Parker 23 fuel tank replacement

Questions about boat repairs with our resins and fiberglass: hull patches, transoms and stringers, foam, rot etc.
bobmaes
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Parker 23 fuel tank replacement

Post by bobmaes » Wed Dec 05, 2018 7:09 pm

I'm replacing the fuel tank on my 1988 Parker 23 SE as part of a total refit / makeover.

I pulled the tank yesterday and as expected it was set in foam, lots of foam. The foam under the tank was about 4 inches thick. I was surprised that the bay between the stringers that the tank was set in does not drain to the bilge, or to anywhere.

I removed the old tank and all the foam and now just have the hull forming the bottom of the tank cavity. I don't want to set the new tank directly on the hull itself and besides that if I did the tank would end up being deeper than the original 95 gallon tank. I'm thinking I could epoxy some sheet foam directly to the exposed hull in the bottom of the cavity. This would raise the new tank to approximately how it was originally.

My question is: assuming this is a good approach, what type of foam to use. I thought possibly the blue polystyrene building insulation foam sold in Home Depot. I think it is by Dow and called Foamular. It is light, cheap, and does not absorb water. I would epoxy it to the hull and then glass over it. The (coated) tank would have neoprene strips 5200'ed to it and then be set on the foam/fiberglass floor in the cavity. The tank would have welded tabs and be fastened to the stringers with air circulating all around.

I would love to hear any advice, thoughts and opinions.

Thanks very much



bobmaes
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Re: Parker 23 fuel tank replacement

Post by bobmaes » Wed Dec 05, 2018 7:35 pm


fallguy1000
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Re: Parker 23 fuel tank replacement

Post by fallguy1000 » Wed Dec 05, 2018 8:01 pm

No. No. No. No. and No.

Foamular has no shear and no compression strength.

Next time you walk by it in the store; press on it with your pinky finger until failure.

Marine foams do not crush.

I will look at the pics and give you some thoughts.

Start with no.
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Re: Parker 23 fuel tank replacement

Post by fallguy1000 » Wed Dec 05, 2018 8:07 pm

If you need to make a bed for a different tank; you would do it with a structural foam.

For example, 12mm divinycel. Then you would shape the divinycel to the tank bottom and glass it with 1708 and epoxy.

Then that base would be installed into the hull and well supported with transverse framing also made with glassed foam.

Then the tank rests on neoprene liner.

If the tank fits the hull already, what are your reasons for raising it? Bilge water?

If you are going with an aluminum tank; no foams are supposed to be in contact with aluminum (ally).

I don't care what anyone says. No foam on ally.
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fallguy1000
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Re: Parker 23 fuel tank replacement

Post by fallguy1000 » Wed Dec 05, 2018 8:08 pm

After I hear back from you; I will post more detailed recommendation.

You came to a good place for help.
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bobmaes
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Re: Parker 23 fuel tank replacement

Post by bobmaes » Wed Dec 05, 2018 10:30 pm

My reasoning for foamular is mainly because it does not absorb water and it serves the purpose of taking up some space in the bottom of the tank compartment at a reasonable cost. The tank compartment is about 21 inches deep and the old 95 gallon fuel tank is only 13 inches deep. Without a few inches of foam between the bottom of the boat and the bottom of the tank, a similar 95 gallon tank will sit too deep in the boat for the way the fill hose enters the tank compartment through the stringer from the side of the boat. The fact that it is cheap compared to structural marine foams is just a nice bonus, not a reason to choose it. I don't want to waste money on overkill.

I don't see where sheer strength comes into play in this application at all. Someone please explain.

I'm thinking that after foamular is covered with a layer or two of glass and epoxy resin the compressive strength will not be an issue. And if the load on the glass and foam is spread out over some surface area (a sufficient number of neoprene strips) the compressive force per square inch from a tank which is also supported by tabs welded to the tank and screwed to the stringers will be small. I am sitting here now with scrap a 1.5 inch foamular in my hands and it is pretty tough stuff, not that easy to dent. Covered with two layers of 1708 or even two layers of 10 oz cloth and I am not putting a dent in it.

The downside I think about is whether it is possible for the initial properties of the chosen foam to change or deteriorate over time and the tank foundation to become inadequate. Or for the assumption that the foam will not absorb water is not accurate.

I think this is a good discussion and please don't anyone think I am trying to be argumentative. I am really looking for validation of my thinking or a good explanation of where I am going wrong. I appreciate all your responses. I think it is always cool if there is a way to do things that is both technically excellent and not as expensive as the usual "marine" approach.

ps the original installation is approx 21 inch deep tank compartment: a 13 inch deep tank about 4 inches beneath the underside of the deck sitting on about 4 inches of foam. The 4 inch space above the tank allows for the fill and vent hoses to enter the compartment and be attached to the fitting on the top of the tank.

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Re: Parker 23 fuel tank replacement

Post by fallguy1000 » Wed Dec 05, 2018 11:23 pm

Foamular does not have great crush strength. I would not want it to delam or powder under 600 pounds of fuel.

I can't add a photo to this post, but just last week I laminated 1708 to 2" foamular for a livewell. I also ran a piece of 2" foamular through my timesaver to make the livewell base have a slope to it for drainage. But the top of the livewell bottom is marine foam. Why? Because if I ever drop a fish or bucket or anything on foamular; it will delam. Three sides of the well will be foamular.

The interesting thing is I also laminated the bottom of the foamular base. I sort of considered it optional, but I had hoped glass would bond well. Someone told me on another forum no need to abrade the foamular with 36 grit. Also bullkaka. The foamular delaminated from the peelply removal. I am now considering removing the bottom laminate and going with glue...go figure.

Do not set the tank on foamular. If there is ever any give; the tank might powder it or delam it.

You are correct that shear is not the issue, but compression is. If the tank weights change through fill cycles, sloshing, thermal change, trailering; it might delam. Does it matter? You guess. I wouldn't want to...

If you don't believe me on the finger test; hit it with a hammer. A hammer bounces on marine foams.

If you are simply trying to raise the tank up four inches; buy one piece of 12mm marine foam. It will cost you about 125-150 bucks. Build some 3.5" high bulkheads and cleat the bulkheads and stringers and set a marine foam base down laminated with 1708.

If you insist on using xps; please at least read this link first.

http://www.sciforums.com/threads/styrofoam-and-gasoline.70796/
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fallguy1000
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Re: Parker 23 fuel tank replacement

Post by fallguy1000 » Wed Dec 05, 2018 11:32 pm

If you ise the xps; plan to keep ot away from any gasoline. This is achieved by glassing all the seams from above and hoping there is no delam.

You can use 12 oz or better mat back tapes to seal off the base.

Of course no fuel leaks is always the real hope, so also double clamp all fittings.

I would never use xps for the fuel area. I would use plywood first as an option to marine foam.
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Fuzz
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Re: Parker 23 fuel tank replacement

Post by Fuzz » Thu Dec 06, 2018 1:45 am

Pieces of plywood going across from stringer to stringer and cleated like Fallguy says would be my choice. Cost would be low and no worry about the foam falling apart later on.

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Re: Parker 23 fuel tank replacement

Post by fallguy1000 » Thu Dec 06, 2018 3:05 pm

A picture of shear failure of xps is on my build page.
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