Tank vent question

109jb

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Just a curiosity question. I'm re-building my 1988 16' Sea Ray and am getting ready to replace the fuel tank vent hose. Don't worry I'm replacing it just as it was from the factory, but am curious as to why the vent hose is 5/8" I.D. That is huge and way more than it would need to be simply for venting the tank, so there has to be another reason for it. Anyone know why??
 

Bondo

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Re: Tank vent question

Ayuh,... 5/8" Ain't so big when you're filling it with a 3/4" hose...

The hose should turn Up from the vent fittings, looping to go Down to the tank....
That'll keep the Water out...
 

109jb

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Re: Tank vent question

I might buy that answer but I don't because the screened opening in the thru hull fitting is only 3/8" diameter. 3/8" diameter and screened, so it will flow about like a 1/4" opening.
 

J. Mark

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Re: Tank vent question

Just a guess here, but 3/8 fuel line flows liquid fuel. If the vent line was the same size, there might be a greater tendency for a siphon to occur when a tank was overfilled resulting in fuel continuing to flow out the vent. By using a larger size line a siphon would not be as likely to occur as the pressure drop going into the larger line would break the siphon.

or maybe there was a sale on 5/8ths fitting and line a long time ago and people just got used to doing it that way
 

erikgreen

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Re: Tank vent question

Is the screen on the hull flat, or one of Sea Ray's bolt head type with screens on each side? Maybe someone replaced it?

I wouldn't question why the line is 3/8", but rather why the fitting is too small.

Mine's the same size, it does ok when I fill the tank, but I can still hear the air hissing out. Smaller would maybe cause a pressure build up in the tank while filling...

Erik
 

Mark42

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Re: Tank vent question

The vent is 5/8 so it won't clog easily by any junk in the tank.
 

PiratePast40

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Re: Tank vent question

I think Bond-o has the simplest answer but forgot to mention why the "air gap" is important.

When kids help wash the boat, they can't resist spraying water full force up into the shiny thing on the side of the boat. The loop (air gap) helps keep water and soap out of the gas tank :D
 

109jb

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Re: Tank vent question

Is the screen on the hull flat, or one of Sea Ray's bolt head type with screens on each side? Maybe someone replaced it?

I wouldn't question why the line is 3/8", but rather why the fitting is too small.

Mine's the same size, it does ok when I fill the tank, but I can still hear the air hissing out. Smaller would maybe cause a pressure build up in the tank while filling...

Erik

The thru hull fitting has of course a 5/8" barb on the inside for the hose, and on the outside it has a single aft facing hole about 3/8" diameter with screen in it to keep bugs out.

I really don't think the fitting is too small because I never had any problem putting gas in the boat.

As for crud. I can see that possibly, but again, the crud would have to getinto the tank and then go up and out the vent to plug the hose. Or, it would have to come in through the screened thru hull fitting, go up the loop in the hose...

Again, I'm not changing the design. Just curious. Bigger isn't really going to hurt anything.
 

Bifflefan

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Re: Tank vent question

5/8 does seem to be a tad large. but thats an engineer for you. "If its worth doing,,Its worth over doing".

As for the reasons given, none of them seem logical to me, but thats me.

Id just stick with the size you have and chalk that one up to the "wonder why" catagory.
 

109jb

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Re: Tank vent question

5/8 does seem to be a tad large. but thats an engineer for you. "If its worth doing,,Its worth over doing".

As for the reasons given, none of them seem logical to me, but thats me.

Id just stick with the size you have and chalk that one up to the "wonder why" catagory.


Yep. That's where I'm at. The 5/8" hose is already in and ain't coming out. BTW. I am an engineer and none of the proposed explanations make sense to me. I was just curious if maybe there was a regulation requiring it, or a logical explanation that makes sense given that the thru hull fitting is the "bottle neck" in the system. I guess I won't question it anymore and just get on with getting the deck in.

BTW, I did the 5/8' hose and opted to not make a removable panel for the fuel tank. I did clean it out and it is in good shape. I didn't even put in an access for the fuel level sender. If I have to get to it I will just have to cut the section of floor out. Both are risks I am willing to take in order to have fewer places where water can get to the wood underneath.
 

chrishayes

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Re: Tank vent question

Yep. That's where I'm at. The 5/8" hose is already in and ain't coming out. BTW. I am an engineer and none of the proposed explanations make sense to me. I was just curious if maybe there was a regulation requiring it, or a logical explanation that makes sense given that the thru hull fitting is the "bottle neck" in the system. I guess I won't question it anymore and just get on with getting the deck in.

BTW, I did the 5/8' hose and opted to not make a removable panel for the fuel tank. I did clean it out and it is in good shape. I didn't even put in an access for the fuel level sender. If I have to get to it I will just have to cut the section of floor out. Both are risks I am willing to take in order to have fewer places where water can get to the wood underneath.


I am in the same boat sorta...I am not putting an access to my tank either. I am however leaving access to all of the fittings and sender. I figured that after reading a bunch of "rotten deck, now what" threads to know that most rot starts at ski lockers and tank access holes therefore, I will have none of those on my boat! guess if I ever have a problem I will have an access door then:rolleyes:
 

109jb

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Re: Tank vent question

I am in the same boat sorta...I am not putting an access to my tank either. I am however leaving access to all of the fittings and sender. I figured that after reading a bunch of "rotten deck, now what" threads to know that most rot starts at ski lockers and tank access holes therefore, I will have none of those on my boat! guess if I ever have a problem I will have an access door then:rolleyes:

Yep. The way my tank is mounted I can get to all of the fittings except the vent. I thought about putting a deck plate over the fuel sending unit, but I figure that if it ever goes bad I will cut a hole then and put the deck plate on at that time. Basically, leave the deck as solid as possible as long as possible is my approach.
 

Mark42

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Re: Tank vent question

There are plenty of inexpensive water tight inspection ports that are flush mount. You would be wise to install them for the fuel sender and hose connections.
 

109jb

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Re: Tank vent question

There are plenty of inexpensive water tight inspection ports that are flush mount. You would be wise to install them for the fuel sender and hose connections.

I know about the water tight deck plates and such. However, IMO, a water tight deck plate is not as water tight as not having a hole there in the first place. As I said, I can access all connections except the vent and fuel sender. If I ever need to access them it will take me about 1 minute with a circular saw. I installed the vent hose by pushing the hose on the fitting as far as it would go and installing 3 hose clamps, one of which is a spring type hose clamp that should maintain clamping pressure on the hose no matter what. I am confident in its security. The only other reason to access it would be if the entire hose needed replacement. If I ever need access it is a simple matter to cut a hole and I know exactly where the sending unit is so I could put a deck plat in at that time. For now, no holes. Again, a risk I am willing to take.
 

chrishayes

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Re: Tank vent question

Yep. That's where I'm at. The 5/8" hose is already in and ain't coming out. BTW. I am an engineer and none of the proposed explanations make sense to me. I was just curious if maybe there was a regulation requiring it, or a logical explanation that makes sense given that the thru hull fitting is the "bottle neck" in the system. I guess I won't question it anymore and just get on with getting the deck in.

BTW, I did the 5/8' hose and opted to not make a removable panel for the fuel tank. I did clean it out and it is in good shape. I didn't even put in an access for the fuel level sender. If I have to get to it I will just have to cut the section of floor out. Both are risks I am willing to take in order to have fewer places where water can get to the wood underneath.

There are plenty of inexpensive water tight inspection ports that are flush mount. You would be wise to install them for the fuel sender and hose connections.

109jb I agree with the above! I would not have covered over mine if I couldnt gain access to all of the servicable equipment. Just a thought. THink of how crazy it would be to cut a hole above a fuel tank that was full of gas:eek:id do it now.
 

109jb

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Re: Tank vent question

109jb I agree with the above! I would not have covered over mine if I couldnt gain access to all of the servicable equipment. Just a thought. THink of how crazy it would be to cut a hole above a fuel tank that was full of gas:eek:id do it now.

The bottom side of the floor is a good 1-1/2 inches above the top of the tank. The closest anything relating to the tank gets to the underside of the deck is the vent which is still 1/2" below the bottom of the deck. If I have to get to the vent I will make a whole tank access panel and I can easily adjust the depth on my circular saw within that tolerance. If I have to get to the fuel sender only I will break a jigsaw blade to a length that won't allow it to get to the tank and jigsaw a hole for a deck plate. No big deal and again I have no worries about doing it. The aft 4 inches of the tank is open and I can get to it. This is where the fuel fill and supply for the engine are. They are not covered. I'm not worried about it at all if I have to cut. The deck is already on and I'm proceeding with my original plan. I have thought about all of the ramifications and as I said I will cut the floor if I ever need access.
 
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