Prop choice for 6 cell Pursuit 32.

[ProfileBroKen]

I am looking for some advice. I installed a Dr Mad Thrust 3674 1600 KV inrunner in a Pursuit 32.

Here are the motor specs (http://www.hobbyking.com/hobbyking/store/__29355__Dr_Mad_Thrust_1620kv_2400watt_90mm_EDF_In runner_6s_version_36mm_.html)

I am using two 3-cell 40C 5000mah packs in series.

With an Octura X642 prop I am getting 52 mph, momentary peak amps around 122 amps and momentary peak watts around 2600, settling to 93 amps and 2000 watts as the boat comes up on plane. After two minutes, used 2200 ma and temps were slightly warm – I could run all day with this setup.

A different story with an Octura M545 prop. 57.5 mph, momentary peaks at 165 amps and 3650 watts, settling to 126 and 2820 watts on plane. After one minute, used 1000 ma and temps were hot, but not excessive.

I want more than the X642, but I don’t want to beat up the electronics as hard as the M545 does. What prop would be the next to try for a happy medium?

[jstolz]

Try a Prather 220.

[ProfileBroKen]

Try a Prather 220.

I finished my prather 220 trials... the absolute best top end was only 48 mph, repeated over several runs. The octura X642 does 52 and comes back cooler than the prather. I guess I need to continue the search...

[TheShaughnessy]

A m445 is all that's left in that range really. Less overall pitch then a 642 but with no tounge it may yield a higher top speed. Hard to say if a m545 is heating things up.

Did you thin the blades at all on that 220? The Prather prop I have seems to have thick blades, also how did it run with that prop, other then top speed being lower?

[ProfileBroKen]

Did you thin the blades at all on that 220? The Prather prop I have seems to have thick blades, also how did it run with that prop, other then top speed being lower?

Mostly just sharpened and balanced the stainless steel prather; yeah, the blades are thick, but not much more than the M545; amp draw slightly less but heat comparable to what I am seeing with the M545.

I've also tried a CNC 1.4 pitch 45mm prop (the shape looks alot like a Octura M with thinner blades) but it wasn't as good as the X642. I guess I have as good as I am gonna get.

[jstolz]

Every one of the Prather props that I have seen have quite thick blades. The Octura M series props that I have have thin blades. The Octura X 6 series props that I have also have thinner blades. Thinning the blades can improve performance of the prop.

[kendt]

You could try a tfl 448 back cut and reduce the dia a bit if the temps are still not to your liking.

[electric]

Beyond the props, you might want to "loosen" the hull up and get more of it out of the water. This will get you more speed, with substantially less amps(heat) and allow you to prop up more. However, there is a point where the boat will become less stable as well. This is the fine "balance" of tuning a boat. I had a Pursuit a number or years ago and learned quite a bit from it. The one big moment came when I completely raised the trim taps up out of the water "1/8" up or more and the boat just took off and actually still handled quite well. As I recall, the batteries were in front of the motor as it came from Hobby City. I ended up putting them on either side of the motor. This moved the Center of Gravity back a bit and again it did a lot for the boat.

As another example. Just yesterday I was working on a new Delta Force mono almost the same as the boat you are running. I raised the trim tabs way up and it ran fast, but unstable. The motor came back cool. Then I slowly lowered the tabs a bit and I lost some speed, but gained some stability and came back with a warmer motor. You are working to get the just right combination of Prop, Center of Gravity, Speed, Heat, Handling. Good Luck.


Let me say it again to be clear, how "wet' your hull rides in the water makes a HUGE difference on how many amps you pull at a given speed. AMPS = HEAT

[ProfileBroKen]

Let me say it again to be clear, how "wet' your hull rides in the water makes a HUGE difference on how many amps you pull at a given speed. AMPS = HEAT

I hear you about tuning the hull. When I first got the boat, it ran extremely wet with CG at 10 inches. I raised the stinger and trim tabs. Much faster but very unstable. Slowly lowered the tabs until the porpoising just stopped. Never really got any chine walking, so all the tabs are at the same level. Believe me, very little of the hull is in the water when she is running all out.

[ProfileBroKen]

Every one of the Prather props that I have seen have quite thick blades. Thinning the blades can improve performance of the prop.

I am slowly thinning the prather. Although it the stainless prop is tougher to work on than the Octuras, I breath a little easier knowing I am not dealing with the "bad" stuff and am using a dremel to power off the extra material. I will try it again once it is a whisper of it former self.

[martin]

Stainless steel is also hazardous to health when grinding or sanding.

[ProfileBroKen]

Stainless steel is also hazardous to health when grinding or sanding.

Thanks for the heads up!

[ProfileBroKen]

After working on the Prather 220 a bit (wearing proper respiratory equipment), I put it back on and found that further prop thinning resulted in a gain of 1.5 mph over the original run. The amp draw and temps are noticably less than they were before. So it is slightly slower than the X642 (52 vs 49.5), but I gain an additional minute of run time with the Prather 220. I don't think this prop will get me faster than the x642, even with more work.

[ProfileBroKen]

OK, I am definitely a convert to prop preparation. I thinned my previously balanced and sharpened Octura M545 prop that was giving me a top end of 57.5. Now the boats hits 60mph on fresh batteries and draws less amps and watts than before all the prop work. Now I need to spend more time on it, I know I can shave even more.

So, grab your respirators and dremel and have at it. It makes a big difference.