Bilge pump set-up help
Printed From: The Fishing Website
Category: General Forums
Forum Name: The Boat Shed
Forum Description: Discuss all things boating.
URL: https://www.fishing.net.nz/forum/forum_posts.asp?TID=105838
Printed Date: 08 Jun 2026 at 10:39pm
Topic: Bilge pump set-up help
Posted By: gizzykid
Subject: Bilge pump set-up help
Date Posted: 08 Dec 2014 at 10:49am
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Hey guys I am after a bit of advice from you knowledgeable gentlemen.
Over the weekend I did a fairly long offshore trip. At the
end of the day the boat was starting to feel a bit sluggish and taking a while
to get up on the plane. When we whipped out the bung at the end of the day
there was a significant volume of water in the hull (bung wasn’t sealing
properly) This got me thinking. With the way our bilge pump is set up
there is no real way of getting rid of any water in the hull until its back on
the trailer and the bungs out. Water on the deck drains to a sealed sump under the transom. This is where the only bilge pump is. At the bottom of the sump are two bungs that drain into the hull. We always leave the bungs in to avoid draining bloody/fishy water (and all sorts of other scraps) into the hull. When the sump bungs are out and there is a lot of water in
the hull this water starts to enter the sump from below (i.e flow back up
through the bungs). So, if we ever got a huge amount of water in the hull we
could always remove the sump bungs and the bilge pump would pump the water out
until it was back to a level below the bottom of the sump. However, there needs
to be a huge amount of water in the hull before it reaches the level of the
sump. Anyway, I figure it is a bit of a safety issue the way it is
presently set-up and I am thinking of installing another bilge pump in the base
of the hull. The problem I face is that the floor is sealed/welded so there is
no access to this area of the hull. I am thinking of getting a hatch installed near the transom so I can install the bilge pump. But Im a bit concerned that this will just create another spot for water to get into the hull. And how do I route the pump hose up through the floor without letting bloody deck water into the hull?? Has anyone got any smart ideas for bilge pump access/hose
setup? Or any photos showing how their boat is setup? Any other advice? I’ll try to upload some photos of the current sump/bilge
pump setup later on tonight. |
Replies:
Posted By: Olfart
Date Posted: 08 Dec 2014 at 11:03am
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Why not simply instal an automatic float switch on the pump? This way, whenever water in the sump gets to a set height the pump will operate and empty the sump out for you. ------------- Semper in excreta sumus, solum profundum variat.... |
Posted By: gizzykid
Date Posted: 08 Dec 2014 at 11:17am
Yeah I agree that that would be a good way to go if the sump
was low enough. The problem is the sump is quite a way off the bottom of the
hull and so there needs to be a really large volume of water in the hull before
the sump begins to fill and the bilge can go to work. Where there is only a small to moderate amount of water in
the hull the sump and bilge are above the water and cannot do anything to
remove it. The current setup is probably a bit hard to visualize
without photos. |
Olfart wrote:Posted By: Otto
Date Posted: 08 Dec 2014 at 11:38am
| What type of boat is this |
Posted By: Kevin.S
Date Posted: 08 Dec 2014 at 11:47am
| I think I can visualise your setup and see what you mean. The area you have water in is supposed to be a sealed under deck flotation chamber, and the only access to it is the bung in the back of the boat. The best solution (although probably not the easiest) is to work out how water is getting in there and stop it. If the bung isn't sealing then replace it. I think you are right when you say installing a bilge pump will just give another access point for water, making holes in this chamber stop it being sealed and so destroy its buoyancy. |
Posted By: MacSkipper
Date Posted: 08 Dec 2014 at 12:22pm
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Gizzykid it sounds like you were unlucky in that your sealed buoyancy chamber developed a leak - as you and others say developing a way to drain will provide another ingress route for water - if you have a major event and boat has flipped or submerged you want buoyancy chamber to remain sealed at all costs. I wonder if leak slowly developed and you did not notice till leak got bigger or till on a longer trip? As I have understood it the problem with this design is interior drains into Hull - you should have separate bungs for interior area and buoyancy chamber - so you can drain interior then chamber and check whether buoyancy chamber is dry after each trip? Personally I would fix leak in chamber and then keep an eye on chamber and check after EACH trip no water getting in at all so if leak reoccurs you notice straight away.. ------------- Good fishing trip nothing breaks, great trip catch fish. |
Posted By: Otto
Date Posted: 08 Dec 2014 at 6:27pm
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Still curious on the type of boat as this may offer some solutions But, as others have said finding and stopping the leak would be first as if you put a pump in you'll also have to put in a breather so as air can get back in as the water comes out. Guessing it's a tin boat so one option would be to put some soapy water in the hull on a hot day full sun and with the pressure building maybe signs will show. I used water proof grease to seal bungs on a past boat for the same reason. |
Posted By: cirrus
Date Posted: 08 Dec 2014 at 6:34pm
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Was the bung fully tight. Once left the bung with less than a half turn from tight. Basically almost fully tight but not quite. Was surprised at the water that came in. |
Posted By: Tzer
Date Posted: 08 Dec 2014 at 7:30pm
If I've got this right what boat builder in their right mind would have bung holes in a sump that can drain directly into its bouyancy chamber . Issue now is that if alloy you have the possiblity of unseen corrosion happening in the bouyancy chamber.Best thing to do is have the holes welded up (if alloy) and possibly install a bigger capicity pump in the sump. |
Posted By: Don18025
Date Posted: 08 Dec 2014 at 9:24pm
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Put some new decent washers on each bung and screw them in real tight. Most boats inner hulls leak through the bungs, if the boat builder has done a really good job.
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Posted By: gizzykid
Date Posted: 09 Dec 2014 at 10:52am
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Hey guys
Cheers for all the feedback. I think you guys are basically on the money. Boat is an older bluewater hull. I called the manufacturer yesterday to ask for some advice. They confirmed that the area is supposed to be sealed and that the bungs in the sump should remain closed at all times when on the water. So shouldn’t need a bilge below deck as there shouldn’t be any water here. After having this chat and having a play around yesterday I’m pretty sure the water is coming in from both a slightly leaky bung and through a bad seal around the deck hatch above the underfloor fuel tank. Both easy fixes. Anyway I’ll
grab a new bung and seal up the hatch properly then take it from there. If I’m
still getting water in the hull I’ll need to keep looking I guess. |
Posted By: MikeAqua
Date Posted: 09 Dec 2014 at 2:53pm
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If you wanted to it wouldn't be drama to install a second bilge in the bouyancy chamber, gland for the cables, skin fitting for the hose. Job done. Personally I would instal an autobilge if I was going to do it, with bilge control panel, so if it activayes you will know. |
Posted By: Otto
Date Posted: 09 Dec 2014 at 3:29pm
And another for the vent to let air in which defeats the purpose of a buoyancy chamber. |
Posted By: MikeAqua
Date Posted: 09 Dec 2014 at 3:53pm
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A bilge pump doesn't require a vent. A single buoyancy chamber has no purpose - other than marketing. |
Posted By: Otto
Date Posted: 09 Dec 2014 at 4:12pm
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If something (water) is being pumped out of a space then something needs to replace it. Otherwise we'll have a vacuum. Or in this case it will be sucking around the glands and the leak so more water in. When a boat is flooded and becomes unstable and water is sloshing everywhere and into every space before perhaps overturning a marketed buoyancy chamber somehow appeals to me. |
Posted By: Unclejake
Date Posted: 09 Dec 2014 at 4:21pm
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I haven't read the entire thread, but I'd be well cautious about fitting an electrical device into a sealed chamber on a petrol boat. Forgive me if this has been covered above already |
Posted By: MikeAqua
Date Posted: 10 Dec 2014 at 2:12pm
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Very true. Not advisable where fuel tanks emit fumes e.g. some people put tote tanks in the bilge, which then vent fumes via the breather on the caps. It's supposed to be OK with an underfloor rated tank. Good float switches have sealed switch apertures (or solid sate). The bilge pump motor should be sealed (or it won't work), the bilge pump and float switch should be submerged when the pump activates. This is where separate under floor chambers (fuel and bilge) would be advantageous. But they are rare, on recreational trailer boats.
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Posted By: MikeAqua
Date Posted: 10 Dec 2014 at 3:57pm
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My post pointed out installing a bilge under deck is easy. I didn't say it was appropriate for the OP's boat. However ... Bilge pump capacity is minimal compared to chamber volume. A bilge pump admits air via the outlet hose after (and to an lesser extent during) pumping. Any vacuum will be minimal and transient. Water being so much denser than air, it would have to be quite a hole for more water to enter than air. Depending on the vessel design it may be worse to have water on the deck than in the bilge. Water will slosh around on the deck. Water sloshing around above trapped air reduces buoyancy and stability. Hence my scepticism about underfloor buoyancy chambers. Everyone's rig is different and you have to do your own risk assessment (how bad x how likely) to decide which safety compromises to choose. How much water to capsize vs sink? What height is the deck relative to resting water level? Does the deck have a bilge sump? What is the beneath deck structure like? Is there a rigid underfloor fuel tank? E.g. In my boat swamping and capsize is more likely than sinking, and bilge water is laterally constrained and removable. On that basis I unsealed the rear aft deck plate and installed silly-large bilge pumps.
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Posted By: Pcj
Date Posted: 16 Sep 2022 at 11:23am
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On the subject of bilge pumps. I discovered yesterday(flat water) with extra weight in the boat,chilly bins and all the stuff nephew brings.I discovered that outlet in the transom kept dipping under so water was flowing back in and the auto pump kept coming on. So today have installed a one way valve in the outlet pipe,why wouldnt there of been one before or do some find unnessacary or doesnt cross their mind. Might explain a lot of how vessels take in water and owners dont realise where from?
------------- "Times up" |
Posted By: krow
Date Posted: 16 Sep 2022 at 7:58pm
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I've done the same. Where abouts on the pipework did you put the valve? I couldn't put mine close to the outlet so it's about 1/2m away. I found the water pressure on top of the valve combined with the spring the pump would sometimes struggle to overcome the pressure. I took the valve apart and reduced the spring pressure. |
Posted By: Pcj
Date Posted: 17 Sep 2022 at 1:35am
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same about 1/2 way, test by filling up bilge and pumped out ok.only 1 metre from pump to outlet ------------- "Times up" |
Posted By: Big -Dave
Date Posted: 17 Sep 2022 at 7:26am
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I would only do this on an auto pump, as if you get a bit of crud under the non return valve, it is rendered useless.and with a manually switched pump, you wouldn't notice your bilge filling up. Also, it is a valid point that bilge pumps develop very little pressure, it might struggle to overcome a head of water above the valve when combined with the spring pressure. What about a little rubber flap over the outlet? Or could the bilge pump delivery pipe be routed higher than the outlet before dropping to the outlet, this would minimise any waterline induced back flow. Any restriction in that pipe is a potential blockage, and will reduce pump performance. ------------- you can't fix an idiot with duct tape, but it does muffle them for a while... |
Posted By: Pcj
Date Posted: 17 Sep 2022 at 8:48am
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https://www.burnsco.co.nz/boating/plumbing/fittings-valves/plumbing-valves/trudesign-non-return-valve%20" rel="nofollow - https://www.burnsco.co.nz/boating/plumbing/fittings-valves/plumbing-valves/trudesign-non-return-valve
fitted 19mm and filled bilge and no issues. Yes I thought the same re head and pressure,can get them with a ball in them,had one in the yacht no issue,my rise is only about 500mm pump is good for 1200 head so it says ------------- "Times up" |
Posted By: krow
Date Posted: 18 Sep 2022 at 7:17pm
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I would fill up the head above the valve and retest. Note though the valve can "stick" a bit. I find all good for the day once started. |
Posted By: Big -Dave
Date Posted: 19 Sep 2022 at 6:02am
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1200 is probably the gallons per hour rate. So long as you have tested, no problem... ------------- you can't fix an idiot with duct tape, but it does muffle them for a while... |
Posted By: OneWayTraffic
Date Posted: 19 Sep 2022 at 10:20pm
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All this reminds me of the circles I went in with my build. Seal up everything, fill with foam or leave holes for inspection, knowing water might get in? In the end I went with enough foam to float the boat no matter what and limbers with inspection/ventilation holes. I have tucked all the inspection openings away from where most water will get in, and all the openings are in places where water would not usually sit. If that boat was mine I'd reseal the bungs and be done with it. Remove bungs, look for any evidence of wet wood, dry well and reinstall and reseal. I'd epoxy the bung hole and screw holes as well. If I had any doubts about water getting in unseen I'd cut out an inspection hole in the sole near the back, seal the edges with epoxy and put in an inspection port. This could be as simple as a clear perspex square screwed into place and sealed with marine gasket sealant. Removal may not ever be required, but you will have peace of mind. I'd not muck around with pumps in that space.
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Posted By: Pcj
Date Posted: 15 Jan 2023 at 7:05am
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It appears "Big Dave" correct. Yesterday with he chop filling up outboard well and water flowing through cable hole filling up bilge. Heard pump kick in and run for sometime,upon investigation found ball stuck in one way valve due to crude,removed mechanism and water pumped out, So now thinking to install a on/off tap. Just because of location of outlet being low want to stop water flowing in.Yes maybe a inconvenience butwhat else can one do?? ------------- "Times up" |