Water air vent location

[kish]

Originally Posted by BAD ORCA

Is there any reason why i cant put my fresh water air vent lines on the interior of the boat instead of on the outside of the hull?

I was thinking high up inside of a wet locker about three to four feet above the water line.

Im adding a second fresh water tank in the v-berth so need to add a new vent. I cant think of any downsides. I though maybe it would add to humidity levels inside the boat but my boat never seems to ever drop much below 70% humidity anyways. As long as its high enough to not leak when healed over 30+ degrees...

You are probably overthinking this non problem.
Where is the vent for your diesel tank.?
Presumably outside. Never inside.

What is the difference between fresh water and diesel tank vents.

[BAD ORCA]

Originally Posted by kish

You are probably overthinking this non problem.
Where is the vent for your diesel tank.?
Presumably outside. Never inside.

What is the difference between fresh water and diesel tank vents.

I disagree. I think having your fresh water supply contaminated with salt water 2000 miles offshore is something a man should consider as a potential problem. It may seem trivial to you but the unprepared man is likely the one to suffer disaster. I dont think you can ever have enough information.

My diesel tank vent is high up on my transom. Seems like a good place to keep it. The new diesel tank will be under the starboard settee at the center of the boat. The current vent on the transom is about 15' from that location. I have problems filling the current tank which is about 5' away aft. It backs up constantly and takes forever to fill.

[wingssail]

Originally Posted by BAD ORCA

I disagree. I think having your fresh water supply contaminated with salt water 2000 miles offshore is something a man should consider as a potential problem. It may seem trivial to you but the unprepared man is likely the one to suffer disaster. I dont think you can ever have enough information.

My diesel tank vent is high up on my transom. Seems like a good place to keep it. The new diesel tank will be under the starboard settee at the center of the boat. The current vent on the transom is about 15' from that location. I have problems filling the current tank which is about 5' away aft. It backs up constantly and takes forever to fill.

Vents with long runs from the tank get fluid pooled in the low spots. You could carefully route your vent line so it has a gradual rise from the tank to the vent. I've had that problem.

To solve it:

For water tanks I ran the vent hose almost directly vertically from the tank to the cockpit. The vents are behind a line bags on either side of the cockpit. When the tank is full the water flows out of the vent into the cockpit and out the cockpit drain. It is OK if the vent is small, I am not usually in a hurry to fill the water tanks, slow is OK.

For fuel, I don't want overflow into the cockpit, so the vent is aft, on the transom. But since we like to fill our fuel tanks more quickly I needed a really good vent system (otherwise the fill pipe spouts back and diesel goes everywhere). As I mentioned above, I ran a parallel fuel fill hose from the deck to the tank. I took the inspection plate off and to a welder and had him put a 1.5" nipple on it to accept a hose. So now I have two fill fittings on deck. Open one and put the nozzle in it and open the other for a vent. I can fill at full speed. When I hear the gurgle in the open vent I know the tank is nearly full. It works perfectly.

[BAD ORCA]

Originally Posted by wingssail

Vents with long runs from the tank get fluid pooled in the low spots. You could carefully route your vent line so it has a gradual rise from the tank to the vent. I've had that problem.

To solve it:

For water tanks I ran the vent hose almost directly vertically from the tank to the cockpit. The vents are behind a line bags on either side of the cockpit. When the tank is full the water flows out of the vent into the cockpit and out the cockpit drain. It is OK if the vent is small, I am not usually in a hurry to fill the water tanks, slow is OK.

For fuel, I don't want overflow into the cockpit, so the vent is aft, on the transom. But since we like to fill our fuel tanks more quickly I needed a really good vent system (otherwise the fill pipe spouts back and diesel goes everywhere). As I mentioned above, I ran a parallel fuel fill hose from the deck to the tank. I took the inspection plate off and to a welder and had him put a 1.5" nipple on it to accept a hose. So now I have two fill fittings on deck. Open one and put the nozzle in it and open the other for a vent. I can fill at full speed. When I hear the gurgle in the open vent I know the tank is nearly full. It works perfectly.

Thank you. thats exactly what happens to my current diesel tank when trying to fill it. Im going to have my new diesel tank customized when they fabricate it and call out how many connections i want and where to put them. I really like the idea of the two fill pipes. I could call out having one on each end of the tank. The tank will be 52 gallons and nearly 5' long. The small vent should keep the engine happy while running even with the extra distance from the transom. The engine runs like a charm now and never gives me any problems.

[stormalong]

Originally Posted by wingssail

Vents with long runs from the tank get fluid pooled in the low spots. You could carefully route your vent line so it has a gradual rise from the tank to the vent. I've had that problem.

To solve it:

For water tanks I ran the vent hose almost directly vertically from the tank to the cockpit. The vents are behind a line bags on either side of the cockpit. When the tank is full the water flows out of the vent into the cockpit and out the cockpit drain. It is OK if the vent is small, I am not usually in a hurry to fill the water tanks, slow is OK.

For fuel, I don't want overflow into the cockpit, so the vent is aft, on the transom. But since we like to fill our fuel tanks more quickly I needed a really good vent system (otherwise the fill pipe spouts back and diesel goes everywhere). As I mentioned above, I ran a parallel fuel fill hose from the deck to the tank. I took the inspection plate off and to a welder and had him put a 1.5" nipple on it to accept a hose. So now I have two fill fittings on deck. Open one and put the nozzle in it and open the other for a vent. I can fill at full speed. When I hear the gurgle in the open vent I know the tank is nearly full. It works perfectly.

Regardless of where you put water tank vent on the outside of the boat the hose should loop above the vent. That way any sea water that gets in should stay out of the tank. Think like the loop in your engine exhaust.

My diesel tank vent is a 1/4 inch standpipe inside a vertical portion of the stern rail. The stern rail has three small hole drilled in it six inches below the top of the standpipe. An idea that I saw on a Hinckley. Never had a problem with it. Diesel fuel tank fill hoses are typically 1-1/2 inch ID while the fill nozzle is about 1 inch OD. I don't understand the need for a second vent for filling. There is plenty of room around the nozzle for air to escape.

[BAD ORCA]

Originally Posted by stormalong

Regardless of where you put water tank vent on the outside of the boat the hose should loop above the vent. That way any sea water that gets in should stay out of the tank. Think like the loop in your engine exhaust.

My diesel tank vent is a 1/4 inch standpipe inside a vertical portion of the stern rail. The stern rail has three small hole drilled in it six inches below the top of the standpipe. An idea that I saw on a Hinckley. Never had a problem with it. Diesel fuel tank fill hoses are typically 1-1/2 inch ID while the fill nozzle is about 1 inch OD. I don't understand the need for a second vent for filling. There is plenty of room around the nozzle for air to escape.

You would think but clearly something is causing it to back up and overflow or splash out. The fuel going down the hose is being restricted in some way.

[Dr.No]

I have just rerouted my water tank vent from below the rub rail to a new fabricated dorade box. The fuel tank vent, also located just below the rub rail, will probably be moved/raised to the upper transom.

[wingssail]

Originally Posted by stormalong

Regardless of where you put water tank vent on the outside of the boat the hose should loop above the vent. That way any sea water that gets in should stay out of the tank. Think like the loop in your engine exhaust.

My diesel tank vent is a 1/4 inch standpipe inside a vertical portion of the stern rail. The stern rail has three small hole drilled in it six inches below the top of the standpipe. An idea that I saw on a Hinckley. Never had a problem with it. Diesel fuel tank fill hoses are typically 1-1/2 inch ID while the fill nozzle is about 1 inch OD. I don't understand the need for a second vent for filling. There is plenty of room around the nozzle for air to escape.

I don't exactly understand the need for it either but I do know that blow back of air escaping out of a tank fill is common. A small vent (1/4 inch) some distance from the tank allows very little air flow. Maybe that is the problem with some fuel fill systems. People have to fill very slowly and any spouts of diesel results in diesel running off the deck and into the water which causes a slick and much excitement on the part of the attendant.

In my case the 1.5" fill pipe is close to vertical and has no restrictions but even with a small hose nozzle blow back was a fact of life unless I filled very, very slowly. The second fill pipe used as a vent stops that entirely. I'm not recommending it for anyone else, it's just the solution I found.

[stormalong]

Originally Posted by wingssail

I don't exactly understand the need for it either but I do know that blow back of air escaping out of a tank fill is common. A small vent (1/4 inch) some distance from the tank allows very little air flow. Maybe that is the problem with some fuel fill systems. People have to fill very slowly and any spouts of diesel results in diesel running off the deck and into the water which causes a slick and much excitement on the part of the attendant.

In my case the 1.5" fill pipe is close to vertical and has no restrictions but even with a small hose nozzle blow back was a fact of life unless I filled very, very slowly. The second fill pipe used as a vent stops that entirely. I'm not recommending it for anyone else, it's just the solution I found.

The air flow from the vent is needed for two reasons. Prevent vacuum in the tank when drawing fuel for the engine and allow air into/out of tank as fuel changes volume due to temperature changes.

The "blowback" that you speak of is due to foaming. As the diesel hits the existing diesel in the tank it forms bubbles. The bubbles soon dissipate but filling too quickly does not give the bubbles enough time to dissipate and they overflow. Filling slowly allows the bubbles to burst before they overflow.

If the diesel did not foam there would be plenty of room for air to exit the tank around the fuel nozzle.

[MicHughV]

spiders are one thing....but cockroaches are quite something else...I'm not sure if they drink water, but I have caught them scurrying around by the sink...

in Florida, we have the mud dauber wasps, they like to build their nests inside those little screened vents...which soon plugs up that tiny mesh screen.....

[Matt Johnson]

Originally Posted by stormalong

The air flow from the vent is needed for two reasons. Prevent vacuum in the tank when drawing fuel for the engine and allow air into/out of tank as fuel changes volume due to temperature changes.

The "blowback" that you speak of is due to foaming. As the diesel hits the existing diesel in the tank it forms bubbles. The bubbles soon dissipate but filling too quickly does not give the bubbles enough time to dissipate and they overflow. Filling slowly allows the bubbles to burst before they overflow.

If the diesel did not foam there would be plenty of room for air to exit the tank around the fuel nozzle.

Large power boats don't seem to have an issue with high speed fuel fills. Tank volume the benefit here?

[stormalong]

Originally Posted by Matt Johnson

Large power boats don't seem to have an issue with high speed fuel fills. Tank volume the benefit here?

I've seen that too. Can't really say why.

[MEC]

It is preferred to vent water tanks inside the boat to prevent contamination of potable water with seawater



Water tank vent tubing should be rated for potable water use. Each tank vent line should be routed in such a way to form a loop at the inside of deck, with the tail of the vent routed to the yacht's bilge sump.


On my boat the loop occurs where S1/S2 chainplates penetrate thru deck (ie widest beam).


When filling a water tank, when a tank is filled some water will "burp" out of the vent lines.


Potable water tubing has finite service life. To keep potable water fresh tasting, use the water, keep tanks and vent lines clean.

[MicHughV]

Some years back I came across a yachtie that couldn't get his diesel to start and run.

I offered to help, and we took everything apart that we could, but still no start.

The following day, I pulled up to his boat in my dink and happened to tie up near his fuel vent line. Lo and behold, I noticed it was totally clogged. We removed it, cleaned it out and re-installed it.

Voila....problem solved. Engine ran like a baby!!

[Cheechako]

I don't see a big problem, other than getting the interior wet when filling the tanks... The inside wall of the cockpit is often a good spot for vent fittings or a coaming, if you dont want them outside the hull. In theory you could get a little saltwater using the cockpit wall in a storm, but you can loop up inside.