Why do Bravo 3 propellers get that hard coat of scaling?

LaRea

Every Bravo 3 I've seen has it.  After spending more than a month or two in the water, the props get coated with a thin, crusty layer of fouling, like this:



What is it?  It doesn't happen on my dock neighbor's 312 with Volvo composite outdrives, so I assume it's some sort of electrolysis process from the aluminum outdrive and stainless steel props.  Can anybody confirm that?

I don't care about the fact that it's ugly.  What bothers me is the extra drag from the rough surface.  Drag on the surface of a prop has got to be a real performance killer. 

The coating is extremely brittle, and it will easily come off with light sanding (50 grit - barely need any pressure).  You could sand it forever with 220 grit and it would never come off, but it'll flake off right away with 50 grit.  I've also tried a 3000-psi power washer, and that took off some of it, but not all.  

People say it can be removed with toilet bowl cleaner, but the ones I've tried did absolutely nothing.  

Lastly - is there ANY way to keep it from coming back?  I always clean my props to a nice satin shine every spring, but you'd never know it after a couple months.  No paint will stick to the props, and I've heard nothing but disappointment from people who have tried various prop coatings and treatments.

Michael T

@LaRea. I agree 100%. I think we may have discussed this earlier this year on this forum? My Bllls went in glistening shiny and polished. I'm ocd so I even waxed them LOL Then, I watched the change right before my eyes. When we pulled the boat this Fall I noticed that the SS props on Volvo stern drives from the same area were not nearly as coated. In fact they were almost shiny. A few techs from the marina gathered around the two boats and weighed-in on the conversation. The consensus seemed to be that Volvo may be using a higher grade of SS? I wonder if Volvo has found some secret to bettering their cathode system. I won't even bother to return my props to their shiny polish this year as it will start to re-coat within weeks. BTW I also noticed the SS pins on my drives were more rusted than the Volvo ones. In fact I had one replaced under warranty as it was in such poor shape. I'm  Merc guy but not happy with some of the SS parts they use.

MarkB

Is that blue chips of paint I can see on the prop here and there?

Michael T

@MarkB, mine looks like that too, in places - on mine it is the shiny SS showing through the "coating". I'll be interested to see what @La Rea says!

Black_Diamond

If you use The Works toilet bowl cleaner 100% of that scale comes right off. Never, ever use a wire brush made of steel. You will cause corrosion unless you passivate them afterwards. 

LaRea

I think the blue is just a reflection of a blue shirt I was wearing.  The props had little spots here and there where the coating had chipped off, revealing shiny steel.  If you look at the hub, you can see some of the areas where I tried the power washer.  It worked okay, but I'm not sure it was much of a time-saver compared to sandpaper.

Here's what they look like now:

Handymans342

Why don't one of you guys try "Propspeed" coating. www.propspeed.com

LaRea

I couldn't find any published info on how Propspeed does with the Bravo 3.  The web site claims it will stick to stainless, but they only provide case studies for large boats with bronze props.  Also, they say it's a soft coating that will not survive contact with sand.  

Not to mention, I'd have to reapply every year, which means sanding off all the old coating, which means it's even more work than I'm already doing. 

Handy - you go first!

raybo3

The site said "any metal below the water line". Says works on shafts, trim tabs, rudders...............

Michael T

A few guys i know use CLR, a calcium, lime and rust remover. I know that bthey either remove their props from the drive or tilt the drives down as they fear the CVLR will damage seals. Yes, you can use "muriatic acid" which is Hydrochloric acid, HCl. I have handled this product for 45 years. My construction company used it to remove cement residue from brick work after brick was laid and when diluted 3:1 with water to remove grout from tile after a tile job. That said you really need to be careful handling that stuff and wear gloves and have an eye wash container handy. This acid is rated as a "strong" acid and is very dangerous if mishandled. If using it I would remove the props from the drives to do so as this acid would eat seals for fun.

Handymans342

There is a local Prop guy here that swears by the propspeed. He said it is easy to peel off but wont just wear off. Of course if you are running thru sand it will come off. 

LaRea

@Handymans342 - Does he use Propspeed on Bravo 3 outdrives?  Oceanmax is careful to say that any electrolysis will cause Propspeed to fail, so I wonder if it would work on a B3.

Not that it matters ... I lost interest in Propspeed after I checked the price.  The materials alone would cost $500 to treat a pair of B3s. 

Michael T

.....and probably every boat kept at or that visits a marina is exposed to galvanic corrosion - which makes the lime-like deposits on SS props - that's where mine get them, even though I have an awesome galvanic corrosion preventer (promarine 60)

Handymans342

LaRea, I believe he told me that as long as the props were clean and the proper primer installed, you would be fine. Plus it saves fuel too

MarkB

This is what my props looked like after being in the water at my marina for 2 months.

Michael T

@MarkB, that's what mine look like too. As time goes on, month by month, the "coating" just gets a bit thicker each month.

LaRea

This photo shows my dock neighbor's 310.  Volvo Penta composite drives - the props are virtually spotless.  I don't think he even pressure-washed them when he hauled out.

Michael T

@LaRea - 100% brother. That's EXACTLY what I saw beside my boat the past two summers...... the friggin' Volvos were coming out of the water with clean props and mine had the same hard/scaly coating as yours on them.  What gives?????

Handymans342

Maybe Al knows.

MarkB

Hold on, those volvo props look like polished stainless.  Smoother surface will mean harder for stuff to stick.  It might not have anything to do with the materials and everything to do with the surface finish.

Michael T

My XR props were polished to a far better mirror shine that any Volvo prop I have ever seen. That still didn't stop the "coating" from forming. I wonder if Volvo has discovered some sort of cathode system that protects the props better?

raybo3

Alswagg said:

Easy to clean with miradic acid.  Aka Toilet bowl cleaner.   I can tell you that Merc props are a lot stronger than Volvo. Higher grade of stainless o. A Merc.  Volvo has a lot more brass alloys in the metal.  

Al did answer the question. Something I am not getting here. Does it really matter what the prop looks like if its giving the performance that your looking for. No one can see them in the water.......... Just say'n.....

bella-vita

I would say a scaling prop will effect performance !

LaRea

Especially in the muddy water of the Potomac, nobody can see them!  I only care because it probably affects performance.  

I say "probably" because I can't find any test results.  Any boat propeller will lose some efficiency if the blade surfaces are rough, but I don't know if we're talking 5% or 0.05%.  There's plenty of published data for ships, but I can't find anything for outdrives.   

I'd love to hear from somebody who checked their WOT speed before and after polishing their props.  Maybe it doesn't make a noticeable difference.

Handymans342

Depends on the thickness. I know a 1/32 inch coating affects the efficiency of heat transfer by 10-15%.  

Michael T

I checked my data at new break-in. EC 360 bravo lll X drives bravo XR props. We went WOT for about 10 seconds at 20 hours. It did 51.5 mph on the vessel view 7. A few months ago I posted what we did last summer, I think it was 50 mph. There was more gear on board but a lot less gas so weight was about even. Unless there are chips of scale off the props, it doesn't seem to affect my speed much. I clean the props each year and they seem to coat uniformly. I would guess that if the growth were uneven like with some barnacles etc. that would be an entirely different matter. My boat's speed (of course) is much more affected by humidity, heat and wind....but, to repeat, the "coating" that forms on my props does so uniformly....my 2 cents.

LaRea

After poking around a bit more, I've seen people claim to lose 10-15% in fuel consumption by having barnacles on the props.  Compared to that, the scaling on my props is not nearly as bad, so maybe I'm only losing 5% or less at the end of the season.  But still, that's enough that it's worth polishing the props in the off-season.  

raybo3

I would think that there is a big difference between barnacles and some scaling or discoloration. Boat may not even move if the barnacles are bad enough...... 

Michael T

@LaRea, I agree it's definitely worth trying to clean them to as close to original polish as possible each year to prevent a continuous build-up. I'll get at mine before launch this spring.

Black_Diamond

I tell ya. 5 minutes with The Works toilet bowl cleaner: apply, let it foam, rinse and just like new. 

Michael T

@BD thanks, I'll buy some but I'll have to hide it or the Admiral will get ideas! LOL