Lobsterboat characteristics.

Discussion in 'Boat Design' started by rustybarge, Sep 19, 2014.

  1. rustybarge
    Joined: Oct 2013
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    Location: Ireland

    rustybarge Cheetah 25' Powercat.

    Here in Europe I've never even seen a lobster boat.

    What are the handling characteristics of the hull form, and what sort of power requirements/ speeds suit this hull type?

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  2. sprit
    Joined: Jul 2013
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    Location: Lexington, MA, USA

    sprit Junior Member

    Lobster boats generally have a wide beam and stern, to provide enough area and buoyancy to carry 200 pots.

    They generally have a deep sharp forefoot and high bow, to allow working in rough water during less-than-comfortable days. The freeboard further aft is relatively low, to allow easy working over the sides.

    They have a big inboard engine and large slow propellor, to move all those pots, and they usually move at displacement speeds to conserve fuel, and to move gracefully.

    They have some kind of protection for the propellor (like a long skeg) because they are moving in a field of lobster pot lines.

    There is usually a small cabin and cabin overhang, to protect the helmsman.

    There is usually an open area just behind the starboard part of the cockpit, for a mechanical pot puller.

    These characteristics allow semi-planing speeds when the engine is large enough.

    The underwater lateral plane of the bow and skeg allows these boats to move alongside of a pot without drifting much.
     
  3. rustybarge
    Joined: Oct 2013
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    Location: Ireland

    rustybarge Cheetah 25' Powercat.

    Thanks.

    I'm just wondering how they cope with a choppy sea, as the stern appears to have zero deadrise; it's completely flat, which could produce severe pounding as it falls off the back of a wave.

    I am also worried by the huge Skeg/Keel. If a 12mtr/38' s/d boat that weighs about 10tons needs 250hp to cruise in the middle teens, how much power is an equivalent lobster boat going to need with that draggy keel?

    It looks like a very strange underwater shape for a s/d hull.
     
  4. sprit
    Joined: Jul 2013
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    Location: Lexington, MA, USA

    sprit Junior Member

    The deep forefoot prevents most pounding, even when a lobster boat is cruising to its working areas, and much slower speeds are the rule when setting and pulling pots.

    Not much power is needed at displacement speeds.
     
  5. FAST FRED
    Joined: Oct 2002
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    Location: Conn in summers , Ortona FL in winter , with big d

    FAST FRED Senior Member

    >They have a big inboard engine and large slow propellor, to move all those pots, and they usually move at displacement speeds to conserve fuel, and to move gracefully.<

    The ones I have been on are quite different , most have truck engines , diesels with dry stack and keel cooling as there is almost zero work needed to go from truck to boat motor.

    No winterizing is needed as the keel cooler is 50% antifreez , and a pail over the stack keeps the sleet out.

    The engines run from 200hp to 500hp, depending what was handy at the junk yard .

    Used engines are always a gambol , and like most folks lobster guys have brand preferences. The international folks will buy a good spare or two , as will the Detroit folks. There is usually also a spare tranny , swopped with the engine.

    There is usually a big hatch over the engine , and a similar hatch in the PH cabin roof.

    An engine swop is a 2 man overnight no big deal.

    The poorer folks run gasoline engines , faster , lighter and cheaper at the junk yard.

    The gas bill is only higher between pots , as speed is need to haul a large number and on the way home , and worth it sometimes in the sales price.

    The Hyd pump for the pot lifter doesnt care if its a gas or diesel turning the belt.

    Only at the close or start of a season are many traps carried at one time.

    Going out a few are filled with bait , and after 100ish traps are hauled only a few are required to hold the days income.
     
  6. rustybarge
    Joined: Oct 2013
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    Location: Ireland

    rustybarge Cheetah 25' Powercat.

    I'm becoming confused: Are they displ. Hulls?
     
  7. gonzo
    Joined: Aug 2002
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    Location: Milwaukee, WI

    gonzo Senior Member

    They are semi-displacement hulls. The type is usually called warped bottom. That is a deep vee forward, slowly twisting into a flat stern. The chines are fairly round. The bow has some flare and there is tumblehome aft to make it easier to bring the pots onboard.
     
  8. rustybarge
    Joined: Oct 2013
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    Location: Ireland

    rustybarge Cheetah 25' Powercat.

    What sort of speed are we talking about?
     
  9. groper
    Joined: Jun 2011
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    Location: australia

    groper Senior Member

    I've noticed you ask alot of questions about hull shapes, speed, and required power.

    What you need to understand is, the hull shape has little to do with it. This is without considering extreme, bizzarre or otherwise abnormal boats of course.

    This has been thrashed to death on his forum many times, but you would do well learning about displacement to length ratio. It is the single largest determinant of speed and powering requirement. If you want to go fast , on little fuel, with a modest sized engine, then there is no magic required, only a light hull with a long waterline...
     
  10. rustybarge
    Joined: Oct 2013
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    Location: Ireland

    rustybarge Cheetah 25' Powercat.

    Just looking at the lastest Westmac super 46' lobsterboat to be launched, she's got a beam of 17'; yes that's 17' wide.
    https://www.facebook.com/wesmacboats

    Which makes the conversation about lobster boats quite interesting: why are they so beamy ?
     
  11. rustybarge
    Joined: Oct 2013
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    Location: Ireland

    rustybarge Cheetah 25' Powercat.

    Here she is: 46' by 17'

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  12. rustybarge
    Joined: Oct 2013
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    Location: Ireland

    rustybarge Cheetah 25' Powercat.

  13. Mr Efficiency
    Joined: Oct 2010
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    Mr Efficiency Senior Member

    Boat equipped with 2x390 hp diesels uses less than 4gph at 8 knots ???? :eek:
     
  14. rustybarge
    Joined: Oct 2013
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    Location: Ireland

    rustybarge Cheetah 25' Powercat.

    Here's their launch review in 2012:

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    Ok so that's 7.6ltrs each engine at 8kts/900revs.....

    Let's see, that makes 3.34 gals (uk) at 8 kts= 2.39 mpg!!!!

    Interesting indeed.:rolleyes:
     

  15. rustybarge
    Joined: Oct 2013
    Posts: 533
    Likes: 3, Points: 18, Legacy Rep: 37
    Location: Ireland

    rustybarge Cheetah 25' Powercat.

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