this rig is awesome

Thinking of using this motor http://www.hobbyking.com/hobbyking/s...ner_Motor.html and this ESC http://www.hobbyking.com/hobbyking/s..._w_5A_BEC.html ALL comments good and bad are welcome. Thanks.

What are your speed goals? What voltage are you intending on using? That is a pretty small boat and will be stability-challenged with too much power. I'd aim for 15,000 rpm maximum on the prop speed, so for different voltages these are approximate Kvs and prop sizes:

2S = ~2000 rpm 9x6
3S = ~1350 rpm 10x5
4S = ~1000 rpm 10x6

Props are estimates from power calculators, the ideal prop for your application will depend on your packs, motor quality and ESC.

My latest 34" airboat runs 4S with a 13x6" prop on an older Scorpion 4020-8 motor I had laying around. I haven't tried to prop it for top speed, but it runs in the high 30s with the conservative prop. It uses a pair of .40-sized plane floats and a length of PVC pipe for the "fuselage". Two goals were to keep water out of the prop when running and keeping the airflow clean both into and out of the prop to maximize thrust and efficiency. Both goals were achieved. It looks a bit unconventional, but is not without precedent...

Zozer, thanks for the input. It' a little under 24" and I was going to run a 1450kv motor on a 3S battery (this is what I already have). This is right in the range you are recommending. The prop I was thinking of a 9 x 6 APC, What do you think?. I would like it to run in the high 30's to low 40's mph.

Depending on the motor's size and quality, that prop should give you around 4.4 pounds of thrust at 13,300 rpm and 50 amps, with a pitch speed of 76 mph. Your actual speed will be lower and totally dependent on cell quality and boat design/setup. I'd say it is a very good starting point.





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Originally Posted by zozer

What are your speed goals? What voltage are you intending on using? That is a pretty small boat and will be stability-challenged with too much power. I'd aim for 15,000 rpm maximum on the prop speed, so for different voltages these are approximate Kvs and prop sizes:

2S = ~2000 rpm 9x6
3S = ~1350 rpm 10x5
4S = ~1000 rpm 10x6

Props are estimates from power calculators, the ideal prop for your application will depend on your packs, motor quality and ESC.

My latest 34" airboat runs 4S with a 13x6" prop on an older Scorpion 4020-8 motor I had laying around. I haven't tried to prop it for top speed, but it runs in the high 30s with the conservative prop. It uses a pair of .40-sized plane floats and a length of PVC pipe for the "fuselage". Two goals were to keep water out of the prop when running and keeping the airflow clean both into and out of the prop to maximize thrust and efficiency. Both goals were achieved. It looks a bit unconventional, but is not without precedent...

G'day Zozer,

I like the concept! Where'd you source the floats?

Stretch1

G'day Zozer, I like the concept! Where'd you source the floats?

They'd been sitting around for a couple years, I got them on-line at one of the airplane parts sites like Maxford RC.

http://www.maxfordusa.com/hz-40-fiber-floats.aspx




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Now have the deck glued on, and the main sponson supports epoxyed on. Each of the main sponsons are going to be 1 1/2" further away from the tub then the plans call for to add a little more stability. Also received the rest of the parts for the back. The water intake on the rudder (for the ESC) is a little more then 1/2" below the rear sponson (doesn't look like that in the photo). I am finishing up with the waterproofing (Z-poxy finishing resin) on the deck. Will be about a week before I can get more wood and build the main sponsons, and then start painting.

Have the left main sponson built. Top still needs sanding. I was going to have 1 clear hatch cover all the way across the boat. I decided to make 2 for easier access to battery. They will still be clear. Because of balancing I am going to have to move motor stand from the back to the middle of the boat.

This set up type for all out speed, sponson width helps cancel out prop torque.

Originally Posted by Amp Abuser

This set up type for all out speed, sponson width helps cancel out prop torque.

Your motor mount looks pretty cool. By sponson width do you mean how wide each sponson is or how far apart they are?

Yes the natural design of a rigger having a wide stance up front, others have taken advantage of this with air props. Having the prop in the front of the CG of anything will increase stability allowing more speed in your case without blowing off the water. You should consider a vertical stab in the back if decide to over power the rigger. Say 1500watts as you have a ton of room in the tub for batts with room to move them in the right spot for a cg of 1.5 / 2in behind the sponson.

Notice in the vid a rigger with the prop behind the cg tends to cause adverse steering and of course enjoy a 75mph run with a brushless outrunner.

http://www.youtube.com/watch?v=BhbaulMN_Q8

Originally Posted by Amp Abuser

Yes the natural design of a rigger having a wide stance up front, others have taken advantage of this with air props. Having the prop in the front of the CG of anything will increase stability allowing more speed in your case without blowing off the water. You should consider a vertical stab in the back if decide to over power the rigger. Say 1500watts as you have a ton of room in the tub for batts with room to move them in the right spot for a cg of 1.5 / 2in behind the sponson.

Notice in the vid a rigger with the prop behind the cg tends to cause adverse steering and of course enjoy a 75mph run with a brushless outrunner.

http://www.youtube.com/watch?v=BhbaulMN_Q8

Both front sponsons are now built and epoxyed on. The stance up front (inside of sponson to inside of sponson) is 3 1/2" wider then the plans call for (it's 13" instead of 9 1/2"). Amp Abuser, I am taking your advise and putting the prop in front of the CG. By moving motor stand more towards the front I can now adjust the CG from about 3/4" to about 3 3/4" behind the sponson just by moving the battery. The motor I will be using is 1450kv and 655watts. I will be using a 3S battery. I will run a 4S battery later. The prop is a 9 x 6 apc "style" electric. I am still playing around with adding a vertical stab (or 2 - 1 on each side of hatch).

9x6 should shoot the rigger out of the hole with authority just the top end wont be as peachy. I would imagine you will bust 40 mph. Given the motor kv you should see 12k + at full pull on the striaghts. Can you source a metal shop an have them cut out you an aluminum motor mount?

APC E 9x6