D&D's Mean Machine Sport

[ReddyWatts]

Why is that fluid? Theoretically a 2 bladed prop is more effecient.

[D&D]

I think I've proven for my setup that a smaller diameter prop is probably better. I have pitched up the X440-3 prop, reset the COG so that is not quite so much on the edge, and will change the Controller timing from 7 to 9. Will let you know how it does later today.

[D&D]

Oh, I ment to reply on my last about 3 bladed props. I usually ran three bladed props in my past life because I thought the boats ran smoother and better for racing. But on my 60 Sprint Cat is was definetly faster with a worked X455-3 blade, however; a Prather 260 or 262 was the clear choice for the 90 Sprint Cat. Bottom line, I actually think it os all about the exact boat you are running and it's all around setup. I can't quote sience to you, just the results from running many different cat boats.

[ReddyWatts]

I have experienced the same, just cant explain why. I am seeing large catamarans with 5 blade props. ???

[D&D]

Afternoon results disappointing. Strut flat with the bottom of the boat, COG a little forward from the 57.3mph run, timming up from 7 to 9. Results: X440-3 - the boat was bouncing until top end and that could have been the COG of my bad pitching on the blades 57.6mph. X442 - the boat liked the COG better and ran 57.0mph. Temps were up across the boat, it was very hot here today 92 degress, but it was probably the adjustment to the motor timming.

Results on the X440-3 may have improved some at a different COG setting. I'm going to trim up the X442 and try that, but I'm more hopefull about other props I will have to get after I get back to Indiana.

[Fluid]

Why is that fluid? Theoretically a 2 bladed prop is more effecient.

Theory is nice, but it is results that matter. Even the fastest full-scale boats usually use 3-bladed props. The two fastest FE boats in the world ran 3-bladed props to set their records.

We often have more power than we can get to the water, we need blade area to transfer that power. With two-bladed props you get more blade area by increasing diameter...but that can cause terrible prop walk which hurts top speed. Three-bladed props can have enough blade area without an excessive diameter.

Now two-bladed props can certainly perform very well, but they hold no real advantage because of some imagined "efficiency". Again - what works works.


.

[ReddyWatts]

So, there is less slippage with a 3 blade when using high power and rpm on a surface drive?

[DISAR]

I don't know so much, but Fluid's opinion is very correct. I guess yes, 3 blade props have less slippage

[D&D]

I decided to set the controller timing back to "Normal/7" to cool things back down to preserve my equipment and ran the boat again yesterday. I moved the cog back and the boat ran beautifully at 57mph on the X440-3 prop, I really justed enjoyed the attitude of the boat it looked great.

I also ordered the Y537-3 prop and a backup X440-3 from OSE and will work on those props and test them back in Indiana. Anybody here from northern Indiana? Rochester is my home town.

[kevakov]

D&D, where are you setting the COG , I need to know for the Jagermeister MM I just finished?. I have heard that its anywhere from 8 to 8 1/2 to 9 1/4 . Guess it really depends on the exact weight of the hull with different motors and lipos that that have different weights to them. I'm going to start at 8 1/2 from the transome.

[D&D]

I started somewhere around 9 and one-half inches, but understood that the COG would vary widely based on the specific boat, batteries, and everything else mounted in the boat. I have been well forward of that with larger props and well aft of that with smaller 3 bladed props. Use it as a starting point, but be sure you built into your boat the capability to move the COG freely by leaving space for the batteries to move. In my example I built in a board and velcroed it the length of the hatch opening.

Good luck.

[Fluid]

The optimum CG will depend on the weight of the boat, its power level/speed and the strut position, but mine generally runs best between 8.75" and 9.25".


.

[kevakov]

Thanks for the info, I'm hoping for mid to upper 50's for this hull.

[RIPFENCE]

great looking boat man...i am testing a mm myself but i do not have a good range of props to test with YET...i am curious about your x440 3 blade..i just bought one to try too

[Joe M]

Hi i just built mean machine with same set up motor 15151y hydra 240 prop m445 4s on the second run about one min. in to run blew one of the cap wright out of the esc need help thanks Joe M