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Boat Forum / Cruising / June 2004Water tank vent overboard or bilge
Hello, I have been mulling over the idea of re-routing my water tank vents from the bilge to an overboard thru-hull vent. I would like to stop from filling my bilge with water everytime i fill my tanks. Some people have expressed concern that it opens up the risk of getting seawater contamination in heavy seas and that the boatbuilder probably chose to do this on purpose. Since this is a power boat, I am not worried about creating a siphon from healing over. I was wondering if anybody has any opinions on why this is a good or bad idea and any advice on things to consider if I go ahead with this (such as heights, loops required etc). Thanks in advance! Rob great idear, can't hurt at all. Rob, My water tank vent empties into the galley sink. My old boat vent emptied into the shower stall. I like this arrangement because it does not let in salt water and we can just watch the sink for an indication as to when the tank is full. Cheers Ansley Sawyer SV Pacem > My water tank vent empties into the galley sink. My old boat vent emptied > into the shower stall. I like this arrangement because it does not let in > salt water and we can just watch the sink for an indication as to when the > tank is full. Neither of those locations is the best place for a water tank vent. They're both full of bacteria and can also become clogged--in a sump by soap scum, hair etc...in the galley sink by grease, food particles etc. Plus, if the sump pump fails or the galley drain gets plugged, shower or galley water can back up into the vent and even the tank. Out a through-hull is the best place for a water tank vent...into the bilge a VERY poor second. At least both of those locations allow you to flush out the vent by overflowing the tank out it each time you fill it.  SignaturePeggie ---------- Peggie Hall Specializing in marine sanitation since 1987 Author "Get Rid of Boat Odors - A Guide To Marine Sanitation Systems and Other Sources of Aggravation and Odor" http://69.20.93.241/store/customer/product.php?productid=40&cat=&page=1 > Out a through-hull is the best place for a water tank vent...into the > bilge a VERY poor second. Why is the bilge such a poor second? The water goes in the bilge. The bilge pumps pump it out. What's the problem? > At least both of those locations [bilge or through-hull] allow you to > flush out the vent by overflowing the tank out it each time you fill it. Aside from the problems with galley-sink and shower that you mentioned how do these locations disallow you from flushing the water vent by overflowing the tank as you fill it? You overflow the tank, it goes into the sink/shower and the vent is flushed, no? >>Out a through-hull is the best place for a water tank vent...into the >>bilge a VERY poor second. > > Why is the bilge such a poor second? The water goes in the bilge. The > bilge pumps pump it out. What's the problem? The problem is bilge pumps DON'T pump ALL the water out...which is why most people do everything possible to keep as much water OUT of the bilge as possible. 'Cuz the less water that goes into one, the less there is to turn into a dark smelly swamp. > Aside from the problems with galley-sink and shower that you > mentioned how do these locations disallow you from flushing the > water vent by overflowing the tank as you fill it? You overflow > the tank, it goes into the sink/shower and the vent is flushed, no? Provided you remember to turn on the sump pump--not too soon, or the impeller will fry...too late and dirty water in the sump will combine with the water in the vent and can get back into the tank and overflow...break out the mop. As often as all of us just stick the hose in the water fill and and forget it till water running out the vent reminds us to turn it off, how many of us are that good? :) Venting it overboard is the only solution that doesn't create more problems than it solves. SignaturePeggie ---------- Peggie Hall Specializing in marine sanitation since 1987 Author "Get Rid of Boat Odors - A Guide To Marine Sanitation Systems and Other Sources of Aggravation and Odor" http://69.20.93.241/store/customer/product.php?productid=40&cat=&page=1 > The problem is bilge pumps DON'T pump ALL the water out...which is why > most people do everything possible to keep as much water OUT of the > bilge as possible. 'Cuz the less water that goes into one, the less > there is to turn into a dark smelly swamp. When Geoffrey bought Lionheart, an Amel Sharki ketch, we were horrified to find that all the sinks, shower, everything but the head, of course, dumped all that grey water into the BILGE! Geoffrey wanted to put through-hull fittings under the sinks to get it overboard, directly, but other things needed doing, first, so it got put off. After using this arrangement since last August, including a couple of sea voyages, we've found that this Amel smells a LOT better than his Endeavour 35 sloop BECAUSE of all the grey water sloshing around in the sump down in the full keel, instead of that little trickle of rain and seawater making its way into the "biological soup" of the Endeavour. I think the advanced biology growing in the Endeavour's bilge is killed off by the antibiotic soap the dishes are washed in that also cleans the oil and scum out of the Amel's bilge! Amel has a BIG manual electric bilge pump but the previous owner put in a BIG Rule 4000 gph and a float switch way down in the bottom. The Rule doesn't do well with food solids that make it into the bilge, but I just pull the power to it and flush out the solids with soapy water and the big Amel OEM bilge pump ever so often, when I think of it. For some crazy reason, this arrangement works BETTER! Any ideas why, Peggie? Larry > For some crazy reason, this arrangement works BETTER! Any ideas why, > Peggie? If it does work better, it definitely isn't due to any "antibiotics" in dish soap...there aren't any, in dishwashing liquids or any other "antibacterial" products. It can only be because you have to flush all that garbage out the bilge fairly regularly to unclog the bilge pump...which doesn't happen on the Endeavor. Any boat will smell a LOT better if the bilge is actually flushed out a few times a year instead of only relying solely on periodic doses of bilge cleaner and the bilge pump. SignaturePeggie ---------- Peggie Hall Specializing in marine sanitation since 1987 Author "Get Rid of Boat Odors - A Guide To Marine Sanitation Systems and Other Sources of Aggravation and Odor" http://69.20.93.241/store/customer/product.php?productid=40&cat=&page=1 Not sure how grease etc is going to leap out of the galley sink into the vent. Our tanks are vented into the head sinks via a spout in each. Easy to see when the tanks are full when filling, no problem with contamination from salt water or anything else. Works great! Doug s/v Callista > > My water tank vent empties into the galley sink. My old boat vent emptied > > into the shower stall. I like this arrangement because it does not let in [quoted text clipped - 10 lines] > bilge a VERY poor second. At least both of those locations allow you to > flush out the vent by overflowing the tank out it each time you fill it. > Not sure how grease etc is going to leap out of the galley sink into > the vent Prob'ly won't if you never fill the sink to wash dishes or allow any dirty dishwater to go down the drain. > Our tanks are vented into the head sinks via a spout in > each. Easy to see when the tanks are full when filling... As long as you're in the head while they're filling... or there's no plug in the sink if you aren't. I think the vent should go out the hull. But hey...they're YOUR boats, so whatever floats 'em for YOU is fine with me. SignaturePeggie ---------- Peggie Hall Specializing in marine sanitation since 1987 Author "Get Rid of Boat Odors - A Guide To Marine Sanitation Systems and Other Sources of Aggravation and Odor" http://69.20.93.241/store/customer/product.php?productid=40&cat=&page=1 Comments below. Doug s/v Callista > > Not sure how grease etc is going to leap out of the galley sink into > > the vent > > Prob'ly won't if you never fill the sink to wash dishes or allow any > dirty dishwater to go down the drain. You don't understand how the vents are installed. They are not plumbed into the drains. Just empty into the basins. > > Our tanks are vented into the head sinks via a spout in > > each. Easy to see when the tanks are full when filling... > > As long as you're in the head while they're filling... or there's no > plug in the sink if you aren't. I suppose that not leaving a plug in the drains is a requirement. Not really a problem. > I think the vent should go out the hull. But hey...they're YOUR boats, > so whatever floats 'em for YOU is fine with me. To be really safe, put them in the cockit. That way they will drain out the scuppers and not be so prone to taking in saltwater. Another option is to put them up the mast a bit. I know someone that did this. Overflow will go out the fill rather than out the vent. Problem solved forever. > To be really safe, put them in the cockit. That way they will drain > out the scuppers and not be so prone to taking in saltwater. Another > option is to put them up the mast a bit. I know someone that did this. > Overflow will go out the fill rather than out the vent. Problem solved > forever. I set my water tank vents on the outside of the cockpit coaming just down hill from the deck fill. When the tank is full water flows across the side deck and out the scupper. You do have to be careful to locate the vents so that the overflow will not flow back into the deck fill. Chartered a boat once that had the vent lines run up inside the stantions with a vent hole just under the top lifeline. Worked great but if you were holding the hose when the tank overflowed it would spray you in the face. :-) SignatureGlenn Ashmore I'm building a 45' cutter in strip/composite. Watch my progress (or lack there of) at: http://www.rutuonline.com Shameless Commercial Division: http://www.spade-anchor-us.com Air vents for the water tanks are just for venting air (to allow air to enter when water is being pumped out and to allow air to escape when filling the tank) not for water escape. If you are using them for water escape, be very careful. WHen filling the tanks you better NOT have too much pressure. Even .5 psi can put a lot of pressure on the tops of tanks - 2'x 5'lid = 24"x 60" = 1440 sq in x .5= 720 pound of pressure, enough to cause the lid to buckle and separate. When filling, we always remove the input vent on the top of our tanks and 'watch' the water filling. Even the exhaust vent in the tanks can cause pressure. Hanz >> To be really safe, put them in the cockit. That way they will drain >> out the scuppers and not be so prone to taking in saltwater. Another [quoted text clipped - 11 lines] > but if you were holding the hose when the tank overflowed it would spray > you in the face. :-) Not likely that too much pressure can build in the vent while overflowing out the fill. Doug s/v Callista > Air vents for the water tanks are just for venting air (to allow air to > enter when water is being pumped out and to allow air to escape when [quoted text clipped - 25 lines] > > but if you were holding the hose when the tank overflowed it would spray > > you in the face. :-) >WHen filling the tanks you better NOT have too >much pressure. Even .5 psi can put a lot of pressure on the tops of >tanks - 2'x 5'lid = 24"x 60" = 1440 sq in x .5= 720 pound of pressure, >enough to cause the lid to buckle and separate. I was thinking of writing along this line because I had that issue with my fuel tanks. It's easy to get a lot of pressure. Say a water tank vent outlet (or filler cap) is 6 feet above the tank. By the time water comes out the vent or filler cap you have about 1/5 atmosphere or 3 psi in the tank. Fuel is similar, probably 75% of that pressure. My tank vents are fairly high up a coaming on a center cockpit and the fuel tanks are under the sole. There's 7-8 feet of head. My tanks oozed around some fittings that were not used to pressure and around an inspection port that wasn't really adequately gasketed. > Some people have expressed concern that it opens up the risk of > getting seawater contamination in heavy seas and that the boatbuilder > probably chose to do this on purpose. Do you get sea water into your fuel tanks? They are certainly vented overboard! The boats I have owned have all had the vents mounted through the hull. If you want to assure that you don't get any seawater back in the vent then run the vent line as high as you can, but a vented loop at the top, then run the line back down to the hull. There is no way that any significant amount of spray is going to migrate several feet up a hose. Rod Comments below. Doug s/v Callista > > Some people have expressed concern that it opens up the risk of > > getting seawater contamination in heavy seas and that the boatbuilder > > probably chose to do this on purpose. > > Do you get sea water into your fuel tanks? They are certainly vented > overboard! Not necessarily. Current school of thought is to vent them in the cockpit. No problem with overflow overboard (big fine). No problem with saltwater infiltration. There was an article about it in the past year or so in Cruising Worls or PS or ON. > The boats I have owned have all had the vents mounted through the hull. If > you want to assure that you don't get any seawater back in the vent then run > the vent line as high as you can, but a vented loop at the top, then run the > line back down to the hull. There is no way that any significant amount of > spray is going to migrate several feet up a hose. Spray isn't the problem. Immersion is the potential problem. > Rod > > Do you get sea water into your fuel tanks? They are certainly vented > > overboard! > > Not necessarily. Current school of thought is to vent them in the cockpit. > No problem with overflow overboard (big fine). No problem with > saltwater infiltration. Who's school of thought is it to vent gas tanks into the cockpit? It is certainly illegal to have portable tanks (which place the vents inside the boat) on anything other than an open boat with an outboard. I would think that it would also be illegal to vent the tank inside the boat. It certainly doesn't seem like a wise idea. A properly installed vented loop will prevent any back flow of sea water into a line. No need to create additional problems and/or hazards. Rod |
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