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Old Jul 11, 2006, 03:17 AM
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Joined Jun 2006
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Scratch Built Trimaran Pitchpulting need help!

hey just took my tri for its first sail today and there was a bit of wind and i used the sails of my marble head which were already over sized. Bout 1m squared of sail.
so now i think its time to put a wing on the rudder or dump some weight on the bak of it. sugestions would be good. Thanks
ill try and post pictures soon

http://members.optushome.com.au/nqda...07-06_1523.3gp
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Old Jul 11, 2006, 01:16 PM
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Dick L.'s Avatar
Minnesota, USA
Joined Aug 2002
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OK - you are using an old "M" class sail.

What is hull length, beam width, weight and total height of the leading edge (luff) of the main sail. All combine to create resistance to a pitchpole. Also, the hull design, angle of sail - upwind, downwind or reach, and a few other factors.

Main thing - without a lot of physics, is that the height of the mast is a "lever, that tries to turn over the boat - either sideways or forwards - depending on angle of sail. Sideways can be reduced by beam, less sail, lower mast and lower aspect ratio sail, steering and moveable ballast (if you are quick enough), while pitchpole forward is more difficult.

You can slide moveable ballast back, lower mast height, sail on a deep reach instead of directly downwind, more buoyancy in hulls toward the bow, and possible "T" foil on rudder(s). Basically, the mast and sail are trying to move forward, but hull resistance prevents the "platform" from reacting as easily. The height of the mast (lever) simply overpowers the boat and pitchpole results.

Hard to give better more exact answer without seeing design, and knowing wind strengths. If the tri is at least 1.2 meters in leength (48 inches or so) and you are running a full and high aspect ratio sail, winds shouldn't have been more than about6-8 miles per hour. After that - with a full size rig, it is strictly a gamble. Reduced sail is expected when you get to 10 mph or more. Amazing how fast a tri or cat will go with LESS sail area - especially if they stay right-side-up.
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Old Jul 12, 2006, 02:20 AM
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hey i will try and get pictures of the boat but the luff is 160cm, boat length is 1 meter and the width is also one meter. Yer i was thinking of adding a T rudder but im not sure if i should have it level or slightly angled forward to keep the bak down but it could shlow the boat. This is my first boat that i have built so i was goin for the guess and chek method but if i can get it right quiker then that would be good. Thanks heeps
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Old Jul 12, 2006, 09:59 AM
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Might want to lower the mast height (and sail area accordingly) to something around 50 inches maximum. Less sail are, less mast leverage, less tendency to tip. You are (seemingly) right at the very top of mast height/sail area. Also helps if youuse a "fractional" jib - (not a mast height one) of about 1/2 or 5/8 mast height. That will help keep sail area center of effort lower, which should also reduce tipping and pitchpolling.
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Old Jul 12, 2006, 10:18 AM
Useful Idiot
Asturias, Spain
Joined Mar 2001
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Dick would there be any advantage to a mast aft rig in this case? I seem to remember having seen some experimental cats rigged in that way.
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Old Jul 12, 2006, 10:19 AM
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Last edited by Dick L.; Jul 12, 2006 at 10:20 AM. Reason: duplicate post - sorry
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Old Jul 12, 2006, 10:51 AM
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Minnesota, USA
Joined Aug 2002
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Quote:
Originally Posted by martin richards
Dick would there be any advantage to a mast aft rig in this case? I seem to remember having seen some experimental cats rigged in that way.
Martin -

I think a general answer would be "Yes" - but obviously with some defined parameters.

I tried one rig setup with the mast located on the rear beam, and only one huge headsail. Like a giant genoa. Off-wind it worked, but had problems trying to sail upwind, because I coudn't keel the luff of the sail tight.

Trimarans can have masts "slightly" behind a normal monohull position and get away with it - but if one shifts the rig back and not the daggerboards (lateral resistance) weather helms creeps in. On a catamaran (2 hull) configuration, a look at modern beach cats - Inter, Tornado, A Class, F-18 etc. - indicates a very long bow, with the rig set aft by quite a bit. Keep in mind, that the boards are also shifted back as well to prevent too much weather helm.

Note how much bow is sticking forward of mast in the attached photo. This is about as radical as I have seen, but most have rigs that are slightly "more" than half way back.
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Old Jul 12, 2006, 06:06 PM
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hey got some pictures i will make sail area smaller and move the jib to half way and give u a report of how it goes could be a while tho cause that means making new sail lol i got some pictures of the boat and sails.
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Old Jul 12, 2006, 06:56 PM
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New Zealand, Wellington, Masterton
Joined Mar 2006
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Tim, to my eye the area of the fin looks a little excessive for the hull size.
Whilst it may not help your tip up problem, if you reduce the fin area it will certinaly let the boat go faster with less drag.
As Dick says "less sail area" will be your answer to your tipping problem.
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Old Jul 12, 2006, 08:51 PM
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Tim - definitely make/try a smaller sail set. Do you have any friends who sail 36/600 or 1 Meter monohulls? If so - try one of their rigs just for the hell of it. Dagger board that long (fore/aft) should make the boat point well, but may also cause it to want to stay head-to-wind. Hard to tell where the mast sits on the main hull, relative to board. Also couldn't see rudder size which may be too small.

What I did notice is hard chines! Where sides meet bottom, you have hard corners, which is hard to push sideways through the water. While it may help straight line speed, tacking becomes an issue since the boat doesn't want to change direction. You can't "Bang Tack" these like a monohull because they are too light and no lead to carry them through a tack. Must use a long slow arcing turn. Once wind fills on other side of sails, let sails out until moving well - then trim in sails slowly and begin pointing up toward weather. If you sheet in too fast, the boat will want to head up into the wind. You need to keep boat moving all the time - if you slow too much, you will have no steering and wind up back into "irons" with bow stuck pointing toward wind.

Now the good thing, is since the boat points into the wind, you don't have to "try" to point high into wind. Let boat do it by itself and just concentrate on footing off a bit and keeping up the speed. Even if the boat doesn't point as high as a monohull, your speed should be twice as fast, so you can cover more distance even if sailing a bit farther. Multihull sailing is not the same as monohull sailing. Speed and keeping it moving, and as few tacks as possible up wind are keys. Every time you must tack, you can lose valuable boat lengths to competition.

Good luck
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Old Jul 12, 2006, 10:46 PM
Foamy Season is here! MX2#1
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Elizabethtown, Kentucky
Joined Nov 2005
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neato, should be fast!
mike
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Old Jul 13, 2006, 12:16 AM
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the mast sits just behind the winch on the lower sections of the deck hard up against i tried to design the boat so the mast was just infront of the fin. thanks heeps for the help and i need sails for my iom so i may aswell get some decent ones. ill keep you updated on how the boat goes with smaller sails.
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Old Jul 13, 2006, 05:00 PM
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where are you located? Perhaps some multihulls in your area?
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Old Jul 13, 2006, 05:05 PM
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aust,brisbane,wynnum wadding pool the only multi hull i have seen was one that had been bought from a shop which was a fidji 60 trimaran.
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Old Jul 14, 2006, 12:13 AM
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Tim -

I know Queensland is a mighty big chunk of land - and I have lost contact with Peter Birch who was secretary for the multihull group sailing there and also a Richard Billet. I don't know where Brisbane is compared to other cities - didn't bother to do a MapQuest search, but start with this information, and you may find a someone close enough to help you sort out your tacking problems.

Queensland Radio Control Multi Hull Owners Association Inc

They show a website, but I can't seem to get it to open for me - so start with email.

Secretary: Ken Smith
23 troop street
Jamboree hts QLD 4074

Phone: (07) 33763469

Email: k.r.smith@uqconnect.net

if that doesn't work - try this person, but he is monohull I believe - still he may know of multihull guys and any updates.

Queensland Radio Yachting Association
President:
Graeme TURK
8 Morwell Crescent
NORTH LAKES Qld 4509

Email: gturk@bigpond.net.au

Phone 07 3886 3510

Fax: 07 3886 5170

Good luck !
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