Is there a proven treatment or application for bronze yacht propellers
to prevent their fouling (especially by barnacles) in seawater?

Hi arminius and thanks for the question.

The answer to your question is yes, and I can speak from personal
experience here, having held my RYA (Royal Yachting Association)
certificate for ooh! 20 years

Paints are available but they can cause problems with the propeller in
two ways.
A) The rough finish you inevitably get affects the `clean cut` of the
prop through the water and so diminishes efficiency, and if it’s of
the antifouling type it comes off VERY quickly.

B) Paints (I’m not saying all) over a period of time can cause pitting
of the bronze through chemical erosion, which will have the same
affect as A)


So some solutions are:
1. Put a black bin liner over your prop when not in use, this excludes
sunlight (which the barnacles need to grow) and it acts as a barrier
to keep them from latching on.
2. You can wax your prop which is cheap and can be done quickly (even
in the water if necessary)
3. If you want to spend money you can get your bronze propeller copper
coated, this is more expensive but more effective.
4. Scrape them off with a paint scraper as required!
5. Use your boat more often! (it’s difficult for those barnacles to
latch on to something that’s spinning at high RPM)
6. Remove prop when not in use (not very practical in most cases)

A detailed article about antifouling paints:
“Insoluble antifoulings or antifoulings with low solubility or
erodibility are normally used on high-powered boats (35-50 knots) on
propellers, shafts, flaps, motor bodies, hydrofoil and stabilising
fins, waterlines and generally all submerged parts subject to extreme
wear or abrasion”
http://www.veneziani.net/man_eng/glossario.html#ANTIVEGETATIVA A
MATRICE DURA

Paint for your prop is available here:
“Mercury Performance Paint - Flat Black - Propeller Paint”
http://www.cpperformance.com/search_result.asp?CATEGORY=ALL&MANUFACTURER=ALL&DESCRIPTION=&PRODUCT_ID=525-92-80287850

I hope these tips are of some help to you solving your problem.  If
you think they might be, don’t hesitate to rate my answer.
Happy boating!

THX1138

Search terms used:
"antifouling paint"
://www.google.com/search?hl=en&lr=&as_qdr=all&q=%22antifouling+paint%22&btnG=Google+Search

Thanks for your list of suggestions. Unfortunately none of these
expedients have stood my in good stead over the years. Your #4 is what
I usually have recourse to, but, brrrrrrrr, the water is cold around
here.  Waxing seems to have helped a little but doesn't have much
effect on our aggressive barnacles for more than a couple of weeks so
that isn't much use on long cruises under sail. The real answer to my
question is, alas, there is no proven prop treatment.