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Thread: Help with Hull Classification?

  1. #1
    Member kodiakrain's Avatar
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    Default Help with Hull Classification?

    I have a 38' Commercial Gillnetter,(Sternpicker style) built by Mel Martin in '75 and you've all seen some of these around as they are all over the state. Mine is 38' after a 4ft extension on the stern but most are 32-34'

    Doing Prop Calculation work I can't figure what they would call this Hull, Planing, Semi-displacement, Fast Semi-displacement, etc.???

    It'll do 17.5 knots at WOT, has a 400hp Cummins 6CTA 8.3 which may just "Force it" up on step but it does just get up there at say 2200rpms, Max is 2600rpm.

    I'll try to get some pics of the boat out of water if nobody knows what I'm referring to but I really need to get a feel for what this would be considered. I run it at Displacement speeds/rpms all the time as the fuel burn is outrageous on step but I can't get prop guys to not see the engine size, length, and reduction gear/prop info without trying to tell me I need More and Faster,

    I'm hoping to reprop it for traveling at 10-12 knots more efficiently but not sure how to figure it out

    Any prop calc guys on here, Please PM me if you think you can help with this idea, Pics of hull coming shortly
    Thanks
    Ten Hours in that little raft off the AK peninsula, blowin' NW 60, in November.... "the Power of Life and Death is in the Tongue," and Yes, God is Good !

  2. #2
    Member kodiakrain's Avatar
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    Default Pics of this Semi Displacement or Full Planing(?) hull

    Here's some pics, with that flat stern it looks like all speed and it may be designed that way but reality is that I always carry weight in the hold etc and get about 50% more speed at Twice the fuel consumption if I open her up so......that doesn't punch out too well, and
    I am happy doing 8-10 would be ecstatic at 12kts,

    First is the Bow-on shot


    Then some of the hard chines first on the starboard side looking forward



    Then port side looking aft and the current prop with a fair view of the extended stern, how flat it is, Looks like designed to get up on plane, right?
    Sorry I've spent my career on 10ft deep Full Displacement Offshore vessels so hoping some of the high speed guys can chime in here




    The owner before me was a Cook Inlet Gillnetter for his entire time with this boat and he repowered it for speed with empty holds and a couple gillnets and drum on board, back in '93 when Fuel was cheaper(?) So prop & gear ratio (24x21 & 1.77:1) and main engine (400hp)were designed for use that hardly applies to my situation.
    What do you guys think, I run eighteen hours down the Shelikof just to start fishing 3B halibut, and all the way to Sanak Island, (that's south of Unimak!!)or nearly 60 hours of running at 8kts, 500 or so miles just to begin my Black Cod season, so I am backing off the throttle and looking to use this boat most of the time at displacement speeds.

    Maybe repower? Anyone want a Monster Engine, Cummins name speaks for Itself(?)

    Maybe I'm dreaming, but my last boat was a NW Troller style 7ft deep 42 long and had a Detroit 4-71 burning 2.5gph for 8kts, man that was nice, and even sounded reliable purring along at 1250 rpm,
    Ahhh the good old days
    Ten Hours in that little raft off the AK peninsula, blowin' NW 60, in November.... "the Power of Life and Death is in the Tongue," and Yes, God is Good !

  3. #3
    Member Akgramps's Avatar
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    Default

    Kodiak,
    Your query is beyond my knowledge, however it sure looks to me like it was meant to plane.

    This site might be more helpful...............

    http://www.boatdesign.net/forums/

    John
    “Nothing worth doing is easy”
    TR

  4. #4
    Member kodiakrain's Avatar
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    Default Thanks

    Thanks Gramps, I'll check it over in detail, looks like a good site to have in the Favorites anyway

    I ran into a prop calculator website that was really excellent but they went way beyond just Planing or Displacement, it was something like
    Fast Planing, Moderate Plane, Slow Plane, Fast Displacement, etc.....

    Thus the question for discussion, anybody venture some shipyard knowledge or just lots of experience to throw in there?
    Ten Hours in that little raft off the AK peninsula, blowin' NW 60, in November.... "the Power of Life and Death is in the Tongue," and Yes, God is Good !

  5. #5
    Sponsor potbuilder's Avatar
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    Kodiak,
    I don't think that hull was built to go fast, big heavy boat, look at the skeg where the stuffing box is, its square cut so that doesn't let clean water run into the prop, small reduction gear so you can't run a bigger prop to get more push. I'm thinking you'd need to double the HP to make it go good then who's going to afford the fuel. Looks like there's quite a bit of angle to the shaft also so its pushing water down instead of out. If it were me i'd try squaring the prop(if you still can get the WOT RPM'S) to get a bit more push and buy a Iron Mike(autopilot) so you don't have to fight the wheel when your doing those long slow runs.
    I've seen quite a few of those rigs in the gillnet fisheries and never saw one that moved along well. Amen on the 71 jimmies had one in my lobstah' boat ( 6-71) they keep running & run quite cheap if you don't put the big injectors in them. Good luck gettin'her to run faster but its gonna cost you.

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  6. #6
    Sponsor potbuilder's Avatar
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    See what i mean about clean water being able to get to the prop? This is what they do on some lobster boats
    lobster keel prop.jpg

    Alaska Shrimp Pots

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  7. #7
    Member kodiakrain's Avatar
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    Default not faster but cheaper is right

    Wow Potbuilder that is a good picture, I've never seen that done but looks really good for water to the prop,

    yeah i agree I think it is a displacement hull that the guy shoved a 400hp cummins into to force it up there.
    I'm not really that much into going faster, don't mind eight knots all day and the fuel cost is what is driving the whole question. I just returned from 60 hrs of running (to Homer and cruising the South Kenai coast) mostly at 1000-1200 rpms believe that or not. But I can get 2.6gph at 1000 (agonizingly mellow as it is just above idling and stack temp is only 500F but even coming up to 1400 I climb up to 6gph for 9kts). It doesn't punch out.

    I'm coming to the conclusion as you did that it is really just a displacement hull with too much power, repower some day when there is too much money laying around but for now, I'll probably be idling around.

    And yes, the autopilot is crucial. I have an old Comnav now that actually, (since you mention it), gave me a "rudder error" message that I couldn't solve on this trip so,
    I really enjoyed hand steering for the last 20 hrs, all the way home, Aaaarrrggggghhhhh

    Thanks for the advice, and pic
    Ten Hours in that little raft off the AK peninsula, blowin' NW 60, in November.... "the Power of Life and Death is in the Tongue," and Yes, God is Good !

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