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Old 03-29-2008, 09:49 AM
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Default Drain plug hole VS. Bilge pump

Curious.... can any engineers tell me how much water can enter a boat through the drain plug hole(s)? Does it have to do with the boat's weight or how far down under the surface the hole is?

My current boat has two drain plugs and only one bilge pump, so wondering whether it's strong enough to handle a potential "Oh dang!!!!"
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Old 03-29-2008, 10:16 AM
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Default Re: Drain plug hole VS. Bilge pump

I never heard of a drain plug failing causing a boat to sink. Its either in or its not and you will know as soon as you put the boat in the water. I would be more concerned with a thru hull hose failing.
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Old 03-29-2008, 10:46 AM
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Default RE: Drain plug hole VS. Bilge pump

Unfortunately, the drain plug hole offers much less resistance to water flow than the bilge pump and hoses.

One small drain plug and a big bilge pump, Maybe a contest. Two plugs and one pump? You'll only forget once.

Yes, as the water depth increases so does the flow, so as the boat settles, it fills faster and faster.
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Old 03-29-2008, 11:08 AM
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Default Re: Drain plug hole VS. Bilge pump

I'm just talking theory here (so far, anyway) but if I ever forgot and there are two drain plugs missing, any idea how many GPM we're talking about compared to the 1100 GPM auto pump in the bilge? A 9000 pound boat would suck the water in and I'd rather have two pumps if the flow would even get half-way to the 1100GPM.
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Old 03-29-2008, 11:53 AM
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Default Re: Drain plug hole VS. Bilge pump

The best set-up that I have seen on the various boats that I have owned is an aft bilge pump, a forward bilge pump and a high water bilge pump (with alarm).

As long as you have the battery power to keep them running, that's a good way to go.
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Old 03-29-2008, 12:09 PM
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Default Re: Drain plug hole VS. Bilge pump

Quote:
ABoater - 3/29/2008 2:53 PM

The best set-up that I have seen on the various boats that I have owned is an aft bilge pump, a forward bilge pump and a high water bilge pump (with alarm).

As long as you have the battery power to keep them running, that's a good way to go.


what he said,i also have 2 in the aft.
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Old 03-29-2008, 01:01 PM
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Default Re: Drain plug hole VS. Bilge pump

Uncontrolled flooding is a major cause of sinking of vessels at sea. A three-inch hole located one foot below the waterline will allow 177 gallons of water per minute to enter a boat. The same size hole located at three feet below the waterline will produce a flooding rate of 306 gallons a minute. Any sizeable hole encountered below the waterline will sink the average boat in a matter of minutes. Most people would be surprised to learn a 1500 gph pump with no head pressure will not pump anything close to 1500 gph. So the bigger the better is a must.
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Old 03-29-2008, 01:42 PM
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Default Re: Drain plug hole VS. Bilge pump

I have two 3700s aft, you should have seen the look on my outboard dealer's face when he saw those in the bilge. He asked me why I had two huge pumps, I said "You apparently have never seen your bilge full of water with a puny 1500 struggling."
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Old 03-29-2008, 02:05 PM
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Default Re: Drain plug hole VS. Bilge pump

I know from experience to always have high-flow bilge pumps - larger than the boat requires or is recommended. Back when I had my Wellcraft V-20, I had a single 1000 GPH pump and a secondary 500.

One day I launched and I really don't know how, but the drain plug got removed - I assume by a mermaid(s) or juvenile fish - as soon as I put it in the water (that's my story and I'm sticking to it). I noticed the first sign as I was walking back from the parking lot and the boat looked to be sitting lower than usual. So I pulled the center fish locker hatch and water was almost to the deck. Uh oh... I cranked up the bilge pump (they weren't automatic - I didn't keep the boat in the water, but I always have automatic now). So the bilge pump(s) cranked up and shot water out the side like it was under pressure - didn't ark for 4 feet!

Anyways, the bilge pumps were pumping out faster than the drain plug was letting water in. I installed a drain plug that looked identical to the one the mermaids removed.

Lesson learned. Always have a bigger than required bilge pump. If I had a single 500 GPH or something like that, I couldn't have overcome the flow of water coming in.

I think the flow through a standard drain plug is somewhat limited with perhaps a little more pressure as the weight increases.
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Old 03-29-2008, 07:55 PM
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Default Re: Drain plug hole VS. Bilge pump

You can calculate the flooding rate of any size hole:

Q = 20 x d x square-root of h
Q = flooding rate in gpm
d = diameter of hole in inches
h = depth of hole underwater in feet
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Old 03-30-2008, 05:27 AM
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Default Re: Drain plug hole VS. Bilge pump

so with a 3/4" drain hole and a depth of 2 feet, we do the math: 20 (3/4) x 1.41= 21.15GPM

GPH would be 1269 (21.15 x 60) so a 1500GPM that actually pumped that much ought to keep up with it? Do these pumps actually pump out as much water as they're rated?

....and in the case of my boat with two plugs, we're talking about over 40 gallons/minute if that mermaid makes off with the plugs!!

I just made a dummy-board checklist to hang around the trailer winch (install plugs, remove wheel chocks and chain/padlock, outdrives up, engine keys, beer)
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Old 03-30-2008, 07:08 AM
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Default Re: Drain plug hole VS. Bilge pump

Rick,

I have a small threaded plate on the boat's key ring. The drain plug is screwed into the plate. Very difficult to forget to install the plug before getting underway.
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Old 03-30-2008, 08:24 AM
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Default Re: Drain plug hole VS. Bilge pump

Quote:
bamaboy473 - Do these pumps actually pump out as much water as they're rated? ....and in the case of my boat with two plugs, we're talking about over 40 gallons/minute if that mermaid makes off with the plugs!!
They are nowhere close to "rated capacity".[img]../images/emoticons/frown.gif[/img] Capacity is affected by the type of hose(use smooth), the distance to the discharge, and the heght from the pump to the discharge(head). A decent set-up is about 50% of rated(at best). Do a test, timing how long it takes to fill a 5 gal bucket.

BTW be sure to check yourpump often for debris. Some pumps (Rule)have very fine screens on the intake and can be quickly rendered useless unless your bilge is spotless.

Always carry spare plugsthat stay on the boat and the keyring(fob) is a good idea for the original.
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Old 03-31-2008, 07:32 AM
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Default Re: Drain plug hole VS. Bilge pump

Quote:
GhostShip - 3/30/2008 10:24 AM



Quote:
bamaboy473 - Do these pumps actually pump out as much water as they're rated? ....and in the case of my boat with two plugs, we're talking about over 40 gallons/minute if that mermaid makes off with the plugs!!
They are nowhere close to "rated capacity".[img]../images/emoticons/frown.gif[/img]* Capacity is affected by the type of hose(use smooth), the distance to the discharge, and the heght from the pump to the discharge(head). A decent set-up is about 50% of rated(at best). Do a test, timing how long it takes to fill a 5 gal bucket.

BTW be sure to check your*pump often for debris. Some pumps (Rule)*have very fine screens on the intake and can be quickly rendered useless unless your bilge is spotless.

Always carry spare plugs*that stay on the boat and the keyring(fob) is a good idea for the original.
Measuring the discharge rate is easy to do while the boat's on the trailer at the house. Comparing that to the rated GPM ought to tell whether a second pump is worthwhile to install. Good idea GhostShip
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Old 03-31-2008, 11:10 PM
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Default Re: Drain plug hole VS. Bilge pump

Quote:
gman25 - 3/30/2008 2:16 AM

I never heard of a drain plug failing causing a boat to sink.
I've heard of one.
His anchor was stuck and he was driving around trying to free it and the anchor rope some how found its way over the top of the drain plug and snapped it off leaving just the thread in the hole and no end bit.
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Old 04-01-2008, 09:45 AM
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Default Re: Drain plug hole VS. Bilge pump

Quote:
gman25 - 3/29/2008 1:16 PM

I never heard of a drain plug failing causing a boat to sink. Its either in or its not and you will know as soon as you put the boat in the water. I would be more concerned with a thru hull hose failing.
My father's boat sank at the slip due to the drainplug falling out. It was a 'lever' type plug and the little pivot pin broke. I know this because after we got the boat up, we found all the parts in the bilge. This is why I'll never use a lever type drain plug again.

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Old 04-01-2008, 10:42 AM
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Default Re: Drain plug hole VS. Bilge pump

I could see why you would remove the plugs when you are cleaning the boat at home. I also know why you would leave a plug out while on the trailler (rain ect..). Why would you leave both out? I would think I would always keep at least one plugged. Just my thoughts.
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Old 04-01-2008, 10:56 AM
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Default Re: Drain plug hole VS. Bilge pump

Quote:
kchace - 4/1/2008 11:45 AM
Quote:
gman25 - 3/29/2008 1:16 PM I never heard of a drain plug failing causing a boat to sink. Its either in or its not and you will know as soon as you put the boat in the water. I would be more concerned with a thru hull hose failing.
My father's boat sank at the slip due to the drainplug falling out. It was a 'lever' type plug and the little pivot pin broke. I know this because after we got the boat up, we found all the parts in the bilge. This is why I'll never use a lever type drain plug again. Ken
[img]../images/emoticons/thumbsup.gif[/img]The lever types should only be used on trailer queens(if then).

As to sinkings, A freind of mine launched his 20' Deep V Crestliner and ran it back to the pier, tied it up and proceeded to "party". A few hours later it was all but sunk(bottomed out). If you launch a boat quickly and are running the bildge won't fill "until" you stop. Some deep V's will hold alot of water before it's apparent(over the floor)
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Old 04-02-2008, 05:08 AM
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Default Re: Drain plug hole VS. Bilge pump

Quote:
cJAY - 4/1/2008 12:42 PM

I could see why you would remove the plugs when you are cleaning the boat at home. I also know why you would leave a plug out while on the trailler (rain ect..). Why would you leave both out? I would think I would always keep at least one plugged. Just my thoughts.
There's a stringer running along the keel that takes the weight of the engines along the centerline of the boat. Each compartment will hold water so both plugs get taken out. Actually, if I thought I'd be leaving the plugs out while launching, they'd probably go back in after the cleaning process

My personal ADD reminder is a placard that hangs on the trailer winch handle so I'll check these things before I hook the trailer to the Excursion. Tighten hook strap, plugs, keys, wheel chocks, theft chain unlocked....
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