Navy patrol hull design

Discussion in 'Boat Design' started by Zappi, Oct 24, 2011.

  1. Zappi
    Joined: Oct 2008
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    Zappi Senior Member

    Hi, I am told by the current owner this is a full displacement hull. I'm pretty sure it would be more of a semidisplacement as there is very little rocker in the hull. Attached are a couple pics. I am acquiring this relic in a trade and would like to know thoughts on the design. She is a 1941 Navy Patrol boat built at the Bremerton shipyard. Thank you so much!
    http://www.flickr.com/photos/31915428@N06/6276823477/in/photostream/
    http://www.flickr.com/photos/31915428@N06/6276823561/in/photostream/
     
  2. water addict
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    water addict Naval Architect

    That is most definitely a displacement hull.
     
  3. Zappi
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    Zappi Senior Member

    The round buttocks tells all???
     
  4. water addict
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    water addict Naval Architect

    rounded sections, curved counter in the stern. Planing or semi-planing will have flat sections and buttocks aft to promote stable flow and separation at the stern. If you tried to push a hull like this up to planing speed, it would wander all over the place and be very hard to control.
     
  5. Zappi
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    Zappi Senior Member

    Is a claim of 12 knots flat out then if she has 39' of waterline reasonable? I realize that's higher than hull speed. She is narrow and fairly light. Approximately 14,000, 9' waterline beam and power is 671 I would assume 185hp. Thank you....
     
  6. philSweet
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    philSweet Senior Member

    Patrol boats were designed to be very maneuverable. The complaints mentioned above were more like features. It was their purpose. 14,000# sounds light to me.
     
    Last edited: Oct 25, 2011
  7. water addict
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    water addict Naval Architect

    yep maybe 12 knots is possible with 39' LWL, 185hp at 14000 lb displacement. A more comfortable cruise is probably 9-10 knots though. 185hp seems kinda high for that boat- are you sure boat that? Could be right, just wondering.
     
  8. Zappi
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    Zappi Senior Member

    The boat is quite stripped out on the interior. She served as a fishing vessel out of Ilwaco WA for many years and then this guy removed most associated when he got it. I'm not sure of hp of the engine and trying to figure it out. I'm not sure of it's vintage. 185 hp seemed like a common number for a 671 but there are certainly lower hp versions.
    Would this make for a good sea boat or say an Inland Passage type boat to go to AK? Maybe a bit rolly?
     
  9. PAR
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    PAR Yacht Designer/Builder

    14 knots sounds like a reach to me. 9 knots would have a pretty big bow wave and climbing over this would be unlikely. 9 knots is a S/L of 1.44 and probably the best she can do would be 10 with 185 HP. At 10 knots her S/L would be 1.6, which seems unlikely, even with a 4.33 B/L ratio.
     
  10. Ike
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    Ike Senior Member

    That looks to me like an old Navy YP. YP stands for Yard Patrol. Current YPs are lot longer than this one though. That is definitely a displacement hull and not intended for off shore use. Sheltered waters only.
     
  11. lumberjack_jeff
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    lumberjack_jeff Sawdust sweeper

    If the guy fished out of Ilwaco, it must be reasonably seaworthy.
     
  12. tom28571
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    tom28571 Senior Member

    The consensus is correct. Definitely a displacement hull. It might do over 10 kts but it would not be too happy about it and would use gobs of fuel. 7 0r 8 would be tops for fuel economy, I'd guess. Should be OK for the Alaska cruise. Common sense and good seamanship should be parts of any such trip. It does look like a roller though.
     
  13. Zappi
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    Zappi Senior Member

    Thanks for the replys and info. 14,000 lb displacement not 14 knots. As I think about it... I expect most reasonably salty people to talk in knots but he may be more of a landlubber than I realize. His numbers may be miles per hour. I expect to take her for a spin somewhere around the second weekend of November.
     
    1 person likes this.
  14. Pericles
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    Pericles Senior Member


  15. FAST FRED
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    FAST FRED Senior Member

    6-71 of that vintage for a Navy could be up to 235HP /2100rpm , which makes 12K easier to envision.

    But you wont like the fuel burn!
     
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