWIW, and as I'm finishing the chrimbo wine, my tuppence is this:

As for the ketch rig, from version #1, I'd start with the colin archer rig and adapt. I'd get the bowsprit to follow the sheerline- burying the 'sprit in each wave makes for a nervous life... I'd also not be too hesitant to make the mizzen smaller and the main a bit bigger, as the Main will be the driving sail. I'd also draft it onto card and try to get the balance right on a knife blade, then make the CE lead the CLR by about 20".

Then I'd call an expert.
/forums/images/graemlins/wink.gif

Oh, and version #2 looks as if it will kill you in anything over a F3
 
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