Jon Boat for Dad

Discussion in 'Wooden Boat Building and Restoration' started by foolishone, Aug 15, 2019.

  1. foolishone
    Joined: Aug 2019
    Posts: 6
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    Location: Green Bay

    foolishone Junior Member

    Hey all. My father recently retired and broke ground on a lake house in Missouri. My dad and his brother have owned a home on this lake for many years but he has decided to move down permanently. The lake is aprox. 70 acres and is restricted to "no wake" entirely. I have previously built a small 8' dinghy I used for a couple years. I would like to build a 16ft plywood Jon boat as a surprise for him.

    Width is limited to 5' as the boat will need to be able to share a slip with a pontoon. I started by looking over some plans and how-to's. The boat will be used primarily for fishing; casting for bass and crappie. I'd like to keep the draft shallow so he can get into the lilly pads, flats and flooded timber areas. The boat will be powered by a transom mount tiller handle trolling motor. Additionally, I'd like to have a bow mounted trolling motor so the boat can be moved around when casting from the bow.

    JonBoat.jpeg JonBoat2.jpeg.jpeg JonBoat3.jpeg.jpeg JonBoat4.jpeg.jpeg JonBoat5.jpeg.jpeg

    I've sketched up a few initial ideas. The idea is to build ribs from 2" x 2" which run 48" across the bottom and extend 18" from the sides at a 70* angle. This gives me a 17" vertical height from floor to gunwale. The rear 8' would consist of these 'standard' ribs. At the 8' seam the rise for the bow would begin. Rising 18" over 8' at a slope of ~11*. The ribs continue to run perpendicular to the plane of the floor (thus canted back 11*). At the seam I would cut the rear rib on a -11* angle such that the forward rib sits flush to the cut angle. This allows the forward and rear ribs to be screwed & glued.

    The height of the ribs is reduced as the bow climbs to maintain a horizontal gunwale.

    I think I will sheet the hull in two layers of 1/4." I was originally planning to build a curve into the bow and just kind of got it stuck in my head that I need to use two layers. With a straight slope 1/2" would probably work just as well. Transom is two layers of 3/4" - glued and screwed together.
    I would like to spray foam the frame work and hull before sheeting the interior.

    The idea will probably change a 100 times between now and whenever I actually start building but this is the gist of it.
     
  2. Deering
    Joined: Feb 2005
    Posts: 477
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    Location: Juneau, Alaska

    Deering Senior Member

    Very nice job with articulating your objectives and approach. A rarity on this site.

    It sounds like the boat will remain in the water most of the time. You haven’t stated what you plan to seal/protect the plywood with. The 2” of spray foam between the two plywood panels along with a half inch of plywood is massive overkill for this boat. 1/4” thick sides with a reinforced gunnel would likely be more than adequate, especially if you use fiberglass inside and out.

    Building and aligning the frames sounds like a headache. I highly recommend shifting over to a stitch and glue approach. There are lots of plans available for the boat you’re describing for a modest cost. Maybe something like this
    https://boatbuildercentral.com/wp/StudyPlans/LM18_STUDY.pdf
    Or this Flats Stalker 18 (FS18) - Study Plans https://bateau.com/studyplans/FS18_study.php?prod=FS18
    Or this Sculldugery II 17 Plans https://devlinboat.com/product/sculldugery-ii-17-plans/
     
  3. foolishone
    Joined: Aug 2019
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    Location: Green Bay

    foolishone Junior Member

    I’m waffling between spar/paint and fiberglass. I’ve built a few things in wood and glass, the most relevant is a 5x5x5 hunting blind. I’m more inclined towards spar/paint to keep the costs down but since it’s sitting in the water all the time it might be better to use glass.

    Most of the plans I’m seeing are not showing the flat bottom or have included the bench seats as structural pieces. My dad could have some trouble stepping over the benches so I want to make sure the floor is open. That was my thought when ‘beefing’ things up - removing structural pieces means additional support is needed.

    Again this is all just ideas and sketches while I try to figure out what is best and what I can actually do.
     
  4. ondarvr
    Joined: Dec 2005
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    Location: Monroe WA

    ondarvr Senior Member

    The taper up for the bow can’t start that far back.

    And you don’t need to over build it with thick ply.

    There are many plans for small boats like this around, you should be able to find something that fits your needs. If you can’t find something, then you may not have chosen a good design to start with.
     
  5. foolishone
    Joined: Aug 2019
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    Location: Green Bay

    foolishone Junior Member

    Thank you for the advice. Could you explain for me why the taper needs to start closer to the bow?
     
  6. Deering
    Joined: Feb 2005
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    Location: Juneau, Alaska

    Deering Senior Member

    Fore/aft trim and stability would be affected. Walking forward to operate the trolling motor would cause the bow to depress significantly. Given the intended usage and low speed, the taper yields little performance benefit.

    Regarding structural members, in many designs the seats could be replaced by knee braces and slightly wider gunnels, or a pass-through on the seats. The boat isn’t going to see high loading at no-wake speeds so there’s plenty of margin to work with. Suggest you touch base with the designers to get their thoughts.
     
  7. foolishone
    Joined: Aug 2019
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    Location: Green Bay

    foolishone Junior Member

    Thank you again.

    I went ahead and ordered a set of plans: Jon boat plans wooden boat kits http://www.unclejohns.com/jonboat/building%20plans/default.htm This should take care of the hull layout and I can modify from here to achieve the open floor as you suggested either with knee bracing or pass through seating.

    By designers do you mean the designers of the plans I have ordered or something else?
     
  8. Deering
    Joined: Feb 2005
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    Location: Juneau, Alaska

    Deering Senior Member

    Nice. Yes, if you plan to make significant changes it might be wise to run them past the designer at Uncle Jon’s (assuming they’re available). He/she can tell you if you’re making a dangerous move, or they may have a better alternative.

    Given that the boat will live in the water full time, if it were me I’d coat the plywood, inside and out, with epoxy and a 6oz layer of glass fabric. It’ll add a bit to the cost and construction time, but the resulting improvement in lifespan is worth it. Then paint it as they recommend.
     
  9. foolishone
    Joined: Aug 2019
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    Location: Green Bay

    foolishone Junior Member

    I sent an email to uncle John’s and got a response pretty quickly that they believed it wouldn’t be a problem but he was going to give it some thought and get back to me with some specifics.

    Are we talking about biaxial, woven, or chopped mat?

    What about gluvit on the seams?
     
  10. Deering
    Joined: Feb 2005
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    Location: Juneau, Alaska

    Deering Senior Member

    Just a lightweight woven cloth. You want it to increase the build thickness of the epoxy for waterproofness and to give you some abrasion resistance. Biaxial is generally used to provide structural improvements (it also does the stuff that woven does), but it costs more and is a little bit harder to apply, besides the plywood specified will be plenty strong for your purposes. Chopped mat isn’t suitable for this application.

    Like this - maybe the 7-1/2 oz stuff. Fiberglass Cloth http://www.uscomposites.com/cloth.html
    You’ll see cloth tape on the same page. Use that and epoxy for the seams, with a thickener to make a radius corner for the glass to wrap around. This is basic stuff and not complicated to learn. Here’s a nice resource that gives the basics. Once you learn it you’ll find all sorts of other applications for it too. I like System3 epoxy because it mixes at a simple 2:1 ratio, but there are many quality brands out there.
    https://cdn.shopify.com/s/files/1/1...6_NEW_with_2018_Edits.pdf?2485911027753381509

    Use these techniques on that Unclejons design and you’ll have a boat that’ll last for many years.
     
  11. messabout
    Joined: Jan 2006
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    Location: Lakeland Fl USA

    messabout Senior Member

    The drawing of the side panel suggests that the design is a planing boat. It has a straight horizontal afterplane. The lake is a no wake place which implies that you will have to use low power outboard or trolling motors. It will never be in planing mode. With those restrictions the boat is ill designed for that particular application.

    Better to have a long pram type design that is not inclined to drag its transom the way the Uncle John will. Motors will not work as hard, and batteries will last longer if the boat has some aft rocker.
     
    ondarvr likes this.
  12. foolishone
    Joined: Aug 2019
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    Location: Green Bay

    foolishone Junior Member

    How much of a taper would be appropriate? Should the bow and aft be “mirrored” or would I be better off with less rise? How would the aft rocker effect stability? Will the boat want to tip forward and backwards?
     
  13. Deering
    Joined: Feb 2005
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    Location: Juneau, Alaska

    Deering Senior Member

    Basically you want the bottom edge of the transom to just ‘kiss’ the surface of the water. For your purposes you can start that slope upward at amidships or a bit aft of that. You should try to limit the upward angle from horizontal at 5 degrees or less.

    It will be a bit more sensitive to fore/aft trim but probably not a lot.

    Given the slow speed and already shallow draft, I’m wondering how much it’ll buy you.

    Here’s a design that might be in the range of what you’re looking for. Note the draft shown in the study plans. The Honker 15 (HK15) - Study Plans https://bateau.com/studyplans/HK15_study.php?prod=HK15.
     
  14. messabout
    Joined: Jan 2006
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    Location: Lakeland Fl USA

    messabout Senior Member

    In order to determine the amount of aft rocker or forward rocker (upward curvature of the bottom) you must calculate the expected total weight of the boat and all that it contains. Then you will need to do some arithmetic that reveals the draft of the boat when loaded. (draft is how deep it is setting in the water) When you know that dimension you can then draw the curvature. But you wont be able to determine the draft without determining several other factors that influence draft.

    None of this is rocket science but it does require a basic understanding of Archimedes principles and how to calculate the displaced volume of the boat when carrying the presumed operating weight. Oversimplifying, it goes like this. If the boat pushes six cubic feet of water out of the way when it is a rest, then the displacement will be 6 x 62.4 pounds (in fresh water) = 374 pounds. The dimensions of small boat components are not conveniently measured in feet, but in inches......................here I apologize to the rest of the world that uses the more practical metric system. To translate cubic feet into cubic inches multiply by 1728. Six cubic feet then becomes 6 x 1728 = 10,368 cubic inches. Now the process is to determine the dimensions and certain variables that revolve around the shape of the various sections of the boat. One of the variables is called prismatic coefficient which varies with the boat's design characteristics.

    This kind of stuff need not interest someone who intends to build a simple little fishing boat, so ignore the above bits.
    The Uncle John boat is going to satisfactorily serve the user just as it is. Not as efficient as a purpose designed boat but entirely useful nonetheless. You have the plans, start building, and keep us informed about your progress.
     

  15. Howlandwoodworks
    Joined: Sep 2018
    Posts: 54
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    Location: Columbia MO

    Howlandwoodworks John Howland

    We had a summer home on the Lake of the Ozarks from 1937 to 1984. My dad and I built a 12' John boat out of 1/4' plywood, 1"x2", 1 1/2" transom, and fiberglassed the outside and varnished the inside. We put a square sail on it and would run down the shore line on a light summer breeze, fly fishing for blue gill and bass. Then motor back up and do it all over again. Us kids would use it most ever day we could.
    I think the (dollars per fun ratio) on that little boat was the best I have ever seen.
     
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