Originally Posted by IolantheSF
I'm replacing a bunch of through hulls, seacocks, vented loops, and hose. It occurred to me that if the outlet (e.g. bilge
pump) through-hulls were up at the rail, then there would be less hose needed and less need for vented loops. The seacocks would then be more accessible, being high in lockers instead of down in the bilge
under cabinetry. Has anybody done this? Is there a problem with it? Thanks,
Bilge Pump Discharge Installation
To obtain optimum bilge pump
performance, the discharge hose should be as short as possible, with shortest elevated height possible, with straightest run possible, with hose equal or greater than output discharge diameter, with fewest restrictions possible.
Often the best theoretical discharge location is in the centre of the transom, above the highest anticipated water
level under all conditions.
If the location you have selected cannot possible go under water
under any heeling (including abnormal) condition, then you are correct, you would not need an anti-syphon valve.
If the location could be underwater (but higher than the other end of the hose) you need an anti-siphon valve to prevent water ingress way. IF the location can be underwater, lower than the other end, the boat will fill with water under all conditions.
So here is the major issue with vessel side mounting. When you are heeled, depending on tack, the discharge may be very low in relation to the inlet(good, max output) or high (bad, reduced output).
When level (95% of the time for most boats) high on the rail will reduce discharge vs a lower mounting on the transom, in almost all cases.
Just a note that folks often never consider, should an emergency
arise and the boat is filling with water, immediately sound the alarm
, turn on the pumps and as soon as practical, TURN ON THE ENGINE
This will increase the voltage supplied to the bilge pump
(rated at 13.2Vdc) to around 14.2 Vdc, and it will output much more that if just running off batteries (that could be down around 12.2Vdc)
The few seconds to start the engine
, could give you considerably more time to find the source of the leak and stop it, before the boat is lost
With the engine started and all pumps running, and all crew (if any) pumping or bucketing water out of the boat, if a catastrophic leak can't be located or stopped, call a Mayday, set a course for a travelift or shallow water (which ever is closest), and prepare to abandon ship, if necessary.
Be aware that as soon as the water reaches the tops of your batteries (assuming all bilge pump wiring
connections are watertight and properly made above this level, which few are) all 12Vdc electrics connected to ships batteries, including bilge pumps, will not operate.
Therefore, if you don't have a handheld VHF
with fresh AAA batteries in your ditch kit, it would be very a very good Christmas
present to the vessel this year.
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