Newport 30 Thru-hull replacement

dasnider · #1 (**permalink**) 03-28-2007

Anyone replaced the TH's on a Newport 30 (MKIII)? Mine are the originals from '82 and although I replaced the old plastic valves, I think it's time to replace the TH's themselves. Looks like they're embedded in the hull and then faired over with a layer of gel, so it may be more work than I want... any tips appreciated!

-Dave

KeelHaulin · #2 (**permalink**) 03-29-2007

Dave-

Unless the backing blocks on the interior side are rotten/leaking or heavily corroded I would suggest leaving them alone. Another way to check for corrosion is grinding back the surface of the thru hull on the exterior. If it is bright and shiny with no red spots then it is still sound. The red color indicates loss of lead due to galvanic corrosion.

The reason I suggest leaving them as-is is because the thru-hulls on my N-41 are in excellent condition. When we did the bottom job last year I removed one of the thru-hulls in the stern (the engine raw water intake) and it was in great shape with no signs of corrosion. The only reason I did not put it back in is because I damaged the threads while removing it. The bronze thru-hull I replaced it with was much lighter in construction. The OD of the flange was small and it did not fit perfectly to the molded recess to the hull (there is gelcoat beneath the fitting). So on the forward thru-hulls I ground back the old fairing compund painted the surfaces with epoxy and then re-faired them with thickened epoxy.

JMHO/HTH...

Gorey · #3 (**permalink**) 03-30-2007

The marina put on a class on bonding of thru hulls. He told me that the older boats used a superior type of bronze that is highly resistant to corrosion. My N-30III shows no signs of corrosion or color change. I bonded them anyway to the cutlass bearing zink, 750 Ma of current flowing from thru hulls to zink

KeelHaulin · #4 (**permalink**) 04-01-2007

Quote:

Originally Posted by Gorey

The marina put on a class on bonding of thru hulls. He told me that the older boats used a superior type of bronze that is highly resistant to corrosion.

Interesting... I also noticed the thickness was greater; the old fitting weighed at least 1/3 more than the new one. Could you explain why you would want to bond all of your thru-hulls to a zinc? I thought that any isolated thru-hull (with no direct connection to the electrical; like cockpit/sink drains) should be left without a bonding wire to keep it electrically isolated.

Gorey · #5 (**permalink**) 04-02-2007

Quote:

Originally Posted by KeelHaulin

Interesting... I also noticed the thickness was greater; the old fitting weighed at least 1/3 more than the new one. Could you explain why you would want to bond all of your thru-hulls to a zinc? I thought that any isolated thru-hull (with no direct connection to the electrical; like cockpit/sink drains) should be left without a bonding wire to keep it electrically isolated.

The bonding wire is like a belt and suspenders. On newer boats the thru hull's are bonded. My boat was made in 1985 and the thru hussl look good. I did replace the Marlon plastic valves with brass.

KeelHaulin · #6 (**permalink**) 04-07-2007

Quote:

Originally Posted by Gorey

The bonding wire is like a belt and suspenders. On newer boats the thru hull's are bonded. My boat was made in 1985 and the thru hussl look good. I did replace the Marlon plastic valves with brass.

I would not assume that you need bonding on all thru-hulls; sometimes if there is a grounding problem you can create more problems if the thru-hulls are attached together and have a pathway to the electrical loop. If your thru-hulls are sound now and they are 20+ years old I would not add bonding to prevent them from suffering galvanic corrosion. If they had been corroding there would have been evidence of it by now.

dasnider · #7 (**permalink**) 06-16-2007

Thanks for all the recommendations. I had wire-brushed away the corrosion from a couple of the THs when I bought the boat 3 years ago and it looked a bit pinkish, so I was planning on replacing them. However based on the feedback to this thread I got in there with a file and really got down to bare metal, and it's bright bronze - so I guess I'm OK! Seems there's just a surface layer of reddish corrosion.

A couple of them are weeping so while I had her out I cleaned out between the TH and the gelcoat and sealed it up with epoxy, so hopefully that'll fix the problem.

Appreciate the advice,

-Dave