New to forums with Jon Boat Questions

Discussion in 'Boat Design' started by jnwaco, May 26, 2009.

  1. jnwaco
    Joined: May 2009
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    Location: Waco, Texas

    jnwaco Junior Member

    Thanks Messabout -

    I really like the grating. I'm still looking for some that's about on par with aluminum as far as price goes. I thought about hooks getting caught up in the grating, or dropping weights or other items through the openings. That's not so bothersome with a set of long needle nose fishing pliars.

    Do either of you have a name brand or company for grating that you've seen or heard of being used in boating applications? The colors do make it pretty attractive and it definitely seems like it will last a long time if it's UV resistant.

    I'm also still trying to find out the weight rating on this boat. The USCG tag is long gone and Alumacraft did not return an e-mail. I'm going to give them a call, but they may not know. I tend to be a little weight conscious given the unknown capcity of the boat, the desire to fish shallow, and the liklihood of fishing four people from the boat occassionally. As far as I can tell, the aluminum and plywood would be within 10 pounds or so from each other, depending on how much epoxy or coating you put on the ply. The grating looks to be quite a bit heavier, even though much of it is open.

    Oh, and based on the residue line on the boat from the initial outing, the boat seems to draft about 3-4". That's before i took out the existing plywood and carpeting. I could probably back into the capcity if I dug up the calculations for displacement and measured the angles of the sides of the boat, but....
     
  2. jnwaco
    Joined: May 2009
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    Location: Waco, Texas

    jnwaco Junior Member

    Here are a couple of pictures of the boat. And actually, the first five ribs are broken. This is something I could not have examined when I bought the boat because of the plywood flooring, so I need to deal with it. I did get a bargain on the boat, at $2,000. Carburetor kits, impeller, seals, and lower unit fluid will set me back another $120 or so. I had budgeted about $5,000 to get a boat up and running with trolling motor, new decking, etc. Need new controls for the motor as well. Those will set me back a bit.

    But first, I need to deal with the ribs. Then the flooring and motor. Then....

    You'll might notice that there are four coats of paint on the boat. The original Alumacraft gray, a light blue and a glossier dark blue, and then the newest layer, black, on the outside.
     

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  3. Lt. Holden
    Joined: Sep 2007
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    Location: Western Massachusetts

    Lt. Holden Senior Member

    For the grating try customcompositesok.com

    Didn't see the photos before I posted, I gotta wonder how that happened? On the bottom side of the hull, is there any wrinkling or other signs of stress? Looking at the photo, I would remove the added wooden stringers and try to find C-channel Aluminum that would fit on top of the frames to "sister" over them and then weld them in place.

    It's hard to believe a quality, mass-produced aluminum boat like this would have such damage. As to the grating, I think your search finds that Aluminum is the material of choice, especially since you can weld it across your newly 'sistered'; frames and add a great deal of rigidity in doing so. To alleviate the 'lost sinker syndrome' get marine carpeting and cut it to fit, then have the edges bound (at a carpet binding service, shouldn't cost much) and simply lay it in place. Any time it gets really wet simply remove the carpeting to dry. I have been down the plywood (endlessly sealed in epoxy) and carpet route before and will never go there again.
     
  4. Ad Hoc
    Joined: Oct 2008
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    Location: Japan

    Ad Hoc Naval Architect

    From those pic's it basically looks like the ribs are under sized for the "normal duty" or the boat was run in conditions it wasn't really designed to, or just run aground once, damaged and then somone tried to repair, and did a poor job.

    Also, the repair weld is just on the top exposed surface (the weld bead looks too large for the thickness of plate, perhaps gap filling too). But the underside cannot be welded, where there is a gap to the long't channel section shape, one assumes to provide some kind of strength, but obviously hasn't worked. This small recess will allow sea water to sit and slowly eat away at anything it can that has been left down there. Sounds like you had all sorts of crap, from cleaning it out.

    You also need to be careful with bare wood on ally. The fact that you have a wooden sole doesn't help matter from the pictures. The wood by the looks of it wasn't protected from the ally, this lead to poultice corrosion. You only need to get a little bit of this and then your structure becomes weaker.

    Either add a keelson along the boat the stiffen up the centreline and hence half the span of the transverses, or stiffen up the transverse ribs. Since the existing structure is now weaker after welding it. (you have lost approx 50% of the unwelded strength used by riveting). The fact it has cracked again is evidence of this.
     
  5. jnwaco
    Joined: May 2009
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    Location: Waco, Texas

    jnwaco Junior Member

    Thanks for the suggestions Lt. Holden & Ad Hoc. Very much appreciated. And the best part is I'm learning the proper terms for the parts of the boat.

    I bet the welder can find some sort of aluminum channel to fit over the existing ribs and weld them in place. The ribs are definitely smaller than a similar sized boat made today. I don't think the skin is thick aluminum, maybe 0.063" or 0.1", so the welder will have to be careful.

    I imagine that the 29 year old boat was used on the gulf or big lakes and was "rode hard and put up wet", so to speak. Much of the dirt and grime you see in the photos would not vacuum up and will have to be brushed off, washed off with pressure washer, or just left there. I suspect it is a mix of fine treated lumber and dirt, but it's stuck to the aluminum.

    The bow of the boat appears to have struck something, but the underside of the hull is in good shape, no dents or creases.
     
  6. Ad Hoc
    Joined: Oct 2008
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    Location: Japan

    Ad Hoc Naval Architect

    wow, very thin plate. That may explain the over sized weld beads. Probably MIG'd rather than TIG'd...or just gap filling anyway.

    You now need to decide which way to go....
    1)Stiffen up long'tly, ie add a keelson
    or
    2) Increase the frame (rib) sizes.

    No point doing both. Then decide what kind of section to add and importantly, the grade and filler wire. Since have you any idea what grade of ally the boat is?

    It may also be worth putting on a rubbing strake underneath too, for future 'rubbing' which can be sacrificial. In your case perhaps a 4~5mm FB...ops 3/16". This to be on the underside channel that runs along the length.
     
  7. jnwaco
    Joined: May 2009
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    Location: Waco, Texas

    jnwaco Junior Member

    Ad Hoc - I do not have an idea of the aluminum grade. Is there a way to tell from looking at it? I'm guessing 5052, but not sure.

    If I go with a keelson, will it have to be one continuous piece that sits on top of the ribs or can it be sections that fit in between the ribs? I'm liking this idea because it might require less fabrication than the sister ribs.

    I'm new to boat terminology, but when you mention a "rubbing strake" you're talking about a protrusion from the hull? And this would go down the centerline of the boat? There are already some runners on the bottom of the boat (not sure what they're called - kilgores?) that would rub before a 4mm strake would. You kind of lost me there since I'm a complete beginner with the boat terminology - but I enjoy learning! Thanks for taking the time to help out!
     
  8. Ad Hoc
    Joined: Oct 2008
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    Location: Japan

    Ad Hoc Naval Architect

    Well, considering it looks 'shaped' or extruded, i would say 6000 series. Most 6000 in the US is 6061 or 6063. If you're buying plate, again most 5000 series plate in the US seems to be 5081/5454 or similar. Again, these grades only seem to be generally used in the US.

    If it is the 5454 type, then a wire of 5056A will be needed. If the 5081 type then 5356/5556 type. But either wont have a major affect which ever you use. But if you are buying plate from 6000 series, you will need 4043A type wire.

    The keelson to be one continuous structure from bow to stern. The height depth of the web to be at least twice that of the ribs/frames, with cut outs to allow the ribs to pass through. With a suitable rider/flange to it. It is not 100% necessary for the web of the keelson to be welded to each of the transverse ribs, since the ribs are just being 'supported' by the keelson. But it is best if you can, as a load path for the shear load. Just weld on one side of the cutout, no need for a tight fit. You can make the eight to suit a new sole or any other "eqpt" you wish to add. It makes a suitable seating for it.

    Rubbing strake. It is just a bit of metal that is used for rubbing against, like a bumper on a car. When you boat grounds on rocks or sand, the rubbing strake is rubbed and eroded away, not the main structure, hence it being sacrificial and replaced when needed.

    So a FB of say 2"x3/16" welded along the length of the bottom, just on the centreline. The width 2" (just nominal) is just to suit the width of the channel that is already there, since i don't know what are the dimensions.
     

  9. jnwaco
    Joined: May 2009
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    Location: Waco, Texas

    jnwaco Junior Member

    Thanks Ad Hoc. You are definitely a big help!
     
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