first scratch build at 1:16 scale motor questions

[Mai_t]

thank you as thats pretty much what i needed to know for a reasonable starting point

[785boats]

Mai_t.
I've built a few scale models in my time. You don't need as much power or revs as you might think to get a big PT boat up on the plane.
Power required, is the original boats power, divided by the cube of the scale.
So,
3 x 1500hp Packard V12 engines = 4500hp.
1:16 scale cubed is 4096.
4500/4096=1.02hp.

We usually add 25% for losses, but since you want to go a bit faster let's add 50%
So that's 1.53 hp total.

At 746watts per hp we end up with a total of 1141 watts.
With 3 motors that's only about 380watts per motor.

So 3 x 3674 size motors with a Seaking 60A ESC each will be more than enough. BUT. Getting them in a low enough KV rating will be the hard part.
Even a 4074 size doesn't have a low enough kv that I can find.

The correct props for the boat would be the scale props from Raboesch, Rivabo, or Prop Shop. The 50mm to 55mm 3 blade props only require around 7000rpm for best efficiency under load.
http://www.loyalhannadockyard.com/PROPS.htm

So lets allow for 10000rpm unloaded. (That may even be a bit much.)
If you want to run 6s lipo, then a kv of around 450kv is required.
On 4s a kv of around 675 kv would work.

You may like to look at some outrunners with those kv ratings. Three of these will easily drive the boat.
https://hobbyking.com/en_us/turnigy-...ner-motor.html

Scroll through this build thread of Pat's. He is a master builder. The motor discussion starts on page 6
He used 3 x 3674 1200kv motors on 8.4 volts with 45mm props. His model is only 58" not 61" like yours, but you get the picture.
https://www.rcgroups.com/forums/show...-16-Elco-77-PT

I hope this helps a bit.

[Mai_t]

thats awsome and what i was looking for thank you
pat makes my poor boat look like something from the reject factory but i dont have all his fancy tools but if it floats and moves i'll be happy and our size differance is he is working off a 78' vs my 80'

[785boats]

Yes, Pat's skill & craftsmanship leave a lot of us wanting when it comes to fine scale modelling. When you have a bit of spare time do a search on R/C Groups for some of his other builds. They are truly inspiring.
Just a note on the prop charts. I've always found the Raboesch "A" type 3 blade props to work very well. But at the bottom of the page there are some nice looking WWII 3 blade props from Prop Shop that might work well too. I've never tried them though.

[Mai_t]

ok great thank you

[Mai_t]

think i'll go with pats setup with the 3 blade and i dont mind being off scale that much so long as it um ah looks right :) and thank you for all that
now to show my ignorance to radios i'm trying to find the proper charger for a futaba 7c transmitter with looks like a nicad 9.6 volt 1100 sries sanyo kr1100aau battery with 110ma 14-16 hr charge and looks like a 4 cell since i can feel 4 batteries in the pack and a futaba r606fs 6 channel 2.4 ghz fasst receiver and no idea which battery pack goes with that
thank you if you could help
Mai