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Old 22-09-2012, 18:34   #1
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Corrosion On Thru Hull And Bottom Paint

Hi I - my second time to the forum and have a couple of questions that I hope the members out there can help with. I have made an offer on a 35 sail boat. If the deal is accepted I will obvisously do a thorough survey.
In my own inspeciton of the boat I have found some greenish corrosion on a thru hull fitting that connects to the galley sink. I believe the thru hull is bronze. Next to the corrosion is a green wire that looks as though it should be connected to the thru hull- I am assuming (and not very knowledgeable on this) that the wire is a grounding wire. Another through hull for the holding tank has the same type of green wire attached to it and there is no corrosion on this fitting.
My question is - should this fitting be grounded? Is the green wire the ground source? and as it is disconnected is this the reason for the corrosion?
Should the fitting be replaced or can it be saved?
If this is an isolated problem is it concievable to replace this fitting at the end of the survey and only pay for a haul out once?

Along this same line- during the haul out for the survey the marina will allow me 3 days to paint the bottom.
As I said in the begining I am new to this- so another question.
After power washing for the survey can I just Paint over the existing bottom paint? Assuming the hull is in good condition.
Now a can of worms.
What brand of paint?

Thanks very much for any input Randy
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Old 22-09-2012, 18:38   #2
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Re: corrosion on thru hull and bottom paint

Most people do haulout then seatrial. That didn't make sense to me so I did the seatrial first knowing I would stay on the hard for a while to do some work.

I planned bottom paint and all new through hulls and seacocks. I had no idea what was there before and holes in the boat are the scariest part to me and I wanted this stuff bullet proof.

There was other known stuff I wanted to repair so we stayed out for about 2-3 weeks getting things sorted.

Then the real spending started...

Here is a nice thread on "First things people did on their boats" - What Was First Thing You Did In Your New Boat
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Old 22-09-2012, 19:08   #3
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Re: corrosion on thru hull and bottom paint

Thanks for the reply- I should have noted that a sea trial and 1/2 of the survey will be completed prior to the haul out so the surveyor can spend time on the electrical, fittings, decks etc., everything he can see and touch while at the dock.

But any specific thoughts on the green corrosion? Do you know if bronze (or brass if thats what it is) should be grounded to prevent corrosion?

And can a guy simply apply a fresh coat of bottom paint once its hauled and pressure washed?
Do you have to use the same brand of paint that is currently on the hull?
I'm afraid that will be an unknown answer.

Thanks Randy
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Old 22-09-2012, 23:15   #4
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Re: corrosion on thru hull and bottom paint

Like everything there are two schools of thought on grounding. The corrosion is likely accelerated by stray current in the water, especially if a marina boat. Grounding the through hulls attaches it to the sacrificial zinc system on the boat. (Oughta look at the zincs while it is out as well.)

Having said that my through hulls are not grounded.

Application of bottom paint depends on what you put on and what was there before. Check the compatibility charts for any coating you plan to apply - they are readily available on-line but in very general terms there are two types of anti-foul. Ablative and hard. An ablative anti-foul remains "soft" and chalky and is designed to wear away under water loads or light wiping. A hard coat does not and relies more on chemical protection. In general a hard paint does not like to go on over a soft paint.

If you are going soft over soft you can generally key the paint (like 80-100 grit paper) and apply more anti foul.
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Old 22-09-2012, 23:21   #5
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Re: corrosion on thru hull and bottom paint

Thansk for the reply! I have a lot to learn.
Definitely will check the zincs when out of the water and assume that the surveyor will have info and suggested solutions on this as well.

I appreciate you taking the time to follow up.

Randy
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Old 22-09-2012, 23:34   #6
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Re: Corrosion On Thru Hull And Bottom Paint

You really can't do anything until you own the boat.
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Old 23-09-2012, 09:03   #7
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Re: corrosion on thru hull and bottom paint

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Originally Posted by Ex-Calif View Post
In general a hard paint does not like to go on over a soft paint.
I think we've been over this before. In general, hard paints and ablatives are compatible.

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Old 23-09-2012, 09:09   #8
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Re: Corrosion On Thru Hull And Bottom Paint

Green corrosion is usually OK, but pink is not. Talk to your surveyor about the thru-hulls and the bottom paint--his expertise is what you are paying him for.
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Old 23-09-2012, 18:18   #9
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Re: corrosion on thru hull and bottom paint

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I think we've been over this before. In general, hard paints and ablatives are compatible.

OK - Regardless. Certain paints need to be removed. Certain paints need a barrier coat.

Check the compatibility charts for the product you are going to use.

If you don't know what is on there most will recommend remove or prime.
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Old 24-09-2012, 05:00   #10
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Re: corrosion on thru hull and bottom paint

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But any specific thoughts on the green corrosion? Do you know if bronze (or brass if thats what it is) should be grounded to prevent corrosion?
From the research I did on a corroded valve I came to the conclusion that they should not be bonded. But if you do that they should only be bonded to each other and not connected to the boats bonding. To me things that aren't suppose to carry electrical current shouldn't be connected to those that do. But this can all be battled back and forth and you have to decide which way to go.
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Old 24-09-2012, 05:48   #11
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Re: corrosion on thru hull and bottom paint

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Originally Posted by RLewis View Post
snip
But any specific thoughts on the green corrosion? Do you know if bronze (or brass if thats what it is) should be grounded to prevent corrosion?
snip
Thanks Randy
Randy -
Green coating is OK. As stated above, pink metal color is not. Use a little sandpaper on the green coating (it's called "ambergris") to show the underlying metal. If the metal looks gold it's fine. If it's pink it should be replaced.

BTW bronze, stainless or Marelon (fiberglass reinforced nylon made by Forespar) are the ONLY materials for use in underwater plumbing and through-hulls. Brass should never be used, it will not last due to electrolysis. Nylon or plastic that is not Marelon should only be used on above-water applications.
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Old 24-09-2012, 06:10   #12
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Re: Corrosion On Thru Hull And Bottom Paint

Eventually there are just too many coats of paint. At some point you have to bite the bullet and strip them all off and start fresh. This is not cheap or easy. If the hull looks rough then you probably have too many.
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Old 24-09-2012, 06:50   #13
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Re: corrosion on thru hull and bottom paint

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Randy -
BTW bronze, stainless or Marelon (fiberglass reinforced nylon made by Forespar) are the ONLY materials for use in underwater plumbing and through-hulls. Brass should never be used, it will not last due to electrolysis.
I certainty agree that bronze, stainless or Marelon are the best materials, but just to complicate the issue a little . . .

This is true in american ABYC and NMMA standards (which are voluntary in America), but actually not by CE (European standards) (which are required in Europe).

So, Beneteau (just to pick a major example) actually does use brass thru-hulls, even in its boats built and sold in America.

CE does not specify specific material but only say "material used for a fitting which, within a service time of five years, does not display any defect that will impair tightness, strength or function." and Beneteau claims (And CE apparently has agreed) that brass meets that standard. However, Beneteau somewhat recently changed the specific brass type, because the old ones were in fact not lasting 5 years in some usage (per a Moorings service bulletin) to a brass they believe/hope will be longer lasting.

As a further aide on this American vs European standards issue . . . Most European boats also don't use tinned electrical wire as none of the European codes (not even the commercial vessel codes) require it.
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Old 24-09-2012, 19:18   #14
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As far as the corrosion, use a wire brush on the bronze thru hull, You will quickly see the condition of the through hull. If the bronze looks new under the corrosion, it is fine, if it is pink and brittle, get ready to pay up to $800+ per through hull to replace depending on the quality you use. If one is seriously corroded, the others might be as well.

As far as bonding, you will hear different things. Some are concerned that in a lightening strike, if the through hulls are all bonded, they will break and the boat will sink. If some are bonded and some are not, probably the strategy was to bond every piece of metal within a certain diameter of the mast.

The through hulls are not the ground, the engine block would be the ground.

for bottom paint, ablative paint can generally go over anything. A quick way to tell if you already have ablative on there is to swim under the boat with a coarse scrub brush, start to scrub and if you see a plume of paint in the water, it is ablative or "soft" paint.

Once you pull the boat, try to determine if there is a thick build up of paint. If so, you may need to strip the paint which can be a big project.

Take a few pictures and post what you have questions about.

Good luck and make sure you have some extra $$$ for unexpected things.
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Old 24-09-2012, 21:52   #15
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Re: Corrosion On Thru Hull And Bottom Paint

Thank you all for the great responses.
Don and Shamrock- in your research about bonding can you expand a bit? When the fittings are bonded (and I now understand that its not to the engine as in a ground) is the bonding simply a loop of wire connecting a number of fittings, for instance with in a certain radius of the mast? And, does this bonding wire then attach to the mast? In my situation and from what I can see, the green wire appears that it should be or was planned to be and maybe was at one time connected to this fitting. The other through hull fittings that I can see so far have what appears to be the same green wire connected to them and there is none of the green corrosion present
SailFastTri- I will scrape/brush/sand this fitting to get a sense of the underlying condition of the metal- hopefully it will be in good shape. I have been researching and reading about corrosion but so far I have not found “ambergris” I wonder is this a generic name?

The deal is still not complete- no offer accepted so far. When/if I get to the point of the survey I will get some photos and the opinion of the surveyor and let you all know the result.

Thanks again for all the information- and if you have more please pass it along.
Randy
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