The switch may be one issue, but trust me on this: your pump will never be able to deliver a "dry" bilge, for at least 2 reasons. A) because if the switch was positioned and designed in a manner that would operate the pump until there was no water left, the pump would never turn off, and B) because once the pump goes off, there will be some backwash of water from the hose.  There are some clever designed with sponges and vacuum pumps that might to it, but not a standard bilge pump.

Suggest you take a look at Tom Soko's article in the upgrade section here:
www.catalina36.org/members/technical/upgrades/adding-second-bilge-pump
Similar arrangements are described in Nigel Calder's "Boatowners Mechanical and Electical Manual" and Don Casey's "This Old Boat".

We've duplicated this on our boat, and while it doesn't get rid of all the water, the way the drain hose for the smaller ("primary") pump is plumbed with a loop (as illustrated in Soko's write-up) greatly cuts back on the backwash (and the smaller hose helps as well in limiting the amount of water that flows back).  One still has the original (now "secondary") pump with a large hose size (and no loop) for when the perverbial excrement hits the fan and there's a lot of water to be pumped out in a hurry, activated by a second switch that is mounted somewhat higher.   I find this redundency very comforting.   In fect, we long ago made it a routine, as part of our "closing up the boat" checklist when we leave the boat for any length of time, to check the operation of both bilge pumps, and I've been surprised at the number of times I've discovered that one or the other pump was not working (a loose connection [it is a damp location], some crud wedged in the pump intake, a sticking switch, what have you).

Yes, there are members here who have acheived bone dry bilges -- I, sadly, am not numbered among them!

I think about 1 inch, maybe a little more is normal. I did install a check valve that I bought at West Marine and haven’t had any issues.
Keep sending your questions to the forum - Lots of knowledge sharing and great people.

Mike,

I know this topic has been beaten to death in this thread and in others in the archives. Here are my two cents worth anyway. First, I'd confirm that no bilge pump arrangement will keep it completely dry. I am a proponent of the "dry bilge" school of thought. The only water that should find its way into Jubilee's bilge is from the roller furling mast, i.e. fresh rain water. I keep a small cheap wet/dry shop vac aboard. After rains, I just suck all the water out and pour it down the sink drain. If there is water in the bilge when there is no rain (which is most of the time here in San Francisco Bay), then I know that there is trouble somewhere else and I track it down. I use teflon packing material, so the packing gland is basically dripless. Jubilee's head shower has its own sump. 

Al

Mike,

I agree with those that agree with the inevetible fact that there is no such thing as a "dry bilge"!!!  My Admiral thinks I am nuts (and I may be!) but I am a stickler for keeping ours dry whenever possible.  Some rain water will get in the mast and run down the inside there is no stopping that.  I used to keep a small shop vac..... pain I T A digging it out and all that.  Tried a hand pump... same PITA lining up outlet into bucket.   One day I was cleaning out our aft cabin and came accros a Super Soaker water gun the PO left on the boat and I thought???? hmmm   That is the best thing I have used so far!  I take the bag out of my small trash can in the head,  set it in the dryest end of the bilge and suck her dry!  Even sucks up most of the hair (from the Admiral and her daughter!) and small particles that always find a way down there at the same time.  Who'd a thunk!  

Happy Sucking!
 

Well asking for a laundry list of potential leak sites is another issues altogether, Mike!  Here's my 4 cents worth overall:

• Sucking the bilge dry -- buy a Taylor Made Bazooka Bailer, 5' boat hook with pump inside -- super powerful, suck out and squirt into the galley sink.
• Go for the low profile pump (I used the Whale) at the lowest point and the float switch mounted at a higher level on a piece of Starboard as your PO had installed. 
• I went for the SUPER SCARY one-way valves both at the large diameter hose from the large pump and at the Whale pump before it T-connects into the larger hose.  I used the inexpensive grey plastic ones with the rubber flap inside -- low chance of failure.  Stuck open -- no problem as the back wash just comes back.  Stuck closed -- I check their operation regularly both with switching on manually and running a bucket of water into the bilge by opening the hot water tank release tap and it is unlikely, but then I also have two pumps and two valves, unlikely both would fail... (hey, I'm a risk taker and NEVER close my seacocks!).

List of my "Known Issues" that have been a source of leakage:

• Leaking galley sink drains connections.
• Water from refridgerator drain (I removed the leaking, non-functional foot pump, but I might put a new one back in to prevent cold air escaping...)
• Regular dripping of packing at shaft seal (bought a special narrow adjustable wrench that I leave back there to snug it up as needed to one drip a minute).
• Ruptured fresh water tanks at fittings both on top and below at exit fitting from too much shore water pressue during filling -- requires emptying, drying and sealing with hot melt glue gun and the heavy duty YELLOW coloured glue sticks from the hardware store.
• Water through original center-postitioned bilge through-hull on transom, now covered by a SS plate (manufacturer's mistake?). 
• Water sitting in shallow 'V' shaped hollows along keel aft of the shaft seal.
• Leakage down chain plates (fixed with Creeping Crack).
• Leakage around port holes (bigger repair job...).
• Leaks at several through-deck bolts for hand rails and other fittings.
• Mast leakage (already covered).
• Shower basin leaks into bilge (needs 3M 4200 around the wire hole into the basin for the low profile pump).
• Leaks at all water connections (best to use a heat gun on low setting while tightening the SS hose clamps gently but firmly to soften up the plastic hose and allow for a tight fit.  All connections with below waterline pressure should have Stainless Steel, thick 3/8", not 1/4" wide, DOUBLE hose clamps at each fitting -- ABYC).
• Drill through all water-tight compartments under settees and V-berth along the hull to ensure they all drain into the bilge to discourage black mould.
• Head sink/shower leaks -- also behind head/toilet opening up the drop-down cupboard access.
• Corroded-through hot water tank inside the outer SS box.
• Etc.  (And it's ET-cetera, not ECK-cetera for all my misprounouncing friends out there...  ;-)

Note that I've had the vessel for over 4 years now.  Still finding new sources!  Once you've tracked down and fixed each one you have to dry all sides and compartments that slope into the bilge with a paper towel -- let things sit and then peer into each sloping area with a flashlight to look for drip lines, then track those paths back up to the source.  HAPPY HUNTING!!!

NOTE: My apologies for the recommendation of the Whale SuperSub Smart 650.  While I have one in our shower pan that works fine, the first one I had in the bilge stopped sensing the water level two years ago.  It was sent back to Whale for testing, took TWO MONTHS (not clear what I was supposed to do for a bilge pump in the meantime) and was finally deemed faulty and replaced.  The second one has now failed again -- the manual switch works fine and the pump works, it is the 'electro-static-magnetometer' or whatever they are using for the built-in sensor in the thin 'tail section' that no longer works.  I cannot recommend it.  Rule and other manufacturers make a low profile (although a bit longer) that might prove more reliable.  I'm not replacing it just now, I'll rely on the main pump and I'll suck the bilge a bit drier with the Whale on manual regularly.  Sad that this tech is not up to scratch.

Note further that the photo uploader seems to be rotating the pics 180 degrees.

In the Zodiac I have an Attwood 500 GPH auto float positioned in the lowest corner facing uphill as the 9.9 hp tilts to port when lifted.  It works fine, but I've have had to replace it twice in the spring due to the standing water freezing and breaking the float mechanism. 

Best thing I did was install a 6" x 12" solar charger on the top of the battery box that trickle charges the battery.  I've had it on there for 3 years and even with the pump coming on several times a day (the 'guaranteed' no-leak fix I paid our local dinghy guy for two years ago has begun to fade...) the battery stays topped up for starting, no problem. 
 

Hi,

You might consider to change the mechanical switch to an electronic one. During our almost 30 years with our C36 we have notice that when healing during long time, the classic switch sometimes connected the pump although no water was in, other times , got blocked with devries and did the same.

So we move to an electronic switch and voila! Perfect! The electronic can be regulated so starts operation only after continuisly detected water at certain level, and the most important, stops the pump after 15/20/25 sg no water is detected so normally no water is coming back. 
Saying that, does not provide a totally dry bilge.

I fully agreed with Matheuw, you should only got water after rain, any else should be check. At a certain point, we had salt water coin in in, just when sailing, We got crazy but finally discover it was through the through hull sea cock that discharge water from the anchor well. 

Sometimes we also had, sweet water and it was coming from the water tanks, when overfilled. The installed vent is not  it enough if you are filling the tanks with a lot of water presion.

Just some thought,

Regards

Hereby, the electronic switch we use now.

Regards

Super soaker works quite well.  Discharge down kitchen sink, put a towel over cushions just in case...the admiral shows up & sees water spots.   

Add some lemon juice concentrate to suspect leaking tank.  Then taste the drips to confirm....

You could add food colouring to trace the leak, too, but to detail the 'burst tanks' issue, the squeezed vent hose could cause problems if it gets pinched while filling, but once the tank has been excessively pressured a few times, you are likely going to have problems at the several weak points: the outlet fitting, the inlet fitting, the large access fitting and the vent fitting.  I had leaks on all four after attaching screwed-in fittings to the filler opening and connecting the shore water to them and turning it on full blast to speed up the filling process....yeah, I know.  Live and learn...  So none of those fitting are designed to handle full pressure, but they seal back up fairly well with the yellow 'extra strength/heavy duty' hot melt glue gun sticks as the gun will melt the plastic of the tank and fittings to acheive a complete 'weld'.  Tried the Marine Goop with some success on the large top fitting. Access to the center aft tank outlet fitting was only possible by cutting open the plywood box at the port side, fore-end of the box. 

The vent hoses of the two aft tanks are connected by a T connector and the portion from the center tank was lying on the inner hull below the top of the tank.  I got in there with nylon zip ties and secured the hose against the underside of the bed platform and this seems to have helped to eliminate air locks, although the vents still tends to burp and hiccup a bit before the water eventually runs out of the vent indicating that one tank after the other has filled completely.  I've had no more ruptureing issues since being more cautious, although one of my nephews did turn the water on full blast one time.  Seems it might take repeated high pressure fillings to cause a problem. 

Moral of the story, if you have removed the safety feature (not sure if it was planned?) of an open filling port by adding fittings, FILL SLOWLY (takes up to half an hour for the center tank). 

I recently purchased the Dry Bilge System (www.drybilgesystem.com).  It consists of a sensor which activates with about 3/16” of water, a control unit and a diaphragm pump. Once it senses water it turns on and runs for 10 seconds after the sensor reads dry.  Pretty cool unit.  I just did a temporary install without permanently mounting the pump or control. While testing it, it is powered off a jumpstart battery and the discharge is temporarily run to the sink. My testing was successful and it takes the bilge to dry..  We are expecting some rain in the next few days. When I get to the boat on Friday, if she is dry I will mount the control unit and pump next to the A/C, in the settee in front of the sink and run the discharge hose to the stern and install a new throughhull (or possibly tap into one of the existing discharges at existing throughhull. The electric hookup will be an easy run to the house batteries. Check out the website - he has a nice installation video. I spoke with him with a few questions - nice, knowledgeable and helpful guy. If anyone wants, let me know and I will post some photos when I get to the boat later in the week.