Bilge pump lines from pump to thru hull

[sndog]

Was wondering about bilge pump pipe systems. I am currently installing 10 bilge pumps. 5 normal, 5 high water. The normal ones are 3700 gph, and the high water ones are 6600 gph. I was wondering about the output of them to the thru hulls. I am using PVC, sch 40, hooked to the thru hulls via rubber adapters, the same type of adapter is being used from the pump to the lines. My question is do I need to have the pipes go up some, like in my photo attached, before going down, or is it safe to have them level or a slight incline upwards before dropping down to the bilge pumps? Thru hulls are above the water line. Normal is maybe 12 to 14 in above the water line. High water is maybe 24 to 30 in. Another photo shows the approximate location for this set of thru hulls.

I was also wondering if PVC is an ok choice for this application given it is isolated from the hull and pump via the rubber adapters. And any additional input on this? My boat originally had 2 bilge pumps. The 5 areas are essentially sectioned off from each other. Ball valves will be installed as well

Thank you in advance.

 

[mvweebles]

I'm having a hard time visualizing your question, but I did catch that your thru-hulls penetrations are 12-14 inches above waterline (high water are higher). In my opinion, these should have a vented loop run high on the inside. Reason being that in beam seas they are at risk of backwashing into the bilge. Plus, if the high water pumps are ever called upon, these will be submerged and will add to whatever is causing the flooding. Frankly, in my opinion, all bilge pump outlets should have a vented loop.

As for use of PVC, I've never seen it done for bilge pumps but I don't see a problem with it.

10 bilge pumps seems like a lot. What kind of boat is this and how will it be used? Typically, not all compartment are at similar risk of high water intrusion.

Peter

 

[Pete Meisinger]

What kind of boat requires ten new bilge pumps? Perhaps your money could be better spent on other repairs and preventive maintenance.

That being said, you plan looks good. Seems like awfully long runs to the outlet. I wouldn't be concerned about the slope too much, you can always install backflow preventers.

PVC looks to be a good choice, at least to me.

But ten pumps ? Whats going on?

pete

 

[jgwinks]

I believe AYBC requires all power boat through hulls below the level of 7 degrees of heel to have a seacock, and I don't think I'd want a seacock on a bilge pump outlet. Pretty useless if the valve is closed. On sailboats it's the level of the sheer as they can routinely heel over that far. On my boat 7 degrees works out to 11 inches so your 12-14 is probably fine. But as Weebles said, if you need the high water pumps, the regular ones might already be underwater. That would be a really bad thing. The pumps should be running, but they'd be facing the pressure of the outlets being submerged and might not pass much if any water. And if one failed or clogged, it would contribute to the flooding.
On my last sailboat which only had a good spot for one pump, I mounted two. A little one, 360 gph as I recall and with as short a hose as possible to handle nuisance water, and a much larger one above it. I don't think the big one ever came on the whole time I owned the boat. As it was a sailboat, both outlets were at the gunnel. I did that to minimize the amount of water backflow when the pump stopped. The big one would backflow enough water to turn itself back on.

 

[jgwinks]

I like the idea of pvc pipe though. Much smoother so better water flow, and probably cheaper than quality hose. But WAY harder to install which is probably why we've never seen it before. Some of the sanitation plumbing on my boat is pvc pipe and it works fine.

 

[sndog]

I'm having a hard time visualizing your question, but I did catch that your thru-hulls penetrations are 12-14 inches above waterline (high water are higher). In my opinion, these should have a vented loop run high on the inside. Reason being that in beam seas they are at risk of backwashing into the bilge. Plus, if the high water pumps are ever called upon, these will be submerged and will add to whatever is causing the flooding. Frankly, in my opinion, all bilge pump outlets should have a vented loop.

As for use of PVC, I've never seen it done for bilge pumps but I don't see a problem with it.

10 bilge pumps seems like a lot. What kind of boat is this and how will it be used? Typically, not all compartment are at similar risk of high water intrusion.


Peter

I agree with 10 pumps seeming excessive, but my issue is as follows, the aft room, is cut off from the rest of the ship till about 5 ft of water is in it. It has my two rudders, which use Lasdrop Gen II seals. Plus a Stern thruster. The engine room, which is midship, has a fuel tank that divides it down the middle and will not have water flooding to the other side till about 18" to 24" in height. Mid-ship area, outside the engine room, is the least needed, as the risk is low for water intrusion, but the engine room will spill into this area around 15" up. I could cut the normal one here, but not worth it to me for one normal pump savings.
Then the bow area, this will start to spill into the mid-ship area at a height of around 20". I could save a high water pump here, but again, for a one-pump saving, and having some additional peace of mind, I am good with leaving it.

 

[HeadedToTexas]

Compared to Sch. 80 PVC and especially compared to flexible hose, Sch. 40 PVC is brittle. Secure the pipe runs well and make sure nearby items can not lean on or rest on the pipe.

 

[sndog]

What kind of boat requires ten new bilge pumps? Perhaps your money could be better spent on other repairs and preventive maintenance.

That being said, you plan looks good. Seems like awfully long runs to the outlet. I wouldn't be concerned about the slope too much, you can always install backflow preventers.

PVC looks to be a good choice, at least to me.

But ten pumps ? Whats going on?

pete

The runs you see are from the middle to the first outside wall, they are as short as possible. The boat has an 18ft beam.

Ten pumps is just putting pumps where needed for safety. No repairs are needed, and the boat is bone dry. I am finishing up a refit of it.

Each area will also have an arid bilge pump as well, so I thought about backflow just to stop the amount of water coming back into the bilge, but figured the risk of it possibly clogging or malfunctioning, outwears the water coming back in and the arid bilge pump will suck up any remaining water.

Rudders have new Lasdrop Gen II dripless rudder seals. The prop shafts have new Lasdrop Gen II dripless shaft seals. For below the water line, I have two thru-hulls for waste or other and the remaining water needs to come through two sea chests.

 

[sndog]

I believe AYBC requires all power boat through hulls below the level of 7 degrees of heel to have a seacock, and I don't think I'd want a seacock on a bilge pump outlet. Pretty useless if the valve is closed. On sailboats it's the level of the sheer as they can routinely heel over that far. On my boat 7 degrees works out to 11 inches so your 12-14 is probably fine. But as Weebles said, if you need the high water pumps, the regular ones might already be underwater. That would be a really bad thing. The pumps should be running, but they'd be facing the pressure of the outlets being submerged and might not pass much if any water. And if one failed or clogged, it would contribute to the flooding.
On my last sailboat which only had a good spot for one pump, I mounted two. A little one, 360 gph as I recall and with as short a hose as possible to handle nuisance water, and a much larger one above it. I don't think the big one ever came on the whole time I owned the boat. As it was a sailboat, both outlets were at the gunnel. I did that to minimize the amount of water backflow when the pump stopped. The big one would backflow enough water to turn itself back on.

I thought about that as well if that one is underwater, but my thought on it was if my boat sinks down 12" in the water, it is basically time to abandon ship. I am putting ball valves near the pump in case it needs to be closed though.

 

[sndog]

I like the idea of pvc pipe though. Much smoother so better water flow, and probably cheaper than quality hose. But WAY harder to install which is probably why we've never seen it before. Some of the sanitation plumbing on my boat is pvc pipe and it works fine.

I think in most boats, PVC would be way harder to install and way more money due to the amount of fittings needed. Here, it worked out nicely, but I did isolate it from the thru-hull and the pump to help reduce the vibration load in it. The inside of the boat will also never be freezing as it will be temperature-controlled year-round.

My sanitation piping will be PVC as well.

 

[sndog]

Compared to Sch. 80 PVC and especially compared to flexible hose, Sch. 40 PVC is brittle. Secure the pipe runs well and make sure nearby items can not lean on or rest on the pipe.

Thank you. It will be heavily secured. Currently, just using a string with adjustable knots in it to dry-fit it all together. In this area, there is still two more water pipes needed to run, a sump and ac outlet. Plus there is several electrical conduits to feed some sub-junction boxes, and two AC, 5" insulated ductworks, a pex manifold, and a Moen U Shower controller.