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ContinuousWave: Post-Classic Whalers
170 MONTAUK: Replacement Bilge Pump
|Author||Topic: 170 MONTAUK: Replacement Bilge Pump|
posted 10-06-2005 11:02 PM ET (US)
I tested the volume of the stock bilge pump (rated 1,100-GPH), and found that it pumped 10 gallon per minute or 600-GPH. Not very impressive. Using the same somewhat dubious hose in the 170 with the 15-inch head, I installed a 2000-GPH RULE pump which fits in the same location withou problems with height or size. This time the new pump put out 25 gallons per minute. That makes it an actual 1,500 gallons per hour. There is a marked improvement in the draining of the boat. Works quite well for those days when you partially fill the boat and are otherwise occupied trying to stay alive. The next test will involve changing of the stock hose. Just thought Whalers would like to know. high sierra
posted 10-07-2005 08:17 AM ET (US)
Thanks for passing this along and that's good news that the higher capacity pump fits in the same space. I wonder how much difference there is in current draw between the two pumps and if that has any implications on the 170 MONTAUK? This is a mod I'll likely do as an off-shore boater.
posted 10-07-2005 08:39 AM ET (US)
Was the screen clean on the 1100 gph pump?
posted 10-07-2005 08:40 AM ET (US)
And were the battery conditions similar?
posted 10-07-2005 11:30 AM ET (US)
BigJohn, the 2000-GPH pump uses the same wiring. The current draw is higher but not enough to cause problems. I have had no problems at all with the circuit breaker or wiring using the factory wiring. I ran the heck out of it the day before washing out fish blood and debris.
Chuck, the battery conditions were exactly the same. And of course the screen was clear. What kind of rigger-whaler owner do you think I am? high sierra
posted 10-07-2005 07:33 PM ET (US)
What doesn't compute here is that the 1,100 gave 55% of rated
volume while the 2,000 gave 75%. I'd expect them to be rated
about equally "optimistically", and if anything the lower
rated pump would come out a bit better percentage-wise because
of that more than somewhat suspect stock hose. The hose is
the stuff that's crinkly inside and out, right?
posted 10-07-2005 08:49 PM ET (US)
I don't remember for sure but I think my 1999 Montauk came with an 800-GPH bilge pump which is plenty for a boat of that size, especially a Boston Whaler.
The transition changes at about 1000-GPH where you change from 3/4" hose to 1-1/8" hose. Bilge pump hose is bilge pump hose none are better than the others.
I can't understand why you need 2,000-GPH in a 170, pull the plug and it ain't going to sink.
posted 10-07-2005 11:21 PM ET (US)
There have been some tests that show that the bilge
pump hose that's smooth on the inside flows better than the
the hose that's rough on the inside. I changed from the
rough hose to the smooth hose, and it sure looks like it's
flowing more water. I wish I'd run before and after tests.
It will be interesting to see the results of high sierra's
The smooth hose is more expensive and less flexible than
posted 10-08-2005 03:22 AM ET (US)
Are bilge pumps rated at zero head?
posted 10-08-2005 06:08 AM ET (US)
Pumps used in recreational boats are rated by their manufacturer. I don't know of any standards agency which promulgates standards for pumps used on recreational boats. Perhaps the ABYC. In most cases the rated output flow is under the most favorable conditions, and it is expected that the output flow of the pump will decline if there is considerable lift on the input or head on the output
Anecdotal data about the performance of particular pumps in particular installations is interesting. If you are seeking a test of many brands of pumps with different ratings, the magazine POWERBOAT REPORTS recently tested a dozen or more pumps used in recreational boats.
posted 10-10-2005 02:01 PM ET (US)
All bilge pumps are rated at the discharge with no hose attached.
posted 10-10-2005 03:18 PM ET (US)
Larry - you are right on there - the pump rated capacity is given with no discharge hose. And - at sea level as well - which increases the performance as well.
Chuck mentioned the inside rough surface of the hose - where a smooth hose allows more water to be discharged. That is true too - one wants to make the inside surface just as smooth as possible.
But one thing that fools a lot of people is that increasing the size of a pump and leaving the discharge hose the same - same size, same surface will not necessarily increase the discharge flow rate. Doubling the size of a pump and using the same discharge hose will not double the discharge flow rate - by definition!
The reason is that if one doubles the discharge flow rate of the pump and uses the same hose, the discharge fluid velocity will increase. But the friction head (pressure) loss inside the hose increases as the velocity squared. Therefore, when everything comes out in the wash (pump head balancing the frictional and elevation head losses) - the discharge flow rate is decreased from the stated pump performance.
And the hose is not the only item that decreases flow rate - you still have the exit fitting - from the hose to the outside of the boat. Should that fitting be a sharp reduction in flow area - the losses are quite severe.
So - when thinking of increasing the size of your bilge pump - take some time and rethink the thing a bit. Particularily if you have a Whaler and can run with the plug out. ----- Jerry/Idaho
posted 10-10-2005 06:30 PM ET (US)
Jerry is right about friction loss efecting flow rate. Things that cause friction loss in a hose are elevation, hose fittings, hose diameter (and inside surface), flow rate (GPM) and hose length.
The size of your fittings determines your hose diameter so you can't really change the hose diameter or the elevation but if your hose is unnecessarily long, you can cut it down to make it only as long as it needs to be. By replacing the stock hose with one that is smooth inside and as short a possible will give you more flow capacity.
posted 10-10-2005 06:34 PM ET (US)
That should read: Things that cause friction loss in a hose are elevation, hose fittings, hose diameter (and inside surface), WATER VOLUME (GPM) and hose length.
posted 10-10-2005 10:24 PM ET (US)
This was a test of 2 different size pumps using the same discharge hose and fittings. We all know that there are many factors and theories that can be injected into the test. It was a simple test. There is no great debate. The smaller 1100 pump has a very small impeller in a small housing and is more inefficient than the 2000 gph pump with the much larger impeller. The hose is not efficient and we all know that. The idea of a larger pump to a lot of boaters is not to drain a small amount of rainwater or a small amount of splash but to drain a large amount of water taken on by a miscalculation or accident. We all can take out the drain plug when we have time. But when the boat is floundering and your passengers are not helping by lurching to the low side and you could roll over, gear is floating out over the transom, open tackle boxes are being emptied by the wave action in the boat, your passenger is frozen by fear, and you are looking for the next rogue wave, a larger bilge pump is needed. The water was so cold, the drain plug was not in my mind at the time. Unless you have experienced this scenario, it is hard to realize all the problems that crop up. A large hat and a bucket might help as well.
posted 10-11-2005 11:14 PM ET (US)
Perry: My '97ish Montauk doesn't have an exit fitting. The
hose just hangs over the transom.
All: High Sierra makes a very good point.
And the best bilge pump is a very motivated passenger. Always
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