service port for the fuel tank

[Lyra]

I really feel the lack of a decent service port in the fuel tank.
I thought of making one.
For the connection flange of the cover my idea is to make two SS rings with holes for bolts (or threads or both - yet to be seen what is required) all around. The internal backing ring will be split in half so that it can be inserted through the round opening that will be made in the tank, seals will also be made for in an out sealing (same form as the rings).
1. Has anyone ever made such a port?
2. What would be a proper diameter for this port?
3. Any remarks or ideas for the design   

[tiger79]

If you have a plastic fuel tank, it may well have an access port already - mine has.  The port may be concealed by the boat's structure.

If you want to make a port along the lines of your description, if you make it slightly oval you can make the inner ring in one piece.

[Lyra]

Thanks about the oval shape idea.
Where approximately is your service port located?
Where is your tank located (mine is under the rear starboard cabin bed)

[tiger79]

Mine's also under the rear starboard bed, see pic...

[Yngmar]

Ours also has no service access port, although we're doing fine so far by pumping up the dregs each year with a copper tube shoved down one of the unused take-off ports. This year there wasn't even any dirt at all.

The tank is made of black, roto-moulded HDPE, but a different design than the one in tiger79's picture.

If the need for a service port arose, I'd probably fit something like the one on the bottom of the page here: http://www.hendersons.co.uk/boattank/Tank-access.html

The first use for it would then be to clean out the plastic debris caused by cutting and drilling the holes out of the tank. Definitely only do this after draining the tank completely or you risk the plastic filings floating behind the baffles and becoming inaccessible, creating a problem where before you had none.

[Lyra]

Thanks - seems that although the tank looks quite similar the layout of the ports on the top is different. This opening is hard to miss. Just to be sure I will try to take a look under the structure to see if there is a hidden port somewhere (I doubt it).
Yngmar - my tank is probably like yours. Thanks for the link - if I decide to go on with it I will probably use it, at this price it seems illogical to design and manufacture something by myself.

[kavok]

I think is better before ask to tank manifacturer.
I know that in not sure add a service port to the plastic black Bavaria tank due to se possible twists at full diesel fuel.