cutting access hatch in fuel tank?

Beamishken

Beamishken

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About 3 years ago I got some dodgy diesel complete with water in my starboard tank it never caused any problems with the engine but the pre filter was full of crud that year. ever since then I've dosed up well with biocide but I'm still getting the odd slug of water & black gunge in the bottom of the filter (Racor 900 series)
I'm thinking of cutting an access hatch into the side of the tank as it's easy to get at from the engine bay big enough to get my head in so I can see the bottom of the tank& mop up all the crud from the bottom
My plan is get an aluminium square cut an inch bigger than the hole & making an ally frame to go inside the tank tapped to take 8mm bolts question is how easy will it be to seal the bolt holes & what spacing between holes & what's the leak potential of the hatch
The gunk in the tank isn't causing a problem but it just annoys me when one filter is crystal clear & the other is a bit grubby tank is 600 ltrs & realy poor access to top of tank & guage holes etc
Any better suggestions?
Cheers
Ken
 
I did something similar for my stainless tank:

9921A263-55CD-448D-88B1-E601963B5016_zpszkpaidft.jpg


Rather than insert the bolts from the outside, though, I screwed them into the tapped holes in the inner ring and used them as studs. I also tack-welded the heads in place though threadlocker would probably be fine - or just do them up blimmin' tight and spall the threads :)

The nitrile gasket (cut from a sheet from eBay) grips the studs and stops the whole lot falling into the tank when the lid's off.

The lid is screwed down with dome-headed nuts onto the studs.

The compression of the gasket forms a good seal against the tank material and the lid, and stops any weeps up the studs. No sign of any leakage a year on, and there's about a metre of head in the pipe when it's full.

Pete
 
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I hope I've read that wrong and your not thinking of cutting a hole in the side of your tank because of limited access at the top?
PRV that is a 'proper job'.
 
Yeh maybe should have been more specific the hatch would need to be in the side of the tank I've seen plenty of side access hatches in hydraulic oil tanks but not sure about the implications of a fuel tank
The picture prv posted is something like I had in mind but a good point about fitting studs instead of bolts
The only way to gain access from the top of the tank would be to remove the tank having first removed both engines hence looking for another solution
 
I suspect you would find it almost impossible to stop it weeping.

Some sort of drain , flush , steam clean using the access you do have ( ie existing pipe work )would be a pain but I would think is a better option
 
fwiw,

a friend had a leaking stbrd side tank on his Princess 410 (iirc)
Ended up CUTTING a hole with an angle grinder (I thought it was rather dangerous, OK diesel tank not petrol!),
coming across the baffles (that could be a problem with OP, so keep it in mind!) and then doing something like prv shows in his pics.

Messy difficult job, imho NOT worth it. Find a way to clean in situ without the holes, or buy a stock of filters are replace often ;)

cheers

V.
 
My boat already had a hatch cut into the plastic tank when I bought it that was really badly designed and when I filled the tank it leaked petrol (yes petrol!!) into the bilge.. So I designed a "bomb proof" hatch to replace it..

I used two pieces of 10mm ally plate, the inner one having holes threaded and the outer one having clearance holes.. I then had two fuel grade rubber gaskets cut by water jet, one to go on the inside and one to go on the outside of the tank between the ally plates.. Bolts were placed around the perimeter at 50mm intervals and all torqued equally (torque was tested on a spare piece of ally to determine breaking point)..

To install it I put the inner plate and gasket inside the tank and then used two bits of threaded rod to hold the inner section in place while I got the top section in place and bolted, then I removed the threaded rod and fitted the final two stainless bolts.. Used blue loctite on the threads to provide some isolation between the bolts and the ally and to seal the threads..

So in effect it's double sealed and happy to say it worked perfectly..

Photos can be seen here..
http://1drv.ms/1Ohsi2w
 
vas said:
that's nicely way overengineered!
very well done.
i'd be very impressed if it ever leaks (and if it does, it will be just a case of cutting two new gaskets ;) )

cheers

V.
Click to expand...

Thanks.. I tend to have a habit of over engineering everything I make but with this being a petrol tank failure was not an option so it was double over engineered.. :)
 
vas said:
Ended up CUTTING a hole with an angle grinder (I thought it was rather dangerous, OK diesel tank not petrol!)
Click to expand...

That's what I had to do with mine, it defeated a cheap nibbler and several "metal cutting" jigsaw bits. I pumped out all the diesel I could reach and tipped in some soapy water to dilute the remains, hung wet cloths around the work area to catch sparks, and put the big fire extinguisher within reach :)

Pete
 
Seems like mixed opinions but obviously some people have the hatches & successfully manage to seal them my tanks are aluminium so id planned on using a jig saw
I assume the guys who had to resort to grinders were cutting steel tanks?
The other question is what spacing for the studs?
The debris/ water hasn't caused a problem YET but it does concern me that there is crud in there & I'd feel happier if it wasn't there but obviously don't want to create a bigger problem ie a leaky tank
Decisions decisions!
 
If me I would not cut a hole in the side of a tank - never ever, ever.

This seems to be a psychological problem rather than an actual one, so why not spend your money instead on a polishing system to keep the fuel clean and dry. Any residual muck will gradually come out by routine polishing, especially after the boat has been used and the fuel has been shaken about. Simply set the system to run after a passage for an hour or so per tank.

Three connections per tank with dripless plug in connections.- spill return line; pickup line before pre-filter, and tank drain. I have all female dripless fittings on these connections and male on the flushing filter connections.

I have details of suitable parts for the dripless connections. And they really are dripless, although I also fit ball valves to ensure a completely air tight seal onto the fuel system.

The flushing filter is a Baldwin Water separator filter with a Holley 12v fuel pump drawing the fuel to be polished through the filter (not pumping to it).

I can take fuel from either the pickup or drain and return to any position. With two tanks I can also pump from one to the other. I can also supply one engine from the opposite tank should I suffer serious contamination in one tank.

The pre filter connection allows the pick-up pipe to be back flushed should I ever pick up a slug of crud, but also allows me to use the system to purge both pre and final filters of air when they are routinely changed.

I have not used fuel additives since installing a polishing system. I am currently planning the system for Boadicea. If I find any significant crud then I may give a shock dose or Grotamar or Marine 16, but once this is done keeping the water out keeps the bug at bay. No water = no bug.
 
Both mine have side access as well as top access and I make them as follows:

For aluminium I laser cut the frame from 24 or 30 mm thick plate, make the cover from 12mm plate, clamp the two together and drill the cover and frame together and set the stop on the drill so you don't go right through the frame, the frame is tapped so they are blind holes to prevent leakage.

Monel studding is cut and inserted into the holes with threadlock to prevent them moving.

Tank is drained as much as possible and filled with a special foam we use at work which looks like washing up liquid and reacts with the diesel to fill the tank with this foam.

Frame is held in position against the tank and TIG welded on all four corners and this is done with the tank totally sealed, the frame is fully TIG welded by sequence welding to prevent distortion, then allowed to cool. Tank is cut out using the centre of the frame as a guide and with the framing being as thick as it is, it prevents distortion, foam is fetched out to just below the level of the lower part of the framing so the tank has some remaining in to cover the fuel and the cuts are ground and the hole flanges are TIG welded to the inside of the frame.

Cover is aligned, gasket made and fitted, and cover fitted using monel nuts and washers.
 
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