Speedmaster 20 mono, good day testing

[Andy Brown]

Ian, Good questions and no they are not taken as an attack, but I've got a busy day so I won't be able to respond until later.

 

[Terry Keeley]

Here's some data with the exact same prop but with a little thinner LE and a ton of cup added:

Taking the 1st 5* of the LE as 5.0", the slip is 8.0% and 7.8% respectively. Curves are much smoother, as was the boat!

 

[Ian Inverarity]

Here's some data with the exact same prop but with a little thinner LE and a ton of cup added:

Taking the 1st 5* of the LE as 5.0", the slip is 8.0% and 7.8% respectively. Curves are much smoother, as was the boat!

Terry, looks like a very useful speed improvement, seems you are touching record speeds now! Peak RPM had come down a bit too.

 

[Andy Brown]

Ian,

The progression is needed for one purpose. To maintain blade contact with the water. The prop is a screw. But the water is not solid. When the LE penetrates the surface it screws itself forward according to the pitch of that LE. However, because the water is not solid it gets forced rearward by the initial contact of that LE. So, if the first 20% of the blade forces the water it just contacted rearward, then then next 20% of the blade must have a little more pitch to maintain contact with the water that is moving rearward. The heavier, more high drag hulls require more progression because the water is pushed back faster. Just like spinning your wheels in the dirt! Also the closer the prop is to the surface the more that progression is needed, because the water at the surface offers little resistance. A long prop that runs deep will require less progression because the water is more "solid" down deep.

I ran 114 mph with the Twin 84 using stock full blade 2170's. The progression of those props is no more than 10%, but since I used them at the full 70 mm length they still hooked up and pushed the boat well. If I had cut them to 60mm I would have had to add cup to get the same 114 mph speed.

In conclusion, I only view the prop as the screw that it is. A screw turning into steel does NOT have to accelerate steel backwards to create thrust in order to move itself forward. Nor does a propeller. It only needs something to push against. I this case water. Again because the water tries to move "out of the way" rearward) the pitch of the blade must ever increase to maintain contact with that small mass of water that is moving in the opposite direction (rearward).

Andy

P.S. Ian, I will actually agree that the rearward moving water can be explained with the Mass X Velocity = Thrust equation. The Mass of water is a constant according to the blade area of the prop. So in order to get more thrust (force to push the boat), water must be accelerated to a certain Velocity. This final Velocity becomes the TE pitch times the RPM if the prop is progressed properly. The heavier and more drag the hull, the more the final water Velocity must be. This Velocity of the water is initiated by the LE contact according to the resistance of the hull. The more resistance, the faster the water moves rearward and the more progression of the blade that will be needed to continue contact with the moving water.

So, an LE of 4.0" and a TE of 6.0" @ 28,000 rpm would net out a boat speed of 106 mph( 4.0" X 28K / 1057) The final water Velocity off the TE would be 6.0" X 28K / 1057 = 160 mph.

So in fact the water would move rearward in relation to the boat at 160 mph minus 106 mph = 54 mph.

Andy,

Thanks for taking the time to explain your thoughts on the workings of pitch progression! I am having trouble with some points tho.

In terms of the analogy of a screw into metal, the screw does have constant pitch, or of course it would bind up! But also if the screw had only one turn of thread it would pull itself into the steel with the same thrust (actually more as less torque would be wasted in friction). On the other hand, cut away most of a prop but the LE (which is suggested screws itself into the water) and apart from the obvious structural problems, the prop wouldnt screw itself thru water at the same speed. From the above I would think you would suggest that would be because the prop would not be contacting the water moving back from LE contact?

This is correct Ian, assuming the prop has progression to suit the needs of the boat. So in that instance the boat would slow down. However, let's also look at a prop that had little or no progression such as a Octura 1400 series. It is vey possible to cut away half of a 1400 blade and the boat will not loose any speed.

I wish to understand the mechanism by which water would move away from the working face of the blade after initial contact with the LE. Surely to move away from the working face of the blade which is increasing in pitch means the water must actually be accelerating away from the prop?

Ian, the water would move away from the blade ONLY IF THE the blade DID NOT have enough progression.

What makes it accelerate after it is no longer in contact with the blade?

Nothing! It was the initial LE contact that made the water accelerate to a certain Velocity that can exceed the pitch on the remainder of the blade

What makes it accelerate in response to the drag load of the boat, ie more acceleration with more drag load?

The next time you are at the lake, walk to the waters edge with a 12" steel ruler in hand. Hold one end of the ruler in your hand with your had just above the waters surface and the ruler extended forward in front of you. The ruler should be near parrale to the surface. Now turn the ruler in your has so that it is twisted about 40 degrees. You now have a prop with a long narrow 12" blade and your hand is the hub of the prop. Now snap your wrist to cause the ruler to strike the surface of the water. You will observe several things. #1. YOu will feel the ruler try to pull your hand forward in the direction of the rules pitch. #2. You will see a certain amount of water slash off the surface in a backward motionat a high velocity. #3. You will see water swell up from below the surface and move in the rearward direction. This ruler is straight with NO progression, yet is made the water accelerate away from itself. This is because the rule could not move forward ( screw itself) because it is firmly connected to the ground through your body. If the ruler (or a prop) could spin through the water on it's own and had only it's own mass to move forward it would push very little water backward and move forward with almost 100% efficiency.

Looking at the example raised of the full blade stock 2170's running 114mph and 2170's cut down to 60mm. If the blade chord of the 2170 is reduced as the diameter is reduced then the total progression of the cut down prop is reduced. But the rate of change of pitch on the prop remains the same, that is the pitch change from one 5 degrees of measurement to the next 5 degrees stays the same, as this hasnt been changed by cutting away blade area.

So on the same boat making the same drag load surely the water would move away from the blades at the same rate? So why would the rate of pitch increase on the full blade 2170 be adequate, but inadequate on the smaller blade where the rate of pitch increase is still the same?

Because the water at 30mm deep is not as "Solid" as the water at 35mm deep.

Why would the water move away from the working face of the smaller blade faster?

Because the water at 30mm deep is not as "Solid" as the water at 35mm deep.

Surely the smaller blade needs to have its pitch increased because it is moving less mass of water, so needs to accelerate that smaller mass a greater amount to create the same thrust?

This point can also be viewed such that the lower mass of water is more easily moved rearward by the initial LE contact and the Mass X Velocity = Thrust equation appears to apply both ways.

I hope my questions are not taken as an attack, I certainly dont mean them to be taken that way!

I have been currently working with someone testing very narrow blades with very little progression (10% or less). The result are interesting and may add more to ponder.

Andy

Ian.

 

[Andy Brown]

Here's some data with the exact same prop but with a little thinner LE and a ton of cup added:

Taking the 1st 5* of the LE as 5.0", the slip is 8.0% and 7.8% respectively. Curves are much smoother, as was the boat!

Or 0% slip if your LE face is 4.6"! If it's less than 4.6" then you are still plowing water with the face and you're using up H.P on the TE. to make it happen.

Great to see your speeds go up Terry!

 

[Terry Keeley]

Or 0% slip if your LE face is 4.6"! If it's less than 4.6" then you are still plowing water with the face and you're using up H.P on the TE. to make it happen.

Great to see your speeds go up Terry!

Thanks Andy, ten years later & we're finally starting to catch up! :lol:

Haven't checked the face (back side) yet but I did thin the LE down a fair bit.

It's easy to have it sharp but another thing altogether to have it thin too. B)

 

[Terry Keeley]

Here's some data with the exact same prop but with a little thinner LE and a ton of cup added:

Taking the 1st 5* of the LE as 5.0", the slip is 8.0% and 7.8% respectively. Curves are much smoother, as was the boat!

Terry, looks like a very useful speed improvement, seems you are touching record speeds now! Peak RPM had come down a bit too.

Thanks, my new crew chief is much better than the one I fired last week! :lol:

 

[Ian Inverarity]

Andy,

Thanks for taking the time to explain your thoughts on the workings of pitch progression! I am having trouble with some points tho.

In terms of the analogy of a screw into metal, the screw does have constant pitch, or of course it would bind up! But also if the screw had only one turn of thread it would pull itself into the steel with the same thrust (actually more as less torque would be wasted in friction). On the other hand, cut away most of a prop but the LE (which is suggested screws itself into the water) and apart from the obvious structural problems, the prop wouldnt screw itself thru water at the same speed. From the above I would think you would suggest that would be because the prop would not be contacting the water moving back from LE contact?

This is correct Ian, assuming the prop has progression to suit the needs of the boat. So in that instance the boat would slow down. However, let's also look at a prop that had little or no progression such as a Octura 1400 series. It is vey possible to cut away half of a 1400 blade and the boat will not loose any speed.

I wish to understand the mechanism by which water would move away from the working face of the blade after initial contact with the LE. Surely to move away from the working face of the blade which is increasing in pitch means the water must actually be accelerating away from the prop?

Ian, the water would move away from the blade ONLY IF THE the blade DID NOT have enough progression.

What makes it accelerate after it is no longer in contact with the blade?

Nothing! It was the initial LE contact that made the water accelerate to a certain Velocity that can exceed the pitch on the remainder of the blade

What makes it accelerate in response to the drag load of the boat, ie more acceleration with more drag load?

The next time you are at the lake, walk to the waters edge with a 12" steel ruler in hand. Hold one end of the ruler in your hand with your had just above the waters surface and the ruler extended forward in front of you. The ruler should be near parrale to the surface. Now turn the ruler in your has so that it is twisted about 40 degrees. You now have a prop with a long narrow 12" blade and your hand is the hub of the prop. Now snap your wrist to cause the ruler to strike the surface of the water. You will observe several things. #1. YOu will feel the ruler try to pull your hand forward in the direction of the rules pitch. #2. You will see a certain amount of water slash off the surface in a backward motionat a high velocity. #3. You will see water swell up from below the surface and move in the rearward direction. This ruler is straight with NO progression, yet is made the water accelerate away from itself. This is because the rule could not move forward ( screw itself) because it is firmly connected to the ground through your body. If the ruler (or a prop) could spin through the water on it's own and had only it's own mass to move forward it would push very little water backward and move forward with almost 100% efficiency.

Looking at the example raised of the full blade stock 2170's running 114mph and 2170's cut down to 60mm. If the blade chord of the 2170 is reduced as the diameter is reduced then the total progression of the cut down prop is reduced. But the rate of change of pitch on the prop remains the same, that is the pitch change from one 5 degrees of measurement to the next 5 degrees stays the same, as this hasnt been changed by cutting away blade area.

So on the same boat making the same drag load surely the water would move away from the blades at the same rate? So why would the rate of pitch increase on the full blade 2170 be adequate, but inadequate on the smaller blade where the rate of pitch increase is still the same?

Because the water at 30mm deep is not as "Solid" as the water at 35mm deep.

Why would the water move away from the working face of the smaller blade faster?

Because the water at 30mm deep is not as "Solid" as the water at 35mm deep.

Surely the smaller blade needs to have its pitch increased because it is moving less mass of water, so needs to accelerate that smaller mass a greater amount to create the same thrust?

This point can also be viewed such that the lower mass of water is more easily moved rearward by the initial LE contact and the Mass X Velocity = Thrust equation appears to apply both ways.

I hope my questions are not taken as an attack, I certainly dont mean them to be taken that way!

I have been currently working with someone testing very narrow blades with very little progression (10% or less). The result are interesting and may add more to ponder.

Andy

Ian.

Andy, you have explained your theory quite clearly now, thankyou! We will have to agree to disagree tho. For example the difference in absolute water pressure between 30 and 35mm depth is about 0.05%, and each blade is only at full depth at one part of the rotation, quite a bit of the rotation is at shallower depths. Where the blade enters the water the depth will be pretty much the same.

I am interested in your opinions on diameter and blade area versus pitch progression. On the example of the stock 2170's that ran 114mph, you suggested if the props were cut down to 60mm they would need cup or pitch added to reach the same speed. But could the smaller prop be made to go faster with cupping? What is ultimately faster, larger blade area with less progression or smaller blade area with more progression? Or is the question not that simple, ie it may be that larger/less progression is better for the SAW runs but not as good for heat racing? For my own heat racing boats, mostly monos for a few years, I have worked on larger blade area and less cup to try to maintain corner speed and good acceleration out of turns. But if the LE pitch is the same, the thrust=mass x acceleration means that blade area and pitch progression can be traded off against each other to produce the same amount of thrust, so it should be possible to achieve good acceleration with smaller blades and more cup and still have the same speed?

Ian.

 

[Ian Inverarity]

Thanks, my new crew chief is much better than the one I fired last week! :lol:

Terry, what's next from the crew chief, 2175 cut down to the same size for higher LE (and back face LE) pitch?

Ian.

 

[Tom Foley]

Andy , is n't the roostertail evidence of some slip ? Don't see how you could have a zero slip situation with a fluid .

 

[Terry Keeley]

Thanks, my new crew chief is much better than the one I fired last week! :lol:

Terry, what's next from the crew chief, 2175 cut down to the same size for higher LE (and back face LE) pitch?

Ian.

There's more there for sure, even with this prop.

The new guy only had a couple shots at the track before conditions went away. B)

 

[Tim_Duggan]

I noticed this thread had dropped off the front page - can't have that just yet!!!

This is correct Ian, assuming the prop has progression to suit the needs of the boat. So in that instance the boat would slow down. However, let's also look at a prop that had little or no progression such as a Octura 1400 series. It is vey possible to cut away half of a 1400 blade and the boat will not loose any speed.

Andy,

I'm glad you raised the subject of removal of blade area. I often wondered about this particular aspect all on it's own. We often sacrifice blade area when cutting props to increase L/E or back-cutting to remove steep area's of T/E cup, but wondered if there was any ramifications? (not unlike compromising plug height to maintain TCR and squish area on Head buttons)

Is the amount of blade area itself (mostly distance from L/E to T/E) a critical component to characteristics and efficiency also, or if it is purely there to get the appropriate required L/E, T/E, and pitch progression without requiring abrubt changes to pitch progression?

Would props such as the 1400 Octura's with very little or no progression benefit from massive removal of L/E area, just from the perspective of less blade area rather than any increase to L/E pitch?

 

[Marty Davis]

I noticed this thread had dropped off the front page - can't have that just yet!!!

This is correct Ian, assuming the prop has progression to suit the needs of the boat. So in that instance the boat would slow down. However, let's also look at a prop that had little or no progression such as a Octura 1400 series. It is vey possible to cut away half of a 1400 blade and the boat will not loose any speed.

Andy,

I'm glad you raised the subject of removal of blade area. I often wondered about this particular aspect all on it's own. We often sacrifice blade area when cutting props to increase L/E or back-cutting to remove steep area's of T/E cup, but wondered if there was any ramifications? (not unlike compromising plug height to maintain TCR and squish area on Head buttons)

Is the amount of blade area itself (mostly distance from L/E to T/E) a critical component to characteristics and efficiency also, or if it is purely there to get the appropriate required L/E, T/E, and pitch progression without requiring abrubt changes to pitch progression?

Would props such as the 1400 Octura's with very little or no progression benefit from massive removal of L/E area, just from the perspective of less blade area rather than any increase to L/E pitch?

Tim:

Interesting observations....

If you would like to analyze the way that ANY blade is working and the areas on the surface that are working hard and those that are hardly working, spray the blade with Dikem Red Dye and run the blade enough that the red wears off. You will quickly see the areas that you can remove by looking at the dark red areas. It is also useful to see if you have a gradual bend for increasing pitch. If you find areas where there is a red stripe, it indicates cavitation there.

 

[Tim_Duggan]

Tim:

Interesting observations....

If you would like to analyze the way that ANY blade is working and the areas on the surface that are working hard and those that are hardly working, spray the blade with Dikem Red Dye and run the blade enough that the red wears off. You will quickly see the areas that you can remove by looking at the dark red areas. It is also useful to see if you have a gradual bend for increasing pitch. If you find areas where there is a red stripe, it indicates cavitation there.

Thanks Marty (and Happy Birthday also!)

Have you performed that Dikem test on an Octura 1450, and if so, was there any noticable difference to the dye in the area just after the L/E and the centre of the blade (the zero progression area, just before where pitch is added to ramp up to the trailing edge)?

Tim

 

[Ian Inverarity]

Tim:

Interesting observations....

If you would like to analyze the way that ANY blade is working and the areas on the surface that are working hard and those that are hardly working, spray the blade with Dikem Red Dye and run the blade enough that the red wears off. You will quickly see the areas that you can remove by looking at the dark red areas. It is also useful to see if you have a gradual bend for increasing pitch. If you find areas where there is a red stripe, it indicates cavitation there.

Marty,

The areas where the Dikem remains would indicate that the water is not contacting that part of the blade properly? Would this indicate excessive concavity? If so, how would removing material from that area help?

Ian.

 

[Andy Brown]

I obviously got distracted away from here back in Nov. 19, 2010. No time to continue this in depth subject now (no pun intended), but in the coming weeks I will make time to pick up on this discussion.

Good Boating,

Andy