Thoughts on pipework for bilge thru hulls

[sndog]

So I built a mockup of one of the walls where the thru hulls will be installed in my engine room. There are 4 thru-hulls on each side. 2 for regular, 2 for high water.

The high water uses a 2" line, and the regular uses a 1.5" line. The longer section of the plywood is the bottom. Above this area is a shelf and a fuel line, so neither can be moved. I am looking at going up so as to provide a loop to prevent water from coming in easily. The lower thru hulls sit about 12" above the water line. The higher thru hulls sit about 22". The V's at the end of colored lines represent ball valves. I looked at tigerflex 241 and 244 and found that bending them in that diameter is not too feasible.

Will this work and not kill my pump output capacity more than needed, and is there a better way, or idea?

 

[Mac G]

Sorry but cannot picture exactly what you are doing.
You want to add eight (8) thru hulls for bilge pumps?
How many pumps do you have?
Normally the hose coming from the pump will simply make a high loop well above (say up to the max height of your engine room) and then drop back down to where it exits the thru-hull.
Cannot use PVC pipe attached to any thru-hull fitting - must be flexible hose where that connection is made.
Need clarifcation on big pitcure of what your master plan is here.

 

[jleonard]

Seems like way too many thru hulls and bilge pumps unless I’m missing something.

 

[sndog]

Sorry but cannot picture exactly what you are doing.
You want to add eight (8) thru hulls for bilge pumps?
How many pumps do you have?
Normally the hose coming from the pump will simply make a high loop well above (say up to the max height of your engine room) and then drop back down to where it exits the thru-hull.
Cannot use PVC pipe attached to any thru-hull fitting - must be flexible hose where that connection is made.
Need clarifcation on big pitcure of what your master plan is here.

The U part of pvc, would be the top, where you would normally take the hose to have the high loop.

 

[sndog]

Seems like way too many thru hulls and bilge pumps unless I’m missing something.

It is due to how my boat is divided up. Essentially I have 5 sections. Each section has a normal bilge pump (3700GPH) and one high water (6600GPH)

Due to the height of the water line in rooms, 4 sections need to go into the engine room (2 sections are in the engine room) in order to have access to the shutoff valves if needed.

 

[Bmarler]

Usually, there are limber holes to allow water to drain to the lowest part of the bilge. If that’s not the case, I think I’d use pumps to move water in higher compartments to the lowest one, and use one or two large pumps for overboard discharge.

 

[rslifkin]

Usually, there are limber holes to allow water to drain to the lowest part of the bilge. If that’s not the case, I think I’d use pumps to move water in higher compartments to the lowest one, and use one or two large pumps for overboard discharge.

Using pumps to move water to another part of the bilge seems wasteful. Why not just pump it directly overboard? It's a few extra holes in the boat, but they're above waterline.

Personally, I think most boats are under-pumped, so a setup like this doesn't seem too crazy to me. I've got 5 pumps on my own boat and can think of 1 or 2 more that should probably be added if I can figure out a good way to do it.

 

[sndog]

Usually, there are limber holes to allow water to drain to the lowest part of the bilge. If that’s not the case, I think I’d use pumps to move water in higher compartments to the lowest one, and use one or two large pumps for overboard discharge.

That is not too bad of an idea at all. Though I can take the bow and the midship and just move them to the engine room bilges. The limber holes do not necessarily work for mine, as I have nearly a 3000 gal fuel tank built into the bilge midship.

 

[Fleming]

It is due to how my boat is divided up. Essentially I have 5 sections. Each section has a normal bilge pump (3700GPH) and one high water (6600GPH)

Due to the height of the water line in rooms, 4 sections need to go into the engine room (2 sections are in the engine room) in order to have access to the shutoff valves if needed.

Why do you have shutoff valves in your bilge pumping system?

 

[sndog]

Why do you have shutoff valves in your bilge pumping system?

Just in case. easy to add now, with minimal cost. Though life is much easier with out adding them in.

 

[sndog]

Ok, I have two designs now, one with a loop, one without. The one without would have check valves. Thoughts?

These photos show the loop. Pipes are 2"ID and 1.5"ID

 

[sndog]

These photos show no loops, but would put a clear check valve in line.

 

[sndog]

These are shown side by side for size comparison

 

[RT Firefly]

Greetings,
Mr. sn. MY opinion is put in loops. It not only lends a "steampunk" look to your ER, I'm against check valves in a bilge line.

 

[sndog]

Greetings,
Mr. sn. MY opinion is put in loops. It not only lends a "steampunk" look to your ER, I'm against check valves in a bilge line.

LOL...I like the steampunk look. Just what an ER needs.

 

[sndog]

Greetings,
Mr. sn. MY opinion is put in loops. It not only lends a "steampunk" look to your ER, I'm against check valves in a bilge line.

What do you think about me using a Marelon 90 from the thru-hull and then connecting straight to Trident 241? Would the hard 90 be a concern at all?

 

[C lectric]

Generally check valves in bilge pump discharge lines are frowned upon. THey can stick when you need them to not stick.
Go with a loop.

JMO.

 

[RT Firefly]

Greetings,
Mr. sn. Any advice beyond steampunk is above my pay grade. I leave it to more experienced members to advise.

 

[Mako]

OP I'm unclear if you already have all these pumps, pipes and such, or if it is a plan and the pvc is for mockups, but let me share some input:

1. Don't (ever) use check valves in your discharge lines
2. No ball valves are needed
3. Research whether sch40 pvc is an acceptable material. Can check ABYC or any Class society
4. How about configure your 5 bilges with one bilge pump and one high water alarm
5. Install one central emergency bilge pump, huge capacity 240VAC or engine driven, with a valve manifold leading to each compartment

 

[sndog]

OP I'm unclear if you already have all these pumps, pipes and such, or if it is a plan and the pvc is for mockups, but let me share some input:

1. Don't (ever) use check valves in your discharge lines
2. No ball valves are needed
3. Research whether sch40 pvc is an acceptable material. Can check ABYC or any Class society
4. How about configure your 5 bilges with one bilge pump and one high water alarm
5. Install one central emergency bilge pump, huge capacity 240VAC or engine driven, with a valve manifold leading to each compartment

I am currently mocking this up as I prefer to work in he open to see how it fits together, rather than in a confined space. Learned that lesson the hard way.

Check valves I agree, I have researched and definitely a no no. It appears, with USCG and ABYC, SCH40 is not prohibited above water line applications.

For a central bilge pump, it would be difficult, as the pump would have to pull a suction, as there are fuel tanks blocking the way. Between the bow and midship is a bilge fuel tank. then there is a 30" gap, before it goes into the engine room, and the port and starboard bilges are divide yet again, buy another fuel tank.

 

[Fleming]

I would say the ball valves are not only not needed, "Oh no, my bilge pump is moving too much water, close the ball valve!" but would be as much of a liability as the check valves. All it would take is an inadvertently or accidently closed valve to then prevent your bilge pump from operating with absolutely no up side to having the valves in there.

 

[Bmarler]

I can make a case for valves on the hull fittings if the distance between the outlet and waterline is close, and there’s no real way to increase it.
These pumps can backflow in certain instances, and a shutoff would be nice to have.

 

[cafesport]

There is a reason why that store with the familiar orange shelves and cart isn’t called “marine” depot.

Your insurer and surveyor can probably offer you the best advice on this project. I hope you are willing to listen to them.

Fwiw schedule 40 has no place on a boat other than as a shim for fishing rods, though many boats do tend to use schedule 80 for sewage. 90 degree bends and check valves for bilge plumbing is also a no no. You might want to get familiar with the concepts of heeled waterline and bend radius before drilling any more holes.

Finally I’m really quite surprised that the original designer and builders of your vessel seem to have been so clueless.

 

[CharlieO.]

I can make a case for valves on the hull fittings if the distance between the outlet and waterline is close, and there’s no real way to increase it.
These pumps can backflow in certain instances, and a shutoff would be nice to have.

I thought the vented loop was to prevent this?

 

[TJM]

You (USCG) say PVC is OK above the water line, but at some point, the PVC will be below the waterline closer to the bilge pump? PVC is very shock sensitive and cracks easy. I would never use it in my engine room. The vibration on boats is incredible and will shake things apart.

 

[Maerin]

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.

 

[SteveK]

I thought the vented loop was to prevent this?

Used for intake lines

 

[SteveK]

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.

 

[Fleming]

Used for intake lines

No, used when the slightly above static waterline through hull is below the heeled waterline (and the other end of the hose is also below the waterline) to prevent siphoning water back into the boat. Not just for intakes.

 

[CharlieO.]

No, used when the slightly above static waterline through hull is below the heeled waterline (and the other end of the hose is also below the waterline) to prevent siphoning water back into the boat. Not just for intakes.

Thanks, that was my understanding as well. I thought if the bilge discharge was less than 12"? a vented loop was required/recommended.