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Old Sep 06, 2012, 06:19 PM
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davecrash's Avatar
Canada, ON, Newmarket
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Whats the max rpm?

I converted my Impulse 26 to brushless, Being new to the boats I was wondering what rpm's I should be looking to stay under for prop performance and life of the flex shaft.
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Old Sep 06, 2012, 06:40 PM
I feel the need for speed!
scorpion1's Avatar
Southern U.S.
Joined Jun 2008
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Sport boating is generally in the 20,000 - 25,000 range, 25,001 - 33,000 for racing, and above that for saw.................

My opinion here as the ranges vary depending on who you ask.
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Old Sep 07, 2012, 02:51 AM
Boaters are nice people.
Sneek, Netherlands.
Joined May 2004
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Hi Dave,

What motor did you convert to?
What's the Kv?
Which battery do you use?

Regards, Jan.
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Old Sep 07, 2012, 11:42 AM
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davecrash's Avatar
Canada, ON, Newmarket
Joined Nov 2006
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Quote:
Originally Posted by pompebled View Post
Hi Dave,

What motor did you convert to?
What's the Kv?
Which battery do you use?

Regards, Jan.
I first used a HK B36-55 1800kv, I burnt out that one with a cooling issue and now have a SK3 1900kv. I have a bunch of Zippy 40C in various cell sizes. I was using 6S but was unable to hold full throttle on the 1800kv. I'm going to try 4S and 5S on the next run.
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Old Sep 07, 2012, 12:53 PM
Boaters are nice people.
Sneek, Netherlands.
Joined May 2004
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Hi Dave,

If you horse around at partial throttle, it doesn't matter what motor you select, they will all get very hot that way.
Speedboats like to run full throttle in wide sweeping turns.

With the 1800Kv at 6S you have close to 36.000 rpm under load, for a 26" monohull that's a lot!
As you were not able to run full throttle, I suspect the prop was too big, what did you turn with 36000rpm?

The 3655 has a rather short can, combined with cooling issues and running partial throttle, death by overheating was pre-programmed.

The Turnigy SK3 is only marginally longer and being a ducted fan motor, this one also needs a fitting watercooling jacket, or you'll burn that one up aswell, if you keep horsing around half throttle, fourpole or not.

I'm running this motor in the slightly bigger Arowana:
http://www.hobbyking.com/hobbyking/s..._Inrunner.html
On 4S and a 45 mm alu threeblade, the boat is on the edge.
The motor temperature is barely noticable, but I make 6 minute full throttle runs.

If you play with the propsize (start small: 35 mm, and work your way up) and make sure the watercooling works, I'm sure you can get your Impulse to behave.

Regards, Jan.
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Last edited by pompebled; Sep 07, 2012 at 03:29 PM. Reason: Hull size corrected.
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Old Sep 07, 2012, 02:12 PM
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davecrash's Avatar
Canada, ON, Newmarket
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I tried it today on 4S and 5S with the SK3 1900kv. 4S was fun but 5S was crazy fun, I couldn't hold full throttle on the 5S lol. I'm using the stock prop on the Impulse which is a 26" hull btw. It's a stock 2 blade prop, numbers on it are 4019. I will assume that means a 40mm diameter and 19 pitch. I'm using a silicone water jacket but had a problem with water flow when it was on the B36 motor. The rudder pick up i added wasn't working, I wanted seperate lines for the ESC and motor. on the SK3 today it was cool after both runs.
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Old Sep 07, 2012, 03:32 PM
Boaters are nice people.
Sneek, Netherlands.
Joined May 2004
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Hi Dave,

What happens if you keep full throttle on 5S?

Why is there water in the boat, don't you tape the hatch?

Regards, Jan.
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Old Sep 07, 2012, 03:54 PM
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davecrash's Avatar
Canada, ON, Newmarket
Joined Nov 2006
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Quote:
Originally Posted by pompebled View Post
Hi Dave,

What happens if you keep full throttle on 5S?

Why is there water in the boat, don't you tape the hatch?

Regards, Jan.
It wants to lose control, it gets right out of the water then cavitates.
I noticed water in it after the run, Didn't see any cracks or obvious reasons for the water so i decided to check the cooling system. Pumping water through it at home i noticed water coming from between the jacket and motor. That's the pic over the sink.
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Old Sep 08, 2012, 09:46 AM
Boaters are nice people.
Sneek, Netherlands.
Joined May 2004
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Hi Dave,

What prop did you use on the 4S and 5S testruns?

If you had the same prop on both occasions, it's no wonder you're having handling issues, as at 31.500 rpm under load, you are seriously on the edge of what an ABS hull this size will take without reinforcing the hull to eliminate the flex in the bottom.

I'm not sure what happens according to your description:
"It wants to lose control, it gets right out of the water then cavitates."

A boat doesn't 'want' to lose control, when it's driven beyond the design parameters, it becomes undrivable.
This includes too much hull out of the water followed by spinouts, as there's not enough boat in the water to counteract that.
The only thing that can cavitate is the prop, when you overrev it, you'll have a blender.

Please explain more precisely what you mean.

Regards, Jan.
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Old Sep 08, 2012, 10:53 AM
I feel the need for speed!
scorpion1's Avatar
Southern U.S.
Joined Jun 2008
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1.9 is too much pitch for 5s, thats why its uncontrollable, try an x438-x440 for 5s
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