Bilge Pumping System Design

TheWastedYears · #1 (**permalink**) 09-25-2008

Hi All,

I'm redoing the bilge pump system for my 31'. C-31's don't have a lot of space between the sole and the hull, and the centerboard makes it an even tighter fit, so here's what I'm thinking:

Use a pump w/ both hose inlets and hose outlets (similar to the Gushers and sink pumps) and run a hose down into the bilge. That way, I have a very low intake point and a bilge pump that can be mounted where it's easy to service. So basically, it'd be roughly a 4 ft rise from bilge to pump, and then a 5 ft horizontal line to the stock transom thru-hull.

I plan on installing a Gusher to replace the original manual pump. Would there be any harm in having both pumps tie into a Y so that only one part of the Y accesses the thru-hull at a time? The goal, of course, is to minimize the number of thru-hulls in my boat.

My entire plan is to have three pumps:

Primary Pump: Something small (1200ish) w/ low float
Backup Pump: Something larger (3700ish) w/ higher float than primary
Manual Pump: Cockpit mounted Gusher

Right now, she has a 2" thru-hull for the bilge pump.

Would a manifold allow me to run this off one thru-hull, or would I be better off w/ more thru-hulls? Any advice would be appreciated.

sailingdog · #2 (**permalink**) 09-25-2008

IMHO, you really should have separate throughhulls for the various pumps. Otherwise, they may end up causing problems for each other in an emergency.

BTW, you should also have two manual pumps in an ideal setup, with one usable in the cabin and one in the cockpit. This way if the weather is bad and you're stuck inside the boat and the batteries are dead, you can still pump out the bilge.

TheWastedYears · #3 (**permalink**) 09-25-2008

I was thinking of a Thirtsy-Mate hand pump as a backup to the manual, just b/c it's great in a rainstorm if the cockpit drains clog (seems to happen to me quite a bit.)

sailingdog · #4 (**permalink**) 09-25-2008

A thirsty mate is a navy-style piston pump and a really lousy choice as an emergency bilge pump. It gives you NO mechanical advantage, and generally has a very long and tiring throw to it and moves relatively little water compared to a good diaphragm pump. Navy style piston pumps are great as maintenance pumps, but really suck in an emergency. Diaphragm pumps, like a Whale Mk V are the way to go.

sander06 · #5 (**permalink**) 09-26-2008

Thru-hulls aren't necessarily bad unless they're in a position to sink the boat. The main super-duper bilge pump for our boat has a discharge thru-hull that is high in the stern just under the cap rail. If this discharge point is ever underwater it won't be because of that particular thru-hull. Just as an aside, plumbing multiple bilge pump discharges into a single discharge line is a real bear to get right, if not down right impossible. Your "ultimate-emergency-bilge-pump" discharge might not even need to have a dedicated thru-hull. Just toss the end of the discharge hose over the side and let her rip!! Simple!

TheWastedYears · #6 (**permalink**) 09-26-2008

Good point, Sander. I didn't think of that. If I'm already on my 4th and last pump, things clearly aren't going to be neat and tidy anyway.

I'm still in the process of accounting for all the thru-hulls. This boat had an automatic bilge pump at some point. I found the float switch, but the actual pump seems to be MIA. That still leaves me w/ the annerving question of how it evacuated and where that hose is.

So my concept of using a pump w/ an inlet hose (as opposed to those cartridge based in-bilge units) is a good one?

sailingdog · #7 (**permalink**) 09-26-2008

The only problem with using a pump with an inlet hose is that the pump must be capable of self-priming to that height of head. Most diaphragm pumps are capable of doing this, but most impeller-based electric bilge pumps ARE NOT IMHO. That is why most impeller-type bilge pumps are designed to have the pump sitting in the bilge.

TheWastedYears · #8 (**permalink**) 09-26-2008

I'll have to get some photos of the bilge area, but picture a W where the sides are the hull and the center peak is the housing for the centerboard.

I just don't see how to get a non-hosed pump down into the bilge. The centerboard housing stops where the engine begins (or where the engine would begin if it existed.)

A Rule500 fits down into the channel, but that's not even close to being the size pump I need.