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A Different Sailing Rig for Scrumble…
Lately I have been doing some serious thinking about the sort of rig we want on Scrumble.
I have become quite fixated on a system some would find a little odd, however we seem to take a fair bit of flak regarding the front cockpit so I thought I would just jump right in………
I call this a Dual Cat Rig and think maybe it is a natural for a catamaran.
My version of this came from the concept of two modern american catboat rigs, that is an unstayed mast with a wishbone boom, and a dagger board in each hull. An example of a modern american cat boat rig is at www.wyliecat.com and what it would be like on a catamaran is at www.cat2fold.com
My research indicates the following about how a Dual Cat Rig works:
- Does one sail blanket the other? Yes, at 90 degrees apparent the leeward sail will die, then one can head up to fill that sail or open the other to feed it, so the two rigs are trimmed in an asymetric manner.
- One could use this principle to reef one sail by steering into 90 degrees apparent and then easily reefing the leeward sail.
- Downwind the two sails would be wing and wing.
- The bending unstayed carbon mast and wishbone boom means that the rigs unload automatically with increasing wind as a consequence of design.
- There would be quite a number of reefing options through to the windward sail fully reefed with the leeward sail furled.
- There is the thought from some who have sailed some of the few existing catamarans with this rig or similar that it is a bit slow to tack. The boats with this problem seem also to have the rigs placed at the fore and aft position that one might step a single mast. The advice I have got from catboat builders in the US is that the masts need to be well forward, which also gives plenty of foot in the sails, with a shorter mast and a lower centre of effort. This would also have the benefit of moving the masts forward of the accommodation areas.
- We will get rid of stays & spreaders, multiple halyards, headsails & spinnakers, headsail furler, headsail tracks & adjusters, mainsheet travellers & control lines etc. and we maintain or increase the sail area with two very simple rigs.
- We can get rid of the forebeam support for the forestay, prodder etc and with the anchor stowed in the forward bridgedeck there would be a very simple forebeam.
- There would be only two winches mounted on the deck, immediately forward of the front cockpit, to service one halyard on each mast, the mainsheets with light loads each, thanks to the wishbone and then forward to the front cockpit. The jiffy reefing lines would be led into the front cockpit and the snotter or choker from each wishbone boom likewise.
I expect some serious questions about this to further solidify the idea, as I have researched quite a bit in recent months and have become quite convinced it will work well and have some considerable advantages.
I have some hoops to jump through as for all of the following I will need considerable technical help:
- The masts would have to be carbon, who to build? I suspect I couldn’t do it here.
- Same for the wishbone booms, maybe alloy with carbon fore and aft.
- Where to mount the masts - In line with the forward structural bulk head which would have to be beefed up to at least 25mm with some Uni over and under.
- How to mount the masts - Maybe onto a keel step and supported in a reinforced deck or maybe a trunk?
April 4th, 2005 at 7:42 pm
Comments have now been turned off on this post, due to extraordinary amounts of spam. Please feel free to place comments on other posts. If you wish to specifically comment within this post, you may send it via the Contact Scrumble page, and we will manually place it here. Cheers, Judy.
July 10th, 2005 at 10:28 am
I noticed on the Schionning website that they are working on this concept as well
July 16th, 2005 at 3:00 pm
Tom,
Thank you for the thoughts on the unstayed twin cat rig. While we are thinking:
Here is a link to a site with a discussion of unstayed versus stayed masts. The summation, from our perspective, is approximately in middle of the page.
http://www.sponbergyachtdesign.com/StateoftheArt.htm
I think a possible solution to the cost factor is to have an expert in the subject of unstayed spar design provide a parameters bracket for a spar(s) to fit your boat. Then go shopping for masts that are offered as stock items on production boats and which fit within the parameters. That may be a long shot, but I think the odds are improving as more such spars are being designed for production boats.
Also, Rob Denney of harryproa.com is in the process of developing a less expensive method to build carbon spars without using a mandrel.
The disadvantages/problems that seem most important to me:
1. Assuming a dual cat rig having sail area equal to a standard main+jib, I could not use all my sail area to advantage when on a beam reach. It would, as you point out, need to be detuned or compromised in some way. Perhaps one solution is to simply begin with much greater sail area in the twin cat rig.
2. If indeed the masts would need to be mounted well forward in the hulls, there will be a problem of added inertia in the fine ended hulls. This would cause the bows to be slow to recover from pitching forward/down in a sea way. Possibly this could be overcome with shifting some mass such as tankage astern, but that presents its own set of problems.
3. Placing the masts much forward of the main structural beam of the boat would place additional torsional loads on the hulls as there is no beam nearby to provide a reaction.
As mentioned in another post, some designers are having success with this rig on smaller catamarans, so perhaps there is hope for larger boats too.
July 25th, 2005 at 7:12 pm
Hi Tom,
I have been following your progress ever since you replied to a question I asked or a thread I started, I cant remember where (either Schionnings forum or DavidandJudis forum). I am always thrilled to read of others building cats, I took original motivation and continued inspiration from others like you achieving what I dream of doing.
I have now taken the plunge so to speak and will start building in Gosford NSW in the next few weeks, ATL are cutting my kit now. I have gone with a Schionning wilderness 1230 kit and part of the delay (I signed up in Feb) has been the re engineering needed for a bi mast unstayed rig based on their radical bay (you may have seen both the original 8m and the new 1230 on their website). I will have the plans and the kit in the next week or two and would be happy to correspond with you on the merits of various design options. Please bare in mind though that I am fairly inexperienced, I have never built a boat or worked with these materials (I was a cabinet maker many many years ago) and I cant even sail (YET!!!). Being a non sailor, I chose the rig for the reasons you highlight on your site and because to the non sailor like me it just looks safer and easier to sail and more importantly de power. Not only as you say does the rig lend itself to self spilling but the ability to let the booms run (fully rotating masts) just by releasing the sheets and instantly completely depower is attractive to me, not to mention the lack of stays meaning less maintenance, lack of winches, and a mess of ropes all over……(non sailor!!!) it just looks so neat…..anyway thats my 2cents worth for what its worth, I hope we can correspond from time to time…..Good luck with your project. Cheers, Paul
July 27th, 2005 at 11:49 am
On the rig thing, one is tempted to say take anything, and try to sleep it off. If symptoms persist contact a doctor. I have been building various boats for 25 years, and observing the scene. This is a typical thing that happens to a lot of people about this stage in the build, the unorthodox rig phase. I’m absolutely not trying to be a smartie pants about this, I have seen it over and over. From Dick Newick to the yous and mes. Though in my case I was mostly trying to ditch the specified racing rig.
On the positive, one has to consider that the basic sloop rig is often not the ideal cruising rig. Also there is a rig similar to what you want that doesn’t require a freestanding carbon spar, it is on the Kelsal Coralseacat, which unfortunately has a new name I don’t remember. There is info about this rig on the Kelsal webgroup and yahoo group. Basically there is a wire between the mast tops, which makes them mor conventional in load sharing, and they can be wired up.
On the negative (there is so much)
1) Carbon spars!!! OK neat new technology, I had a boat that was supposed to use this stuff, until the gulf war doubled the retail price for the tow. I kept getting happy talk from the designer about how he could source the stuff for me cheap etc… After several years I just gave up. costs had risen about five fold, and I could never get a comitment price. Wonderful stuff, I have used it a lot for small stuff, but really…
2) Any time you design your own rig, there is a huge chance it just won’t be quite right. The guy who cut the sails for Newick’s “simple” lungstrom rig nearly went nuts getting it right. A lot of things are simple in concept, like the Lungstrun is like what you have in mind in that you can run wing to wing downwind, and people have been trying it for almost 100 years with no success (if defined as better performance than cheaper easily purchase alternatives) So as long as you are prepared to redo something like the spar position to get it right, which would be logical if you are more interested in playing with design more than sailing (my constant problem, so no criticism from me). But it is almost always more difficult than people think. Every new boat with a new rig I have heard of has needed another one, and another, and so forth.
The newick 26 foot try I wanted to build that had an easy to step traditional rig, a split lug, all of a sudden it didn’t work, and they were didling with other things. The Design was called Back to Basics. The plans are still unfinished 20 years after Newick anounced the simplicity revolution to the world. Basicaly nobody has followed his great idea. (You want lots of examples, just ask…)
3) It’s a bit late… I mean you mentioned your forward cockpit, and how good you feel about that, well I agree with you it sounds like a great idea, but what use is it if you have a biplane rig, what do you then need to go forward of. The CSC design by Kelsall was layed out around the idea of a huge central sallon, and minimal use hulls, but yours was designed around a sloop.
I could go on, but I don’t want to be a pain.
Anyway, just a word to the wise. As long as this is what you want to do, then I can’t wait to see it happen, and best of luck
July 29th, 2005 at 8:27 pm
I came to a similar conclusion for a cruising rig. I sure would like someone to build one before I get to that point. I expect it will cost less than the total cost of a conventional rig. The only downside is the interference at 90 degrees apparent. You can always change your course up or down and besides that is the fastest point of sailing anyway.
I like Sponberg’s implementation ideas. A short chord wing mast moounted on a spindle. You don’t need to worry about waterproofing a bearing where the mast penetrates the deck. The other idea is to use a single sided wishbone with the attachment near the mast track. You need a lot less depth in the curve of the boom when it is done this way.
September 7th, 2005 at 10:25 pm
i really like the idea of an unstayed biplane cat rig. schioning has proven the concept. perhaps your intrested in the website of jürgen sass:
http://www.multihull.de/technik/t-Sass.htm
it’s a german site. here’s the main-points:
- he uses a 6.5m beachcat for experimenting
- the sails have luffs around the masts (like the wharram wingsails)
- he reefes by rotating the masts
- a.t.m. he tries the 3rd generation masts + 2nd generation sails
- the bottom leek isn’t longer than the distance of the masts
- through the luffs and the missings stays he achieves a tacking angle of 65° [sic!]
- on the wind (like 35°) the sails are sheeted the same
- a bit off the wind (60°) the lee sheet is a bit less tight than the winward sheet
- on a reach (90°) the lee sail is covered. can be used to reef sails.
- apparent wind 120° the sails can swing in front of the mast and induce rather lift than drag. in theorie you could even achieve boatspeeds faster than windspeed.
- before the wind he sails wing and wing.
i’m intrested in your further progress.
September 12th, 2005 at 9:27 am
I am currently building a strip plank mast (only 16mtrs long) with a 40cm chord supported by a bracket 3/4 up the mast that allows a five stays plus two running backstays ( I am a belts and braces man) and at the base a bearing, this rig can rotate 85 degrees, the bearing housing is able to hinge to (1) rake the mast (2) allow the mast to be raised without a crane. I have only half a mast at the moment so I cant show any photos of bracket etc. got the idea from a rigging book by Brion Toss. Ian
October 16th, 2005 at 10:53 am
Tony Bigras has some thoughts and notes on an unstayed Biplane-rigged catamaran that you might be interested in viewing. Tony sketches out an unique concept of sail deployment while on Beam Reach to avoid ‘dirty’ air on the leeward sail. Here’s Tony’s website URL for that schematic:
www.mala.bc.ca/~bigras/mskeeter/skbplane.gif
Regards, Mark McKinnon
December 1st, 2005 at 10:08 pm
G’day,
I agree with all the positive points, but would make the following comments about the negative ones, in no particular order:
1) Price of carbon seems to be cyclic. At present it is scarce and expensive, may well be a glut and cheap in a few months time. Airbus uses 400 tons per A380 and they are building a couple of hundred of them, plus what Boeing and the US military are using. so there is no way that world wide supply will not soon match demand, at a lower price than previously.
2) Weight in the bows and blanketing. Reduce the first and eliminate the second by throwing away one rig and make the other bigger. The cost will be about 75% as both masts have to be strong enough to capsize the boat, whereas extra sail area goes on the top of the mast which is a lot lighter and hence cheaper.
3) Torque on the hulls: Pretty easy to design for, and does not need the bow beam to be included.
4) Kelsalls rig has a solid bar connecting the tips of the masts and stays. Hios building techniques are sensational, his rig ones less so.
5)Sail cutting. We have done a bunch of unstayed rigs which look good. The main on the boat in the pictures went up today, looks fantastic. A switched on, committed sailmaker is all that is required.
5)No one mentioned longevity. A carbon mast will last almost for ever, if designed and built right. Both these can be bench tested before it goes in the boat, and it should rarely if ever need to be removed. Apart from the running rigging (one halyard, one snotter) there is nothing to be replaced.
6) Ease of use. Once you have hoisted and lowered a mainsail with the rig facing into the breeze, or gybed and let the boom swing round to ddw, you will never go back to stays. There is a lot more on cost and ease of sailing on www.harryproa.com if you are interested.
7) Cost. We have just built a mast for a 15m Harryproa with far higher rm than your boat. Details follow, and pictures are at http://au.photos.groups.yahoo.com/group/harryproa/lst Click on the Visionar… folder. You have to join the group (easy).
Righting moment: 17,820 tonne metres/5,400 ton feet
Mast length: 18m/60′,
Above deck: 16m/53′
Diameter at base: 300mm/12″
Diameter at tip: 100mm/4″
Safety factor: 2.5
Designed weight of bare tube: 119 kgs/262 lbs
Actual weight of bare tube: 117 kgs/257 lbs
Designed deflection with 153 kgs/337 lbs midway along mast: 178mm/7″
Actual deflection with 153 kgs midway along the mast: 175mm/6.9″
Designed tip deflection at capsize: 2.9m/9′8″
Actual deflection at capsize: yet to be established!
Cost of mast painted with top and bottom fittings: $AUS15,000/$US10,800/9,000 Euros
Additional cost for lightweight carbon rcb track bonded on: $2,800/$US2,000/1,680 Euros
I would be interested to know how this compares with conventional stayed rigs if anyone has any costs.
Regards,
rob denney