I intend to put a huge ( 3500gph) bilge midships in my 69 42'. I would rather not make an  1 1/2' thru hull to accommodate it and a reducer to an existing smaller one would defeat the purpose. Could I Y at the sink grey water  1 1/2' discharge and add the bilge discharge?  This "emergency" pump  will be 6-7" above maintenance  pump level. So it should never go on ...right ;)

If it does maybe it might squirt out the sink drain? If that happens I have more things to worry about than a wet kitchen rug! And a heads up that bilge systems have gone to defcon-5 isn't an bad thing.

Am I missing anything here or is this a no brainer...?

thx!

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Gotta stop doing this kind of stuff while I'm still drinking morning coffee #1. Her's that link to that pump at Lowes --- Even stainless steel !

https://www.lowes.com/pd/Basement-Watchdog-1-HP-Stainless-Steel-Sub...

Couldn't agree more Dick. I had Engine raw water diverters on my last sportfisherman and did a GPH test and it wasnt worth the extra fittings, hose clamps, and bonding that I needed to maintain so I removed them. I added 2- permanantly installed 12v 3500GPH pumps one forward and one aft as well as a 110v 3500 capacity pump that was set up with hose and electrical connections already attached that I could put it where needed. I have since added the same setup to my CC. I figure even at a reduced flow rate I can pump 5000 GPH at the spot I need it.    I did put two safety items in when I was setting this up. First I put enough hose so if needed I could put the 12v pump to either side in the stern. i know I lost some flow but of the boat is listing I wanted the pump where the water is.  I also put a GFCI inline with my 110 v pump as a safety as the last thing I wanted was to be knee deep in bilge water trying to repair a leak and have something on that 110V pump short out and take me out. easy to do and short money insurance for the person trying to make a temp repair in the bilge. I could live with losing a boat but I my first job is to protect the crew!  My entire setup cost me $375.00, Seaflow pumps on amazon are privately labled Rule pumps for 1/3 the price.

Dick Morland said:

Engine cooling pumps as emergency bilge pumps ---- This subject pops up frequently and the consensus is that it's a good idea. Well, I'm not so sure about this. However, I know that being against more bilge pumping capacity in a boat is like being against God, Country, Motherhood, Chevrolet, and Apple Pie all in one fell swoop   So, here's my take on it. For purposes of discussion, lets use the Sherwood 11095G pump found on 427F  & 327F engines. See attachment for this pumps output at various rpm's with 3 different cams. Our pump has the 10961 cam. Looking at the chart we see this pump puts out about 20 GPM at 3,000 RPM. This assumes 0 psi of discharge pressure with 1 1/16" intake and outlet porting. Oh yeah, one more small item --- a new condition pump with no end cap or cam wear and a new impellor. Just about every pump I've seen disassembled has noticeable wear both on the end surfaces and cam. Rev your 427 up to 3000 and observe the exhaust. You really think you're seeing four 5 gallon cans worth of water coming out?? Nope, nowhere near it. In addition to wear, our supply and discharge paths are not full size, plus we have restrictive elements such as oil coolers, thermostats, and 2-3 psi pressure relief valves for the pumps output to pass before it is discharged into the exhausts. I'm going to hazard a guess that a normally worn, as installed Sherwood pump in a 427 actually pumps out about 10 GPM at 3,000 RPM. This certainly is enough to handle the heat load of the engine, but 10 GPM correlates to 600 GPH (bilge pump ratings). Even when you multiply it by 2 you only have 1200 GPH, and that's at 3000 RPM.
Now, let's set our pumps up so they can either draw from their normal through hull supply, or from the bilge. First, this plumbing setup is going to include a Y or a T fitting, a couple of ball valves, & misc. nipples and/or couplings & ells. Guess what ? The ball valves you'll probably use will be a further restriction. Wait a minute, we have to have some sort of filter on the bilge inlet to prevent normal bilge detritus from clogging the pump (Yet another restriction). Now for the last thing --- In operation you have to monitor bilge water level so that you don't uncover the inlet filters and let the pumps run dry. Most impellors will self destruct in a very short time if running dry, especially at 3,000 RPM. Perhaps you're seeing my point --- For the expense, complexity, and operating cautions we don't get a real serious amount of bilge pumping capacity from engine pumps. It sounds good in theory, but in practice you can get way more emergency pumping capacity from say buying an extra 3500 GPH with about 12 feet of 1 1/2 hose, a 20 foot power cord with serious alligator clips on the ends, or for 110v use, I see some reasonably priced pumps at home improvement stores. Here's a serious pump at Lowes -- 4400 GPH at a 10' lift. If you have a reliable generator on board, $173 plus some hose money buys you a hell of an emergency pump. OK, stepping off my soapbox now and waiting for the rebuttals !

Mike, think of the pumps buying time not salvation.   A pump won't keep ahead of a large hole but it will help extend time to fill and reduce the time 'til empty or rate of gain.  Discussing this with an experienced friend he told me no pump can out perform a scared man in the bilge with a bucket.  The scared man should make sure he isn't the last to abandon ship.

A 6in. perfectly round hole with smooth edges will flow approx 33,000 GPH or 550 GPM @ at 1 to 2 ft. head or level differential.

The bad news is that  the 3500 GPH Rule pump is out sized by a factor of 10. The good news is that most holes are not perfectly round nor smooth edged so they will flow substantially less.

I agree with Dick's comments about using the raw water pumps as an emergency bilge pump. I would also add that redundancy is key in emergency situations. The big issue I have with using the raw water pumps in addition to very limited capacity is that by using them for an added purpose, you are adding to the possible list of failures.

It is very bad to have a hole in the bottom of your boat. It is an extremely bad problem if you have no engines and you have a hole in the bottom of your boat.

Tim Miller is 100% correct in his position that the emergency bilge pumps are to buy time. It is important to realize how fast things are going to go bad in a situation such as a ripped out rudder.

I would add that there should be a plan in place in how you would address a hull breach such as a ripped out rudder or a shaft log. Just putting some thought ahead of time into how would you at least partially plug up a 6 in. hole.

Dick also referred to some pumps with given flows at a given head. Many of the popular bilge pumps do not advertise their pump curves, they just rate it at a certain capacity. The problem is that many of these lower cost pumps have very flat pump curves and their flow drops off substantially with a slight increase in head height. Very likely that the 3000 GPH pump you bought only flows 1500 GPH after you have it installed.

Exactly how you pipe the bilge pump is as important as choosing the correct size of pump. Too many fittings, check valves, poor choice of hose or piping materials will substantially decrease the systems performance. This is why sharing a sink drain thru hull is a poor choice.

Mike H said:

Those are excellent points Dick. 

My question is how much water will come in through say a 6”x6” hole? That’s about the size I would expect if say a rudder was ripped out as happened to someone on lk St Clair last year. That’s the point of these big pumps right? Hit a dead head, rip out a shaft log etc.

Only one thing worse than a big leak -a big leak AND a dead engine because the pump is burnt out . I like Dick's idea of hose a big battery clips - gives you a lot of options - maybe you need the pump at the stern or the bow - maybe you can help someone else ( at the dock or on the water ) High water alarms are a must - all the capacity in the world won't help you if all your pumps are running and you don't know it - those little pump lights are hard to see sometimes . Although I have a high water alarm ( sound and light ) I should add a buzzer on the fly bridge .

Hi Dick

I always enjoy reading your comments and respect your opinion. I have employed the by-pass system on my motors annually to winterize the engines when wet storing. I can speak from experience when I say it takes bout a minute and a half to move 10 gallons of antifreeze through the system at 800 RPM. This is based on how much antifreeze she pulls out of a bucket attached to the by-pass hose until I see a good stream of pink flowing out the exhaust and fog the engine (There are several steps in this process to ensure water is out of the system down to the intake.) While simple math would suggest this equates to 26 GPM at 3200 RPM, we both know it doesn't work that way. I have never tried this at 3000 RPM, but applying some quick hydraulic calculations I am guessing I could pull 18 GPM through each motor. Addressing friction loss in this system is negligible. Friction loss through an 1 1/2 Y at 150 PSI is calculated at 5 PSI. I do not know exactly what the raw water pump puts out for pressure, but I would guess it is no where near this. Even having three appliances, a screen, a 1/4 turn valve, and a Y or T fitting will not be a noticeable loss. Loss through the engine would also be minimal due to low pressure. Loss through the exhaust would be non-existent due to the diameter of the pipe.

All that being said, the idea of using my engines to de-water my boat is not my idea of a good time. In my case, it would mean that the 8000 GPH pumping capacity (4, 2000 GPH pumps) in the bilge either can't keep up with inflow, or have failed. Employing this system in an emergency falls under whatever it takes to get you home. I agree that this would be a last resort option due to the potential to damage to your engines. As far as damage to the engines, in a catastrophic hull breach, moving an extra 1000-2000 GPH could make the difference between re-powering the boat and replacing the boat. 

Did I mention I carry two, portable, 3500 GPH pumps with 30' of roll flat hose?

Mike, according to calculations for roof drains, a 6' diameter pipe will allow 33,000 gallons per minute  hour at gravity fed pressure.

I agree with Kevin on the amount of time it takes to drain a 5 gallon bucket using the engine pump. My bucket drains in less than half a minute at idle. Not saying this is the best method of pumping in an emergency; a good bilge pump is probably better. Plus to use the engine pump, you have to get down there and do the switching, while a bilge pump is automatic.

As far as tearing your rudder out and leaving a gaping hole:  in 2015 I hit a rock at about 10 knots and put a 45 degree bend in the rudder shaft. It did not tear out the mount nor leak a drop. So I think you can stop worrying about that. And for most of you, your prop will hit before the rudder does. My rudder is a few inches below the prop.  That rock hit damaged both.

Jim

That should have read 33,000 gallons per hour.

If one really wanted 30-60,000 gph one solution would be to fit one engine with a belt take off with an electric clutch(sort of like car ac clutch) and have it drive a large  mounted self priming semi-trash pump rated for the gph. They are not uncommon and the boat engine has more than enough reserve HP even at cruise. This way one could perhaps make it home with a 6'' hole--or buy enough time to reduce the size of the hole. Hopefully one would not also be close to running out of fuel! I think the expense could be kept at around a $1000 give or take based on ones abilities.

Wow! 

Ronald Zick said:

A 6in. perfectly round hole with smooth edges will flow approx 33,000 GPH or 550 GPM @ at 1 to 2 ft. head or level differential.

The bad news is that  the 3500 GPH Rule pump is out sized by a factor of 10. The good news is that most holes are not perfectly round nor smooth edged so they will flow substantially less.

.

Mike H said:

Those are excellent points Dick. 

My question is how much water will come in through say a 6”x6” hole? That’s about the size I would expect if say a rudder was ripped out as happened to someone on lk St Clair last year. That’s the point of these big pumps right? Hit a dead head, rip out a shaft log etc.

They were going about 20 in an older Sea Ray. Hit a submerged tree, mangled the prop, shaft, stut and ripped the rudder out. There’s alot of momentum even at that speed to do significant damage.

Jim Frens said:

.

As far as tearing your rudder out and leaving a gaping hole:  in 2015 I hit a rock at about 10 knots and put a 45 degree bend in the rudder shaft. It did not tear out the mount nor leak a drop. So I think you can stop worrying about that. And for most of you, your prop will hit before the rudder does. My rudder is a few inches below the prop.  That rock hit damaged both.

Jim

Yeah, but it’s also a Sea Ray, so you have to factor that in too. ;)

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