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Old 08-18-2016, 08:30 AM   #1
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Plug the hole

One of the most meaningful comments I've seen in awhile appeared in another thread here:

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Originally Posted by psneeld View Post
The practical reality is to know enough damage control to greatly reduce the inflow to where it is more than manageable for the pumps.
I felt pretty comfortable with my current setup: 4 pumps with a total nominal capacity of 8500 GPH on a 40' boat.

However, when changing the depth transducer this week I realized a failure of even that single small fitting would overwhelm all my pumping capacity and sink the boat.

The math is pretty straightforward. Even assuming all 4 pumps work correctly my effective pump rate would probably be 4000-5000 GPH. The transducer fitting, a 2" hole located 2' below the waterline will admit about 6700 GPH.

Absent quickly acquiring more pumping capacity or stemming the flow, the boat is going to the bottom.

That is just an example, but my takeaway is the importance of the advice above: Be ready to deal with flooding situations by limiting the ingress of water--don't just expect to rely on your pumps.
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Old 08-18-2016, 08:35 AM   #2
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If you wish to be accurate a pail held to catch the pump overboard outflow and a stop watch might be a huge surprise.
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Old 08-18-2016, 08:45 AM   #3
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I read an account some time ago where a guy's pumps were not keeping up. He closed the raw water intakes for his engines, disconnected the hoses and ran the engines to the yard near WOT with someone watching the water level so he didn't run the engines dry.

Don't know if that was an urban myth or not!
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Old 08-18-2016, 09:08 AM   #4
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I also read somewhere about some folks that tee and valve the raw water intake for just that purpose. It would be easy to do. However, like you said, the process would require a "watch" to make sure the engine (s) didn't run out of raw water.
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Old 08-18-2016, 09:14 AM   #5
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Quote:
Originally Posted by menzies View Post
I read an account some time ago where a guy's pumps were not keeping up. He closed the raw water intakes for his engines, disconnected the hoses and ran the engines to the yard near WOT with someone watching the water level so he didn't run the engines dry.

Don't know if that was an urban myth or not!
I've been thinking about a T connection off my raw water intake to my starboard engine. Run a hose from the T with a valve to the bottom of the bilge. In an emergency, shut the engine raw water intake sea cock in the hull and open the valve to the bilge. You could adjust both valves to pump more or less water from the bilge watching the temp gauge on your engine.
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Old 08-18-2016, 09:25 AM   #6
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Quote:
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I also read somewhere about some folks that tee and valve the raw water intake for just that purpose. It would be easy to do. However, like you said, the process would require a "watch" to make sure the engine (s) didn't run out of raw water.

I have that set-up installed on both engines. Groco SSC after the seacock and before the sea strainer. Ideal to use a supply hose, with a bilge strainer of some sort, from flooded bilge to the SSC.

Haven't had to use it. I assume it would take some adjustment to get the right amount of raw water to the engine and at the same time suck enough water out of the bilge. I also assume a watch would be necessary.

The SSC we have on our AC raw water intake might work similarly, too, in that bilge compartment.

These are mostly installed for ease of flushing. For the engines, I think crash valves would be better, but I couldn't afford to do that much change at the time.

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Old 08-18-2016, 09:27 AM   #7
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Using raw water inlets as crash pumps works IF!!!!!!!!!!!!!!


1. your engine raw water pumps are big enough to really matter....this alone is most often misunderstood. Especially as you need to run at high RPMs for them to be effective.
2. you are sure your bilge is clean enough not to clog those intakes or destroy your raw water pumps in the process.
3. you weigh a temporary clogging that might burn up your impeller with loss of propulsion when the flooding may come under control without them.


When I had a sportfish with twin 3208s, I considered it.


With my trawler and a wimpy Lehman single water pump...I am better off with additional electric pumps. Only if I was about to give up would be to just remove the top of the strainer basket because at that point, it would be well under water anyway and everyone else would already be in the abandon ship mode.
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Old 08-18-2016, 10:03 AM   #8
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We have a 120v submersible sump pump with 11/4 inch discharge hose , it is stored in a milk crate in the lazerette. It take about a minute to get the pump up and running... it will flat move some water...
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Old 08-18-2016, 10:37 AM   #9
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If you want to move water, not much seems to come close to trash pumps.


Have seen more than a few homeowners try to save their boats with home depot 110V sump pumps. While sometimes they do the job, often they didn't.


My point about damage control is always the bottom line.


I have raised boats with a diver laying across cockpit cushions stemming the flow over a low spot in the cockpit while 2 or 3 trash pumps putting out over 10,000 gallons per hour couldnt keep up till we slowed the inflow.


Have enough pumps to keep up with major seeps and trickles, but bottom line is...keep the water out at any cost. Generally pumps lose till the major issue is resolved.
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Old 08-18-2016, 11:12 AM   #10
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At least with the sailboats we always had large sheets of dacron that could be used to help stem the flow from the outside.

I have always thought the best emergency pumps were these. I looked into them on my sailboat but never did it. I haven't yet looked into it for my NP43.
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Old 08-18-2016, 11:15 AM   #11
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Quote:
Originally Posted by psneeld View Post
If you want to move water, not much seems to come close to trash pumps.


Have seen more than a few homeowners try to save their boats with home depot 110V sump pumps. While sometimes they do the job, often they didn't.


My point about damage control is always the bottom line.


I have raised boats with a diver laying across cockpit cushions stemming the flow over a low spot in the cockpit while 2 or 3 trash pumps putting out over 10,000 gallons per hour couldnt keep up till we slowed the inflow.


Have enough pumps to keep up with major seeps and trickles, but bottom line is...keep the water out at any cost. Generally pumps lose till the major issue is resolved.
...and keep your insurance up to date and your life raft ready!
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Old 08-18-2016, 11:41 AM   #12
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I keep a heavy tarp on board with lines attached which will reach around the hull. The plan would be to drop the tarp off the bow and work it into place to cover hull damage and slow water intrusion. By slowing the flow from the outside of the hull, water pressure is working with you rather than against you. Not recommended doing this with the prop(s) spinning.
Also keep the the usual tapered plugs, foam balls etc. readily available.

Dave - those shaft driven pumps seem like a good option.
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Old 08-18-2016, 11:48 AM   #13
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Quote:
Originally Posted by psneeld View Post
If you want to move water, not much seems to come close to trash pumps.


Have seen more than a few homeowners try to save their boats with home depot 110V sump pumps. While sometimes they do the job, often they didn't.


My point about damage control is always the bottom line.


I have raised boats with a diver laying across cockpit cushions stemming the flow over a low spot in the cockpit while 2 or 3 trash pumps putting out over 10,000 gallons per hour couldnt keep up till we slowed the inflow.


Have enough pumps to keep up with major seeps and trickles, but bottom line is...keep the water out at any cost. Generally pumps lose till the major issue is resolved.
Exactly right I didn't mean to imply that this was the end all... It is like a crash pump it is just another means of getting water out of the boat that shouldn't be in there in the first place...
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Old 08-18-2016, 06:13 PM   #14
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dhays - looked at the FastFlow link - just occurred to me that I have no idea what my screw/shaft speed is. I don't think it's anywhere near 1200-2000 rpm. I'm also sure it's all over the place depending on boat. Anybody know "typical" numbers?
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Old 08-18-2016, 06:39 PM   #15
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Typically 2.5:1
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Old 08-18-2016, 06:48 PM   #16
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Quote:
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dhays - looked at the FastFlow link - just occurred to me that I have no idea what my screw/shaft speed is. I don't think it's anywhere near 1200-2000 rpm. I'm also sure it's all over the place depending on boat. Anybody know "typical" numbers?
Me either.

I just looked and my marine gear ratios I believe is 1.96 to 1. So if I am running at 2000rpm that would have my shaft turning at roughly 1000rpm right? I normally run at 1400 rpm which would be about 700 shaft rpm. But if my boat was sinking, and going faster didn't increase the rate of inflow, I would be going as fast as I possibly could. The extra fuel burn would only help lighten the boat.
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Old 08-18-2016, 07:46 PM   #17
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Interesting post! We have a small 18 foot Poulsbo skiff with a 6 hp yanmar. On a voyage a couple years back the sea water pump (salt water cooled) gave out while some distance from civilization.
Disconnected the bilge pump, hooked the discharge hose to the engine port, and placed the bilge pump in our 'sanitary' bucket into which bailed saltwater was placed. It worked to make the 6 mile voyage. We since carry a complete water pump spare as it is only three nuts to remove.


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Old 08-19-2016, 05:58 AM   #18
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Many offshore sailors would purchase soft pine tapered plugs and tie them to each thru hull.

Not a bad insurance even for an inshore boat.

Slow the leak and you don't need the 6 inch pump.
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Old 08-19-2016, 07:38 AM   #19
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Quote:
Originally Posted by AusCan View Post
I keep a heavy tarp on board with lines attached which will reach around the hull. The plan would be to drop the tarp off the bow and work it into place to cover hull damage and slow water intrusion. By slowing the flow from the outside of the hull, water pressure is working with you rather than against you. Not recommended doing this with the prop(s) spinning.
Also keep the the usual tapered plugs, foam balls etc. readily available.

Dave - those shaft driven pumps seem like a good option.
That was the tactic used in the wooden sailing ship days to slow water entry enough for the pumps to cope. Probably captain Cook had to resort to that when he holed his vessel on the Great Barrier Reef and had to go into what we now call 1770 I think, to make repairs.
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Old 08-19-2016, 07:42 AM   #20
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If you use the main engine as a pump via the raw water intake, and you are a single screw vessel, increasing the speed of the boat will dramatically increase the amount of flow coming into the vessel due to water pressure on the hull.
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