which cat for me?

Discussion in 'Multihulls' started by Grizz, Aug 31, 2008.

  1. Grizz
    Joined: Aug 2008
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    Grizz Junior Member

    HooBoy, this one could stir some sand off the bottom...

    I had a sudden explosion of synapses that reversed my heavy displacement syndrome. I went through a phase of developing a sharpie for the final frontier when I was hit with the benefits and advantages of catamarans. Specifically, the wharram tikis suddenly dispelled all my prior biases toward multihulls when I was trying to make a sharpie do everything the cats can do, and failed.

    The design goal was to produce a boat I could sail anywhere, thin or thick water, beach most anywhere, and be reasonably comfortable in most anything.

    My last boat was a steel commercial fishing boat displacing over 50 tons. I always said that if I ever got a smaller boat it would have to be a lot faster. Now I'm into the sunset phase of life and need more exposure to those elements the seaman can't stay away from.

    If I had a tiki 26 right now I could fulfill about 93 percent of my needs and desires. I can sail back to SE Alaska and gunkhole the spots I missed in a half-life of beachcombing. I can sail across to HI, and north to Dutch, and West to here again if I get that much time.

    I like lots of stuff about the tikis. I love the lashup of the crossbeams. I always said that next to welding, lashings are the strongest way to attach stuff to boats. I have over thirty years experience doing that and can rely on line that way.

    Tikis aren't the only possible solution, but they may be the cheapest, and may also be the quickest.

    So what's the problem?

    I do not like plywood/cloth/epoxy materials. Don't want to build one, can't endure too much exposure. And don't trust them against the stuff that goes BUMP in the night.

    I would want the "pod" for on-deck watches out of the weather, for sleeping when solo, for their luxury. For a heat envelope in high latitudes, and shade in low ones...

    So then I start seeing the other competing designs and see that you can get a lot more enclosed space, and start to wonder if that displaces, get it?, the tikis. But I want the convenience of regularly taking the beach as well as the passage making options.

    But the final kicker is this: I want an aluminum cat. I know what I want and why. I want to cross the deep in a metal boat. And I eliminated steel as my material of choice by natural selection.

    The tikis look susceptible to the origami method of hull production. Some other cats with "dory" bottoms, or squared bottom sections even more so because I could use an aluminum channel for the bottom and have enormous strength.

    I realize the metal boat is heavier in comparison to the composite models, to a point. What point is that?

    So maybe the Question is: what is the best small aluminum sailing cat design to equal the medium size wharram cats?

    I hope I've ignited a long and good and beneficial discussion. Let's enjoy it.


  2. sandy daugherty
    Joined: Jun 2008
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    sandy daugherty Senior Member

    The short answer is "there isn't one. build it your self."
    And I predict the discussion will tend towards objections to your criteria rather than "OK if thats what you want". They will fall into conventient categories, tentatively described as:
    "26 feet to Hawaii and back?"
    "What cat can't be beached?"
    "Durability; aluminum vs figerglass"
    "Alergic to Epoxy, so what"
    and finally
    "Sailing to windward in a keel-less boat"

    I recall an aluminum fiasco with lots of confident self-agrandizement that broke up on the first day, I think from the San Francisco area. It didn't fail because it was aluminum, but it may raise a few points for discussion here. I suspect that the problems traced back to some arbitrary decisions made in the dreaming stage.
  3. Grizz
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    Grizz Junior Member

    Thanks for the reply Sandy. This being a design forum, I thought we could discuss designs. I intend to build it myself. I can fit, frame, and weld metal boats. That's not an issue.

    I invited discussion, and we can't keep out those with little or no experience. I'm hoping to gain the perspective of those with equal or greater experience.

    BTW, a raft made of trash just crossed, a tiki 21 circumnavigated, can anyone question in good faith the sea keeping qualities of catamarans?

    Thanks again for the response. I am interested in everyone's point of view, and good at spitting out the watermelon seeds...

  4. Richard Woods
    Joined: Jun 2006
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    Richard Woods Woods Designs

    A Tiki 26, like most small plywood multihulls, uses 6mm, 1/4in plywood. The boat is designed round that skin weight. Very roughly a sheet of 6mm ply weighs 20lbs, or 2/3rds lb per sqft. Allowing for the paint and glass sheathing that you won't need on an aluminium boat maybe you could have a skin that weighs 1lb/sqft

    As a metal worker you know how thin a 1lb/sqft aluminium sheet will be. You will also know that it isn't really possible to build aluminium boats using less than 3mm (1/8) plate

    In other words, you cannot sensibly build a multihull in aluminium unless it is over 40ft long

    Hope this helps

    Richard Woods of Woods Designs

    1 person likes this.
  5. northerncat
    Joined: Jan 2007
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    northerncat Senior Member

    In other words, you cannot sensibly build a "sailing"multihull in aluminium unless it is over 40ft long
  6. Grizz
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    Grizz Junior Member

    OK, that's a start, 40 feet.

    But for the sake of erasing my ignorance, how much volume would have to be added below the waterline of say, a given length tiki, to provide the necessary displacement to float the heavier hull?

    And that hull weight isn't more performance squashing than, say, a large crew with tons of personal property and huge electrical appliances, is it?

    But if 40 feet is it, so be it. Lots of trampoline space for snoozing.

    Any pictures or drawings of the smallest aluminum cats around?

    Thanks for responding. I should have mentioned the notice in my wheelhouse: No Task Will Be Evaded Merely Because it's Impossible.

    Even if the impossible takes longer...

  7. Gary Baigent
    Joined: Jul 2005
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    Gary Baigent Senior Member

    alloy cats

    Pajot's first Elf Aquitaine (67 feet) and the Peyron brothers alloy cat, theirs' was around 65 I think - plus the first 54 foot Paul Ricard foil tri and a few other French multihulls, were all big boats and none of them were particularly light, and they dented too. You need many, many stringers and frames with light skinned alloy construction, a huge amount of fiddly work. I think you should reconsider wood or foam sandwich construction and build a 35 or above cat - there are literally hundreds of good designs out there.
  8. Grizz
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    Grizz Junior Member


    Here's a 28 foot cat that would adapt well to aluminum build. Right shapes, plus extra displacement to handle the weight difference.

    If the weight difference is only .3 pounds per square foot, then this design should be buildable in aluminum; it's a tiki with extra volume to support the extra plate weight. Or not?

  9. Howaya
    Joined: Sep 2003
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    Howaya Junior Member

    Probably an inconvenient location for you and I'm uncertain it is still available, but not long ago there was an aluminum cat in FL for sale. It was about 33 feet LOA. Even if the cat isn't right for you, the engineer who built it may have some insights for you. Just a thought.

  10. Grizz
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    Grizz Junior Member

    Here is a tiki30 in aluminum. I think this boat sold in Nz. Obvious she doesn't sit light on her lines, but the boxcat's greater width should make the boat much more burdensome.


  11. Grizz
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    Grizz Junior Member


    Do you have a link to that boat? Thanks..,
  12. dsuursoo
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    dsuursoo Senior Member

    remember that aluminum's a real ******* to work. yeah, the tools are pretty easy to use, not as noisy, but your welds have to be PERFECT. glass/carbon would be a lot easier, given that. you'll need special gas, a covered work area, unless you're not building it yourself...

    and unless you're using some of the aerospace aluminum, it's not going to be very much more durable than composite, perhaps even less. the ductility could be your downfall.

    but hey, if you can do it, balls to you man.
  13. kengrome
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    kengrome Senior Member

    Yeah, right.

    Catamaran hulls do not have to be 'tall and slim' regardless of the fact that this is the way most have been built over the years. There is nothing wrong with building them 'wide and shallow' if you're willing to lose some benefits while gaining others -- such as shallower draft for example -- and in this case it would be perfectly acceptable to build a short multihull in aluminum.
  14. bill broome
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    bill broome Senior Member


    there's noise, and condensation, and weight, and some serious welding..

    and because you're the nervous type, wants to live forever.


    1: how bout a composite, aluminum bottom, lighter plywood above. doesn't have to glassed, plywood is quite strong by itself.

    2: if you don't demand min draft, put a plank keel under your wood/glas boat. you can still get out and walk ashore, but are unlikely to puncture a narrow hull above the fin. add a couple of extra layers of cloth underwater if it will unclench your knees.

  15. the1much
    Joined: Jul 2007
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    the1much hippie dreams

    which cat for me?
    i would get a tabby,, they are great mousers,, and very independent hehe :D;)
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