Prop and what does what

[Nason]

On a fishing prop from the hub to about 1" from the tip of blade (elephant ear tip) what does this control ? Slip?
On the tip of the blade (elephant ear part) about 1" to center what does tip cup control? More lift?

[zul8tr]

Your question is a bit difficult to understand. So to start read here for some basic background then ask.

http://www.mercurymarine.com/propellers/about/overview/

[pdt]

the very first inch nearest to the hub is what is starting to bite the water, thus this is the start of the pull forwards.
the very last inch is what is best to say is what is leaving the blades and can be sort of described like the wind of the back of a car spoiler,
the actual angle the blades are set at is what defines bow lift or transom lift.

you need the prop guru's to explain it fully, but be warned its not a short story, its very complex, but realy good to read.

[omcstratos]

the very first inch nearest to the hub is what is starting to bite the water, thus this is the start of the pull forwards.
the very last inch is what is best to say is what is leaving the blades and can be sort of described like the wind of the back of a car spoiler,
the actual angle the blades are set at is what defines bow lift or transom lift.

you need the prop guru's to explain it fully, but be warned its not a short story, its very complex, but realy good to read.

I think you are wrong about that. The first inch nearest the hub doesn't bite before any other part of the prop. The entire leading edge is what "bites". That's why pitch is perpendicular to the line from the hub to the tip of the blade. It is just due to "angular velocity" that you have to have more cupping nearest the hub.

You might be confusing pitch with rake

[pdt]

the first inch is the nearest to the hub , that's also nearest to the gearbox and also the nearest bit that bites due to this area has the water being pushed away from the gearbox
causing the drag etc.
this area is under more pressure from the very outset,if not then why would all these race guys look for the thinnest gearboxes etc like the little ones on the omc .
the entire leading edge is not a straight line on most props,its actualy curves if you look at it.
the blade itself also curves unless we are talking home made old fashioned blades.
you do not have more cup nearer the hub neither, go look again and youl see its not more near the hub.
im sitting here looking at a prop right now to make sure im 100%correct.
if this was true then how could cupping be simply added to a prop ? many people have added more or less cup to a prop at the river bank when testing.
you can buy many props that do not have cupping at all, then have them cupped, or even double cupped !!!!!!!

your confusing the blade itself being thicker at the hub, this is because its the area with the most strain, it has to not only to do the work like other parts of the blade but has to
keep the entire blades outward energy from ripping the blade from the hub,
Blade to hub is a very dodgy area to thin down, as this can be lethal if it goes wrong.
im sure there is plenty of people in the racing fraternity who have seen a blade tear from the hub of a prop, I have only seen it once and hope never to see it again.

Oh and pitch is not a constant the entire length of blade, don't ask me how I know this, ask ron he can explain that better.

[omcstratos]

the first inch is the nearest to the hub , that's also nearest to the gearbox and also the nearest bit that bites due to this area has the water being pushed away from the gearbox
causing the drag etc.
this area is under more pressure from the very outset,if not then why would all these race guys look for the thinnest gearboxes etc like the little ones on the omc .
the entire leading edge is not a straight line on most props,its actualy curves if you look at it.
the blade itself also curves unless we are talking home made old fashioned blades.
you do not have more cup nearer the hub neither, go look again and youl see its not more near the hub.
im sitting here looking at a prop right now to make sure im 100%correct.
if this was true then how could cupping be simply added to a prop ? many people have added more or less cup to a prop at the river bank when testing.
you can buy many props that do not have cupping at all, then have them cupped, or even double cupped !!!!!!!

your confusing the blade itself being thicker at the hub, this is because its the area with the most strain, it has to not only to do the work like other parts of the blade but has to
keep the entire blades outward energy from ripping the blade from the hub,
Blade to hub is a very dodgy area to thin down, as this can be lethal if it goes wrong.
im sure there is plenty of people in the racing fraternity who have seen a blade tear from the hub of a prop, I have only seen it once and hope never to see it again.

Oh and pitch is not a constant the entire length of blade, don't ask me how I know this, ask ron he can explain that better.

Ok, i meant progressive pitch rather than cupping

[pdt]

I think we get the usa / uk English problems ha ha

its strange how we say the same things yet mean different, I get it a lot when im on usa sites.

we are on the same path, just slightly apart ha ha

[champ20B]

On a fishing prop from the hub to about 1" from the tip of blade (elephant ear tip) what does this control ? Slip?
On the tip of the blade (elephant ear part) about 1" to center what does tip cup control? More lift?

Hello. This is what it is: The leading edge is not necessarily the entire length of the side to the tip (opposite of the trailing edge), but rather the first edged part of the blade that is the closest point to the beginning of the hub. The rest of this edge is the "slice", easy to figure. The theoretical pitch is relatively the same from the hub to the tip of the blade, however there looks to be a twist from a side view. This is due to relative pitch angle from the center axis point of the prop.((as example; the angle of the blade will be steep on whatever pitch, closer to the center compared to a less agressive angle farther toward the blade tip)). That is because the circular travel is of farther distance toward the tip, compensating for a lesser angle of blade, less around toward the center needing a steep angle. Now, as for the concavity in a prop blade(high pressure side), this is what a progressive pitch is. Theoretically, this is supposed to work like a variable load design. The leading edge is a shallow angle to pull off the load whereas the trailing edge becomes steep to gradually direct the water more aligned to the axis in relation, thus increasing speed capability. Now, the little curled up rim at the trailing edge toward the tip, is your cupping. What that does is to hold water on the blade like a river dam, so as to reduce cavitation. This is if you run the prop blades partially out of the water for performance operation. Now, as you look at the prop from the side, the blades may seem to lean toward the rear at the tip. If they do, as some props dont have this design, this would be referred to as "rake". This is to direct rearward in a more concentrated angle of thrust (or smaller diameter) thus having longer blades at the lead and slice. It also helps in the angle of hull planing for performance purposes. I hope this helps.

[Fastjeff57]

Excellent write up! Into the Keeper File it went.

Jeff

[pdt]

what is Double cupping ?

ive heard this said many many times, and cannot understand how you can double cup a single blade.

someone here will probably explain it nice and easy..
or is a double cupped prop just a bit more agressively cupped than normal ?
looking on the net there is too many different answers, and most don't know their arse from their elbow.

[champ20B]

what is Double cupping ?

ive heard this said many many times, and cannot understand how you can double cup a single blade.

someone here will probably explain it nice and easy..
or is a double cupped prop just a bit more agressively cupped than normal ?
looking on the net there is too many different answers, and most don't know their arse from their elbow.

Cupping is a curled up lip @ only a few degrees (around [3] I suppose). This helps to hold water on the blade when it is running out of the water a bit, and adds a theortical increase of pitch around (+1) inch.This is to simply increase efficiency with less slip. This is not to be looked at as a speed increase, but as an RPM reducer of approximately 200 RPM. Double cupping is something that is not often seen, as it is a very aggressive cup that can be up to twice the standard. It would be a good idea to discuss it with a propeller expert from a reputable shop, if one feels that a regular cupping isn't sufficiently doing the job. Double cupping can "otherwise" have a very negative effect on performance. I hope this answer is accurate.

[pdt]

yeah already know what cupping was, just never sure what people meant by double cupped.

[fs5]

a lot of guys run double cup over here for racing in the surf and soppy offshore stuff.