Why not pex everywhere?

My 2001 Mainship 390 has pex tubing, but from the factory came with the compression-screw on fittings that are all being replaced as I come across them with crimped connectors or shark-bite style if I’m unable to crimp something. As I’ve been doing this and staring at other various hoses I’ve been wondering, why not pex tubing and connectors more places?

I’m not advocating replacing anything like through hull water intake hose, I’ll stick with the marine water hardwall hose for that stuff.

What about all the super cheap corrugated type bilge discharge hose? They used the same stuff on most sink and any other type of drain I come across.

I also noticed my supply connections for the A/C-heat units are cheaper hose. I know most will say not skimp there and I agree, but I’ve thought about it.

Some places may be more challenging with bends and turns, and I’m not fond of adding connectors in any spot I can’t easily monitor. I’ve heard there is something called “flexi-pex” that may handle bends better.

I’d be curious about your thoughts on this. Thank you!

I think flexibility is a big factor, especially as you get into large hose/pipe sizes. Marine hoses can bend and hold a curve without kinking, where PEX has very limited ability to do that. So you end up adding elbows to PEX which reduces flow. Also PEX is a bit smaller ID vs hose. And I wouldn’t want to use any fittings that contain steel or brass with salt water.

Another consideration are the various hose ratings that marine hose has. I don’t know what the specs are behind those ratings, and whether PEX meets them. That’s regardless of whether they have been certified.

I'm not sure if the 'flex pex' that you mention is the rounded ( in a coil). I will post pics, and I mentioned in an earlier post that I had a leak of the old polybutylene hose originally installed on my boat. I replaced all lines with pex, using a combination of straight pieces when it was appropriate and the coiled when needed. I alreadly had a compression tool, so all my fittings are compression fittings and of course they are all where I can get to them.

Pex sizes correspond to copper tubing sizes. Things like bilge pump hoses
and other drain hoses will not be easy to replace with Pex without changing the fittings.

Get rid of the corrugated hose, particularly in bilge pump discharge application. But just use quality smooth wall hose.

I re-plumbed most of my water system in PEX though.

Northern Spy said:

Get rid of the corrugated hose, particularly in bilge pump discharge application. But just use quality smooth wall hose.

I re-plumbed most of my water system in PEX though.

Click to expand...

Right. The only advantages of corrugated stuff is it's cheap and easier to route due to it's flexibility. The corrugations slow the water flow which you do not want to do for a bilge pump. The smooth walled vinyl hose with the braid inside (from the hardware store) would better and about the same cost or just a little bit higher.

I like PEX for plumbing but not for discharge hoses. I use SaniFlex hose for discharge if the size works, smooth bore and very flexible. For making 90 degree turns in PEX I use hose benders found in plumbing supply stores. It makes a 90 without kinking the tube and no fittings to leak or restrict flow.

twistedtree said:

And I wouldn’t want to use any fittings that contain steel or brass with saltwater.

Click to expand...

Great point on the saltwater. Not an issue currently but probably will be someday.

Kind of on the same subject, my boat has no p-traps on any of the drains. Just the undesirable bilge hose running straight out as a drain. Some of the bends are collapsing and it’s just a matter of time before clogs or leaks happen.

Has anyone added p-traps? I think I’ll be mating any trap I put in with hose just because of access issues but adding traps seems like a good idea. Or is there a reason traps aren’t used on boats?

Thanks

I don't use P traps on boat sink and shower drains. It is my understanding that P traps in house plumbing are to create a seal so that sewer gas does not back up into the house.

Sent from my SM-T500 using Trawler Forum mobile app

As Portage_Bay mentioned, the trap in a house drain is to block sewer gas from coming back up the drain. No such problem on a boat where the drain goes right over the side, so no reason to have a trap. And no traps means the drains are harder to clog as well.

Portage_Bay said:

I don't use P traps on boat sink and shower drains. It is my understanding that P traps in house plumbing are to create a seal so that sewer gas does not back up into the house.

Sent from my SM-T500 using Trawler Forum mobile app

Click to expand...

That is correct. No advantage in a boat, and if you winter in a cold climate they're one more thing to winterize. I'm from Michigan so that's something I pay attention to.

Just have them drain straight out, no P traps needed or desired. You can use spa type hose for these non critical applications. Smooth bore but not quite as flexible.

Pex-A is more bendable and kinks can be repaired with a heat gun. I think the black plastic 90* bend on the blue tube on the righthand side of the photo below is what Comodave is refering to.

Rob

Great points after I thought about what PTraps are for I had the same thought.

Just had to think a little harder!

Datenight said:

Pex-A is more bendable and kinks can be repaired with a heat gun. I think the black plastic 90* bend on the blue tube on the righthand side of the photo below is what Comodave is refering to.



Rob

Click to expand...

Cool. I used a couple of those on the head faucet replacement. I thought it was the right thing, confirmed!

Datenight said:

Pex-A is more bendable and kinks can be repaired with a heat gun. I think the black plastic 90* bend on the blue tube on the righthand side of the photo below is what Comodave is refering to.

Rob

Click to expand...

Exactly.

I recently replace all of my hot water lines with pex. It fixed all my hot water leak issues. I also bought blue for cold. The job was so hard to complete on my 55 I said hell no to the cold, not unless I have to. Three or four times I thought it was going to be impossible to complete just the hot but we got it done. Scary moments after cutting lines then not being able to proceed. Many obstacles but we got it done. No more leaks for months now.

On a previous 46’ I replumbed the whole boat. It was a big job. I think I used SeaTech fittings and tubing. I ordered 10’ sticks so they were straight. The straight pieces were much easier to work with than the rolled tubing. The rolled tubing really wouldn’t straighten out well and wouldn’t go straight in hidden areas, instead it would just curl up and not go on through.

I too did my whole boat but with the crimp stainless rings as suggested by Rick B.

I ordered the more flexible pex and it came in a roll...but a snap to straighten and feed with care though dead areas or rebend into tight 90's with the 90 degree curved supports. Super to work with and also nice to feed a continuous length and cut where a branch was necessary.

The stainless ring crimps are easy to install one handed when you have to reach into a hard to reach area,,, not one leak to start with or for many years.

To me it was one of the easiest jobs on the boat....maybe because I rearranged just about everything in the engine roon to make installs and repairs easier.

I re-plumbed my boat with Pex A, using the Uponor expander system, no rings or crimps. I found both the coiled tubing and the straight sticks to be stiff and hard to work with. Doable, but it certainly isn't very flexible. I put in many 90 degree fittings to cope with the stiffness at the curves. But, my overall impression of Pex is positive and that it's a good way to go.

twistedtree said:

I think flexibility is a big factor, especially as you get into large hose/pipe sizes. Marine hoses can bend and hold a curve without kinking, where PEX has very limited ability to do that. So you end up adding elbows to PEX which reduces flow.

Click to expand...

Just a note that you can buy PEX radius guides that approximate the allowable bending of PEX. and which will hold the bend at that ratio when secured to a wall/frame. From memory a 90 degree bend using this consumes around 8 - 10"
Alan

Bend supports generally bring the PEX to its tightest allowable 90-degree turn without folding or crimping. Turn radii differ according to PEX pipe diameter. For 1/2-inch PEX pipe, the tightest radius is usually 5 inches.

https://www.thespruce.com/how-to-bend-pex-tubing-5087288

jgwinks said:

That is correct. No advantage in a boat, and if you winter in a cold climate they're one more thing to winterize. I'm from Michigan so that's something I pay attention to.

Click to expand...

If they dump into a gray water tank a trap will do the same thing as at home, keep the stink from wafting back up the drain. I've got two shared gray tanks that include shower, head and galley sinks and sometimes they get a bit nasty smelling. None of the drains from the sinks, nor the showers, are high enough to allow for direct-overboard draining, thus the gray tank.

I don't have traps under mine, just use stoppers in the sink drains instead.

Even without traps I still put antifreeze down both the galley and shower drains, better safe than sorry come next season.

In a previous boat we had a huge shower sump glassed into the hull. Occasionally when the wind was blowing into the vent we would get a horrible smell from an old unused shower drain. I took the hose off the sump from that drain and ran it to a new vent on the other side of the boat and then the smells wel away. Maybe you need to vent your sump.

jgwinks said:

Right. The only advantages of corrugated stuff is it's cheap and easier to route due to it's flexibility. The corrugations slow the water flow which you do not want to do for a bilge pump. The smooth walled vinyl hose with the braid inside (from the hardware store) would better and about the same cost or just a little bit higher.

Click to expand...

Isn't the interior of the corrugated hose smooth? I think the corrugation is only on the outside.

I agree on using the bend supports for good swept 90 deg bends. The only down side it access to get the pex in location and to make the initial bend, and the relatively large bend radius. But I use them when possible as my first choice.

twistedtree said:

Isn't the interior of the corrugated hose smooth? I think the corrugation is only on the outside.

Click to expand...

Generally not, at least in the case of the cheap bilge pump plastic hose. It impedes flow and can collect debris in the grooves. I never use it. I want my pumps to pump their absolute best. Good voltage and good discharge hose.

twistedtree said:

Isn't the interior of the corrugated hose smooth? I think the corrugation is only on the outside.

Click to expand...

I have found 2 types of corrugated hose:
On the bilge pumps, as originally found aboard, the corrugated hose is quite thin, no more than 1mm wall, with corrugations that are ~3mm, so present on both inside and outside, with a smooth portion ~ every foot, to allow clamping to the pump and the thru-hull fitting. This is cheap and ubiquitous.
I have changed out the thin, cheap stuff for a proper, smooth hose 1" diameter to match the output fitting on the bilge pumps. My dinghy pump is smaller, and the run is short, so it has the small corrugated stuff.

In other locations, a larger diameter hose has "corrugations" on its whole length, but a smooth interior surface. No clamping spots present or required.

I used PAP (pex al pex) because I had it left over from building a house with radiant floor heat. It has a layer of aluminum that allows the tubing to be bent and then stay bent. That allows you to snake it around without using as many fittings. More expensive, but saves buying fittings and simplifies long feeds. You need to use crimp fittings. Also, these clips can make the project tidy.

I've also used PAP as flexible conduit for 12V projects. I had 150 feet left over from my home building but am down to about 20 now.