Mean Machine Catamaran (Sport)

[txboatpilot]

Wet sponsons versus running on the last few inches can mean 5-10 mph more speed.

I have never seen a Skunky hull, it may be a great design or it may be stinky. The MM, while heavy, has excellent design features and can carry the weight very well with enough power. This is due to the wide tunnel, the tunnel entry and the sponson bottoms. That weight helps in rougher water, which is really the cat's forte anyway.

Tx, how is the attitude of the cat when making passes? Is it flat, or is it runing on the back of the sponsons? Your speed with the CF45s is about right for a boat that is running tight. Try to fly it higher and see if the speeds increase. Move the CG back and angle the drives with 1-2 degrees up at the back end - do it with the boat on a flat table, not "by eye" just holding the hull. If turning is compromised, just chop the throttle for an instant as you begin the turn, then feed in throttle. That will drop the bows and let you turn tighter.

I run in a oval mostly, no straight line stuff.. I like to practice in my local ponds, as if there were a oval course..Skunky was running on the last 5-7" of the sponsons.. I will try your tips! My first test run was 33mph and I did not have a lipo warmer! My lipos were cold, I am going to pick up a heater to pre-heat them next time..

[Fluid]

It can be confusing trying to compare two different catamaran hulls, even with the same approximate lengths. The design of the tunnel and sponsons can make a huge difference in speeds, even with the same motor/cells. Too, how high do you fly the hull when making "speed" passes? Wet sponsons versus running on the last few inches can mean 5-10 mph more speed.

I have never seen a Skunky hull, it may be a great design or it may be stinky. The MM, while heavy, has excellent design features and can carry the weight very well with enough power. This is due to the wide tunnel, the tunnel entry and the sponson bottoms. That weight helps in rougher water, which is really the cat's forte anyway.

Tx, how is the attitude of the cat when making passes? Is it flat, or is it runing on the back of the sponsons? Your speed with the CF45s is about right for a boat that is running tight. Try to fly it higher and see if the speeds increase. Move the CG back and angle the drives with 1-2 degrees up at the back end - do it with the boat on a flat table, not "by eye" just holding the hull. If turning is compromised, just chop the throttle for an instant as you begin the turn, then feed in throttle. That will drop the bows and let you turn tighter.


.

[SJFE]

On Robby76's first run with his 2-10XL, 2-16 cell twin cat was running 32 mph,

I didn't know Rob had a MM. The only cat I ever seen him run was his big old kyosho conversion. I will have to look him up cause now I'm confused..lol...Like thats a rare thing hahahahah.

[txboatpilot]

I would be interested in buying the two SV motors.

I am going to hang on to them until I get another Ammo 36-50-2300...

[txboatpilot]

The hull Mr Watts is refering to is almost 40 inches if my memory serves me. You should be mid to high 40s on a 30 cat around 10 pounds with your setup easy. Heck my Jolly was mid 40s on 16 nimh @ 8 pounds 5 inches longer than the MM.

I thought Reddy was refering to the M/M.. It is 29" long...

[ReddyWatts]

I would be interested in buying the two SV motors.

[SJFE]

The hull Mr Watts is refering to is almost 40 inches if my memory serves me. You should be mid to high 40s on a 30 cat around 10 pounds with your setup easy. Heck my Jolly was mid 40s on 16 nimh @ 8 pounds 5 inches longer than the MM.

[txboatpilot]

The weight savings wont be enough to offset the weight of the Hull...IMO.... M/M are heavy hulls compared to most DF, H&M, and skunkworks.. I would like to see you try it, but even with 4S1P, i dont see it doing more than 35mph with x447's... I will run a 4S1P in the SK-II, just too see what the gps says..

[ReddyWatts]

I was going to run it on a single lipo for both motors in parallel, since they use around 40 amps each. Half of the weight. 4S1P. I thought that was the big advantage of using SV 4-pole motors. I would not give up on it yet, it just does not add up.

You really need to adjust the struts on the twin. On Robby76's first run with his 2-10XL, 2-16 cell twin cat was running 32 mph, then he adjusted his struts for a big increase in speed. It ended up going 43mph in a 42" 12 pounder. It is a cool sounding boat.

Use bigger props. ABC props has a better selection of L/R props.

Play with the CG.

The twin props should turn inward for more speed.

[txboatpilot]

I think another cool "sport" setup for the Mean Machine would be to install two Super Vee motor/esc combos with a dual prop drive (X447'S) on one set of 14 cell NiMH batteries. It should run in the mid forties. 50's on 4s lipos???

The 2 - 6 pole motor setup should be very reliable. Use a little longer rudder than normal.

http://www.offshoreelectrics.com/pro...d=dh-blcomboaq

Reddy, I built a twin cat with 2/SV27 motor and esc combos. The hull is a Skunkworks 30" cat.. I ran it on 2/4S1P lipo's 3700mAH, they are about the same weight as 14cells... I put the gps in with CF45's counter rotating, and got a best of 33 mph.. I have s&b x447's to try, but I think with all the extra weight it needs a higher KV motor.. I am switching the motors out to Ammo 36-50-2300's to see if that will get it over 40mph?? I have other props, so I can always go down.. Here is a the thread on the twin..http://forums.offshoreelectrics.com/...ead.php?t=2400

[ReddyWatts]

Results of the 60 mph Mean Machine setup.

Fluid

I run the 1521/1D in my Mean Machine spinning an m440 on 4S and it does ~60 mph for 6 laps on a 1/8 mile course. Nothing gets very hot, and it uses around 3600 mAh of capacity. It certainly does not draw 200+ amps, its closer to 125 amps.

[Rex R]

bump (suggestion, sticky this thread)

[ED66677]

No Craig 8XL has less torque than 10XL
Max rpm is 50000 and 70000 with ceramic bearing

[Craig]

So the smaller the number 8xl has more torque than a 10xl? What is the max you can spin an xl motor? C

[ED66677]

Craig, a 10XL under 21 cell will spin more than 41000rpm and give a max power of 1660Watt at 66amp, witch is enough, if you need more power you need to use then a 9 or 8XL, less turn more amp and higher KV, but increasing cell count increases rpm you will then reach a situation where you spin fast, drain many amp, but spin a very small prop, if the prop is too small it won't be able to transfert the 1660watt from the power plant to the water, a reasonable (as far as I know) slip between prop and water is around 15%, this mean a 2" pitch prop will move a boat of 2" minus 15% of 2" (hope my frenglish is clear enough), in this particular case the slip will considerably increase 30-40% (I guess), so you will have plenty of power but will only waste it, because the prop is just not able to!
So you need a bigger prop and the only way with a 10XL under 21cell is to use gear

As steven said use a bigger motor KB45 8XL that has a lower KV but a lot more torque, you will avoid the gear, and you'll have the possibility to double the available power... and so for 10 extra bucks!