building a PM38 a few questions

Discussion in 'Boat Design' started by rocco611, Jul 30, 2020.

  1. rocco611
    Joined: Jan 2019
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    Location: Madera Ca

    rocco611 Junior Member

    I am part way through the build of a PM38 (Popular Mechanics free plan ) as my first boat build. Started out with rough fir lumber , its nice being able to joint and plane lumber as I need it and start with straight boards. I will look for good plans for my next build ( inboard barrel back) I see how important good plans are after having to decipher the pm38 plans. I am using marine plywood , silicone bronze screws and quality epoxy resin. I have poly primer and urethane automotive paint left over from car restorations. I plan to resaw some rough mahogany boards I have for a planked deck ,unless there is an easier way? I have enough parts around to build a nice trailer, so I think I can have this boat finished without a great deal of expense. Its coming together quickly and has been fun so far. The expensive part is finding an EPA compliant outboard. The lake that is nearby where I would use the boat only allows clean running outboards . I had thought about buying a new outboard but that would likely put me upside down financially with this project when I decide to sell it. I have checked craigslist and some other sites and haven’t any luck finding a suitable compliant motor in the 20 to 30 hp range. Maybe someone can suggest a source for used motors I haven’t tried ?. I have thought about selling the boat without a motor and leave it ready for paint . Not sure there is much demand for this boat but if I break even on it that wouldn’t be terrible. Maybe I have wasted my time by not building the boat I wanted to begin with, I wasn’t that confident in my skills starting out, but it has turned out to be much easier than I thought. I have learned how to build proper scarf joints (I found making long scarf joints that are stronger than the original wood bind up in the table saw unless I use a jig where I can clamp the board securely on both sides of the cut. ) and now have a handle on the rest of the joinery as well. I suppose its better to learn with cheap fir than waste expensive hardwood on mistakes. I am really looking forward to building the planked deck. For the deck, I know varnish seems to be the standard for uv protection over epoxy , but I am wondering if automotive clear wouldn’t be a better choice. The clears I use over candy apple base coats are supposed to have the best UV protection, but I have never seen any documentation how they compare to marine varnish. I know the marine varnish I used on the boards of my car trailer lasted about two years in the sun. not that I would leave the boat out in the elements but the automotive products are much more durable.
     
  2. bajansailor
    Joined: Oct 2007
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    bajansailor Marine Surveyor

    Your PM 38 sounds like an interesting project Rocco.
    Do you have any photos of her that you can post, showing your progress so far?
    And would it be possible to post a copy of the PM plan(s)?
    Re the deck finish, be aware that whatever finish you apply will be very slippery to walk on when it is wet, unless you add some non skid material (eg sand) to it.
     
  3. rocco611
    Joined: Jan 2019
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    Location: Madera Ca

    rocco611 Junior Member

    here are the plans, I will post some pics early next week,
     

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  4. fallguy
    Joined: Dec 2016
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    fallguy Senior Member

    The investment in a nice four stroke 20hp is worth it. Interest rates are low, buy now before we get smacked with inflation.
     
  5. fredrosse
    Joined: Jan 2005
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    Location: Philadelphia PA

    fredrosse USACE Steam

    Interesting boat from 1962. Building in 2020, nearly 60 years later, will require some adjustments. All the 1962 glue and caulking should probably be replaced by Epoxy. Finishing the exterior with light fiberglass cloth and Epoxy would also make the build far more valuable.

    38 hours build time?? I think that is a far too optimistic time, I would require 2x to 3x that amount of time at least. Any other opinions here?

    $38 materials cost?? Certainly not in today's world. For example, back in 1962 we would use 3/4 inch Type A/B plywood for sheathing an ordinary framed house, and that stuff was nearly void free, at about $5.00 for a 4 ft x 8 ft sheet. Today's plywood quality dictates that this PM38 boat would need to be made with true marine plywood, probably in the vicinity of $60.00 a sheet for the thickness specified in the PM article. All of the other framing lumber, generally very high quality and easily obtained in 1962, would need to be also high quality for the 2020 build, another cost boost to say the least.

    The article states that 38 horsepower is needed for the stated 38 MPH speed, and that may be correct, but probably somewhat more if the actual build is going to weigh more than 200 pounds stated in the the 1962 write-up. Modern rules for construction and safety equipment may also change the actual weight and costs. Any other opinions here?

    One other thing observed, the article states that, if a Bronze prop is used, it should only be for fresh water use, and if used in salt water, then an Aluminum prop should be used. Is this in any way correct?
     
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  6. rocco611
    Joined: Jan 2019
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    Location: Madera Ca

    rocco611 Junior Member

    A few pics
     

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  7. rocco611
    Joined: Jan 2019
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    Location: Madera Ca

    rocco611 Junior Member

    I notched the frames this morning and installed the chines and bottom battens, looks like I am going to have to shim two of the bottom battens (outermost batten on each side). where the twist to meet the front most frame. about a 1/8 lower than the chine. the rest of the batten and the keel are perfectly flat .
     
  8. rocco611
    Joined: Jan 2019
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    rocco611 Junior Member

    More pics
     

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  9. rocco611
    Joined: Jan 2019
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    Location: Madera Ca

    rocco611 Junior Member

    Few more pics
     

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  10. bajansailor
    Joined: Oct 2007
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    bajansailor Marine Surveyor

    She is coming along nicely!
    However the strongest impression that I get is that she is going to be relatively heavy, especially when compared to a more modern 'stitch and glue' type of boat, which would have much less framing.
    When you fitted the plywood sheets onto the stringers and frames, have you glued and screwed them on?
    If you have only used screws (no glue), did you bed the plywood down on anything, or is it wood against wood?
     
  11. rocco611
    Joined: Jan 2019
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    Location: Madera Ca

    rocco611 Junior Member

    I got the bottom attached using thickened epoxy using 1" silicone bronze screws. scarfed the front edge of the plywood where the 1/4 plywood for the bow will attached , question, plans say use fiberglass tape for the seams, I do have that, but I am considering glassing the entire bottom of the boat, is it necessary? I will be going over the resin afterword with automotive paint system, poly primer surfacer, gold Urethane basecoat, candy red brandywine bascoat then Urethane clear
     
  12. bajansailor
    Joined: Oct 2007
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    bajansailor Marine Surveyor

    Excellent re how you are gluing and screwing all your joints.
    I am thinking that from a strength point of view, the boat will be massively strong, and you do not need to sheath the hull in glass and epoxy to gain extra strength.
    However it would be a good idea to use glass tape on the seams, and especially on the keel, as the keel will be coming into contact with the trailer every time you recover her.
     

  13. rocco611
    Joined: Jan 2019
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    Location: Madera Ca

    rocco611 Junior Member



    thanks, for the comment :) I did glue the plywood using thickened epoxy, then screwed it down . I used wheat cake flower for thickener, I did shim two of the battens at the front and the keelson toward the back then were down about 1/8 of an inch, then went over it with a autobody sanding board and a straight edge till everything was flat. might be overkill I guess .

    Plans say the boat should be about 200 lbs when complete. I think that estimate is optimistic even using fir,
     
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