What causes prop "blowout"?

[Mark Hofman]

 

[Mark Hofman]

Oops, hit the Enter key instead of the tab.



Back from Lake of the Ozarks, and I experienced a couple of "new" things with my boat. This was the first time on big water, running flat out for extended periods of time (15 to 30 minutes). A couple of times, it felt like the prop wasn't getting a bite on the water. Once was in a tight turn (which makes sense, because the prop was probably cavitating under the load), but once was on a hole shot. It only happened once, and I was using the same procedure as I always do - steady increase in throttle with full negative trim until up on plane, then back off the throttle until I get the trim set. I didn't notice any over-reving. Is this something that just happens with bigger outboards?



On a separate issue, I churned up some mud in one cove. How big does a prop ding have to be before it throws the unit out of balance? I have one nick I can feel by running my finger along the blade edge, but it is smaller than a pin head.



MO

 

[Staci Matheis]

You're in good shape on all counts, Mark!

Now don't go messin' up OUR boat before the 19th!



me!

 

[Kenny Lively]

MO,

My experience with prop blow-out had to do with the "cups" being gone from the blade tips. I had a 24 pitch trophy on an 896 w/200EFI. i had bent one of the blades and sent it to a prop shop to fix when it got back it wasn't the same. Had bad planing problems, and often would blow-out, got worse the longer i had it. I lived with it for a while, then finally sent it to another prop shop. Not the same shop (no longer in business), and i can see why. The new prop shop said the "cups" were completely gone, not even there. They fixed it, it ran and performed like a new one. Hope this will help.KENNY

 

[Rob LaMoy]

Just had mine re-cupped last year. BIG difference. Plus Mo, if you tighten down your jack-nuts, it couldn't hurt! LOL Couldn't resist. Seriously, sounds like you have it pretty well figured out. In turns it can blowout if not trimmed in, and on hole shot too, if trim isn't down. In rough water though, at full speed and trim, you will occasionally blowout as the boat may leave the water entirely off of a wave, and when the prop leaves, you will red line. Upon re-entering the water, the prop is rotating too fast to grab. You have to slow it down to get the rotations in sync with the current boat speed. Nothing you can really do about that, except slow down in rough water.

 

[Mark Hofman]

Thanks, guys. Your comments made me realize that I didn't provide enough information. The prop is an aluminum, Black Max 14x23 3 blade.



Would churning up some mud be enough to remove the cup from a blade? It was enough to take the shine of the paint, and from the front edge of each blade, but not enough to strip the paint of the skeg, prop or bullet.

 

[Mark Hofman]

Bob:



Help me with a couple more questions: If I wanted to do that, put a SS prop on and use the Black Max as a spare, would I just go to a Mercury dealer and tell them, "I want a Trophy small hub in 14x24 for a 2002 150XR6"? How would raising the motor one hole affect using the Black Max if I wanted to swap out for running in rocky, shallow water?

 

[Mark Hofman]

I haven't had it out yet in what I would consider a warm climate, but with a medium load (two people, tank of gas and fishing gear) it will turn around 5200, 13 to 15 psi on the water pressure guage, and run between 56 and 58 depending on the trim setting. I noticed after the mud incident that I'm having trouble getting it up above 55 now. I don't really need or want more speed, just something that is a bit more durable and doesn't blow out as much on the hole shot or in turns. I was thinking that, if I go to stainless, it would be for the same diameter and pitch, since I liked the performance of the Black Max when it was brand new.