10 foot jon material thickness (Plywood+Fiberglass)

Discussion in 'Boat Design' started by Turbopleb, May 17, 2020.

  1. Turbopleb
    Joined: Sep 2019
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    Turbopleb Junior Member

    Hello, I am planning to build a dirt cheap plywood+glass jon boat, the design very similar to a Lowe L1040.

    As the boat will be very small, and I will at most put a 4-6hp outboard on it, I was wondering if I could get away with 4mm (5/32") plywood on all places, I'm planning on doing 2-3 layers on the bottom and 1 inside with 300g/m2 (approx 9 ounces per square yard) fiberglass weave.

    For such a small outboard, would the transom have to be thicker more than making a thicker plate for the engine mount?

    The goal of the boat is to make it as light and cheap as possible without compromising actual safety.

    Thanks in advance!
  2. bajansailor
    Joined: Oct 2007
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    bajansailor Marine Surveyor

    Here is a link to the Jon Boat which Turbo has in mind.
    2020 L1040 Riveted Fishing and Hunting Boats | Lowe Boats https://www.loweboats.com/jon-boats/l1040-jon/

    Re plywood and glass, will you be using marine plywood and epoxy resin, or ordinary 'cheap' plywood and polyester resin?
    If the latter, it will probably come back to haunt you later on - how long do you want to keep the boat for?
    I think that I would be inclined to use 1/4" / 6mm marine plywood, and add a layer of glass cloth with epoxy on the outside, while coating the inside with epoxy.
    Re reinforcing the transom, you could use an offcut of your 6 mm plywood to make a doubler in way of where the outboard motor is secured.
  3. Turbopleb
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    Turbopleb Junior Member

    Will be using normal plywood, will not have it for a long time really, just a boat to do the local stream. Will probably buy a 17 foot hardtop to go out on the big lake in a couple of years. Aside from the wood, what are the effects of choosing polyester vs epoxy?

    Seems like your plan is to have the rigidity through the plywood, while I planned for the fiberglass to be the main structural component, any big differences or just a preference?

    Reason for choosing normal ply and polyester is mostly cost, I could probably get away with a complete hull glassed and done for fishing for about 250-300 usd.

    I'll consider doing a thicker transom material at least, maybe 7mm.
  4. Turbopleb
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    Turbopleb Junior Member

    Just had a look at epoxy vs polyester, will go with epoxy in the end, allegedly stronger and holds better without cracking.
  5. messabout
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    messabout Senior Member

    Turbo: fiberglass will not be a major structural component. Not even close unless you make it almost as thick as the plywood, in which case the boat would be beastly heavy and the material would have cost a plenty. . The epoxy/glass envelope is for the purpose of protecting the ply bottom from scrapes and wear from ordinary use. It also keeps the ply from absorbing as much water as it would had you not added the epoxy/glass skin. Skin is the operative word. One layer of six ounce glass and epoxy filler will be less than one thirty second of an inch thick.

    Good luck with your project.
    hoytedow and bajansailor like this.
  6. ondarvr
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    ondarvr Senior Member

    You could probably pick up a used aluminum boat for that price. Expect to spend at least double what you first think you will on the project.
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  7. kapnD
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    kapnD Senior Member

    Light and cheap to my way of thinking means upgrade the quality of the plywood and skip the glass entirely.
    A well constructed wooden boat with a proper paint job should do nicely, provided it’s not kept in the water and properly stored when out.
    The large flat areas of the floor will need reinforcement, probably strakes on the outside, seat inside.

    Hear, hear!
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  8. Rumars
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    Rumars Senior Member

  9. gonzo
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    gonzo Senior Member

    These are photos of a dinghy I built in about 5 hours, including fiberglass and painting. The sides and ends are pine boards (1 by 12 planed down to 7/16) 11mm by 310mm. The bottom is 3mm house underlayment. There is one layer of 3/4oz mat with polyester on the seams. What you see is after two years outdoors (never covered) and often staying a couple of days in the water. Unfortunately, I gave it to my grandkids and some a$$hole stole it.
    Last edited: May 18, 2020
  10. Turbopleb
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    Turbopleb Junior Member

    Okay thanks for the info, thought that it would be plenty strong since most boats are built out of solely fiberglass today. Will revise my plan for 7mm plywood (9/32"), Would it be needed to use 12mm plywood for the bottom? (1/2")
  11. Turbopleb
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    Turbopleb Junior Member

    Sadly there's no market for these types of boats here in Sweden unless purchasing new. The reason for making a boat myself vs. getting a used one is mostly because there's none which fit this category really.
  12. Turbopleb
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    Turbopleb Junior Member

    Thanks for the info! Looks like the closest I can get is 7mm plywood (9/32"), will probably do fiberglass anyways because our climate is really hard on things. Maybe two layers bottom and one layer inside?
  13. DCockey
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    DCockey Senior Member

    Gonzo - that is a nice looking dinghy. An example of how a bit curvature can improve the appearance compared to a rectalinear box.
  14. clmanges
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    clmanges Senior Member

    The 'good paint' argument has some solid support--13 years service with next to no maintenance and no mention of glass/epoxy:

    The White Boat http://hvartial.kapsi.fi/white/white.htm
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  15. BlueBell
    Joined: May 2017
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    BlueBell . . . _ _ _ . . . _ _ _

    Just don't forget paint also costs money, has to be applied, has weight and must be maintained.
    But it does cost less, is easier to apply, and weighs less.
    bajansailor likes this.
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