trimaran hull shapes

Discussion in 'Multihulls' started by harrygee, Aug 6, 2012.

  1. harrygee
    Joined: Feb 2010
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    Location: Tasmania Australia

    harrygee Junior Member

    Hi All

    I'm planning to build a new main hull for my existing 27 foot tri, which currently has a Soling keel-boat hull as the main hull. I've been sailing the converted Soling for a few years and it's done everything that I could've asked but it does have an issue with trying to exceed the hull speed. It does 15 knots easily enough if there's enough wind but it throws a lot of water around in moderate conditions before it gets going.
    I had planned to build a long, skinny, rounded shape but several modern tris that I've looked at have near-flat sections aft, some having flat sections for most of their length. I can see that a boat will tack easier with flat sections, will have better floor space for a boat with accommodation, will trail better and will tolerate loading but is there any speed advantage, compared with, say, an egg-shell shape?
    I realize that I'll lose some of the handling of the existing boat, which tacks and sails donuts like nothing else I've sailed. I use the boat for round-the-buoys racing and just blasting around.
    I'm an experienced builder and will probably build with solid glass over a male mold, for economy.
    Basic specs, existing boat; 27' loa, 20' lwl, 19' boa, 780 kgs (I expect to lose 100 kg), 13" draft (4' board down), sail area 310 sq ft, cost very little so far.
    Thanks for any input.
    Harry
     
  2. Corley
    Joined: Oct 2009
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    Location: Melbourne, Australia

    Corley epoxy coated

    You will definetely visit Jenny Craig with the conversion because your current boats pretty heavy for a trimaran of that length. You might like to look at the hullshapes that Ted Warren drew for his Warren 23 (actually 25'). There are more pictures in the thread from HASYB for inspiration I really like the boat and think it would be an ideal boat for daysailing and racing. Your chosen construction method is probably the most economic but will yield a heavier than is necessary boat paulownia/composite strip plank or foam sandwich would be lighter and yield better performance.

    http://www.warrenmultihulls.com/w-23.htm

    http://nand.net/~josh/boat/index.html
     
  3. Silver Raven
    Joined: Oct 2011
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    Location: Far North Queensland, Australia

    Silver Raven Senior Member

    Gooday 'taswegian'. Some questions - please. How long do you want the main hull to be ?? - the longer (within reason) the faster - potentially - - How much do you want the whole boat to weigh ??? how much do the beams & the floats weigh ??? Are the floats raised up or canted ?? Was the length of 27' just because that's how long a Soling was ??? Why not something like a 'Hughes' 31' trimaran with sliding connectives' - from the Hughes design site - - the main hull is a great practicle & useable hull shape. The sections - shown in the 'brief' are really fabulous. How wide do you want the whole tri to end up ???

    Great project you've got in front of you . Good luck & do keep us informed. I'd sure like to know the design ideas that you want to incorporate into your decision. Thanks for asking your questions here - I'm sure many of us will learn for your travels. Ciao, james
     
  4. luckystrike
    Joined: Feb 2010
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    Location: Germany

    luckystrike Power Kraut

    Hi Harry,

    lets say so, the flat underwater body has no real disadvantages against the really round one. You have a slightly higher wetted area (around 2%), therefore the "flat", which is a little rounded for compound curves (material stability and stiffness), is producing some dynamic lift, reducing w.a. and creating some sort of planning. The flat bottom has important advantages adding longitudual stability, countering nosediving and hobby-horsing.

    If your homewaters are not a general a light wind area, I would choose the slightly flatter bottom.

    I agree with Silver Raven, take a look at Kurt Hughes bulkhead shapes for the smaller tri's, my favorites are the Tomcat 30 and the 26', a little more speedy than the 31. The slight "V" in the bottom is a result from Hughes plywood building method "Cylinder Molding" and can be full round with grp.

    You will build with solid grp? I think this will be a little to heavy to make it stiff enough if you have a cabin. Think about sandwich or strip planking, or Cylinder Molding with ply and Epoxy. If your amas are meeting the charakteristics of Kurts hulls, you have a very cheap, fast and powerfull design package.

    Best Regards, Michel
     
  5. Corley
    Joined: Oct 2009
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    Location: Melbourne, Australia

    Corley epoxy coated

    If I recall the boat correctly it was just like a little daysailor/racing style trimaran if you go to the larger Kurt Hughes style main hull it might be a bit more boat than the OP wants. Is that the path you want to continue down or are you looking at more of a cruiser/racer style boat?
     
  6. luckystrike
    Joined: Feb 2010
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    Location: Germany

    luckystrike Power Kraut

    May be Iam inflenced by the austrian Soling to Trimaran conversion that has a cabin. And in my homewaters it is "normal" to have a cabin on a boat 26 or 27' feet long.

    http://members.aon.at/trimaran/Fotogalerie.htm

    But Kurts boats, and especially the 26, are so simple and sleek, that the wing and cabin could be left and you have a perfect mainhull for daysailing.
     
  7. Corley
    Joined: Oct 2009
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    Location: Melbourne, Australia

    Corley epoxy coated

    no arguments here Kurt draws great boats and the telescoping beams would make a straightforward adaptation to the existing floats.
     
  8. harrygee
    Joined: Feb 2010
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    harrygee Junior Member

    Thanks all
    There's so much information in those replies, I'm going to spend a few days checking it out. I like the look of that Warren in the US, there's a lot of information in those pictures. I'd grab it at the asking price. I do deliveries but I don't think I'll be taking that on. And if I did, I'd need another project.
    The reason for building in solid glass is just economy. It's been a "what if" project from the start. I've been into multis for 30+ years so my Soling, though a thoroughbred, was in need of some "improvement". I built the amas in solid glass (foam decks), the beams in oregon / gaboon ply / double bias, the beams sliding onto the amas in sockets. The amas weigh 70 kg each, the beams 35 kg. The amas are 140% (current weight), 25' long.
    With the help of a fellow "junior sailor" (combined age 130 years) the boat is easily assembled in two hours and I leave the boat on the mooring.
    It's an open boat with no other purpose than to feel good.
    Weight is not critical as there are no hot multis to compete against. Our sailing conditions favour a bit of weight as we often encounter "dead spots", with no wind at all, when the heavier monos will glide past me and reach the next breeze - I've sat and watched the whole fleet pass me, unable to steer for an hour. We also get severe squalls, hence the moderate sail area. (Okay, the sails are Etchel sails on a Dragon rig, to replace the Soling rig and sails that collapsed in a bit of wind).
    I may keep the deck, as heavy as it is, because it's a good working platform.
    The waterline beam now is 5' so I think I can improve on that.
    Thanks for the input.
    Harry
     
  9. idkfa
    Joined: Sep 2005
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    Location: Windward islands, Caribbean

    idkfa Senior Member

    One great advantage a rounded hull has over a squared one is in strength and stiffness, especially if you're not using coring. It also helps with tacking and having rocker also helps tacking.


    Having little-no rocker also reduces hobby-horsing, but this is more the function of the amas: The vaka can ride whereas the amas submerge. Having a flared stern (straight bow) can provide some longitudinal stability. ie. differing shape/volume/reserve-buoyancy at the ends.
     
  10. stove
    Joined: Mar 2013
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    stove Junior Member

    Harrygee, any chance you will share more info on your Soling trimaran, I'm also in the process of building a tri made up out of Tornado amas and a Soling 27.
     
  11. harrygee
    Joined: Feb 2010
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    harrygee Junior Member

    Hi Stove and All

    The new boat has been in the water for a month but I don't yet have a clear picture of how it goes.
    I had a leak at the centre-board case which resulted in 150 kg of water below the sole, slowing the boat and making it handle like a pig. I thought I'd got the numbers badly wrong but, when I hauled her out, found the problem.
    She now sits right, with the transom well clear and the bow an inch clear, one float 7" clear when empty.
    All-up weight (empty) about 680 kgs, the new hull being about 400 kgs including the Soling deck, which is heavy.
    The new hull is 29', the rudder making it 30' overall. Waterline beam is 20". draft 16".
    The hull shape is a fine oval at the bow, becoming egg-shaped, then becoming a 6" flat aft. With high buoyancy in the stern of the main hull and in the bows of the ammas, the pitch-damping can be felt through the seat of the pants and works very well. Tacking is not as quick but nothing would be as quick as the converted Soling. When carrying the extra 150 kgs, tacking was awful.
    Performance is still being evaluated but she's faster than the converted Soling in all conditions so far. I've only done a couple of races and I'm able to stay with the Etchells to windward in light conditions (their strength), sail away in fresh wind and reaching. Running square, she matches the Etchells when they fly their spinnakers and I don't, I have to learn the angles and get my spinnaker sorted out. The one (no spinnakers) race in which a multi turned up, we sailed away from a Farrier 9 metre. The Farrier looked heavy and we were dragging around 150 kgs of the bay.
    This coming weekend is our club's Regatta weekend, when we'll get up to 80 boats from all over to race against and I hope to have the spinnaker working and see how she goes in a 24 mile race and a round-the-buoys demolition race.
    I'll try to get a photo organized.
    Stove, none of this is much good to you but I'm happy to share what little I've learned.
    The Tornado hulls look as if they have less buoyancy than my home-made amas but they may do the job if you're thinking of a light-as-possible day-sailer like mine. I wouldn't think they'd be adequate for a Soling with minimal accommodation. They'll have less than 100% buoyancy, an arrangement which was once described as "safe, semi-submersible floats" by a designer who now offers safer, bigger floats. They could be extended without too much work, I should think, a 5' extension giving you about 100 % (off the top of my head, not calculated).
    Good luck with it.
    Harry
     
  12. stove
    Joined: Mar 2013
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    stove Junior Member

    Hi Harry. I'm very excited about the photos of your "new" Tri. I hope the results without the water ballast will be what you hoped for. I would love to see more of your "old" Soling Tri as well. I would appreciate some info on the beams you made (dimensions, plywood thickness, type of glass used etc.)
    The plan so far is to keep the soling pretty much as it is. (open deck day sailer) without the keel and original rudder, pretty much a copy of yours. I might go with a center board and not a dagger board like yours only for safety. She will be sailed inland on a big dam where conditions don't get too rough. I'm very worried about the mast after reading your posts, any advice to avoid what happened to your original mast would be appreciated. I did get a main sail with the Tornado hulls that are still in good condition. The sails on the soling are really old and worn.(Spinnaker is good). What did you mean by scalloping the hull in one of your posts? I want to keep the fore deck with the self tacking jib, might widen the area aft of the mast right up to the aft bulkhead, would love to see the deck layout of your tri because it seems your cockpit extends all the way to the back. I want to keep the mid part free of winches etc so that I can pitch a tent across both trampolines with a cutout in the floor of the tent above the "mid" cockpit area.
    I will probably add some water stays as well and use only aft running side stays if I' going to use the roachy Tornado main sail.
    Sorry for all the questions but I am very excited about what you've done and maybe you can help me avoid some of the pitfalls.
     
  13. harrygee
    Joined: Feb 2010
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    Location: Tasmania Australia

    harrygee Junior Member

    Hi Stove
    The beams are made of curved, laminated oregan, 6" deep tapering to 4.5" where they meet the ammas. There are 1" wide laminations, capped top and bottom with 3/8" gaboon ply, 8" wide, the whole wrapped in 2 layers of 450 gm (1.5 oz) double bias, all epoxied. A glass fairing was then added. My beam is 19'. The beams end in tapers which slide into glass sockets on the ammas. The ammas are held on by sailing forces but I have security lines. The beams are held to the (reinforced) deck by four glass saddles, made of 9 layers of 450 gm double-bias and epoxy. It's all guessametrics but nothing shows any hairline cracks.
    The Soling mast should cope. I had seen a need for aft lowers to stop the mast pumping forward and tried "temporary" spectra, which worked so well that, eighteen months later, they still worked until I was caught in a sustained 40 knots in a narrow bay with no system of reefing and nowhere to hide. The lowers broke at a chafe point and the rig dropped.
    I replaced the rig with a Dragon rig, which is 6' taller and almost the same section, (thinner in fact). With some better stays, the new rig is going ok. So far.
    I use Etchell sails, which don't have much roach so I have retained the adjustable backstay, though I'm nervous about induced bend.
    My side stays are not adjusted when sailing. They attach to the ammas about 5' aft of the mast. With all the flexing, the leeward stay dangles around. The rig is triangulated by the side stays and forstay, the spreaders and jumper-strut forming diamonds to keep the rig in column.
    I did fit an aft cockpit on the Soling conversion, to simplify the transom-hung rudder. The new hull is more sensitive to weight distribution so I'm back in the main cockpit, with a pushrod to the rudder.
    I've cut a hole at the aft cockpit to fit a 3 hp outboard, which gives about 5 - 6 knots (just done it, will know more after this weekend.)
    The Soling makes a good conversion, the flat sections aft helping to reach 15 knots or so in a good wind, with awesome spray. The new hull does better with no speed hump and no spray.
    As a Soling conversion, the ammas just kissed the surface and tacking / spinning was sensational. I've now raised the floats a little - there's not much downside in a boat that's just built to go, with no accommodation.
    My new centreboard case (same board) is off-centre to allow more working room near the mast.
    I'm learning by doing, not an expert and I expect to have more bloody noses down the track but it's all fun and has cost very little so far. The Soling cost A$3000, with mast, sails, trailer (sort of). The conversion cost a bit more than that (convenient memory, I don't recall exactly), the rig cost me a donation. the new hull A$2000. Good value. My paraglider cost more and the medical expenses more still.
    I'll get someone to help me with photos after next weekend's regatta.
    Harry
     
  14. stove
    Joined: Mar 2013
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    Location: South Africa

    stove Junior Member

    Hi Harry, what would you suggest the sizes should be of the additional front stay and side stays if I skip the back stay. I will keep the original upper and lower side says as well.
     

  15. harrygee
    Joined: Feb 2010
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    Location: Tasmania Australia

    harrygee Junior Member

    Hi Stove
    My forstay and side stays are 5 mm (just over 3/16"). The geometry means they're not heavily loaded. the backstay is not structural and is released at times. My original cap shrouds are no longer taken to the deck, they're attached to the base of the mast as a diamond. If they were still taken to the deck, all the load would come onto them as the flex in the boat would ease the side stays. I also have the normal Dragon diamond stays (4mm) for the top half of the rig.
    My aft lowers are taken to the deck to stop the mast bending forward. They're adjusted to allow the side stays to take the load, the lowers just keeping things in line. The lowers are placed so that the boom touches them at the same time as touching the side stays.
    I'm progressively fitting staylocks to all rigging but, though reusable, I've yet to find a way to reuse a shroud - removing the staylock taper wrecks the end of the wire.
    Harry
     
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