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Old 15-04-2010, 19:19   #1
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A Fiberglass Tankage Thread

one of the projects im most looking foward to this summer is building a huge f.g. water tank under the v-berth, and a 20 gallon f.g. holding tank in the head.

i have a pretty good idea of how im going to go about it, but the few questions i have are...

Baffles - is there some standard to use to determine how many baffles? how close they should be? do i need them in the 20 gallon tank?, maybe 1 i suppose

fittings - those of you that have built one, what do you do for fittings, for the holding tank i will need 3 x 1-1/2" fittings and 1 x 5/8" can i get pvc that will fit 1-1/2 hose well and glass that it on? this would be ideal for a cost effective standpoint. if that will not work, how do you do the fittings?

access plates - i understand they should be big enough to provide access to (almost) all of the tank, are they plastic hatchs that are affordable and reliably water tight? or am i better off building my own? if i do build my own, is it as simple as glassing in some threaded rods, a nice fat rubber gasket and using wing nuts to hold them down?

thanks guys, and you all know a picture is work a thousand words so if anyone has and tankage construction pictures they could share that would be invaluable

all the best,

Ben
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Old 15-04-2010, 20:31   #2
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You may find the info here. Its been a long time since I read it but it should be of interest to you.

http://www.epoxyworks.com/18/pdf/tanks.pdf
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Old 15-04-2010, 23:48   #3
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For fittings, I would use fiberglass exhaust pipe and glass them in.

ciao!
Nick.
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Old 16-04-2010, 20:13   #4
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thats all you got for me nick?
thanks for the west article, i have put it in the file, interesting that they do not outright endorse f.g. tanks for potable water, i thought the general concensus was that they are fine if painted with a FDA approved coating??
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Old 17-04-2010, 08:15   #5
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Originally Posted by pressuredrop View Post
thats all you got for me nick?
It ain't much, isn't it? ;-) It was the only smart thing about fittings I could come up with...

Quote:
thanks for the west article, i have put it in the file, interesting that they do not outright endorse f.g. tanks for potable water, i thought the general concensus was that they are fine if painted with a FDA approved coating??
West describes a wood-epoxy composite construction for the tanks, not fiberglass. However, all the remarks they make are concerning the properties of epoxy as in any method used for building the tanks. Basically they say that when you mix the epoxy "resin-rich" and thoroughly, there shouldn't be any leeching of substances from the hardener.

So yes, if you coat it with a FDA approved coating, which adheres well to epoxy, you are okay.

ciao!
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Old 17-04-2010, 08:54   #6
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Pressuredrop, I built a 80 gallon fuel tank in the bilge of my boat and 2 water tanks 1 on starboard under the settee the other on port. They are about 60 gallons each. They are all built with epoxy and biax cloth. The tanks are all built in place with a 90 degree flange glassed in to accept the lids, those are pre-cast onto a piece of melamine that was waxed and buffed. For the inspection ports I purchased 2 aluminum ports (expensive) for the fuel tank. I made my own for the water tanks with the method you have described using Buna rubber as a gasket glassed in the bolts. For fills you can use the method that Nick describes, I did use barbed through holes for mine. The pics are of the fuel tank built into the bilge.

I do not think you will need a baffle for your holding tank but if it is long and skinny you may want to put in one. From what I have read, after about 30 gallons you need to start adding baffles.

Jack
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Old 17-04-2010, 08:59   #7
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All 3 of my water tanks are all fiberglass...all have baffles but I can not tell you how many or their configuration...as are my fuel tanks.

My holding tanks are Polly...If I were building them out of FG I would not put baffles in those...Marine sanitation is full of enough problems with out adding more to the mix.

Edit:...Nice work Stevens
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Old 17-04-2010, 11:20   #8
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Huge tank in V Berth.... huge = 50 gallons?

One point - weights and balances. By my reckoning 50 gallons is about 225 litres which (thanks to the metric system) is 0.225 tonnes which is as far from the centre of balance of your boat (in the V Berth) as you can get so that's going to push the bow down a bit particularly when you have guests in thge Vberth. You might have 1/2 ton in there.

Just a thought...
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Old 17-04-2010, 11:32   #9
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Aloha Ben,
I can't tell you exactly where I read it but a baffle should be added every 18 inches which is what I'm intending to do. Minty's post is important. If it is a large tank for the v berth then the weight will be high and in the bow. If you also store an anchor and chain there and have a windlass above it might not be good to have a really large tank too.
kind regards,
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Old 17-04-2010, 11:38   #10
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So generally speaking, one wants fuel and water tanks in the middle of the boat. But holding tanks in the ends is not as bad because when one is at sea they are generally empty. Plus holding tanks are smaller anyway.

Regarding baffles, I assume they are needed only in the horizontal dimensions... I need to replace a largely vertical fuel tank that holds about 60 gallons and I don't think the old one has any baffles.
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Old 17-04-2010, 18:45   #11
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jack - pretty work indeed, at 80 gallons, you must have some baffles in the tank... got any pictures of those? and your homemade cleanout ports? while your at it

mintys - appreciate the concern, my v berth is a little further aft then unsual, the front is not exaclty pointy, i have a huge anchor locker then small sail locker then v berth. i was going to put it towards the front, but youve deffinetly made me recondsider. if i move it to the back of the v berth i will get more tankage and be pretty close to amidships, but it will be more on one side then the other

p.s. big is > 100 gallons
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Old 18-04-2010, 00:05   #12
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Quote:
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p.s. big is > 100 gallons
100 gallons = 455L = 0.45 tons (if US gallon then 0.38 tons)
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Old 18-04-2010, 06:04   #13
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correct, should be about 800lbs when full
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Old 18-04-2010, 07:57   #14
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My 35' Sloop has a 30+/- gal tank under the v berth, and a 50 +/- gal tank under the stb settee.
Neither have baffles. Baffles or not, you need to be able to clean the whole tank, thru the inspection cover.

The tanks in my boat are orig, and the inside surface of the hull acts as part of the tank. It's worked for 40 years so far.
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Old 18-04-2010, 07:58   #15
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you must have some baffles in the tank... got any pictures of those? and your homemade cleanout ports? while your at it
Look close at the top right pic the green strip is the top of the baffle there is a 12x2 plank after obscuring the view of the second chamber. I am having problems with my camera and can not get the pics of it, has the ones with the access ports on it plus tons of others Jack
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