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Old 23-04-2019, 22:55   #1
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Keel tank construction

Hi all,

Background: I am turning the space in my encapsulated keel into a fuel tank. I am sick of the boat leaning to port or starboard, depending on whether I have more fuel than water, this way I can have water on both sides, balancing use as I go, and put the fuel down low.

So the hull was laid up 40 years ago in vinyl ester. It was laid up thick, at the keel it is around two inches thick, solid fibreglass. (NOT some kind of composite construction.)

I have a good clean space in the keel that would give me a 280 litre fuel tank, using the keel sides and the top of the encapsulated ballast as three sides of the tank, and a couple of (existing) bulkheads for two more sides (front and back), then a lid on the whole lot.

I would use vinyl ester resin to turn this space into a tank. Access to this bit of the keel is very good (under main cabin sole, not engine), and I would build a big hatch into the top for cleaning etc. Not too concerned about pollutants getting into the tank as I will pump from this tank to the day tank using an electric transfer pump and filter system I already use on the existing tank.

My questions: I am wondering what to do about the existing "walls" of the new tank. That is, the keel sides and the existing bulkheads. Should I just sand them back with something rough (say 40 grit paper) and paint them with vinyl ester, or should I line the whole lot with vinyl ester and fiberglass sheet before I put a lid on?

(FWIW, the hull has never had problems with osmosis, so I assume the layup was well done originally, even if it was a little too thick.)

When it comes to putting a lid on the whole lot, should I epoxy the plywood top to the hull first and THEN line with vinyl-ester, or will this lead to adhesion problems? (I've read stuff that suggests vinyl ester over epoxy may be a problem.) Maybe epoxy on the outside of the joins for strength, and vinyl ester on the inside?

Over to the brains-trust.

Matt
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Old 23-04-2019, 23:20   #2
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Re: Keel tank construction

Get one made out of 1/2" poly and drop it in. If you make the top over sized you can glass in some battens and screw it down. If you put the filler in a corner you can just pull it out, slosh around some degreaser and hose oit out upside down, no inspection hatch required.
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Old 23-04-2019, 23:31   #3
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Re: Keel tank construction

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Originally Posted by RaymondR View Post
Get one made out of 1/2" poly and drop it in. If you make the top over sized you can glass in some battens and screw it down. If you put the filler in a corner you can just pull it out, slosh around some degreaser and hose oit out upside down, no inspection hatch required.
I looked into this, but it seemed like it was going to cost a fair bit, particularly if I wanted to use most of the space. At least AU$500 to get something that used 70% of the space, and then'd I have to remove one of the bulkheads.

Any places you'd recommend I check out for prices? I may have missed someone good.
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Old 23-04-2019, 23:46   #4
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Re: Keel tank construction

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Originally Posted by GILow View Post
Hi all,

Background: I am turning the space in my encapsulated keel into a fuel tank. I am sick of the boat leaning to port or starboard, depending on whether I have more fuel than water, this way I can have water on both sides, balancing use as I go, and put the fuel down low.

So the hull was laid up 40 years ago in vinyl ester. It was laid up thick, at the keel it is around two inches thick, solid fibreglass. (NOT some kind of composite construction.)

I have a good clean space in the keel that would give me a 280 litre fuel tank, using the keel sides and the top of the encapsulated ballast as three sides of the tank, and a couple of (existing) bulkheads for two more sides (front and back), then a lid on the whole lot.

I would use vinyl ester resin to turn this space into a tank. Access to this bit of the keel is very good (under main cabin sole, not engine), and I would build a big hatch into the top for cleaning etc. Not too concerned about pollutants getting into the tank as I will pump from this tank to the day tank using an electric transfer pump and filter system I already use on the existing tank.

My questions: I am wondering what to do about the existing "walls" of the new tank. That is, the keel sides and the existing bulkheads. Should I just sand them back with something rough (say 40 grit paper) and paint them with vinyl ester, or should I line the whole lot with vinyl ester and fiberglass sheet before I put a lid on?

(FWIW, the hull has never had problems with osmosis, so I assume the layup was well done originally, even if it was a little too thick.)

When it comes to putting a lid on the whole lot, should I epoxy the plywood top to the hull first and THEN line with vinyl-ester, or will this lead to adhesion problems? (I've read stuff that suggests vinyl ester over epoxy may be a problem.) Maybe epoxy on the outside of the joins for strength, and vinyl ester on the inside?

Over to the brains-trust.

Matt
Matt, I think I would use the existing space as a mould, that is create an entirely new tank fully within the space that you have so that it is a complete tank without lid, not a number of sections glassed together. When cured set about making a lid to suit and glass solidly to the newly created tank. That way if there is any movement there are no joins below to crack or possibly weep fluid. If you wanted to you could line the space with some very thin material (possibly a foam)before glassing that would keep the tank truly separate from the hull. Also check out which resin type is suitable for fuel storage.
Cheers.
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Old 24-04-2019, 00:49   #5
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Re: Keel tank construction

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Matt, I think I would use the existing space as a mould, that is create an entirely new tank fully within the space that you have so that it is a complete tank without lid, not a number of sections glassed together. When cured set about making a lid to suit and glass solidly to the newly created tank. That way if there is any movement there are no joins below to crack or possibly weep fluid. If you wanted to you could line the space with some very thin material (possibly a foam)before glassing that would keep the tank truly separate from the hull. Also check out which resin type is suitable for fuel storage.
Cheers.
OK, that's one approach I had not considered. I have some PVA mould release, so I could just coat the hull and bulkheads with it, then build the tank in-situ.

One downside, just thinking about it as I type, is that I would have to remove two bulkheads from within the keel space.... or create multiple (three) tanks... I don't feel all that happy about removing them... but I will have a look at them and see what comes to mind.

FWIW, I would be VERY surprised if there was any movement in the keel of an old Swanson built like mine, but better safe than sorry.

Vinyl ester does seem to be the preferred resin for fuel tanks. My resin supplier was emphatically in favour of it (And they could have sold me epoxy at half the price again).

I made a polyester day tank, and it is a few years old with no problems, but it's only 60 litres and if it starts to fail I can just pull it and toss it. No so with the keel.

A bit to consider, thanks for the ideas.
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Old 24-04-2019, 19:37   #6
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Re: Keel tank construction

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Originally Posted by GILow View Post
I looked into this, but it seemed like it was going to cost a fair bit, particularly if I wanted to use most of the space. At least AU$500 to get something that used 70% of the space, and then'd I have to remove one of the bulkheads.

Any places you'd recommend I check out for prices? I may have missed someone good.
Welded poly tanks are replacing metal tanks in a lot of marine services and many of the former metal tank builders have taken on building poly tanks.

The former owner of a marina I spend a fair bit of time in did what you propose in the keel of his ferro boat. Him and another marina client bought and cut the tank components from sheets using a jig saw and welded them up on site. You can rent the hot air guns they used and it appeared to need far less skill than metal welding.
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Old 24-04-2019, 20:45   #7
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Re: Keel tank construction

You might check what they did in the refit of a Pearson Rhodes 41, it was a tank designed to fit in over the ballast in the keel made of ss or aluminum (can't recall). Somehow I would be suspicious of fuel storage as you have described, but I suppose it is possible.
https://www.cruisersforum.com/forums...s+of+note.html
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Old 24-04-2019, 23:39   #8
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Re: Keel tank construction

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You might check what they did in the refit of a Pearson Rhodes 41, it was a tank designed to fit in over the ballast in the keel made of ss or aluminum (can't recall). Somehow I would be suspicious of fuel storage as you have described, but I suppose it is possible.
https://www.cruisersforum.com/forums...s+of+note.html
Thanks Don, but no, not interested in adding aluminium or other tanks. I've investigated that avenue to death.

Really trying to get some responses on the original question, which was about how to apply vinyl ester resin.

These boats came with the keels configured as tanks, 40 years ago. Apparently it hasn't killed anyone yet. And built in keel tanks of this sort are hardly unusual.
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Old 25-04-2019, 05:34   #9
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Re: Keel tank construction

Are you sure the hull is laid up in vinylester? I surveyed a Swanson 42 that had osmosis, nothing serious but definitely a lot of small blisters.
Usually due to cost factor the first couple of layers of glass are vinylester resin then they switch back to polyester resin to save cost.
I like the idea of making a mould out of the keel space, much easier to lay up a couple of layers of glass then when dry you can finish it in a workshop. You could also fair up the inside hull area with a bit of pink car bog. Nothing fancy, just enough to give a bit fairer surface and cove any hard corners. Then roll on some flo coat with a fine roller. Then once cured a bit of release wax before taking a mould.
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Old 25-04-2019, 05:53   #10
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Re: Keel tank construction

I was going to say same thing. I donít believe vinylester emerged until the 80s. I think pre-mid 80s polyester was used exclusively. Iím not 100% on this
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Old 25-04-2019, 06:03   #11
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Re: Keel tank construction

if the fuel is diesel then epoxy will work.

https://www.epoxyworks.com/index.php...nk-guidelines/
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Old 25-04-2019, 14:27   #12
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Re: Keel tank construction

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Are you sure the hull is laid up in vinylester? I surveyed a Swanson 42 that had osmosis, nothing serious but definitely a lot of small blisters.


A 42? Interesting. Iíve heard of osmosis in a lot of the smaller boats, but pretty rare on a 42. Mine was built by a bloke who didnít trust fibreglass so had it laid up thicker than standard. (Makes it a PITA to find skin fittings, thatís for sure.) Perhaps he also specified solid vinyl ester because it smells like vinyl ester wherever Iíve worked on the interior. And the PO is pretty sure it is vinyl ester.

Building a tank that is separate to the boat would involve removing the keel bulkheads or having three separate tanks and I am reluctant to do either of those.

Many of the Swansons of this era still have their original keel tanks though there was a 36 here on CF a few years back who had osmosis in his keel tanks. The rear keel tank on my boat had been coated in something in the past that made me think theyíd had some problems too.
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Old 25-04-2019, 14:44   #13
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Re: Keel tank construction

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I was going to say same thing. I donít believe vinylester emerged until the 80s. I think pre-mid 80s polyester was used exclusively. Iím not 100% on this
I was surprised too. The story came out because I called the original main owner after doing some work on the interior and getting really worried about the smell. It did not smell like polyester at all.

He explained the weird history of the boat. It was not build by the Swanson Brothers because the bloke who commissioned it wanted the hull thicker (much thicker) than normal and the Swanson Brothers (correctly) said that was silly and wouldn't do it.

So later, when they were hiring out the molds to home builders, he hired the mold and had a Sydney boat builder lay up the hull with and extra ton of resin and fibreglass. Yes, a ton. It is believed that he had it laid up in vinyl ester. (and it smells like it too, quite different to normal polyester, whatever it is.) He spent so much money on the hull he could not afford to even put a deck on it, so sold the hull to two brothers who did the initial fitout, before they had a falling out and sold it, 75% complete, to the main owner, who is the guy I have been in touch with and got the full boat history. He sailed it for 42,000 miles through the South Pacific so has been a great help. He also added a further ton of ballast, so she's about two tons over weight. Makes for a nice smooth ride, but not great in light winds.

No osmosis. That's a nice thing.
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Old 25-04-2019, 14:47   #14
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Re: Keel tank construction

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Yes, I noted that. But most sources seem to agree that vinyl ester is better for tanks when it comes to blocking chemical penetration. Since bond strength is not an issue for my construction plans (aside from the lid) I decided to stick with vinyl ester.
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Old 25-04-2019, 14:49   #15
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Re: Keel tank construction

Thatís why I am not keen on built in tanks. I have surveyed a few boats that have had osmosis inside and outside their tanks. One yacht that sticks in my mind had like a line of osmosis where the tank started and finished.
I cannot see any reason why you cannot line the keel area with a couple of layers of chopstrand/vinylester and put a lid on it for a fuel tank.
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