Massive bilge pump idea

[a64pilot]

Originally Posted by Steady Hand

Obviously I don't see it that way.

But, why do you think so?

The scenario is written as it is to restrict the pump's use to a single battery that may be usable and movable to a higher position if needed during water rising over the sole.

And while some boats may have large battery banks, I think it is best to consider what one would do in a case where you have the minimum available to you (i.e. A single battery), and, in this case a single electric pump.

I think its silly, cause your down to one battery of unknown capacity and your asking how many amp hours can we get out of it.
It is like saying I have two months pay saved up, I can cruise on $1,000 a month, how long can I cruise for? Ya think maybe knowing how much money you have in dollars and not two months worth is needed to answer the question?
In your scenario I can tell you, your screwed, better use the last amps in that one battery to call for help on the radio to get that engine going or what does it matter if you have enough amps to hold off the sinking for 30 min as opposed to 60?

[Steadman Uhlich]

Originally Posted by a64pilot

I think its silly, cause your down to one battery of unknown capacity and your asking how many amp hours can we get out of it.
It is like saying I have two months pay saved up, I can cruise on $1,000 a month, how long can I cruise for? Ya think maybe knowing how much money you have in dollars and not two months worth is needed to answer the question?
In your scenario I can tell you, your screwed, better use the last amps in that one battery to call for help on the radio to get that engine going or what does it matter if you have enough amps to hold off the sinking for 30 min as opposed to 60?

You are entitled to your opinion, but I don't share it (i.e. That is is silly to consider a scenario like this.)

The use of a scenario such as this is to get one thinking of what one would do when faced with this situation, and to consider the variables, the knowns, the unknowns, and the possible actions to take.

As with any scenario, there are variations in how people respond to the challenge, and that is part of its purpose too.

For that reason I don't see this scenario or challenge as silly at all.

As I see it, it is part of good seamanship to consider what could happen and to anticipate limitations.
______________

As for "you are screwed" being part of it, I can agree with you on that. Finding oneself in a situation like that would cause anyone to feel they were "screwed." The key then is to think of the best response/action. Calling for help via the radio, while one has the ability to do so, is certainly a reasonable one.
______________

Rather than derail this thread, I decided to start a new thread focused on just this scenario I posted above. So, if someone wants to discuss the scenario in any way, I invite them to do so there via this link. This is not to say I think it is not pertinent to this thread too, but simply that it may be better to consider it as a stand alone topic of discussion.

Here is a link to that new thread on CF:

How Long Will Your Bilge Pump Last in Emergency?

http://www.cruisersforum.com/forums/...ml#post2280499

[sailingharry]

Originally Posted by Exile

https://en.wikipedia.org/wiki/Laminar_flow

Interesting consideration, except over my head. Any chance of someone explaining this limitation as applied to some of the pump scenarios that are being considered? Would hate to take any additional time & money trying to make myself feel more secure when it is in reality an exercise in futility.

Laminar flow is a condition that occurs when fluids flow for short distances at slow speeds. Fluid at the edge is "stuck" to the edge, and (for a pipe) fluid at the middle is going the fastest. The entire rest of the fluid flow profile is a smooth curve, going from min to max and back again. As fluid flow rates increase, this falls apart. As travel distance increases, it falls apart. As surface roughness increases, it falls apart. On your boat, laminar flow has completely broken down someplace in the first foot. In a typical bilge pump hose, it has broken down someplace in the volute of the pump, and it never reestablishes.

Turbulent flow is represented by, well, turbulence. The fluid flow profile is essentially flat, with all fluid in the pipe going at the same rate (and also going in a very turbulent manner, not all molecules going in the same direction). It occurs very fast in non-laboratory conditions.

Laminar vs turbulent flow can be determined by calculating a Reynolds Number, or Re. Reynolds Numbers above 4000 are turbulent. Water flowing at 60 GPM, or 3,600 GPH in a 1.5" pipe (rather typical values for the discussion we've been having) has a Re of 1.2e6 (1.2 million). That's somewhat higher than 4000, and so we can assume the fluid is turbulent.
(for those who want to play along at home, read up on Re here: Reynolds Number and here: Water Flow in Tubes - Reynolds Number)

The reality is that we rarely have laminar flow in any pipes. The good news is that it really doesn't matter. Go back to my initial idea of a pool pump. They are designed to be used in 1.5" diameter pipes, and they are designed to produce 3, 4, even 5 thousand gallons an hour. If laminar flow were an issue, and if turbulent flow were "game over," well, those pumps wouldn't be very useful in a pool!

Also in that initial post, I provided a link to show how to calculate head loss in pipes. A 3600 GPH flow through 1.5" PVC pipe (it's the information I had -- flexible bilge pipe will have similar losses, although somewhat higher) produces a head loss of 20 feet (or about 10 PSI) in a 100 foot pipe. And as shown above, that's way outside the realm of laminar flow.

Harry

[sailingharry]

Originally Posted by Steady Hand

Assume your 35 foot boat is taking on water through a 2 inch hole, 3 feet below waterline. That hole puts 4,152 Gallons Per Hour (GPH) into the boat.

The pump has the following specs:
Rule Evacuator Pump 4000GPH uses 20 Amps, 1.6 HP, 12 volts.

How many Watts does that take? You found a formula and calculated:
I (Electrical) HP = 746 Watts. Therefore P(Watts)= 746 X 1.6 HP = 1193.6 Watts.

Big Question: How long do you think that pump will run (at rated speed, not a trickle) if you have only that one (start) battery available to use?. Please post your guess below.

Couple thoughts:
* A 4000 pump is good for less than 2000 GPH in actual use. So it won't really stem the tide much.
* The 20A rating is right -- the 1.6hp rating is WAAAAAY off. It only uses 20A (actually, I suspect that's the fuse rating, not the pump rating -- the pump probably draws more like 15A).
* At 20A, with a partially dead Group 31 battery with a full capacity of around 100Ah or less, assume you can get 50Ah out of it, so you can run the pump 2, maybe 3 hours.
* If the 1.6hp rating is right, then the current draw is around 100A, and the pump will run maybe 30 minutes tops.

Harry

[boatpoker]

Originally Posted by sailingharry

they were on a well-found and ARC-compliant boat in moderate weather, and over a 4 hour period unsuccessfully battled slowly rising water levels without finding the cause.

Sinking, cause unknown + well founded = does not compute.

[Cadence]

Originally Posted by sailingharry

So I was reading the story of the 39 foot aluminum hull Noah, sailed by Alexander Grefrath and crew, that went down on the 2016 ARC. Short story, they were on a well-found and ARC-compliant boat in moderate weather, and over a 4 hour period unsuccessfully battled slowly rising water levels without finding the cause. They abandoned the boat in a safe and orderly fashion with expectations that she would sink in the next several hours. Full story here:
Three crew and two children rescued from sinking yacht in Atlantic

It gets me to thinking about oversized bilge pumps.

Some background/basis for discussion:

• For water volume, you could consider 40 feet long x 12 feet wide x 2 feet deep water x .3 (factor for hull shape not being a real cube) x 8 gallons per cubic feet, and you get about 2300 gallons of water. Let’s use that as a target volume that, if it could be removed, would have the boat perhaps dry enough to continue the fight to find the leak.
• Practical Sailor did a report on super duty submersible bilge pumps a few years back (Sept 2010), all “labeled” as around 2000+ GPH pumps. They tested them through a 3 foot hose with a 3 foot vertical lift (a very low total head, in my opinion), and found them to max out at 1800 GPH – and with more hose/head, they would be even lower. Figure an hour and a half to pump out the 2300 gallons I’ve suggested. Maybe longer. Not a really good answer! Granted, if they had this in addition to whatever pumps they already had going, it would probably have sufficed.
• Note that head loss in a pipe can be calculated. Assume 15 feet of 1.5” pipe at 3000 GPH. Assume two 90 degree fittings at 5 feet (effective length) each, for a total of 25 feet of pipe. 100 feet of 1.5” pipe at 3000 GPM has a head loss of 14 feet, or 3.5 feet of head for 25 feet of pipe. Add in another 3’ of head for lifting out of the boat, and we’re talking 6 feet of total dynamic head. Good reference here: Plastic Pipes - Friction Head Loss
• Engine driven pumps are a big improvement. For $1200, plus whatever it takes to hang it on your engine, you can get a Jabsco 50270 that puts out 60 GPM/3600 GPH and self primes to 8 feet. This would have saved the yacht, for sure. Even if they couldn’t find the leak, they could have run the engine for ½ hour every 4 hours, and sailed for the nearest port. But it’s an expensive option. Note that a rubber impeller pump is essentially a positive displacement pump, and as such has little loss with hose runs.
• Even a 20 GPM manual pump would take 2 hours to pump out the water that accumulated in 4 hours – that’s a tiring task!

So, now for my thought. Yes, if you can physically fit an engine pump, and can afford an installed cost of $2K or so, then it’s a slam dunk. But how off the wall is this idea. A swimming pool pump has a powerful pumping profile. A 1 HP unit can be easily run off an inverter or generator (draw is under 1kW – theoretical 750W maximum -- and the actual pump power of this installation can be calculated at under 3/4 HP using a 60% pump efficiency). Note that a 100A alternator will essentially provide all power requirements, so battery will not be drawn down. A Hayward 1HP pump has performance specs here: Hayward Super Pump 1 HP Single Speed - SP2607X10 - INYOPools.com that show for 20 feet of total head (lowest plotted value), it can produce 85 GPM or 5000 GPH (and yes, that means that the head calculation above is wrong – but still a lot of flow!). The pump will self prime to 10 feet, and they come standard with a big, easily serviced strainer. And installation is much more flexible than an engine pump.

A pool pump at under $500 (and Hayward is a premium brand – other brands cost even less), easily installed, with a 1kW inverter and a 100 Amp alternator (many cruising boats have at least this combination) would have emptied that sinking boat in under 30 minutes. This combination is 1/4 the cost of an engine driven pump, with 50% more flow rate.

Thoughts?

Harry
Rantum Scoot
’79 Sabre 34
Mill Creek, Annapolis

Sounds like a boss idea?

[boatpoker]

Just to feed the fire ..... Bernoulli shows that a 2" diameter hole, 6' below the water will allow 192.5gpm into the boat so you'd need an 11,5550gph pump before even considering friction loss and head.

[roland stockham]

Fit one or two Rule 3800gph pumps clear of the bilge floor so they stay clean and dry ready for an emergency and use an smaller electric impeller pump (water puppy or similar) to clear 'normal' water ingress. Anything smaller is a wast of time on any boat. Engine driven pumps are great because they don't burn out so can run 24/7 but you still need the rule because by the time you are aware of the leak and get the engine started it may be two late.

These will keep up if you open a 1 1/2" seacocck. Your pumps should be capable of keeping up if you loose the largest hull opening.

PS not sure what to do if you have a drive leg, if that goes you would need a fire truck!!

[boatpoker]

Originally Posted by Steady Hand

Assume your 35 foot boat is taking on water through a 2 inch hole, 3 feet below waterline. That hole puts 4,152 Gallons Per Hour (GPH) into the boat.

Using Bernoulli's formula I come up with 8,166gph for a 2" hole, 3' below the waterline.

[CarlF]

I think folks should take another look at the Fast Flow pump attached to the propeller shaft. Pumps astonishing amounts of water. No maintenance, no setup. Flooding situations are full of confusion and fear. It's not a good time to figure out how to start a gasoline engine that's been in a locker for two years.

And while diesel engines can fail they are damn reliable. Most boats' electric systems short out before the water rises to the sole. Most diesels will run underwater - until its air intake goes under.

Fast Flow Emergency Bilge Pump

And while on the subject, think about how to stop the leak. The old fashioned tapered plugs attached to the seacock aren't useful for most leaks as they need a perfectly round hole to work. Most leaks are cracks or splits.

Keep several tubs of this stuff:

https://www.youtube.com/watch?v=888wQhRcmjQ&t=6s

[Cadence]

Originally Posted by Cheechako

I'm more in the camp of buying a boat designed and also built to survive than trying to fix the "ultimate leak" after the fact. (Thick hull, long keel, non spade rudder, tapered bronze seacocks , everything in known new or near new condition.)
But if you want to remove a lot of water get a Honda Gas trash pump. Pre-think and pre-rig it for your ultimate emergency.

Keep the water out.

[roland stockham]

Originally Posted by boatpoker

Using Bernoulli's formula I come up with 8,166gph for a 2" hole, 3' below the waterline.

Formulas are a fine starting point, I recommended the Rule option because I know it works in practice. I have tested it in harbour by opening 2 x 1 1/2" inch seacocks and it kept up. (on a 35' deep keal boat). I have also used it 'for real' after a collision ripped all the stantions off down one side leaving large holes which is why I recommended a spare, they do burn out!! make sure the wiring and switched are up to it as well.

I also carry a spare portable mains pump as a backup but for emergence your pump MUST be permanently installed, anything else is to slow.

An odd reality is that for a bigger the boat you may not need bigger pumps. The extra volume give you more time to deal with things before the water is above the floorboards. Remember the 'crash' pumps job is to keep the water down for long enough for you to ram something in the hole.

[Steadman Uhlich]

Originally Posted by boatpoker

Using Bernoulli's formula I come up with 8,166gph for a 2" hole, 3' below the waterline.

Thanks for posting that.
I don't mind being corrected anytime.
I know mistakes can happen, and I do want to post accurate numbers, but often refer to others more knowledgeable for some facts/numbers/calculations and I don't claim to be an expert on bilge pumps.

I should have double checked the numbers I quoted, by using a second source, rather than just one.
_______________

Where did I get that number?
I read it in an earlier post on bilge pumps, and this is what I noted from what Gord May posted in that thread (sorry I don't have the thread link now). Since Gord is dependably accurate, I can only assume I must have copied and pasted it and introduced some error in my notes. Here is what I had in my notes from that earlier Bilge Pump thread:

"Approximate Flooding Rates, for smooth holes at selected depths, are calculated using the formula:
Flooding Rate in gpm = 20 x d x square-root of h
where:
d = diameter of hole in inches
h = depth of hole underwater in feet (head)

Hence, for a 2" dia hole at 3 Ft depth:
Q = 20 x 2" x root 3 = 20 x 2 x 1.73 = 69.2 gpm (4,152 Gal per Hour)"
___________

So, I used the 2" hole at 3 foot depth = 4,152 Gallons per hour (seen above in Gord's post) in my scenario.
__________

Here is another source (a chart published by a marine hardware company) that I should have used to compare with the calculations up above:

Here is a chart that gives an idea of how small diameter holes in a boat can flood a boat quickly. http://www.cruisersforum.com/forums/...1&d=1352065660

Looking at that chart one finds:

A 2" hole 3' below the waterline will flood a boat at 139 Gallons Per Minute.

139gpm x 60min = 8,340 Gallons Per Hour

While that last number is a bit different from yours, it is close enough and certainly much larger than the number I posted earlier based on my notes (about the calculation method). About 8,000GPH IS much more than 4,000GPH.

So, thanks again for catching that earlier error.

[roland stockham]

In practice what you can fit will depend more on the layout of the boat, power available etc. How fast a bot floods also varies, does she have a collision bulkhead, is water checked by limber holes etc. The numbers look alarming if you calculate things like a 2 inch hole 3ft down but in practice few boats are likely to find themselves with such a scenario. Seackocks are vulnerable but usually max 1.5" and rarely more than 2' down on a small boat (a bigger boat can fit multiple pumps and has more time to deploy them). Probably the worst is to loose the shaft but it is very unlikely you will completely loose it, more likely is a seal failing.
I believe the test of opening a couple of seacocks to see how long the pumps keep the water down is a good emergency scenario.
When it come down to it fit the best pumps you can and service the liferaft for the things they can't cope with!
I would also say keep the bilges clean - most common failure is that they get blocked with debris.

[boatpoker]

Originally Posted by Steady Hand

Thanks for posting that.
I don't mind being corrected anytime.
I know mistakes can happen, and I do want to post accurate numbers, but often refer to others more knowledgeable for some facts/numbers/calculations and I don't claim to be an expert on bilge pumps.

I should have double checked the numbers I quoted, by using a second source, rather than just one.
_______________

Where did I get that number?
I read it in an earlier post on bilge pumps, and this is what I noted from what Gord May posted in that thread (sorry I don't have the thread link now). Since Gord is dependably accurate, I can only assume I must have copied and pasted it and introduced some error in my notes. Here is what I had in my notes from that earlier Bilge Pump thread:

"Approximate Flooding Rates, for smooth holes at selected depths, are calculated using the formula:
Flooding Rate in gpm = 20 x d x square-root of h
where:
d = diameter of hole in inches
h = depth of hole underwater in feet (head)

Hence, for a 2" dia hole at 3 Ft depth:
Q = 20 x 2" x root 3 = 20 x 2 x 1.73 = 69.2 gpm (4,152 Gal per Hour)"
___________

So, I used the 2" hole at 3 foot depth = 4,152 Gallons per hour (seen above in Gord's post) in my scenario.
__________

Here is another source (a chart published by a marine hardware company) that I should have used to compare with the calculations up above:

Here is a chart that gives an idea of how small diameter holes in a boat can flood a boat quickly. http://www.cruisersforum.com/forums/...1&d=1352065660

Looking at that chart one finds:

A 2" hole 3' below the waterline will flood a boat at 139 Gallons Per Minute.

139gpm x 60min = 8,340 Gallons Per Hour

While that last number is a bit different from yours, it is close enough and certainly much larger than the number I posted earlier based on my notes (about the calculation method). About 8,000GPH IS much more than 4,000GPH.

So, thanks again for catching that earlier error.

Just Google "Bernoulli equation". It'll pop right up.