Alaska fishing hull

Discussion in 'Boat Design' started by coldwaterak, Nov 26, 2011.

  1. coldwaterak
    Joined: Aug 2009
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    Location: Alaska

    coldwaterak Junior Member

    Ive recently had the opportunity to be part of a refit for a steel seiner that fishes western Alaska. The project took an exisiting hull and while sponsoning also redesigned the bow. While the project is coming to a close I have toyed with different variations of the hull with the concept of a future new-build.

    The attached images are the basic shell of where i have arrived with various goals in mind:
    -Heavy weather, both on the bow and following seas
    -Hold capacity, hence the overly wide beam
    -Maintain the 58' length and still produce a wide seaworthy boat (limit regs)
    -Ability to shed water, taking water over the bow and decks
    -Limit roll, reason for reverse chine

    The fisheries in Alaska presently have produced a situation where boats will fish salmon in the summer (bigger capacity, bigger profit) and then longline and pot fish in the winters.... All atop a 58' "limit" seiner hull.

    More than anything I would like some suggestion, criticisms on the design... Anything that might blatantly stick out to some of you that I might be overlooking.

    [​IMG]

    An example of a vessel built for the same purpose:
    http://www.fredwahlmarine.com/Saint Paul.html
     

    Attached Files:

  2. Easy Rider
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    Easy Rider Senior Member

    In head seas I'll bet she'll slam under those reverse dead rise chines. I'd put the chine 1.5 squares up and go conventional there. Perhaps a little less hollowness in the forefoot will giver her more speed and less tendency to plunge. I like the vertical stem w the 58' rule and the QBBL is about right. Should function well at any displacement. What's you're thoughts on going wider?
     
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  3. BATAAN
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    BATAAN Senior Member

    There have been several similar projects done in WA here and they all have applied bulbous bows.
     
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  4. BATAAN
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    BATAAN Senior Member

    Oh, I see. A bulbous bow would get it over limit length, my bad.
     
  5. Easy Rider
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    Easy Rider Senior Member

    BATAAN,
    Probably not most as most have a racked stem.
     
  6. Ad Hoc
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    Ad Hoc Naval Architect

    You would do far better with a double chine that that "reverse chine" you have. Currently what you have shall add a lot of drag. Double chine will be less resistance.

    If you wish to limit roll, than you need to look at the GM..get that right..then add bilge keels. BK are far better than that reverse chine, which is counter productive to what you want.

    So, first off, do a GZ curve of with your reverse chine and one with a double chine configuration. Ensure you have a proper weight and centres estimate to obtain a realistic GZ curve.

    You also need to ensure you have plenty of freeingport area, since with seiners, studies have shown that too much freeboard has more of a detrimental effect than the metacentric height, on stability.

    Some principal dimensions would be nice too.
     
  7. gonzo
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    gonzo Senior Member

    The maximum length only rule has produced a lot of bad boats.
     
  8. BATAAN
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    BATAAN Senior Member

    Yah, there are few rules in the ocean but longer is better is one of them.
     
  9. viking north
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    Location: Newfoundland & Nova Scotia

    viking north VINLAND

    Don't know if this is applicable but on the Newfoundland /Labrador coast there are times one has to deal with ice-- Don't think those reverse Chines would be a good feature under such situations, I suspect they would provide a high impact area coming down off a sea onto burgy bits.
     
  10. gonzo
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    gonzo Senior Member

    Can you use flapper stoppers to slow the rolling?
     
  11. Ad Hoc
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    Ad Hoc Naval Architect

    If the boats SOR is to be designed for ice conditions, then the hull plating is increased accordingly. Boats don't bash ice per se, they rise up over it and the weight of the boat crushes the ice.

    If the sea is 'mush' then again, the plating thickness would account for that buffeting of the water/ice mix. Double chine or reverse for that matter has no relevance in that instance. However, a double chine would facilitate this action far better than a reverse chine.
     
  12. viking north
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    viking north VINLAND

    Ad Hoc certainly agree on the engineering aspect but most fishing craft that I have operated are designed and built for the so called "typical operational conditions". This of course for pratical as well as an economical reasons. As an architeck you probably face this situation often in design work. The old "trade off" situation again. On the NFLD/LAB coasts we do but not often encounter that mush mixed with bergy bit situation and one can be guaranteed to face it once and awhile. My thinking was as you stated in sheet ice,the boat rises up over it causing it to break and flip vertical. To complete the process, the hull then drops and those verticallly oriented ice "chizels" would then impact the reverse chine edges and all hell breaks lose, whereas on a curved or regular chined hull the vertically oriented ice is quazi smoothly deflected outward. Even then the cannonading is an unnerving experience. It was just old memories and visions returning and thinking wow don't figure a reverse chine would be a good design here and as you confirmed from a professional, much better not to have those protruding ridges present.--- Geo.
     
  13. coldwaterak
    Joined: Aug 2009
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    Location: Alaska

    coldwaterak Junior Member

    I couldn't agree more that the length limit has forced a design that is far from ideal. On the other hand, personally growing up within the fisheries, the limit has probably saved the private market for individual fisherman. But there is only so much you can squeeze out of 58'.

    I also want to add that another design aspect that many fisherman try to hold on to as much as feasibly possible is the shallowest draft possible. Salmon fishing tends to force the boat right up on the coast, right were the fish are moving. Provided the design is correct, fishing with a "slack tank", semi full fish hold is common practice. Reverse/wide chines and rolling chocks are the result....

    With that said, expecting to have a boat that can then head out into heinous weather and fish the open ocean is a catch 22. Going back to what I said about using the fish-hold, many boats will "tank down" and run through weather with a full fish hold, either water, fish, or nets/gear.

    My apologies, these considerations bring a ton of variables to consider, but its the reality of what is expected in these boats....

    Regarding the ice, that is a good point, but not a huge factor to consider... I have already "softened" the chine up forward, but during winter fishing the boat will most likely be tanked down pushing the chine shelf well below the water line. The only time I expect them to be breaking ice is when they are leaving the harbor...

    Again thanks for all your feedback I really appreciate your input. I am trying to come up with a volume for the fish-hold and fuel tanks to give some accurate numbers for displacement.... empty, slack, and full. Also I need to make up my mind about going with a free-standing mast?
     
  14. gonzo
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    gonzo Senior Member

    I have worked on trawlers too, and they have to be the most uncomfortable boats in existence. The full bows makes them pitch violently and their rolling is too fast. We used to lash ourselves to the bunks because in the downwards pitch we would be airborne and often be thrown off into the deck. Sleep was impossible, the best possible was dozing off. The fatigue contributes to accidents and lack of safety. If there are going to be rules on vessel size, they should include other parameters than overall length only.
     

  15. coldwaterak
    Joined: Aug 2009
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    Location: Alaska

    coldwaterak Junior Member

    I've added a pdf that you can view and spin/rotate the model to get a better feel for the way the chine/hull is designed...

    This definitely is a work in progress and I will post another revised version soon with the chine shelf updated as well as the bow shape...
     

    Attached Files:

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