Tiger. I think we are getting at crossed purposes here and my syntax is not really clear. Sometimes my brain works quicker than my fingers type. :-) You are correct the adaptor fits
under the "deck fitting". On top of the deck below the plastic deck fitting.
It can be split to retro fit under the deck fitting on top of the deck and is sealed down and clamped using the through deck fixings, without removing the breather hose or the filler pipe. I hope that clears any misunderstanding?
The cap lid that screws in is sealed with the O ring, the actual cap is not vented, but the lower fitting
is via the second smaller vent hose connection I previously mentioned. The description from Perco is slightly misleading or ambiguous or just badly written. The extension fitting raises the filler cap above the deck by 3/8 of an inch to stop any splashed water or water on the deck entering the tank when the cap is removed for filling,
not when it is closed or sealed closed.
To comply with the EPA standard and the European boat directive the cap or lid has to seal and be water resistant. However, they have again been a bit careful in the description by using the phrase "The ring will not prevent water from entering the system if the cap becomes submerged or substantially flooded". This is because the O ring set up is not a tapered fit that gets better under pressure or vacuum like a compression fitting on an air line or vacuum pipe fitting. It is a flat or nearly flat compression seal and has to be in good order to work.
The lower part of the deck fitting (the plastic part) has a vent below the O ring, working through the vent tube and the vent fitting. It is this part that they refer to in the installation information you posted. It is not the Cap that vents it?s the lower part of the fitting, the plastic part through the second smaller hose tail.
I had a 2003 B 32 (Renovatio) the filler cap was on the transom and was never a problem because even with a bad O ring water never lays on a sloping surface. I also sailed a 2004 B32 (Tenacious B) the filler was on the deck. Rain and salt water constantly washed over the deck filler. Especially when the boat was sailed hard. Water in the diesel forced the owner to leave the boat in Brighton for a week and I helped him to pump the tanks dry of 45 ltrs of water and diesel before fitting a new O ring and sailing it back to Southsea marina in very poor conditions.
Two years ago I saw Tenacious B at Weymouth. The owner was trying to empty the tank having been towed in with water in the fuel. Knowing the boat and the previous owner, I offered some help. I undid the filler cap and showed him the perished O ring. He then told me they had come down from Gosport in rough weather around St Albans head, there had been a lot of water on the decks for sustained periods. QED
Yes you could fit another type of fitting, providing there is a clear breather tube and fitting as described in the Perco fitting instructions for the vent tube (marine fuel vent). However, the existing fitting meets all the standards, is water tight, (unless substantially submerged) and has to be un-damaged, and inspected on regular basis. (say 3 months or so). Just like everything else on you boat if you want it to be reliable.
Finally, at last I hear you say
My current boat (2015 Bavaria 37) has the same setup stupidly, some may say, the deck filler cap is located on the aft starboard deck. This area is constantly awash with sea water, rain and fresh water when we wash down. The cap is frequently submerged, over washed or under an inch or so of water for some time. The breather fitting is just below the toe rail and the gauze or mesh does get rusty and needs to be cleaned and picked out with a sail needle every few months, then brushed with a fine stainless steel brush. Nevertheless, we don't get water in our tank or in the Racor filter/separator I fitted because, I regularly check the O ring and keep the mating surfaces clean and lubricated with silicone grease (not Vaseline).
Hope this clears any misunderstanding, Fair winds and safe sailing.
Ant.
