Hi John - Bruce is accurate in his description. The original keel tank sits/sat on a glass or metal (probably glass), three-sided insert. Basically, this was a base to help support the fuel tank...although, it seemed like a great deal of the weight was also supported by the sides of the keel. I assume that Per designed this in to give the Vega some kind of bilge, because without it, the only conceivable bilge would be the space located aft of the fuel tank, or the space between the top of the fuel tank and the cabin sole.
The drain plug on our Vega (a series II) is at the starboard aft end of the keel, or bilge, depending on your preference parlance. There is a small area, lets say about 10 inches in length by 4 inches port to starboard, that may be slightly lower than the rest of the base of the bilge. Presumably, that is where any excess water should accumulate when she is dry docked. Removing that plug presumably drains the water.
I mentioned in an earlier post that I would not glass over or cover the plug if I were leaving the fuel tank in the bilge. With the fuel tank in the bilge, the area under the tank, about 8 inches worth vertically, is virtually inaccessible. The area aft of the tank, which is not much space anyway, is also virtually inaccessible. I mention this as "virtually inaccessible" because as you have probably learned, a Vega owner figures out a way to get to, change or repair just about anything on the boat regardless of where it might be located. However, I digress.
As long as the tank is in the bilge, it is extremely difficult to ensure that the bilge is drained in dry dock without removing the bilge plug. One can imagine the issues that might ensue should that water freeze in the enclosed space.
That all said, if the tank is not in the bilge, it is an easy task to sponge out the bilge to ensure it is dry. It is also a simple matter to take a look to see if any water has accumulated in the bilge.
The place where the plug comes into the bilge was difficult to see. I ended up removing it and sliding a screw driver into the hole to check its location.
As an added note, another advantage to relocating the fuel tank to another location is that when I drop part into the bilge, which I have done many times, they are easier to retrieve. The downside is that it creates a fairly large amount of unused space and removes weight from below the water line. People have found ways to accommodate for this change, sometimes putting extra chain down there, or possibly a water tank or bladder. I usually store a case of wine held in place with a piece of netting cinched to two pad eyes located where the batteries used to be stored. This creates a problem as the season goes on, because the weight slowly moves from the bilge to the belly. I am looking at some alternatives, possibly building a watertight fiberglass box, or maybe welded plastic, in order to store tools and spares down there. But then I'll need to find somewhere else to store wine. Maybe under one of the settees?
As always, mine are not the definitive comments on the subject; other peoples experience may differ and prove dramatically more apt than my own. My apologies for the long reply. I'm on vacation, enjoying a cocktail and feeling just a little verbose.
Cheers!
Jack
Bella - V2620
