Bilge pump mounting position

Rupert Bear · 04 October 2004, 22:34

Silly question time but hey, the only silly ones are the ones you don't ask, right?
Rule bilge pumps, is there any reason why you can't mount them horizontally? the exit route for the pipe and various other things are easier in this orientation although I know that I won't get the sump quite empty I am not too bothered about that.
Just want to make sure that they are not designed to run in the remains of the bilge water and running it completely dry on its side will not bugger it up.

limeydal · 05 October 2004, 03:16

Don't know why not! The literature says they are safe to run dry so shouldn't be a problem. Just a little more stress on the mounting bracket I would think as the weight is now flexing it instead of pushing right down. So bouncing around in a RIB might cause the bracket to fail.
I just fitted a rule 1100 with electronic level sensor to my XS-550.
However couldnt face drilling a large hole in the transom until I knew I had the right setup. So found the rule fitting married nicely to 1" solid PVC pipe.
So put a rule elbow right off the pump and then up an over the transom.On the other side of the transom I put another elbow downwards ;so prevents the pipe from moving.If I ever want to change the pump; the push fit rule elbow just slides off. No hose clips to unscrew!
Seems to work well so far!
cheers Dal

Simon B · 05 October 2004, 07:30

RB,

We have a 4000gph monster fitted to our RIB (got it cheap and really shifts it) it tends to run dry as soon as air enters the pump through the grating. I think this is because that is the bottom of the impellor but havent tested it yet.

when it does this it entrains loads of air into the little remaining water left to pump, thus pumping it very inefficiently. With the pump on its side I would hazard a guess that it would start to do this as the water level reached the top of the grating and the pump then "sucks a vortex"

Ian Austin · 05 October 2004, 07:34

Rupert
If you mount the bilge pump on it's side there is a very strong chance it could cause a vortex (pulling in air) which wold cause the impeller to cavatate and with a head of water it will not pump, the only way to get it to pump again it would have to be switched off to let the water in the pipe to return to the bilge, you do not have to use a stiff pipe to get rid of the bilge water, you could use a colapsable pipe there for it would find it's own route.
HTH

Pete7 · 05 October 2004, 07:40

Limeydal,

Why is there an elephants trunk inside the boat ?

Pete

swginn · 05 October 2004, 07:54

I can answer that one for you. The elephants trunk is actually tapered and goes around the cables exiting an underdeck wiring loom and to above water level. This stops any water ingress to the under deck loom. The under deck loom is watertight anyway and does leave the hull completely void sealed. This is just there to prevent any water entering the underdeck loom and reaching the centre console (where the cables enter the loom). I guess it's a bit overkill as the water level would need to be very high in the boat for it to enter the console. I suppose overkill is the better solution when working on RIBs though.

ashbypower · 05 October 2004, 07:54

Hi I think you'll find it's the
underdeck ducting outlet. However on the 550 I've seen it had a witchs hat.
I could be (and most probably am) wrong.

Brian

limeydal · 06 October 2004, 00:09

Brian,
hope this clarifies things,
cheers Dal

ashbypower · 06 October 2004, 10:38

Cheers Dal, I guessed it would be something like that. Unsure what arrangement our 550 is coming with, but certainly like the layout of your's

Do let us know how she goes when Skeg is sorted and the Suzi is "Run in".

Brian

lc0021 · 06 October 2004, 22:06

Mmmm ... I notice from the photograph that the exit from pump is tight over the top of the transom and then exits below the level of the transom..

Is it not necessary to put a large U bend on it to stop water syphoning back when the exit is under water - say in the stern wave when slowing down ??

Richard B · 06 October 2004, 22:41

Quote:

Originally Posted by lc0021

Is it not necessary to put a large U bend on it to stop water syphoning back when the exit is under water - say in the stern wave when slowing down ??

Don't worry about water siphoning in thru' a 1" tube, just worry about the wave coming over the top! You can control the stern wave with the throttle, anyway.

limeydal · 06 October 2004, 23:19

On the outside of the transom, the pipe only turns down enough to lock it in place.So its outlet is actually about 3/4 " below the top of the transom.
Havn't noticed any problem with flow back as yet; but if it does I will have to get up courage with a big drill and run it in flexi hose up higher through the transom. Hate to do that as dont want to get too crowded with wires and pipes.
On one side I have the VHF antenae and the other side, the Mount for the Nav.lights.So wanted to keep a space nice and clear to put a transom mounted swim ladder at a later date;
cheers Dal

limeydal · 06 October 2004, 23:26

Richard,
was undecided about that for a while when ordering the boat.
Whether to go for a longer shaft on the engine and have greater freeboard,which I thought "safer" . But on thinking again, If the boat gets swamped, thats a lot of water to empty out.Whereas with lower freeboard a lot of that just flows straight out over the transom.
So not sure what the "experts "think; but I went with the lower freeboard(As also I dont carry a heavy loading on the boat)
cheers Dal

lc0021 · 10 October 2004, 08:31

Quote:

Originally Posted by Richard B

Don't worry about water siphoning in thru' a 1" tube, just worry about the wave coming over the top! You can control the stern wave with the throttle, anyway.

Sure - I realise you can control the sternwave with the throttle under most conditions.... and it's not really the quantity of water I'm concerned with - it's the back pressure on the pump - the issue is that if the exit is (say 2 inches) below the level of the transom - you now have the pressure of the stern wave coming back up the pipe and acting against the pump (which may be pumping at the time...) BEFORE the water is coming over the top...

I wondered if this

(a) would lead to situations when you effectively have no pumping action or

(b) might either damage the pump or blow a fuse from excess load....

lc0021 · 10 October 2004, 08:37

The reason I mentioned this is because I just fitted a bilge pump - and I wasn't happy about drilling the transom - for all the usual reasons about putting another hole in the boat - etc - as well as hagving this thing about the back pressure... I had searched for a one-way transom fitting to no avail - If I had found one I may have gone ahead with the Black & Decker... - so I ended up putting a large (18 inches...) U-Bend on the exit hose and taping this on the A Frame with the exit hanging just below the top of the transom... (not pretty - but reasonably well disguised)...