Fiberglass pontoon construction

Discussion in 'Boat Design' started by southern_boy, Sep 14, 2017.

  1. southern_boy
    Joined: Sep 2017
    Posts: 10
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    Location: Georgia

    southern_boy Junior Member

    Hi all, I am new here and this is my first new post. I have done a lot of searches and read a lot of post but have come up empty handed. I was wondering if someone could point me in the right direction. I am looking for information on fiberglass pontoon construction in general. I have recently took on a relatively large repair project and I am questioning a lot of things I have seen from the original manufacturer. Any help what so ever would be great! Thanks in advance.
     
  2. TANSL
    Joined: Sep 2011
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    Location: Spain

    TANSL Senior Member

    Welcome to the forum. Could you ask any specific questions to begin with?
     
  3. southern_boy
    Joined: Sep 2017
    Posts: 10
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    Location: Georgia

    southern_boy Junior Member

    Absolutely, thank you. This is my mothers house boat and I am trying to do a good job rebuilding the pontoons. I will try to keep it as short as I can with a little history as well. I have 2-32' and 1-28' pontoon removed from a house boat at the moment. It all started a blister repair which included pretty much the entire pontoon. Our original plan was to grind all the gelcoat off followed by a vinyl ester layup, Duratec primer and gelcoat. During the grinding 2 of 3 of the pontoons started leaking water once we got down to raw glass. Further inspection revealed water intrusion from the top side. We where left with no choice other than to remove them and from the house boat to gain access. We found it apparent that a bad painted application of gelcoat was done on the top. There was chipping, flaking etc. and the top side was recessed around 1/4" between the side flanges. So, we opened them up only to find out all the wood had to come out down to the original mold. At this point we have everything cut out, grinded down and dry.
    They are constructed with 1/2" plywood bulk heads ever 4' and what I would imagine you would call the stringers (2x4s) between the plywood on the bottom side. On the topside the glass was backed with a veneer type plywood and 1x2 strips which had pretty much fell apart due to the water intrusion.

    So here are some of my questions. Why would they recess the topside center 1/4" between the flanges that bolt to the floor system only to hold water? We are thinkin we should build the tops back flat with a better plywood backing than veneer, allowing it to basically sit on top of the bulkheads, then drilling the bulkheads for ventilation. Also, they had a plastic thru hull fitting on the top side which I assume is for the ventilation and possibly a pressure test? Would there be a location or a better way of venting these to avoid a non accessible topside penetration? I'm also not fond of the plastic thru hull fitting they used. The man that is helping me also claims that 2 layups with polyester resin and 1.5 ounce mat is plenty strong enough for the bulkheads and stringers. Since the original material was spray in with a gun I just don't know, I do know it was quite thicker than what we are doing now. He works at a fiberglass shop but they build columns and things of that nature, not boats.

    Also, I have been trying to think of a bullet proof coating for the topside of these pontoons. My gut tells me to look in a bed liner material vs another gel coat application to seal them permantly? I have been told if the glass is grinded down and the proper primer used that it would be solid. Removing these from the house boat is not something I want to do again EVER.
     
  4. BlueBell
    Joined: May 2017
    Posts: 51
    Likes: 1, Points: 8
    Location: Victoria BC Canada

    BlueBell Ahhhhh...

    You may want to seek some professional advice in this case.
     
  5. jorgepease
    Joined: Feb 2012
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    Location: Florida

    jorgepease Senior Member

    That fitting is needed to relieve pressure for sure but you should also have some inspection hatches. I don't know what you are talking about the recess, best to post a pic, if you are scared of water intrusion use foam core instead of plywood and I wouldn't use mat, I would use epoxy as it's more waterproof. You haven't mentioned if this boat is powered, what speed it's driven at etc...
     
  6. ondarvr
    Joined: Dec 2005
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    Location: Monroe WA

    ondarvr Senior Member

    2 layers of 1.5 oz CSM isn't very strong, there should be some 24 oz roving or 2408 in there to add strength.
     
  7. southern_boy
    Joined: Sep 2017
    Posts: 10
    Likes: 0, Points: 1
    Location: Georgia

    southern_boy Junior Member

    [/QUOTE]

    Here is a good picture of the topside, you can see how top is recessed around 1/4". I plan on rebuilding these flat so they will shed water better. I can't see how any water should get in these from the topside if they are built correctly.

    I figured out a good plan for the fitting. I plan on picking up a SS one and raising a small area up around 1/2" to mount it on. It's completely covered by the front deck and the raised area will keep water from pushing against it. Even with sealant I wouldn't trust it from leaking on a flush area.

    It's only used on a fresh water lake, at least as long as my mother owns it. On top speed it's a slug, I'm not exactly sure of the top speed but I would guess 20mph or lower.
     

    Attached Files:

  8. southern_boy
    Joined: Sep 2017
    Posts: 10
    Likes: 0, Points: 1
    Location: Georgia

    southern_boy Junior Member

    Here is a good picture of the topside, you can see how top is recessed around 1/4". I plan on rebuilding these flat so they will shed water better. I can't see how any water should get in these from the topside if they are built correctly.

    I figured out a good plan for the fitting. I plan on picking up a SS one and raising a small area up around 1/2" to mount it on. It's completely covered by the front deck and the raised area will keep water from pushing against it. Even with sealant I wouldn't trust it from leaking on a flush area.

    It's only used on a fresh water lake, at least as long as my mother owns it. On top speed it's a slug, I'm not exactly sure of the top speed but I would guess 20mph or lower.[/QUOTE]
     
  9. southern_boy
    Joined: Sep 2017
    Posts: 10
    Likes: 0, Points: 1
    Location: Georgia

    southern_boy Junior Member

    Here is another picture of the topside, notice how the gelcoat had chipped loose. There was a lot of these areas.
     

    Attached Files:


  10. southern_boy
    Joined: Sep 2017
    Posts: 10
    Likes: 0, Points: 1
    Location: Georgia

    southern_boy Junior Member

    Thanks, I will lot into this today. I have just been running off a comparison that the factory used a chopper gun.
     
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