Small Tri's under 20', any mention of foils is banned..

Discussion in 'Multihulls' started by waynemarlow, Jan 13, 2015.

  1. Doug Lord
    Joined: May 2009
    Posts: 16,679
    Likes: 346, Points: 93, Legacy Rep: 1362
    Location: Cocoa, Florida

    Doug Lord Flight Ready

    Anthony, you can use small amas if they are a planing design like Sizzors or like the ones on Bethwaites HSP shown below. Displacement amas that are shorter than the main hull can cause lots of drag as the boat speeds up.
     

    Attached Files:

  2. waynemarlow
    Joined: Nov 2006
    Posts: 432
    Likes: 45, Points: 28, Legacy Rep: 134
    Location: UK

    waynemarlow Senior Member

    The longer displacement hulls only cause more drag if 2 hulls are in the water. If the centre hull is just skimming and mainly supported by the leeward hull which is a modern planing type then the drag is not unsimilar to a cat, but you have a lot more RM.

    In theory if we get Ama bouyancy value right we can carry our full sail suite right from only a few knots when the crew can balance the boat to nearly have both amas out of the water, on a relatively fat wide skiff like underwater shape. The wind gets up and now the leeward Ama begins to immerse and the central hull begins to lift, the water drag is much the same. When the wind really starts to get up the planing leeward hull now carries the majority of the load. The RM has increased as the leeward begins to take more of the loadings.

    I would love to build an HSP type for racing, a bit like an Indian Canoe with training wheels, as I think the manouveribility and excitement must be second to none, would I want to coastal race it or put my family on for a day trip, ah no. Definitely it has its merits but I think not that applicable to this thread.
     
  3. AnthonyW
    Joined: Oct 2012
    Posts: 115
    Likes: 10, Points: 18, Legacy Rep: 19
    Location: Cape Town, South Africa

    AnthonyW Senior Member

    Thanks for the replies. Still curious on ama % references and calcs, but this is not the thread for it so will pop the question out on its own thread.
     
  4. Corley
    Joined: Oct 2009
    Posts: 3,777
    Likes: 194, Points: 63, Legacy Rep: 826
    Location: Melbourne, Australia

    Corley epoxy coated

  5. Doug Lord
    Joined: May 2009
    Posts: 16,679
    Likes: 346, Points: 93, Legacy Rep: 1362
    Location: Cocoa, Florida

    Doug Lord Flight Ready

    Looks like both amas are in the water when she's level? And that's with a single person on board.

    click--
     

    Attached Files:

  6. waynemarlow
    Joined: Nov 2006
    Posts: 432
    Likes: 45, Points: 28, Legacy Rep: 134
    Location: UK

    waynemarlow Senior Member

    Looks like very little wind and speed meaning the leeward hull has little pressure on it.

    A lot of Tri's went with one Ama clearing the water at rest but the flip flop problem when not sailing is such a turn off that a lot of those boats lowered the amas so that the Amas just touch the water when at rest.
     
  7. Corley
    Joined: Oct 2009
    Posts: 3,777
    Likes: 194, Points: 63, Legacy Rep: 826
    Location: Melbourne, Australia

    Corley epoxy coated

    The Pulse looks pretty good to me for a boat which is like every other a compromise. I think they have struck a pretty good balance between performance and a comfortable and simple day boat that is easy to trailer and reasonably lightweight. The performance racing crowd like to flatter themselves that they drive sales but most people don't choose to race.

    There are some good ideas in this boat. I like the carbon ring frame for the front beams and mast compression it would allow a more open cuddy than the usual compression bulkhead type arrangement. The synthetic waterstay arrangement is also interesting. The price point seem reasonable for an entry type product.
     
  8. upchurchmr
    Joined: Feb 2011
    Posts: 3,272
    Likes: 250, Points: 83, Legacy Rep: 579
    Location: Ft. Worth, Tx, USA

    upchurchmr Senior Member

    Wayne,

    I checked out the Lhindal A cat build.
    Looks to me like the foam would be about 4x the cost of strip planking in cedar. It certainly should be lighter especially if you use graphite instead of glass.
    Is that another 4x cost increase?
    While I would like as much performance as possible it won't be as a result of gold plating the materials.

    I had hoped you had specific suggestions of "curvy" trimarans that I could look at.
    I am looking for plans.
    And I have seen the Kurt Hughes 19, etc.
     
  9. waynemarlow
    Joined: Nov 2006
    Posts: 432
    Likes: 45, Points: 28, Legacy Rep: 134
    Location: UK

    waynemarlow Senior Member

    I am not sure about the cost of cedar planking as it really doesn't interest me for a number reasons, principally working with wood is time consuming compared to foam which is quick and easy and can be easily formed into nice curves with low heat processes.

    I would guess others would enjoy the wood thing and they will go that way.

    But there are other issues to take into account, carbon prices are coming down and it has other benefits on small surface areas of limiting the weight by reducing the amount of resin with added strength. There's nothing nicer than sailing an all carbon boat, it just has that really stiff feel and the boat feels as though it wants to accelerate with every puff of wind, something I haven't felt in wood and glass boats.

    On that basis I would pay 4 times the cost as in the great scheme of things, the costs of the materials for the hull is only a small proportion of the total cost and if that extra material cost creates a lighter boat with better sailing feel and gives a better future selling price, then I'm all for that.

    As to curvy sassy looking modern plan based boats, yes you have a point that there are limited plans as yet available. I am not sure the Scarab flat panel type of build will ever give us the type of modern look I'm looking for but they do give fast build times and light weights for the amatuer builder. Perhaps in the near future we may see one of the top designers appear with a fresh 2015 style of boat, like the Pulse 600 or the SeaRail in plan form.
     
  10. redreuben
    Joined: Jan 2009
    Posts: 1,913
    Likes: 185, Points: 63, Legacy Rep: 349
    Location: South Lake Western Australia

    redreuben redreuben

    Medium tech.
    I would look at Paulownia rather than cedar and basalt or Sglass rather than carbon. An acceptable middle ground perhaps ?
     
  11. upchurchmr
    Joined: Feb 2011
    Posts: 3,272
    Likes: 250, Points: 83, Legacy Rep: 579
    Location: Ft. Worth, Tx, USA

    upchurchmr Senior Member

    Can you ship me some Paulownia? :p
    It is available in the USA but I might as well buy a good foam.
    :D
     
  12. 2far2drive
    Joined: Nov 2011
    Posts: 116
    Likes: 11, Points: 0, Legacy Rep: 82
    Location: Houston, TX

    2far2drive Senior Member

    Yea paulownia is quite expensive here. I even did research about buying a few acres and starting a timber stand of it for local boat building due to its high growth speed. Still might!

    Mrupchurch I have had the same material battle for years and I finally realized that many designers are correct about costs. Its the rig that puts a very serious dent in your pocket!!!! But I'm with Richard woods on this, foam build is almost worthless below 20ft. The weight savings can be found by just going to a gym or packing less beer.

    Fwiw, I've been watching seastallions new build (stretched dierking outrigger) and its strip plnk, WRC. Very affordable! So far about $350-400 to build a 24' hull!!!!! Clc pricing is very good and almost as low as local suppliers, and its already planed!
     
  13. upchurchmr
    Joined: Feb 2011
    Posts: 3,272
    Likes: 250, Points: 83, Legacy Rep: 579
    Location: Ft. Worth, Tx, USA

    upchurchmr Senior Member

    2far,

    You might think about a local wood.
    Cotton wood is not generally considered useful for anything. But some areas cut it for lumber and I had a local sawmill cut up a tree for a historically accurate chuck wagon.
    There is a guy who builds them for ~#40K. Cottonwood was the original wood of choice because it is light.
    Most have a very twisted grain which probably wouldn't work.
    A 75' tree cut into 1" planks was going to be $150. Wish I didn't have to buy that much just to try it out.

    BTW, I have a Tornado and a Hobie16 rig, so that cost is already sunk

    I also have a lots of weight reduction that can be done at the gym, if I wasn't reading this forum. :D
     
  14. waynemarlow
    Joined: Nov 2006
    Posts: 432
    Likes: 45, Points: 28, Legacy Rep: 134
    Location: UK

    waynemarlow Senior Member

    Why build in foam or wood

    I'm sure that it been covered a zillion times here on this forum but as we are specifically talking about a 20 ft Tri, then the question has to be asked, wood or foam core ? as its about this size of boat that there could be a cross over of value for money.

    In my view its a no brainer, foam is widely available from multiple sources, is very light, relatively in expensive, uses minimum resin to bond to the outer sheath, easy to curve and shape, generally holds its value better than a wood core boat and a couple of dozen other reasons to use foam. In particular though for me is that I can make one phone call and 24 hours later that foam will be on my doorstep, no mucking about in wood yards, no preparation, nada, just get on and build.

    And in the other corner, wood, any views
     

  15. cavalier mk2
    Joined: Mar 2010
    Posts: 2,132
    Likes: 56, Points: 48, Legacy Rep: 214
    Location: Pacific NW North America

    cavalier mk2 Senior Member

    Tilting at windmills again eh? (They were wood!) Check out the competition life span of modern dinghy and cat classes, as the structure softens up they have to be replaced using more petro chemical resources. Contrast this with the better fatigue properties of wood which is a renewable resource that will help the atmosphere carbon scrub and produce oxygen while growing and use less of the petros. Personally I think to have sustainable sailing we need to concentrate on sustaining life on this rock called Earth. Hooray for forestation!
     
Loading...
Forum posts represent the experience, opinion, and view of individual users. Boat Design Net does not necessarily endorse nor share the view of each individual post.
When making potentially dangerous or financial decisions, always employ and consult appropriate professionals. Your circumstances or experience may be different.