Through-hulls (mushroom type): Do you bottom paint them?

[Rachel]

I masked off my new through-hulls, then bottom-painted the boat. Partway through, someone at the yard asked why I had masked them off, at which point I looked around and saw that they were bottom-painted on all the other boats (Chesapeake Bay).

"Okay," I thought, "I'm just thinking of my low-fouling, freshwater roots. Everyone else must paint them." (And I can't remember if they were painted or not on the cruising boat; there were only three, so their importance paled in comparison to all the other projects.)

So, I've been waiting for a warmish day to paint them (the hull is done). Then I read Tim's log of Equinox today, and I saw nice, shiny bronze through-hulls in a field of green bottom paint. [Edited to add: That it turns out simply had not been painted yet, for logical sequencing reasons.]

Now I'm wondering again. Not that I want them barnacle-choked, but once painted I can't go back, so it seems worth checking into.

What say yins? (Especially Chesapeakers, but I'm curious in general now.)

Rachel

[Tim]

Paint.

[bcooke]

Paint.

[Ric in Richmond]

Paint

Glad you still own your alberg too.....

[Quetzalsailor]

Paint.

You may wish you could paint up inside them too. We're also on the Chesapeake, in Swan Creek: shallow, warm, the model for the premordial soup we're all decended from. I always thought that stuff doesn't grow in the total darkness inside a fitting but the fibrous plant that grew inside the engine intake throughhull taught me otherwise. That same plant likes the LeComte's below water deck scupper discharges, too.

[John, CD28]

Several folks (not here) have told me not to paint a bronze prop. I don't recall the reasoning but they were pretty sure the sky would fall if I did. It seems all the bronze props in the yard are bare while all the bronze thru-hulls are painted over.

If we regularly paint bronze thru-hulls, then why not paint a bronze prop?

John

[Hirilondë]

If we regularly paint bronze thru-hulls, then why not paint a bronze prop?
John

Props can benefit from bottom paint just as anything below the waterline. But most bottom paints build up so fast it starts to deform the shape enough to matter in thrust. They make special bottom paints for props and shafts for those who have lots of money to put into reducing build up.

http://www.propspeed.com/index.html
http://www.jamestowndistributors.com/us ... pray+Paint

If I recall, the Propspeed goes for a couple hundred dollars or more for a small kit.

Live with inefficiency of regular bottom paint, clean it a lot or buy really expensive paint.

[David]

I've never had antifouling paint stay on a prop. What is the secret?

[Tim]

Painting a prop with the usual antifouling gunk can throw it way out of balance. A propeller is a precision item that shouldn't be gunked up.

[John, CD28]

Would a modern ablative paint avoid the build up problem on the prop? Perhaps it would wear off entirely, leaving the prop clean & bare mid season.

Maybe you'd have a clean bare prop half way through the season. This would be better than half the garden mid way through.

yes? no? (I dunno)

John

[Rachel]

Thanks - I will paint them, inside and out.

I've painted the prop already - gave it "the treatment," which consisted of a light blasting, followed by Interprotect as a primer coat(s), then hard anti-fouling (Interlux Ultra, if I remember correctly), sprayed on. The primer-as-chemical tie-coat is supposed to help keep the paint on the prop.

I wondered about "globbing up" the prop, but was told that on a low-speed boat, and with careful paint application, it would be fine.

I've seen good results with Prop-Speed (the shiny yellow stuff) on other people's boats, but one thing I'm not so fond of is that you can't touch it up, according to the manufacturer, but rather have to remove it and start from scratch.

[David]

This time around I barrier coated the prop with epoxy, then primed with Primacon. Maybe it will work, maybe not.

[LazyGuy]

While I prefer my prop "al fresco" a good friend, that docks in brackish water swears by treating the prop with Ospho and then painting with CSC micron along with the rest of the bottom.

Yes, I do paint the through hulls and reach up with a small brush to get inside the bore to keep the barnacles out.

[earlylight]

I have had good luck with the procedure in the Interlux painting guide. It is a little time consuming, but I seldom have any fouling with the boat in the Chesapeake Bay for 7 months. You can access their painting guide at
http://www.yachtpaint.com/usa/

This is a photo of my running gear immediately after power washing at haulout. Boat was in water from 1st week of April until 4 days after Thanksgiving.[/url]

[Maine Sail]

Props and thru-hulls are generally made of different bronzes. Many props are made of Manganese Bronze, though some are NiBrAl. Manganse Bronze has a considerable amount of zinc in it depending upon the composition used to make the prop. Most marine grade Manganse Bronze is comprised of roughly 58% Copper 39% zinc 1% iron 1% tin. Though different alloy compositions of Manganese Bronze can see zinc content as low as 25% and as high as 39%. The copper in bottom paint can lead to de-zincification of a Manganese Bronze prop which is not good for it.

Thru-hulls & seacocks are generally, and I use generally carefully as who knows what's coming out of China these days, made from a very low zinc content bronze. This Bronze for valves and thru-hulls is usually referred to as Silicon Bronze and is comprised of roughly 96% copper 3% silicon 1% Manganese. Again, who knows what is what these days so a call to a manufacturer is sometimes a good idea. Silicon Bronze has virtually no zinc so should not suffer from de-zincification like Manganses Bronze or Tobin Bronze. Painting thru-hulls should pose minimal threat if they are in-fact made from silicon bronze..

Prop shafts made of bronze were mostly made from Tobin Bronze which also has a higher zinc content and also does not like copper anti-fouling paints. If you paint a Bronze prop shaft or prop you should really keep up with your zincs so the zinc in the shaft or prop does not become the sacrificial material. better yet it may be wise to use a paint that is safe for underwater metals..

Bronzes are not all the same and there are many different grades of bronze that really should almost be called a brass due to the zinc content but because of the added tin or other alloys they are referred to as bronze instead of brass. I've personally never understood why most props have such a high zinc content and are made from Manganse Bronze and not something with more corrosion resistance...?

I paint my thru-hulls but not my prop, shaft or strut..

[Rachel]

Maine,

My prop has two coats of Interprotect on it ahead of the bottom paint, as a tie coat, so I think that should protect it from the copper, but thanks for the info.

I'll probably prime the through hulls with Interprotect too, since I still have some on hand, (they are US made bronze, by the way).

Rachel

[Ronin120]

A little late to the party; definitely paint. Like Maine Sail, not the prop or shaft. I clean them once a month, more often if actually sailing the boat...

[Idon84]

Very interesting... Didn't know any of this. I'll paint.

[Quetzalsailor]

I have used the Interlux epoxy primer and ordinary bottom paint on the previous boat (a Morgan 27) prop. Once. Rough and not effective; everything grew on it and the boat did not move with the hydrodynamics damaged. Others in the marina paint theirs, but none of the 'serious' types. I learned to dive on the boat every weekend and scrape (plastic scraper) and scrub the prop clean, after I gave up on the paint.

Quetzal's prop is deeper, and I'm not enthusiastic about swimming that deep in the gloomy waters of Swan Creek. I've taken to using Interlux's spray zinc paint sold for the purpose. It goes on smooth (after the prop's yearly spring cleaning) and seems to be at least as effective as anything I've seen in the marina.

[David]

Here is an interesting article by a surveyor concerning the use of brass/bronze thru hulls and dezincification leading to sinkings.

http://marinelosssurveyors.com/2T-H.pdf

David

[Rachel]

David,

I only had time to read quickly through that at this point, but I took from it that both boats had brass fittings, and not bronze. I don't think brass is really ever suitable for use below the waterline - in my mind not lumped in with bronze (which is suitable).

Did I mis-read something?

Rachel

[David]

No you didn't misread. Take a longer look when you get the chance. It isn't anything that hasn't been discussed on this forum (but one of the reasons I said earlier in a thread to beware of bronze because anyone can cast it it in their backyard). The article discusses the lack of standardized information about what alloys (especially zinc instead of tin) fittings contain, it discusses how the amount of torque on the threads can exasserbate dezincification, and shows some interesting cross section photos.

The author's summary is in part:
..."Codes and Standards are more and more important as the primary yardstick of quality. Codes and Standards are unclear and ambiguous relative to acceptable materials for metal thru-hull fittings used in seawater.
• Brass and bronze are generic terms, like steel and stainless.
• Advertising descriptions are unreliable.
• Field identification of particular metal alloys with any degree of accuracy is next to impossible."

[Rachel]

No you didn't misread. Take a longer look when you get the chance. It isn't anything that hasn't been discussed on this forum (but one of the reasons I said earlier in a thread to beware of bronze because anyone can cast it it in their backyard).

David,

I took a longer look, as you suggested, and here is what I'm understanding (bolding and italicizing mine):

Testing3 on the failed aft head thru-hull fitting was done, and it was discovered that this factory original fitting is an alloy of high zinc content Brass!

Being completely surprised to find a brass thru-hull fitting on a blue-water yacht from a highly respected builder, we undertook some research to see if this may be a larger problem. On the web, we discovered a Marine Accident Investigation Branch report4 on the investigation of the flooding of the UK charter-fishing vessel RANDOM HARVEST. This vessel also heavily flooded and nearly sank resultant to a high zinc content Brass head inlet thru-hull fitting

Reading further, I understand the writer's point to be that some builders may have used sub-standard brass fittings, and that the labelling and illustrations in some catalogs can make it less-than-obvious whether you are getting quality bronze or not. And she notes that seacocks are not labeled as to how much you should torque them on installation.

As usual, you have to do your research and be careful. But if you do buy good-quality bronze fittings, they are just that: Good quality. Nowhere does she say that good bronze fittings are dangerous (which I felt your initial post about this article implied, and is why I reacted the way I did) when you said that "brass/bronze" through hulls had led to sinkings:

Here is an interesting article by a surveyor concerning the use of brass/bronze thru hulls and dezincification leading to sinkings

I know that a number of people (myself included) come to this forum to do some of their research, and as a fan of bronze, I don't want to see it lumped in with brass as the cause of these boats' sinkings, if that is not what actually happened.

In fact, the author happens to use my very brand of seacocks and through hulls as an example of good, UL-listed seacocks (Conbraco). Before I bought mine I called around to check on their "ingredients." I did find that, for example, the more economical Grocos are not made in the USA and have brass wetted components. Not good. But not a scar on bronze.

So I believe that if you check things out, and buy good-quality US-made bronze fittings, like those made by Conbraco, Groco (higher end), Spartan, and the like, you won't be getting backyard-cast bronze fittings or brass fittings.

That's not to say that bronze is infallible, because it isn't. It can still have problems. But not with the same frequency of brass.

If I've gone wrong in my understanding, I'm open to being shown the light.

Rachel

[David]

Rachel,

I'm not arguing against bronze. My point in presenting the article is that it is relavent to the discussion and the fact that mystery bronze--that being bronze with a high level of zinc instead of tin (which I call brass and why I said brass/bronze eariler in the post) shows up in critical systems such as thru hulls. I also liked the pictures.

David