Best way to take measurements for installing new boat deck?

Discussion in 'Boat Design' started by KismetFI, Oct 27, 2020.

  1. KismetFI
    Joined: Sep 2020
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    Location: Fire Island, NY

    KismetFI Junior Member

    Finally finished up the stringers and bulkheads this past weekend. I will be adding three layers of grey gel coat to the bilge, last layer with wax (figured this would be an easy way to seal everything up/semi protect the glass/makes it look nice in the lockers). Next, I will be installing the tank and adding rigging tubes, one 4" wide PVC tube for the rigging and one 2" wide PVC tube for the pick up line (all running to the transom/connected to the stringers.

    Anyways, I have been going back and forth on the best way to take measurements for cutting the 1/2" marine plywood 4x8 sheets I have. The deck length is only 16' and the max beam is 7' 1/2". Figured I will use three sheets to keep things simple. Would an easy way to take the measurements be to use card board and cut out a dummy deck and then transfer that over to the ply and trace accordingly? Not sure if there is a measuring technique that boat builders typically use.

    For the decks, I will be using one layer of 1.5 oz chop on the bottom side of the deck and two layers of 1.50 oz chop for the top side. I think this should be good.... I will also be painting with 3 layers of grey gel coat as well.

    All suggestions are welcome and thanks for your time and effort!
     

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  2. Blueknarr
    Joined: Aug 2017
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    Blueknarr Senior Member

    The technique I use.

    Starting at the transom as "zero" mark every foot. Six inches where the hull changes shape.

    Take measurements perpendicular at each stringer mark. A small square and yard stick work well

    Snap a chaulk line on the plywood directly above where the stringer should end up.

    Transfer the one foot (six inches) measurements from the snapped line.

    Connect the dots at the end of each perpendicular.

    Stand back to verify that it looks promising.

    ...

    Cardboard template for the bow where there isn't a stringer to measure from.
     
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  3. bajansailor
    Joined: Oct 2007
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    bajansailor Marine Surveyor

    I think it would be better if you use a layer of cloth with epoxy, rather than CSM and polyester on to plywood?

    The CSM will use a lot more resin than the cloth, so it might not be much more expensive, and it will be much more durable.
     
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  4. KismetFI
    Joined: Sep 2020
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    KismetFI Junior Member

    Awesome advice, thanks!
     
  5. KismetFI
    Joined: Sep 2020
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    KismetFI Junior Member

    Great suggestion! I used up all of the poly resin I bought, so I could certainly use epoxy on the deck!
     
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  6. kapnD
    Joined: Jan 2003
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    kapnD Senior Member

    Three coats of gel coat in the bilge is vast overkill. There are paints specific to this application that do a great job at far less expense and effort.
    Whatever coating you use will only be as good as what’s beneath it. From the pic, it looks like a lot of prep needed before applying a finish.
    Second Bajansailors suggestion about the chop (CSM?), a woven fabric will be much stronger and more durable.
    Don’t leave the backside of any plywood raw! Cut/fit/sand/glass before install
     
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  7. Squidly-Diddly
    Joined: Sep 2007
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    Squidly-Diddly Senior Member

    guys that measure and cut vinyl flooring around door jamb moulding etc use roofing tar paper. If you don't get it right the first time you cut the paper back then use another piece to try and get better fit and tape that to main piece.

    For fitting around stuff without solid floor to work on I like Plasti-Core COROSPLAST 72 in. x 36 in. x 5/32 in. Twinwall Plastic Sheet-COR-3672 - The Home Depot https://www.homedepot.com/p/72-in-x-36-in-x-5-32-in-Twinwall-Plastic-Sheet-COR-3672/202771364

    This is also what they use for all those political campaign signs, so "harvest" a few dozen of those.
     
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  8. KismetFI
    Joined: Sep 2020
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    KismetFI Junior Member

    Thanks for the input, much appreciated! I second that three coats of Gel coat may be overkill. My only concern was the fact that I did the lay up with poly unwaxed resign. I want some kind of protection/semi protection where water may get to and sit (back bilge, very unlikely). I figured gel coat with wax may be the easiest application and assist. Perhaps Interlux Bilgekote would work better? The discoloration is beneath the resin, comes from the original hull, she is a 1977. I grinded and cleaned the hull as best as I could without going over board. I will certainly looking into the epoxy deck with a woven fabric. Thanks again!
     
  9. KismetFI
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    KismetFI Junior Member

    Good advice, thanks!
     
  10. Barry
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    Barry Senior Member

    There is an extremely easy way that takes less time. Which way are you running the plywood, 8 feet front to back or crossways 4 feet front to back. Let me know and I will send you the method
     
  11. KismetFI
    Joined: Sep 2020
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    KismetFI Junior Member

    Hey thanks, any input is welcome! I will be running the boards crossways 4 feet front to back. Figure I will have less sections by doing it this way. Thanks for your time and effort!
     
  12. Barry
    Joined: Mar 2002
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    Barry Senior Member

    This is the technique that we used when building aluminum boats to 1) scribe the bow curve into stringers, 2) scribe the side trays/stringers onto the side of the hull where the bow curve came into effect and 3) scribe the plywood
    prior to applying Duradeck to make a deck as you are doing. (it can be used to make a pattern for a bulkhead in either a round hull, or developable surface hull. But to do so in one piece, you need to have the plywood come down from the top)


    1) Take a 3/16 inch to 1/4 inch sheet of plywood, and mark out full length 8 foot lines on one side of the sheet at say 6 inch intervals
    2) If the widest part of the hull is 7'6", cut the ply at say 7'4" and drop it into the stern of the boat with the long side of the ply against the transom. I will assume that the transom is straight
    3) Push the ply to one side of the boat until it hits. (another assumption, the first or even the second 4 foot sections may be straight in which case you can just measure your deck sheets)
    4) Take a compass, the type with a pencil on one leg and the pointer on the other. If the hull area is tapered inward moving forward, there will be a gap at the transom. Say it is 2 inches (again not likely in the first couple of sheets)
    5) set the compass to 2 1/2 inches and holding the compass perfectly vertical, the pencil on the sheet, the pointer on the boat hull, and keeping the compass at 90 degrees to the keel, carefully run the pointer along the boat and
    the pencil will transfer this profile to the plywood. The idea of marking out the 8 foot lines on the ply is to give you a visual so that the compass is 90 degrees to the keel\
    6) cut this edge with a jigsaw and drop it in place, and check your fit. If you were careful, the fit should be within a 1/4 inch of the side of the boat. Then set the compass at say 1/2 inch, remark, recut, drop it in, and that is one side done

    Two options here,
    1) flip the plywood over to check to see if the right and left side were mirror images. If so you then measure the width ahead from the transom 4 feet forward and lay this pattern out, mark and cut the deck ply and install it
    2) If the first curve is not right, flip the ply back over, and then slide the ply over to the left side, rescribe and cut.

    Measuring the boat width front and back then apply the patterns to fit.

    You can do this easily up until say the final bow piece. At the bow the curve will be coming in quite tight.
    Before you were pushing the ply into the sides to get your pattern. At the bow, to make things easy, you can cut your 3/16 ply to the width of the last deck ply and make a LONG scribe as now you may have as much as a 4 foot gap.
    You can make your own scribe by making a 4 foot long 1/4 by 1 inch by stick, drill a hole in one end that will accept a round pencil and on the other, cut a point. The point will run along the edge of the boat and the pencil through the hole
    Make a 3 foot scribe, cut the ply, push it forward, make say a 10 inch scribe and cut, move is forward and you will be in range of using the compass.

    As aluminum is expensive, it was imperative that we did not waste much. We used a Log Scribe that gave us options of moving the pointed end in various positions as well as a spirit bubble to ensured that the scribe was vertical or horizontal. This scribe was available at Lee Valley, made by Veritas

    It is fast and extremely accurate. The cost will be a $10 sheet of 3/16 ply of cheap paneling. You can use corroplast but it is a little harder to cut smoothly in curves

    As the width will be getting narrower as you move forward, you just use the same 3/16 for the entire boat
     

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    Last edited: Nov 1, 2020
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  13. KismetFI
    Joined: Sep 2020
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    KismetFI Junior Member

    Barry, thank you for the detailed information here. This is great stuff and seems manageable! I am in the process of building out a car tent so I can do some work over the winter on the hull. I will be sure to send over some pictures once the deck is on. Thanks again for your time and effort!
     
  14. Squidly-Diddly
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    Squidly-Diddly Senior Member

    might be nice time to learn basic drawing in CAD. Use the dimensions you know you can get accurate with straight pulls of the tape measure, or using 4x8' sheet as Framing Square, then make sure other measurements all jibe with what "Find Dimension" feature of CAD says.

    PS-I'm still waiting for nice simple CAD program feature that will simply print out on A4 paper a full scale set of Blue Prints (or 1/2, 1/4, 1/100, 1/48 or any other scale for that matter). Seems like that feature should've been there 15yrs ago.
     
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  15. KismetFI
    Joined: Sep 2020
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    Location: Fire Island, NY

    KismetFI Junior Member

    I have never used a CAD program, would be fun to jump in and check it out. Thanks for the input!
     
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