gregjones

Hi Folks,

I am running a 1.1 meter Hobby King Vantage with leopard 4082-1500KV, 180A Turnigy ESC and 2 x 5000mah 3S 30-40C batteries in series.

The prop I have is an Octura X447.

A mate has a nitro boat on a similar size hull and he has fitted a three blade prop and it seems to have improved performance.

Can I do something similar and if so what are the implications for the set up?

Which prop would you recommend for the set up?

Thanks

Goldenduff

I'm a plane guy, hopefeully not in both senses.......but from plane props

If you change the prop you will change the load on the components. I think 3 blade props are in general less efficient. Why not go for a bigger 2 bladed prop? If you want to go faster (run times will be shorter) and you keep the voltage the same (same 3cell 11.1v) to get more power you must increase the amp draw.

Your 30C pack can theoretically safetly put out (30C x 5000mah= 150amps). I would treat this figure (150amps) as very optimistic for two reasons. Manufacturer's hype and the less stress you place on the lipos the more cycles you will get. Your ESC is rated at 180amps. Obviously pick the lower number of 150amps and take away a safety margin, call it 120amps max draw.

All you have to do is change the size of the prop until you are drawing around 120amps. The larger the diameter the more thrust/acceleration, the larger the pitch the faster top speed.

That's how to do it with a plane, I think heat is a bigger problem for you so keep an eye, or finger! on the motors and ESC. Beef up their cooling.

Good luck! 

Von Ohain

Power wise, adding an extra blade is roughly the same as adding to the diameter.
I'm also a plane a guy, and what the rule of thumb on planes is that adding an extra blade is the same as adding 2.5 to 5 centimeters to the diameter of an airplanes propeller (within the size range commonly used for rc planes).
I guess its the same principle for boat.

Efficiencywise, 3 blades is worse than 2 blades.
Noise wise, 3 blades is better than 2 blades.
And this latter reason, together with propeller ground clearance, is why especially powerful and large models often prefer 3 or more blades.

I also "heard" that 3 blades give the boat more stability than 2 blades.
Im not sure if there is any truth to that.
Personally I have experienced better stability on my 3 blade prop, than on some 2 blade props.
But I have also seen better stability from 2 blade prop to 2 blade prop, so this trait can be due to other factors aswell as far as I know.

gregjones

Thank you for your reply.
As I am running two of these batteries in series does that mean everything is doubled? So am I risking blowimNg my esc as surely I must be 5000 x 30c = 150 amps x two = 300 amps which should blow he 180 rated speed controller.

Or have I got it wrong.?!
thanks for your wisdom

gregjones

Thank you. I will play about bit

TheFridge189

I know on full size boats, that 3-blade prop is much smoother in the water. I also know that A 3-blade prop will result in better acceleration vs a 2 blade prop, however the 2 blade prop is better at speed because it doesnt have that 3rd blade creating drag in the water. Don't know if this applies to rc, but I know its the case with the full-size boats!
Nikko

Goldenduff

I think te only performance gain your friend got with the 3 blades perhaps better quality prop and more current draw. You could achieve the same by increasing a reputable prop's size until you reach a determined amp draw. Increase pitch for speed and Siam for acc.

Diesel6401

My Feedback: (1)

If you have of the same props in diameter i.e x447 and x447/3 the 3 bladed will have quicker acceleration and hold speed in the turns better trade off is slighty higher amp draw. The 2 bladed will typically have higher top end and pull less amps then it's 3 bladed brother. I also fly, and comparing/using the same thought process on boats that you use in planes you'll prob end up smoking something on the boat. They are 2 different animals and should be treated as such.... JMHO

Von Ohain

When you plug your batteries in series, you double your voltage but not the mAH rating.
If you want to double your mAH & C rating, you must put your batteries in parallell.
Putting them in parallell will, in turn, not double the voltage.
If you want to double both voltage and mAH & C rating, you need 4 battery packs.
2 and 2 packs in parallell, wich is then coupled in series.

Goldenduff

In parallel you will double the mah but I don't think you will double the C rating?

Von Ohain

True. My bad. You will double the maximum amp draw, but not the C rating.

Goldenduff

Doubling the max amp draw in effect doubled the C rating?

Von Ohain

Max amp draw = C * mAH
If you parallell two equal packs, you double your total mAH rating, and hence also total amp draw

The C rating stays the same, total mAH rating and total max amp draw does not.
If you got two 5000 mAH 30C packs in parallell, or one 10000 mAH 30C pack, its effectifely the same thing.

Internal resistance also halves when you parallell two packs.
Internal resistance doubles, if you put two packs in series.

Goldenduff

I'm glad I said I wasn't sure as I stand corrected!

srt10

My Feedback: (20)

Oh my goodness!
pulling 120amps cont would give you only about 2min runtimes.. and hot motor and esc for sure

the performance of the prop depends on size, either it be 2 blade or 3 blade
I like to run a tad smaller 3 blade vs 2 blade and it gives my boats a better ride...
but most of my props are 2 blade
I think I'm upto 25-26 props right now [:-]

Goldenduff

I agree, the original post asked about inc performance. This would generally reduce run times (unless your performance judging criteria are endurance). I was just giving the workings for max performance as anything less will be safe.

srt10

My Feedback: (20)

??????
it comes down to setup with your strut as well..
telling someone to pull X amount of amps on a FE setup is not the right way to build a FE boat, specially when your suggesting max amounts IMO
these are not planes that you get static thrust on the ground and then they float around and pull much less amps in the air while in flight..
they have constant drag and pull lots of amps running in the water, and most of the time WOT
two different beasts

Goldenduff

Fair enough. I never told him to run x amps.  Just what would be safe. Think I mentioned cooling would be an issue. Obviously many more considerations if anyone chooses to run a maxed out modification.

gregjones

thanks for all the info. I swapped my octura prop x447 for an x 648.  Result was a snapped flex shaft within about 10 seconds!

Hydro Junkie

Going from a 400 series to a 600 series added at least 50% more rotational drag on the prop due to the higher pitch. If you have been hitting high 40's with the 400 series, try cupping the tips a little for that "extra boost". Just out of curiosity, how thick was the flex cable that broke? If it was less than a .187, it was too thin to handle that kind of prop load. I won't run less than the .187 on my .18, .21 and .45 powered boats and use a .250 on my .67 nitro powered scale boats. Anything running gas power I'd also use a .250 cable.

gregjones

The flex shaft is 4mm. Sorry but I don't follow your measurement sizes.

Hydro Junkie

Sorry, I didn't notice you were on the other side of the pond. That being said, let me make it easier to understand:
An X400 has a pitch that is 1.4X diameter
An X600 has a pitch that is 1.6X diameter
By going from a 447 to a 648 your pitch increased from 65.8 mm to 76.8 mm. This probably increased the torque on the flex cable enough to snap it
On the flex cable sizes, a .187 cable is 4.5 mm while a .250 is a 6 mm, both being standard sizes in the States. For my boats that are powered by 3.0 to 7.5 cc, I run the 4.5 mm cable while anything larger, including my 11 cc powered scale hydroplanes, I run the 6 mm cable just to prevent cable breakage