using composites in stringers and deck

Discussion in 'Materials' started by Guest, Jun 11, 2003.

  1. Guest

    Guest Guest

    i am rebuilding a fiberglass bay boat because of rotted stringers and deck. i am looking at nida core as replacement material. does anyone have any construction technique information or alternate (less expensive) materials? thanks
  2. tgundberg
    Joined: Dec 2001
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    tgundberg Junior Member

    For composite stringers, you really only need a core that holds shape and stabilizes the shear webs, so a low density foam (around 3 or 4lb PVC or urethane) works well. Another "rule of thumb" is to use uniaxials on the top or cap of the stringer and double bias (+-45 degree) material to tab the stringers to the hull. Laying up the stringers may be easier to do with foam as opposed to plastic honeycomb.
  3. L.DOSSO
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    L.DOSSO Junior Member

    airex is a good material for stringers.It weights between 5-6 lbs/cu.ft.
  4. War Whoop
    Joined: Jun 2003
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    War Whoop Senior Member

    Use one of the foam cores very easy to work and stay away from that waxy honey comb!!
  5. J & J
    Joined: Oct 2003
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    J & J Junior Member

    Deck material

    I am very pleased I found this site your knoledge is a great asset.
    I am about to take a Willam Garden Force 50 deck off and replace everything. I would like some tips on what to use as replacement material. Please keep in mind that I will be replacing the teak deck at some point. I want strong wave resistant decks that can take a crashing wave if need be. Also the cabin may need to be replaced. Please note this is not the vessel but a good picture of a Force 50 deck. It would seem that they all had some problems but allot were fixed and some were not. The balsa core deck rotted because the screws for the teak were never beded and let water in and the decks rotted.

    Attached Files:

  6. Greavous
    Joined: Jan 2004
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    Greavous Junior Member


    I'll have some info for you in a week or two because I'm doing the same project. 18' Bayhawk with rotted decks. I have a friend who builds boats in Victoria, Tx. and he has used and recommeded NidaCore to me. He gave me a scrap of the 3/4" core with 1.5 oz. mat layers on each side. Maybe 20"x5" and you can suspend it over two blocks and stand in the middle. I have 6 stringer at about 10.5" O.C. so I'm sure it will be super. Once the floors in we are going to fill the bilge area with expanding 2lb. foam. No more wood for me.
  7. troy morse
    Joined: Mar 2004
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    troy morse New Member

    Troy Morse,Fireman,fishing guide,boat builder

    Iwouldn't use the expanding foam in the way you are talking.I've seen a lot of boats that had to be redone in as little as 4 years.If you get any water in the hull,condesation,holes etc ,the foam will hod it ,then rot your deck sooner or later.I recommend that you place foam in before the deck loose,notch your stringers at the transom so that any water can be drained out.You can use the type of foam you are talking about but try laying down a plastic film first and after you pour it, with a piece of ply wood over the top to flatten it.The bizqueen also protects your fom.When it sets remove the board,shave off excess foam and plastic,paint any areas that you cut with a foamsealer .Lay it back in and instal your floor.Any water that gets in will drain out on the trailer.You never have problems with stringers or floors ,Skibarge and others have done this for years and have a good reputation .I have done this to many boats will excellant results.I've dug and shoveled out several boats with waterlogged foam who did as you are talking about doing.Lot of work,do it right the first time.Just my opion,Troy
  8. Greavous
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    Greavous Junior Member

    Well as usual, I think its too late for your approach now. I have completed the floors and decks and everything is glassed in, cabosiled radiused and glassed again. I just can't see cutting everything back out and starting over. I did make provisions for drainage between the stingers along the transom ends just in case of a leak. The foam system we are using isn't a mix and pour system. The 2 parts are in large heated tanks and is injected. The story I get is that it makes a more water resistant closed cell foam. I guess we'll just have to wait and see what happens.

    Any suggestions as to additional preventative measures I can take now that I'm committed?
  9. dwalradt
    Joined: Apr 2004
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    dwalradt New Member

    Stringer And Foam Replacement

    Thanks everyone for the valuble info. I am new to this site and am currently replacing the stringers, foam, and deck on an '87 Wellcraft 210 Classic. I will be putting a gelcoat on the new deck inplace of carpet. I have been researching this project for about a week now and am receiving some conflicticting advice. I am a novice and have never rebuilt a boat before. I have a few questions. 1. What type of resin should I use? I have been told polyester but am reading negative postings about it. 2. What type of wood should be used for the stringers and suports for the foam? It looks to me like Marine Ply was used originaly, however it is hard to tell since they are pretty much gone. From the looks of things, the intension of the stringers was to hold the foam for forming and fasten the deck? Is this the case? Is the foam intended to be a support as well as floatation aid? Like others I have read, I want to do this rite the first time. Bass will be here soon.
  10. brad123
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    brad123 Junior Member

  11. afarkas
    Joined: May 2004
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    afarkas New Member

    Stringer materials

    I myself am new to this but have done allot of research and question asking.

    Definitely use epoxy resin (West system) it's much stronger and it's water proof. If the boat was built with epoxy you wouldn't be having to rebuild it now. As far as wood I'm using white oak for the stringers, It's used for allot of outdoor furniture I'm told. But it must be white oak. Any other typer of oak will rot in no time. I've also heard of people using PT, I guess even some manufacturers use it, hard to believe. Another option is mahogany but if you're properly glassing & sealing everything over, it shouldn't be necessary.

    For ply I'm using marine grade fur ply and epoxying the crap out it.
    Foam???? I don't have a clue

    Good luck,

  12. JR-Shine
    Joined: May 2004
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    JR-Shine SHINE

    I would say the Nidacore might be OK for the deck, but I would use a foam for the stringers. DIAB has a new foam (renicell) that might a good choice, but I think any PVC foam would do the trick - we stock Divinycell H80.

  13. Guest Eric

    Guest Eric Guest


    I have a 19' Celebrity 1995. mt aft starboard is rotted clear up to the helm.
    I have started to rip up the floor and removed saturated plywood and rotted supports, are they stringers also the foam is saturated. Frustrated but determined in NJ. This boat has been kept in rack storage since 2000. decks seemed fine when I purchased it used in 2000. I am ripping it all out for now but will appreciate any advice. Thanks

  14. Greavous
    Joined: Jan 2004
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    Greavous Junior Member

    Sounds like you bought the same probles as I did, firend!

    This is how I approached my rotten mess...

    If it is rotten, remove it. As I started cutting out my floor I noticed that the repair was going to look pretty patched rather than new and monolithic. I figured that if the floor had rotted through in some areas then the rest of it was probably on its way to rotting to some degree everywhere. I then adjusted my small circular saw to the thickness of the plywood and glass and followed the gunnal wall all the way around. I was correct, looked like all of the bottoms layers of the plywood were getting grubby.

    Once the floor was out and the debris all cleaned up you can inspect the rest of the craft. My Bayhawk had styrofoam planks between the stringers and they were heavy and waterlogged. Trash. My stringers were in fine shape with an exception of a spot or two which I repaired using a penatrating liquid epoxy and some hole drilling. Easy repair for my situation which was limited in size. If your stringers are wood take a small drill bit and drill a few holes into the stringer. If the sawdust looks like fresh wood, light in color, all is probably well. Look for dark areas and test those too. All of the holes you drill need to be filled to prevent a place for new rot to start. I used a 5 min. epoxy to fill mine.

    If your stringers are shot I'm not too sure what you will need to do. My guess would be to get you boat as level as you can in a place where you will not need to move it later, and can work in it. Then cut the stringers out one at a time and replace with new. If this is the case I would cut carefully and use the old stringer as a pattern for the new one. Replace and glass it in and then cut out the next one and do it again and again. Holding the shape of the hull is the concern and the one at a time method/level method should work. Also, you could suspend the new stringer at the proper floor level by using straight board placed perpendicular to the remaining/existing stringers.

    I made the mistake of putting off the cable chase which needed to go under the floor and ended up having to cut out some new floor to do it later. Originally the steering and control cables were routed above the floor and under a cover screwed to the floor (rot location) so under was better for me.

    The plan was nitacore but I used BCX 1/2 plywood and glassed the undersides and edges prior to attaching them to the stringers with liquid nails and stainless steel screws at 8" on center. Once the floors were screwed to the stringers (pop a chalk line along the centers of the stringers for a guide) I then used a 4" cloth tape and glassed across the 1/4" gap between the new floor and the gunnal wall. 2 inches each side all the way around the boat. I then sanded any high points smooth and then using some cabosil mixed in resin I made a radius in the corner between the floor and side. I used a piece of 2" PVC pipe (several actually, I'd just throw the used one away rather than clean it up) to strike the radius. Once that was done I used a 10" wide roll of 1.5 oz. mat and glassed over the cabosil 5 inches each way. I also used the cabosil to fill the seams in the floor and the countersunk screw holes.

    A note about fiberglass resin. You need to use an un-waxed resin to avoid sanding between layers. If you use Bondo brand it will be waxed and drys to a non-sticky surface. The wax will need to be removed before you apply anything over it. The trade-off is less work but everything will feel sticky to the touch untill you finish the floor vs. sanding and itch. I used lots of rubber gloves and did less sanding.

    Once the floors were in I then filled the spaces under the floor and between the stringers with 2 lb. polyurathan expanding foam. This means drilling a bunch of holes in the new floors, pouring the foam and chasing the expansion from stern to bow. I would block off the first hole and the foam would fill forward to the next hole. Block off the second hole and uncover the first to allow some pressure relief and continue. Once it was done, I mashed down the foam and filled the holes with cabosil and then chopper gunned the decks and floor and gunnals.

    It was a lot of work but the results are nothing short of Bad ***! A very solid stable craft.

    Good luck
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