Looking to Build a Boat

Discussion in 'Boat Design' started by chada, Sep 25, 2008.

  1. lewisboats
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    lewisboats Obsessed Member

    I find it easier to position the pieces individually, select the grid size and zoom in on the individual coordinates in the picture and copy them down. Freeship's output in the txt files basically runs around the outside of the panel shape in a circular type motion rather than using a station and intersection method and can be a real pain to try and lay out on a sheet of plywood. My method involves eliminating any panel that is doubled so you only have one of each, then aligning each panel in turn with 0,0 then copying the intersecting coordinates along the panel. You select the spacing via the boxes on the right. If it has a transom make sure to go into the layers properties and enable developable for the close hull layer as it isn't enabled by default. Freeship is a surface modeler so it won't give you frames per se. You will have to export offsets and select certain points out of the mass of coordinates that will represent the locations of your framing. What you will have is a shape of the EXTERIOR of the skin of the boat, from there you will need to subtract the thickness of you planking material from the #s to provide you with the surface of the INTERIOR of the skin and the dimensions of your framing. Remember...this is only for one specific line on the interior of the skin so you will have to bevel the framing to match the curvature of the skin, or use this line as the widest point of the framing and fill the remaining gap between the skin and the framing with a fillet and fiberglass. There are other ways to do this by creating intersecting layers also, then taking the coords from that. Remember that a surface has no thickness so any athwartship surface will only be good for the points it intersects and will have to be adjusted for the thickness of a 3d panel.

    Steve
     
  2. chada
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    chada Junior Member

    Be back Later

    Gone to the flats for the Specks and Reds
     
  3. kengrome
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    kengrome Senior Member

    Chada,

    The boat you've been drawing looks good but it has very little in common with the Bolger Diablo -- the boat in the small line drawing you posted earlier. If you want a Diablo (which is reported to be a VERY good boat by the way) you should just buy the plans from Dynamite Payson and build one. Otherwise you would save a lot of time and money simply by glassing the inside of your existing boat ...

    Yes I'm suggesting that you may want to reconsider fixing your existing boat. If you glass the inside it will cover the existing frames and stiffen the boat tremendously. You won't have to worry about scratching or tearing a hole in the glass this way either, because the aluminum skin on the outside will protect the inside glass liner for decades and perhaps forever.

    You don't have to do much sanding either. Just apply the glass and epoxy carefully so the entire inside of the hull and frames are covered as smoothly as possible, then roll on another coat or two of epoxy before painting.

    This is probably the solution that will give you a useful boat again in the fastest time with the least amount of work and at the lowest cost.
     
  4. chada
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    chada Junior Member

    Ken

    I have tried to fiberglass the aluminium and over a period of time in this heat
    peels in the matter of a couple months
     
  5. kengrome
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    kengrome Senior Member

    Yes I know that patching small places on the hull will delaminate after a while, but that's not what I am suggesting. I am suggesting a complete and full custom liner of epoxy (or polyester) resin and fiberglass installed inside the hull.

    In this situation it won't matter if the resin delaminates from the aluminum -- or paint that may still be covering the aluminum -- because the composite liner will never actually come out of the boat once the resin flows into and completely fills all the little gaps and spaces at the frame/hull interface and the whole thing cures to become a stiff, one-piece, form-fitting structure.

    You can always wrap the glass around the gunwales and onto the top outside of the hull too if you're worried about the liner coming out. This alone should alleviate any worries you might have in terms of the liner 'getting away' from the hull somehow ... :)

    By the way, this is one place where I might actually consider using polyester or vinylester rather than epoxy. No matter what resin you use it is likely to delaminate eventually. If this is what's expected, it may simply make more sense (financially speaking) to use polyester instead of epoxy.

    The whole concept here is that it's the filling of all the aluminum joints with resin that's going to prevent the liner from 'popping out' of the aluminum shell. Once you've filled all these little gaps with resin and glass -- thus creating an extremely tight fitting custom plastic liner -- it will stay exactly where you put it even after the resin delaminates from the aluminum.

    So you see, this is not a simple glass/epoxy patch on a flat part of the hull that I'm talking about here. This is actually a form fitting liner that will remain in place via its mechanically ideal shape as a perfect match for the inside of the hull. The resin's adhesive characteristics have very little to do with the way such a liner will work.

    I hope this better explains why I made this apparently unusual suggestion ... :)
     
  6. chada
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    chada Junior Member

    Ok I see what you are saying. Epox the entire inside of the hull.

    I have approxiately 50 yds of 12oz biax and 100yds of 9oz chop 7.5 gallons of US Composite 635 Epox resin.
    could I just take and do 3 or 4 layers on the oustide of the hull after a good waxing
    and make a outer shell and flip it over and reinforce the interior of the Epox shell.
    This would also give me the ablility to raise the freeboard to about 20".
    Does this sound like a do-able plan.
     
  7. kengrome
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    kengrome Senior Member

    Not just epoxy (or cheaper polyester resin) but fiberglass too. Since the glass will be used mainly to hold the resin together and not for structural strength, 6 ounce cloth would be fine, or 9-10 ounce if you already have it. I wouldn't go any thicker with the glass if I were you, because all it is being used for is to waterproof the hull and stiffen it up a bit. The hull structure already exists in the aluminum.

    You could do this if you want but it's a lot more work and cost than my suggestion. If you're looking for a faster and simpler solution you might want to consider using your 9 ounce mat on the inside of the hull (make sure it's compatible with epoxy first) and extending the gunwales higher by screwing a couple of boards onto the existing gunwales before you start the glass/epoxy work.

    I guess I just don't like the idea of using the existing hull as a mold because it's only like a two or three day job to reinforce / waterproof the existing hull with my 'inside glass liner' method. If you build a new hull instead you'll have to invest a lot more time and effort no matter how you do it ...

    You'll probably want to fill and fair the outside of the new hull and this means lots of sanding. You'll use twice as much paint because you'll have to paint both the inside and the outside of the new hull. You'll use up 5 times the epoxy instead of saving it for another (more important?) project later. You won't know where or how many ribs or stiffeners to put inside the new fiberglass hull because it won't be the same structure as the existing aluminum boat. The end result will more than likely be way heavier than the original boat + inside liner. And you'll have to dispose of the aluminum boat at the end of it all.

    Of course if you're looking for a new boat or a big project then maybe you'll enjoy using the existing hull as a mold. But I would build a boat of your own design first (or one of mine) before I would mold a new boat from any aluminum jonboat I have ever seen before.

    -------------------------------

    Here's a garvey / pram / jonboat (call it whatever you like) that gets maximum use out of standard sheets of plywood to create a very efficiently driven, stable, shallow draft hull. It has a sharp bow to spread the water aside and a deadrise forward that transitions to a completely flat bottom aft for ease of construction, ease of moving around inside the boat, lots of initial stability, and fuel efficiency.

    It looks like it has more freeboard than your boat too, and freeboard is something you said you want to raise for the safety of your little girl. It's always good when boating with kids (and old people like me) to install a re-boarding ladder so they can get themselves back into the boat in case of a mishap, too.

    I designed this boat to need no ribs inside the hull so it is super-easy to keep clean and dry inside. The boat's structural strength comes from the inwales, outwales and spray rails which are not shown here but are nevertheless part of the boat's features, and a flotation box forward, and a splash well bulkhead aft, and built-in seats, thwarts, etc.:
     

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  8. ancient kayaker
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    ancient kayaker aka Terry Haines

    If the old jon boat meets your requirements apart from its cracked ribs, is it feasible to just reinforce the ribs? I notice you don't seem to have made up your mind yet so the least work done the less time and money wasted.

    It's hard to advise without at least a picture but I assume it has interior ribs formed on a press with sheet aluminum which are either welded or riveted to the skin. I would think sheet aluminum of the same thickness riveted over the cracks and sealed with epoxy would restore its integrity. Leaky bouyancy volumes can be filled with foam, seats can be replaced by ply ...
     
  9. kengrome
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    kengrome Senior Member

    Chad, if you're still thinking about using your existing boat as a mold, or fixing the existing hull via my method or another one, posting some pictures might help us to provide better suggestions.
     
  10. chada
    Joined: Sep 2008
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    chada Junior Member

    Ken,

    I have looked very closely at the jon boat today. I will try to get pictures of
    my findings.

    I have noticed that 7 of the 10 ribs are cracked and 5 of those completely
    in half.

    I have notice after turning the boat over that spine of the boat has been
    damaged. There is about a 1in drop in the spine 8' from the bow onto the aft section.

    Since I carry my daughter out in this boat to fish.

    I believe that I am going to skin the outside of the boat with 1/8in mahogany
    and raise the gunwales the extra 4" and put a floor over 3" high ribs and fill the floor with PU Foam 2 Part.
    Then design the interior to meet my needs.

    Does this sound like a good plan or a dangerous plan.

    Not scared of any project and with it coming the winter season I am going to
    have alot of time on my hands to work on a project like this.
     
  11. BHOFM
    Joined: Jun 2008
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    BHOFM Senior Member

    It seems to me you are trying to find the hard way to
    do things. Just sell the aluminum boat for scrap and
    take the money and build a jonboat. You can use common
    lumber and glass and epoxy and it will last a long time.

    This little number could be extended and the sides raised
    with little trouble. If you want it stronger use 3/8 ply
    instead of 1/4.

    I don't see any reason to have the aluminum boat in
    the middle of all new stuff. just extra weight and it is
    still a broken boat.

    Please don't be offended by my suggestions. I am really
    trying to help, and save you some grief and money.

    http://www.svensons.com/boat/?p=Utility/JonBoat

    One more thing, aluminum needs to be very clean to
    get anything to stick to it, you would need a lot of
    mechanical fasteners to make it solid. Water could
    collect in any voids and cause real problems in a short
    time.
     
  12. chada
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    chada Junior Member

    BHOFM,

    I was just using the jonboat a jig to lay the wood.
    It would be removed after the skin was complete.

    Chad
     
  13. kengrome
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    kengrome Senior Member

    This won't matter if you cover them with glass and epoxy, especially if you put two layers on the ribs. Just get then straight before you start glassing so the boat's correct shape is retained after the epoxy cures.

    You can probably straighten this out if it bothers you, or just leave it as is. You'll still be doing a great job of strengthening, reinforcing and stiffening the existing hull by installing the new epoxy/glass liner, and if you never noticed that spine damage before you'll never notice it later. Boats don't have to be perfect all over, they just have to keep the water out and you inside ... :)

    I don't like PU foam in contact with wood or buried in the floor, so I would not be in favor of this type of rebuild -- but that's just my personal opinion. Here's another opinion:

    I think flotation foam belongs in the hull sides or in the ends of the boat (or both) but not beneath the floor. Not only will the foam in the floor absorb moisture and encourage rot more readily in this location, but if the boat ever takes on a wave it will become unstable and try to float sideways or upside down rather than floating in an upright and level position.

    I know you have a lot of time to work on this all winter, but wouldn't you rather work on it as little as possible -- and spend the rest of your free time with your little girl?

    I guess I'm still of the opinion that you should install the epoxy/glass liner as I described earlier, because this will fix your existing boat quickly and inexpensively. Then if you don't like what it looks like, and if you still have plenty of time on your hands, just get a set of plans for a new boat you really want, then build that boat from scratch.

    Maybe your daughter will enjoy helping you build the new boat, and after fixing the old boat you will have two of them next spring instead of just one!

    :)
     
  14. chada
    Joined: Sep 2008
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    chada Junior Member

    Ken,

    I can see what you are saying.

    I rather start it now then wait becuase of the flounder season in Jan.

    I have decided just to build a ply hull around the old boat and remove the ply hull from the old boat.

    And goto work on epoxy and glassing it inside and out. Since I would be sandwiching
    the wood between 1 layer of 12oz biax and 1layer of 9oz chop inside and 2 layers of 12oz biax outside.
    would this be enough if I was to use a 1/8 mahogany. That puts a thickness of about 1/2 to 5/8"
    for the gunwales and the floor and use 1/4 for ribs and livewell and seating.

    Last question promise. Whats is your recommendations on the ribs, seating, livewell and dry storage.
    Thickness of ply that is
     

  15. kmorin
    Joined: Apr 2005
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    kmorin Senior Member

    repairing an aluminum jon boat

    chada,

    You may have already given up the idea of adding metal to your metal boat but I'd like to encourage you to consider some other ideas. Welding isn't the only way to add metal- riveting - even pop rivets will hold a large load if they're installed correctly.

    First all the knees or bent tube frames or shape pressed frame knees that have failed probably could be "sistered" as the wooden boat guys say. In this case you'd simply jig saw or band saw a knee of 1/8" or 3/16" plate that you rivet to the sides of the existing original shapes that are broken. A pair of 'knees' like an L on both sides of a frame that had 6" legs on both the bottom and topsides would go a long way to making her firmed up.

    The next idea is related to the first. Mos to these lightly framed press formed boats don't have much width to the topsides/sheer extrusion. Often this small cross section material is fitted over the topsides and riveted together but because it isn't very wide it will flex inboard and out. That flexure puts all the side load movement on the knees which have failed so this part needs to be beefed up.

    You can purchase all sorts of aluminum angle extrusions at the local metal supplier. They may no have what you want now, but they can get it if you're not in a barn burning hurry. I'd suggest you consider a 1/8" 1-1/2" x 3" or even 4" un-even legged angle extrusion in the 6061 T6 alloy.

    By clamping this extrusion UNDER the existing sheer rail/rub rail/ sheer cap extrusion you could add a great deal of stiffness to the topsides and the rivets already hold the sheer cap so adding another row or two is not going to hurt. This angle would be 1-1/2" vertically and 3-4" horizontally so the sheer would be stiffened from moving side to side.

    Last, but not least, you might consider removing the top sheer extrusion by drilling out the existing rivets, carefully, and adding another plank of aluminum to the tops of the sides - replacing the rail cap on the new metal or add another angle at the new sheer height? by overlapping a new plank or topsides extension then riveting that overlap seam you'd have a deeper boat.

    There are plenty of ways to recover this boat as long as the hull sheets aren't actually torn- all without welding. You can rivet stiffeners onto most of these hulls' parts and they will continue to work for you in the years to come.

    Riveting is time consuming -even blind or pop rivets take time to get a good grip, but the work is cold not hot and the tools are simple and may be close at hand?

    Mixing wood, epoxy and aluminum,as described here isn't good practice.


    good luck,with your boat, and thanks for being a good parent and thinking first of protecting your fishing partner.

    cheers,

    kmorin
     
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