Pump Float and Three-Way Switch Install - Page 3 - SailNet Community
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post #21 of 39 Old 05-23-2008
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Max-

Depends on how deep the opening for the through hull is.

The formula for flooding is:

Q = 20 x d x square-root of h
Q = flooding rate in gpm
d = diameter of hole in inches
h = depth of hole underwater in feet

So, if your through-hull is 3' below the LWL, then you've got Q=20 x d (1) x h (sqrt 3) or 20 x 1 x 1.735 = 34.7 gpm.

A Rule 1500 pump supposedly does 1500 GPH, or 25 GPM. However, if the bilge pump hose has any head (vertical rise) that number drops significantly...so figure that a Rule 1500 would actually pump 15 GPM or so... You'd need a much bigger pump to keep your boat afloat.

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Last edited by sailingdog; 05-23-2008 at 01:55 PM.
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post #22 of 39 Old 05-23-2008 Thread Starter
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I have a manual pump to the cockpit, I do not know if it is high volume, by its size sitting on top of the keel in between the bolts, it probably is not. A second one is a good idea. I would need a third output line and another hole in the hull though?
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post #23 of 39 Old 05-23-2008 Thread Starter
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Quote:
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Max-

Depends on how deep the opening for the through hull is.
Saildrive leg, seacock 2 inches above the floor.
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post #24 of 39 Old 05-23-2008
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Max-

What is the hull draft on your boat... how deep is that part of the hull???

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post #25 of 39 Old 05-23-2008 Thread Starter
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I have not measured, but it is not much:







These pics are not great as they were taken with the blackberry, but they will give you an idea of the wetted surface.

Spec'd draft is 5.4.

Last edited by max-on; 05-23-2008 at 02:13 PM.
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post #26 of 39 Old 05-23-2008
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I'll bet SD has the formula for calulating volume of a cylinder in s/f memorized . . . I'm too lazy to look it up.

But them again max, that boat is so flat it must plane!

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sold the Nauticat
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post #27 of 39 Old 05-23-2008
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Quote:
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Could not see any value in having an off position - especially in conjunction with a float or electronic sensor switch.
A hard wired 3 position is what I accustomed to on my last 3 boats. Lots of reasons for the OFF - Stuck float while sailing so pumping dry for X amount of time IF you can get down there and fix it right away or Not = burning out the pump, Cleaning or checking the float and bilge area. I like the Green to Red indicator on my NC but I had a Pumping indicator on my previous 2 boats. If I'm dumb enough to leave the boat without putting the switch on Auto - I deserve trouble.

Stan
'Christy Leigh'
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post #28 of 39 Old 05-23-2008
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Max-

From those photos, I'd estimate, you're looking at 2' of head on the pump thruhull... so about 28 GPM.


TB-

FYI Volume of cylinder: Pi * R^2 *h

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post #29 of 39 Old 05-24-2008
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Practical Boat Owner (UK) this month reviewed bilge pumps. They liked the Vetus EB80 and Plastimo 1400 in the large size pumps as well as the Atwood Tsunami; all did about 45 liters/min at 1 meter of head, with 12v input. The Tsunami was rated well also for efficiency, ie...water moved per amp. The Rule 27D was mid-pack to upper mid-pack ib flow rate, head and efficiency.

The most interesting pump they reviewed was the new Whale Supersub 500 which only pumped 35 liters/min rated and 15 liters/min at 1 meter head tested but it's compact size and ability tyo fit in a narrow or shallow bilge impressed. Most impressive was that it drew just over 1 amp versus 3 amps and higher for the other pumps tested. It pulls water down to 12 mm and it sounds like it would be an excellent housekeeping pump.

Note that the numbers cited in their tests were at 12 volts, admittedly a low voltage situation.

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post #30 of 39 Old 05-24-2008 Thread Starter
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Thanks Sailaway.
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