Ice loads on FPR boat hull

Discussion in 'Boat Design' started by Alik, Mar 28, 2012.

  1. Alik
    Joined: Jul 2003
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    Alik Senior Member

    Working on patrol/rescue boat capable to operate in thin ice at slow speeds. Schillings is to LR SSC, sandwich hull; they have some requirements for ice belt but do not specify the loads.

    Any ideas how to define ice loads, say from 50mm broken ice? I found a lot of papers on icebreakers, but those are not relevant...
     
  2. longcours62
    Joined: Jul 2011
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    longcours62 Junior Member

    Sorry I have no idea concerning the rules.
    What I can say : in ice + 20 cm tickness no troubles for our hull
    (except for the antifouling paint:( !)At small speed.
    But the main problem is at very small engine revolution(700 rpm for Perkins 215C)
    when few blocs go on each over it stop the boat and when you push the trottle the succion don't let any time to some blocs going back to the surface and they pass directly under the hull to the propellers.
    And with the noise of the ice you break and push you heard that too late .
    Our hull at the bow and under water line is 12 mm thickness and for more details concerning the (relatively ) light structure you can find details at :
    http://long-cours.62.over-blog.com/article-structure-77349567.html
    and for the form and structure at :
    http://long-cours.62.over-blog.com/album-1911172.html

    Best regards
     
  3. Tim B
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    Tim B Senior Member

  4. Ad Hoc
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    Ad Hoc Naval Architect

    I did have a very good internal LR document, for new rules, but i can't seem to find it.
    But I do have snippets/cuttings from the preamble.

    ice force = Fa.P^(0.36).Disp^(0.64).V^1.28

    Fa = factor to account for the hull form at the bow. I can't find the ref, so I'm assuming a relation of the angle from 0 to 1.
    P = ice crushing strength
    Disp = displacement
    V = speed.

    If I can find it, I'll post it.
     
  5. Alik
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    Alik Senior Member

    Thanks this would help.
    Actually we are trying to make ice belt but use sandwich in the area, with steel protection on stem and chines.
     
  6. philSweet
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    philSweet Senior Member

    Hi Alik-

    Another way to look at the problem is to try to limit the amount of damage the operator can do (Or the speed at which the damage can be done). I used to fiddle with construction equipment and that was the mentality I usually used- assume max power will be applied at some time or another by the operator and try to design the machine to take it. A skilled and desperate operator can get a piece of equipment into some pretty strange situations. Can you spec the drive so that the available thrust is kind of wimpy at low speed? Otherwise, I think you need a core that exceeds the strength of ice. The steel is nice for abrasion, but the hull has to take the load. Globally, I'd be inclined to ignore the steel banding. Which is what you are trying to not do if I read you correctly.
     
  7. Alik
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    Alik Senior Member

    Yes, sure we limit the speed; I put 4kts as limitation for fwd speed. The boat should be able to get out of base with some amount of broken ice, it is not an icebreaker. LR SSC accepts speeds not over 15kts for FRP high-speed craft, and also requires steel protection.
     

  8. Alik
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    Alik Senior Member

    Also another question: is it necessary to use dry exhaust?
     
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