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Replacing a fuel tank on a Fairline Squadron 52

December 21, 2018

Removal and replacement of a corroded fuel tank in an 18-year-old Fairline Squadron 52

Fuel tanks don’t last forever, and replacing them means making some big decisions… Including removing your engine and half a flybridge sometimes. Most fuel tanks last for 15 to 20 years if properly installed and maintained.  In this Fairline’s case, they lasted a good 18 years.

She arrived here at Berthon in late September and after a lift ashore we began a full inspection of the fuel tank and surrounding area.

The owner of this Squadron 52 knew that there was fuel in the engine room, and hoping for the best we all wanted it to be either linked to the gen set or maybe a fitting off of the tank. We began with a simple pressure test which came back positive for a leak; after checking whether it was air escaping from the top or added fuel in the bilges, it was, unfortunately, the latter meaning the fuel tank had either a pinhole problem or a structural one which would mean it was definitely perished. After emptying the tank of fuel and by feeding an endoscope down inside and around the hard to reach areas, we were finally able to get an idea of how severe the corrosion really was along with a fairly positive location for the leak.

The Squadron 52 was designed with 2 fuel tanks, one port and one starboard; these tanks sit within a tray with a rubber floor. All well and good if the tank does leak as it is contained within the tray, but regrettably there isn’t a drain from this tray, so any water that does wend its way into the engine room has nowhere to go but to sit around the bottom of the tanks. This was probably the source of/and accelerated corrosion.

To add to the issue, aluminium (including many marine alloys) is a highly anodic material and it can deteriorate quickly. Aluminium rapidly corrodes when in contact with water and, and especially salt water. It is subject to weakness when it sustains flexing, such as when the fuel moves around (even with the 3 baffles to reduce the fuels movement) as the boat beats across the Solent, along with repeated temperature changes and the expansion and contraction of the metal. And then, of course, there is the problem of joints which rely deeply on the experience and knowledge, or lack thereof, of the welder or fabricator.

Many boat builders and designers fit the fuel tank within the vessel and seal the cockpit or superstructure on top without leaving much space or even a proper way to thoroughly inspect or even replace the tank, resulting in, if you do find corrosion, or even worse, a leak in your tank, a need to remove the cockpit carpet, floor, headlining, along with the majority of the furnishings, from your boat to remove the tank. Some designers have the good sense to install a removable panel in the cockpit floor so that owners can regularly inspect the fuel tank thoroughly and even a soft patch above it in case it needs to be removed; Fairline ticked all these boxes but even then a soft patch isn’t that soft, for instance during this repair.

Thankfully the owner of this motorboat noticed a problem with his vessel and brought it straight to us.

Consider that just two ounces of petrol, or the same amount of gin as you’d put in your gin and tonic while sitting out on your aft deck in the afternoon, has a similar volatile aftermath as a couple of sticks of dynamite. It is more than enough to ruin a good day out! However, this boat as most others, runs on diesel.

With the news of how severe the corrosion was, it was decided that the fuel tank would be removed and replaced, as opposed to repairing it or simply installing a large bladder within the damaged tank. A plan was put into place as to how the tank would be removed, and the vessel was placed undercover in one of the big-blue-sheds. Access to the soft patch itself from the flybridge (seen in the photo below) was relatively simple but you will note the beams ends that supported the deck had to be cut for the engine and tank to be withdrawn. Needless to say, an easy fix was being drawn up to replace the soft patch with easily removable floor stiffeners in case in another 18 years the engines had to be removed again. The floor beams in the saloon were designed to be easily removed, but to lift the engine, the entire port side seating and cupboards had to be extracted, so in this instance, the soft patch wasn’t as soft as expected.

With a clear path for the engines and fuel tank to exit she was moved outside to one of our static cranes where the port engine was lifted. We then began the huge job of removing the damaged port fuel tank.

This is where it got interesting. Clearly the boat had been built around the 1300 litre 1.3 cubic meter tanks. With a bit of wiggling and multiple engineers and riggers pulling the tank, it freed upon which we noticed the entire aft corner of the tank had severe corrosion and a very definite 4mm hole. You can see for yourself in the below images.

The dimensions of the tank were sent off and soon we had a brand new fuel pre pressure-tested tank ready to be installed, before which the entire engine room was steam cleaned and to prevent the tank from sitting in a pool of water, and just in case any water was to wend its way inside again, 2 drains were installed in the port tray and one to the starboard tray ensuring the egress piping ran to the lowest point.

The tank was insulated, installed with fastening straps, connected, filled and re-tested and subsequently the port engine was replaced.

While our team were down in the engine room they also touched up any bare metal on the engines in Volvo green. Flaking paint on the turbo was also removed and touched up.

With the engines in place it was now down to our shipwrights to rebuild the boat. This included replacing the soft patch, rebuilding the upper helm and also the entire port side of the saloon.

The original design of the soft patch had metal supports running throughout, welded and permanently fixed into place; we have now redesigned this with the frame work sitting in aluminium C brackets, securely bolted through and into place. It still supports the soft patch although it does allow the patch to be removed quicker and more efficiently if there is ever a need to lift an engine or fuel tanks again.

As an aside, it is always good to do some additional work around the engine room, now that accessibility is less compromised; IE cleaning, painting, checking fuel and water systems etc.

Once afloat we turned our attention to preparing for a sea trial with a simple descale of the engine coolant system, using Rydlyme, a biodegradable, marine descaler designed to carefully dissolve calcium, rust, barnacles and other deposits that hinder the performance of the water systems; the serviced engines were then started and run up to temperature; the first flush of Rydlyme emptied and the whole exercise repeated a second time. Obviously new coolant was then added.

Tests on the wet cell batteries were carried out and two were replaced.

With the engines installed, cleaned and up and running she underwent a very comprehensive sea trial. Berthon have a long history with designing, building, refitting and restoring commercial, MoD and professional vessels along with a multitude of leisure yachts and motorboats. A sea trial is vital at the end of any such job. Procedures have been refined through working with these commercial authorities, professional Captains and owners of leisure yachts. The success of the refit only becomes apparent with use and we are delighted that she has now resumed her normal cruising pattern with Berthon Marina her new home only a few weeks after being lifted ashore for investigations.

The topsides were cut back using a 3M cutting compound, to improve the appearance of the oxidised gel coat, followed by a full polish and wax with Farecla Polymer polish, leaving an excellent even high gloss finish; Farecla also protects the less-oxidised gel coat against further UV degradation. While outside our valeting team also cleaned and polished all the normally forgotten more out of reach areas including the arch, metal work and lights.

Up next was the engine room, to make any future anomalies jump out identifying a new issue.

Our valeting department was then called in to finish create the necessary sparkle and shine, ready for owners and guests alike (see the finished product in the photo below).

What can you do to protect yourself from escaping fuel occurring?

  • First of all, inspect your tanks regularly, look and touch the tanks’ tops, sides and most of all the bottom, as this is where it is susceptible to corrosion from bilge water. If the tank is held in place by straps or easy to remove brackets, loosen them and look under them too.
  • Second, you should always get use to ‘safe starting’. The best fume detector is your nose. Before you use your boat and every time you are at the fuel dock refuelling, open the engine cover and take a sniff. Don’t even turn on the bilge pump until you’ve looked into the bilge and had a quick sniff around; families do not like the oily stench of diesel and it can cause sea sickness.

Please contact our Berthon Yacht Maintenance and Refit (YMR) team if you have any questions, queries or issues regarding your vessel’s fuel tanks as leaving an issue too long, or not repairing it correctly can create more trouble. A stitch in time saves nine!

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