Expeditionyacht.org

Being an expedition yacht able to carry a helicopter you tend to end up in places where jet fuel for your helicopter is not readily available.  So we decided early on we wanted to be able to carry some extra jet fuel to be able to refuel the helicopter.  In an earlier post about this subject, we wrote we had planned to adapt two former diesel fuel tanks for this purpose. Class rules require a cofferdam to surround the jet fuel tank as well as a double hull if the tank is on the outside like in our case.

Our initial idea was to basically add plating to the inside of the tank  walls and hull to create the cofferdam space (about 20 cm wide)  and make this hull inspectionable with an inspection camera like this one from Ridgid .  Making the cofferdam wider to allow access would mean ending up with almost no fuel storage space and rules require you can inspect a cofferdam but don’t specifically say how big it has to be.  But how to keep corrosion at bay and what about not being able to weld this plating on both sides? 

So we started looking at other solutions like a tank we could remove.  To store about 3 to 4 m3 of jet fuel (780-1038 gl.), one big tank would not be practical (how to get it in there?)  Several smaller tanks?  To start with, that would clearly violate the KIS principle.  But then we learned about bladder tanks and we came accross the website of Australia’s Turtlepac and thought, if they can do that kind of stuff with a bladder tank – like throwing filled tanks out of helicopters - it will work for us!  The obvious advantage of a bladder tank in our application is that when empty, you can easily remove it through the manhole and inspect the outer tank!

Unfortunately, there was no information whatsoever available on the Internet about yacht applications approved by a class society so I decided take my case to always very helpful gentlemen of Lloyds Register in Ft. Lauderdale to see how they felt about the idea.  I met with one of their surveyors and the news was good.  Yes, there was a precedent of the use of bladder tanks on (classed) yachts.    But we had to make sure the tank would not collapse while being emptied because they want fixed connections to the tank for filling and venting.  Flexible hoses – not normally visible as they are hidden in a cofferdam – that could  move and possibly allow parts rubbing into each other, resulting in some kind of failure were a no-no. 

Mmm…  a bladder tank that maintains its shape?  How then would we get it at its intended location or remove it for inspection.  But they mentioned there are companies that manufacture a foam specifically for use in fuel tanks (also called fuel cells) that could be inserted into the tank to keep it from collapsing, maintain its shape and allow fixed connections.

A little more Googling and we ran into so-called explosion suppressant foam made by  Crestfoam among others.  To see why this foam is called ‘explosion suppressant’, it’s enough to watch the video below.

So thanks to the helpful advise of Lloyds Register and with a little planning from our side and a lot of ball-shaped foam pieces from Crestfoam it looks we have now overcome the major hurdle to create jet fuel storage that will meet class requirements.

As you can see from the picture below, these fuel cells can be made in any size of shape to fit the particular needs of your yacht.  Of course, they will have to be pressure tested by the class society but the pressure is not that high and as you can imagine, these tanks can meet those requirements easily.