Looking for a bit more speed

[Muskoka1]

Hi guys, need some advice on prop choice.

I have just finished my first boat build. It's a 51" Mountain Hobbies Viper Mono. Motor is a TP Power 5650 850kv running 12s. Esc is a Hobbyking 180a HV, good to 14s.

I have props from x457 up to x470 and have tried them all. The boat so far has reached 56 mph per my gps.

My question is about prop size and motor / esc heat. If I run one of the bigger diameter props, x465, x467, x470 she does 56 mph at about 5/8 throttle, but comes back with everything pretty warm / hot. I'm not experienced enough yet to try and push the throttle any further.

If I run the x457, she still does 56mph, but I'm able to run full throttle, and she comes back just warm. Sorry I don't have any numbers to give you. I have a Eagletree logger coming from OSE, the one I ordered 7 weeks ago from Hobbyking never arrived, not unusual for them, another Paypal dispute, could write a book about how incompetent they are. Ok, back on topic.

I'm not sure if the heat build up with the bigger props is because their just too much for this boat, or because I'm only able to run the system at 1/2 to 5/8 throttle? I'd like to push the bigger props, as she feels like she has a lot more speed in her, but 56mph is pretty intimidating with a 24lb, 51" boat, and I don't know what she will do. I don't know if going past 5/8 throttle will give me more speed, or just fry everything inside.

It's my understanding that the motor and esc run best at their rated outputs. So, I'll assume that I need to prop the boat in a way that allows me to use full throttle all the time, while keeping the heat under control. Like I said, I get the same speed with a x457, as I do with a x470, but the x457 is full throttle, the x470 is 1/2-5/8 throttle.

Sorry if it should be simple, just not sure what to do. Prop to allow me to use full throttle, or get the confidence to push the bigger props. If I push the bigger props am I just going to smoke everything, or will the system be "cooler" if I run the big props at full throttle instead of half, and I'll gain the extra speed.

I hope you understand, and can share some of your experience and knowledge. Should add, my goal when I built this was to reach 60 mph, so I'm close.

Glen

[Fluid]

A few photos are always helpful as speed is not just about the prop size. Strut position and CG are important too. You're right, you do not want to run your boat at part throttle for any extended time, that is very hard on the ESC and will overheat it quickly. Since you did not run the larger props at WOT we don't know if they draw too many amps or not. That is a pretty hot setup BTW, most would run a larger, lower Kv motor on 12S with a big boat like that, so be careful. One P or two P? What timing advance are you using?

What you want to do is run the boat with the x457 for one minute at full throttle, bring it in and measure the heat in the ESC, motor and packs immediately. Use a heat gun and wright down the results. Now let everything cool down, put on the x460 and do the same again, noting the temps. If they are not too high, then run for another minute and check. If they are okay, go to the x462, etc. You will eventually burn up the ESC by using too much part throttle, that can be as bad as too much prop. By working up in prop size slowly you reduce the risk of damage plus you learn a lot more about your setup. It does take some time to do it right, but if you rush it will cost you $$$.


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[rickwess]

56mph is pretty fast for a 51" mono.

How happy are you with the Mountain Hobbies hull? Pics please!

[Muskoka1]

Thanks for that, batteries are 6s 5000 40c + 6s 4400 40c x2, in series, 12s 9400mah. Motor timing is 12 (7y Wind), PWM Frequency is 10kHz. Stinger is fine and cg is spot on (running at 30%). There's a guy that builds full size sport/race boats and he quite often stops and chats. He's commented on how well she runs, and said he'd like some of his to perform that well.

With the x457 and 3.5 to 4 minutes of speed runs it's just warm, I would call it barely warm. I tested that a week ago, as well as working my way up in prop sizes. The point is, at half throttle with the bigger props, it's as fast as the x457 at full throttle. I don't know if the heat problem is because of "too much" prop, or my fear to run wide open with the bigger props. She will surely do a lot more than 56mph, she's doing that at half throttle, and still wants to go. I have a TP5670 670kv, and a 300a speed controller on the way, I ordered them the other day. I'll put this current stuff in another build.

Guess I'll just play with the new motor / esc and work my way up with the props until I can do constant 60mph speed runs for 3-4 minutes (60mph was my goal with this boat), and come back without overheating anything. Might even be able to do that now, just have a fear of keeping the throttle pinned with the big props, it gets a bit scary at that speed, although it has no bad tendencies, it's just the speed that makes me back off. In other words, it might do 70mph just fine, and come back just warm if I could get the courage to run it wide open with the bigger props. I guess that's a gamble I'm not willing to take.

Yes, 56mph is pretty fast, but I'm on a big lake, with tons of room.

This is my first hull purchase so I'm not the guy to critique the build of the boat. It seems fine to me, runs great at 56mph. The finish is nice, came with rails mounted 5" apart. I installed everything else just going by pics he sent me of "full" builds he had done, and anything I could find on the internet. I've never drilled into a hull prior to this.

A few pics.....turn fins not on for pics, tired of hitting my leg on those razor sharp things. The hatch is not clamped, it's just sitting on top.

20140711_193623 (Custom).jpg20140711_193612 (Custom).jpg20140711_193630 (Custom).jpg20140711_193644 (Custom).jpg

Glen

I have a Gopro 2 and Mobius, I'll try to get someone to take some video so you can see it run, maybe tomorrow.