Rule 2000 not lifting

[Jammer]

Originally Posted by rslifkin

The diaphragm pump would be in addition to the big Rule, not instead of. So you'd want/need what you've already got anyway, just possibly with a change to the height of the float switch for it.

The diaphragm pumps don't move as much water. The received wisdom on CF is that you should have more than one electric bilge pump anyway. But I'm not sure, in practice, how common that is. People tend to encourage others to install more safety gear than they actually have on their own boat.



In addition to the manual pump, my boat came with one bilge pump, a diaphragm one. It moves 240 gph and uses 3/4" hose. In principle I would like to add a "crash pump" at some point--a centrifugal pump much like the one you're installing now. The installation would be involved. It won't happen this year.


I've been tempted to assemble a bilge pump with a suitable length of 1.5" layflat PVC discharge hose and a power cord with a powerpole connector on the end for emergency use, and leave it in a locker somewhere. With a spring clamp on the discharge hose to hold it to a gunwale. That would require less installation and would have the advantage of being able to be used to assist other boats. It would also be more convenient to move e.g. away from sources of clogs. It would perhaps be less convenient that flipping a switch in the event of an emergency.

[rslifkin]

Originally Posted by Jammer

The diaphragm pumps don't move as much water. The received wisdom on CF is that you should have more than one electric bilge pump anyway. But I'm not sure, in practice, how common that is. People tend to encourage others to install more safety gear than they actually have on their own boat.

In addition to the manual pump, my boat came with one bilge pump, a diaphragm one. It moves 240 gph and uses 3/4" hose. In principle I would like to add a "crash pump" at some point--a centrifugal pump much like the one you're installing now. The installation would be involved. It won't happen this year.

I've been tempted to assemble a bilge pump with a suitable length of 1.5" layflat PVC discharge hose and a power cord with a powerpole connector on the end for emergency use, and leave it in a locker somewhere. With a spring clamp on the discharge hose to hold it to a gunwale. That would require less installation and would have the advantage of being able to be used to assist other boats. It would also be more convenient to move e.g. away from sources of clogs. It would perhaps be less convenient that flipping a switch in the event of an emergency.

I definitely agree with most boats having inadequate bilge pumps (especially from the factory). Both in terms of not enough pumps and too-small pumps. Ideally, you should be able to break off the lowest underwater hull penetration in the boat (engine intake, depth transducer, prop shaft are the likely candidates) and have enough non-manual pumping capacity to keep up with the inflow while you assess and mitigate the situation. And even more than that doesn't hurt, as there's no such thing as "enough" pumping capacity in the event of a hull breach due to collision or severe grounding.


In the main engine room bilge on my boat I've got all centrifugal pumps currently. 1 small (Whale supersub 650) to deal with nuisance water (this boat won't ever have a perfectly dry bilge due to stuffing boxes, etc. so I don't care about the 1/2" left in the bottom) and a Rule 3700 mounted higher as a backup.

Because the 3700 is mounted higher than I'd like (doesn't physically fit any lower in the bilge due to size) I've been considering adding a third pump (not sure what size yet) at an intermediate level, as I'm already in the process of adding a high water alarm float in that spot (so it's easy to make the #2 pump and alarm share a float, just with a 10 second delay relay on the alarm).

My forward and aft bilges only have a single smaller centrifugal pump, although both can overflow to the engine room bilge (and I've been looking at options for adding a second pump to at least the aft bilge). Based on pump specs and a somewhat conservative de-rate for hose restriction, etc., I consider my real world pumping capacity to be 5 - 6 gal/min (300 - 360 gal/hr) for each of the 3 smaller pumps and ~40 gal/min (2400 gal/hr) for the big pump. The jet of water from the discharge of the 3700 when testing it is rather impressive. I probably don't test it as often as I should though (beyond a float lift to make sure it runs) as testing requires flooding 100+ gallons of water into the bilges (enough to overflow to both forward and aft bilges, as I have to fill to nearly the top of the hollow keel sump).

[Celestialsailor]

I wonder if there is a programmable float switch that could handle the extra drain back.

[rslifkin]

Originally Posted by Celestialsailor

I wonder if there is a programmable float switch that could handle the extra drain back.

Some of the electronic switches (like the Water Witch and the Whale switch) have a timed shut-off delay. You could also build something similar with a regular float switch if you power the pump through a relay with a delay-off timer in it.

So you place the switch based on when you want the pump to turn on. Once the water drops below it and the switch turns off, the pump runs for a few more seconds to remove the rest of the water below the switch level. Then when the pump shuts off, the drain-back doesn't raise the level high enough to trigger the switch back on.

[Nord Sal]

Originally Posted by boatpoker

Does anyone know how to calculate the difference in flow rate between corrugated hose and smooth hose due to friction loss ?

One needs to determine a system curve for each configuration. These curves show the head required to produce a given flow rate depending on the size and length of the suction and discharge lines and what fittings, valves, etc. are in the lines. These curves are completely independent of the pump.

A smaller diameter line will have more head loss to pump the same amount of flow than a larger flow and thus require more pressure from the pump to push it. Head loss in a conduit is directly proportional to the velocity of the fluid squared. Velocity in the conduit is inversely proportional to the diameter squared. So, if you double the diameter of a conduit, the velocity of the fluid will reduced to 1/4 that of the smaller conduit [(1/2)^2] at the same flow and the head loss in the larger conduit will be 1/16th that of the smaller one [(1/4)^2 ].

I drew a couple of crude system curves on the rule pump curve to illustrate the principal. The point where there is zero flow corresponds to the static lift, in the OP's case that would be 6.5 feet. The curve to the right represents the static lift plus all the dynamic head losses (friction loss and minor losses in fittings). The system operates where the system curve and the pump curve intersect.

People say that the pump manufactures cheat the specs. This isn't true, it's just that people don't understand that the specs are just for the pump, not the system! The pump manufacture doesn't know how the pump will be installed. If I were to spec a large pump, I'd get a pump curve somewhat like the one's Rule provided in my example. It'd be my responsibility to determine how that pump would work (or not!) within the system I designed.

As was said above, with everything else equal, the larger line will always produce more flow than the smaller line and the height of the lift is what matters, not the weight of the fluid contained in the line.

It's hard to know what's wrong with the OP's system. It should be able to pump with a static lift of 6.5 feet (its shutoff head, i.e., zero flow, is 21 feet), but it sounds like he's getting no flow at all. It literally could be as simple as the power leads being reversed.

[thinwater]

A submerged pump is NOT lifting water. Yes, this is just terminology, but it's been buring my eyes. In fact, as long as the impellor is submerged, the suction head is slightly positive. And BTW, the NPSH (net positive suction head) is defined as the static submersion head plus atmospheric pressure.



Suction lift is that distance below the pump to the bilge water level. Discharge head is the distance above the pump, and consists of static head (height the water is pushed) plus velocity head (the speed of the water in the pipe) plus discharge pressure (zero if just out a fitting). The suction head is subtracted from the calculated discharge head, but in this case will be zero (or slightly positive if the sump is deep).

[Jammer]

Originally Posted by Celestialsailor

I wonder if there is a programmable float switch that could handle the extra drain back.

There are not any marine ones that I'm aware of.


There are adjustable ones for other applications, like this Little Giant 599929 switch:

I am not sure how well it would hold in a marine environment. The contacts are meant for AC but would probably be fine for 12v if used with a relay.

[Celestialsailor]

I wanted to conclude the thread by sharing the finalized version of the system. In the picture you can see the 4 ft. depth of the bilge and at the bottom of it, being a very tight area. The green hose is the 1 1/2" manual bilge pump line attached to the strainer. The white corrugated is 1 1/8" line goes to the Rule 3700. I used #10 wire and tested an almost 0% line voltage drop. Because of the small bilge volume area, water drains back from the hose, into the bilge and floats the switch and turns the pump on. So I installed a check valve and raised the switch an inch more. The second photo shows the column of water exiting the boat.

[rslifkin]

Why only 1 1/8" for the 3700 instead of 1.5? It'll definitely move more water with the bigger hose. Also, ditch the cheap corrugated hose for something better quality and smooth bore. That'll also get you some more flow.

[Celestialsailor]

Originally Posted by rslifkin

Why only 1 1/8" for the 3700 instead of 1.5? It'll definitely move more water with the bigger hose. Also, ditch the cheap corrugated hose for something better quality and smooth bore. That'll also get you some more flow.

You’re correct about a smoother hose. I’m looking. The problem I had was both rise and run. Although the flow is restricted, the rise increased. The system was s working adequately.