Water Tank

Paulam

.
Apr 16, 2022
34
Catalina MK 1 Point Roberts, WA
Hello re 1987 Catalina 36. My main water tank develops pressure when filling. Vent line is clear. Any ideas?
 

jssailem

SBO Weather and Forecasting Forum Jim & John
Oct 22, 2014
23,313
CAL 35 Cruiser #21 moored EVERETT WA
If your water pressure pump is off, then your filling water at a rate greater than the vent line can manage. You say the vent line is clear. Where does the vent line run?
  • Is it kinked so that it shuts down the air escaping from the tank?
  • Does the vent line vent into the open fill fitting? Are you putting water into the tank and the vent line at the same time?
 
Jan 7, 2011
5,667
Oday 322 East Chicago, IN
I would think that one of two things could be happening…

1) The vent isn’t really clear….
2) You are filling faster than the vent can let air out of the tank.

Or maybe a combination of these 2.

Greg
 
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Paulam

.
Apr 16, 2022
34
Catalina MK 1 Point Roberts, WA
Thanks for getting back to me. I blew the vent line out with compressor. Then I blew through by mouth it is clear. Vents into cockpit. I have tried filling very slowly. Still builds pressure. With inspection cap off I have run the pump/tap, water level drops as you would expect. Turn tap off water level rises to top of inspection hole. The water is not coming from side tank. Level remains the same there. I would guess that if I kept doing this eventually the water level in the tank would drop and stay dropped.
This may have been going on since I have owned the boat 4 years. The only reason I got onto this now is I sprang a leak in the tank. This prompted me to look down there to see what was going on. Thats when I noticed the pressure. You can see a slight dome in tank. None of this makes sense but it is whats happening.
 

Paulam

.
Apr 16, 2022
34
Catalina MK 1 Point Roberts, WA
Thanks for getting back to me. I blew the vent line out with compressor. Then I blew through by mouth it is clear. Vents into cockpit. I have tried filling very slowly. Still builds pressure. With inspection cap off I have run the pump/tap, water level drops as you would expect. Turn tap off water level rises to top of inspection hole. The water is not coming from side tank. Level remains the same there. I would guess that if I kept doing this eventually the water level in the tank would drop and stay dropped.
This may have been going on since I have owned the boat 4 years. The only reason I got onto this now is I sprang a leak in the tank. This prompted me to look down there to see what was going on. Thats when I noticed the pressure. You can see a slight dome in tank. None of this makes sense but it is whats happening.
PS i have seen water coming out the vent outlet.
 
Jan 7, 2011
5,667
Oday 322 East Chicago, IN
We must be missing something….

How many tanks do you have? How are they connected? Do you fill the tank with a hose in an open deck fill? Or do you have a city water hook up?

Does the tank have an inspection port you can open?

The pressure you are seeing does what? Spews water out of the deck fill? Is the tank full at that point?

Greg
 
Oct 26, 2008
6,295
Catalina 320 Barnegat, NJ
What makes you say the tank is pressurized? It sounds like your only evidence is a slight dome in the tank. That could be its natural condition ... particularly with summer heat. If you fill the tank nearly to the top with the inspection port closed, you should be able to hear a release of air by cracking open the inspection port if the tank is pressurized. If you don't detect any air escaping, it's not pressurized.

Also, if you have a feed to the pump from 2 separate tanks, you should close the valve to one tank and only draw from the other. For best practice, draw from just one tank at a time. I can't really follow what you were saying, but it sounds like you are connecting the 2 tanks and the water levels are merely equalizing. If this is what you are doing, you shouldn't. The pump doesn't work very well that way. I don't really know the explanation but I'm pretty sure that you are simply doubling friction losses in the feed lines when you leave both tanks open when pumping water. That has a bad effect on the pump and it pumps water less efficiently.
 
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Paulam

.
Apr 16, 2022
34
Catalina MK 1 Point Roberts, WA
Apologies for late response - out on the boat. There are two tanks. Center 25 gallons and starboard 17 gallons.
Re pressure, when I unscrew inspection cap after filling the water sprays out.
Water is drawn from both. It makes sense that Catalina would set it up that way. Without need to switch over.
Filling is through fill caps on both sides. As I said this may have been going since long before I bought the boat 2021. I had no reason to notice this until the main tank sprang a leak and I started looking around down there. Thanks for your responses. As a friend said "if it aint broke dont fix it" :)
 

jssailem

SBO Weather and Forecasting Forum Jim & John
Oct 22, 2014
23,313
CAL 35 Cruiser #21 moored EVERETT WA
Water is drawn from both. It makes sense that Catalina would set it up that way. Without need to switch over.
This is the wrong conclusion.

Most manufacturers install two tanks so that you have a spare should the water in one be contaminated. They also provide a stop check when one runs dry; the second tank is all you have left.
There are instances when tanks are connected as you suggest, but that would leave the opportunity for you to run out of water without knowing the water is gone.

You should not guess; further inspection is needed. Look for a manifold that will allow you to control the flow of water from the tanks.

With plastic tanks, the tank can be overfilled, creating tank pressure.
 

Paulam

.
Apr 16, 2022
34
Catalina MK 1 Point Roberts, WA
Thanks - that also makes sense. Keep my eye out for another Catalina Mk1 around here and see that set up. In the mean time the original problem is fixed no leak, dry bilge.
 
Jan 7, 2011
5,667
Oday 322 East Chicago, IN
My O’Day 322 has (had) 2 tanks…port and starboard. There was a valve that allowed me to pick which tank was being used.

I eventually removed one for the space and I didn’t need 60 gallons of H2O usually.

Greg