ORIGINAL: BIKERBOBW
I am new to the forum; but will watch with interest your build as I too am about to build a Higgins .
<p class=''MsoNormal'' style=''margin: 0in 0in 0pt''>The PT boat is at a scale of <st1:time hour=''13'' minute=''20''>1:20</st1:time> so therefore will be about 48” long and guessing at a finished hull weight of 2 lbs .
A Higgins at 1:20 scale will be 46.8 in long and will displace 11.74 lbs at the scale waterline. In order to achieve a displacement of 2 lbs at the scale waterline you'd need to build it at 1:36 scale (26 in long).
ORIGINAL: BIKERBOBW
I am hoping to get it up on a plane and a run time of 30 mins. Is this run time achievable and realistic?</p><p class=''MsoNormal'' style=''margin: 0in 0in 0pt''>I am considering Gaupner speed 600 or Astro marine 425 motors running on 12 volts each; with all 3 running forward and only the ctr<span style=''mso-spacerun: yes''> </span>capably of reverse. Will these motors achieve my desires or will smaller motors work?</p><p class=''MsoNormal'' style=''margin: 0in 0in 0pt''>What would you recommend for batteries Gel cell or NimH cells? If NimH how should the pack be built to achieve the run time; 10 cells in series = 12 volts but how many in parallel to achieve run time?</p><p class=''MsoNormal'' style=''margin: 0in 0in 0pt''>Finally can you recommend a ESC that can handle the above? Will I require a ESC for ea motor?
Awaiting your thoughts</p>
The original engines were rated at 3600hp each x 3 engines. To achieve the same sort of full speed performance at 1:20 scale (11.74 lbs displacement) you will require 3 motors of 335.7 watts each - at 12v that's 27.9 amps each x 3 motors = 83.7 amps. To run at full speed for 30 mins will require a 12v 42 Ah battery pack or to put it another way 175 1.2v 2400 mAh cells wired in series and parallel. Of course you wouldn't run at full speed for the full 30 mins would you? So you could settle for a lower current rating in your battery pack and therefore less cells.
To achieve the same sort of full speed performance at 1:36 scale (2 lbs displacement) you will require 3 motors of 57.6 watts each - at 12v that's 4.8 amps each x 3 motors = 14.4 amps. To run at full speed for 30 mins will require a 12v 7.2 Ah battery pack or to put it another way 30 1.2v 2400 mAh cells wired in series and parallel.
The problem with electrics is that to obtain good planing performance and endurance requires a large power source and a large power source is heavy which in turn reduces performance. So, generally you can have lots of performance and little endurance
OR lots of endurance at displacement hull speeds (ie no planing). There is a 3rd option if you have deep pockets - use brushless motors and LIPO or A123 batteries as used in model aircraft. The brushless motors are powerful and relatively efficient and the batteries mentioned are lightweight but with good power outputs. You will also require speed controllers that are designed for these motors and a battery charger designed for these batteries.
Or you could just put a gas motor in it and plane all day
