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What's this stuff in my water tank?

peaman

Sustaining Member
So today, I cut an opening in two of my water tanks to install a cleaning and inspection port. I was disgusted by what I found inside and am glad I will have inspection ports now.

Any idea what the stuff is that's in my tanks? and best way to prevent it? I just bought the boat, so I don't really know the history of the tanks. (the white crumbs are from cutting the opening.)
 

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gabriel

Live free or die hard
Probably algae that forms from letting water sit in the tank. The solution would be to drain when not in use and rinse with a bleach solution or something similar that would disinfect the tank.
 

Frank Langer

1984 Ericson 30+, Nanaimo, BC
Peggy Hall (and others) have written quite alot about how to keep both water tanks and holding tanks clean and odour free. You may want to search a bit, as there is lots of good guidance. Some people also install a water filter in their water line between the tank and the water faucet, but that's only effective if you clean it or add charcoal as a regular maintenance item.
Frank
 

toddster

Curator of Broken Parts
Blogs Author
That is dried-up biofilm. It’s in the pipes in your house too, but you can’t see it, so you don’t worry about it. Clean out the system as best you can. Maintain residual chlorine as per WHO guidelines. 8 drops of household bleach per gallon. For my tanks, that works out to a capful per fill. Avoid filters unless you suspect chemical contamination - they are excellent habitat for bacteria and have a zillion times the surface area = a zillion times the biofilm. (“Test” results on the label are only valid for a few hours after installation.) I did make a Baja filter for water similar to the one described in Practical Sailor for filling tanks, but that’s just to remove gross contamination. (My marina is plumbed with white PVC pipe - they couldn’t make a better system for growing black algae if they tried.)
 

peaman

Sustaining Member
Thanks for an excellently detailed response, toddster!

The tanks cleaned up pretty well with minor scrubbing using a bit of dish detergent and bleach. And with my new clear inspection ports, I'll be able to keep an eye on them.
 

nquigley

Sustaining Member
Thanks for an excellently detailed response, toddster!

The tanks cleaned up pretty well with minor scrubbing using a bit of dish detergent and bleach. And with my new clear inspection ports, I'll be able to keep an eye on them.
I'm really keen to add these ports - not so keen to see what's inside my tanks though.
What size of (clear) inspection ports did you get? (i.e, what hole size did you cut?)
Did you install one or two ports per tank?
What part number did you order, and from where?
Can you reach all corners of the tank from the port(s).
 

peaman

Sustaining Member
Got a photo of the inspection port you used on the plastic tank?
This is a 6" deck plate, Beckson DP-W-C from Defender, installed in a 6-1/4" opening and bedded with recommended silicone sealant. My tanks are not big, largest dimension of 36" in the stbd tank, so only one access per tank. I can reach all corners of the tank by hand (I'm not a big guy).

I will cut a smaller, 2" opening in the covering board on the port and stbd tanks so I'll be able to glance inside by just lifting a cushion. That's not required on the forward tank, since that tank is separetly secured and the covering board is not screwed down.
 

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nquigley

Sustaining Member
This is a 6" deck plate, Beckson DP-W-C from Defender, installed in a 6-1/4" opening and bedded with recommended silicone sealant. My tanks are not big, largest dimension of 36" in the stbd tank, so only one access per tank. I can reach all corners of the tank by hand (I'm not a big guy).

I will cut a smaller, 2" opening in the covering board on the port and stbd tanks so I'll be able to glance inside by just lifting a cushion. That's not required on the forward tank, since that tank is separetly secured and the covering board is not screwed down.
I'm planning to start the same project this weekend - the clear deck plates arrived yesterday from Defender.
> Silicone sealant: what type did you use to bed the inspection ports in place? (what was 'recommended'?)
I'm imagining that some types might not stick to the rotomolded plastic the tanks are made of (polyethylene?)
> Inspection holes in the cover boards: what size holes do you recommend for good viewing through the deck plate?
Since the exact position of the deck plates isn't critical, I might drill the cover board holes first, to make it easier to position the deck plates right under those holes.

Thanks!
Neil
 

Mr. Scarlett

Member III
I don't think many things will stick to the border of the inspection port either. The sealant is just that - for sealing. It forms a gasket and if it's not starved out of the joint by overtightening, it should be watertight. The ring will have small ribs on the underside around the perimeter that help key the sealant and give water a hard time migrating up and down and outward.
 

peaman

Sustaining Member
to start the same project this weekend...
They recommended silicone sealant, no specific brand. I don't recall which I used, just a "good" brand from the hardware store. I agree with what LemmyK wrote above.

I drilled a 2" hole in the covering board, just because that's what I had at hand. 1-1/2" should work, maybe even 1-1/4". 1" is probably too small. With clean tanks and clear water, the best indication is in the reflection of a flashlight beam off of the surface of the water, so you need room for your light, and clear room to see the reflection.

There are some considerations in placement of the deck plate.
1) I wanted it to be close to the center, for best access, visually and manually, to all corners of the tank.
2) I wanted to avoid the molded-in model number of the tank, both so I could read it, and to avoid the possibilty of a leak due to the "texture" of that number.
3) Another surface defect occurs as a result of the manufacturing process. It is effectively the umbilicus, or belly-button of the tank. Besides a 1-1/2 or 2" circle on the tank top, there may be a cylinder of polyethylene 1/2" in diameter extending into the tank at that same location.
4) Finally, my forward tank is secured by a couple of planks, maybe 1x4, running fore and aft over the tank. I shifted one of those planks about 1/2" to allow the deck plate to be installed between them and not under one or the other.

The deck plates may weep a bit past the O-ring seal when the tanks are full. The clear cover will fog in some circumstances, making viewing more difficult. But with my 2" opening, I have no problem seeing the reflection of the flashlight beam.
 

peaman

Sustaining Member
The wall of the tanks is about 1/4" thick. I placed masking tape over the approximate area where I wanted the opening and drew the cutting circle on that. Then, after drilling a starter hole, I used a jig saw to cut the opening. I placed the cut circle so it included the "umbilicus" plug.
 

bumbugo

Member I
We are about to undertake this project ourselves. The deck plates arrived yesterday.
Did you also drill holes in the top of the tank to fasten down the deck plate or just use the silicon sealant?

Thanks. This is a very good idea!
 

nquigley

Sustaining Member
I used screws and sealant. Full tanks may still leak a little when sailing at steep angles or in a sloppy seaway - the polypropylene tanks are a bit flexible so I can imagine the sealant having trouble keeping the water in 100% (?)
 

bumbugo

Member I
I used screws and sealant. Full tanks may still leak a little when sailing at steep angles or in a sloppy seaway - the polypropylene tanks are a bit flexible so I can imagine the sealant having trouble keeping the water in 100% (?)
Thank you. Here I go!
 

peaman

Sustaining Member
Thank you. Here I go!
Hold on! So above, I noted that the deck plate manufacturer recommended silicone, so that's what I used. That was about a year ago. This year, I made a couple changes in plumbing with end result that filling tanks could create internal pressure, and I found that the tanks would leak between the sealant and the tank material. I was very disappointed.

I'm not sure what sealant would be best for sealing between the very slippery polyethylene tank, and the plastic deck plate. I would try 3M 4200 first, or maybe butyl would be a good choice. But silicone apparently will not assure a leak-tight joint between the deck plate frame and the polyetylene tank.

Good luck!
 

Jerry VB

E32-3 / M-25XP
I also installed clear inspection plates in my tanks over winter. Probably the same Beckson ports (6"). I used silicone caulk for sealing them and used screws with washers and "nylock" nuts on the inside to mechanically fasten them. I applied the caulk and installed three of the six screws loosely, let the caulk cure, and then installed all six screws tightly. I then installed 8" (plate diameter) screw-out ports in the plywood covers so I can easily access the tank access ports. Warning: if you do the plywood access ports, make sure the 8" is the port diameter, not the overall diameter. DAMHIKT

This spring when I filled the tanks totally full (to overflowing) via the deck fill, I had a slow seepage out the ports (the screw-in plate, not the ring-to-tank seal). I was disappointed that the port's o-ring sealing wasn't perfect but that was probably an unrealistic expectation in retrospect. Once I pumped enough water out of the tank to relieve the pressure the seepage stopped. Hopefully there won't be any seepage when sailing and heeled over with full-ish tanks. I have not had a chance to check that yet.

Inspection port installed on the tank:
1654648639237.png

With the plywood on, 8" screw-out port not installed:
1654648473782.png
 
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toddster

Curator of Broken Parts
Blogs Author
When I built my house, to pass inspection for the Drain Waste and Vent system, I had to plug up all the drains and fill the system with water until it poured out of the rooftop vent - four stories high. With no leaks. So it’s possible. What event this test is supposed to simulate, I can’t imagine. :rolleyes:
 

Saverio

Member III
Hello, in Italy we put in the water tank before filling it, 2 caps per 100 liters, AMUCHINA concentrated disinfectant solution.
 
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