Aluminum Stringer Replacement

Discussion in 'Materials' started by Boater Man, Feb 28, 2008.

  1. Boater Man
    Joined: Feb 2008
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    Location: South Carolina

    Boater Man Junior Member

    I am in the process of rebuilding a 1968 Correct Craft San Juan 24' True Inboard boat. The previous owner let the boat sit out in the weather, and after tearing up the floor and removing the wet foam I have noticed that my stringers are about 90% good and 10% bad.

    I have read on this site and elsewhere about stringer core material not being a structural element to begin with if layed up with at leat 1/4 inch of glass.

    My question is this. Why couldn't I just use aluminum angle stock and through bolt it the entire length of the stringers, then fiberglass over it and encapsulating so as to creating a more rigid hull without ripping out any stringer material? Has anyone ever done this or something similar?

    Thanks for any and all comments.
     
  2. Landlubber
    Joined: Jun 2007
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    Landlubber Senior Member

    Boater Man,

    If you feel the need to do this, you would have to form the alloy to suit the current hull shape, intimately connect it to the hull, most likely with a polyester bog (because you have to use polyester resin over it), and then glass over the whole thing to form the stringers again. Why would you wish to do all that when making foam stringers is soooo easy and then glassing them anyhow?

    KISS principles apply to boatbuilding more so than any other industry.
     
  3. tuantom
    Joined: Jan 2005
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    tuantom Senior Member

    I had a similar situation in my 1967 24'er. The foam had turned into a sponge and saturated the stringers; but they weren't rotten except in an isolated area where the builder had cut through the stringer to run the fuel hose. I cut the fiberglass off the top of the stringers and let them air dry for a couple of months, then I epoxied 3 layers of 1708 biaxial cloth over them. Seems really solid. I didn't measure how thick it was, but the total is now the original layer of mat and woven roving + the three layers I added.
     
  4. Boater Man
    Joined: Feb 2008
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    Boater Man Junior Member

    Landlubber,

    Since my stringers are 90% good I was hoping not to remove them from the boat. There are no areas where the stringers are totally rotten. The 10% are slightly soft when poked with an ice pick. There are eight stringers 22' long in this vessle (straight and not curved). Are the foam stringers necessary? Or could I just layer over the existing stringers without the alluminum as long as I build it up to 1/4 inch of glass?

    I am really interested in doing this in such a way that if the stringers ever did rot it would not matter. They would forever be encapsulated. I am trying to get totally away from wood as a structural member for this boat. Many other Correct Craft owners go back with wood stringers at the first sign of softness, but when their kids or grandkids enherit the boat they will be doing the stringer repair all over again, and that is what I would like to avoid! It seems that tuantum did this to a small area of stringer with success, but I wonder about doing the entire stringer system?

    Any other thoughts? Thanks guys! Very Helpful! I'll try and post some pictures of what I have now.

    [​IMG]
     
  5. Boater Man
    Joined: Feb 2008
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    Boater Man Junior Member

  6. Boater Man
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    Boater Man Junior Member

    Trying to get larger pictures

    Sorry for this.

    I am still learning how to navigate and insert images. I'll try one more time. Please be patient. Thanks!

    [​IMG]
     
  7. Boater Man
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    Location: South Carolina

    Boater Man Junior Member

  8. Boater Man
    Joined: Feb 2008
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    Location: South Carolina

    Boater Man Junior Member

  9. Boater Man
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    Boater Man Junior Member

    Yes.......Previous link in post#8 will give you all a LARGE PHOTO of what the stringer system looks like!
     
  10. rwatson
    Joined: Aug 2007
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    Location: Tasmania,Australia

    rwatson Senior Member

    I can really identify with the desire to avoid future repairs, but I think that adding aluminum may present a few problems. I have had a look at the big photo - which is very handy

    The 1st one - ensuring a close bond has been mentioned, to truly support the hull and avoid voids.

    2 -, if you "encapsulate" the aluminium with fg, you are building in the inevitable damp spots that will absorb seawater and start corrosion. You will never get 100% perfect coverage, and expansion of metal and working of the hull will create problem voids because FG is really hard to bond to metal.

    3- the expense and weight of aluminium with a sufficient thickness to contribute structural strength would be excessive.

    I think the key is your comment about the core material being of no consequence with a good fibreglass cover.

    I cant tell from the photo how thick the fibrglass shell around the stringers are, but from the general 'feel' I would bet that the rotten wood wont affect the hulls integrity very much.

    The most efficient (time and money) method is remove all paint and foreign material with grinders over the rest of the stringers (which you would have to do with aluminium anyway), pick out any damp wood you find and fill with a lightweight filler, then recover all the stringers with a substantial layer of cloth. You should aim for around 5mm thickness, including the existing layer.

    You are going to avoid all the headaches of coping with layers of dissimilar materials, the unnecessary expense of marine grade aluminium, get better structural strength for less cost in money and time. Even trying to cut the aluminium to the correct dimensions around the various hull "lumps" would give me the willies. Fibreglass just forms itself to the right shape.

    If the remaining wood rots in future, the new owners can be confident that the strength is there, and the repairs wont be all that difficult.
     
  11. Boater Man
    Joined: Feb 2008
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    Boater Man Junior Member

    rwatson,

    I will go the fiberglass only rout instead of aluminum. The fiberglass that is covering the stringers now is a polyester resin over cloth. Should I go with polyester again or epoxy? As I understand it polyester will not stick to epoxy, but epoxy will stick to polyester. Also, do you know of good mail order places to get material? I have done small fiberglass repairs, but nothing this large. Any other pitfalls that I should try to avoid as I take on this fiberglass project? Thanks for any and all info!
     

  12. rasorinc
    Joined: Nov 2007
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    Location: OREGON

    rasorinc Senior Member

    Check out Raka epoxy. Good prices and they handle cloth also. Came out on top when tested against 5 other brands. Stan
     
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