Pt 305

Discussion in 'Boat Design' started by rambat, Jul 18, 2010.

  1. rambat
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    rambat Member at large

    I am one of many volunteers re-building a WWII PT boat at the WWII museum. This week I'll be posting my progress to define and loft this remarkable 66 year old design. If anyone has any parts, info or stories of these original "Special Operations Craft" please post.
     
  2. hoytedow
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    hoytedow Fly on the Wall - Miss ddt yet?

    I learned this on Wikipedia.: "....PT-305 (Higgins 78-foot), which had the stern blown off by a German mine in the Mediterranean and yet returned to base for repairs...."
     
  3. J3
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    J3 Junior Member

    I don't have any experience to offer you any advice on this, but I will definitely be following this thread eagerly to follow your progress :)
     
  4. rambat
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    rambat Member at large

    PT Deck

    Today I input the deck surface, as usual we had conflicting dimensional data. One drawing showed a jig built to laminate the "standardized" deck beams to a 85' radius arc, regardless of beam. The Hull lines showed a smoother CL deck hump so I went with that, the beams are proving less than absolute ridged and some hold their shape after being released from the jig better than others. The deck longs will do more to help form a support grid to create a final fair surface. It easy to forget that old boat building used a full-size loft process between the designers and the builders so the drawing dimension must not be trusted when it involves anything needed to be fair. In todays shipbuilding the lofting stage is integrated into the design phase due to 3/D CAD for full size lofted faring. Thats why its important to do this 3/D model for our re-build since it is so cut up. The picture shows the Keel in its proper position, it had dropped 4" but due to the rot and shrinkage it was hard to tell if not for our lofting checks. This 78' PT 305 was cut down to 65' for use as an Chesapeake oyster boat after its Med tour. We have to re-create the aft 13' completely and that section will be the easiest of all!
     

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  5. rambat
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    rambat Member at large

    PT stringers

    The model now has offset surfaces to define the planking thickness and tops of the framing. The three outboard stringers ride on top of the transverse frames and the inner one has a lightning hole arrangement with a Steel plate scab.
    Now we can plot our sections with these geometry's at every frame. Deck longs and engine foundations (3) next. Need to hurry, it seems to be creaking in the cradle, dying to be reborn.
     

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  6. rambat
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    rambat Member at large

    Week 1

    This is going to take a few more days, the model is shown semi-transparent to show how the frame depth is represented by an offset hull shell, The stringers and deck beam are boxed like beams. Very critical geometry of the shaft lines is now projected to make sure our scrounged struts/supports are correct (they are) I'll create the new engine foundation templates after modeling a 3/D motor, align them with the shafts and give some gap for shimming. The actual 3 required engines are magnificent Packard V12, 1400 hp Av-gas gulping beast. These WWII engines and mechanicals are works of art designed before CAD drove so much of the process.
     

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  7. kach22i
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    kach22i Architect

    David, which computer programs are you using for both documentation and illustration purposes?

    Keep up the good work.
     
  8. rambat
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    rambat Member at large

    Program

    I am using RHINO 3/D for both the modelling an the images displayed. Finally built and placed the Packard engines. Will bring up the engine foundations to match up with the engine rails. We are planning on a framed support of the engine rails with some plexi sight windows to align our shaft lines prior to hoisting them into place.
     

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  9. kach22i
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    kach22i Architect

    I think this is one project you should package into a booklet or book complete with the people process and story involved, and include the artwork/drawings you have produced.

    If you at least plan on some organization along those lines now it will make the post follow up that much easier.
     
  10. hoytedow
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    hoytedow Fly on the Wall - Miss ddt yet?

    The PT-305 Story. I like it.
     
  11. rambat
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    rambat Member at large

    Aft

    The PT 305 project is moving ahead with the frame-up of the missing 13' hull aft to the transom. Here are some images of the new framing derived from the hull model and some interior shots to see what we have to tackle in bringing this warhorse back into spec and one day run it again on open water.
     

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  12. hoytedow
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    hoytedow Fly on the Wall - Miss ddt yet?

    Thanks for keeping us updated.
     
  13. kach22i
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    kach22i Architect

  14. Squidly-Diddly
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    Squidly-Diddly Senior Member

    didn't Sea Ray have a patent on that combo deep/shallow vee-hull?

    I remember reading Sea Ray said their combo hull was like a deep vee at planing and a shallow vee at rest for high initial stability, and they had a patent.

    Maybe it was that theirs was 'combo' all the way to the stern, where as the PT boat stern looks like a single angle of Vee.

    Personally, I think the whole business of patenting a hull shape is pretty silly, short of some new amazing breakthrough in the magnitude of the hovercraft or hydrofoil.
     

  15. upchurchmr
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    upchurchmr Senior Member

    Ramrat,

    Good luck on you modeling. When I first joined an Aerospace job I was to "re-model" an aircraft wing section from paper drawings to digital. It was a terrible job due the the assumption of "common knowledge" between designers and tooling/ manufacturing people. Many of the exact definations on the paper just didn't exist and the actual part was driven by the manufacturing people - some of the existing features in metal could not be readily defined in the cad system I used.
    Even better than that, after I released the design, the cad system maker changed some of the capability/features and no one could understand the way the digital model was drawn. Eventually the model was completely done again.
    You should not have my problems, since you apparently don't the drawings.
    Just don't ignore any information you might have from people who actually built the boats. Do you have any such source?

    Good luck, my dad rode one of these after Korea in SF Bay as a crash rescue boat. His stories of jumping from one 20' wave crest to the next during a storm were enough to stop me wanting to really go to sea.

    Marc
     
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