Vinyl ester keel tanks

Discussion in 'Materials' started by Matthew Dunk, Apr 25, 2019.

  1. Matthew Dunk
    Joined: Apr 2019
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    Matthew Dunk Junior Member

    Hello all,

    I have a Swanson 42 with an encapsulated keel. The keels on these boats were often given a lid to turn them into tanks, for either diesel or water. Mine had the aft section of the keel converted into a water tank, but it became polluted over time so I pulled the lid off and left it open to keep it dry and smell free. I have plenty of water storage without it.

    Now I would like to convert the middle section of the keel to a fuel tank. The hull was, I believe, laid up in vinyl ester (it certainly smells like it and the history of the hull build claims it was vinyl ester). There is no osmosis after 40 years, which tends to support this belief.

    Due to the presence of two bulkheads in the keel where I would like to make the tank, I am reluctant to put tank inserts in as I would have to resort to three small tanks, which would be a pain to build, and very expensive to buy. As it is, these bulkheads will make great baffles. I am also reluctant to remove the bulkheads as I do not know for sure if they are providing compression support for the keel. It is unlikely, but I simply do not know.

    My question is about the application of the vinyl ester.

    The inside faces of the keel are good and clean, a bit rough as they are just raw unpainted fiberglass. I am not sure if I should just sand back the faces and coat with a few coats of vinyl ester resin on its own, or whether it would be better to use resin and glass? I have never worked with vinyl ester before (just polyester and epoxy until now) so I am not familiar with its behaviour other than the fact that it seems to be the preferred resin for tanks due to its chemical construction when cured. (otherwise I would have used epoxy) I do not know if I can build a good enough barrier without the glass fibres, or conversely, if adding the fibres would actually reduce the effectiveness of the barrier. I do not know how the vinyl ester resin will behave when it comes into contact with the fully cured hull.

    Can anyone advise me on these aspects of vinyl ester and how I should proceed?

    Matt
     
  2. rwatson
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    rwatson Senior Member

    This topic has been discussed many times all over the internet of course.

    My short experiment with Vinylester left me gagging and very ill. It smells like burnt office chairs when curing, and I can't imagine working with it in a confined space.
    I haven't read that Vinylester is especially good for fuel tanks. Do you have a reference ?
    I would start with Epoxy both from an application and an engineering POV myself.

    A quick search came up with a couple of starting points

    "I've been quoted as referring to fiberglass as the "forever" tank material. While this may be hyperbole on my part, fiberglass is exceptionally long lasting, provided the proper resin (vinyl ester or epoxy) and scantlings are used." More discussion at
    https://www.passagemaker.com/technical/diesel-fuel-tank-design

    And from these forums.
    epoxy fuel tanks https://www.boatdesign.net/threads/epoxy-fuel-tanks.278/
     
  3. Matthew Dunk
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    Matthew Dunk Junior Member

    Extensive reading and direct advice from my resin supplier, who could have sold me Epoxy at half the price again, say that vinyl ester is the best option for the job. This is not about structural strength, it is about permeability, and according to the reliable sources, vinyl ester is the go. No particularly good references to quote, this is just knowledge I have picked up as I go, and I am confident in it, particularly in light of what my supplier is saying. Also a friend who certifies aircraft was adamant that vinyl ester is the go, and I trust his 50 years of experience over something from the web.

    I am happy with this aspect of the choice, otherwise I would stick with Epoxy which I know well and work with frequently. Certainly nicer to work with than poly or vinyl esters. But again and again I see references to needing special epoxies and even Wests seem a little careful in their wording in their tank building guide.

    No, my question is really for people who have more experience working with vinyl ester than I do. My understanding is that it behaves a lot like poly ester, but I am not thrilled about building this thing without more to go on than an educated guess.
     
  4. ondarvr
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    ondarvr Senior Member

    Most of the current VEs are no different than polyesters for lamination, the odor is different, but that’s about it.

    There are charts for choosing the correct resin for different fluids, so make sure the recommended VE is up to the task.

    The hull should not be used as part of the tank, it should be separate for safety purposes.
     
    Last edited: Apr 26, 2019
  5. Matthew Dunk
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    Matthew Dunk Junior Member

    Can you elaborate on this?
     
  6. ondarvr
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    ondarvr Senior Member

    At one time it was common to use the hull as part of a fuel tank, but the regulations changed and I don’t believe that’s an option anymore.
     
  7. Matthew Dunk
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    Matthew Dunk Junior Member

    Well, if you are quoting ABYC, fine, but I am in Australia, and we have no such restrictions that I am aware of. But that's an issue of regulations anyway, not safety. Don't wish to get into the quagmire of figuring out which regulations apply to a 40 year old boat, or even make sense.

    Diesel is very safe to store, and I've never heard of anyone having safety problems with diesel keel tanks. Smell, yes. Leaks, yes. One recent mention of osmosis too.

    I suppose a diesel leak would make the floor slippery. That's a safety concern. And there's the odd internet rumour of carcinogenic fumes too. But frankly, if it any of these things are happening it's time to start again. There should be no leaks and no fumes if it is done even remotely well.
     
  8. Mr Efficiency
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    Mr Efficiency Senior Member

    They probably don't want fuel leaks from holed boats.
     
  9. Matthew Dunk
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    Matthew Dunk Junior Member

    Yep, that would make sense. Mind you, my hull is two INCHES thick at that point, so I won't lose much sleep over the issue.
     
  10. Matthew Dunk
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    Matthew Dunk Junior Member

    Well, I am no expert on the ABYC standards, but this link appears to be to a copy of the standards:

    https://law.resource.org/pub/us/cfr/ibr/001/abyc.H-33.1989.pdf

    Not that these standards apply to me, but using them as an indication of what is preferred design, nothing I could see said that what I am doing is against those rules.

    And H-33.7.d(1) states "Diesel or heavier fuel oil tanks may be integral with the hull. If reinforced plastic laminated core construction is used where the hull is integral with the tank, the core material shall not deteriorate from contact with diesel fuel and shall not permit fuel to migrate."

    Can't see any problems there. 2 inches of solid vinyl ester fiberglass probably won't "permit fuel to migrate".

    Has this standard been superceeded? Appears to be 1990.
     
  11. rxcomposite
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    rxcomposite Senior Member

    Pure resin is a preferred method as water barrier followed by a surfacing mat as a tie coat. If your surface is good, just sand it and wipe with acetone for a good grip.

    VE is sometimes labeled as epoxy. Maybe it is just a blend but certain blend is marketed as fuel tank sealer.

    You have mentioned baffles. It is built in to reduce the sloshing of fluid.
     
  12. Matthew Dunk
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    Matthew Dunk Junior Member

    Thank you, that is EXACTLY the information I was seeking. I didn't know about the labeling ambiguity, but I trust my supplier who is a specialist resin and composites supplier and explicitly stated that I should use vinyl ester instead of epoxy.

    Yes, the existing bulkheads will make good baffles, my only decision will whether to add fore and aft baffles to dampen down side to side movement in the tank. The tank will be 370 mm wide at its widest, not sure if that warrants an extra baffle or not. One of those gut feel calls I reckon will be easier to make when I am doing the work.

    Thanks again, I will follow your construction advice.
     
  13. Mr Efficiency
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    Mr Efficiency Senior Member

    Epoxy is not that compatible with fuels, not the commonly used varieties anyway. Vinyl ester is the obvious choice.
     
  14. Matthew Dunk
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    Matthew Dunk Junior Member

    Umm... really? Why are you stating this?
     

  15. Mr Efficiency
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    Mr Efficiency Senior Member

    Because it is the case, apparently, there are special epoxies for fuel tanks.
    "A common type of epoxy phenolic resin is epoxy phenol novolac, in which the phenolic resin is a phenolic novolac resin, consisting of short polymers between 10-20 repeating units. These resins are often used as coatings or resistive top coats for drums, pipes, floors, tanks and automotive parts."
     
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