I completely agree with you, the tank will breathe as the temperature changes but how much?
I'd guess about 10% would more than cover it and that amount is nowhere nearly enough to explain the quantity of water you had in the tank.
Even a 50% air change every night will not explain it.
There's not much more to say about this unless someone else can add some input, perhaps we should call in an expert from a scientific forum, there's plenty of them out there.
If you're happy to live with it I say good for you, I wouldn't.

BTW, being a 1" breather I'd be looking at that very carefully remembering that the transom outlet must be way higher than where it fits into the tank.
Are you sure the water can't get in there mate?

Only time will tell Fed.

Like I said occationally I may have to drain a little water from the seperators but nothing like what happened that day

The last trip I'd done prior to that was down to The Hump & recall running out of fuel on the front tank & switched over to the rear tank & there was no water or very little in the seperators else the motors would've stopped on that day & they didn't.

When I started them up a couple of weeks ago then ran out about 500 meters or so they were running on the fuel already in the the fuel lines & injection canister once that got used up the water came through.

Now that water wasn't there on trip prior nor do I have any leaks odd though when I filled up the front tank a couple of weeks back I haven't had a drop of water come out from that tank since easy to know if there was cause it would've shown in the seperators & that tank was bone dry prior to filling.

Best I can figure out is the theory that fuel expands push's out the air in the tank then the fresh air which re enters carrie's new moisture.

Dont think visiting scientific forums would be of any help as those guys wouldn't have had the benifit of knowing how wet or how my rig is set up & they could only make an educated guess.

No different to if you visit say a doctor with a ailment he'll schedule tests for the following week by which time the symptoms have disappeared & unless the right tests are done you'll get told there's nothing wrong with you

Well I finally remembered to bleed the internal fuel canisters on the motors 2day last trip out a couple of weeks back the starboard motor was running sick coughing & farting & would cut out @ idle a reeal piss off when you're lining up the boat to drive up onto the trailer.

Actually bled out quite a bit of fuel just to make certain didn't really want to pull out the injectors & must say there must've been a bit of water in one ofhe canisters cn approx 00 ml came out B4 the motor stopped coughing & farting settled down to a nice smooth rythme.

Pumped a little extra fuel out of the tanks as well just to check & it was clean no water ! which led me to believe I made the correct call inicially condensation & maybe a bit of bad fuel from the servo

Have you considered this:: Heavy rain generally comes after heat, IF that is the case, then the fuel tanks in the bottom of the boat will cool after the boats exterior cools, thats when the rain is heaviest, why wouldn't contraction of the fuel tank SUCK water in the breather.

So the condensation has just stopped happening by itself?
Well isn't that weird, could global warming have changed our climate that much?
HaHaHaHaHa!

SUMO it's what I tryed to explain to Fed whom I might add didn't want to hear a bar of it

When this prob occured on my boat you have to remember I had not taken it out for @ least a month prior & the front tank was dead empty know this for a fact cause I had to swap over to the rear tank.

Which in all fairness plays on the point of expanding fuel getting pushed down the breather line in my case something around 3 meters & when it receeds new humidified air gets sucked back down the line.

The front tank being empty had no such probs but the front tank being @ least 2/3rd's full did add to that some very interesting info I found out a couple of weeks ago when I went out & bought some new fuel & breather hose for my little boat which cost me aroung $150 for 5 meters of 5/16 fuel line hose & 4 meters of 1/2 hose.

The hose was over twice the price of the stuff I've got in my big boat it's got a far better UV rating not to mention more importantantly it's interior contruction dont know if the guy was talking out of his :drop the daks: or not but claims were made the new stuff didnt attack water like the stuff in my big boat does completely different rubber.

Next time I take the floor up on the big goat I'll replace the lines on it just to rule them out see on the front tank 25mm alluminium tube runs out all the way to the transom where it is welded into the transom plate & yet to have a water prob with that tank where as the rear tank is a recent addition & has hoses runing back & forth.

So the condensation has just stopped happening by itself?
Well isn't that weird, could global warming have changed our climate that much?


Fed initially told you we had something like 3 weeks of bad weather there was alot of humidity in the air I may not be 100% correct but I nut thing out by ellimination I just dont go by what other peeps say or choose to post on the net like your mate [size="6"][/size]I Pissed In You Tank David Pascoe[color="#FF0000"][/color] reckons he did

Strange how you only get condensation in one tank, what do you think about that?

Weight ratio on boat Fed I always run the front tank dry 1st just habit I guess & all I can put it down to is with no fuel in there to expand & contract guess no fresh air enters either.

Did take the big boat out for a run yesterday & both motors were purring I must've gotten all the water out

That's like driving around in a car without a fuel cap.
You only need a pinhole to relieve any pressure anything larger is only used to stop any physical blockage that may occur from salt build up or crap or insects etc.

Well read back Fed I said my breather line is around 5 meters long

How quick would a pin hole opening block up with such a small orifice ????????????????

Not to mention pressure buildup in the tank

Everything is done for a reason in the small boat breather lines aren't such are big run so I used smaller dia

ps] In the big boat it may me 25 mm tube but it's got a 3 mm wall thickness so opening is 19 mm

I didn't say to use a pinhole, all I said was that's all that was needed to relieve the pressure, 5M or 50M it makes no difference.
Larger sizes are used to stop any physical blockages but there is no way you need to go to 1".
Does this tube slope downhill from the transome to the tank, if so then what stops rainwater running down it?

Well you better look up my boats manufacturer Fed & have a go @ them cause breathers came with the boat & are welded in

I've build quite a few tanks over the years & have to agree with what they've done makes perfect sense to me esp with tanks below a sealed floor.

Breather line rises around 80 cm's tucks under the gunnel where its tacked into position then welded into the transom.

Even my fuel lines out of the tank were around 15 mm dia with a 5 mm wall thickness B4 I replaced the tank with the 2 new stainless ones

Just because they make boats doesn't mean they know what they are doing.
Is the breather welded where it passed through the floor, perhaps they used a 1" tube to make it easier to weld with the heavier wall thickness. I didn't say 1" was wrong other than the explosive potential and it doesn't need to be so big to function properly, you'd have to agree with that. I'd hate to light a match at the transom outlet on a hot day. :o
The fuel lines could have been oversized for the same reason I guess.
The whole thing's a bit awkward thinking about built in tanks below a welded sealed floor, how are you supposed to inspect this stuff? Interest eh?

I totally agree Fed seen some shonky work & there's always the case employee's leave a Co to start their own brand without having a clue other than how to slap a boat together but in my case I think they built my tub well except there were no drain off holes along the ribs which resulted in corrosion within the hull that's why I rebuilt the boat last year.

Original fuel tank was bolted in & with all such type boats with sealed floors an inspection panel gets sealed into the floor allowing access & yes breather & fuel filler tubes are welded through the floor this is done so no water spills into hull, short hoses are then used to conect these to the tanks.



Just as much if not more chance of an explosion with a smaller orifice it's no more dangerous if fact alot safer than having breather inside the boat where fumes can get trapped back inside the boat @ least the way my setup is fumes disipate into the air



Wouldn't have done it any othe way fed remember my hull is 5 mm plate & if you were to say weld 8 mm tube to it best you could hope for would be a 1.6 mm wall thickness dosen't make for a good weld even though it's only stitched & there a good chane you'll blow a hole cause you need to pump up the amps to melt the alloy

Do you make this stuff up as you go?

Just replying to your suggestions thats all & use my noggin in the process

If you've got a small escape route for pressure then there a bigger pressure buildup inside the tank isn't there ???????

A larger opening relieves pressure from the tank @ a quicker rate

Not relevant when you consider the slow speed of the pressure build up.

Have you ever modified any of this system from new?
What size is the breather at the tank, 25mm? (And is it the same as the one in the old tank)
Was there ever a fitting on the transom that covered the breather outlet or something?

This has gone way past condensation although it may be part of the cure.
Are the original manufacturers still in business, I'd be interested to see what they say about this, don't want to see the good ship Jumpy go BOOM!

Maybe FED put the water in th tank!!!

See, I think Ive figured it out!!!

Brather size isnt so relevant I dont think, Some fuel tanks are actullty fitted with one way valves that allow expansion but no suction, Ie i think i reffered to diffs in an early post (stop them sucking in water when they are rapidly coold when doing a river crossing) (this can place axle seals at risk of popping out of position so extended breathrs are a better option)

However moto X bikes also run a one way valve.

It's easy to imagine a hot diff sucking in some water when it cools quickly, they say trailer wheel bearings are prone to the same thing.
I believe it.

Here's food for thought for you Fed !

Another advantage of having a large breather is ??

I refered to pressure buildup inside the tank well pressure can also build up when filling tank as well & nothing worse than those silly fuel pumps cutting out on you because the fuel has come up the filler line.

I get no such probs because my breathers get rid of pressure buildup in the tank very nicely & i know went tank is full when a bit of fuel comes out the breather, no spilt fuel enters my boat

Yep an extremely valid point especially with those rubber things they use on the pump necks now.
I just don't feel comfortable thinking about a 19mm vent pipe without a flame arrester fitted.

Well when you finally get to see the Boat you'll see for yourself & eill agree it's a very good set up

Think it's a bit hard trying to explain things I have this saying that I think is quite good

Show Me, Dont Tell Me


Not everybody thinks the same or can picture things the way they are explained

Cant recall but think on my old big moored boat the breathers were quite large on it as well bear in mind I had 2 off 1000 litre tanks on it & the fuel was diesel no petrol

Go and Google "flame arrester" mate.
Unless there's something you haven't told me then you're sitting on a bomb.