Tank vents

zoidberg

zoidberg

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I've seen diesel-tank vent tubes looped and secured close under the stern deck on sailboats, and others where a s/s tube with wire gauze is fitted, to project slightly above the deck.
Could some knowledgeable soul detail the pros and contras of each approach?
 
Not entirely clear what you’re describing. When you talk about looped and secured by the stern, do you mean that the vent pipe doesn’t actually exit the hull? If so, then any fuel overflow will fall down into the bilges where it’ll stink the boat out. Having a stainless (or more usually chromed brass) vent through the hull means that any diesel spillage is dumped outside the hull. Does that make sense?
 
I'd rather have a diesel vent where I can sit with one hand on the fuel supply nozzle and the other with a clump of kitchen roll to catch the spill. Even better if it were designed to spill into a recess that could contain the spurt that I miss because I was thinking about something else. Most that I can remember are in the coaming and the spill gets to the toerail and along to the rope around the stern cleat within milliseconds.
 
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The main purpose of the vent is to let air into the tank as diesel is consumed. For this use it should be perfectly ok to end the tube inside the boat. But, when you fill from a high capacity pump a lot of the air that is displaced is forced out through the went. If you accidentally overfill, a lot of diesel foam will come out of the vent tube, and you do not want to have that in you locker or somewhere else in the boat.
If the tank is ventilated though a opening at the stern, there is a potential for getting sea water in the diesel if you are hit by a big wave from aft. To avoid this you may put a T connection in the tube with a closed half a meter tubing that collect and trap any water going the wrong way. The wire mesh is there to keep spiders out and act as a flame barrier in case you used on a bensin tank.
I recently saw in an X-yacht, the diesel tank was vented though the pushpit. Several 6mm holes were made in the underside of the top horizontal tube of the pushpit and the hose from the tank was connected to one of the hollow bolts. Neat
 
In my view the diesel vent must be as high as possible.

I would place a vent with a primitive gauze as high under the outside of the cabin roof.

On my boat I have a wheel house and my vents are just under the outside the wheel house roof.

I have also seen tank vents mounted through the side of a hatch garage.

Both of these help to stop and spills with filling or when the boat heals but allow and spillage to be mopped up before it can spill into the sea.
 
Thanks for those thoughts. This is a 'major 'refurb' and I've removed the old protruding brass/gauze vent which exited up through the strern deck. The question of how best to replace it, and what with, arose.... and hence the question.

I think I'll get a replacement steel+gauze end piece, but secure that INSIDE the stern locker up as high as practicable - then see how I get on with that. I can drill an 'ole and remount it 'externally' should that become desirable.
 
How about taking a clear plastic bottle and secure the end of the hose, with or without the end piece, inside the bottle, so that any diesel spill is captured by the bottle. If it stays dry, it is all well, but if diesel spill is a problem, you at least don't have to mop it up.
 
You could just add a fuel trap to the vent (required by USCG in US on all new builds). They work, problem solved. Many designs.

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zoidberg said:
I think I'll get a replacement steel+gauze end piece, but secure that INSIDE the stern locker up as high as practicable - then see how I get on with that. I can drill an 'ole and remount it 'externally' should that become desirable.
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That needs to be higher than the filler tube cap otherwise it will overflow during some filling operations.
It must never be in a situation where fuel can run onto the cockpit sole from the locker floor. If it does it will become a skating rink & be dangerous when the boat heels. It will get on the soles of the crews shoes & be transferred below & make the cabin sole slippery as well.
Anything in the locker that gets coated in fuel will stink. Get it on fenders ropes & the girlfriend's swimming gear & it will be all over the crew's hands before you know it.
 
Yes, Day'Dreamer, and thank you.
There's something of a dilemma here, and I'm feeling my way towards the best compromise.

The product 'Thinwater' has shown may be a good answer.... thanks.
 
Been away for some time, so don't know what Zoidberg's boat is. I'd agree that ideally a tank vent should lead to the highest point you can manage. As mentioned already this could involve threading a tube up the pulpit uprights. That should give at least 24 inch head. If you have or are thinking of one of those arches you can get even higher!

Rob.
 
When we got our current boat the fuel was badly contaminated and I had to get 700 litres pumped out at Tommy Neilsons Shipyard in Gloucester Docks, and not only pay for the pumping but also a 200 quid envioromental charge and for 400 litres of fresh fuel.

The 400 litres was introduced by a small electric pump from 2 X 205 Litre drums of red diesel. The fuel gauge was removed so the air vented as the tank filled was from that aperture, not the normal tank vent. The fuel gauge was replaced.

A couple of hours down the Canal was a fuel depot where another 400 litres was added - it has a huge tank capacity, almost 900 litres.

It kept blowing back from the filler aperture - the chromed brass shielded vent on the transom was blocked with insect nests.
I managed to clear this with a thin wire. The air hissing out under pressure cleared the rest.

Now, when filling with water or fuel - the vents are close to each other - I block one for a few seconds with a fingertip, the pressure builds up as the tanks fill, and then take my finger off. A satisfying hiss tells me the pipes and vents are clear.

Our boat is a long keeler so the large tank is right in the bottom of the vessel, just above the bilge sump and keel. The fuel vent never vents fuel, but the water ones vent water.
 
The US EPA started requiring evaporative emissions controls (carbon and vent controls) on gasoline fuel boats a few years ago. Although the rules do not apply to diesel, some of the overfill-prevention gadjets are pretty handy. It makes filling the boat more like filling your car, which is nice.
 
Both of my tanks vent into the anchor locker.
I have an optometric detector that senses when the fuel reaches within a couple of inches of the tank top. (However, I can't find the operating instructions and I can't identify it! It works by sensing total internal reflection once wetted.)
 
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