Gen

05

05

Gen

05

05

Dic

22

22

Scratch Built hull, water jet and cooling pump made from Coroplast and junk Yellow Boat 3 Power Test

Cooling pump testing here

Test results

Dynamic losees

29.5 Watts

2.3 Amps

Peak power

532 Watts

47.5 Amps on a 3C

Impeller

30 X 30 two blade

Quite pleased with test results pretty good match motor to impeller it seems. Tried a 30 X 35R impeller which drew too much current the 30 X 30 seems just about optimal.

Test results

Dynamic losees

29.5 Watts

2.3 Amps

Peak power

532 Watts

47.5 Amps on a 3C

Impeller

30 X 30 two blade

Quite pleased with test results pretty good match motor to impeller it seems. Tried a 30 X 35R impeller which drew too much current the 30 X 30 seems just about optimal.

Home brew cooling small centrifugal pump made from junk, with a scoop on the hull. The pump is mounted directly above the scoop and primes its self with the standard trim at rest.

I also found that if I re-introduce the out let from the cooling circuit into the jet ramp, there is a tendency for the water to be sucked through by the main drive when the throttle is up thus improving cooling flow at high loads, a win win. I wanted a pump because taking a tap from the pressure side of the jet outlet uses some thrust and is only available at speed, with low throttle or stopped there is no flow and this I thought would cause over heating when stopping after a long high power burst, which I do when surfing at Sumner.

The tiny pump on test

The cooling circuit. I found that if I re-introduce the out let from the cooling circuit into the jet ramp it helps with coolant flow.

Turnigy 450 H2218 Brushless outrunner 2100KV with water cooling added, big bore pipes just because that the brass I had in stock.

I also found that if I re-introduce the out let from the cooling circuit into the jet ramp, there is a tendency for the water to be sucked through by the main drive when the throttle is up thus improving cooling flow at high loads, a win win. I wanted a pump because taking a tap from the pressure side of the jet outlet uses some thrust and is only available at speed, with low throttle or stopped there is no flow and this I thought would cause over heating when stopping after a long high power burst, which I do when surfing at Sumner.

The tiny pump on test

The cooling circuit. I found that if I re-introduce the out let from the cooling circuit into the jet ramp it helps with coolant flow.

Turnigy 450 H2218 Brushless outrunner 2100KV with water cooling added, big bore pipes just because that the brass I had in stock.

Spec.

Model: 2218

Turns: 6

Cells: 2~4S

Kv: 2100rpm/V

No load Current: 1.9A/10V

Max power: 500W

Weight: 67g

Shaft diameter: 3.17mm

Dimensions: 27.2 x 36.5mm

Recomended ESC: 2~4S/50A

Hobbyking SS Series 90-100A ESC with a water cooling plate added its an overrated ESC so should do the job easy. Will need a BEC I have a 5A in stock also.

Spec.

Spec.

Weight: 85g

Size: 70x50x13mm

Cells: 2-7S Li Po

Max Current: 90A [over 70A use 6S only]

Burst : 100A

No BEC

Generally the larger jet is much more effective at lower throttle in the bath, this will be better for trolling in the swamp. On the lake speed remains to be seen, but I can't believe it will be disappointing given the flow and power levels I'm getting on test. I suppose its possible the nozzel velocity is lower than the NQD jet, that said I have read that if the ratio of nozzel velocity is greater then 6:1 then all will be well with the world.

Given the area increase from 3.14159 cm² to 4.818 cm² which is an area increase of 1.533 at the same nozzel velocity the mass flow would increase by 1.533 times.

So every second the following would seem to add up

So as we know the NQD 20 mm jet pushed around 950 grams on Yellow Boat 1, the nozzel velocity must be around 3.023 Meters / Second with no losses? This is where I get into the realm of I don't understand :O fluid dynamic being so complex, although non compressible fluids like water are less complex mathematically than the calculations for air for example

Just for fun with an exhaust velocity of 22.5 Meters per Second that's around 80 kph

Every second a bar of water from the 20 mm jet has a volume of 7069 cm³ So the mass flow would be 7.069 Liters per second so 7.069 Kgs sec

Every second a bar of water from the 30 mm jet has a volume of 10841 cm³ So the mass flow would be 10.841 Liters per second so 10.841 Kgs sec

## Definition from Wikipedia

So transpose the above to make kg the subject

With no losses I recon 500 Watts could move 22.22 Kgs to 22.5 Meters a second in one second. Sounds like a lot of water 22.2 Liters Umm???

However the impeller is probably only 60% efficient this is true in air a turbine can only be 59.8 % efficient its called the Betts limit I think.

So 22.2 X 0.6 = 13.33 umm 13 Liters a second sounds like a lot ?

One way to test this is to measure the amount of water the pump moves over a fixed period of time, simple then to workout all the things we want to know.

Generally the larger jet is much more effective at lower throttle in the bath, this will be better for trolling in the swamp. On the lake speed remains to be seen, but I can't believe it will be disappointing given the flow and power levels I'm getting on test. I suppose its possible the nozzel velocity is lower than the NQD jet, that said I have read that if the ratio of nozzel velocity is greater then 6:1 then all will be well with the world.

Given the area increase from 3.14159 cm² to 4.818 cm² which is an area increase of 1.533 at the same nozzel velocity the mass flow would increase by 1.533 times.

So every second the following would seem to add up

So as we know the NQD 20 mm jet pushed around 950 grams on Yellow Boat 1, the nozzel velocity must be around 3.023 Meters / Second with no losses? This is where I get into the realm of I don't understand :O fluid dynamic being so complex, although non compressible fluids like water are less complex mathematically than the calculations for air for example

Just for fun with an exhaust velocity of 22.5 Meters per Second that's around 80 kph

Every second a bar of water from the 20 mm jet has a volume of 7069 cm³ So the mass flow would be 7.069 Liters per second so 7.069 Kgs sec

Every second a bar of water from the 30 mm jet has a volume of 10841 cm³ So the mass flow would be 10.841 Liters per second so 10.841 Kgs sec

One watt is the rate at which work is done when an object's velocity is held constant at one meter per second against constant opposing force of one newton.

So transpose the above to make kg the subject

With no losses I recon 500 Watts could move 22.22 Kgs to 22.5 Meters a second in one second. Sounds like a lot of water 22.2 Liters Umm???

However the impeller is probably only 60% efficient this is true in air a turbine can only be 59.8 % efficient its called the Betts limit I think.

So 22.2 X 0.6 = 13.33 umm 13 Liters a second sounds like a lot ?

One way to test this is to measure the amount of water the pump moves over a fixed period of time, simple then to workout all the things we want to know.