Cold molded boat without 90 degree side planking?

Discussion in 'Boat Design' started by serdarbas, Feb 11, 2024.

  1. serdarbas
    Joined: Nov 2023
    Posts: 5
    Likes: 1, Points: 3
    Location: rotterdam

    serdarbas Junior Member

    I'm currently building a Slipperlaunch and I'm about to start the final side planks.

    But I made two mistakes:
    1- I ordered the planks without enough width for 90 degree (parallel, lengthwise?) spiling. I never anticipated that the side planks requires such a crazy spiling.
    2- I ordered quarter sawn mahogany planks.

    1- Since the width of the planks 5.5 inch (4 inch planking planned) I can only make short planks on bow section of the boat.
    2- Spiling required on bow / sheer section is so severe that 90 degree grain direction of quartersawn planks will have 60 degrees grain direction on the other end. It will literally make wave patterns on the hull.


    Possible solution??
    There is so few resources online regarding side planking and every single one of them uses 90 degree planking.


    I've made some tests and I've noticed that if I follow the curvature of the boat:
    1- I will need minimal spiling thus very long planks.
    2- Directional quartersawn grain direction.

    I have no clue how it will look like.

    I used some scrap plywood for testing:
    (Planks becomes parallel to hull on aft section)


    Here is a boat that is built this way:


    What is your expert opinion about this?
    Whenever I go smart, I end of screwing up big time.
    There is no source on this, I'm flying totally blind here.
    I'm afraid to create an aesthetic abomination.

    Thank you!

    Attached Files:

    bajansailor likes this.
  2. Will Gilmore
    Joined: Aug 2017
    Posts: 920
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    Location: Littleton, nh

    Will Gilmore Senior Member

    How about starting at the sheer, use narrower strips, say 3/4", maybe including a taper, 1" in the middle, steam them, if you need to, follow the deck line.

    I don't think you need to spile, just let it run over, cut and sand at the bow, plane at the sheer and at the chine. Adjust the taper and go wider as you climb towards the chine. Narrower planks won't need to run a long. You'll lose less wood.

    BlueBell and bajansailor like this.
  3. Rumars
    Joined: Mar 2013
    Posts: 1,774
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    Location: Germany

    Rumars Senior Member

    Simple answer, paint the topsides.
    It really depends on the look you can live with. Paint will allow you to plank however you like, because the grain isn't going to be visible. If you want a traditional varnished look the planks have to be spiled, to imitate carvel planking that follows the sheer.
    Anything else depends on your preferences. You could for example use some double sided tape or hot glue to temporarily fasten the mahogany full size to the hull, parallel amidship. This will leave you with gaps between plaking in wider areas, and some overlaps in narrower ones. Now wet it out with some alcohol to see the grain and scribe some pencil lines to represent the grain in the gaps. Rearrange the planks over and over until the result pleases you.
    Remember, only the varnished areas have to look good, everything under the waterline gets antifouling and can be planked at any angle, it won't show.
    BlueBell likes this.
  4. philSweet
    Joined: May 2008
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    Location: Beaufort, SC and H'ville, NC

    philSweet Senior Member

    Mahogany is just fantastic for everything except cold molding, as I learned the hard way 30 years ago. I agree with Will that the only hope for an aesthetic varnished topsides if the planks don't lay with minimal spiling is to go narrow and edge set the planks. Mahogany is frustratingly difficult for this. You will probably need to strip at 1 1/4 inches to get it to take the edge set. Try a few pieces, and if you think 1 1/2" will work, use 1 1/4 ;) Or you can try to spile every third plank from a bit wider stock - say 2 pieces 1 1/4 edge set, then a 2" piece spiled to reduce the edge set on the next pair. Don't be too concerned if you have to put in a couple cheaters down near the waterline.

    In order too hold the strips in place, I converted a 4' oak 4x4 into about a thousand pieces 4" x 1/4" x 3/8 and put a screw near the middle and a small chock block under the opposite end. I could clamp three 1" strips per night because I could reach over two strips with the oak clamps. I clamped every 2 inches, but my strips were only 1/8" thick.
  5. fallguy
    Joined: Dec 2016
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    Location: usa

    fallguy Senior Member

    I have a cold molded 1960 Carver. The boat was intended for paint and is all mahogany. The planks were laid 45 at the end.

    I removed the old paint and bright finished it and it is still a great look.

    Stop worrying. It will look great. You can hide any spiling by keeping the planking narrower, but I don't think it will matter; the boat is going to be really great looking.

    Whether you rerip all the planking is up to you, but I'd try first to not unless just not working to lay..

    Rumars, as always, gives great advice about how to finesse the job. And PhilS some good tips as well.
    Will Gilmore likes this.
  6. Howlandwoodworks
    Joined: Sep 2018
    Posts: 223
    Likes: 80, Points: 38
    Location: USA MO

    Howlandwoodworks Member

    I did top and bottom planks as full size board or as large as possible then scribed the next planks to it. Then both sides of the last center plank.
    Keel was not set in this photo, waiting for water line test in tank.

    Will Gilmore likes this.

  7. Howlandwoodworks
    Joined: Sep 2018
    Posts: 223
    Likes: 80, Points: 38
    Location: USA MO

    Howlandwoodworks Member

    I looked for a similar boat and copy what has come before you even in solid planking, its going to lay around the hull shape the same.
    The hull shape will dictate a lot of what happens as the 2D object lays around a 3D shape.
    I calculate equal number and size of planking for every 6th rib and hoped for the best.

    Young boat builders are influenced, old ones just steel.
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