Why

I was in the process of modifying my bilge pump setups and found myself needing more "exits" for things. This got me thinking about conserving holes instead of making more.

The Job

I wanted to combine several pump outputs into a single exit point of the boat. The most likely place to do this was the sink drains. I did this"combining" in two places, the head and the galley.

In the head, I had the sink drain itself, the shower sump, and the forward bilge pump to combine. Here is a "schematic" of what I did in the head. Click for a readable picture!

I had several things to consider:

1) the likelihood of having more than one "user" of the thru-hull
2) the angle of the two additional flows as they entered the drain hose
3) the overall flow rate after the combination
4) back-siphon issues

Here is what I rationalized for each:

1) I didn't think the first one would be a problem as the shower and sink would be only intermittent use (hopefully the forward bilge pump as well!)
2) I found a 3:1 PVC pipe coupler where all three inputs angled into the output
3) The exit thru-hull was already as large as any I would have used individually (1-1/2")
4) I thought that the sink drain itself being open and over 3 feet above the water line would provide a good anti siphon air inlet, and I made sure I put a loop in the hoses at least as high as the sink

So here are some pictures of the head setup. This is the "combiner" under the sink. The center tap is the sink drain, the left and right black hoses are the shower sump and the forward bilge pump outputs. The shower sump is the one with the 3/4" elbow..

The optimum combining part just happened to be right where a shelf was under the sink, so I had to make a cutout for the PVC fitting.

This is a picture of the "combined" outputs going to the thru-hull. I wanted to make a nice smooth curve downward with the hose and have no bends or kinks..

I did the same think at the galley sink using only one additional "input", the emergency backup bilge pump. Again, I looped the output well above the sink level and decided that the sink drain provided plenty of air input for anti-siphoning. The white hose is the old sink drain, and the black (I know, it's corrugated) is the backup bilge pump hose.

Results