2 water tanks, 3 tank vents?

[Boomerang]

Our 42 LRC has a 2 domestic water tanks, 1 under the owners stateroom queen bunk and one saddle tank under the master stateroom floor extending into the aft part of the engine room under the generator. Just as depicted in the ships drawings, there are 2 vents, one for each tank, located high on the aft deck on the transom. The port transom vent is for the bunk tank and the starboard vent for the keel tank. There's 1 fill for both tanks, filling the bunk tank first and gravity feeding the keel tank as the bunk tank is filled. The pump draws from the lowest keel tank, which makes sense. My question is, when I fill the tanks, water comes out of the transom vents when full, as expected. But there's also a 3rd vent on the port side of the hull, aft of midships that spews water when the tanks are full, also! The drawings list this vent as a fuel tank vent for the port fuel tank, yet our 2 fuel tanks are in the forward half of the boat, with their respective vents on the side of the hull close to the fills.
It's not the end of the world but it would be nice to know what the vent was intended to do and why it was plumbed into the system. It looks like original equipment (copper tubing) so I don't think it has anything to do with the onboard water maker that was added at a later date. I've tried tracing the line but it heads toward the middle of the boat where the water tanks are and then I loose it behind the generator and aft engine room bulkhead.
Any guesses, anyone?

 

[Boomerang]

Also, I tried posting pictures of the vent locations and the ships drawings because a picture is worth a thousand words but the forum wont allow me to upload any images. Perhaps due to my lack of posts , IDK. Oh well.

 

[SKYCHENEY]

Many of the tanks on these boats have more than one vent. I think it depends on the shape of the tank and the baffle locations. My fuel tanks have two vents each, one near each end.

 

[Boomerang]

Many of the tanks on these boats have more than one vent. I think it depends on the shape of the tank and the baffle locations. My fuel tanks have two vents each, one near each end.

Huh. Good to know. I can't say I've ever noticed multiple vents per tank on another boat before but I was never really looking for them either! This 3rd vent was just very obvious to me since it's clearly visible from the port side boarding gate while we're tied to a floating dock for the winter season. At our home berth we tie starboard side to and our dock is fixed so I never really noticed it. It must be plumbed to the aft-most tank under the bunk because it seems it would be the first to drain if it were plumbed to the lower tank while both tanks were filled to capacity since it's 18-24" lower than the other 2 vents. What the heck... we have too big of an improvement punch list for me to worry about something thats working just fine!

 

[Beachcomber]

Shawn,
If memory serves me correctly the side vent is for the lower saddle tank. It should start to flow when that tank is full. The rear vents will flow when both tanks are full.

 

[Boomerang]

Shawn,
If memory serves me correctly the side vent is for the lower saddle tank. It should start to flow when that tank is full. The rear vents will flow when both tanks are full.

Thanks. I guess it is plumbed to the lower tank. I can see the copper tube from the vent until it gets behind the generator directly over the tank. I can also see the metal access plate on the top/front of both tanks. Both tank plates have 1 gauge and 1 vent fittings on them. The upper also has another fitting that was apparently added for the output of the water maker. The 1 1/2" fill fitting from the deck is also visableon the plate of the upper bunk tank. The lower tank has the pickup fitting for the pump that serves both tanks since the lower is gravity fed from the upper but I cant see where the gravity feed connections are on either tank. Probably under the sole in the aft stateroom. All 3 vents start overflowing at the same time when the system is full but as long as it's working, I'm not too concerned too much about it. It was more of a curiosity, especially since the ships papers showed the port one as being a fuel vent.

 

[Boomerang]

I wish I could attach pictures to make things more interesting but still no luck.

 

[cww]

These boats have extra keel tanks that were formed into the hull with the appropriate baffles but just not used by the factory, and I've read a bunch of stuff over the years plus had a dock neighbor who did it, where some people commission those for more fuel or water. Other people convert water tanks into fuel tanks because once you install a watermaker you don't need to carry 300+ gallons of water around anymore.

What I'm saying is 30-40 years on, there is no real guarantee that whatever is in your factory plumbing diagram is what you're actually looking at. My 53 has two water tank vents all on the port side of the boat. As someone noted above, the way you know they're full is by waiting until both vents overflow. I'm not sure about the LRC's but my current dock neighbor is a 42 LRC so I can ask him if you like?

 

[Boomerang]

These boats have extra keel tanks that were formed into the hull with the appropriate baffles but just not used by the factory, and I've read a bunch of stuff over the years plus had a dock neighbor who did it, where some people commission those for more fuel or water. Other people convert water tanks into fuel tanks because once you install a watermaker you don't need to carry 300+ gallons of water around anymore.

What I'm saying is 30-40 years on, there is no real guarantee that whatever is in your factory plumbing diagram is what you're actually looking at. My 53 has two water tank vents all on the port side of the boat. As someone noted above, the way you know they're full is by waiting until both vents overflow. I'm not sure about the LRC's but my current dock neighbor is a 42 LRC so I can ask him if you like?

Wow that would be much appreciated if you happened to bump into them and thought to ask. Again, we have the MkII and I'm pretty sure the MkI had the water tanks one under each separate bunk in the aft stateroom and the saddle tank I'm using as water tank is a fuel tank in the MkI's...one of four on the MkI I think... and it did indeed have the vent on the side of the hull where ours is a water vent. Again, not a huge deal because everything is working but I'm the sole person who works on and maintains our boat so it's always nice to know what makes everything tick!

 

[SKYCHENEY]

These tanks were never molded into the hull. They were all built separately, pressure tested, and then installed in the boat, held in with tabbing. The keel tanks were set in foam and then tabbed in.