Smallest plumbing pipe diameter

[ChrisOB]

Was there a consensus on pex vs the clear braided hose? I am in the process of replacing water heater, sink drains etc. I will do some of the hoses near the pump and starboard seatee tank as they are accessable and worse for wear. The longer lines to head, cockpit shower, bow, and stern tank (yes somehow I have all 3 tanks) will come later. I am not a homeowner so my gut tells me to just use the re-inforced clear tube with SS hose clamps. I understand pex is big in houses, unsure how it handles 10 foot waves and vibration in a harsh environment. I have a tentative plan to cross to the Yucatan if COVID settles down, so I'd prefer robust vs convenient.

[waughoo]

Pex is what I am using as I replace things aboard.  That said, I am using the Uponor system which requires a rather expensive expeander tool.  You can rent one for pretty reasonable prices at plumbing shops so that wouldn't stop me from recommending it.  The pex connections are so incredibly reliable and leak free vs barbed plastic fittings and hose clamps.  That is my MAIN reason for wanting to switch. 

[KWKloeber]

find the SS crimp rings to be the best compromise.

I second and third that.   
The data I have seen on (licensed) plumber blogs and also most plumbers I know won't use the copper compression rings.  If there's a failure they say 8/10 times it will happen on those vs. on the stainless steel crimped (cinched) fittings.

Good point about PEX fittings (all types) and being proven on a boat, crashing around in heavy seas.  I wonder???

[rmjohns]

I replaced my plumbing lines last years. I started out planning to replace all the clear reinforced vinyl with pex.  I did do all the pressure side with the red/blue with crimped connections. When it came to running the pex from the front/aft tanks, those pipes are run up and down through lockers, I came to conclusion that it was better for me to just replace the clear vinyl with clear vinyl.  I was going to have to put a bunch of 90 degree elbows in the runs and I figured that no connectors in the clear vinyl was better than pex with a number of 90 degree connectors hidden away in lockers or less accessible places.   
Plus access for the crimper was going to be challenging.

I will say I was surprised at how ugly the original clear vinyl was. There was dirt inside the tubing and the tubing itself had become sticky. It's a job to replace, but well worth the effort in peace of mind.