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Old 19-09-2016, 05:05   #1
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Budget friendly diesel tank for those who don't get on well with fibreglass.

Hi Cruisers,

I thought I should post this here in case it can help someone facing a similar problem.

In summary, our engine day tank is pretty well buggered. At least 20 years old, it was a basic stainless tank that had become brittle and leaky over time. I wrapped it in fibreglass last year as a quick fix, which worked ok, but I don't trust it at all. Also, being a stock tank it did not make full use of the space available so could only hold about 50 litres. Ok, but not great. So I looked for a replacement. Options are an even smaller stock stainless tank ($400 for 40 litres only, they've changed the dimensions and the new 50 litre will not fit), a poly tank (plenty of options up to 55 litres but very expensive at $500 plus) or build my own fibreglass tank. (But I don't work well with fibreglass).

So I fretted for a while then had an idea. I wondered if I could buy prefabricated fibreglass panels and assemble a tank from those. A few phone calls put me in touch with a fibreglass fabricator who had some 4 mm thick panels (gelcoated on one side) hanging around from a old job which they were happy to give me in exchange for a carton of beer. They also sold me polyester resin at bulk prices (I had to bring my own tin) and told me to help myself to the chop strand off cuts box. So for AU$90 plus about AU$40 for the various fittings (main filler, pickup, breather, return line and transfer filler line) I was ready to go. I cut the panels to make a simple box, taped it into shape with masking tape and glassed it together over three days. I found I could make nice radiuses on the inside corners by tipping the box at a 45 degree angle and then filling the subsequent trough with resin. (Hence the three days, there were 12 individual mini pours just for the internal corners after I had done the two layers of CSM to make the box). In all I added about 3.5 kg of resin and glass to make the tank. Total weight is about 12 kg. Total capacity is 63 litres which is a nice bonus. Pressure tested it today and it held pressure fine (3 psi). I still have to epoxy in the brass fittings but I need warmer weather for that so it will be a couple of days. Total build time between 6 and 8 hours so far.

I didn't think to take photos during the build because I didn't think it would be of much interest to anyone. It is only now I thought maybe it would help someone in a similar situation. I had taken a couple of internal photos for my records in case I needed to modify the tank later, so I will add those.

I hope this helps someone.

Matt

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Old 19-09-2016, 07:49   #2
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Re: Budget friendly diesel tank for those who don't get on well with fibreglass.

Here is a link to a must read article (IMHO) for anyone that is thinking of building their own tank. It's on the West Epoxy website.

WEST SYSTEM | Modifying and Customizing Boats - Wood/epoxy composite tank guidelines
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Old 19-09-2016, 08:53   #3
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Re: Budget friendly diesel tank for those who don't get on well with fibreglass.

As mentioned in article, and from personal training and experience as a Surveyor in the SAMS organization and ABYC certifications, in the USA, tanks need to have a label from the manufacturer stating compliance.

A home built tank would be a red flag! But to each his own, just wanted to put this out there to save someone a possible headache down the road.
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Old 19-09-2016, 13:32   #4
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Re: Budget friendly diesel tank for those who don't get on well with fibreglass.

Interesting point, they are very common here in Oz but I understand they are a little frowned on elsewhere.


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Old 19-09-2016, 13:44   #5
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Re: Budget friendly diesel tank for those who don't get on well with fibreglass.

GILow:

Cleaning port(s)?

It came out looking nice, good on you.

Ann
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Old 19-09-2016, 13:55   #6
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Re: Budget friendly diesel tank for those who don't get on well with fibreglass.

GILow,

No worries, resourcefulness is necessary when cruising on a budget. I've done some things I wont mention here I see lots of stuff going on in Panama where I am now, due to parts availability etc. You have to keep the boat going, right!

It does look nice, chances are if the fittings and finish look factory, no one will look any further.
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Old 19-09-2016, 14:29   #7
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Re: Budget friendly diesel tank for those who don't get on well with fibreglass.

Quote:
Originally Posted by DeepFrz View Post
Here is a link to a must read article (IMHO) for anyone that is thinking of building their own tank. It's on the West Epoxy website.

WEST SYSTEM | Modifying and Customizing Boats - Wood/epoxy composite tank guidelines
Those guidelines are impressive and helpful.

Usually you just get a CYA "don't even go there" from manufacturers if you want to do something out of the ordinary. This is refreshingly honest.

I was going to build a small but exactly-the-right-size gasoline tank for my skiff out of plywood, 'glass and epoxy, but the complication of finding the right fill cap, and a reality check put an end to that.
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Old 19-09-2016, 15:00   #8
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Re: Budget friendly diesel tank for those who don't get on well with fibreglass.

Quote:
Originally Posted by Ann T. Cate View Post
GILow:

Cleaning port(s)?

It came out looking nice, good on you.

Ann

Yep. One big one to add. Wanted to pressure test before I added the port because it will introduce another gasket.




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Old 19-09-2016, 15:06   #9
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Re: Budget friendly diesel tank for those who don't get on well with fibreglass.

Actually, the important part of this thread was supposed to be about using premade fibreglass panels. This is a technique I think might help people who, like me, don't get on very well with fibreglass construction. I've done a fair bit of it over the years and I always feel disappointed with the level of finish I achieve. This tank came out looking crisp and clean, as against the usual lumpy monsters I am prone to creating.

For those where regulations make this unwise (or in my case I would not consider this construction for petrol even though we have a boat in the family with built in fibreglass petrol tanks) this might be an acceptable way of constructing a water tank.


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Old 19-09-2016, 15:15   #10
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Re: Budget friendly diesel tank for those who don't get on well with fibreglass.

^^^^^
Quite so. Nice job. Smiley face for the cleaning port.

It does seem a possible way for water tanks. Although, there are many polyethylene water tanks available from which to choose, in the US, anyway.

FWIW, we have had excellent use from some s/s water tanks fabricated for us in NZ. They need to be kept off the hull, and secured, but were strong enough to not flex, so did not work harden and crack, like your diesel tank did.

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Old 19-09-2016, 15:29   #11
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Re: Budget friendly diesel tank for those who don't get on well with fibreglass.

Quote:
Originally Posted by Ann T. Cate View Post
^^^^^
Quite so. Nice job. Smiley face for the cleaning port.

It does seem a possible way for water tanks. Although, there are many polyethylene water tanks available from which to choose, in the US, anyway.

FWIW, we have had excellent use from some s/s water tanks fabricated for us in NZ. They need to be kept off the hull, and secured, but were strong enough to not flex, so did not work harden and crack, like your diesel tank did.

Ann

Yes, water tank choices are much better, I've got my eye on a pair for the keel that will use an impressive 90% of the available volume, and they are just a standard off the shelf item. Of course our boat came with water tanks built into the keel, normal for at least Australian boats of the era, but totally unhygienic by the time the boat is 40 years old.

Strangely, there are also plenty of petrol tank choices. I don't know enough chemistry to understand why a plastic tank approved for use with petrol is not approved for use with diesel. Seems the wrong way round to my mind, but I would not risk second guessing the manufacturer.


And of course the big problem I faced with most prefab tanks was the lack of fittings for return lines and breathers. Even the stainless monster from Whitworths did not have enough connection points.


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Old 20-09-2016, 05:56   #12
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Re: Budget friendly diesel tank for those who don't get on well with fibreglass.

You mentioned using polyester resin I think.

That won't bond so well to your fully cured panels, so you might keep that in mind.

Or so they say; I have no experience as to how much weaker. Vinylester resin works, but from what I've seen, that is more expensive than epoxy.
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Old 20-09-2016, 06:05   #13
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Re: Budget friendly diesel tank for those who don't get on well with fibreglass.

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You mentioned using polyester resin I think.

That won't bond so well to your fully cured panels, so you might keep that in mind.

Or so they say; I have no experience as to how much weaker. Vinylester resin works, but from what I've seen, that is more expensive than epoxy.
For practical purposes I considered that there would be no bond at all. Of course I roughed up the panels with 60 paper and a good wipe of acetone, but really the idea behind the panels was to provide just the framework for the tank itself. That way I was able to lay up a new tank inside the panels using CSM and poly resin. Easy.

The only bit I was not totally comfortable with was anchoring the baffle plates, given that I knew they needed a mechanical bond more than any other part of the tank. In the end I (hopefully) solved the problem by over engineering the lattice.

Matt
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Old 20-09-2016, 06:22   #14
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Re: Budget friendly diesel tank for those who don't get on well with fibreglass.

I forgot to mention the biggest positive of this tank. Finally the filler point is in alignment with the cockpit filler cap so there will be no more annoying blow back when filling from a jerry can. And I can use a dipstick to check the fuel level instead of the mirror and torch I currently use to read the gauge.

Getting a bit excited about this tank now. Should get to try it out on Friday.


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Old 20-09-2016, 09:30   #15
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Re: Budget friendly diesel tank for those who don't get on well with fibreglass.

We recently had a new fuel tank made for our Taswell 43. It was made out of 10mm wall close-link polycarbonate, and has worked well for the last 4+years. But we do have one issue.....the tank has poly fittings installed for the refill inlet and vent, tank sender, fuel supply, and return line. Metal fittings were screwed in....but they all leak (just a little wetness around each opening). Anyone have any idea on a good product to use on the threads to seal them tight?
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