Thoughts on pipework for bilge thru hulls

[Bmarler]

I thought the vented loop was to prevent this?

They will, if there’s room for them. I would install them if I could, but my 50 year old boat has precious little space between the cockpit floor and the waterline.
And with the through hull fittings so close to the waterline I like having a valve there if I need to change a hose.

 

[twistedtree]

I think most of this has been covered, but here goes anyway.. I am NOT intimately familiar with this aspect of ABYC, so please confirm, especially WRT to the details.

- I believe that within a certain distance of the heeled waterline (and below of course) a shutoff valve is required. And even if not required, they can be useful for service purposes.

- Similar to above, within a certain distance of the heeled waterline, you need to have a vented loop to prevent siphoning back into the boat. Also think about a boat that is experiencing constant side seas pushing water against those thruhulls. If at all in doubt, I would install a vented loop. And the vented loop needs to be a certain distance above the thruhull.

- A thruhull and attached piping needs to be able to withstand a certain force on it. Essentially, you need to be able to stand on the assembly and not have it break. I don't think the PVC would withstand the test.

- The PVC does look very steampunk (thanks RT, I had to look that one up), but the obvious question is why not take the more common approach of hoses looping up to an anti-siphon loop, then hose coming back down to the pump? There is probably a good reason, but I missed it.

- In general, I see no advantages, and only disadvantages to PVC in this application.

 

[rslifkin]

I'm not sure if the side load requirement applies to through hulls placed above the heeled waterline. IIRC, the determination for that on a power boat is something like whether it'll be above water at 7* of heel with the boat loaded to maximum design displacement.

 

[Greg QS]

NO NO NO Just NO

The weight of the water in a 3/4 " hose is .19 bs per vertical foot
The weight of water in a 1.5" hose/pipe is .77 lb per foot.
That is 4 TIMES the back pressure. So you thought of a larger pipe Not to kill pump capacity, will do just that!



So , If you are using check valves, sometimes needed to stop cycling , the large pvc capacity my overwhelm the pump output and not allow to open the valve and discharge due to the 4 TIMES head pressure.

If no check valve is used you will have a larger capacity ( the same 4 x) of water trapped in the discharge pipe that cannot be pumped overboard. . This will create a higher possibility of cycling the pump due to the backwash of 4x the water not discharged. You will have more 4x water in the bilge as compared to the smaller discharge hose.at all times due to the back flow of the discharge pipe.

Keep the discharge runs as short as possible. Minimize the discharge to the pump discharge,

Again Pumping into a larger pipe will decrease the flow due to the 4 x increased head pressure of the water and give you a 4x higher backwash affect. .


Simple math the bigger the pipe the bigger the back pressure and volume.

Here is a chart.
Pipes with Water Content - Weight and Volume

 

[Iggy]

I have not read every word from every post. So forgive if I bring things up that's been posted.

I do know for an inspected boat, say a launch. Shut off valves are needed at the thru hull. How do I know, the U.S.C.G. came down to my Club and told us. We asked "Why". They said if the boat starts to sink, its a way water can get in.

If it was my boat, I would not use PVC. Its very rigid, there for it will need a lot of support. The bouncing or moving from wave actions could cause the joints to leak. With hose to can only leak at two places. PVC pipe, at every joint.

In a nut shell, I just don't think PVC can take the pounding. I don't want to find out in a emergency.

 

[twistedtree]

NO NO NO Just NO

The weight of the water in a 3/4 " hose is .19 bs per vertical foot
The weight of water in a 1.5" hose/pipe is .77 lb per foot.
That is 4 TIMES the back pressure. So you thought of a larger pipe Not to kill pump capacity, will do just that!



So , If you are using check valves, sometimes needed to stop cycling , the large pvc capacity my overwhelm the pump output and not allow to open the valve and discharge due to the 4 TIMES head pressure.

If no check valve is used you will have a larger capacity ( the same 4 x) of water trapped in the discharge pipe that cannot be pumped overboard. . This will create a higher possibility of cycling the pump due to the backwash of 4x the water not discharged. You will have more 4x water in the bilge as compared to the smaller discharge hose.at all times due to the back flow of the discharge pipe.

Keep the discharge runs as short as possible. Minimize the discharge to the pump discharge,

Again Pumping into a larger pipe will decrease the flow due to the 4 x increased head pressure of the water and give you a 4x higher backwash affect. .


Simple math the bigger the pipe the bigger the back pressure and volume.

Here is a chart.
Pipes with Water Content - Weight and Volume

It's true that there is more water volume in a larger pipe, but the pressure of the water column is based only on the height, and is independent of the pipe size. The pressure 1' down in the ocean is the same as 1' in a 2" pipe, and the same as 1' in a 1/2" pipe. So in all cases the water column pressure that has to be overcome by the pipe is the same regardless of pipe size.

Backpressure is just about the flow resistance, i.e. the additional resistance when the water is moving. I think a bigger pipe or hose always offers less flow resistance, so less backpressure above and beyond the pressure from the water column.

 

[delirious duo]

no matter the install with PVC it would have to be treated as fragile in the bilge and missteps in weather and your replacing it. It’s too brittle and any cold weather even more so. Just my opinion and I’m clumsy.

 

[rslifkin]

For those saying 1.5" hose is crazy huge for a bilge pump, it's not. It's huge for a tiny toy pump used to remove the last little bits of water. But for a bigger pump, it's normal. As an example, the Rule 3700 has a 1.5" hose connection. And their 4000 gph model uses 2" hose. Going smaller with those pumps would absolutely destroy capacity due to increased resistance in the smaller hose.

 

[Greg QS]

I apologize for my incorrect input.

Darn it I know that . That why we use water column references. Makes no difference of the diameter or LxW of a container of fluid, only the depth of the container/tank.

Now volume of the container = weight of the container. Witch is different thing. I was thinking of that for support of Tanks I have restored tank beds in the past. This was what I was incorrectly thinking of .


This is why pressure senders work on tank systems on boat regardless of demotions only height is used in the senders calc of capacity (for regular shaped tanks)



I stand corrected.

My concern would be the back flow of the water into the bilge without the use of a check valve in the system Also think of the weight of the system while supporting you pipes/hoses .

 

[Fleming]

I do know for an inspected boat, say a launch. Shut off valves are needed at the thru hull. How do I know, the U.S.C.G. came down to my Club and told us. We asked "Why". They said if the boat starts to sink, its a way water can get in.

Ha Ha! Sure, if my boat is starting to sink I'm going to go shut off the seacocks for my bilge pump outlets. That'll save it.

 

[SteveK]

Using PVC with multiple joints is akin to using solid copper wiring on board, only a matter of time for failure. But still have not heard what pumps will drive the water out. Will pipes below gooseneck remain full or drain back to bilge?

 

[Iggy]

Ha Ha! Sure, if my boat is starting to sink I'm going to go shut off the seacocks for my bilge pump outlets. That'll save it.

Thats what we told them.

 

[Snapdragon III]

It's a little hard to understand what you have going on, but I would not use PVC for this. I think you would have more chance of sinking your boat from this setup, than you would if you just removed all your bilge pumps. My solution would be to get smaller pumps for the primary pumps, that can use normal 1" hose, which will be easier to make the bends you need. Huge primaries will just lead to lots of water washing back from the pipe when they turn off, and is overkill. For the large secondaries I would use welded Stainless steel pipe since it looks like you have a steel boat. Just fab them up, and weld them into the side of the hull. It will be a pain in the ass, but likely not too bad. Fixing the paint will be the worst part of it. If you don't want to weld I still like the plan of the primaries with smaller normal hose, and just do the big ones in PVC. 24" above the waterline seems way less dangerous. Get the right size plug and have it hanging on a string ready for an emergency. The problem with PVC is that when it fails, it tends to completely shatter. It won't just spring a leak, it will break off.

 

[sndog]

The use of 1-1/2 and 2" pipe for bilge pump discharge seems to be significant overkill. How big is this vessel? What criteria was used to determine the size of the piping? I would not use PVC on piping connected to a thru hull. I see no problem, in fact recommend using 1-1/2 PVC on waste lines, but they're self-limiting inasmuch as they connect to a holding tank, and if the pipe breaches, that liquid is already on board, it won't impact the vessel's seaworthiness other than making a hella mess. These proposed lines, OTOH present a significant potential for lots of water to come aboard if breached. The thru hull would need to meet ABYC impact and shear force recommendations, and a seacock at the hull penetration might be in order. Do some math on how much water can come through those combined diameters vs. smaller ones. If there must be a high capacity dewatering capability, perhaps a crash pump might be a consideration.

I thought it was overkill on 2", but when I did the calcs, it does show 2" is what should be for my hight water bilge pumps. The PVC is not directly connected to the thru-hull, it is either through a hose, or a rubber coupling, depenind on on where in the ship it is. These lines are specifically for the bilges. Not below waterline, not allowing ingress of water at all. They are specifically for egress of water if something occurs. And has been stated, these are bilge lines, above the water line.

 

[sndog]

Read this twice but did not see what pumps will be used. What power will they use?

Fire/trash hose size plumbing can move a lot of water, getting holed would not be much concern.

The pumps being used for normal bilge is 3700GPH 24VDC@7.5A pumps. There are 5 of these. For high water bilge, they are 1hp, 6600GPH Ridgid sump pumps, powered by 120VAC @8.1A, there are 5 of these. Both of these are run off of a low voltage (24VDC) control system. Each pump runs off of two floats. If either float is triggered, the pump turns on.

All pumps are at the same level in the bilge, in their respective compartments. The float sensors are run at two different heights; one for normal bilge, and one for high water bilge.

 

[sndog]

I think most of this has been covered, but here goes anyway.. I am NOT intimately familiar with this aspect of ABYC, so please confirm, especially WRT to the details.

- I believe that within a certain distance of the heeled waterline (and below of course) a shutoff valve is required. And even if not required, they can be useful for service purposes.

- Similar to above, within a certain distance of the heeled waterline, you need to have a vented loop to prevent siphoning back into the boat. Also think about a boat that is experiencing constant side seas pushing water against those thruhulls. If at all in doubt, I would install a vented loop. And the vented loop needs to be a certain distance above the thruhull.

- A thruhull and attached piping needs to be able to withstand a certain force on it. Essentially, you need to be able to stand on the assembly and not have it break. I don't think the PVC would withstand the test.

- The PVC does look very steampunk (thanks RT, I had to look that one up), but the obvious question is why not take the more common approach of hoses looping up to an anti-siphon loop, then hose coming back down to the pump? There is probably a good reason, but I missed it.

- In general, I see no advantages, and only disadvantages to PVC in this application.

The force test on them, from how I have read the ABYC codes, is specifically for any below waterline applications.

 

[sndog]

NO NO NO Just NO

The weight of the water in a 3/4 " hose is .19 bs per vertical foot
The weight of water in a 1.5" hose/pipe is .77 lb per foot.
That is 4 TIMES the back pressure. So you thought of a larger pipe Not to kill pump capacity, will do just that!



So , If you are using check valves, sometimes needed to stop cycling , the large pvc capacity my overwhelm the pump output and not allow to open the valve and discharge due to the 4 TIMES head pressure.

If no check valve is used you will have a larger capacity ( the same 4 x) of water trapped in the discharge pipe that cannot be pumped overboard. . This will create a higher possibility of cycling the pump due to the backwash of 4x the water not discharged. You will have more 4x water in the bilge as compared to the smaller discharge hose.at all times due to the back flow of the discharge pipe.

Keep the discharge runs as short as possible. Minimize the discharge to the pump discharge,

Again Pumping into a larger pipe will decrease the flow due to the 4 x increased head pressure of the water and give you a 4x higher backwash affect. .


Simple math the bigger the pipe the bigger the back pressure and volume.

Here is a chart.
Pipes with Water Content - Weight and Volume

I thought of the larger pipe, given calcs and given GPH of pump capacity.

My pumps should only come on if there is a major issue occuring, as everything is dripless on my boat, and is designed to not have seawater splashing into it, anywhere. If there is a slight amount of water, the arid bilge pumps will remove it. My bilge pumps listed are for removing large quantities of water from something going wrong. So, in the 2" pipes, the longest run, puts about 8 gallons of water in the pipe.

These are big pumps, designed to move a lot of water.

 

[Mako]

OP, with the large quantity of hoses you need for your five bilges, I understand the desire to avoid WestMarine to source the 2” ABYC-compliant hose.

How about pricing out trash pump intake hose. Flexible with rigid walls. You could stand on one in 15°F temps and not crush the wall. Think about what happens to PVC at that temperature.

You’re designing for worst case after all.

 

[sndog]

OP, with the large quantity of hoses you need for your five bilges, I understand the desire to avoid WestMarine to source the 2” ABYC-compliant hose.

How about pricing out trash pump intake hose. Flexible with rigid walls. You could stand on one in 15°F temps and not crush the wall. Think about what happens to PVC at that temperature.

You’re designing for worst case after all.

I avoid west marine, way too overpriced. I pick up hose, trident 241, for about $2/ft for 1.5" and $5/ft for 2". PVC I used due to the how to run it for the 2" lines.

The reason I learned people typically do not use it.......the time it takes to install it. Running my 1.5" hose took an hour to run and clamp. the 2" PVC. Took a day to run and have it fit properly.

I will look at the trash pump hose. Though I was looking at suction hoses for . The Tigerflex hose is a great price, but shipping killed it for me.

For PVC, also, some areas, such as the middle of my ship, where I need to add flooring, I ran 1x 2", 2x 1.5", 2x 1.25", 1x 1", on each side as I did not know what my final game plan was going to look like. I am glad I did, as it makes life much easier.

So yes, PVC works, is code compliant, the time of installation is absolutely horrendous.

Also, as a side note, the PVC is all protected, as are the hoses, so there is no risk of them being stepped on in the bilge.

 

[sndog]

Here is what I did.for.the port side so far.