Prop experts opinion needed

[GlennN]

I currently have an aluminum 11 1/8 X 13 prop on my ‘99 640lx. It has some damage from previous owner. I’m looking to replace it with the exact same prop measurements and same brand since it seems to perform really well. In shopping the brand I currently have I’ve found I can do an exact swap in aluminum or upgrade to a stainless at only a $60 difference. Here’s the question my partner in crime is bringing in. Since there is no or less flex in stainless how much of a difference in performance could or would this make?

 

[Major Mark]

when I had my Opti 115 and switched alum to SS, I dropped from a 19 to 17 pitch

 

[Cyco]

You should get a better holeshot. The other thing to think about is if you fish an areas where you think you may hit something, stick with aluminum.

 

[byron cooley]

when I had my Opti 115 and switched alum to SS, I dropped from a 19 to 17 pitch

I am assuming that you have a 50hp?

 

[byron cooley]

I am assuming that you have a 50hp?

Meant for major mark

 

[byron cooley]

Meant for major mark

Oops glennN

Meant for major mark

 

[Starbanker]

I currently have an aluminum 11 1/8 X 13 prop on my ‘99 640lx. It has some damage from previous owner. I’m looking to replace it with the exact same prop measurements and same brand since it seems to perform really well. In shopping the brand I currently have I’ve found I can do an exact swap in aluminum or upgrade to a stainless at only a $60 difference. Here’s the question my partner in crime is bringing in. Since there is no or less flex in stainless how much of a difference in performance could or would this make?

SS props are far better. What you get is thinner and better cupped. Props have a high and low pressure side, the back of the blade has low pressure which causes the water to boil at lower temps which is the cause of cavitation. Cavitation will damage the rear surface of the blade and decrease performance. Cupping the blade (additional curves to the primary curvature) decreases the prop's cavitation tendencies. Aluminum isn't strong enough to allow much cupping. The word cavitation is often misused, what I just described is cavitation, ventilation is when air is introduced in front of the blade. The flat plate above your prop is sometimes called an anti-cavitation plate, it is an anti-ventilation plate to prevent your prop from pulling air down from the surface into the prop. SS props are usually much more expensive. They also are more durable and repairable. Aluminum prop edges are blunted easily just from water alone, much more so in shallow water where the prop will pull up sand from the bottom. Aluminum props are easily damaged from cavitation, you can see this in pitting on the back side of aluminum props and the more pits the worse the cavitation gets.

 

[byron cooley]

What motor is on your 640LX

 

[GlennN]

SS props are far better. What you get is thinner and better cupped. Props have a high and low pressure side, the back of the blade has low pressure which causes the water to boil at lower temps which is the cause of cavitation. Cavitation will damage the rear surface of the blade and decrease performance. Cupping the blade (additional curves to the primary curvature) decreases the prop's cavitation tendencies. Aluminum isn't strong enough to allow much cupping. The word cavitation is often misused, what I just described is cavitation, ventilation is when air is introduced in front of the blade. The flat plate above your prop is sometimes called an anti-cavitation plate, it is an anti-ventilation plate to prevent your prop from pulling air down from the surface into the prop. SS props are usually much more expensive. They also are more durable and repairable. Aluminum prop edges are blunted easily just from water alone, much more so in shallow water where the prop will pull up sand from the bottom. Aluminum props are easily damaged from cavitation, you can see this in pitting on the back side of aluminum props and the more pits the worse the cavitation gets.

Wow, that’s why I ask. Incredible amount of knowledge in there. Thank you!

 

[GlennN]

What motor is on your 640LX

50hp 2 stroke Mercury

 

[byron cooley]

50hp 2 stroke Mercury

Can't really help you with that one although 13 pitch sounds about right.
My 640LX has a modified 75hp optimax and has no problem spinning a 22 pitch Laser II to 5650 rpm

 

[GlennN]

Can't really help you with that one although 13 pitch sounds about right.
My 640LX has a modified 75hp optimax and has no problem spinning a 22 pitch Laser II to 5650 rpm

No problem, I just stuck with running what I had at least for this year. Thanks