HotPursuit

I was thinking the same wow!! 4200 prop speed = 141.6 somthing off.

pbam22

I didnt need 1300 to turn 1.24 when I had the boat . I 1000 turned them fine wt 38 merc props .Im the one who change that boat to 1.24 from 1.36 I wanted better top end and got it . AJ

CcanDo

The rule of thumb some use as a start size for prop pitch is,diameter x 2= pitch or 16 1/2" x 2=33" pitch.

One formula for finding speed follows;Prop pitch divided by gear ratio, divided by 12",then that number divided by 5,280 ft. (one mile),then that number times 60,provides a factor. The factor is then multiplied by any engine RPM to find speed,with no consideration for slip.

I've been of the opinion,the prop blade is most efficient when it enters the water at a 90* and most parallel to forward motion. In other words,minimum pitch and taller gears,subject to available torque and horsepower,at reduced engine RPM.

The 40" pitch vs. a 33" has the blade flatter to the water,therefore doesn't the 40" require more time to plane and have less acceleration? Granted,the properly cupped and raked 40" should produce bigger top speed numbers. However,in sprint application,the smaller pitch is my personal preference.

I'm still curious about the 1.24 GEARING possibly turning harder than other ratios ???????

CAL MAN

all i can say is that boat was a rocket

bripar77

I may be off sometimes with RPM's vs. speed as I have not really had the chance to go out and focus on just testing. Should be able to go out and really do some testing now that most or all of the bugs are worked out. One thing nobody has mentioned is that in Salt Water (I think where AJ ran the boat mostly) I am guessing the boat sits a little higher in the water so that may effect Prop size and speed. Is that true? This boat does run good but it does take some time to get up to speed. Also I usually run at Lake Mead and Lake Havasu and it is hot and dry, meaning last weekend between 110 and 118 most of the day. This does rob power no doubt. I have also been hesitent to really run this up past 5300 just because of soem issues we have had with the motors and I wanted to boat the whole weekend. I also run 30% race fuel to 91 Octane and 5 lbs of boost before last weekend when we bumped it up to 7 lbs. We had a problem with bolts used for the pully's being to long and I lost one pully off of each motor and of course the belt. The bolts of course sheared off and it was Thursday night before 4 th of July. Got lucky and found somebody with some parts on the 4th of July in Havasu City. But that took all day.

plumbers crack

theres no way to figure out where you will be until you dial it in with an honest wide open run.Until your gremlins are straightened out and you can achieve wide open throttle you have no base at which to start from.If the boat is sluggish, it could be motor issues timing, or who knows what.We have almost the same boats and mine is a rocket.Yes im running 1;35 gears but old mercury 4 blades no less.I have been getting the small bugs out and have made some decent passes but im not done yet.Im looking for 5 blades and I will post when I run them.

Pro1

Those 4 blades vibrate.

Joe

...just ran the same trap, but between 1.29's and 1.35's. Either will work exceptionally well. The choice is 160+ MPH w/ a bit less mid-range or 145+ MPH w/ MASSIVE mid-range(and still the abiity to put on larger 5 blades to hit the 160's, taking it much, much longer to get there). After speaking with quite a few of the well known guys, I chose the 1.35's, and will do two sets of props (16 1/2 x 36's & smaller diameter 40's, which will be difficult to get on plane, but will hit the top speeds on the "Havasu" type, flat water, long straights poker runs).

Hope that helps.

PS: running the merc 1075's for power

joe

bripar77

Joe are you going to run that boat on Texoma? I am thinking about making atrip there in August to check out the area and run the Skater. Any suggestions?

GATORONE

What RPM's were you turning big daddy