NOT having an automatic bilge pump can get very messy too.
I "lost" the grease fitting in the stuffing box but didn't know about it.
Pumped out the bilges and blamed someone for not leaving the boat dry after
using it. Just happed to visit 24 hours later- water was over the
floorboards. Made about 5" water in 24 hrs. Another 3" and the bilge pump
outlets would have been at water line, say another 8 hours and she would
have been gone.
I've now fitted a second battery, and a float switch. Bilge pump runs off
the second battery only. Also re-routed the bilge pump hoses to have a nice
high loop to prevent syphoning back into the boat. Next step is an alarm -
I'm considering either time delayed "bilge pump float switch closed" ( to
detect blown fuse, blocked pump or the pump actually running for a long time
...) or separate float switch from the other battery. I've got an old
mercury switch which might make a good alarm. Or perhaps both alarms ....
In comparing the risks of bilge pump pumping fuel leak overboard vs. boat
sinking, I figure that if it sank the fuel would escape anyway.

If fuel leak is a real issue then a bilge pump switch which works on
conductivity would seem the way to go - it should not respond to fuel in the
bilges. But I'd be concerned that conductivity might not work if the
sensing wire got coated by a small quantity of oil and then would not sense
water...

I agree that trying to home develop a reliable bilge pump switch is probably
not worth the effort. But it's certainly worth thinking through the
consequences of all sorts of events - like fuel leaks, switch failure, pump
failure, flat battery etc etc. And "some one else" forgetting to open the
closed sea-cock before starting the engine ...
If the aim is to prevent sinking of the boat, perhaps using a hydrostatic
system connected to a thru-hull is the way to go. This would turn on the
bilge pump if the boat was too low in the water. Leakage of fuel into the
bilges would not be an issue.
My approach is that I'm more likely to lose the boat by sinking than I am to
have a significant leak when the boat is unattended. Hence I'm doing my
best to protect my insurer by maintaining my fuel system and fitting
automatic bilge pump and ultimately an alarm. I've not had this discussion
with the insurer, but I figure I know more about my boat than they do. I
guess I could also turn off the fuel at the tank whenever I leave the boat,
but it's not normal practice around here, and forgetting to turn it on can
have nasty consequences too.

You can get right into this risk assessment / hazard analysis stuff. And I'm
not suggesting that you should not minimise risks and try to engineer them
out. But ultimately if you are not prepared to accept that there are risks
in everything we do, perhaps you should not have a boat ...

David







"Lew Hodgett" wrote in message
link.net...

"Dazed and Confuzed" writes:

What do you do when the boat is unattended if you don't have a level
switch?

Close any open seacocks when leaving the boat for extended periods.

And what do you think about an electronic level switch?
snip
What technology?

Capacitance, hydrostatic, and vibration are all possibilities, and all
have
a down side.

Vibration would be my choice since it is not affected by conductivity or
lack of it.

Having said that, sloshing around will be a major problem. Level switches
like steady state conditions.

It's a bigger engineering problem than it's worth IMHO.

Having an automatic pump on an unattended boat can get VERY expensive.

As an example, spring a fuel leak and allow 10-20 gallons to drain into
the
bilge, then pump it overboard while the vessel is unattended.

Need I say more?

HTH


--
Lew

S/A: Challenge, The Bullet Proof Boat, (Under Construction in the
Southland)
Visit: http://home.earthlink.net/~lewhodgett for Pictures