Feels like spun hub but isn't

[seasick]

Unlikely but in theory it is possible for the drive shaft to have a slipping pinion gear (exactly how I don't know) or even worse and less probable, the driveshaft could be slipping in the power head where the splines connect. You would think that would make a horrible noise.

When the boat revs increase and the hull seems to lose power, do you hear ventilation or blow out ? It should be obvious.

 

[tech_dog]

If the boat also is 30 years old (or more) is it possible that the bottom flexes or has become a little concave on the trailer??? Just a thought.

The boat has been on a new trailer for six months. You just gave me a new worry...

 

[Beyond A Wake]

try to check by attaching a fish line to back end and pull forward and attach somewhere further up front and see how it follows the bottom, or shows air in between boat and line if there is a concave area. Easier said than done I'm sure but if yes then that can affect the direction water leaving the bottom and maybe even create turbulence?? You could also for peace of mind just knock on the bottom to detect soft or hollow delaminated spots, again probably unlikely if boat is generally in a good condition, and bottom is usually showing blisters if there is a problem. If boat never was kept for longer periods in water all of this is mostly unlikely scenarios.
Just a thought and more likely I still believe you are spinning the hub.

H

 

[family affair]

I'll throw this out there - your prop is worn out. Seriously. If you have been running the same prop for 27 years, the diameter of the prop has changed due to wear. My guess is the diameter has changed enough to change the geometry of the prop, and/or enough thickness of the prop has changed impacting flex characteristics under load. Find the same prop, but a lot newer and give it a go.
Also, if a slight change in dimensions around the prop barrel to the gearcase can cause exhaust to exit in front of the prop causing a loss of traction.

 

[PointedRose]

I was thinking along the same lines as FA.
the reconditioned prop may have required some grinding down to smooth out, so perhaps now a smaller prop than before

 

[tech_dog]

I'll throw this out there - your prop is worn out. Seriously. If you have been running the same prop for 27 years, the diameter of the prop has changed due to wear. My guess is the diameter has changed enough to change the geometry of the prop, and/or enough thickness of the prop has changed impacting flex characteristics under load. Find the same prop, but a lot newer and give it a go.
Also, if a slight change in dimensions around the prop barrel to the gearcase can cause exhaust to exit in front of the prop causing a loss of traction.

Yes, it's a 30 year old "black stainless" Yamaha prop with a few small dings before I had it reconditioned. Your diagnosis aligns with the problem happening once or twice before reconditioning, and more often after, but I'd think I'd be able to trigger the ventilation with my repeated full throttle hole shots if it was just the prop.

I'm still trying to hone in on it, but it now seems like it occurs after we get out of the bay and into the swell, and I'm imagining the outboard bouncing up just a bit as the boat shoves its way out. I've never had it happen on bay-only days, i.e. a morning out wakeboarding with the kids with a dozen fast-starts under load.

I can't argue with your reasoning, 30 years of leaving tiny particles of stainless in my wake, so I'll bump "bad prop" up my probability list.

Thanks,

T.

 

[tech_dog]

Unlikely but in theory it is possible for the drive shaft to have a slipping pinion gear (exactly how I don't know) or even worse and less probable, the driveshaft could be slipping in the power head where the splines connect. You would think that would make a horrible noise.

When the boat revs increase and the hull seems to lose power, do you hear ventilation or blow out ? It should be obvious.

Mechanically, the 30 year old engine sounds great. Based on feedback above I've all but discounted a drive train issue.

Until my last outing I was fixated on spinning hub because I didn't think a well-proven configuration would suddenly be ventilating. The "feel" of it is what I'd expect from ventilation, so I'll focus on the trim and prop next time I'm on the water.

Thanks,

T.

 

[family affair]

Yes, it's a 30 year old "black stainless" Yamaha prop with a few small dings before I had it reconditioned. Your diagnosis aligns with the problem happening once or twice before reconditioning, and more often after, but I'd think I'd be able to trigger the ventilation with my repeated full throttle hole shots if it was just the prop.

I'm still trying to hone in on it, but it now seems like it occurs after we get out of the bay and into the swell, and I'm imagining the outboard bouncing up just a bit as the boat shoves its way out. I've never had it happen on bay-only days, i.e. a morning out wakeboarding with the kids with a dozen fast-starts under load.

I can't argue with your reasoning, 30 years of leaving tiny particles of stainless in my wake, so I'll bump "bad prop" up my probability list.

Thanks,

T.

FWIW, my props lose bite in certain types of chop along with load conditions too. They work great 80% of the time, but the other 20% is when I really need them to perform well.
I haven't read all the details of your post, but did you talk to the prop shop about adding a little cup? Cup can be very subtle on the leading edge of the prop. The reconditioning might have removed just enough to cause a problem. Adding some back is relatively cheap. Less than $100 typically.

 

[tech_dog]

I haven't read all the details of your post, but did you talk to the prop shop about adding a little cup? Cup can be very subtle on the leading edge of the prop. The reconditioning might have removed just enough to cause a problem. Adding some back is relatively cheap. Less than $100 typically.

I called the shop that did my prop and let him know what I'm dealing with, and that I was leaning towards getting a new prop. He immediately asked me to bring the prop back in so he could check, and he offered to add additional cup free of charge. I was just looking for info and feedback, but it would be nice if this turns into a solution.

Like you, he seemed to think lost cupping could be the root cause.

Thanks,

T.

 

[Ekea]

can you post a pic of the lower unit and prop as well as how the boat sits on the trailer?