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[NFMike]

Take a flat bottomed boat - not a barge, but a powered vessel with a shaped bow and stern and about 70% of the hull between flat bottomed.
Where would you put a bilge pump extraction point?

It seems to me that you'd need two, or maybe even 3 or 4, to ensure that water was pumped out before the boat sank - assuming of course the pump can drain it faster than the water is coming in.
I say that because if for example the pump is near the stern and water enters at the bow (leaking bow thruster perhaps) then the boat will get bow heavy and the water will never get to the pump (well not till the boat is doing a passable impression of the last minutes of the Titanic).
I'd expect boats with curvy bottoms (down boys) won't have so much of an issue with this as water will tend to quickly collect at the lowest point, but with a flat bottom there isn't really a lowest point until the boat gets off level when it becomes a coin toss as to where the lowest point ends up.

Anyone had any experience (probably bad I'd think) of this? Anyone even considered this 'problem', if it is one?

[Netleyned]

I would put the pump at the lowest part of the hull,normally towards the stern in a narrowboat in the engine compartment as the stern normally sits a little lower than the bow.
If the hull has frames along it's length you will need limber holes in each frame to enable the water to run aft.

Ned

[NFMike]

I would put the pump at the lowest part of the hull, ...

So would I. But the lowest part of this particular hull is 200mm wide and 600mm long .....

Oh yes, there are no frames or obstructions as it is.

[boatmadman]

I think I would consider making the hull into 2 water tight compartments if possible, and fit 2 bilge pumps.
Ian

[Netleyned]

In that case Mike I would put a spirit level in her when afloat and find the lowest point.

Ned

[Subculture]

Making the boat watertight is the best policy IMO. Ask a submariner for tips!

If that seems too much trouble, then how about laying some preshaped angled polystyrene foam inside so that the water will collect at designated single point, where you could place a single pump.. The angle could be very modest, so the foam needn't take up a lot of space, and the weight of foam is neglible, so now worries about stability- plus it will help keep the boat bouyant if you sprung a leak that the pump couldn't handle!

[NFMike]

I think I would consider making the hull into 2 water tight compartments if possible, and fit 2 bilge pumps.
Ian

I had that thought, but reluctant to spalsh another £30 on a second pump and controller.

In that case Mike I would put a spirit level in her when afloat and find the lowest point.
Ned

LOL. But unfortunately there is the small matter of free surface effect.

Making the boat watertight is the best policy IMO. Ask a submariner for tips!

If that seems too much trouble, then how about laying some preshaped angled polystyrene foam inside so that the water will collect at designated single point, where you could place a single pump.. The angle could be very modest, so the foam needn't take up a lot of space, and the weight of foam is neglible, so now worries about stability- plus it will help keep the boat bouyant if you sprung a leak that the pump couldn't handle!

I did think about watertighting, but it's hard to do, and if something springs a leak your plan is scuppered anyway.
I'm glad you suggested the polystyrene - I'd been thinking that myself, but thought maybe it was the drugs  (I was also thinking squirty foam.)

[Subculture]

PU foam in a can can get a bit messy, and it tends to stick to everything, including stuff you don't want it to stick too!

[boatmadman]

I had that thought, but reluctant to spalsh another £30 on a second pump and controller.
LOL. But unfortunately there is the small matter of free surface effect.
I did think about watertighting, but it's hard to do, and if something springs a leak your plan is scuppered anyway.
I'm glad you suggested the polystyrene - I'd been thinking that myself, but thought maybe it was the drugs  (I was also thinking squirty foam.)

Well that is a thought, but when compared to the overall cost of the model, in terms of your time as well as cash, its not really a lot for peace of mind is it?

Have a look here:

Cheap as chips waterpumps
http://www.ebay.co.uk/itm/290600401745?ssPageName=STRK:MEWAX:IT&_trksid=p3984.m1423.l2649

As for a controller, how about something like this:

http://www.ebay.co.uk/itm/LONG-Water-Level-Sensor-Liquid-Float-Switch-Tank-Pool-/290458324956?pt=UK_BOI_Industrial_Automation_Control_ET&hash=item43a0aa4fdc

There are other water level switches available, just do a search on ebay.

Ian

[Netleyned]

If free surface is an issue just placethree or four longtitudinal baffles a couple of cms high if the stern or bow is lowest not forgetting to leave gaps at each end lol
Whether the pump is running constant or switched auto you should not get an uncontrollable roll
What are you building and why do you think you are making a leaker

Ned

[Bob K]

Even a ship with moderate freeboard can get swamped by wash or freak-gust waves, as I have experienced to my cost.  Subculture's prevention solution should always be the first option.  Make the decks and hatches as waterproof as possible to limit ingress.
A long narrow warship with a fairly flat bottom will tend to rise at the bow with speed, so around 1/3 from the stern is a good position for a bilge pump when the bottom is level under neutral ballast trim. 

[NFMike]

Well that is a thought, but when compared to the overall cost of the model, in terms of your time as well as cash, its not really a lot for peace of mind is it?

You're right, at £600 odd for the whole caboodle I'm trying to make sure it doesn't end up on the bottom - just looking for the most cost effective and reliable method of doing it.

Cheap as chips waterpumps
http://www.ebay.co.uk/itm/290600401745?ssPageName=STRK:MEWAX:IT&_trksid=p3984.m1423.l2649

£2.50 including postage from Hong Kong. They must be rubbish.
I've ordered a couple anyway 
The float switches look a bit large, but I'll have a poke around for others. Thanks for the links.

What are you building and why do you think you are making a leaker

I don't think anyone building boats or ships (scale or 12":1') expects it to be a leaker. But they still manage to fill up with water at frequent intervals. This particular one is an AHTS so will get a lot of water across the rear deck, but I'd probably be going through this exercise with any model. Things sometimes break.
My history with the sea and aircraft has taught me that "assume" doesn't make an a*s of u and me - it makes you dead. So I try to prepare for the unexpected. It's a boat, therefore it will get water in it (I've already done a test with a propshaft and plastic tub to see how much will come in that way). So now I'm planning how to try and get that water out again - elegantly if possible.

Subculture's prevention solution should always be the first option.  Make the decks and hatches as waterproof as possible to limit ingress.

Of course, but as I saw recently on YouTube, you forget to fix a hatch down and ... glug, glug.

[Bob K]

If you are going to fit a bilge pump I would recommend the one from Hunter Systems, just £10.95, and it does shift quite a lot of water.
http://shop.huntersystems.co.uk/submersible-pump-459-p.asp
The controller for it is £21.95 and has a neat two prong water sensor which avoids messing around with floats.
If it senses water it switches on, and can be mounted right on the bottom of the hull.

Note additional under deck sealing panels with magnetic catches.  However good the pump is if you get swamped it can only give you more time to get the boat to the side for recovery.

[offshore1987]

raise the floor and put a wel init? i.e a low point? normaly near the stern 

Dan

[NFMike]

£2.50 including postage from Hong Kong. They must be rubbish.
I've ordered a couple anyway ...
The float switches look a bit large, but I'll have a poke around for others. Thanks for the links.

Just an update on this.

The cheap pumps arrived from HK a few days ago and I got round to testing them and also the one I got from Hunter's.
This is the two types:


The one on the left is the Hunter unit in black, on the right in white is one of the Hong Kong jobs.
Clearly the pump casings are different, but both are gear pumps. The connections on the Hunter are larger, about 4mm against 3 on the HKs.
The motor casings are similar enough to probably be the same make, but there are other differences. The HK has a metal end plate, the Hunter is plastic, and the windings on the Hunter's armature are visibly finer than the HKs' which fits with the Hunter being rated 6...12V and the HKs 3...9V.

I tested the units by making them pump water from a bowl into a measuring jug. I used a small, variable voltage power pack to drive them.
I used the 12V setting for the Hunter. It drew about 1.2A and moved 600ml in 30 seconds.
I used the 9V setting for the two HKs. They drew about 2.2A and 2.4A and moved about 380ml and 480ml in 30 seconds respectively. BUT, my little PSU is only rated for 1.2A, so I reran one test to measure the motor Volts instead of Amps and it was only about 3V. Presumably if given the full 9V they would perform better, but also draw more current.

Since my boat has a 12V system I had thought that if these cheapies were OK I could drop the volts using a regulator or even a resistor, but that was predicated on an Amp or so of current. If we're looking at maybe 3A that becomes more of a job and the cost will trade off.

I'm also conscious of purpose. Worst case (nearly) is the boat is damaged, disabled and leaking in the middle of a lake. The bilge pumps need to run until rescued and the difference between 2A and 6A on battery life could be 'the difference'. So I've decided to get a second Hunter unit.

The HK pumps would probably be fine for something less vital - working fire monitors or thrusters maybe. I don't need such things at present, but unfortunately posting them in the UK would cost almost what I paid to get them from HK, so instead of trying to move them on they will go in the future ref box for now.

I couldn't find a float switch that I thought would be suitable, mainly for reasons of space and control of the switching level, so I've also ordered a second Hunter level switch.

[Subculture]

The Chinese pumps don't like being run fast if they go dry. Unless they've changed the spec (unlikely) the plastic is super soft , and the keyway for the driven shaft soon rounds off and knackers the pump- ask me how i know! This happened when running at 6-7volts, BTW.

The pumps are nicely designed, if they'd used a better material, they would have been great little units, as they stand I advise giving them a miss until the manufacturer raises its game (won't hold my breath on that one!). However they're probably fine if kept to about 3-5 volts.

For bilge pumps I would have thought a centrifugal unit would be better- you want high volume and low pressure, and they're ideal, plus you don't have worry about gears stripping.

[tobyker]

If you've got 12v available, what about car windscreen washer pumps? The one  in my Picasso feeds from the bottom so you could mount it upright in the boat, and make a simple float switch with a slab of foam and a microswitch.

[essex2visuvesi]

I have one of the white pumps on my huntsman for water cooling the main drive motor and esc.  I will also add a coil to the pump motor if it starts getting too hot

The way I have mine setup is on a 3 way TX switch and avintage ESC as the modern ones all seem to squeal at lower throttle settings
Pos 1 off
Pos 2 35% (This gives a "scale look" water flow)
Pos 3 75%

Im thinking about using the Helicopter mixing option on my TX to make the pump proportional to the drive

[NFMike]

For bilge pumps I would have thought a centrifugal unit would be better- you want high volume and low pressure, and they're ideal, plus you don't have worry about gears stripping.

In theory yes, but at the time of purchase in model sizes no one tells what type of pump it is and not even what its delivery spec is. (Although at these sizes I don't know if the performance of gear to centri is much different in use.) I know these are gear type cos I unscrewed the cover to look inside. Gear stripping shouldn't be a big issue if the inlet is screened to prevent debris going in, but if not then yes.
With a centrifugal you'll need a non-return valve too to stop water entering the boat that way.

[essex2visuvesi]

Gear stripping shouldn't be a big issue if the inlet is screened to prevent debris going in,

I put a fuel filter from my Nitro RC heli in the inlet line

[Subculture]

It was the shaft key stripping on the gear I was referring to. Unfortunately this is a fairly common problem on pumps with plastic gears, I guess that's why the better quality pumps use brass gears. A centrifugal pump will only fill up if the outlet is located below the waterline.

I agree that lack of performance data is a hinderance when selecting a pump. This website lists quite a lot of information, although I wonder at the accuracy of some of the specs listed there.

http://www.wiperblades4u.co.uk/replacement-washer-pumps/

[roycv]

Hi Mike and others, I have just received my very cheap Hong Kong pump and also just tested it.
It runs very strongly on 6 volts.  With water etc the current is just under 4 amps at 5.5 volts all measured.

Under test at the above power (22 watts) it pumped 500ccs of water in 44 seconds.  Squirts water quite a long way!

I think I might use some old 2000mAh AA cells for the job in the boat, just squirting water, not critical bilge pumping.
regards Roy

[NFMike]

It was the shaft key stripping on the gear I was referring to. Unfortunately this is a fairly common problem on pumps with plastic gears, I guess that's why the better quality pumps use brass gears.

Oh, right. But I suspect the cause may be the same - foreign body ingested, gears jam solid, motor inertia breaks the weakest link ...

I agree that lack of performance data is a hinderance when selecting a pump. This website lists quite a lot of information, although I wonder at the accuracy of some of the specs listed there.

http://www.wiperblades4u.co.uk/replacement-washer-pumps/

Browsed about half a dozen on that site and only found one (a Universal one) with specs. That was 12V, 2.5A, 1300 ml/min. The Hunter unit does 1200 ml/min for half the current. Clearly the Hunter has a much more efficient motor that either this one or the Hong Kong ones we have mentioned here.
I'd also be wary of windscreen pumps for 'emergency' pumping as they are probably short-time rated - the lower current of the Hunter one should be less likely to overheat.
I noticed while originally researching pumps that many of the ones on offer for model boats are "are not designed for continuous running, they should be run in bursts of up to 30 seconds, followed by a 2 minute cooling period" which suggests windscreen pump to me. BTW that quote is for a Graupner unit that costs twice as much as the Hunter one and only shifts 900 ml/min. But at least is does say what it moves; and that it's a gear pump.

[NFMike]

... just under 4 amps at 5.5 volts all measured.

Ouch!

[Subculture]

There was no foreign body ingested into the pump. I was using fresh clean water out of the tap to test the pumps on the bench. Regarding the specs on the site I linked to, although not every pump is specced, there are certainly quite a few- think you need to take a look again.

Also bear in mind that the pumps will pull more current when under load. If they're just running unpressurized they will tend to run at much lower currents.