Composite boards for hull?

Discussion in 'Restoration Projects & Questions' started by 1964dyne, Apr 1, 2010.

  1. 1964dyne

    1964dyne

    Joined:
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    Boat Model and Year:
    1964 Tournement Skier
    Is it a bad sign that when you are cutting the fibreglass floor out that you can feel the wet pulpy rotten wood spray go all over you? Yes, there are some issues. I have read the posts about replacing with the balsa wood. I have the outside layer of fibreglass, I have a layer of wood, another layer of fibreglass, another layer of wood, and finally a last layer of fibreglass that is the floor of the boat. Another issue I have is that it appears that the floor is rotten all the way up under the deck. This was a prototype boat. There is no access to this area accept for where the old wood feeds up under where you would put your feet.

    I am thinking about using deck composite wood to replace the rotten wood. I know that this may offend some true die hard Hydrodyne lovers, but if it works, it would be a great rot proof permanent solution. I also realize that the composite will be heavier than new balsa or fir, but I don't think it would be as heavy as the rotten wood I have buried in the floor now.

    I have also talked to someone and they stated that it may be possible to put in a sub floor. I have also read some postings about putting in a bilge. I am not sure that this is possible, there is like little or no depth in the boat, the gunnels are not very tall. I do think that the addition of a bilge may be beneficial in that I could put in some floatation.
     
  2. jim

    jim Hydrodyne 18 Specialist

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    The newer (and new) boats have the outer skin, then a layer of "end grain" balsa, then an inner skin. The stringers are on top of the inner skin. and the raised floor is on top of that.

    Many high end boats are built this way. It is very strong construction.

    The balsa in your boat is not end grain. The grains run for and aft in the boat and the water can propagate all over the place, and does. The end grain balsa is dipped in resin before it is placed in the hull. Any water intrusion is usually only local because of the grain running vertically in the core. These boats are far less likely to soak the entire core.

    That is how I would rebuild it.

    jim
     
  3. 1964dyne

    1964dyne

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    1964 Tournement Skier
    Thank you for the advice on the floor. I went to Lowe's today and found 12 inch wide, 5/8 inch thick, and 12 foot long composite boards. The area that I will be filling is 4.5 feet wide and 11 feet long. These boards will work well I believe. At this point, and this could change in a few minutes, I am planning to do the following:
    -Cut out the composite boards and fit them in.
    -Remove the boards.
    -Put down a coat of resin and epoxy.
    -Lay out the composite boards on the epoxy before it dries.
    -Cut stringers out of 2 by six composite.
    -Fibreglass over the composite boards and fibreglass in the stringers.
    -Put down a new floor.

    Now, previous to this, the floor of the boat was the bottom of the boat. When going over waves you could see the floor flex. I am hoping that adding the stringers and the floor will make it stronger. I am also going to new seats in, regular ski boat seats. I will be putting my original Hydrodyne Ski Boat seats on eBay. I am thinking of using composite boards for the floor also, I would hate to put down plywood to have it only rot in 4 or 5 years.

    I am also thinking of putting some type of floatation on the port and starboard sides of the stringers. Any advice on this?

    Chad
     
  4. jim

    jim Hydrodyne 18 Specialist

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    The balsa core Dynes do not rely on the stringers for strength or stiffness. This includes both the end grain and the early long grain cores. This is per Ab Crosby. He claims the stringers are there only to support the floor. That is why your boat did not have stringers. He also claims that a .38 caliber pistol bullet would not go through it.

    Your boat flexed because it no longer had structural integrity because it was soaked. Those types of cores were prone to soaking, that is why they went to the end grain. I understand your concerns about the wood. If the composite boards are not sealed up and sealed to each other the water will get between them in my opinion. This adds more weight.

    The sandwiched end grain core provides the stiffness of the boat.

    It is your boat to do with as you please. I can tell you that the 18 hull performance is sensitive to weight.

    I will not place foam flotation below the water line. Crosby tried it for a while and it was prone to soaking also. I do not believe there is such a thing as true closed cell foam. I have seen that stuff soak also. The foam should be in the bow, stern, and under the gunwales in my opinion.

    Please understand that this is all just my opinion. I have been wrong plenty of times. My boat is a 78 and the core is sound. The floor has been replaced once in 97. I am 72 so I think it will last the rest of my active life and more.

    These boats need to be kept dry when not in use.

    jim
     
  5. 1964dyne

    1964dyne

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    Great advice. I will seal up the composite. I don't plan on taking on any friendly fire. A .38 caliber bullet eh... I minimize exposure to water and keep the boat hoisted in my boat house. OK, that is the past 4 summers. As for the 42 years before that... I was told that it did sit under water for a while. I am nervouse about the balsa wood, after what I have experienced.

    Chad
     

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  6. jim

    jim Hydrodyne 18 Specialist

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    I understand your reluctance about the balsa. I felt that way at first too. I discussed it with Ab Crosby Jr years ago.

    After 20 years of study and living with the boat my conclusion is that an end grain balsa boat built the way the Dynes were built is less likely to pick up water than a foam filled boat. And that is where the Dyne get's all of it's strength.

    I had a foam filled boat that became saturated because I left it out at the dock all summer without a cover. It picked up about 1000 pounds. The foam was mush.

    I talked to a ski club 15 or more years ago that bought a new inboard which supposedly had closed cell foam. They weighed it before they put it in the water and at the end of the season. It picked up 300 pounds!!

    I am not trying to talk you into anything, but if your boat was under water it would have picked up water no matter what the core in my opinion. If foam core boats live in cold climates the water freezes in the winter and shatters the foam so it can pick up more water if left out. The end grain balsa prevents the water from spreading.

    jim
     
  7. 1964dyne

    1964dyne

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    OK, I have gone with the composite, don't hate me... I know that it is not sticking with the true form of a hydrodyne. But after digging our all of the rotten balsa and fir, I wanted to try something different. It is going very well. I put the first boards in last night. The composite is fairly flexible and easy to work with. I cut it into 1 and 7/8 inch strips. Just like with the balsa and fir, I staggered by joints. Tonight I put in the rest of the strips. The first ones went pretty quick. I basically did the middle, no funkey custs. The ones I did tonight went up under the bow and went along the sides, a lot of funky cuts. I haven't seen where anyone else has tried this. It seems very sturdy with just the first layer. I know it will be a little heavier than the balsa, but the balsa that was in there was drenched in water, so I do not foresee a change in performance. I will keep posting updates, success or failure.
     

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  8. jim

    jim Hydrodyne 18 Specialist

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    Don't feel bad about the composites. The new Dyna-Ski can be ordered with all composite at extra cost.

    I do not believe you will need another layer. Just glass in the first layer and put stringers and a flat floor on top of that. The later boats were built that way. The stringers are there to support the floor, they should be glassed in too.

    There is composite floor stuff available too. While you are at it you could put some seat anchors on the bottom side of the floor. I have used Aluminum plate then drill and tap from above. You could also use nut plates.

    jim
     
  9. PJP

    PJP

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    There are several options for the flooring and stringer materials.

    Boat Panels are a special plywood with no voids, etc. I'll try and come up with a picture of a boat panel as I think I still have a sheet or two around the garage. If you resin coat all the sides the plywood or any wood will last a long time.

    Many boat factories had quality control problems and some still do! So one boat may be much better than another boat from the same company. Same thing with hand laid vs chopper guns. Some operators are great with a chopper gun and some suck. Some folks take their time and lay the glas properly and some don't. Remember that some workers will take the easy way out every time and you have to hope they did not build your old or new boat!

    There are several composite options available. I'd find a local boat repair shop (not an autobody shop) and ask them for what they would use and perhaps could sell you.

    If you go the composite route make sure you use thick enough materials as the non wood products are not as strong so thicker is a good idea.

    My 1987 Hydrodyne has never had the transom or floors touched, even the carpet is original. I garage the boat in the off season and tend to keep it covered when not it use. It has been put away wet and rode a lot. When it was put away wet I always tried to uncover it and let it air dry on the next nice day though. Sometimes I wish I had a canopy but I like my view without the boat canopy.
     
  10. 1964dyne

    1964dyne

    Joined:
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    Boat Model and Year:
    1964 Tournement Skier
    Some new pix of composite floor and stringers.
     

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