Bravo III Prop Install

rasbury

Well, the PLAN is this weekend to finally bring the boat home and get ready to dunk it and see if I solved or at least better identify my water leak- finished installing the bellows right before Irma came through and has been in storage since. River was just opened this past weekend so I'm able to launch and check it out- have not put the props back on yet. I searched for a specific thread on installation but did not find one although recall some discussions about prop alignment- which makes no sense to me as they run counter to each other anyway. Is there really a specific way they are installed in relation to each other??

randy56

the manual clearly states that B3 props do not need to be timed.

RWBLACK6

For installing B3 props, ALSWAG told me the following; after placing 1st prop on, turn blade up at 12 o"clock. Then place the next prop on with blades at 10 and 2 o:clock. He said , you do not want 2 prop blades lining up directly behind the gear box. As always , I follow his advice.  

raybo3

I called Merc and was told that there is NO timing or alignment.

rasbury

Well then! I will accept all your answers- there would be no harm then installing the way Al suggests as there appears to be no wrong way anyway.

Wish me luck,,,,,

J3ff

I did mine in water.... Didn't pay attention to anything

rasbury

10-4

raybo3

Here is the e-mail response from Merc...........
Ray,
There is no special timing of the props. Service manuals for engines and drives are available from local dealers or by calling our Publications Department at 920-929-5040, option #4. Have your serial number ready when ordering.
Thanks,
James
MerCruiser Consumer Support

2017-00054090

randy56

@Alswagg, I have to ask what is prop burn?  a burn mark on the prop? how does that effect performance from a burn ? what is the cause?   

Handymans342

Not Bravo 2. Lol

randy56

Found old thread, hard to imagine the water getting so hot it damages props.
Why would Merc. tell raybo3 it did not mater?

https://rinkerboats.vanillaforums.com/discussion/6147/do-bravo3-counter-spin-props-need-to-be-aligned

Michael T

Why would a company say that a procedure "didn't matter"?

Does anyone remember the issue with servicing the jet engines on the DC 10s?

The proper way was to disconnect the engine from the huge bracket that connected it to the wing. That took about 200 man hours. Some genius found that you could remove a few huge bolts and drop the engine ( a few hours of work) - unfortunately - reinstalling it that way easily cracked the attachment bracket over time.

One DC 10 crashed at Chicago after its engine fell off on take-off. Plane crashed with the worst death toll in U.S. aviation history.

All DC10s grounded - none even allowed to fly into U.S. airspace.

Checks of all mounting brackets on every DC 10 done - dozens of more DC 10 brackets in imminent danger of failure.

Seems ALL of the airlines had shared the short-cut to save time/money!

The genius who thought-up the short cut caused many millions of dollars of damage and just under 300 deaths.

As my grandfather used to say you can do it fast or right - pick one.

ALL my boats - ALL my maintenance - of EVERYTHING I own......done right.

Who do you want working on your boat/car/sled......?

I'm with Al.

trip_n

@handymans342===prop soot

randy56

Mine looked sort of like that, not as bad. Cleaned up with the works toilet bowl cleaner. not prop burn. algae 

raybo3

J3ff said:

I do have prop burn... But more like alge burn Grrrr.  

Looks like marine growth to me...........

rasbury

Well Handy not yours lol.  Prop burn happens at high speed and high rpm.  Not at speeds just above no wake  - that's some funny stuff.....I will time the props and will look for the thread or check the manual.....thanks Al as always! soot on the props...yuk yuk yuk....

Handymans342

Putting my new Hill Marine 4 blade props on next week

Black_Diamond

Prop burn is really cavitation.  Bubbles forming at the blade surface that erode the metal.  Common in pumps with metal impellers, can be very damaging.

randy56

Since a few day's ago hearing about prop burn for the first time. I've some research. Here's the good description found.
https://youtu.be/5bj5kjh3l9o

Black_Diamond

I clocked my 4x4 props.  Always did my old 3x3's too.  Takes zero effort and maybe 30 seconds of your time.

Black_Diamond

Here is an easy to read explaination:

https://www.thoughtco.com/cavitation-causes-and-remedies-2293276

Michael T

In short - hydrodynamic cavitation is caused by the explosion of tiny bubbles created by pressure differentials across the surface/edges of a propeller. The  (new) and largest container ship in the world has two propellers (4 blade I think) that cost a million dollars each to pour, cut robotically and X-Ray. Many propeller designs were tank tested to find the best design to reduce propeller "eating" cavitation. You also have anti-cavitation plates on your marine engines that help a bit too. Cavitation also affects skegs etc.

Glassguy54

On Bravo III dual prop set ups, it just makes sense to index the props so that  the front  prop has the blades at 12:O'clock, 4:O'clock & 8:O'clock, and the rear blade at 6:O'clock, 10:O'clock & 2:O'clock, doesn't it? That's how mine were.

J3ff

I do have prop burn... But more like alge burn Grrrr.  

LaRea

randy56 said:

Found old thread, hard to imagine the water getting so hot it damages props.

It's not heat -- it's low pressure.  If the prop generates a localized spot of low pressure, even cold water will boil into bubbles of water vapor.  When the bubbles collapse, that's when the damage happens.  Look at the wikipedia page for cavitation.

LaRea

Also, I thought the timing only applies when both props are 3-blade.  If you have a 3-blade and a 4-blade, there's no way to align them.  

randy56

Images, not just for go fast, and bass boats, the fourth picture is a ship propeller. So handy and his massive powerful diesels can have it also.
 
.

Handymans342

So what causes the cavitation?????