Since our roly poly trip back from Barrier we have had a recurrence of problems as described in my post in July last year. Bad smells, self filling holding tank and difficult discharge with the macerator. It came to a head (pun intended) last week when I decided to try the new self-pumpout facility at a Westhaven marina, and found that there was no flow from the deck fitting and a vacuum was being pulled on the holding tank. We stopped the pumpout and disconnected the port vent hose from inside the boat, behind the mirror in the master bathroom. We restarted the pump and emptied the holding tank without further issue, so it was obvious that vents were blocked again. We then repeated what we did last time using a garden hose to flush out the vents to the outside and, yes, they were well blocked.
I had always been wary of the thru hulls (we call them skin fittings) on the holding tank vents because they are of a type that you cannot even see the discharge ports, let alone clean them out from the outside. I decided enough was enough and I would look at replacing them. These are the type, and they seem to be quite common on Silvertons. I checked them out at our local marine store and, sure enough, they have about 8mm (3/8") dia holes in the centre section, which have a fine SS mesh insert!! They look great and are well designed for fuel or water tanks - although I have heard of issues with insects building nests in them. The recessed head and the mesh prevents water ingress into the tanks from the outside but those are precisely the reason they shouldn't be on holding tanks. If you ever get effluent into the vent line (eg from overflowing it), it cannot help but get stuck in the fitting. So that's just plain DUMB
So... out came the port fitting and this is what I found
Only one of the 4 holes was clear even after flushing it out with pressure water and there was still an awful lot of crap inside the head The only reason it was still even partially working was that one of the corroded mesh screens must have blown out under the water pressure.
I found some 1" replacement fittings that were a reasonable match for the other (which is the water tank vent, by the way) - the irony is that the replacements cost $12 each and the original ones were over $50.
But wait.....there's more! And its even DUMBER!
As I said earlier, the port vent fittings are easy to get to by simply removing the mirror in the master bathroom.
The starboard is not so easy as the only access is through a small removable panel inside a locker built into the transom.
I managed to wiggle my way in and could reach the fittings, but noticed that there was a thick green wire wrapped around them. While it was the size of the earthing (ground) wires, it was not actually wired to anything. Then I found the other end, wrapped around and tied to the 12ft long, 9" diameter exhaust pipe from the starboard muffler to the underwater exhausts. Silverton's very own patented exhaust support system!
I would like to think the Sophisticated Silverton rear mounting was only supposed to be temporary until a permanent solution was found - which was then overlooked - and not a case of someone's thinking "what the eye can't see the heart can't grieve over". Normally, the exhaust outlet is out the stern quarter on a 453, but mine has underwater exhausts that exit behind the rudders, so there's an extra 3-4ft of exhaust pipe to support as well. That's an awful lot of weight hanging off a piece of wire and two through hulls. Oh, and as you can see, the main exhaust also supports the genset exhaust pipe.
So...I cannot replace the vent until I remove the wire, and I cannot remove the wire until I make a proper support for the exhaust pipe. I have decided to address these issues after Easter, when we intend to go cruising for a week. At least I know one of the holding tank vents is working properly.