in theory

[river_ratj40]

my question is concerning jet pumps, but it would relate to props as well. Thats how I will state the question.

If two boats were identical, and two motors were identical, and two props were identical, in theory, those props turning the same rpms would produce the same speed, right?

is that statement right?

disclaimer- i do understand that there will always varibles, no two boats, motors, props, are exactly the same

but if you take the varibles away and only look at the same two props turning the same amount of rpms, one would think that the speed would be similar.



(reason for asking, two flat bottom jon boats, turning the same size impeller, the same amount of rpms (according to tach) was 10 mph different on top end, and the weight of the two boats were very similar.)

[ima75man]

my question is concerning jet pumps, but it would relate to props as well. Thats how I will state the question.

If two boats were identical, and two motors were identical, and two props were identical, in theory, those props turning the same rpms would produce the same speed, right?

is that statement right?

disclaimer- i do understand that there will always varibles, no two boats, motors, props, are exactly the same

but if you take the varibles away and only look at the same two props turning the same amount of rpms, one would think that the speed would be similar.



(reason for asking, two flat bottom jon boats, turning the same size impeller, the same amount of rpms (according to tach) was 10 mph different on top end, and the weight of the two boats were very similar.)

set-up, would play a part,maybe at least 5-7 mph.

[genea01]

my question is concerning jet pumps, but it would relate to props as well. Thats how I will state the question.

If two boats were identical, and two motors were identical, and two props were identical, in theory, those props turning the same rpms would produce the same speed, right?

is that statement right?

disclaimer- i do understand that there will always varibles, no two boats, motors, props, are exactly the same

but if you take the varibles away and only look at the same two props turning the same amount of rpms, one would think that the speed would be similar.



(reason for asking, two flat bottom jon boats, turning the same size impeller, the same amount of rpms (according to tach) was 10 mph different on top end, and the weight of the two boats were very similar.)




is the motor height and you said the boats are the same right

[MHARDEE]

my question is concerning jet pumps, but it would relate to props as well. Thats how I will state the question.

If two boats were identical, and two motors were identical, and two props were identical, in theory, those props turning the same rpms would produce the same speed, right?

is that statement right?

disclaimer- i do understand that there will always varibles, no two boats, motors, props, are exactly the same

but if you take the varibles away and only look at the same two props turning the same amount of rpms, one would think that the speed would be similar.



(reason for asking, two flat bottom jon boats, turning the same size impeller, the same amount of rpms (according to tach) was 10 mph different on top end, and the weight of the two boats were very similar.) Switch props if higher speed follows prop , difference is in prop , if it does'nt then its in boat (bottom ,set-up, etc )IF YOUR TALKING IMPELLERS , IF ONE HAS A WORN WEAR RING AND IMPELLER , WILL MAKE A LOT OF DIFFERNCE

[50hptiller]

yes in theory they would, all things being equal. the first enemy is drag.....reduce it as much as possable. you said boats and setups were similar, that leaves a lot of room for differances. study the faster boat closely. a little bit of change can do a lot......a fiend had a jetski that sucked up some rocks and ate up the impeller, so he file'd it smooth and lost a 1/4" dia, it wouldn't even plane off .. good luck

[fyremanbill]

The theory is correct. The difference in performance tells you that something is not set up the same between the 2 boats.

[river_ratj40]

"Or the faster omc has some mercury parts on it"


this could be the answer to it..................:p (hope not)


and i completely understand how the set up, height, drag, impeller, even motor variations are completely different.

i was just making sure (in a perfect world) that they should be the same.

thats my research, to see what is different between the fast boat and the slow boat.

thanks guys

[zul8tr]

my question is concerning jet pumps, but it would relate to props as well. Thats how I will state the question.

If two boats were identical, and two motors were identical, and two props were identical, in theory, those props turning the same rpms would produce the same speed, right?

is that statement right?

disclaimer- i do understand that there will always varibles, no two boats, motors, props, are exactly the same

but if you take the varibles away and only look at the same two props turning the same amount of rpms, one would think that the speed would be similar.

(reason for asking, two flat bottom jon boats, turning the same size impeller, the same amount of rpms (according to tach) was 10 mph different on top end, and the weight of the two boats were very similar.)

-------------------------------

Well of course if all were identical and they were run at the same time on identical water and wind conditions with identical drivers they would theoretically have the same speed. But the variables are real and can't be neglected.

1st water drag is the biggest killer of speed since it has a density about 780 times greater than air, theoretically for the same representative area, drag coefficient and velocity the water will have about 780 times greater drag force. So as already stated reduce water drag.

2nd as also stated the setup is critical, motor height and angle, weight, position of weight.

3rd aerodrag reduction

4th motor condition

5th prop needs to be right for the setup, a trial and error process to get it right.

[david bryan]

does one propeller flex More than the other

[Mark75H]

If they were discussing props, I'd say it was probable and maybe even likely ... but this thread regards jet pump impellers.

[Bill Van Steenwyk]

All other things being equal as you state, what if there was damage of some type in the intake, other internals, or thrust section of the impeller housing that was disturbing the water flow and consequently the speed/efficiency of the water column being expelled. I would think that the interior housings (made of aluminum?) could be very much affected by sand, dirt or other foreign material sucked into the housing along with the intake water, thereby eroding the interior of the housing, the impeller, and otherwise affecting the outflow of the pump, reducing velocity and decreasing speed.

Possible?, I don't know for sure, but it sounds plausible if everything else is exactly equal as has been previously mentioned, especially about the drag of water over a surface.

[50hptiller]

do yall do anything to reduce the amount of aireated (caint spell) water coming off the back of the boat? it seems to me if you could reduce that then you could raise the motor to just before the intake breaks the surface and reduce pump housing drag...also what about a "skid plate" from the back side of the intake to the underside of the pump all the way to the back of the output? do yall run a trim system on the back of the pump?..... dunno just a thought.... i never seen one up close of got to play with one but i sure been looking at em