Blackjack testing data
 

So I got out today to do some more testing. I had 5 props to test, 2 pipes, strut settings, and a few other things. Started out OK but got run off by duck hunters. Moved locations and had the boat cut off way out and had to wait for a boat to bring it in (long story, normally have a jet ski or kayak..)

Here are the results thus far with 1" pipe and strut at 7mm:

X-472-47 mph, 16,320 rpm

X-572-37 mph, 15480 (may have been binding)

X-670-43 mph, rpm???

P-275-46 mph, rpm? (no tach, last weekend, strut 5mm)

Went to a 2" and lost 2000 rpm with all of them

Seems like it wont pull anything other than the 472. With it, the boat was violent, hard to drive, and floating on air. All the others it was lazy, and would not get on the pipe.

Do I need more prop out of the water for the 72mm 2 blades that I am running?

RE: Blackjack testing data
 

472 seems to have been your best prop there. Setup for that should be between 9.5 mm and 6 mm gap between sponsons and prop shaft ferrule. 6 being 70% and 9.5 being 60% of the radius in the water. I'd be starting at 60% and working my way down. I've expect that the 2" should be usable you just need to find the right length for it. For me it's 14" to the end of the band or 13" to the center.

RE: Blackjack testing data
 

There is no way to get 9.5 mm...................the stuffing tube would almost be on the bottom. I tried to bend it up a little but it wont move. Guess I need to get aggressive with it. Is it normal to have to move it up that far? I would think more prop out would slow the boat down, but I guess if it gains 1000-1500 rpm it may pickup.

RE: Blackjack testing data
 

How are you measuring?

Also did you make sure your setup was neutral?

RE: Blackjack testing data
 

Everything is neutral.

Measuring from the bottom of the collar on the flex shaft to the table with the boat flat on it.

RE: Blackjack testing data
 

What is the maximum gap you can get?

RE: Blackjack testing data
 

About 7. Any more binds the flex shaft against the top of the stuffing tube.

RE: Blackjack testing data
 

Whats is worth to lose the clutch?

RE: Blackjack testing data
 

I don't have any data to support it either way. The con's are a spinning prop that you need to be aware when launching the boat and you'll need to develop the toss technique to prevent it from stalling when it hits the water. The pro's are less moving parts to break, less weight to spin up should mean quicker to rev and you can ditch the water pump.

I miss starting it floating in the water but other then that it's no big deal. My clutch failed early on due to poor manufacturing standards. One of the stand offs that holds the clutch bell frame was shorter then the others causing it to place the clutch bell at an angle other then perpindicular to the output shaft. This lead to a premature failure of the brazed joint between the bell and the square cable receiver.

Fewer parts to break is always a plus.

RE: Blackjack testing data
 

So far my best results have come with the strut at 5mm. You really do need to get a 6717/3 or a 7016/3 prop. My best pipe length has been 12 3/4 to center (RCMK stock 5hp). Did you only test the props or did you move the strut any?

RE: Blackjack testing data
 

Got run off before I had a chance to move the strut.......................wouldnt go higher without binding anyway.

RE: Blackjack testing data
 

Try moving it up and down as much as the stuff tube will let you before bending it.