water tank

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mollymawk's picture
mollymawk
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water tank

Hey guys,
when filling the water tanks, when I use the full capacity,  I have a curvature/bulp. The venting is not working properly, and it is difficult to get there. does anyone have tips ideas to fix that problem?

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pkeyser
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It's normal for the water tanks to show deformation when full. They have relatively thin walls and hold a lot of weight @8+ pounds per gallon. Your vent is probably working because if it  wasn't, it would take a long time to fill a tank and lots of water spray would be blowing out of the deck filler. The water pump would also not be very effective, as it would be creating a vacuum in the tank.
Try disconnecting a vent hose and blowing through it to verify it's not plugged up.

Paul & Wendy Keyser
"First Light"
Rye NH
2005 C36 MKII #2257
Wing, M35B

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KevinLenard
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Posts: 209

When we got our boat I noticed a leak from the main tank that turned out to be a fracture at the outgoing spigot.  I then found another leak around the access hole.  Fixed both with a hot melt glue gun and heavy duty glue sticks.  Permanently closed the access hole.  I eventually re-routed the vent hose, shortening it so that it had no dips in it that dropped below the top of the tanks and caused air blockages.  I now just top up the tanks until water comes out the vent hose.  Works great, no leaks.

Kevin Lenard
"Firefly"
'91 C-36 Mk. "1.5" Tall Rig, Fin Keel, Hull #1120, Universal M-35 original (not "A" or "B")
CBYC, Scarborough, Lake Ontario, Canada

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Siler Starum
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It is actually a design mistake: normally the vent-pipe area should be around 125% of the inlet pipe area.
And on Catalina's we see that the vent-pipes are even smaller which is causing this problem that tanks (water and the black water) are showing deformations.
Unfortunately the abnormal is now considered as normal... 

Durk Nijdam
S/V "SILER"
Catalina 36MKII - 2001 / hullnr. 2013
Stavoren - Holland

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pkeyser
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Durk-
Why should the water tank vent be 125% the size of the inlet? Water is virtually incompressible while air is very compressible and pressure differences will equalize quickly unless the tanks are filled with a fire hose. I can understand why the vent size should be larger on the holding tank (to better support the breakdown of waste), but I think the water tanks and fuel tank vents are adequate. 

Paul & Wendy Keyser
"First Light"
Rye NH
2005 C36 MKII #2257
Wing, M35B

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Siler Starum
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Posts: 113

This 125%-rule is a rule which is used in the professional Standard Shipbuilding Practice, described in the Rules and Regulations for ship design by Classification Societies and considered as sufficient to prevent an overpressure in the tank-construction. The max test-pressure general indicated for a static tank or tank construction is 0.2 bar. 

Durk Nijdam
S/V "SILER"
Catalina 36MKII - 2001 / hullnr. 2013
Stavoren - Holland

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pkeyser
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Thanks Durk.
Catalina and other American recreational boat builders are guided by the ABYC rules: American Boat & Yacht Council. I'm guessing their guidelines are different for large commercial vessels. A cruise ship taking on thousands of gallons of fresh water or fuel  would certainly need large diameter tank vents to speed the process and insure no over-pressure occurs.

Paul & Wendy Keyser
"First Light"
Rye NH
2005 C36 MKII #2257
Wing, M35B

Cwhit
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Posts: 14

Funny this subject just came up.  We're new owners of a 2000 C36 mkii.  Just yesterday, I decided to flush the fresh water tanks as they had been sitting unused for almost 2 years.  After filling them up to capacity at the dock, I noticed water coming into the bilge from forward and aft (not too much, maybe a gallon total or so).  When I checked the top of the water tanks, the forward and aft starboard tanks where seeping water out of the sight window cap.  The previous owner mentioned this in the maintenance logbook, during his early observations in 2013.  I drained out a few gallons from each tank and it stopped, so I'm guessing I won't top them off each time (which is fine since we don't cruise that far for now, and I don't want all that extra weight if we don't need it). 

Interesting, if not somewhat an inconvenient design.  Wondering if tanks at 80-90% capacity sloshing around in rough seas will leak through that sight cap?!?

Chris

"Summer Wind"
2000 Catalina 36 MKII, #1885, Standard Rig, Wing Keel
Home Port: Lighthouse Point, FL

"I fly, I sail, I throw caution to the wind.
Drift like a stratus cloud above the Caribbean..."
--Jimmy Buffett

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Siler Starum
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and why are we all accepting that our water tanks are leaking through the inspection hatch because of the deformation, caused by very little overpressure when we fill the tank?

Durk Nijdam
S/V "SILER"
Catalina 36MKII - 2001 / hullnr. 2013
Stavoren - Holland

Cwhit
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Posts: 14

A very good point!

Chris

"Summer Wind"
2000 Catalina 36 MKII, #1885, Standard Rig, Wing Keel
Home Port: Lighthouse Point, FL

"I fly, I sail, I throw caution to the wind.
Drift like a stratus cloud above the Caribbean..."
--Jimmy Buffett

True Wind
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Posts: 139

I don't see a standard for water tanks in the ABYC standards. Hmm? Just for the record if ABYC decides to make new standards or amend current standards it doesn't mean that boats manufactured before those standards have to be upgraded to the new standards. I have the same problem with my C36. The tanks leak, the bilge turns on then they find a state of equanimity then I am at peace. One with the tanks.

2003 Catalina 36

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