Location of diesel vents?

[mm Iowa, USA]

It has come time to locate and install the vents for the diesel tanks. There are two tanks, one each, port and starboard. The fills are located in the side decks. I am using Vetus splash guards. The top of the tanks are about 16 inches below the underside of the side decks. This is new construction, a center cockpit sailboat. The tanks are outboard of the cockpit.

Where do I locate the vents? If in the topsides, they will be about 4 inches below the deck due to the width of the carlin and deck thickness. There would only be room for a 3-inch high inverse loop. If ever sailed “rail down” I fear water incursion into the tanks. If located in the cockpit combing, there may be the constant odor of diesel whenever one is in the cockpit. The third choice is to locate the vents in the topsides, but loop the hose to the top of the combing. This does not feel like a clean solution and adds about 4 feet onto the length of the vent hose.

This is only my second boat and I need your thoughts, suggestions.

TIA

mm

[Hwyl]

I like them high, I've seen them on Dorade boxes and have seen them in stanchions (with a water trap below).

[JimConlin]

Here's an example of tank vents in stanchions. A nice detail.
http://www.santotoday.com/gowestsf/s...tank_vents.htm

[SV Papillon]

This is what I am going to do, similar to my last boat. Tank vented in cockpit locker next to fill station also in locker, both in a single containment or possibly a small trap-tank on the vent before the containment, both with isolation valves. Vent should be min 1" fill 1 1/2". IMHO tanks should be pressed when ever possible, you should have a permanant containment when filling and be able to fill at a decent rate without worry. Also daytanks fuel vents etc do not belong in superstructure of the boat including stantions, just my opinion.

Jake

[seo]

A vent on the outboard side of the cockpit coaming works pretty well. In most cases, there isn't a lot of smell coming out of the tank vents. If you're determined to go out through the side of the hull, your idea of running the loop up inside the coaming to give it plenty of "freeboard" when the vessel is heeled makes a lot of sense. The vent hose is pretty cheap. Another good location is on the transom/counter. Fumes are vented downwind of the rest of the boat, and even when heeled way over the transom is not immersed on most boats.
The idea of running the vent riser up inside a stanchion base is very clever. Remember that NFPA standards require a "flash screeen" like what you see in the outlets of the vents you can buy at the store. No matter how unlikely that a spark could get inside a stanchion, those are the rules. If I went with that design, I'd fit a little cap on top of the vent tube, to prevent drips inside the stanchion (water drops running along the lifelines, seeping into the inside of the stanchion, and then dropping, PING!, right down your vent riser.
Two other points on tank vents:
1) Make sure that the vent line goes steadily up to a high point, and then steadily down to the discharge fitting. No dips that can trap water. I puzzled for quite a while one winter day trying to figure out why a fishing boat's engine kept losing prime. Turned out that there was a dip in the vent line, filled with ice.
2) The reason I found that ice block was that I was using a trick that I invented (like the wheel). When trying to get fuel to flow up through the tank fitting, and then flood the Racor filter and engine filters so that they can be totally purged of air, I got in the practice of taking off the vent tube (at the hull), and blowing some pressure into the tank, which forced the fuel out through the feed tube. In this case, the vent tube was obviously blocked, and the solution was pretty easy.

[SV Papillon]

Not that anyone would intentionally spill fuel...but it can happen. It should be noted that in the PNW Wa state and Ak in particular the clean water policy and enforcement have gotten extremely strict. This is mostly in large metro areas but has been growing, IE they are going after people for small spills, a half a cup, and giving them substantial fines. I would put as much thought into containment as I would into preventing water getting in. Also if this is a cruising boat picture yourself filling your tank in a rolling anchorage with a large Baja filter on the deck fitting using some weird ass jerry can that the local panga dude has, and not spilling anything.

Jake

[kc8pql]

I put my vents on the back wall of the cabin. Cabinets on the inside cover the hoses.

[johngsandusky]

Mine are in the top center of the transom.

[mm Iowa, USA]

Jim, locating the vents inside the stantions was on my list of building tips to incorporate in this build. Final location of the stanchions and their proximity to the carlins eliminated this possibility.

Jake, I am hoping the large splash guards work as well as they used to be advertised, to stop spills from happening.

This boat has a center cockpit. There is no way the proper slope can be maintained to the transom.

If several of you can locate your vents in and/or beside the cockpits, I will probably place them on the outside of the combing.

Thanks for the replies so far. --mm

[GWB]

Mine go into the lazarette, one from each side into a tee in the middle of the boat then into a catchment bottle (vented into the lazarette)
Never smell anything and water cannot enter... except if that would be the least of my worries...!

[boattruck]

Iowa, Tank vents generally work to let air in, the only time you stand much chance of experiencing odor is as you fill up, our boat has the vents built of copper loops on the cockpit coaming and we have never experienced any odor... Cheers, Steve

[seo]

Mine go into the lazarette, one from each side into a tee in the middle of the boat then into a catchment bottle (vented into the lazarette)
Never smell anything and water cannot enter... except if that would be the least of my worries...!

This may be a system that works well, but it doesn't comply with the standards. I personally can find fault with the standards. On the small side, they're still steeped in the paranoia of exploding gasoline-fueled boats. (Been there, lugged crispy boaters to ambulance. Bad scene) On the other end, they may have been influenced by some of the more colorful tugboat and supply boat extravaganza, with diesel fuel shooting fifty feet out of a vent stack because some jackass in the engine room forgot to shut off a transfer pump.
All that said, the rules are still the rules. If there's a casualty involving a fuel system, and the system isn't 100% ticky-boo, then the underwriter has a card in his hand. Will he play the card? Against who will he play it? Dunno, but he has the card.

[seo]

Iowa, Tank vents generally work to let air in, the only time you stand much chance of experiencing odor is as you fill up, our boat has the vents built of copper loops on the cockpit coaming and we have never experienced any odor... Cheers, Steve

Steve, you make a very good point. With very big tanks, in places with a big temp variation, strong sunshine, black hull, yadayada, you might see some discharge on a hot day. But I don't think we're talking here about a boats with 42,000 gallons of integral steel tanks in a black-painted hull.

[kc8pql]

I've never smelled diesel from my vents. Two 40 gal. tanks.

[Todd D]

Mine are in the cabin house sides about 18" above the side decks. The hoses loop up about 6" above the vents. Never smell diesel even when refueling.

[GWB]

This may be a system that works well, but it doesn't comply with the standards. I personally can find fault with the standards. On the small side, they're still steeped in the paranoia of exploding gasoline-fueled boats. (Been there, lugged crispy boaters to ambulance. Bad scene) On the other end, they may have been influenced by some of the more colorful tugboat and supply boat extravaganza, with diesel fuel shooting fifty feet out of a vent stack because some jackass in the engine room forgot to shut off a transfer pump.
All that said, the rules are still the rules. If there's a casualty involving a fuel system, and the system isn't 100% ticky-boo, then the underwriter has a card in his hand. Will he play the card? Against who will he play it? Dunno, but he has the card.

I hear you......but I'll take my chances. I have used this in rough weather and get no sploosh..my return line switch is right next to the supply line switch, so catches your eye. (when I say switch I mean 2 way ball valve)

[seo]

As said above, your system probably works fine.
I think the standards are pushed by very real anxiety about gasoline vapors, which is a very real thing. And also by the very real problems found on tank ships, where the condition of the P/V valves (pressure/vacuum) are a real subject of attention to ABS, USCG, and any tankerman who doesn't want a cracked hull or an uncontrolled blow off of cargo vapor, or both. Having spent many happy months riding around on top of 7 millions gallons of gasoline I came to believe that they weren't just making stuff up.
But a forty gallon diesel tank, non-integral to the hull, is a very different kennel of dogs. Or was that a kettle of fish?

[wizbang 13]

My 40 gal diesel tank vents right up to the cabin deck beams. Lil rubber hose, never gave it a second thought in 3 decades. Just avoid looping so it do not "burp".
Yup, no problem.

[skaraborgcraft]

I had a 5 gallon diesel tank which was a cylinder shape. It had a peice of copper pipe soldered to the fill screw cap that was about 6 in high. Tank was in the middle of the hull under the cockpit sole,accessable from inside,it never leaked.