New Emergency Bilge Pump Install

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mattnj

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I am currenlty installing a high capacity (2000g/hour) emergency bilge pump, which will be above the existing bilge system on a seperate switch and should hopefully never get used...

Regarding the installation a couple of things:-

1) should i have a stopcock on the skin fitting, it seems a bit pointless as i cant ever imagine wanting to turn it off (or is there a reason i should have one)

2) i have bought a non-return valve to go in the pipe, does this go at the bottom, near the pump or middle, or near the top by the skin fitting, any preference?

3) In the unlikley event of the boat being heeled over so far that the skin fitting is underwater, will the non-return valve provide suitable siphon protection.

4) How do i drill a hole through the hull (35mm dia, what type of drill is best) and do i need to treat the core of the hull with anything before sikaflexing in the skin fitting?

Any comments appreciated, Thanks
 
I would have a seacock on the skin fitting; in emergency you don't know what may happen to the boat's trim, and only the integrity of the pipe and installation stands between being afloat or not.
 
Matt,
I have installed a dual system, one for each tack, as my bilges are very shallow. You could put a Y junction to minimise on hose run, but I reckoned if I needed the extra capacity, that would be the system inhibitor. So I have 2 hoses and 2 skin fittings.
I have installed the non return valve quite close to the pumps to minimise the flow back. Not worried if there is a pint of water in the hose.
I put an upward loop in the pipe before the skin fitting, same as the heads discharge and the engine exhaust. Should prevent flow back, but even if it does, its not getting past the non return valve.

No stopcock on the skinfitting, similar to the engine exhaust and the standard Jeanneau bilge pump installation.
My aft area was a bit crowded, so I had to be careful where I put them.

Height above water line for the holes in the hull I judged from the existing engine, webasto and standard bilge pump. Figured if that had worked OK for 5 years, then that would be OK for the new installation.

I measured twenty times, and drilled a 6mm pilot hole, then checking it was OK before committing to full size.
Masked the area to prevent gelcoat chipping or tearing.
I used a standard tank cutter in a multispeed drill, and just let the tool do the work at a slowish speed.
When complete, I cleaned up the holes and put 2 coats of epoxy in the void ( I dont have a cored hull, but if you do, dig it out and refill it properly)
Remove the masking tape.
Then applied Sikaflex sealant (don't use the adhesive!)in large measure
and installed the skinfitting. Had a mate removing the excess on the outside as we squeezed up.
Left it to cure for 24 hours, then hooked up the hoses with double jubillee clips and strung up the hose (I tie-wrapped it to the Exhaust hose) to get the non return loop height.
 
Mmmmm..........................emergency bilge pumps, there is a body of folk who would say it is far better to repair than pump, doesnt matter what size bilge pump you have, a decent sized hole, will overwhelm just about any pump. Mind you I do have an engine driven pump!!
 
ccscott49 said:
Mmmmm..........................emergency bilge pumps, there is a body of folk who would say it is far better to repair than pump, doesnt matter what size bilge pump you have, a decent sized hole, will overwhelm just about any pump. Mind you I do have an engine driven pump!!
Click to expand...

Yep, you still need to fix the hole, but you need to remove the water both during the fix and after you have fixed it, most of the bilge pumps most boats have fitted are just hopeless, i tried filling the bilges from the hose the other day and the standard pump was a joke

i am more confident that my new system (2 x seperate 2000gph pumps) with seperate skin fittings and electrical connections and 28mm bore pipe will shift a serious amount of water in an emergency. I also have a T in the raw water feed to the engine to the bilge so if things get really bad and its starting to get deep inside :-( you can have the engine pumping out too...

this is worth a read !
http://www.yachtsurvey.com/bilge_pumps.htm
 
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A hose slipping off a seacock, or a seacock breaking off the skin fitting, will let in about 70 gallons per minute. That's 4,200 gallons per hour. You don't have long to find and plug the leak.
A high capacity electric bilge pump system is going to give you time to find the problem, because it doesn't occupy you pumping, but will be overwhelmed quite quickly. You can calculate for your own boat how much water she will accomodate before the seacocks are covered and the leak becomes trickier to find.
A small boat lets in as much water as a large boat through the same size hole, so pumping capacity can't be based on size as suggested in that article. In fact you can argue that you need more capacity in a small boat because it will sink with less water in it.
I think that knowing where the potential ingress points are, and how to seal them quickly and efficiently, is the first priority. This is why I like seachests, or manifolds, because they concentrate the problem area and you can find the problem faster. I also like coffer dams around ingress points.
An engine driven pump is the best of all options because of its capacity and because it doesn't rely on battery capacity. A big Edson-type manual pump with a long handle, and a crewmember to work it, is next best.
I'm assuming the most likely ingress point is a seacock/ through hull. A catastrophic incident with a reef or container is pretty well impossible to legislate for.
An exhaust temperature sensor is a good option because if your cooling water flow stops it's possible for the exhaust pipe or silencer to melt before the engine alarm goes off.
Just some thoughts.
 
Salty John said:
A small boat lets in as much water as a large boat through the same size hole, so pumping capacity can't be based on size as suggested in that article. In fact you can argue that you need more capacity in a small boat because it will sink with less water in it.
Click to expand...

The flow rate for a given size hole is dependant on the head of water (depth in this case) as well as the size of the hole. It is likely to be more in a bigger boat.

Your point re a smaller boat foundering more quickly is valid, though.
 
makes me feel more comfortable.....whack a temporary bung in there to drop the hole size by say 50% and my twin 2000gph pumps should be able to hold up fine!
 
Playtime said:
The flow rate for a given size hole is dependant on the head of water (depth in this case) as well as the size of the hole. It is likely to be more in a bigger boat.

Your point re a smaller boat foundering more quickly is valid, though.
Click to expand...

I concur. The water pressure would also be affected by the displacement of the boat would it not?
 
Previous posts are very good advice as always, just a point I would add, is buy yourself a professional core bit and holder, they make the job very easy to do, I have drilled a few thru hulls with diy ones, they do not compare, you will get a lovely clean hole swiftly and easily.
They are available in all good tool outlets, I use www.toolstation.com (just a satisfied customer) and not expensive to buy.
Good luck
 
mattnj said:
makes me feel more comfortable.....whack a temporary bung in there to drop the hole size by say 50% and my twin 2000gph pumps should be able to hold up fine!
Click to expand...

May I just add a few notes of caution regarding 2000gph pumps?

* These pumps are rated in US gallons, so a "2000gph" pump will not pump quite as much as you might think.
* The rating is quoted at zero head, and with a centrifugal pump will drop according to the actual height you're pumping the water to. In a yacht, this may be 5 or 6ft. For a 3ft head, Attwood pumps say there's a 23% drop in output - obviously it'd be an even bigger loss for a 5 or 6ft head.
* The rating is quoted at 13.6v pump voltage, so you'd need the engine running to get near to the quoted output.
* Pumps this size draw a fairly high current (10-12A), so the supply wiring must be heavy enough to ensure you get full voltage at the pump.
* You need to use smooth-walled hose for best results.
* A larger hose diameter will reduce frictional losses and give better performance. Many pumps have a "stepped" outlet spigot, allowing use of 2 or more hose sizes - fit the biggest you can, and make it as short as possible.
* A non-return valve will reduce flow and may get clogged. I'd fit a vented loop instead.

In reality, a "2000gph" bilge pump in a yacht is lucky to shift much more than 1000 imperial gallons an hour.
 
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