Filling 60 footer keel with cement concrete or epoxy resin concrete?

Discussion in 'Fiberglass and Composite Boat Building' started by Ebrahim2020, Nov 17, 2013.


60 feet fiberglass boat filled with

Poll closed Nov 22, 2013.
  1. Resin concrete

  2. cement concrete

    0 vote(s)
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  1. Ebrahim2020
    Joined: Nov 2013
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    Ebrahim2020 New Member

    I have built a 60 feet long
    18 feet beam,
    7 feet depth,
    4 feet draft, displacement boat for Diving using fiberglass. I have filled the keel with gravel mixed with cement for the concrete inside the keel. But the boat owner is refusing to take the boat. because he wanted to be filled the keel with concrete mixed with epoxy resin and also put six 18mm steel rod inside the keel.

    Can someone explain the the difference between the two methods? is this really matter?

    I have attached a detailed diagram.


    Attached Files:

    • Keel.jpg
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  2. bregalad
    Joined: Dec 2010
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    bregalad Senior Member

    The poll in meaningless.
    Structural considerations aside you had a contract (or agreement) to build it one way and you changed an important construction detail without approval by the client or, I assume, input from the designer.
    You have a problem
  3. SamSam
    Joined: Feb 2005
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    SamSam Senior Member

    You have a problem. I think the epoxy keel with steel forms a better beam for longitudinal strength. Un-reinforced concrete is a weak beam.

    Is the keel attached separately or is it poured into the hull?
  4. michael pierzga
    Joined: Dec 2008
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    michael pierzga Senior Member

    Dont know. I have used concrete as internal ballast in steel and fiberglass boat keels with no problem.

    I have never heard of epoxy concrete.
  5. SamSam
    Joined: Feb 2005
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    SamSam Senior Member

    It depends on if the keel is intended as an element of strength or as simple ballast weight.
  6. Milehog
    Joined: Aug 2006
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    Milehog Clever Quip

    You really don't understand the concept of a reinforced structural beam?
    If I were the owner I'd be wondering how many other hidden corners you cut.
    Enjoy your new boat.
  7. kapnD
    Joined: Jan 2003
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    Location: hawaii, usa

    kapnD Senior Member

    You might be able to save the project by casting a new beam above the bogus one.
    Dowels would have to be drilled and epoxied into the concrete beam to tie them together.
    In any case the designing engineer will be the authority you need to consult.
    An epoxy concrete reinforced beam is VERY different than some concrete ballast, If I were the owner, I'd have you cutting me a large check...
  8. PAR
    Joined: Nov 2003
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    PAR Yacht Designer/Builder

    Filling a keel hollow with epoxy, concrete(?) and six 3/4" rebars just isn't reasonable. Concrete has been used for generations will little ill effect, if done properly. Both an epoxy or concrete mix will work, though one will be considerably cheaper. I wouldn't bother with epoxy, as it just adds to the cost, for next to nothing.

    Now, if the epoxy was used with lead pellets, pig iron and/or boiler punchings, with a very high filler to goo ratio, then you'd have a good reason to employ epoxy. Concrete (mortar actually) with a very dense mix of boiler punchings can maybe get 175 pounds a cubic foot. Epoxy can get closer to 250, but you'll pay for this in gallons of resin, though the lower CG from the improved density is desirable. Personally, I don't see the need for this on a displacement mode diving boat. Similarly, epoxy and lead shot, pellets, wheel weights, etc. will gain you 500+ pounds per cubic foot, which is great for the CG, but is it really necessary for this type of vessel. I do epoxy and lead shot fairly regularly and it's easy and dense, but almost always on a sailboat with a hollow keel and it's just poured in and vibrated down.

    Basically it boils down to what the design called for, as has previously been suggested. I don't any difference structurally with either approach, though you could lower the CG by an inch or two if the denser mix was employed (maybe). Frankly, an inch or two in the big picture, will make no noticeable difference in the boat's handling. The only way you can significantly alter the CG is with a lead casting or a epoxy and lead shot (pieces) mix.

    I think you're in a barrel, as the client made a ballast request and you didn't sufficiently explain why his approach (concrete, minimum steel bar and epoxy) is no better then a straight concrete (stone aggregate) mix. You may have some luck, if you had the designer offer this explanation, but expect a price reduction for the substitution.
  9. Greatlaker221
    Joined: Sep 2014
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    Greatlaker221 New Member

    Repair on Hershine 37

    The fiberglass covering the concrete filling the keel of my Hershine 37, probably never bonded with either the hull or concrete. The water intrusion into the keel area resulted in a crack due to ice damage. Pictures are in my blog.

    My question to you is, If I chip down to good concrete, what should I replace the layer with? after reading this, a layer of epoxy/mortar poured up the the turn of the bilge, then glass over that with heavy cloth/epoxy to create the new bilge. What type of epoxy/mortar would you specify in this case. Thanks,
  10. PAR
    Joined: Nov 2003
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    PAR Yacht Designer/Builder

    Other than making the epoxy thicker, there's no advantage to mixing mortar with epoxy. The problem you have is the original overcoat to seal the ballast in place, wasn't sufficient enough to keep out water. Clean out the affected area, grinding back to good, unfractured 'glass, then lay in some fabric and resin to again seal the ballast in, but with enough fabric and resin to insure it's water proof. Any of the common marine grade epoxy products will do, as they all have similar physical properties.

  11. gonzo
    Joined: Aug 2002
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    gonzo Senior Member

    If you had a contract or agreement, it doesn't matter which is best. Honestly, I can't see any reason for you to not to install a few metal rods. You can get a diamond saw and cut enough material to make space for the rods and lay new fill. Otherwise, you could also reach an agreement for a large price discount.
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