New Trimaran/Skiff Design

Discussion in 'Multihulls' started by Chris Ostlind, Feb 22, 2009.

  1. Chris Ostlind

    Chris Ostlind Previous Member

    This is the first in a series of four new multihulls that I will be introducing over the next few weeks.

    Over the last 6-7 months, I've been doodling around with a design for a boat destined for the homebuilder's market that pays homage to the very cool Weta trimaran out of New Zealand.

    This boat is mostly built in 4 mm marine plywood with glass/epoxy laminates inside and out. It departs from the plywood build process with a strip built foredeck and curved transition surfaces in the cockpits.

    I've posted an article describing the boat on my website:

    I'd like to hear any comments that you may have regarding this boat.

    Attached Files:

  2. Doug Lord

    Doug Lord Guest

    Does the main hull plane? Apparently, if I understood you correctly, the ama won't support the weight of the boat without being totaly immersed-is that right?
    PS- the crossarm transition into the amas looks much better than the Weta...
  3. grumpy old man
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    grumpy old man Junior Member

    oh no not the planing trimaran debate again :(
  4. Chris Ostlind

    Chris Ostlind Previous Member

    No, Grumps... no planing tri debate on this one.

    There is a skiff-like main hull, minus the racks, or wings, which may be able to afford some of the characteristics of the typical, well sailed skiff. It all depends on the person driving the boat.

    The amas are smallish, at 100%, for what some might call a "normal" trimaran. The ama buoyancy is augmented by the sliding ballast system (crew) who should be able to move about as needed on the tramps to keep most of the heeling moment loads off the amas.

    I see the ama role in this design as what some might call a, gust driven capsize preventer. You may even wish to call them training wheels if you're in the right mood. High performance skiffs deal with this capsize situation as a matter of normal sailing until the crew get very familiar with the boat and raise their skill level. For a more family oriented boat, though, I was looking to emulate the Weta example of providing a large measure of enhanced stability so that the boat could be sailed briskly by novices.

    I see the owners of the Montage as initially using the ama buoyancy quite a lot when they first get the boat and sicover how to sail it efficiently. As their skills increase, they will probably be more active on the boat and get out on the tramps more, reducing the amount of, ama to water, contact. This will reduce wetted surface and they'll see much faster sailing as a result. Less aggressive sailors will simply enjoy the boat as a trimaran and they will regularly have the Montage heeled over on the leeward ama with less use of the tramps for righting moment.

    There is another tangible benefit for the small ama volume of this design. As a boat that is targeted for the homebuilder's market, it's important to understand that not all homebuilders are going to be able to keep the amount of resin used to an absolute minimum. Excess resin use would drive up the overall weight of the boat. Smaller amas have much less of a chance of seriously impacting the overall weight of the boat due to the reduced surface area.
  5. grumpy old man
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    grumpy old man Junior Member

    with there being dozens of old hobie 14/16 cats laying around the backblocks for prices as low as $200 fully rigged wouldnt a 'skiff'type design thet would incorporate the hulls, fully battened rotating rig and kickup rudder system be a cheaper way to go to encourage cheap 'performance sailing
  6. Chris Ostlind

    Chris Ostlind Previous Member

    H14 rig as option?


    I looked at using an H14 rig, as the size of the stick and the sails was just right for the boat. Turns out those H14 mast and sail pairs are fairly tough to find. The Turbo jib option is even harder as a used item. That means that all sorts of other rigs, such as the 420 setup, are just as viable and as it turns out, they are much easier to locate.

    I do spec an H14 rig as the preferred setup for another boat I have recently completed, but I do not see that design as having the same kind of large scale appeal as the Montage, so finding the available rigs will be much easier.

    The Hobie rudder hardware could be a very good solution with a different, lighter weight blade.

    I did not consider H14 hulls for the Montage for two reasons.

    One: the hulls are just as difficult to locate and when you do find them, there is a good chance that they are spongy and would need lots of stiffening. That would add weight pretty fast and kill the whole notion of where the boat should be headed.

    Two: the H14 hull shape has been known to contribute to the business of pitchpoling, they carry their biggest volume well aft of where I would like to see it for a trimaran ama and... I simply do not care for the lines.

    There are thousands of H16 rigs, hulls rudders... the whole thing, all over the world, but the rig is stupendously huge for this boat at this particular size and this specific purpose.

    I like using H16 rigs for my design work for all the reasons you mention, just not on this one.
  7. Doug Lord

    Doug Lord Guest

    In this case I don't see any debate at all: skiffs plane-no ifs ands or buts....
  8. grumpy old man
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    grumpy old man Junior Member

    only when theyre going fast enough... otherwise theyre a displacement v/l like every thing else
  9. grumpy old man
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    grumpy old man Junior Member

    maybe aslightly bigger version than the one youve drawn may tempt the person with the h16 sitting under the mango tree to do some thing with it particularly if he/she has got kids to introduce to the fun of sailing but doesent want to drown them when the pitch pole happens.... I rejected a very good offer on one of my old tornados for that reason ... backm in the early eighties there was a design called a tremolino?? that did a cat to tri conversion using the tornado for the donar parts ... i only ever saw one on the water... and as it was a quiet day the performance was as to be expected ... quiet. This was in the days before assys and prodders and screechers so it appeared to have similar speed capabilities as the old rl 24.. but in a lot more comfort.. no heel I cant remember who designed it but it was in a similar vein top the tramp tri only not folding
    ps the hulls of a ply tornado back then wieghed in at 100lbs (each) light for a 20 ft hull
    Last edited: Feb 24, 2009
  10. Chris Ostlind

    Chris Ostlind Previous Member

    I was staring at the ceiling last night and thought of something very much like that, Grump. A big brother tri at about 17' for speedy family sailing would be just the ticket for an H16 rig. Like you said, they are everywhere, well known by the smallest of sailmakers and the mast is not too hefty for a simple raising on the launch ramp, or beach.

    Dick Newick's Tremolino was certainly a boat with a very clear vision. There's a whole cadre of enthusiasts around today who cherish their Trems and for good reason. They are fast, fairly easy to sail and have very forgiving tendencies.

    I have done a boat with a similar conceptual daysailing approach called the Laguna 20. The main hull is built in marine ply and the rig, rudder, ama hulls and sailing hardware come directly from a Nacra 5.2 or 5.7. The amas fold on a simple, single strut system. The boat easily fits within trailering limits anywhere in the world. None have been built as of yet, but I'm thinking it should be a fairly quick machine in the hands of a typical recreational sailor.

    There is also a 22' version of the same design that employs cat hulls from a Tornado, or a host of 20' beach cats with a decided preference for the cats that have large volume with a distinct forward bias to the volume distribution.

    There are, literally, dozens of design ideas for boats of this type in the under 22' category... so, there should be a lot of fun in the years ahead as interests and market trends develop.

    Attached Files:

  11. Chris Ostlind

    Chris Ostlind Previous Member

    Just had one of those insightful, Homer Simpson DOH! moments, when I realized that the website page for the Montage didn't have the specs posted. I had put them in when I originally built the page and somewhere in my editing frenzy, they got clipped.

    So, they're up now on the site and also here...

    Montage Specifications

    LOA 15’ 6”
    BOA 12’
    BOA main hull 41”

    Sail Area
    Main 110 sq. ft.
    Jib 38 sq. ft.
    Screacher 102 sq. ft.

    Displacement 650 lbs.
    Weight 235 lbs.

    Sorry for leaving that out.
  12. Fanie
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    Fanie Fanie

    Looks good Chris, but does the main hull plane?


    Looking good.
  13. sigurd
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    sigurd Pompuous Pangolin

    The montage:

    1) Humm, what is the middle hull for again? Can you sleep in it?

    2) Can you right it alone?

    3) Why is the middle hull so wide?
  14. grumpy old man
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    grumpy old man Junior Member

    I ran a h16 rig on a hartley 18 trailer sailer for a few
    years ....sailied it single handed most of the time there wasnt another t/s in the club that could get any where near me... I kept the rotating rig 1 reef point for the windy days and no jib for the realy windy days lot to be said for the control of a fully battened rig rarely seen outside of cats in the eightys... now the tornados are out of the olympics there may be a few of those available for conversion soon get yer pencil out chris!!

  15. redreuben
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    redreuben redreuben

    Chris O'
    you have a great eye for hull shapes and you have potentially plugged some big holes in the diy boat market. But you also have eleven renderings advertised on duckworks that have been "coming soon" for how long now?
    The Laguna 20' you have "done" is at what stage, rendered in a computer or built?
    I believe you would sell truckloads of plan sets for some of the ideas you have floated, I myself am dead keen on the Backbay/Doubloon concept, so please finish some jobs and stop teasing us.
    from Oz
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