View Full Version : Discharge Bilge pump into Motor well? Yes or No?
02-24-2006, 07:23 PM
Is is acceptable to discharge the bilge pump into the motor well. I am finishing the build of the 15' runabout Rascal. The sides of the boat are curved near the rear, so it is unlikely that the stainless through hull fitting will sit flat against the mahogany. The Transom is 2 1/2" thick and I would prefer not to drill through it. Can I discharge the 500 gpm Rule Bilge into the motor well, which has two 1" drain tubes? The guys at the marine store where I bought the fitting thought it was OK, but I not sure it's the best way to go.
02-24-2006, 07:35 PM
Most of the small outboard boats I've seen discharge the bilge via the motorwell.
I'm not saying that I'm any authority on what's good and proper, just that you're not reinventing the wheel.
The only drawback that immediately leaps to mind is that, if the boat does go down by the stern for whatever reason, the bilge line could become a siphon INTO the bilge more easily than if the discharge were higher.
02-24-2006, 08:52 PM
ive heard of a couple boats sinking when the discharge in the motor well went under. Id mount it higher for safety sake which probably means near the shearline in a small boat
02-24-2006, 10:18 PM
That little Rule 500 is not a real pump. Get a 1500 or better yet a 2000. Anything less is a toy. Hook it up with a Water Witch electronic switch, floats are notorious for failure. Or just upgrade your p.f.d.'s. it's your call.
Though not a legal requirement, I'd agree with the advice given above to go for a 1000 gph pump. Canadian regulations - which I believe are similar to the USCG regs in this matter - dictate a pump capacity of not less than 900 gph for boats over eighteen feel LOA, and (within reason) you cannot have too much bilge pumping capacity, even though your Rascal is a smaller boat. The increase in cost is maybe fifty bucks for the larger pumping capacity system.
As for the discharge location, I don't care much for discharges into the motor well. My take on the construction regs phrase "overboard discharge" is that it means discharging overboard, not "discharging someplace onboard that will eventually drain overboard", but that's just me. Besides, pumping the bilge into the motorwell will encourage staining of your motorwell and transom from the crud that accumulates in the bilge (take, for example, what malodorous crud accumulates in the WBF bilge ;) :D ) running over your boat. I'd locate the discharge through-hull just above the waterline at some convenient location on the hull side, and deal with the siphon issue by looping the discharge pipe up to just under the sheer and then down to the through-hull. An in-line check valve between the through-hull and the highest point of the pipe loop will take care of any siphon problems.
02-25-2006, 10:10 AM
Rather than purchase a 1000 gph pump, wouldn't it be better to have 2 500 gph pumps? The likelihood of two pumps failing simultaneously is extremely small, therefore less likely to run into problem of no working pump onboard. In addition, I already have the one pump, and the bilge is split by the keel, creating two mini bilges.
Here is some info I just pulled off the Jabsco (Rule pump) website relative to installation of a check valve in the discharge line and preventing siphoning.
Can I install a check valve on the discharge of my bilge pump to keep water from running back through the pump?
No. A check valve should NOT be installed in the discharge line. As submersible pumps create very little discharge pressure, they may not be able to overcome the resistance or weight of the column of water or weight of the check valve flapper or poppet itself. The pump may therefore have an airlocked condition.
How can I prevent possible siphoning back through the discharge line and thru hull?
For anti-siphoning protection, install a vented loop in the discharge line.
So rather than install a check valve in the pump discharge, I'll vent the loop high to atmosphere, to prevent any siphon action on the discharge hose. I tend to agree that the smaller bilge pumps are more "toylike" than the larger units, and this is probably why they don't generate sufficent head pressure to overcome the cracking pressure of some check valves.
02-25-2006, 11:12 AM
In a recent issue of MAIB Robb White related some good experience with the Rule automatic instead of float-switch type pumps. See if you can find that article. One of the areas he mentioned was servicability. Good luck whatever.
02-25-2006, 11:23 AM
you can install as many of the little rule pumps as you want, when they grow up they might be real pumps. As for the gph, they won't even aproach 500 gallons per hour, at free flow. If for some reason you get downflooded you want some (a lot,as much as is practical)emergency pump capacity. I know, you think it will never happen. I swam around in a lake once thinking the same thing, my 16 foot skiboat nowhere to be seen. Get some decent pumps and plumb them to specs !!!
02-25-2006, 12:33 PM
SpeedBoy I'm dealing with the same question .I've decided to run two 700 GPH pumps on my 24 footer . I filled a 4.5 gallon bucket( joint compound ) with water , poured it in my splash well , and counted the seconds required for the well to drain out the 2 drain holes through the transom I provided .I converted this to gallons per hour and compared with the 1400 GPH my pumps can theoretically produce .
Ha-hemm...no where close ; I'm going to have to drill some more holes . That being the case , I see no point in me routing the water through the well . Maybe the 2 pumps can share the same exit through the transom , Starboard side ? This would be good , since I'll have a bracket on the Port side to support a small trolling motor ( back up power ).
Another question I have is how fast the splashwell should drain any water comeing in the transom cutout ? Clearly you want it gone before the next exceptional following sea comes aboard ,but too many holes would let the average seas surge in . Maybe I should add a pair of big , failsafe holes with check valves ? My splashwell developes about 8 in. depth below the transom cutout .
[ 02-25-2006, 12:44 PM: Message edited by: Bill Perkins ]
03-02-2006, 05:19 PM
In my buddies Montauk the stock installation is to pump into the motor well. I have caught it syphoning back into the boat on several occasions. So, I would suggest a a check valve if you do this.
Bilge pumps are weird problem. They work better the lower you put the discharge line, but if you put the discharge line low to the water line or below the water line you have potential leak issues with back check valves and broken fittings.
03-02-2006, 06:15 PM
Bear with me. Most pumps are rated on a gph discharge assuming a level discharge. Most (if not all) boat bilges are somewhat below water level. Soooooooo....you're bilge pump is going to be pumping uphill. This means it has to fill the pipe and push water uphill and so it won't pump the rated gph. The higher you put the discharge the safer you are from downflooding, BUT...the less efficient your pumps will be. A check valve in the line will significantly increase the resistance furthe reducing the pumps efficiency and adding a very possible clogging hazard. Flapper valves outside the through hulls offer less resistance and probably work as well. Each pump should be plumbed to it's own through hull. This means totally separate plumbing runs or 2x the water flooding back from the high end of the loop.
Since smaller pumps can use smaller plumbing (less backwash) a good strategy is to employ two pumps set at different levels. A small (250 or so) pump for regular discharge of normal seepage preferably set in a sump. And a honkin' big ole "She be goin' down" pump set a few inches above that. It may never go off, but if it does it's going to do a lot more than a pair of 500s in tandem.
03-02-2006, 06:43 PM
Ok, so a pump is nice to have at times...but all this whoopdedo for a 15' runabout??
Is this gona live in the water uncovered or on a trailer?
What Lorelei said. Amazing but true about the gallon rating.
I use those automatic (tries to pump every 60 seconds or so) bilge pumps on the whalers I deal with. Usually last about of 6 weeks of major abuse. If you can mount one in such a way that kids won't stand on it and fuel tanks won't bounce on it ("we weren't really wake jumping"), it'll probably last a lot longer. I found the noise intrusive to start with, but like them now.
Then again as Lorelei says, I'd put a honking 1000 gals pump higher up ( actually only the float switch would be higher up). I agree with MMD but I'd be tempted to put the discharge for the small bump in the motor well. Be creative with the discharge for the large pump, but remember it's hardly ever going to pump.
Every bilge pump is too big and too expensive until you need it, then it is much too small and cheap. ;)
A note of clarity about my earlier post, if I may: I suggested a check valve to be installed between the through-hull and the highest point in the discharge hose, which I had suggested should be looped up under the gunwale. In this position, the pump will not be working against the check valve, as the bilge water will flowing "down hill" from the gunwale. But, yes, the pump will have to overcome the uphill push to the gunwale.
03-02-2006, 07:30 PM
The little 500 Rule will be just fine. (build in some flotation, upgrade the pfd's, maybe an epirb, and you will be ok). In an emergency I have never said "man. I wish that pump didn't move so much water".
03-02-2006, 07:56 PM
I noticed in the latest Jamestown Distributors 2006 Buying Guide on page 69 they sell
VENTED LOOPS: Non-corroding molded in glass filled "Marelon" vented loops prevent siphoning of water back into the head, feature valve at the top to allow entry of airand seal as water passes.
They have a 3/4" version ITEM #FOR-903001. Seems like this one piece item would take care of the siphoning issue on my Rule pump with 3/4" discharge.
3/4" Vented Loop (http://www.jamestowndistributors.com/product;part;13978;process;search;text;vent)
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