Hi all, first time poster. Bought a Newport 30 Mark iii a couple of years ago. Just pulled it out for the first time yesterday and saw some pitting etc on the propeller shaft spar. Any resources for spar replacements?
1985 Newport 30 Propeller Shaft Spar
- Thread starter Robertelee1031
- Start date
Congrats and welcome.
I think you mean strut, not spar, correct?
Pics would help.
No need to apologize! I figured that's what you meant. I do that at times, think on thing and type another; like a brain short circuit.
Can you post a pic?
I might not be worried about the pitting but would be worried about what looks like pink areas. Hard to tell from the pictures but if it is really pink that might indicate the loss of some integrity.
Look up pink bronze shaft strut.
Can you wire wheel or grind off some of the surface and see what the metal really looks like.
Is there a professional in the yard you could ask for an opinion?
Look up pink bronze shaft strut.
Can you wire wheel or grind off some of the surface and see what the metal really looks like.
Is there a professional in the yard you could ask for an opinion?
I don’t know the acceptable level of corrosion on the strut, so I can’t comment on that part. I will say that’s a healthy looking shaft zinc considering the pitting on the strut. Is the shaft under the zinc clean enough for a good connection between the two? Are the prop shaft and strut both electrically connected to the engine?
Our boat yards locally don't let us work on our boats when on the hard. They have of course offered to quote on replacing it. We have asked them to clean it up and coat it. We try to get three years between bottom paint so are thinking we put a zinc on it, and plan for it three years from now. Having a hard time looking up a strut online or finding other wrecking yards in the US (we have one here locally, Lynden WA) but they dont have a Mark iii currently.
Pinking is a sign of the zinc in the bronze leaching out, this significantly weakens the zinc. It probably won't fall off but it is more likely to develop cracks. It needs to be replaced. A prop shop should be able to help you. Or have a foundry cast a new one. Casting a new on won't be cheap. You have a good foundry near by, talk to them.
www.porttownsendfoundry.com
Port Townsend Foundry LLC—Made in the USA
A custom and production nonferrous foundry specializing in marine hardware. Castings are tooled, poured, and finished in-house at our facility in Port Townsend, Washington.
Unless you find the reason for the zinc leaching out and correcting the problem, in three years it will be worse. You probably won't find a direct replacement. A prop shop can probably build one or a foundry cast a new one.
I would. I think this is incorrect advice. See Richard's post.
While the shaft zinc might look intact, in that construction, the cutlass bearing inside the strut isolates the shaft and the strut. That's why "rudder" zincs or strut zincs are used on these two close but isolated pieces.
You might check into your neighbor's experiences with zincs in your marina. Three years is a looong time for zincs to last. In California, before I moved here in 2016, I'd get three to six months before my diver, who came monthly, had to replace one or both (shaft and strut). My experience here now has been more, but not much more than a year.
And, for sure, have someone knowledgeable help you check the condition. Even if they don't let you "work" on your boat in the yard, who is actually going to stop you bringing a portable dremel with a wheel or even some sandpaper to slough off a bit of the strut surface?
Good luck.
Sorry, wont be three years between zinc, we check them monthly with our gopro (dive in the summer) and replace seasonally in water. We are on a three year pull out schedule for bottom paint etc. The yard where the work is being done has inspected and believes that it is structurally sound, they will clean it up and have photo's for the next time we pull out for comparison. Thanks for all the input. Really appreciate it
Here's an excellent thread on this topic:
Strut Gone Pink - Failed During Cutlass Bearing Replacement
Based on this, I would:
Strut Gone Pink - Failed During Cutlass Bearing Replacement
Based on this, I would:
- try to figure out how to determine the condition of the strut;
- if it's O.K., bond it to the engine in side the hull.
I agree. I was assuming the strut was (designed to be) bonded, in which case it would be protected by the zinc.
True, pure bronze is copper and tin but I think if you look you will see that many shaft struts are made of manganese bronze. Manganese bronze can have a significant zinc content.
look up "manganese bronze shaft strut".
I think that is why many "bronze" struts have their own dedicated zinc anode protection.
For example, this is from the Catalina direct parts site:
Prop Strut Zinc Anode
Part #: Z5074
$13.13
Zinc anode sized specifically for struts used on Catalinas. Although the struts are made from military grade 70 manganese bronze they contain about 25% zinc and should be protected by a zinc anode if in salt or brackish water or if in a marina that is "hot" with stray electrical current.
A proper zinc anode
The alloy used by the manufacturer is military grade 70 manganese bronze. Selected for its corrosion resistance and strength, it is still as much as 25% zinc. With age, a process called “bleeding” can occur when the iron and zinc, elements in the alloy, come to the surface significantly reducing the strength of the bronze. This can make a strut's normally bronze color appear pink.
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Depends on the particular alloy. Bronze used for prop shafts and struts contains zinc.
Bronze - Wikipedia
en.wikipedia.org