Composite Rowboat

Discussion in 'Fiberglass and Composite Boat Building' started by Scott M.., Oct 13, 2020.

  1. srimes
    Joined: Sep 2008
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    Location: Oregon

    srimes Senior Member

    Easiest "fix" is to use a trailer instead of putting it on the roof. Then you can also keep the motor and batteries in the boat.
    If you insist on putting it on the roof look into loading systems. Boat Loaders for cartoppers, tenders & fishing boats | Enlightened Boating https://www.enlightenedboating.com/product-category/boat-loaders/ popped up first in my search.
    Without a loading system long boats can be easier to load than short, as you can lift up one end at a time.

    Your description of what you want the boat to do doesn't exactly match with your design description. The bow of a jon boat works great for rowing. It's the stern that's a problem. Make the stern like the bow and you'll have a good simple boat.
    For high load capacity, good rowing, and a bow that goes over waves in a short boat you want a lot of rocker (not just curved in the front, but the back as well, and a pram bow may be best.
    Pram Kits http://gregboats.com/pages/prams.html
     
    bajansailor likes this.
  2. Scott M..
    Joined: Oct 2020
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    Location: Newtown, CT

    Scott M.. Junior Member

    Thanks for all the ideas and suggestions. Please keep them coming.

    I think I'm pretty set on making my own custom hull design. I just don't think I will find anything close enough that is worth modifying and come out as light as I want.

    I also look forward to the challenge of working on something new and its pretty cool to tell people its a one of a kind boat.

    The good thing is I own a lot of tools and are use to tackling challenging projects.

    I bought a C6 corvette with a hydrolocked motor and tore that down and fixed it, that was a first.
    I have restored a 1976 corvette and painted the entire car, another first. I also built a one man pontoon boat that comes apart into multiple pieces so I don't have to carry anything over 30lbs.

    So I like challenges and I need something to do to keep me busy during the long New England winter.

    As far as my ultimate boat, I want it to be strong and durable but yet extremely light. I want something that if I take it down a river fishing and it hits a rock its not going to crack in half and I have no intention of hanging it in my living room as a piece of art.

    Fit, form, and function are my priorities, where as surface finish, smoothness, orientation of fabric, etc. is all secondary to me.

    I found some foam board I had laying around so hopefully today or tomorrow I will make my model to be able to load some photos up.

    Thanks again for all the help, I couldn't do it without you folks.
    Scott
     

    Attached Files:

  3. Rumars
    Joined: Mar 2013
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    Rumars Senior Member

    You might want to revisit that rock hitting idea.
    Let's do some backwards design. Approx. surface area for the 14ft version, 9sqm, target weight 27kg. So we have a design goal for the laminate of 3kg/sqm. Reserve 0.4kg/sqm for fairing and painting and we have 2.6kg/sqm left for the actual sandwich. The foam is 80kg/cum, every mm weighs 0.08kg/sqm. 10mm foam weighs 0.8kg/sqm, this leaves 1.8kg/sqm to divide between the two skins, that is 0.9kg/sqm each side wich must be shared between fiberglass and resin. That means 400gr/sqm of fiberglass per side, with a laminate thickness of about 0.4mm. More then enough for the boat to "not crack in half" but not something you go rockbashing with on a regular basis.
    You simply have to live with the compromise, light weight means no rockbashing, no dragging the boat on hard surfaces, etc. OTOH plenty of people live with canoes with half that amount of fiberglass on cedar cores, and they don't complain about durability.
    The above calculation is only an example, don't use it for an actual boat, it is here to exemplify the limitations you face.
     
  4. Scott M..
    Joined: Oct 2020
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    Location: Newtown, CT

    Scott M.. Junior Member

    Now that is some serious number crunching but I completely get where your going. I just haven't had access or researched enough yet to do the math to figure out approximate final weight. I guess where my mind is at is in the end I get a boat design I think will serve me for my all around goals and using more advanced materials will result in something lighter than your standard row boat.

    Once I get the final hull concept which I think I'm close, made the model today, just have to do some final sanding and then I can have everyone take a look and tell me if it will work or I should make some changes.

    At that point I can calculate surface area and determine materials to use which then gets me to calculating weight.

    When I mentioned hitting rocks, I didn't necessarily mean to use it like I would be white water rafting. I just meant it more like a river drift boat that can occasionally hit obstacles in the water like logs, sticks and possibly a rock.

    My main use is for it to be a lake fishing boat that I can put on top of my truck so I don't need a trailer but yet I want its maximum width to be 47" at the top so it will fit between the wheel wells of my truck for making short trips during a camping outing or to go to a nearby lake.
     
  5. bajansailor
    Joined: Oct 2007
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    Location: Barbados

    bajansailor Marine Surveyor

    Just a thought Scott - how about making a two part boat that bolts together?
    There are many different types of nesting dinghy where the bow section stows inside the stern section, and the two bolt together in way of their facing bulkheads.
    You can even make the joint a bit more sophisticated with quick release clamps and male / female sections that lock together.
    If you had a 14' dinghy, you could perhaps have the aft 9' or 10' stowing on the roof of your truck, and the forward 4' or 5' section stowing inside the truck?
     
  6. Scott M..
    Joined: Oct 2020
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    Location: Newtown, CT

    Scott M.. Junior Member

    I did see some of those and they are pretty awesome.

    Yes I kinda have that as my backup plan if the overall boat weight turns out to be too heavy.

    I would just cut my boat where it starts to taper down to the front and add two stainless steel flanges with a bulb seal between them for water tightness.

    That would give me the rear 2/3 of the boat to stick up top and the front 1/3 could go in the back.

    The other thing I started thinking about thanks to one of the posts is mounting a winch on my front bumper and have a swing up vertical post with a roller that I pin to hold vertical on my roof rack. Then you just run the cable over the top to the back of the truck and hook to front of boat and hoist it up on the roof rake.

    Time will tell ultimately how this turns out. Like my pontoon boat some times you just have to start with the general idea and then figure it out as you go.

    But that's what makes it so cool doing a one off project.
     
  7. gonzo
    Joined: Aug 2002
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    gonzo Senior Member

    I don't think you can build a 60 lb boat with a 1000 lb load that can survive hitting a rock. Either you minimize the load, or have to live with a heavy boat.
     
  8. Scott M..
    Joined: Oct 2020
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    Location: Newtown, CT

    Scott M.. Junior Member

    Hello all,

    Finally got a chance to complete my foam mockup of my design concept.

    Foam is a little rough to save time but it clearly shows what I'm after.

    Please take a look and see if you see any potential issues.

    Next step is to start to make full size foam mold to lay material and foam sandwich.
     

    Attached Files:

  9. tpenfield
    Joined: Dec 2016
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    Location: Cape Cod, MA

    tpenfield Senior Member

    I made this pram dinghy out of foam boards and fiberglass. . . .

    [​IMG]
    .
    .
    [​IMG]

    Its not as wide or long as what you are planning (only 8.5 feet x 4.5 feet), but my challenges/learnings were as follows . . .

    The foam core weighed 35 lbs. The finished boat weighed about 125 lbs, but could have been about 100 lbs with some better layup planning.

    Obviously, poly-based resin will eat the foam core and that was my main challenge. I used a polyurethane coating over the foam to protect it from the resin and that was only marginally successful.

    Not sure that heat shrink wrap will work better as a coating of the foam, but you can always test a small piece to see how it works out.

    I used vacuum bagging to get the fiberglass/resin to fit tightly to the core. That seemed to work OK, but I wished I had a better way of spraying the resin for quick application. You will want a hard/strong core material in high stress areas (oar locks, engine mounting/transom, etc.)

    Also, using a coating between the core and the fiberglass, the fiberglass was not well adhered to the core. I suspect you may have that issue with your intended approach.

    In hindsight, if I used epoxy resin instead of poly resin, I could have done away with protecting the foam core as the epoxy would have adhered to the foam with no adverse effect to the core.

    To make the boat more rigid/strong, I made 45˚ angle in-fills at the corners of the hull. This type of construction, and having generally 'strong' shapes in the details of the hull, can allow you to use less fiberglass resulting in less weight.

    Looking forward to some diagrams, which I think will help everyone visualize what you are planning.
     
  10. Scott M..
    Joined: Oct 2020
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    Location: Newtown, CT

    Scott M.. Junior Member

    Wow, I'm not sure which I'm more impressed with, the small boat you made or how fast you wrote all that after my post.

    My plan is to just use the foam to create the shape to lay the material over the top not become the actual boat.

    The only foam will be maybe what people seem to be recommending to use between the fabric layers.

    The reason for the heat shrink plus wax and mold release is to have a layup surface that is smooth, resistant to the heat of the poly resin and ultimately be able to release with minimal issues.

    My plan of course before I go do this to full scale is test it out on small pieces.

    One other thing I might have to do before laying on the shrink wrap to have the surface be smooth is coat it with a skim coat of bondo and sand it out. Pink foam board has a tendency to get dinged during the shaping process.

    BTW: Didn't put it on the foam model but I'm planning to put two stability strips running the length of the boat equally spaced from center and then cover them with some thin stainless steel, so I can drag the boat without damaging the fiber layers.

    Thanks for the response and keep them coming.
    Scott M.
     
  11. bajansailor
    Joined: Oct 2007
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    Location: Barbados

    bajansailor Marine Surveyor

    Scott, one problem with the shape of the model that you have built is that most of it is essentially comprised of flat panels.
    And flat panels are much less stiff than curved panels of the same thickness.
    Hence you will probably need to have a foam core to get the required stiffness unless you increase the lay-up of the single skin hull, and / or add stiffeners - all of which adds extra weight very quickly.
    I built a single skin GRP pram dinghy some years ago - it is 7'6" by just under 4' beam, and it weighs about 60 lbs - half the weight of Ted's foam cored pram which is only slightly bigger.
    But my dinghy is plenty strong enough to do it's job, and every panel is curved, apart from the bow and stern transoms.
     
  12. Scott M..
    Joined: Oct 2020
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    Location: Newtown, CT

    Scott M.. Junior Member

    I guess where my head was at with the flatter bottom is for general stability when fishing they have a tendency not to rock side to side, where as curved hulls get a little more tippy and rock when moving slowly during fishing activities (moving from spot to spot with a trolling motor).

    I guess if it would be better I could come out from the center line at a slight angle on both halves instead of going straight across. That then makes the straight section more like 21 inches, plus it would have the strip for additional stiffness. What do you think of that idea?

    Can you elaborate on the foam core since that seems to be the way to go for improved stiffness and lower weight across my lower 42" floor span.

    What type of foam would you use, density and how thick would you make it.

    Lastly is this a better approach overall, rather than using more exotic materials like kevlar or carbon fiber. That seems to be the genral concensus but I don't want folks to think its trying to do this the cheapest way. In the long run with all the time this will take, material costs is virtually insignificant.

    My plan for the transom to have increased strength is to use a sheet of aluminum honeycomb between the fabric. The material is extremely light and very strong. This might even be a potential material to use on the overall boat rather than foam. You can buy it in sheets in all kinds of thicknesses and opening sizes.

    Thanks
    Scott
     
  13. container
    Joined: May 2019
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    Location: new zealand

    container Junior Member

    Sounds like what you are aftet is a well built glass over ply or red cedar dory. The one thing all of these exotic materials have in common is they are absolutely not suited to a rock bashing canoe, even dragging it up the sand every now and then will be too hard on it. There is a reason no one makes this kind of boat out of carbon/foam/kevlar/aerospace ali honeycomb. Not because it is too expensive/too hard, because it is unsuitable.
    The cheaper price is just a by product of building the boat out of suitable materials for the task you wish it to perform
     
  14. srimes
    Joined: Sep 2008
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    Location: Oregon

    srimes Senior Member

    For super light weight and impact resistance look at skin-on-frame construction.

    As for shape, look at real boat designs. There are reasons they look like boats. Your model looks like a barge with a bow inspired by viking longboats. A barge is great for stability and load capacity as long as it isn't moving or is moving very slowly.
     

  15. gonzo
    Joined: Aug 2002
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    Location: Milwaukee, WI

    gonzo Senior Member

    Skin on frame is light weight, but fragile. It is a very unsuitable method for impact resistance.
     
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