Bravo 3 Propeller Problems (Cavitation & Cracks)
 

Gone through 6 BravoThree rear propellers. One in less than 2 hours hard run time. The rear, especially on the port side of a Formula 400SS with 415/502s (upgraded exhaust).

Both drives replaced on a Mercury Warranty upgrade in February 03 (3Xs) and that did not resolve the problem. The first two props were older style, the last 4 were all the newer HD castings. Mercury has warrantied 3 and awaiting credit on the 4th. I run them hard and they get some cavitation then crack. See attached photo showing pre crack condition. Mercury does not appear to have an explanation and does not acknowledge any other people having this problem.

Any suggestions or help on this issue appreciated. (HoustonProp come in).

Ed

I was told by my prop shop,(Bronson Hill) that my cracked bravo 1 32 was likely from overtrimming. He pointed to the cavitation marks and their relative position on the blades to support his case. I had him place as much tip cupping for bow lift in the new prop and now attempt to run with less trim although the boat likes the trim. I was told that Merc wouldn't warranty the cracked blade even if it hadn't been labbed.

I thought about the trim issue and ran the boat glued in when the last two cracked. The cracking sometimes occurs before the cavitation damage appears.

bravo III props
 

I have not seen this before on this set-up,the cavation burns ????

this is caused by a disturbance of some type or another? nicked edge. Blunt edge not rounded ,a sharp edge will cause this,or flow not direct to the propellers b(bottom of boat)//??????

THE CRACKING I HAVE SEEN AND KNOW THEY ARE BRITTLE.

WHY NOT SURE.

THE WAY TO GET TO A TRUE HONEST ANSWER IS TO SEND THE CRACKED PROPS AND A BRAND NEW PROP to a METALOGIST?SPELLING,

THEY WILL COME UP WITH THE ANSWER IT WOULD COST SOME BUCKS TO HAVE THIS DONE BUT they would have the real answer.casting issues.or whatever?

WE WORK ON GAS TURBINE BUCKET'S(BLADES) AND SEGMENTS AS WELL and know some people in the Turbine indusrty that you could send them to.rotate the prop take a picture down the( EDGE) So we can see it better.Darin I can weld and stop the crack,but let look at some more pictures

also what shape is the skeg in ,nicks ect and if aI remember,I have seen new props that the leadind edges's are somewhat beveled,from the way the casting was made,poor design ,this would cause the cavation burns, and cupping they are not supposed to be cupped at all either prop.on this set-up.

cracking
 

the cracking is something to due with the tensile strength,it's to brittle,they were not cooled properly.

This would be like taking a stainless prop heating it red hot and throwing it in a bucket of water to cool it down.

big mistake,after that you hit it with aHammer and it will shatter like glass,I have seen prop shops do this,not good it ruins the prop for life.JUST SO THEY CAN KEEP WORKING ON IT FASTER ,INSTEAD OF rotating the work and let it cool properly by air at room temperature.

also look at the discolorations of the prop looks like rust ,in the hub barrel inside and surface of prop lightly,this is because the prop has a very high CARBON CONTENT, STEEL; NOT STAINLESS

MAGNETS ARE NOT SUPPOSED-TO STICK TO TRUE STAINLESS TAKE A MAGNETIC Business card throw it on the prop or any prop and it will stick,find something that you know is stainless and watch the magnet will not stick,it's just the way it is but they should hold up ,if not they should be replaced,sorry you are having such a bad time with this and I am sure it's very frustrating.

That is one rusty prop. (Added some light to see better)

I Don't know how
 

you did that,??But ThankYou!

this show's the high carbon content in these props , it's terrible when you pay that kind of money:mad: and get something like that.

Thanks US1FOUNTAIN,for putting a little light on the subject.

:D Darin

Thanks for the pic enhancement, also! I’ll take pics of existing props. Rust is prevelant on both and cavitation burn present on port (Its too cold to run hard now). I do not think that the forward props rust as bad as the newer style rear props but they do rust. Wilmington Propeller, where I took the first two to be repaired, said forget it because of casting problems and high carbon content. Advised by Mercury rep. that problem was solved by new castings "B" (See Photo). Obviously did not fix problem.

“Scott” at Mercury is supposedly working on the issue but as yet he has never contacted me. I just keep returning props and get new ones or credit. Seems they would want to resolve the problem also. I feel sorry for those who do not have lifts and have to wait tell it gets real bad before discovering the problem; by them the props are usually out of warraty period or so bad that it is impossible to determine if crack caused by strike or too much carbon.

Anybody out there know “Scott” from Mercury in the Warranty, Technical, or Customer Support Section?

Re: I Don't know how
 

Simple, I just used the flash! ;)

are all the props the same pitch?

Absolutely. Front prop on both drives new also. Switched from 26" to 28" and 26"s had same problem but were the older casting without the "B" stamps and were immediately replaced with 28s when the exhaust upgraded and all rear 26s cracked (3).

After first couple of 28" props I smoothed front prop thinking a burr might cause cavitation on rear, but to no avail.

Nothing on bottom to cause cavitation either and same problem occurred with original Bravo 3 drives as is occurring with new Bravo 3Xs. The 400SS is a stepped hull. Hope your feeling the pain and frustration!!!!! (And I do appreciate any suggestions and help.) Hopefully somebody else with the same problem will find their way to this thread and it will assist them.

THERE ARE THREE SETS ON E-BAY FOR SALE ,NOT ONE SET SHOWED ANY SIGN OF THIS PROBLEM?

The Bravo 3 props are available both with and without cup. Have you tried a set with cup? Seems like the cracks are caused by the cavitation, cup may reduce or eliminate the cavitation as long as the cavitation is not caused by some other source than the props.

As far as the rust goes I would have to disagree. The Bravo 3 props are made of "true" stainless steel. The Bravo 3 props have a satin finish which will rust much faster than a polish finish. Even overnight, and this is true with just about any satin finished prop, some more than others.

There are more stainless alloys than you can count. Stainless steel is just what it is called; stain-less. It's not called stainproof. If they were steel they would be completely covered with heavy rust. Props have to use a high strength alloy to survive in the environment in which they work.

The "marine" grade stainless is 316, which is not magnetic. It is the most resistant to corrosion in the marine environment. 316 is not strong enough to make a prop with. Most Mercury props are made with 17-4 Stainless steel which has a tensile strength twice that of 316. Herring and Hydromotive use 15-5 Stainless Steel, for a very specific reason, which has different properties than 17-4 . Of course every lot of props made have a slight variance in the composition of the alloy used so some may rust a little more than others.

Matt

Matt, why would a satin vs polished finish be more prone to rusting? Same material, just a different finish.

Also to add to your SS lesson, some stainless alloys do have magnetic characteristics. In other words, some SS are magnetic. ;) Just a bit of info.

Yes, you are correct, some stainless steel is magnetic. That was my point, even though your props are magnetic they are stainless steel. A magnetic is not a definitive test to determine if the material is stainless or not.

Since satin props have a "scratched finish" much more of the meta isl exposed, therefore corrosion is much greater with a satin finish. That's why with a polished prop the inside of the can will rust before the blades do.

Matt

Thanks. I always wondered why non polished SS parts were more likely to show rusting, but never knew why.


Yes, the magnet test/check is a misconception about SS. that I see mentioned here all the time.

Added Note: Only mentioned this as a general observation whenever this comment is mentioned on any topic. Not meant to question the knowledge of anyone in this topic.

BravoIII PROPS
 

ARE YES BOTH CUPPED AND UN CUPPED ,BUT THERE ISNT A PROP THAT IS NOT magnetic,this is due to the high carbon count in the props more steel,than stainless,as far as stain finished props on the BravoIII the are not they have a dura tumble finish which is very smooth and has no deep surface scratches what so ever,they are totally different thana qoute SATIN FINISHED PROP.but in the same essence they are not polished either.

bottom line is looks like there are some casting issue's as far as tensil strength causing them to break,or they Mercury would not be re-placing them like this.

Even if there are casting issues that still doesn't explain what's causing the cavitation.

Actually there is almost no carbon in any stainless alloy. The rust has to do with different levels of Molybdenum and Nickel in 17-4 stainless as opposed to 316 stainless. There is less than .07% carbon in 17-4 and 316 stainless.

Matt

Carbon is non-ferrous however, nickel is ferrous. Over a certain percentage of nickel, the alloy will exhibit magnetic attraction properties.

edbo07
 

ThankYou for the phone call and go ahead and send the other pictures we talked about,and we will get it resolved.

nice talking to you and we will talk soon.

Darin