Leaking diesel tank on 2018 Jeanneau Yacht 51

[Elemy51]

I have a 2018 Jeanneau 51 yacht. I am the first owner and have never done any modifications or even cleaning of the fuel tank, I have basically left it alone. Today after filling the diesel tank at the fuel station in St Maarten, noticed an strong diesel smell and discovered a leak of 30-40 litres of diesel under the tank and in the engine compartment. Further inspection showed a crack around the “send” valve … not in the seal or where the valve meets the tank, but in the tank plastic itself. Has anyone else experienced this? Is it possible to repair, or do I need a new tank? How would I get a new tank?
Thanks in advance, this has definitely confounded my cruising plans…. 🤨

[Zanshin]

That's terrible! I've got the same tank and layout and just checked for cracks; both in the main tank and in the 2nd tank that I had installed when I ordered the boat.

The pictures make it look like stress fractures, but that sender doesn't have enough mass to do anything like that to the thick plastic of the tank.

What is that litte red screw-like thing to the right of the sender in the images? I have nothing like that on my tank.

[Charlie-Bravo]

That doesn’t look nice, and the clean up really needs the tank removed or you will be sniffing diesel for years.

As for a repair, this is also easier with the tank off the boat. 
Polypropylene/ polyethylene mouldings don’t glue (regardless of some glue manufacturer claims) so it will require surgery , cutting out the damaged area plus an inch or so, and making a patch and gasket to suit, the patch ideally would be through bolted with either another patch on the inside or perhaps a reinforcing ring around the bolting.

The ‘sender’ unit could be mounted in the new patch.

Before repair, and once tank is off the boat, hit the area around the manufacturer markings with a small hammer, there is just a chance that this tank sat in the sun for a month or two just after manufacture and became brittle, or, as many poly rotational mouldings are, it is made from a blend of virgin and recycled material and your tank has a contaminated area, doesn’t happen often but the hammer will go through the tank top if it’s bad, but bounce off nicely if it’s basically good …… don’t tap it, hit it.

If you are a long way away from tools and equipment, I guess you could clean the damage with some spirit best you can , and sikka it , running just with half a tank until you get somewhere better for repair / replacement.

CB

[jy51]

Just a though, is it possible to heat seal this type of plastic, does it melt easily, maybe a soldering iron smoothed over the crack? 

[loredo]

I've fought with a leaking "plastic" water tank in the past.  I can confirm that NOTHING will stick to the polypropylene/polyethylene plastic. Nothing! Wasted time... Also, I tried what Charlie-Bravo suggests, gaskets of all kind, through bolted, you name it... to no avail.  After a short time the tank would leak again. 

YET, nothing is lost!  These tanks can be welded. I found a guy who did that job almost for a living.  He came on board with his tools and welded the tank inside to boat. (I would've needed to destroy half the internals of that boat to get the tank out.)

He had a tool to melt the plastic of the tank and then added more plastic to it.  Similar to welding steel.  That took him +/- 30 minutes. The tank never leaked again.

A trick to get rid of the diesel smell.  Once you've pumped out most of the diesel, use Cat sand / Kitty litter to absorb the remaining fuel. The sand will absorb fuel AND the smell.  Don't ask how I know.

Hope this helps a bit.

[Zanshin]

What temperature is this weld happening at? I'm sure all of us know the stories about welding around gasoline tanks, even ones that have been empty and disused for years. While diesel has a flashpoint of 52°-93°c and gasoline is way down there at -45°C. I can't imagine that this weld can be done on a fuel tank rather than a water tank.

[loredo]

I have no clue about the temperature used.  For sure the diesel tank needs to be emptied and probably filled with water during the welding process. Still, it can be done.  A major project for sure but still better than having to take the tank out for replacement.

[loredo]

I did a short search on Utube. This looks similar to what was done on my water tank but with different tools.

[Charlie-Bravo]

In an earlier existence I was a welder, a bit later on became a polymer fabricator, and welded poly with a hot air gun and filler, rollers and squishing clamps …… but there is no comparison to be had between welding metals to polymers, the poly results are to my mind feeble and often crack open a month or so later, you just can’t melt and flow a ‘proper’ fused joint and the mechanical properties of the finished article never seem to be near the same as the parent , but, it kind of sticks together better than glue, and sure it suits some situations, but not this one in my opinion.
Despite my experience I never measured the temperature whilst welding polymers, but roto moulding similar things to tanks would set the oven to around 250 deg C , some things hotter some cooler depending on size shape and fill density of the item, it’s a ‘see what happens’ approach, usually followed by some swearing at the first few runs, ……. so to melt poly 180 + deg C , although it will go floppy before this. 
So, tank off the boat would be wise IMHO.

Mechanical patches can hold well, the OP has 4 of them , the connections to the tank in the pictures, so just needs doing well with good gasket material.

I do wonder if the tanks are installed before the deck is attached to the hull, but also note in the owners manual that under periodic maintenance we are supposed to remove the tank and give it a good wash and dry occasionally, ………… sure we all follow that advice religiously. 

CB

[Zanshin]

This was my hull under construction, just before the tanks, engine, generator, etc. were put in. Waaay before the deck was married to the hull

[Charlie-Bravo]

How on earth do you wash out your tanks in the galley !

CB

[S/Y MAKAI]

Jul 5, 2023 18:25:17 GMT Zanshin said:

This was my hull under construction, just before the tanks, engine, generator, etc. were put in. Waaay before the deck was married to the hull

Off topic, apologies for hijacking the thread. How on earth did you get pictures of your vessel under construction? I know that some car manufacturers take pictures from the assembly line, but does Jeanneau do the same? Would love to see the inner workings of our SO 490...

[loredo]

Zanshin,

those internals look vaguely familar. (Hijack, I'm waiting for dishy to be delivered)

Charlie-Bravo, the water tank I got welded... I sold that boat in 1998. I'm still in contact with the owner. The welded tank is still not having leaks.  Maybe it was only luck?

I don't know the situation in the J51, the Jeanneau's I've owned, in none of them would it have been possible to get any of the tanks out.  The major problem being the doors one needs to get the tank through. The bulkhead would need to be removed...

Elemy51, I would also check if the breather of the tank is operational.  Could it be that it is blocked? That would mean that the tank collapses when emptied --> causing the failure.  If where you're now a repair is impossible, I would clean up the mess, slab some sort of sealant on the crack,  get myself several jerry cans and keep the tank less than half full.  Somehow that should help you to get where you can get a proper repair done?  Sorry for the major problem!

[Elemy51]

Update: as the OP, I appreciate all of the expertise and advice. I thought an update would be in order. I enlisted the help of a fuel tank expert here in Saint Martin. He concurred with the general conclusion that most repairs would be temporary at best and replacement was the best option. As I am planning to sell my boat soon, I did not want this to detract, so I decided to replace the tank with an original part.

In terms of diagnosing why the tank cracked, we: 1) checked the vent to ensure it was not blocked (which could create a vacuum if the tank emptied), and everything was open, 2) verified that nothing had been in contact with the tank or put any pressure on it, and 3) unscrewed the send unit and measured its height and the height of the tank itself. This revealed that the send unit is exactly the same height as the height of the tank interior. This means if there was even .5 cm of flexing, the send unit would be putting upward pressure around the opening. The tank expert commented that they should have put a spacer around the send unit opening to ensure this wouldn’t happen.

I contacted my dealer, who contacted Jeanneau. They informed me that this was not under warranty even though the boat is less than five years old…(Note: I realize that the hull is no longer under warranty, but I was hoping maybe a part like the tank would be. No luck.) They sent me a photo of the tank to verify it was the same part… And lo and behold, in the replacement tank it appears there is a white spacer under the send unit top where it meets the tank. I am attaching that photo… those of you with similar tanks or boats may want to check if you have that spacer. Mine was Hull #31 of this model so maybe they figured out that design flaw.

In case you want to know the damage… The replacement tank will cost USD$1008 and the air freight from France to St Martin was quoted at $1500+. So I was thinking I may fly to France and bring the tank back as oversized baggage… The dimensions and weight fit the Air France limits and the cost of a R/T ticket is $1,200. Crazy.

In the meantime, I have cleaned up all the diesel and the boat smells fine. I continue to use the tank to run my generator while I am on the hook. I keep the fuel level less than half full. I have no choice, as I am living aboard. I am planning to try a temporary fix with either sikaflex or JB plastic weld… just until I get the replacement tank. Or any thoughts on duct tape?? 🤔

Once again, thanks for your thoughts and tips!

[Elemy51]

[Zanshin]

Thanks for updating the thread with your findings.

Regarding getting the replacement tank, can you speak with Jeanneau in the USA and source the tank there? Shipping to SXM from Florida is going to be under US$100 and take just a couple of days via cargo ship.

[John]

Another option if you cannot find someone locally to weld it , an inspection hatch could be fitted where the crack is if there is a flat surface , the original fitting could be moved .To remove the diesel smell a citrus degreaser will break it down , we have used this with great success .