What do you think of an ice belt?

Discussion in 'Metal Boat Building' started by scphantm, May 17, 2014.

  1. scphantm
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    scphantm Junior Member

    I designing a 75 foot klipper barge for the river system of Pittsburgh. The issue that comes to mind is the fact we had 2 to 4 thick ice on the rivers and a good 12 to 20 inch high drifts going down the river this winter. I'm worried about being moored and have a drift come by and tear me open.

    At the moment my flat bottom keel is .75, my chine is .5, and my verticals are 3/8 of AH36 with a 1/4 inch deck of most likely hot rolled. I need to finish the framing. Obviously these numbers will be adjusted as needed when I can start doing the structural analysis on it.

    The question is since I expect the ice flows to get even worse over the next decades, do you think an ice belt at the water line is a good idea? I'm thinking an outside layer of AH36 welded to the outside as a doubler. That way I get the extra strength and it's in a spot that's easy to repair if needed.

    Is it a good idea or am I thinking too damn hard
     
  2. hoytedow
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    hoytedow Carbon Based Life Form

    A picture is worth a thousand words. How about a sketch of what you are pondering?
     
  3. TeddyDiver
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    TeddyDiver Gollywobbler

    You can weld it on the inside too so it's out of sight. Better thou having more framing and stringers under the exposed area. Problem with ice is not abrasion..
     
  4. TANSL
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    TANSL Senior Member

    The problem with ice is not only abrasion, but is also the abrasion, so that an increase in the thickness of the plates, on the outside, is recommended.
    The ice protection normally consists of:
    -shell plating, more thickness, but only in the flotation.
    - frames spaced half the standard separation.
    - at least one stringer to half the height of the frames.
     
  5. JSL
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    JSL Senior Member

    Ice 've belts are common & have been used for decades
     
    Last edited: May 17, 2014
  6. scphantm
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    scphantm Junior Member

    With the way I'm building it, basically using chain hoists to fold the steel over the frames, I'm worried about making the vertical plates any thicker as I may not be able to form the metal. That's why I thought of a belt and I think it would be easier to put on the outside.

    All the docs I can find are about building ice breakers. I don't want to break ice, I just want to make sure I won't wake up early one morning with wet feet because an ice flow tore me open.

    Anyone know a book or site that would allow me to speak a little more intelligently about it? And I can post what I have designed so far when I get home
     
  7. Eric Sponberg
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    Eric Sponberg Senior Member

    Scphantm--TANSL has stated the essentials of ice belt strengthening. Much of the extra load caused by ice is pressure of the ice on the hull that tries to bend the plate and framing structure inward. The pressure can come from the boat moving through ice, or ice moving against the hull--it doesn't matter, both types of loads are kind of the same. In Classification Society rules, ice strengthening usually involves doubling the number of frames in the hull where strengthening is needed--i.e. putting extra frames between all the normal frames--plus extra plate thickness. The extra frames make the whole hull structure 8 times stiffer, and doubling the plating thickness makes the plating 4 times stronger.

    Yes, ice belt strengthening is a good idea. I'd recommend it.

    Eric
     
  8. scphantm
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    scphantm Junior Member

    Awesome. Thanks. Now when you say double the frames, would I be doing full height frames, meaning from the center line all the way around the inner hull to the bottom of the deck or do I just need to run them to the top of the belt with a lateral to tie its top into the two adjacet full height frames

    For anyone curious, yes, I plan on finding an architect to review and bless my work before a single item is ordered, I'm just trying to get as much done now as close as I can so I can start doing realistic estimates to work out the financing.
     
  9. Eric Sponberg
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    Eric Sponberg Senior Member

    Since this is not an ice breaker, I recommend running the extra frames from the chine up to the deck edge. It would serve little purpose to run them only to the top of the extra thickness belt because a lot of the strength and stiffness of the frame comes from its end connections. You want to connnect the ends of the frame at each end--the chine and the deck.

    Eric
     
  10. TANSL
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    TANSL Senior Member

    The intermediate frames must be located above and below the waterline. Their ends need to be embedded. Therefore, depending on the shape of the chine, is likely to have to extend them underneath the chine and maybe have to put a longitudnal reinforcement on the bottom to fix properly lowest ends of frames. "Floating" frames are not very effective.
     
  11. JSL
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    JSL Senior Member

    If there are longitudinal girders on the hull bottom & side in proximity to the ice belt, these could be used as the headers for the intermediate frames.
     
  12. tom kane
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    tom kane Senior Member

    I think that an ice belt should be built like a modern auto, it`s designed to crush in around the passenger compartment and take the shock and damage and outer panels are more easily replaced... Similar to a dogem crash rail. Extra strong may not be strong enough to take the pressure and chafing of the ice and damage the essential hull instead.
     
  13. AndySGray
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    AndySGray Senior Member

    How about Sponsons?

    If you're talking about adding a plate to reinforce the water line, why not move it out a few inches from the hull with plates welded to the 'outside' of the hull as spacers - e.g. 3" x 12" verticals with the top and bottom angled appropriately and spaced as per your frames, reduce the spacer width to fair in at bow and stern.

    Cap the top and bottom with plate and you've created a brutally strong box girder which is far more rigid than just 2 layers of steel.

    OK not suitable for some of the prettier hulls but this is common commercially, so not out of place on a barge style hull, and also can be a retro-fit add on to an exisiting hull.

    IIRC, in addition to protection, there are benefits in terms of stability too.
     

  14. scphantm
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    scphantm Junior Member

    Hey, that's a really cool idea. My prelim math says I need transverse frames at 48 inches so a box girder would simplify things on the interior
     
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