T&T: Bilge pump through-hull

[Peter Bennett]

Sunday, May 27, 2007, 5:55:29 PM, Wesley wrote:

WPE> I welcome comments on a recent change that I made.  When I purchased my
WPE> trawler it had a primary bilge pump and a backup sharing a single 1" hose to a
WPE> through-hull.  Two inch and an eighth pump outlets sharing a single one inch
WPE> hose seemed inadequate so I separated the two outputs and plumbed the backup
WPE> to the unused black water through-hull near the keel.  The primary is
WPE> connected to a through-hull at the waterline and both have vented loops.  I
WPE> have no enthusiasm for drilling more holes than necessary through my hull but,
WPE> at the same time, I am concerned that discharging well below the waterline may
WPE> result in resistance that will seriously compromise the discharge flow.  So,
WPE> should I go back and drill another hole at the waterline?

WPE> Thank you in advance.

WPE> Wesley

I like bilge pump outlets to be well above the water line - that way
there is minimal chance of water flowing in through the outlet.
Remember that the common centrifugal bilge pump has _no_ check valve
to prevent reverse flow.

Because water will easily flow backwards through an inactive pump, you
need to add external check valves in _both_ pump outlet hoses if you
want to have two pumps share a through-hull fitting.


-- 
Peter Bennett, VE7CEI    Vancouver, B.C., Canada
Lien Hwa 28 (AKA Polaris 30) "Sea Spray"
GPS and NMEA info: http://vancouver-webpages.com/peter 
Vancouver Power Squadron: http://vancouver.powersquadron.ca