I designed my own boat, will it float..?

Discussion in 'Boat Design' started by AndyPandy, Oct 6, 2018.

  1. AndyPandy
    Joined: Oct 2018
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    Location: UK, South East

    AndyPandy New Member

    ...and will it move through the water OK?

    I've never really built anything, expect a dolly for my Mariner 9.9, which I run on my Honwave T38-IE.

    I have a hankering for a bigger boat, but purse strings are tight, and I really liked the idea of building my own boat.

    I looked online for plans, but nothing really matched my requirements. So, I designed my own.

    It is designed to be as easy as possible to build, without complicated angles, so basically a tub.

    Could I ask for your critique, and perhaps an idea of whether it would function at all on the water?

    It would be used on the non-tidal river Thames, in the UK, and not at much speed.

    Here is the 1/10th model I made up from some beer boxes: https://i.imgur.com/SakQjhc.jpg

    It's 45cm high, 4.5 metres long, and 1.8 metres wide. Though the transom would be cut down in the middle, as I have a s/s outboard currently.

    Cheers,
    Andy
     
  2. Blueknarr
    Joined: Aug 2017
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    Location: Colorado

    Blueknarr Senior Member


    Welcome to the forum.

    Will it float? Probably. Make it out of 2nd boiler plate probably not. What is the planned building material? How many people and how much stuff do you plan to float in it?

    That simple shape will have a fair amount of drag slowing it down. Some changes would increase its efficiency, but also increase the complexity of its build. How committed are you to keeping it box simple?
     
  3. AndyPandy
    Joined: Oct 2018
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    Location: UK, South East

    AndyPandy New Member

    Hi Blueknarr!

    I'd build it from plywood (marine or exterior, I haven't decided yet) maybe 12mm for the bottom, and 9mm for the rest. glassed on the outside, and epoxied and painted on the inside (stich and glue, so filleted and taped seams). The bow and pilot seat would be full of foam for buoyancy.

    Box would be so much easier to build (I have limited space, and tools), but I'm curious to know what changes would make a significant difference to performance, and why.

    I want to carry 6 pax. including pilot, and a medium sized spaniel.

    Looking to soak up knowledge from those with experience!

    Cheers,
    Andy
     
  4. Blueknarr
    Joined: Aug 2017
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    Location: Colorado

    Blueknarr Senior Member

    Stitch and tape is a great first build technique. Marine ply could last decades longer than exterior, especially if not fully encapsulated in epoxy.

    Since it is only intended for displacement operation, adding rocker to the bottom so that you are not dragging a transom eddie.

    4.5 X 1.8 M is way to large of a plywood panel with out framing!!!

    45 cm is very low free board

    Either my conversions ate off, or plywood isn't sold as 4x8ft sheets in the UK, or your wasting plywood.

    I think you should look at Glen L or other online sources to see if a preexisting design could be used. Try looking under a subheading of 2 or 3 sheet skiff.
     
  5. bajansailor
    Joined: Oct 2007
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    bajansailor Marine Surveyor

    Andy, this 4.3 m Garvey Dory looks like it might be pretty close to what you are after?
    Spira International Inc - Nola Garvey Power Dory Plans http://spirainternational.com/hp_nola.php

    Please don't try to save a few quid by designing it yourself - you will be spending a relative fortune in materials anyway, and the cost of plans will be peanuts in comparison.
    In fact, for the anticipated cost of the materials alone you could probably buy a fairly nice little fibreglass motor cruiser for pottering about on the river with.
     
  6. Blueknarr
    Joined: Aug 2017
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    Location: Colorado

    Blueknarr Senior Member

    $70 US for the Nola plans. That's cheaper than one sheet of mistake plywood.
     
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  7. AndyPandy
    Joined: Oct 2018
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    Location: UK, South East

    AndyPandy New Member

    @Blueknarr adding a rocker would complicate the build for my simple mind. The curves add in angles I'd rather not have to deal with. I understand that the rocker aids turning, but otherwise a flat bottom should be faster.

    I was thinking about adding some framing, as it would make it easier to put together. Also if I do this, then I may as well but-block the long pieces together, to save me working out how to scarf the ply with what tools I have (I have a small hand plane!).

    The sheets sold here are 2.44m x 1.22m, so 4 x 8ft sheets. I'm aware that there would be wastage, as well as needing 4 pieces for the bottom.

    The problem with all the plans I've found is that there's limited seating (for those 6 pax I want), and/or lots of angles that would make adapting them to suit difficult.

    This is an example of what I'm trying to achieve (albeit on a much simpler scale!): SS 201 I/O | SunDeck Sport https://www.hurricaneboats.com/sundecksport/ss-201-i_o

    So, lots of seating, and a console built in.

    Are there plans for a boat like this?

    Cheers,
    Andy
     
  8. rwatson
    Joined: Aug 2007
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    Location: Tasmania,Australia

    rwatson Senior Member

    The complexity is only in you mind, as is not really more difficult than sitting on a sheet of ply so it bends 6 inches.

    Also, this design will be considerably faster. The curve leading into the flat stern will provide more maneuverability, quicker planing and better top speed.

    You certainly could use some temporary framing to help with construction, but at this size it's really not a structural benefit. If you added a bench seat along the centre, and a small deck at the front, you would have all the reinforcing you could possibly need.

    Yes, scarfing is a bit complex. Its main benefit is that it creates a smooth curve, without a hard spot. That's only a small issue with a boat this small, and won't be a problem to use a Payson Joint ( butt joint with backing plate),. You can even just use epoxy and fibreglass while building, and put the backing plate in after the hull has been assembled.

    This is a classic case of a champagne taste and a beer budget.
    For the size of boat you want, 6 pax is a really tight comfort fit, and a console in a 1.8 wide is pushing the envelope, but cane be done.

    This might be closer to your needs with better seating, AND an optional Console AND Easy to Build for beginners.

    plywood_jon_boat_GF14_640.jpg

    jon_boat_kit_GF14_640.jpg



    Jon Boat 14 (GF14) - Study Plans https://bateau.com/studyplans/GF14_study.php?prod=GF14
     
    Last edited: Oct 7, 2018
  9. fallguy
    Joined: Dec 2016
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    Location: usa

    fallguy Senior Member

    Tortured ply, monocoque is what you are after.

    The thing about boats....people have been designing them for thousands of years. Every person that comes along thinking their design is so much better ends up sad (hydrofoils excluded).

    Ditch your design and find one off the shelf.

    Building a boat is no small feat. A place like bateau.com has a builder forum with people eager to answer build questions.

    Your design will have stern drag and track poorly. It may also drag at the forward end of the bottom at the low end of engine rpms which would get very odd indeed.

    In a tortured ply build of a jon boat; the bottom panel is bent up at the bow for smoother entry. A perfect example was provided by rwatson. They have 3 sizes.

    Will your design work? Yes, poorly.

    Typically, scarfing joints are used for seams of 6mm ply and my brother prefers a hand plane and an eletric sander.
     
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  10. bajansailor
    Joined: Oct 2007
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    bajansailor Marine Surveyor

    Another possibility (just one of many boats out there where plans are available) -
    Tropic 14 https://bowdidgemarinedesigns.com/tropic-14/
    Interesting photos and videos in the link.
    Although I don't think that it quite what you are looking for, the info is still good for reference.
    The Jon Boat in Mr Watson's link above does sound ideal really for what you have in mind Andy.
     
  11. AndyPandy
    Joined: Oct 2018
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    Location: UK, South East

    AndyPandy New Member

    rwatson - "This is a classic case of a champagne taste and a beer budget." Hah, you're spot on!

    bajansailor, that's a beautiful boat! If only there was a console in the design. I'm also really keen on the side seating, as opposed to horizontal.

    That said, I'm wondering how many people it takes to lift the boat into a trailer after it's built.... :)

    Cheers,
    Andy
     
  12. BlueBell
    Joined: May 2017
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    Location: Victoria BC Canada

    BlueBell Ahhhhh...

    Andy Pandy,

    The post above is worth repeating, it's good advice.

    The best existing design is the one that most closely meets your needs in a boat.
    That is, it does what you want it to do, and does it well.
    Preferably, in order of priority.

    Good luck, post pictures of what you end up doing.
     
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  13. rwatson
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    rwatson Senior Member

    That boat would be about the same weight as a ply boat. Mark Bowdidge uses strip planking, infilled with epoxy to create the excellent shape, using very light weight wood for a core.
    The build photos on his web site will give you some insights into the amount of work needed.
    That is a level above stitch and glue though , and not for the beginner.
     

  14. Tiny Turnip
    Joined: Mar 2008
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    Location: Huddersfield, UK

    Tiny Turnip Senior Member

    Andy Pandy - lots of good, clear advice from people with considerably more experience and knowledge than me. Lots of good examples of suitable or near suitable boats too. Here are some thoughts which I can't see raised above.

    1) The curvature of ply sheets adds considerable strength without weight, and a curved (tortured) ply design will need considerably less framing, and thus weight than a flat ply design.

    2) What is the intended use of the boat? Is it pleasure boating/picnicking/ferrying, or fishing, or... Fishing will require rather more room and stability than just sitting and cruising.
    Do you intend to keep it on the water, haul out, or trailer each trip?

    3) The weight of a small boat is something I find very important when out of the water. for me and a friend, around 100kg bare boat for two people to lift and manoeuvre is the upper limit. I suspect that you will be looking at a heavier boat if it is to take 6 people, so the manouvreing is a consideration.

    4) It would seem to me that the consol and the mechanical/electrical linkages it will require add a lot more complexity, and looking at the sternward position you propose for it, I can't see that it offers huge advantages over just the outboard.

    5) Here is one of the designs for a 15'8" on Hannu's Boatyard. It might be close to something that would suit, though a slightly lower capacity. 4 sheets of ply. Whereas I haven't built one of his designs myself, his approach to de-mystifying and simplifying boat building is what gave me the confidence to start building small, simple boats myself. I'd recommend reading this build page and the discussion.

    A 15'8" fishing punt | Free Boat Plans http://hvartial.kapsi.fi/wpunt/wpunt.htm
     
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