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Is it Normal for Props to Lose Traction?


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I have a 2008 Sig. 330 (now the 350). Bought it last September and really haven't had the chance to spend much time on it due to the "hard water" here in Michigan at the present time. When moving the boat to my permanent location I noticed that when accelerating to get on plane, if I did it too fast the props would lose traction and seem to spin as if there were a hub issue, but if I backed off, it would grab again with no problem. Engines are 350 mag, Merc with Bravo III drives. I'm wondering if this is normal and I was trying to accelerate too fast for the weight, or if there actually is a problem with the hubs. The trip was 250 miles and no other issues, it only happened when getting on plane. Thoughts? Thanks, Greg

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My props " lose traction " as the blade becomes less than near perfect. Small surface imperfections start to cause the black paint to chip or errode away. Striking very small stones in shallow water can put dings into the surfaces of the prop that runs in a NEAR VACUUM condition with high loads.

If the prop is operating at maximum thrust & vapor vacuums when at WOT. The dings cause " prop blowouts " loss of thrust. There is sometimes a rumbling of the drive when blowout occurs. That is the prop ripping apart the water molecules & causing large vacuum pockets on the props OVERLOADED surfaces.

My blowouts becamce so bad I could not make fast turns at higher speeds.

I could not do a WOT from a dead stop either. Lots of little annoying prop losing thrust conditions

To the prop shop........1 time in 10 years & 175 hours on the clock. Can not complain.

Some props are designed to blowout. Why would anyone want that ? A incorrectly designed or selected prop will cause blowouts.

Putting in higher powered engines & not changing drive ratios & or props. Several ways to create blowouts under high acceleration loads.

Many ways to cause " blowouts............Hopefully you only have a ding or what looks like tiny holes in the surfaces. Prop shop.

Prop shop repairs are cheap & usually do the trick.

Some boat designs are setup for medium sized engines. They never blow out. Put in a bigger & higher HP engine & the prop is to close to the hull . Oh well.

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I have a 2008 Sig. 330 (now the 350). Bought it last September and really haven't had the chance to spend much time on it due to the "hard water" here in Michigan at the present time. When moving the boat to my permanent location I noticed that when accelerating to get on plane, if I did it too fast the props would lose traction and seem to spin as if there were a hub issue, but if I backed off, it would grab again with no problem. Engines are 350 mag, Merc with Bravo III drives. I'm wondering if this is normal and I was trying to accelerate too fast for the weight, or if there actually is a problem with the hubs. The trip was 250 miles and no other issues, it only happened when getting on plane. Thoughts? Thanks, Greg

Bravo 3s have a splined shift. So there can not be any slippage there. I would check the props for damge and if the props were ever changed out make sure there the right pitch & size for your boat. Did your RPM go up or down when this happened?

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Bravo 3s have a splined shift. So there can not be any slippage there. I would check the props for damge and if the props were ever changed out make sure there the right pitch & size for your boat. Did your RPM go up or down when this happened?

Props are not damaged or dinged. That was the first thing I checked. The RPM's do go up when this occurs, then I back down the throttle and they grab again. The props seem to do a good job otherwise.

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I wonder if the props were installed properly with regard to the timing of the blades Greg. Large inner prop blades at 12, 4 and 8 o-clock positions and the smaller outer prop blades at the 2, 6 and 10 o-clock positions. If the blades were not installed and timed properly it could result in cavitation (air/vaccum/voids) when the props are spun at higher RPMs under load.

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Sorry to start with the obvious, but before you start analyzing the props, just one question: how were the lower units trimmed when you had the blowout? We're you trimmed fully in or were you trimmed up some?

Drives were trimmed completely down when this occurred... That was the first thing I checked when it happened, but I am open to any input or ideas you may have.

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I wonder if the props were installed properly with regard to the timing of the blades Greg. Large inner prop blades at 12, 4 and 8 o-clock positions and the smaller outer prop blades at the 2, 6 and 10 o-clock positions. If the blades were not installed and timed properly it could result in cavitation (air/vaccum/voids) when the props are spun at higher RPMs under load.

You, know, that is something I am aware needs to be done, but to tell you the truth, I didn't check it when they pulled the boat out of the water. I will check on the prop timing. Thanks for the input.

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I wonder if the props were installed properly with regard to the timing of the blades Greg. Large inner prop blades at 12, 4 and 8 o-clock positions and the smaller outer prop blades at the 2, 6 and 10 o-clock positions. If the blades were not installed and timed properly it could result in cavitation (air/vaccum/voids) when the props are spun at higher RPMs under load.

This is were I am leek on! for 12 years I have had both Merc & Volvos and alway taken the props off and on & never lined anything up. Its always worked out!

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Like said, make sure the timing is correct for the two props. I have the same setup and can hammer down with no cavitation on the props. Most of the time I don't do that, will apply power slowley so that it comes on plane smoothly using a little less fuel. I will have the drives full down and tabs full down.

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On painted props if the paint starts to " wear away " on all the blades edges, evenly ? I always consider that " cavitation " in optional higher powered boats. Good chance you need a prop shop trip.

Can not help S S or Bronze...........I have seen racing props with almost microscopic pin holes on all the blades in a band around the prop.. Too much power. Not enough blade area. Some rudders will get the tiny holes in the blast zone of a prop.

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Like said, make sure the timing is correct for the two props. I have the same setup and can hammer down with no cavitation on the props. Most of the time I don't do that, will apply power slowley so that it comes on plane smoothly using a little less fuel. I will have the drives full down and tabs full down.

MPM,

Thanks for the input, I was hoping you might weigh in as I thought you had the same set up as me. I will definitly check timing and may consider going wuth a set of 4 by 4 props. I did note some damage to the skegs when I pulled the boat out of the water. It looked like a rip saw on the leading edge of the skeg, which could be causing my issues. I will know more in a couple weeks when I am able to get back to the boat when the marina opens back up. I appreciate the input. Greg

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