Replaced prop with the "same" spec prop. Loss of bottom end.

[Bman1337]

So I've got a 16 ft javelin bass boat with a 70hp Johnson that I had a 13x19 prop on ever since I got the boat well at first you would have to have somebody sit on the front desk to get the thing to want to come out of the hole but it did fine on plane. Then put a hydrofoil on it and that seemed to correct that issue. Well as the years went on that prop got bent up. But performance never really got worse if anything the hole shot actually got better. Well my last time out I bent one of the blades far enough that the boat just kept porpissing on plane. So I replaced it with the same spec prop. Now it's back to hole shotting like a dog. However on plane it does great. No porpissing. Can't even make the prop slip out. It's just bogging bad out of the hole. It didn't used to do that. So either the bent prop was acting like a lower pitch? Or the prop allowed for more slip and allowed the engine to rev out and hole shot better?

 

[racerone]

Did you hit something with the prop ?

 

[airshot]

If you bent a blade that bad, you should be getting serious vibration ...perhaps that first prop had been reworked/ repitched before you damaged it and the numbers don't match the pitch.

 

[Bman1337]

If you bent a blade that bad, you should be getting serious vibration ...perhaps that first prop had been reworked/ repitched before you damaged it and the numbers don't match the pitch.

That old prop was a factory OMC prop I doubt it had been reworked. But when I got the boat years ago it behaved kinda like this. Slow out of the hole usually requiring someone to sit on the front deck. That's when I installed the hydrofoil and that helped.

It's a pretty good amount of bend but even with the bend it wasn't really vibrating. And it came out of the hole great. Would even come out decent with 3 people. Now it's slower out of the hole with just me than it was with 3 people. Top speed was much different , but I was also on some pretty tore up water today so not sure what the actual top mph is.
What I noticed is it's bogging the motor alot more to hole shot. With the old prop it definitely sounded way better rpm wise. So all I can figure is something about the way the prop bent over time helped the hole shot while hurting the top end behavior.

The big difference on top end is the porpissing is completely gone and you can trim up all you want it won't slip out. The old prop you could trim up enough to cause the prop to slip out. And there was a small sweet spot to not be porpissing. So the top end behavior is much better.

 

[Bman1337]

Did you hit something with the prop ?

Oh I hit plenty of stuff with the old prop over the years.

 

[airshot]

One bent blade will not change your hole shot and you will get a noticible vibration, dings mabey not, but a bent blade..yep !! You have an engine issue !!

 

[Bman1337]

One bent blade will not change your hole shot and you will get a noticible vibration, dings mabey not, but a bent blade..yep !! You have an engine issue !!

It definitely isn't the engine. It was running great that last time out. That didn't up and change after a prop.

 

[jimmbo]

Yo say you replaced it with a 'Same Spec' Prop.
Same Brand, and Model?
How old was the so called Factory Prop?
Was the old Prop Vented?
Do both props have the same Blade Shape, Contour, Rake, and Cup?

 

[Bman1337]

Yo say you replaced it with a 'Same Spec' Prop.
Same Brand, and Model?
How old was the so called Factory Prop?
Was the old Prop Vented?
Do both props have the same Blade Shape, Contour, Rake, and Cup?

The new prop is a solas. Most affordable replacement at the local shop. The old prop is an OMC prop. No venting on the old prop. The solas is definitely a heavier made prop. Much thicker blades. So far as the contour, rake ,cup I'm not sure on those terms in reference to a prop

 

[jimmbo]

So you have a completely different prop replacing the old one, so results are going to be different. There much more a Propeller than just Diameter and Pitch.
You say the Solas has thicker Blades. Thinner Blades are more Efficient than thick Blades. Contour, would be referring to the Blade's overall shape.
Cup is a flaring of the Trailing Edge or Tip of the Blade. This can help a prop grip the Water better. Cup on trailing Edge adds a pitch, while a Cup at the Blade Tips increases Rake
Rake is the Angle that the Blades are pushed/bent back from. Heck, here is a link that explains far better than I ever could

Prop Blade Rake: Not Easy to Explain, but Crucial for Optimal Boating

A boat propeller is a complex object, and every shape and angle impact its performance. - A boat propeller is a complex object, and every shape and angle impact its performance.

www.mercurymarine.com

 

[Bman1337]

So this is the bent blade. Atleast the badly bent. One of the others Is bent alittle bit. I straighten it back out best I could tonight so gonna try it and see what the difference is.

 

[jimmbo]

Convergence Ring is also missing

 

[Bman1337]

Convergence Ring is also missing

Yeah that came off awhile back. What does that ring do?

 

[Bman1337]

New solas prop.

 

[Bman1337]

Original prop. I do think the solas has more cup. Where as this one doesn't seem to have much at all.

 

[jimmbo]

OD 12 22. Could that be code for 12" Dia, and 22" Pitch?

The original prop don't look like it had any Cup, OMC didn't start putting cup on its AL props until around the mid 80s. The Solas, has some Cup on the Blade Tips

 

[Bman1337]

I'm fairly certain it's a 13x19. But it's possible I got the wrong prop. And the engine is a 1992. After straightening out that prop best I could I took it back out today and just like that the hole shot is back to being decent. But it definitely can't hold onto as high of top end without the porpissing.

 

[tpenfield]

Cupped prop. . . probably making the difference.

 

[jimmbo]

A 19 with Cup is different than a 19 without Cup. Some will say it is like adding an Inch or 2, but is a bit more involved/complicated than that

Somewhere on that prop, the Dia and Pitch should be shown

 

[jimmbo]

I can't find any reference to OD 12 20 on Solas site. Was that prop new or a rebuilt?