Prop polishing?

[egneg]

I would have to say that a polished prop doesn't give u anything because its already spinning so fast that it doesn't make a difference whether its polished or not, anybody correct me if I'm wrong! That's just a guess from me

Do what you like ... It won't make enough of a difference to matter.

[mtbenjamin77]

scuffing the bottom of the boat creates a thin layer of air pockets on the bottom of the boat. the boat is actually riding on air, not water, thus reducing friction/drag. the prop however needs the friction to move the boat forward, atleast on one side, the face of the blade. the back of the blade doesn't move the water. I polish the face of the blade and satin finish the back. this helps the face of the prop grab and move the water, the satin finish on the back side helps reduce drag and allows the prop to spool up.

[T.C.]

I don't mean to hijack the thread, just curious as to what the reasoning some have for not polishing ?
I would think a non polished surface would promote air bubbles and thus cavitation ?
I would also think any and every little speed trick you could think of would add up in the end ?
It's the whole combination not just one part that makes these run and the prop is a big part of the combo.
What do real boats do ?
T.C.

[Megabiker98]

My dads (real) boat prop is polished both sides. I think it's mainly all just preference and what u like

[hydro_pyro]

In the "real world" of performance boats, the fastest props have a fine satin finish created by straight grit lines in the direction of water flow over the blade. Polished props are only for cosmetics.

[skidbump]

Satin Finish

In the "real world" of performance boats, the fastest props have a fine satin finish created by straight grit lines in the direction of water flow over the blade. Polished props are only for cosmetics.

I have been working on surfboards for 20 years and this is what the science behind a sanded/satin finish is in the pro surfing world(should apply to any hard surface to water scenario)

A sanded/satin finish causes water to stick to the surface of the object, the idea is that water on water is less resistance than a water to surface scenario, so effectively, having a sanded finish will cause a water on water planning effect, this should be the slickest way for any object to pass through water. Hope that makes sense.

[martin]

Skidbump your spot on re scuffed surfaces on hull bottoms, the scuffed surface allows a thin membrain of water to attach to the hull surface. So you end up with the water attached to the hull sliding over the lake water rather than a shinney surface of the hull which has more drag.

[kevinpratt823]

scuffing the bottom of the boat creates a thin layer of air pockets on the bottom of the boat. the boat is actually riding on air, not water, thus reducing friction/drag. the prop however needs the friction to move the boat forward, atleast on one side, the face of the blade. the back of the blade doesn't move the water. I polish the face of the blade and satin finish the back. this helps the face of the prop grab and move the water, the satin finish on the back side helps reduce drag and allows the prop to spool up.

Maybe I'm reading you wrong, but this doesn't make sense to me. The back(rear) of the prop is the part moving the water, not the face. It throws the water back and outward, creating the thrust cone, and when this is happening, the face of the blade (in a partially submerged prop anyway), is making very little if any contact with water because as soon as it hits the surface it is scooping water and throwing it back. This is precisely why when balancing props we remove material from the face, not the back, so as to avoid effecting the pitch. It is the pitch of the prop and the sharpness of the leading edges more than anything that count, and also the thickness of the blades, not so much the surface. The idea is to allow the prop to cut through the water with little resistance, allowing the pitch to move water back, not create friction.

[domwilson]

I've found that McQuires Mag wheel polish works great.

[hydro_pyro]

Maybe I'm reading you wrong, but this doesn't make sense to me. The back(rear) of the prop is the part moving the water, not the face...

Indeed, you're reading it wrong. When someone talks about the "face" of the blade, it's the side of the blade that exerts force upon the water. The term "back side" of the blade refers to the low-pressure side which is facing forward, so the term can be confusing. Material is generally removed from the "back side", while preserving the shape of the "face."

[kevinpratt823]

Indeed, you're reading it wrong. When someone talks about the "face" of the blade, it's the side of the blade that exerts force upon the water. The term "back side" of the blade refers to the low-pressure side which is facing forward, so the term can be confusing. Material is generally removed from the "back side", while preserving the shape of the "face."

Thank you for clarifying, what is your interpretation on the whole "the prop however needs the friction to move the boat forward, atleast on one side, the face of the blade."
that sounds counterproductive to me.......? Unless you were looking to widen the thrust cone.........

[Heaving Earth]

so many theories ive heard over the years. ive tried polishing and not polishing without any noticeable difference between the two.

[Rumdog]

Yup. Polishing is just wasted energy. Looks nice though.

[martin]

Yes you would be better off spending the time doing something more productive on a boat else where than bothering with highly polished props, they do look nice but i wouldnt bother. Just making sure their nice & sharpened & balanced does me.

[mtbenjamin77]

Skidbump your spot on re scuffed surfaces on hull bottoms, the scuffed surface allows a thin membrain of water to attach to the hull surface. So you end up with the water attached to the hull sliding over the lake water rather than a shinney surface of the hull which has more drag.

What you're talking about is called laminar flow. But the issue is not really drag its that the hull needs to be able to freely separate from the water.