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Bilge Pumps


The CS27 seems to have been designed by someone who was incredibly optimistic, or perhaps hadn't benefited from a long and distinguished chain of best practices.  I'll give them a break, after all, my boat is 34 years old and a lot has changed since then.

There are three separate bilge areas in my boat
  1. Engine pre-bilge:  A shallow bilge directly below the engine.  It is isolated (excepting overflow) so that oil spills are not automatically  discharged overboard.
  2. Keel bilge: This is the main area in which water collects, and extends from the cabin to the forward v-berth bulkhead.  It has structural baffles with limber holes.
  3. Bow bilge: In some CS27s, this bilge is connected via limber holes to the keel bilge.  That's really how it ought to be, but for some reason, my boat has this area isolated.  I would like to find someone with a better-equipped CS27 who could send me some pictures of this limber hole configuration so I can try to drill out some holes myself.  It's not immediately apparent to me where this ought to be done.

The original bilge pump configuration I inherited with the boat was entirely manual.  It consisted of a Henderson MK-IV pump mounted in the cockpit.  This pump discharges through a 1.5" through-hull mounted on the port side near the transom approximately mid-way between the toe rail and water line.  A very low quality plastic two-way Y-valve selects between a hose in the pre-bilge, or a hose in the main bilge.

This configuration has its merits...
  • No need for electricity.
  • High capacity.
  • Y-valve consolidates hoses and shares a through-hull.
It also has some downfalls...
  • Lousy quality Y-valve was selected.  I'm surprised the handle hasn't already broken.
  • Not being electric, it depends on you not getting tired.
  • Not being automatic, it depends on you being present to work.
  • The hose choice and installation means that you need at least 3-4 inches (or more) of water in any bilge before you can pump.  It also means that you'll never get a dry sump without a sponge or additional small hand-pump.
  • No redundancy.  If this manual pump breaks, there's no "plan B".

Pump Functions
The concept of deploying a separate de-watering, or maintenance, and high-capacity pump seems to have a universal acceptance.  The idea is that 99% of the time you don't need high capacity; You just need to keep the keel sump dry from the daily trickles.  A large high capacity pump uses more electricity than necessary, and has a higher volume hose that will drain back into the bilge when it's done.  This makes it less suitable to the job at hand.  A smaller de-watering pump can be installed with a smaller diameter hose.  This will use less amp-hours, and minimize the flow-back.

In summary, the main bilge pump area ought to have two pumps.  One to take care of smaller volumes, with a primary goal of dryness, and a second with a high-capacity which is to be used in emergencies.  This also provides a degree of redundancy, which is a good thing.

Pump Capacities

Practical Sailor (October 2010) recommends for vessels in the 30-35' range a 1,000 to 1,500 GPH maintenance pump and a 2,000 GPH pump as a backup.  My boat falls below this size guideline, although I'd follow it if I could.  One of the big problems the CS27 has in designing a bilge pumping system is the narrow bilge.  It's not easy to find pumps that fit into the available spaces without raising them up (which increases water level).

In considering the constraints of bilge dimensions, and overall vessel size, I am planning to have a 1,000 to 1,500 GPH pump as a backup / emergency pump and a 500 - 750 GPH primary de-watering pump in the aft bilge.  The pre-bilge pump can be just about any size as that area will overflow into the main bilge if any serious amount of water is entering.

While it would be ideal to significantly increase the pumping capacity of the vessel, there is a significant challenge posed by its inherent structure.  The baffles in the bilge will only permit a certain area to be removed from them for hoses.  I feel that it would be safe to remove volume for a 1.25" and a .75" hose, but to fit two 1.25" hoses would be too much.  Unfortunately, this significantly limits my pumping capacity.

This is illustrated in the photo to the right.  You can see two of the baffles, each with approximately a 1" limber hole at the bottom.  Adding an additional small hose would be no problem with some careful Dremel grinding (the baffles are hollow).  Adding another large hose would be a lot of area to remove, and a challenge to route in the engine compartment.

New Design


The real priority for me is not convenience, but safety.  The most important pump to install is the emergency pump as its high capacity will be much more important than convenient de-watering.  An equal priority is the manual bilge pump, which also has a high capacity, but more importantly will work if the boat's electrical system is compromised.  With these two devices I will have redundancy as well as a fair capacity for purging excess water from the boat.

Engine Pre-Bilge

The engine pre-bilge collects the water from the stuffing box.  Although not a significant volume, it does add up over time.  I plan to replace my stuffing with WL Gore packing material which will cut down even further.  This area also collects any water that comes through the cockpit locker lids.  Although it doesn't have a lot of water inputs, this area is a pain in the neck to pump out because it's under the engine and requires removing the steps for access.  Not convenient.

The plan will be to install a single inexpensive and low capacity pump (500gph) with a non-return valve.  The Whale Super Sub 500 with 3/4" hose is a perfect fit for this space.  A typical 3-way bilge pump switch will be installed for control, although it will most likely only be used for OFF and momentary ON.  Auto carries too much risk of accidental oil discharge.  I may also use a momentary on switch in place; It depends on how the switches lay out aesthetically.

Keel Bilge

The keel bilge is the low-point in the point.  As such, it is where the focus of emergency water purging.  It is also where most of the water in the boat accumulates, so a de-watering pump will get regular use here and provide redundancy.

Primary De-watering Pump

A 500-750 GPH pump using 1/2" - 3/4" tubing with a non-return valve will serve as the primary and de-watering pump for the boat.  This pump is to be mounted in the aft-most keel bilge section.  Pump must fit within a box having the following dimensions: 7" H x 4.5" L x 2.5" W

After reviewing PS recommendations and product overall dimensions I have selected the ShurFlo Bilge 500.  ShurFlo pumps are highly rated in Practical Sailor, and considered to provide excellent performance for the price, as well as reliability.  The real decision maker for me is that it's the closest fit to the narrow aft keel bilge of any pump I can find.

This pump will use a 3/4" Trident XHD hose and a return valve to minimize backflow.  As this is not an emergency pump, and does not have high capacity, the risks of a problem due to return valve failure are minimal.

ShurFlo Bilge 500 Bilge PumpSecondary Emergency Pump

A 1500-2000 gph secondary high-capacity pump will handle emergency water purging.  The high capacity pump will be mounted higher than the primary, and will not use a non-return valve for safety reasons.  This pump is to be mounted in the forward-most section of keel-bilge where the largest space exists between keel bolts.  This pump must fit within a box having the following dimensions:  7" H x 7" L x 4.5" W.

After reviewing PS recommendations and overall pump dimensions, the Attwood Sahara 1100 pump appears to be the best fit for this role.  It has one of the best tested GPH rates in real-world scenarios and is an excellent fit for the area.  Having said that, it is twice the cost of a very close second-place pump, the Shurflo 1000.  I have decided that the extremely good performance and economics of the Shurflo pumps will make this an easy decision for me.

This pump will use a 1-1/8" Trident XHD hose.

Bow Bilge

At this time I'm not planning to install a pump in the bow.  I'd rather pursue a clean set of  limber holes to get the water into the keel bilge.  I'm also not sure of how I can install a through-hull in in the bow that I'll be happy with.  The alternative would be to tee into the sink drain since this would be a low-volume convenience pump, but I'm not keen on using tees.

So, the plan will be to join the bow bilge to the keel bilge.  A limber hole will be drilled either into the bulkhead where the bow meets the head, or on the center line.  The center line appears to be the factory standard configuration, but with no access to the bilge under the v-berth sole, it's very hard for me to see where I'm drilling, and that makes me uncomfortable.

This will be a work in progress...

Electrical Design

  1. Primary (De-watering) Pump: ShurFlow Bilge 500.
  2. Secondary (Emergency) Pump: ShurFlo Bilge 1000.
  3. Pre-Bilge Pump: Whale Super Sub 500
  4. All pumps will be controlled by independent Blue Sea Systems 8263 bilge pump switches.
  5. Power to all pumps will be direct from the house bank positive bus.  See overall Ravat Electrical Design.
  6. All pumps to have appropriately sized fuses integrated into the switches.
  7. All wire gauges to to be sized according to 3% drop tables.
  8. All wire to use adhesive lined heat-shrink connectors.

Plumbing Design

  1. Primary (De-Watering) Pump: Shurflo Bilge 500
    1. Hose: 3/4" Trident XHD ($1.99/ft.)
    2. Length: <tbd>
    3. Non-Return Valve:
  2. Secondary (Emergency) Pump: Shurflo Bilge 1000.
    1. Hose 1-1/8" Trident XHD ($2.49 / ft.)
    2. Length: <tbd>
  3. Pre-Bilge Pump: Whale SuperSub 500
    1. Hose: 3/4" Trident XHD ($1.99/ft.)
    2. Length: <tbd>
    3. Non-Return Valve:
  4. Through-hull Strategy
    1. Manual bilge pump retains its own dedicated 1.5" through hull (existing).
    2. De-watering and Emergency pump to have dedicated through-hulls.
    3. Fittings Required for new through hull
      1. 1-1/8" Through Hull with barb fitting (90 degree)
      2. 3/4" Through hull with barb fitting (90 degree)
  5. Hose routing
    1. Hoses looped high in cockpit coaming near cabin bulkhead in port cockpit locker.
    2. Hoses to be secured with zip-ties and tie-blocks throughout travel.
    3. Hoses to follow original path through bilge.
    4. 3/4" hose to follow 1-1/8 hose by grinding out space above larger opening (with Dremel tool).


Every project begins with research to learn the background requirements, product options, and installation best practices.  Here's a few of the key ones I used.