Thru-hulls, seacocks, and hoses!

[Maine Sail]

Originally Posted by transmitterdan

Take a big sheet of GPO3 and prop it against the wall at about a 30 degree angle. Do the same with a piece of G10. Check back in 6 months and tell me which piece you want keeping the water out of your boat.

Are you sure you are using real GPO-3? I have tested both GPO-3 and G10 for drill & tap and in 1/2" with 5/16" X 18 bolts drilled and tapped they both exceed ABYC standards and both have deflection characteristics under the 500+ pound load that are darn similar and vastly exceed the blue-light special marine ply that the vast majority of builders use for backing blocks...

In testing I have had seacocks fail before a single drilled & tapped 5/16" X 18 bolt pulled out of 1/2" GPO-3. The difference is GPO-3 is a thermoset polyester resin, & G10 is made with epoxy resin. Not too many boats are made with epoxy but plenty are made with polyester... Both products will destroy tool blades!!! Water absorption of both products is also comparable with G10 at about 0.15% and GPO-3 at about 0.2%. What is it for the plywood found on most boats...?

Which ever product you can get for the least money will far exceed the needed strength or water absorption properties required. I use more G10 but only because it is more popular and the pricing reflects the volume of G10 vs. GPO-3. GPO-3 should be a lot cheaper but often is not..

[velella15]

While you're at it, use solid t-bar hose clamps to connect all hoses. I am in the process of replacing all slotted hose clamps (which can fail) with these. This is important these days as many sailors do not turn off all seacocks when leaving their boats - the old saying "don't let a yacht float on her plumbing" springs to mind!

[bsurvey]

why do you even want metal through hulls. marelon will last forever or at least your life time and there are no corrosion or bonding issues

[transmitterdan]

GPO3 will bow significantly over time under just the stress of its own weight. In one sense this is "good" because a thicker piece will more easily conform to a shape compared to G10. But I worry about putting GPO3 into significant compression because over time it may flow away from the compression points and possibly loosen the fasteners. G10 is much harder and less likely to "squish".

Because it is a polyester resin we have always sealed GPO3 with a waterproof sealant to ensure it lasts for many years. But we may be overly paranoid. We never use it where it will be in contact with water for any length of time. I know the electrical power industry uses it extensively for high voltage insulation inside big switchgear such as substations and switching yards and they generally never coat it with anything. It costs them much less than G10.

I believe there are various "grades" of GPO3 depending on the manufacturer.

[leftbrainstuff]

Originally Posted by pmagistro

Ok, I'm working on overhauling my Bristol 29.9. I'm replacing pretty much all of of the thru-hulls, seacocks, and all of the ancient plumbing. I want to run this by you all and gather some opinions.

For the seacocks, I'm basically planning to do what Compass Marine recommends at Replacing Thru-Hulls and Seacocks Photo Gallery by Compass Marine How To at pbase.com. Groco says to use 316 stainless bolts or lags. I'm not sure whether to bolt through the hull from the outside, lag into backing blocks from the inside, or purchase Groco backing blocks and bolt into the hex nuts. Thoughts?

And hoses...oh hoses. I've been agonizing over the options for hoses and think I have it figured out:

- For the 3/4" freshwater system (non-pressurized), I'm planning on using Trident Marine Reinforced PVC Water Hose, likely from Discount Marine Supplies.

- For the 1 1/2" sewage lines, Trident 101. ~22ft. Any leads on the best place to buy this?

- For the 3/4" holding tank vent line, Trident 148.

- For the 1 1/2" cockpit scuppers drains and sink drains, also Trident 101. ~10ft. I know these don't need to be odor safe, but I can figure out a better (ie cheaper) hose to use that's still adequate for critical below the waterline use.

- For the 1 1/2" potable fill lines and manual bilge pumpout, Trident 148 or 144. ~20ft.

- For the 1 1/8" automatic bilge, Trident 148 or 144.

Looks like it's easy to buy 50' lengths of Trident hose at a good price from Discount Marine. I'm wary of Shields after reading reviews, etc but it's definitely easier to go to WM and buy shorter lengths of the equivalent Shields hoses. Thoughts?

I'll take any thoughts, suggestions, or other ideas!

Thanks!
Phil

The trident hose seems to be a good option.

We did a full audit and non destructive inspection of our bronze groco thru hulls. On our Liberty 458 they're all 31 years old or less. All are in good condition.

I would not use ss bolts on the exterior of the hull. Follow grocos best practice.

Sent from my SM-N900T using Cruisers Sailing Forum mobile app

[zstine]

I used 1/2" GPO3 for backing plates all the time with no issues. Very easy to make and much cheaper than buying from Graco. I don't see the need to buy 'marine' hose for anything that's not subject to sea pressure. PVC fittings, hose, etc. get from a home plumbing supply and spend less than half the 'marine discount' price. You can get identical Apollo valves from a plumbing store (not hull/flange valves) as marine supply at 70% discount. best luck!

[Ziggy]

Originally Posted by transmitterdan

I don't like GPO3 fiberglass in a bilge because it is not as water resistant as G10. If the budget allows I would use G10 over GP03. Also, GPO3 is not as dimensionally stable as G10. McMaster-Carr has both types of fiberglass I believe.

GP03 works just fine. After several years, my GP03 backing plates look like new, with no sign of deformation. According to McMaster-Carr, the water absorption is about the same as G10 (0.2-0.3% for GP03, 0.15% for G10). Compressive strength also in the same ballpark. A big difference in price, however.

[Nicholson58]

Originally Posted by jpstevens

I used Compass Marine's system and was very happy with the results. Set in thickened epoxy and filleted around the edges, that pad ( I built up my own) is not going to move.

GOOD plan. I use 36 oz Fab-Mat and epoxy. BTW, you can find NOS GROCO through hulls and other stuff at Wolf's Marine in Benton Harbor, Michigan. Usually about 1/2 normal price or less. Call and ask for parts.

[CarlF]

Don't forget to install vented loops! Many older production boats skipped this critical plumbing safety.

[Terra Nova]

Originally Posted by velella15

While you're at it, use solid t-bar hose clamps to connect all hoses...

No, except on large exhaust hose. Use non-perforated, like Awab.

[Hilbert]

Originally Posted by pmagistro

For the seacocks, I'm basically planning to do what Compass Marine recommends at Replacing Thru-Hulls and Seacocks Photo Gallery by Compass Marine How To at pbase.com. Groco says to use 316 stainless bolts or lags. I'm not sure whether to bolt through the hull from the outside, lag into backing blocks from the inside, or purchase Groco backing blocks and bolt into the hex nuts. Thoughts?

Compass Marine has three articles related to replacing thru-hulls and seacocks and together are compreshensive:
Seacock & Thru-Hull Primer/Pre Information Photo Gallery by Compass Marine How To at pbase.com
Replacing Thru-Hulls and Seacocks Photo Gallery by Compass Marine How To at pbase.com
Seacock Backing Plates / Alternate Method / No Through Bolts Photo Gallery by Compass Marine How To at pbase.com

I had a few thru-hull/seacocks to replace and I tried a couple methods. This is a 3/4" for raw water engine cooling.
I through bolted with silicon bronze (to avoid anaerobic corrosion) on a base that I created with epoxy and layers of 1708 biaxial:




This is 1 1/2" for a cockpit scupper.
I drilled and tapped 3/8" G10, using the no through bolt method:




After trying both methods, I prefer the no through bolt. The Groco backing plates would have been adequate, but I didn't know what material they used for their threaded inserts. I also prefer that the backing plate be sized exactly, not something that fits both 3/4" and 1" seacocks.

Originally Posted by pmagistro

And hoses...oh hoses. I've been agonizing over the options for hoses and think I have it figured out:

I use hoses supplied by the marina. They were priced competively, of good quality and they gave me rolls that I could take to the boat and cut to length. I paid for only the exact length that I used. When ordering online, I always ended up paying extra for conservative measurements and having to order in 1 ft increments. I used AWAB clamps.

Having used both GPO3 & G10, I would go with either one depending on price and application.
Here I used 3/8" GPO3 to construct a bowsprit and backing plate:



Good luck with your project.

[thedude0]

A useful website The Motorsailer Project | Logs

[Nicholson58]

Originally Posted by leftbrainstuff

The trident hose seems to be a good option.

We did a full audit and non destructive inspection of our bronze groco thru hulls. On our Liberty 458 they're all 31 years old or less. All are in good condition.

I would not use ss bolts on the exterior of the hull. Follow grocos best practice.

Sent from my SM-N900T using Cruisers Sailing Forum mobile app

I suggest you consider Raritan super high flex sanitation hose. This stuff can bend in very short radius.