Brass Propellers - Too Thin?

[HeideMarie]

I've had this vessel for 9 months and just had the bottom cleaned.

The diver told me that my propellers were getting too thin and should be replaced.

Below is a pic from the survey 9 months ago...

The survey never mentioned this as an issue. I couldn't find really anything about thinning prop blades in my online research --- only found one resource that noted excessive metal lose in aluminum propellers --- but these are bronze/brass.



I'll be taking her out in the next few weeks to bottom paint, so I can visually inspect myself then....

Any thoughts here? Is this something I should do immediately or put it in the plan for sometime in the next couple years?

 

[Comodave]

No way to tell by the photo. I would pull them and take them to a good prop shop and get their opinion. Also have them scan the props to see if they are in proper shape. Also it maybe looks like you have the half height nut on last. The full height nut should be on the shaft last so it can carry the load. Seat the prop, put the full height nut on and tighten it to fully seat the prop, remove the full height nut and put the half height nut on and tighten it. Then put the full height nut back on and tighten it up.

 

[HeideMarie]

Thanks, ComoDave.

Wasn't looking for a Dx -- just curious if thinning props are actually a thing.

Appreciate the reply and will do...

 

[Comodave]

Yes, it can happen. Not sure exactly how to tell how thin is too thin but a good prop shop should be able to tell.

 

[psneeld]

Also.....can't tell but the large nut holding the prop on (other than it probably should be the second one on) looks like it is pretty well wasted. Or I think it looks that way as the photo blow up gets a bit fuzzy there.

If it is not looking pretty much like a perfect nut and a nice gold color versus mottled pink, then your props could be trashed too. The edges of the props will get feather and wear off fast if you had too much galvanic action on the props/nuts. Usually the props have a fairly square edge about 1/8 or a bit more on the trailing edge.

Best to take the props and nuts to a decent prop shop and have them evaluated as previously posted.

 

[jleonard]

By all means have your nuts evaluated. The ones on your prop shaft that is.

 

[HeideMarie]

Thanks folks, appreciated. Will do. None of that was noted on the survey.

 

[psneeld]

Have a close up?...if you do I might have a better idea...just a "guess" based on squinting at blowups of the above pics.

Never fully trust a survey.

 

[Taras]

Take a close look at the props when you haul out and get a second opinion from the Yard Manager regarding the condition of your props. Props can "thin" out due to corrosion. The way to prevent this is to be sure your "bonding system" is intact with good connections and good zincs in the water. Usually, a telltale sign of props corroding and thinning out is the trailing edge of the props lose their smooth shape and small chunks start to disappear from the trailing edge.

 

[Comodave]

I wish people would say anodes instead of zincs. Zinc is one type of anode, not the only one.

 

[Comodave]

Thanks folks, appreciated. Will do. None of that was noted on the survey.

Not surprising…

 

[HeideMarie]

Take a close look at the props when you haul out and get a second opinion from the Yard Manager regarding the condition of your props. Props can "thin" out due to corrosion. The way to prevent this is to be sure your "bonding system" is intact with good connections and good zincs in the water. Usually, a telltale sign of props corroding and thinning out is the trailing edge of the props lose their smooth shape and small chunks start to disappear from the trailing edge.

Yes - thanks - the diver did replace all the zincs/anodes which had almost completely deteriorated in just 9 months.

Will definitely get a second opinion from the Yard Manager...

Whether new props or these props, I will add anti-corrosion coatings (e.g. like Petit Barnacle Barrier, etc).

 

[psneeld]

Don't bet the ranch on many yard manager opinions....a prop shop will be the ones that really know.... they are the souls that have to recondition the prop (if asked) and have a reputation for prop repair to worry about.

I have known a few yard managers that know a lot of basics but being a jack of all trades, there can be quite a few weak opinion areas.

Of course the size and experience of the yard or the manager can have a lot to do with the value of the opinion.... so weigh what you hear with a few other opinions.

 

[Comodave]

Paint for running gear isn’t for anti corrosion but rather anti fouling. Don’t expect it to stop corrosion. Go to a prop shop. Have them give you an opinion on the props and if they are decent then have them scan them.

 

[BruceK]

Seems to me prop thinning is part of the life of a prop. Every antifoul it`s taken back to bare metal for priming,or when it gets burnished for propspeed, material gets removed and the prop blades get thinner.

 

[Simi 60]

Brass?
You sure about that?

 

[Simi 60]

Seems to me prop thinning is part of the life of a prop. Every antifoul it`s taken back to bare metal for priming,or when it gets burnished for propspeed, material gets removed and the prop blades get thinner.

Butchers take metal
Others carress them gently

 

[psneeld]

https://www.passagemaker.com/channels/dont-fall-for-the-brass-line


"If its primary constituent is copper, why is brass so susceptible to corrosion? Because many of the brasses also contain a substantial amount of zinc, they are especially susceptible to a type of corrosion referred to as "dezincification." This is a process whereby the zinc selectively corrodes leaving a porous copper shell that retains its shape but little of its strength. A dezincified brass propeller can be identified by its splotchy reddish or pink coloring. Contrary to popular belief, many propellers are fabricated from a brass alloy (by definition, in order to be considered a true bronze, a copper alloy must contain little or no zinc) and, as such, are especially susceptible to dezincification. To protect this often-substantial investment, it is imperative that sacrificial zinc anodes be monitored and renewed when necessary. In a stainless steel/Aquamet shaft, brass propeller combination, once the zinc is gone the next least-noble metal (or metal most likely to corrode) is the brass prop. It will begin to corrode, sacrificing itself for the shaft, which is nobler. Brasses are susceptible to other forms of corrosion in addition to dezincification. Ammonia, a common ingredient of household cleaners, will readily attack brass, causing it to weaken and crack. Mercury is also an enemy of brass, as is the aforementioned polluted water."

 

[SoWhat]

A 'thin' prop does not fall into the category of urgent repair in my opinion.
Thinning would most likely be a result of aggressive cleaning at the end of each season. If a yard winterizes the boat they are apt to polish the props to a smooth bright finish.

I would be more concerned if diver reported significant pitting or large areas of pink coloration.

 

[psneeld]

Hit something with a thin edge damaging it and the resulting vibration might set up an urgent repair at a very inconvenient time.

The difference in strength of a thinning edge whether from wear or corrosion only occurring at the blade edges (which I have personally seen a few times) and a normal blade is dramatic.

 

[koliver]

Some props are thinner than others.
I have a pair of spares, that the boat came to me with. One set weighs significantly more than the other. Those I use and keep the "thinner" ones as spares. In use, I could tell no difference. On examination after 20+ years in the locker, the "thin" set have tarnished and now appear dull. They were shiny when I put them away. They don't look pink, nor do they look thin, they just weigh less than the others. Maybe that original thinner design is what your diver is reporting.

 

[psneeld]

Some props are thinner than others.
I have a pair of spares, that the boat came to me with. One set weighs significantly more than the other. Those I use and keep the "thinner" ones as spares. In use, I could tell no difference. On examination after 20+ years in the locker, the "thin" set have tarnished and now appear dull. They were shiny when I put them away. They don't look pink, nor do they look thin, they just weigh less than the others. Maybe that original thinner design is what your diver is reporting.

Could be different alloys...thus thinner but just as strong.

Without a lot more info....only a couple of pics and a lot of guessing...who knows?

Probably a good yard guy or a local decent prop shop.

 

[TJM]

I bet your head is spinning with the array of responses? Most are good and accurate.
Prop thinning is mainly caused from polishing or conditioning of the prop over many years.
Dezincification is real and as noted turns metals into "sponge like" brittle surfaces. Zinc metallurgically dissolves easily (alloy for anodes) when surrounded by copper. The evidence is the pink hue, which resembles etched copper.
As mentioned a Prop shop is best, let the yard manager tell you where to get some food for lunch. Some props can be very thin due to their materials, Brass, Nibral etc....
I don't think a surveyor would ever pick up on a prop condition. As far as your nuts, the first nut is the thick one and takes all of the load, the second nut is thinner and is the locking nut which only prevents the first one from backing out. There might also be a cotter pin thru the threads.

 

[SoWhat]

Hit something with a thin edge damaging it and the resulting vibration might set up an urgent repair at a very inconvenient time.

Hit a rock with a thick edge and you will likely need an urgent repair at a very inconvenient time.

A divers characterization of something as "thin" would not have me rushing off to haul out. What is "thin"? Did he measure the leading edge of a new propeller and compare it to the thickness of the current propeller? What points on the propeller did he measure? What is the tolerance of his measuring device? Clearly he is merely expressing an opinion based upon unknown experience.

OP: Don't cut across Nixes Mate and you won't hit any rocks.

 

[psneeld]

Hit small pieces of floating wood and some thin edges can curl enough for a vibration.

Back in the old days when we dug out slips using commercial vessel propeller wash...I would wear blades thin in just a couple years and hitting even clam shells would curl the edges. New/normal props don't and will not deform when worn blades will. Sure there is no exact rule of thumb...but if his IS thin from wear or corrosion, it bears looking at and remedying at a convenient time.

Got LOTS of experience with wearing out running gear and hitting bottom as part of my second career.

According to US Navy engineers and many pros I know...the thin nut goes on first (after the large nut sets the prop and is removed).

The thin nut then goes on and then the big one last.... when torqued, it unloads the forward thinner nut and now the big nut (with more threads) carries most of the load.

While many will say it doesn't matter as so many boats have been going around for years with the big nut first...all I can say is true...it probably doesn't matter but the majority seem to think bug nut last.

https://www.passagemaker.com/channels/propeller-nut-myth-busting

"Contrary to commonly held beliefs, when assembly is complete, the half-height nut should be against the propeller hub, having been installed first, while the full-height nut is farthest from the propeller hub, having been installed last. The logic for this seemingly counterintuitive approach goes like this: when the first nut is installed and torqued down, it carries all the load or tension. When the second nut is installed against the first nut and it is torqued, much of that load or tension is transferred to the second nut. Thus, it only stands to reason that the second nut (the one that carries the majority of the load), should engage more of the propeller shaft with more threads.
I know for all you gearheads out there this appears to be heresy or worse, and you are wondering if I’ve lost my nut-and-bolt mind. When I first began proliferating this information several years ago, it was met with the hue and cry of many in the boat-owning and marine repair and boatbuilding communities, proclaiming it sacrilege, barbaric, and just plain stupid. Some even claimed that I had intentionally misled folks to drum up business for myself and my colleagues in the industry by propagating a spate of lost propellers. Even today, whenever I share this approach, the skeptics come out of the woodwork.
Rest assured, not only is this approach one I wholeheartedly endorse, but it’s also backed up with good engineering and it’s endorsed by propeller manufacturers, the Society of Automotive Engineers, the American Boat and Yacht Council, the U.S. Coast Guard, and the U.S. Navy. The latter spells this procedure out in excruciating detail in chapter 75 of their sublime (if you like this stuff) NavShipsTechManual (Chapter 075-5.3.4, Fasteners). It can be downloaded as a pdf, courtesy of Uncle Sam; I keep a copy on my iPad for “light” in-flight reading."

 

[Comodave]

That is absolutely correct. The full height nut goes on last.

 

[psneeld]

Just posting it for info....like many boating things done "differently"......there have been many reports it's never made a difference and I don't recall any lost props because of nut sequencing compared to other failures.

Guess the cotter pin helps and people are gentle with reverse more than not.

 

[Rufus]

Our OA came from the factory with the skinny (castellated) nut on the outside....

 

[Comodave]

Our OA came from the factory with the skinny (castellated) nut on the outside....

Doesn’t make it right…

 

[Old Sea Dog]

Following this thread with interest. Will be hauling out new to us '79 GB 36. For the life of me, I can not remember the sequence that it currently has. Hauled out for survey 2 weeks ago. Hauling out August 3rd to replace 4 plastic thruhulls at waterline and possible replacement of other thruhulls. I will bring my BFWrench to rearrange to Navy standards if needed. Located in Marathon. Again I continue to learn and re-remember.

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