Thread: Help determening final drive specs for hydrofoil project

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  1. Help determening final drive specs for hydrofoil project 
    Hey there, im new to the whole RC-Boat thing and ive taken on the task of building a boat from the ground up and im looking for some advice.

    I am currently trying to figure out what i can expect from the drive system i have designd for my 26" hydrofoil, basswood structured boat, with fiberglass hull.

    I plan to use:
    2 X speed 8.4v 10amp 67watt 26K rpm (no load) and 19k rpm (w/ load)
    each driving its own propeller

    i have picked out some good U-Joints but im afraid they may still be to weak at high rpm. do you think i should use flex joint couplings instead?

    also what size propeller should I use for this setup, and and should I use gears to increase the RPM's. I am currently planning on an almost 2:1 gear ration to step the rpm without load to 50k and a 45-55mm propeller. I have no idea what I should really use tho having no experience.

  2. Cool  
    Join Date
    Humble, TX
    A boat that size will not even plane with the two tiny, low-powered motors you mentioned. Overdriving the props with a gear box will make the boat slower than direct drive.

    We need to know more about your boat, a photo or two would be great.
    - Why do you want to use two motors?
    - How many volts do you plan to use?
    - What speed are you looking for?
    - What radio will you be using?
    - How much do you want to spend?

    We need at least this much information to be of any help. That is probably why no one has answered your post, until now.


    well first off, money isn't much of a problem. i think il set like a $1000-$1500 cap for all drive components including things like speed controls batteries and all that

    overall speed is unimportant I just want this baby to fly.

    I have no experience with radios so im gonna be learning as I go. Any suggestions would be great.

    For the dual motors, I was looking at specs and it realy seemed that for the weight to power/ speed ratio they were the best choice. Plus, the props will be countersunk so i figured the simplest way to get that rotation would be with the two different motors, because I know if I used one, I would end up having some serious gear work getting it all aligned.

    For the hull, My plans have changed, and I plan to now make the basswood structure, lay it with a thing layer of glass, then make a series of molds out of that plug, from which I could mold the final product. I know this is a HUGE hassle for one hull and is really not the ideal setup, but I knew right away after starting the frame I was gonna be way overweight.

    The foils are gonna be fairly significant thought with a 8" front span and a fairly equivalent rear span. Final rear strut and span are awaiting finalizations of drive components to determine certain specifications.

    The only photo I have is of my first hull design and it is now under complete overhaul. Length will remain the same, as well as some of the foil and strut design. It will have a much more fluid dynamic (not blunt) bow with a thinner, strut including less reinforcement at the top and bottom.
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    Last edited by guitarplay; 09-11-2008 at 12:01 AM.

    Quote Originally Posted by Fluid View Post
    A boat that size will not even plane with the two tiny, low-powered motors you mentioned. Overdriving the props with a gear box will make the boat slower than direct drive.


    Great info Fluid, not to change the subject, but gearboxes seem to be the craze in N-1 mono these days. I have a system that's faster than everyone's as direct tdrive and was wondering if a gearbox would help but as I guessed it won't.

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