Bilge hose - important difference!

[Fr. Frank]

A friend and I did a test last night on the difference between corrugated plastic bilge hose, and smooth-wall hose. The results were surprising to me.

Using a 600 gallon steel stock tank, and a 325 gallon clear sprayer tank with exterior volume markings, we measured the output and amperage draw of two bilge pumps using the different hoses. We placed the pumps in the bottom of the stock tank, and then hooked the pumps up to a battery for 15 minutes.

My friend then had a beer (one during each test). I had a diet Dr. Pepper. (one for all 4 tests)

The first pump used was a new Attwood 500gph automatic bilge pump from WalMart. Using a 6' long piece of straight wall 3/4" garden hose, after 15 minutes the measured output was approximately 180 gallons, or about 620 gallons per hour. The amperage draw throughout was about 1.9-2.0 amps.

Repeating the process with 5' of corrugated 3/4" bilge hose gave us an output of approximately 95 gallons, or 380 gallons per hour, with an amperage draw of 2.2 amps.

The next pump we used was a 2 yr. old Rule 1250 manually switched pump, with a 1 1/8" output. Using 5' of fiber-reinforced straight-wall bilge hose, we got an output after 15 minutes of about 320 gallons, or 1280 gallons per hour, at 2.7 amps

Using 5' of corrugated bilge hose from West Marine, we got an output of only 240 gallons, or 960 gph, at 2.9 amps.

People, the difference may be between sinking and floating. These pumps are obviously rated for using straight-wall hose, NOT corrugated hose. Using corrugated hose provides less output while using more electricity.

While I expected a slight difference, I didn't expect so dramatic a difference. And I have corrugated hose hooked up to all three of my pumps in my bilge.

(Yes, I have THREE bilge pumps in a 20' Seafari, all 1200 gph rated. Two at the transom, and one in the bow under the cabin. I discovered the hard way that with 5 persons on board, and three of them sunning on the cabin deck, a Seafari will begin to sink bow-first when the drain plug is left in the engine well instead of being stuck in the little hole in the transom)

[76Red18]

That is suprising. I had kink problems with smooth hose so I used the kind from West Marine that has the black spiral band around it (almost smooth on the inside but hard to clamp) for the 3 pumps on my 18'er; 2 1500s and a 750 auto all on seperate batteries.

[cSickNick]

Using a 6' long piece of straight wall 3/4" garden hose, after 15 minutes the measured output was approximately 180 gallons, or about 620 gallons per hour.

Minor math correction 180 x 4 = 720 GPH. Just wanted you to know i was paying attention.

Interesting results, but the real question is "how long did your battery last before the young ladies sunning in bikini's got wet??"


- Nick

[eggsuckindog]

The issue I've had is the wire reinforced hose will not hold when clamped and will come off, at 1 1/8" seacock fills the boat quick.

[Fr. Frank]

For the test. I used the 1 1/8" hose that has threads running through them, but not wire. After the test I used that piece to replace the corrugated hose on one of my pumps

[McGillicuddy]

Wow. Thanks! That is truly valuable research, not sure what hoses I have on the Seafari (still rewiring) but that will be definitely addressed. I would have never guessed the the difference to be so significant. Fantastic info. Send that to Mythbusters...

ps. what kind of mileage did you end up with on the 90 Optimax?

[Fr. Frank]

Unable to get my navman working. My estimate is about 5.3 to 5.5 gph at 23-24 mph, or about 4.5 mpg. I ran for one full hour (timed) on a 6 gal. portable tank, and still had about 1/2 to 2/3 of a gallon left.

[rhody98]

And the head difference matters too - height from pump to discharge. I dont know your setup Father, but the relative elevation of the pump and the water levels in the two tanks will impact the results. I would expect you would get higher flow rates if the 600 gal tank is topped off versus the water level just above the pumps with a garden hose keeping the water level static. So your results for both hoses are probably even better than actual conditions in a boat where the lift is, say 18" (2'?).

I came across results from pump tests Rule financed in 1997, all with a 3' head (lift).
Attwood 500, smooth hose = 302 gph, corrugated hose = 242 gph.
Rule 1100, smooth hose = 682 gph, corrugated =530 gph.
Rule 2000, smooth hose =1,052 gph, corrugated = 880 gph.

So in a boat where a bilge pump is lifting water 18" (or whatever), can we guess that actual results may be somewhere between Fthr Franks #'s and the Rule test #'s? In any case it should be apparent that pumping at the manufact. rated output is unlikely to happen.

Also, interesting to compare these to flooding rates: a hole 1 ft below waterline, 1" in dia. lets in 20 gpm - that's gal per minute which is 1,200 gph! A 2" hole 1' below the waterline is 79 gpm, or 4,740 gph. I will stop now before I convince myself not to launch this Spring...

I should list my source, its a book my wife got me for Christmas, Boatowner's Mech and Elec Manual.....spent more time with it than the socks.

[Fr. Frank]

One thing we can all learn here - the single 500 or 800 gph pump just isn't enough under any circumstances.

I have friends who snicker at me because I have three 1200 gph pumps in a 19'8" boat. I later snickered at one of them when he "sank" his V20' Wellcraft while he was grounded on a sandbar. The waves washing over the transom and down through the cable access were more than his little 500 gph West Marine pump could keep up with and he came back to find saltwater had filled his bilge completely and was over the deck - all while his little pump was working as hard as it could. His boat was sitting hard on the motor's lower unit and the hull bottom, and canted over as the tide continued to fall.

Fortunately for him, he had a SeaTow card in his wallet. They could have called it salvage, not assistance, and he would have been out his $1k insurance deductible. As a member, they loaned him a gas-powered 20,000 gph pump, and pumped him out in a few minutes. He was then able to get off at high tide. As it was he had to completely rewire the boat.

More pumps, more gph is better, smooth wall hose is important.