Hull material for arctic cruising

Discussion in 'Materials' started by Autodafe, Jun 18, 2008.

  1. Autodafe
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    Autodafe Senior Member

    Hi folks,

    I want to build a catamaran suitable for Arctic and Antarctic cruising. The tested choice for icy waters is steel, but this is obviously too heavy for multihull use.
    I torn between ally and timber (coldmolded or marine ply). At the moment I lean toward timber, because I'd be more comfortable nudging 'bergs with 25mm of ply than 5mm of aluminium (equivalent weights).

    Any thoughts from designers and cruisers with cold water miles under their belts would be greatly appreciated.

    Thanks.
     
  2. Landlubber
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    Landlubber Senior Member

    Steel.
     
  3. SamSam
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    SamSam Senior Member

    Ice eats wood.
     
  4. TeddyDiver
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    TeddyDiver Gollywobbler

    Wooden boats have been coated with (different kind of) metal plates succesfully. Also glass fiber gives some ice resistance..
     
  5. MikeJohns
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    MikeJohns Senior Member



    Welcome to another Tas-Man (I'm in Margate)



    You really need to post all your design criteria before getting down to materials and design ; Size, storage, tanage, preffered rig, desired performance, draft limitations, equipment and machinery to be absorbed. Number of people aboard...........etc

    Another important consideration if you want to motor in ice is prop immersion depth and protection.

    Aluminium is a good option. Metals yield at the point wood and GRP ruptures so you get some 'insurance' for free.

    But the southern ocean is a questionable theatre for smaller multihulls, if it is to be a large one then steel could be feasable. I also have doubts that a multihill will be easy to maneuver through ice since you cannot put your bow in the gap and motor ahead to separate or break through.

    Even Ferro boats have been modified for Lloyds ice requirements for cruising in the Antarctic. You can also use collision mats when nosing through it.

    Cheers
     
  6. Autodafe
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    Autodafe Senior Member

    Thanks for the input so far.

    I quite like the idea of thin plating over wood... I'll have to think on that idea.

    I'm in Hobart Mike.

    The plan at the moment is 13m LOA multi-chine, biplane junk rig, twin diesels (30-40hp ea). Open bridgedeck with accommodation for 2-3 only. Draft around 600mm with board raised (largely determined by the props). My initial estimates had displacement at 5t empty to around 7.5 cruising, but that was before I added ice strengthening to the design requirements.

    As far as Ice performance, I'm not aiming to get serious in icebreaking, but I want to be able to potter along summer exposed coasts without worrying too much about the smaller drift ice.

    I have some reservations about Aluminium in sailing cats as I feel the long, thin hulls and beams are susceptible to Ally's intrinsic endurance limit, but I guess that can always be allowed for in design.

    I have wondered about prop protection, and I love to hear some possible solutions?
     
  7. MikeJohns
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    MikeJohns Senior Member


    Tunnels, guards, bar skegs, deeper immersion of the prop, stronger prop, propshaft and bracket, special props, you meet all sorts of solutions.

    With a relatively small catamaran it's debatable whether any of this is really feasable. Motoring slowly ahead with good viewing is probably as good as anything for such a vessel.
    Outboards are easy to repair the shear pins.

    Cheers
     
  8. SamSam
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    SamSam Senior Member

    Lumps of ice are different, as is serious icebreaking. A 1/4" skim coat of ice can eat a hole in a boat at the waterline real quick.
     
  9. lazeyjack

    lazeyjack Guest

    it is a well known fact that al al gains strength in cold waters, wood in the high lats, not really. cat in artic circle,? well unless youa re one very very good sailer, I would revisit that option Monos can forgive mistakes, , cats, never do
     
  10. Autodafe
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    Autodafe Senior Member

    Thanks for the input guys.

    I see your point samsam, I think I've settled on metal hulls as the safe option.

    Seaworthiness is something I'm putting some thought into at the design stage lazeyjack, but I actually chose a cat principally on the safety aspects. I prefer an upside-down cat that floats to a mono that will *probably* self-right before filling with water.
     
  11. Landlubber
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    Landlubber Senior Member

    Autodafe,

    A well designed steel mono, deep keel, in the water not on the water is a thing of beauty in serious conditions.

    I had one of my boats down to the gunwales once at sea, there was so much foam around us that the boat could not get normal bouyancy, she was sailing bare at 6 knots and a metre low on the waterline, but still completely dry and safe down below. I have a lot of faith in such a vessel. She was a slightly modified Halvorsen Freya, I can only recommend her design as being very seaworthy. I still have her lines plan, and expect to make another one some day.
     
  12. NordicFolkboat
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    NordicFolkboat Junior Member

    The Fram was sheathed in greenheart, and made it across the arctic ice sheet in one piece. But steel is probably much more practical.

    Are you sure a catamaran is a good idea in Arctic waters? Sure, it will float when capsized, but you would be really exposed to the elements on it. I would think it's better to bring a proper life raft just in case the monohull doesn't self-right.
     
  13. MattZ
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    MattZ Junior Member

    Steel is the strongest, and if properly engineered it doesn't need to be as heavy as you think.

    Fiberglass would be another good choice. Ive will kill a wood hull.

    MikeJohns had a comprehensive list to which I would like to add: bring a spare prop and tools, including wetsuit/drysuit. Just an idea I had. I've been tinking with the idea of a boat for Arctic cruising, and that's one of the ideas I came up with.
     
  14. Autodafe
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    Autodafe Senior Member

    Thanks for the interesting note on the fram NordicFolk.
    A number of early wooden vessels seem to have been successfully strengthened for ice service, but mostly it involved 2-3" of extra planking, which is a bit heavy (and costly) for my project.

    I have serious reservations about liferafts. In all the highly quoted major yachting disasters of recent history (Sydney Hobart '98, Fastnet, Queens Birthday) liferafts appear to have cost more lives than saved.
    I am inclined to think that a better option is a thick drysuit, which, as MattZ mentions, has other uses as well.

    Safety conscious cats these days are designed with survival compartments in the hulls. These are above the inverted waterline and have access from the underside of the bridgedeck. Not comfortable, but out of the weather and drier than a liferaft in a storm.

    Thanks for the tips Matt, I agree entirely on carrying spares for the prop (for all cruising, not just high latitude).

    I was surprised to discover when I got quotes that Alloy costs no more per kilo than marine ply where I am, so Aluminium is where I'm thinking at the moment.
    I compared approximate material weights when designed to Lloyds SSC standard and Alloy and ply are very similar (ply to local USL standard as Lloyds doesn't cover it) but mild steel was over a tonne (~80%) heavier for hulls only (bridgedeck to be ply for insulation and light weight). While the weight with steel was workable the extra speed and/or payload with alloy is too tempting.
     

  15. NordicFolkboat
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    NordicFolkboat Junior Member

    Where in the Arctic are you planning to cruise? Barents sea, Greenland sea, Northwest passage, Bering sea?
     
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