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Monthly Archives: September 2013

 

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Applied as a spray, Pettit claims Zinc Coat Barnacle Barrier will protect propellers from barnacle build-up.

I still haven’t figured out why the bronze propeller on my boat is the first thing to become encrusted with barnacles after a haul-out. After all, the main constituent of bronze is copper, and my Pettit Horizons antifouling is loaded with copper and it does its job very well elsewhere. But propellers are generally left bare, probably because modern ablative coatings wouldn’t last long due to the high velocity flow across the spinning blades.

Strictly speaking, my prop is probably a manganese bronze which really makes it a brass. Are you confused yet? Well, a brass is an alloy primarily between copper and zinc, typically with 60% copper. True bronzes are usually an alloy of copper with silicon or (now less common) tin. Brass is an inexpensive alloy and very easy to cast into intricate shapes. Unfortunately in a marine environment brass is very susceptible to corrosion and that’s one reason why a small amount of manganese is added. The zinc and copper are not a homogenous mix. Zinc rich areas are electropositive relative to the copper rich areas and consequently zinc dissolves from the surface by electrolysis in the zinc rich areas.

If your freshly polished propeller has a blotchy pink appearance than it is likely to have already suffered some “dezincification.” Some of the zinc has gone leaving a weak, spongy copper rich areas. This can eventually lead to structural failure. That’s why propellers should have some form of galvanic protection, typically in the form of a zinc anode attached to the shaft.

Rainbird's propeller shows signs of dezincification.

Rainbird’s propeller shows signs of dezincification.

In spite of these areas being copper rich, they are still prone to marine fouling, which is perplexing. Perhaps copper in antifouling is just more readily available to prevent fouling.

I normally polish the propeller with a fine abrasive and leave it untreated. At a recent haul-out, the boat yard suggested that I try Pettit’s Zinc Coat Barnacle Barrier to prevent barnacles growing on my propeller. This comes in a spray bomb and the instructions recommend 3 coats applied one hour apart. This is easy enough. So why would zinc work as an antifouling? The zinc in my prop obviously doesn’t do the job so why should I expect this to work? Once again, maybe it’s availability, and as the yard pointed out, when was the last time I had seen fouling on a zinc anode?

Time will tell if this is an effective solution and I’ll keep you posted.

 

 

Ready for launch; Rainbird's propeller after three coats of Zinc Coat Barnacle Barrier.

Ready for launch; Rainbird’s propeller after three coats of Zinc Coat Barnacle Barrier.

 

 

 

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The Classic Boat Festival in Victoria was a great opportunity to experience the beauty of wooden boats.

The Classic Boat Festival in Victoria was a great opportunity to experience the beauty of wooden boats.

I didn’t venture far aboard Rainbird this summer but I certainly made the best of our spectacular weather. Here are a few interesting boats I passed during my travels. I know nothing about the history of these vessels but their uniqueness caught my eye.

Beautiful strip-planked Wildwood, built on Vancouver Island, seen here in Maple Bay, on her way to the Victoria Classic Boat Festival.

Beautiful strip-planked Wildwood, built on Vancouver Island, seen here in Maple Bay, on her way to the Victoria Classic Boat Festival.

Stern view of Wildwood at the Victoria Classic Boat Festival.

Stern view of Wildwood at the Victoria Classic Boat Festival.

Taz, seen in Lyall Harbour, Saturna Island, BC.

Taz, seen in Lyall Harbour, Saturna Island, BC.

Looks like a steel hull to me. Seen in Lyall Harbour, Saturna Island, BC.

Looks like a steel hull to me. Seen in Lyall Harbour, Saturna Island, BC.

 

Meg, Lyall Harbour, Saturna Island, BC.

Meg, Lyall Harbour, Saturna Island, BC.

Captain Tolley's Creeping Crack Cure fixed a leaking hatch coaming.

Captain Tolley’s Creeping Crack Cure fixed a leaking hatch coaming.

After an unseasonably hot spell this spring, the heavens opened and the resulting deluge found its way through the nooks and crannies in the parched teak of my fore-hatch coaming. Thankfully the drips ended up on the cabin sole rather than the bunk.

The cause of the leak was traced to a joint at the corner of the hatch, which had separated very slightly, allowing water to penetrate. I was about to leave Rainbird for a few weeks so I rummaged through the glues and caulking box and pulled out a squeeze bottle with an interesting and humorous label; Capt. Tolley’s Creeping Crack Cure.

It’s a thin white liquid, which disappears in the blink of an eye into fine cracks by capillary attraction. It solidifies and the instructions say that you should keep applying it every 30 minutes until no more is absorbed. A final application after a further 24 hours is recommended.

Well, I followed the instructions and the following day doused the area with a hose and was pleased to see that the leak had stopped. That was four months ago and it still hasn’t come back.

I’m not sure I would trust it as a permanent cure. Doing the job properly would involve dissembling the joint and rebuilding it and that’s no small task. For now I will just keep an eye on it.

The 60ml bottle cost me around $12 and this amount will go a very long way. I can see it will be another valuable weapon in the battle against entropy.