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Discussion Starter · #1 ·
Thinking of moving my diesel tank vent inboard. It's now at the back of my double-ender's hull. My idea is to re-route the hose and place the vent on the outside of the cockpit coaming, above the filler cap.
Advantages: 1. I can see it and clean it up if it overflows when I fill up. 2. Any overflow will stay in the boat, not create an illegal oil slick. 3. I can more easily keep out any blockage (ie from insect nests etc) that could impede fuel flow to the engine 4. I might hear the fuel whistle better as I fill the tank.
Disadvantages: Don't know--any you can think of? Would the smell be that powerful? I figure they're always outboard for a reason--but I know what it is.
Thanks in advance for your thoughts, insights or experiences.
John V.
 

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The only downside I can think of is that if the new location of the vent isnt high enough between the cockpit combing and the bulwark, any boarding wave that 'sloshes' rearward along the deck may begin to fill the vent.

I have a cowl vent (for a propane locker) in this area on a Ty37 and sometimes when the side deck becomes fully 'awash', I get minor seawater flooding into the propane locker .... which has a small bottom drain.
 

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Good point, Rich H. I'd thought of the location at the aft end of the hull as exposed to waves, but a flooded side deck is possible, too. I'll see if I can mount it higher than the bulwark.
Thanks.
On a boat with high bulwarks, and the side deck narrowing as the space goes aft, you can get quite a hydraulic ramming effect when the deck is briefly filled to the top of the bulwarks and the water is moving aft and cant drain fast enough though the scuppers.
FWIW - Bob Perry on many of his earlier designs, seems to mount the tank vents quite high on the cabin/coach roof sides and well above the level of the bulwarks ... probably in mind so that they are never 'underwater' even if the decks are momentarily flooded to the level of the high bulwarks.

Just a passing thought - If you have a boom gallows on your boat, Id perceive that running a vent hose well up inside one of the standing legs of a gallows could be a good place to put a tank vent. High inside a hollow and 'vented' stanchion would be another possibility.
 

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a. Yes, the smell will be bad and will settle in the boat.
b. For any flammable fuel this is a very serious code violation. Hope no one ever fills gasoline by accident; very bad, easily a one-time-only mistake. Even winter blend can be scary.

A much simple solution might be to install a Raycor Lifeguard separator or equivalent. No more overflows, depending on the geometry.
 

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Discussion Starter · #7 ·
Just a passing thought - If you have a boom gallows on your boat, Id perceive that running a vent hose well up inside one of the standing legs of a gallows could be a good place to put a tank vent. High inside a hollow and 'vented' stanchion would be another possibility.
That's not bad. I could go up inside the wet locker and through the cabin side. That way I'd also have clearance for a high loop.
I wonder if, as pdqaltair says, the smell would be a problem in that position.
 

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If the engine is drawing fuel ... probably not
If the tank is warming in the noonday sun, it will probably stink if there's no air blowing across the vent area ... just like any other boat with a fuel tank vent.

Having a 'high loop' is good if you have the space.
If there's space enough for a loop and you have a 'big' tank, Id recommend to apply a hydrophobic 1-2µM 1 sq. ft. 'capsule' filter to prevent the ingress/aspiration of fungal spores and bacteria. Ditto on 'water tanks' but 0,45µM.
 

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Discussion Starter · #9 ·
I thought it would be an easy winter project but some of the issues you've all raised are worth further exploration. So, I think I'll wait till summer and experiment with a length of hose.
Thanks for all of your input.
John V.
 

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My diesel vent would suck water when motor sailing in following sea's, which was not good. I did not have room for a large loop in the vent hose, so I vented the tank inside the boat with a over flow bucket at the end of the vent hose. When I find the time I will mount the vent hose high up inside the radar mast. Which will take care of the smell.
 

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If the engine is drawing fuel ... probably not
If the tank is warming in the noonday sun, it will probably stink if there's no air blowing across the vent area ... just like any other boat with a fuel tank vent.
I am concerned about during fueling. Normal venting would be insignificant.

In my mind, any design where fuel comes out the vent is unacceptable. Likewise any design where fumes can drain into the cabin or bilge. Like electrical systems, you don't "get around to fixing it right" later. Fuel systems are important and these problems are a mater of design. I have never owned a boat with either fault.
 

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I am concerned about during fueling. Normal venting would be insignificant.

In my mind, any design where fuel coming out the vent is normal is unacceptable.
Agreed... I think this is a case where perhaps the single most overpriced item in the West Marine catalog is still an excellent investment... :))

fortunately, it can be found elsewhere for a bit less, Hamilton Marine has one of the lower prices, but still absurdly overpriced, considering it's little more than a piece of plastic... Still well worth the money, I'm always mystified why they're not more common. I have never found one on any boat I've ever delivered, sure would have been nice to have on the Valiant 42 I ran recently, those things are always a challenge to fill without a bit of a spill...

Fuel Whistle Fits All Boats 5/8"" Fuel Lines



Only downside, it won't be very effective when filling your tank from a jerry can, especially if using a filter... You need a consistent and reasonably high rate of fill from a fuel hose to produce the whistling sound...

As to the original question, I believe vents should always be above deck level, at a minimum... I also like to have a small 'cap' out of PVC or similar that can be placed over the vent in heavy weather - with of course a fail-safe 'reminder' arrangement to remove it prior to running the engine again :)

I've situated my vent high up inside one of the cockpit coaming cubbies, well out of the weather, works well for me...
 

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I am concerned about during fueling. Normal venting would be insignificant.

In my mind, any design where fuel comes out the vent is unacceptable. Likewise any design where fumes can drain into the cabin or bilge. Like electrical systems, you don't "get around to fixing it right" later. Fuel systems are important and these problems are a mater of design. I have never owned a boat with either fault.
Theres not much one can do vs. normal diffusion of fuel oil vapor through a vent other than application of carbon granule, etc. vapor traps (a quite high maintenance item).
The vapor pressure of #2 diesel oil is quite low in comparison to other volatile fuels. Youll probably have more unburnt oil vapor due to incomplete combustion coming out the engine exhaust system than from an open vent for a quite a long time. If this is important to you, you can always blanket the fuel oil with nitrogen gas or one of the nitrogen containing 'bubble/foam compounds' used to blanket UHP technical oil, etc. storage tanks. Imagine for a moment hundreds of millions of home fuel oil tanks that are directly vented to the atmosphere.

As regards to liquid fuel coming out a vent ... that is usually a result of poor tank design/geometry where the inlet nozzle of the tank discharges from the top of the tank directly as an open flow to the bottom of the tank or its partially full contents. Such creates and air/liquid emulsion as bubbles/foam caused by the high surface tension of the oil versus 'velocity' in the presence of air). A tank inlet nozzle should obviously be at the top but the discharge should be continued towards the bottom and the outlet of that inlet pipe 'should' discharge onto the side/bottom (at an angle) to prevent 'foam outs' - IMO. Still foam-out can be adequately reduced by the installation of a 'bubble / foam' trap in the vent close to the inlet nozzle ... just a tight bundle of small sharp hollow 'needles' inserted in the (vertical) vent line (with gravity liquid drain port on the upstream side), the bubbles becoming 'pierced' thus collapsed, etc. Such is quite common in fermentation technology where 'foam outs' from fermentation vessels is a common possibility.
The real issue of fuel oil foam-out is the use of 'high speed' high volume flow pumps and nozzles ... incompatible with most 'sailboat' and small boat tank design ... so high speed fuel delivery systems should be prudently avoided unless the fuel flow regulation can be quite SLOW to keep the oil velocity within reasonable limits - a fuel depot problem.
Further, for that high flow pump situation .... never operate such a high speed nozzle by yourself at a depot; but, request that the 'dockhand' operate it, as if he/she creates the spill, its the depot's environmental fine and penalty problem and not yours. I always tip the jockey on those high speed nozzles.
Ultimately such high speed nozzles will probably be required/mandated to have a 'switchable' control (orfice plates, etc.) to limit the speed of flow for when filling 'small' boat tanks.

;-)
 

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I also like to have a small 'cap' out of PVC or similar that can be placed over the vent in heavy weather - with of course a fail-safe 'reminder' arrangement to remove it prior to running the engine again :)
A good way to implode a thin walled tank during 'great' atmospheric temperature swings ... as most boat 'fuel tanks' arent 'vacuum rated' and dont have 'rupture discs' to relieve such vacuum when 'over pressurized (vacuum)'. The larger the tank's external surface are the greater the risk of implosion. A 2 psi difference would equate to ~300 pounds per square foot of tank surface. Common lift pumps in good condition can generate upwards of 6psi vacuum or about 900 pounds per square foot. :-(
 

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Install a fill whistle on the tank fill, install an aft facing vent just below the fill inlet on the outside off the boat and you shouldn't have any problems. Here's the one I use for my gas tank and never had a problem of any kind.



Good luck,

Gary :cool:
 

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Factoid: Only a very small vent hole is needed for day-to-day and engine running. Like a pinhole or a use a tiny filter thing like on sealed electronics. For fueling, bigger the better unless the fill pipe is short, vertical and straight.
 

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A good way to implode a thin walled tank during 'great' atmospheric temperature swings ... as most boat 'fuel tanks' arent 'vacuum rated' and dont have 'rupture discs' to relieve such vacuum when 'over pressurized (vacuum)'. The larger the tank's external surface are the greater the risk of implosion. A 2 psi difference would equate to ~300 pounds per square foot of tank surface. Common lift pumps in good condition can generate upwards of 6psi vacuum or about 900 pounds per square foot. :-(
Good advice, as always...

Fortunately, I don't believe my tank is "thin-walled", nor does the PVC cap I place over the vent to deter the possibility of water intrusion create an airtight seal... It's really just a splash guard, little more, I'm sure if my vent was ever fully immersed, the cap would float away, and water would intrude...

Still, I'd want to remember to remove it, before running the engine...

:))
 

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Good advice, as always...

Fortunately, I don't believe my tank is "thin-walled", nor does the PVC cap I place over the vent to deter the possibility of water intrusion create an airtight seal... It's really just a splash guard, little more, I'm sure if my vent was ever fully immersed, the cap would float away, and water would intrude...
:))
No 'vacuum or pressure rating' (physically tested to 1.5 to 2X that value) = 'thin walled'. And, youre left to 'guess' how much internal vacuum will cause 'the distortion' --- could be a quite costly mistake on a BIG tank with flat sides, top, etc.

I like your idea of that 'spray cap' ... belt and suspenders (and maybe velcro, too) for 'important stuff'. :)
 

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Imagine for a moment hundreds of millions of home fuel oil tanks that are directly vented to the atmosphere.
;-)
Perhaps a note of sarcasm? Fair enough.

However, Home heating oil tanks are vented outside of the home, according to IBC and NFP. NEVER inside the house.

Case in point. Some years ago, my company contracted to clean up a home where the basement had been filled with 1500 gallons of diesel, because the vent was in the basement. The fuel company was NOT found responsible.
 
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