How much power is needed ?
 

I am finally back to finishing the (6) 48" dropped sponson hydros. Hull alone is 6 lbs. I have 10 ..2.2 amp. Dewalt cells, A Novak Super Rooster ESC that handles a car battery with a 41 # thrust trolling motor easily.

How little power will a ready to run 10 lb. boat need to run surface or submerged at 20...25... or 30 mph ?
I probably will need to buy from Hobby City in China. :eek:
Money is a big problem with 6 ESC & 6 motors. I am using the seperate Octura flex drive shaft & seperate rudder setup.

RE: How much power is needed ?
 

What motor options and ESC have you looked at? It's hard to judge a power system for such a large boat running at fairly low speeds.

Based on some of the specs already present, I would say use a slow final unloaded RPM speeds such around 20 000. This should be low enough to spin a large prop. Spinning a large prop will allow the hull to produce enough thrust to get on plane, especially since your pitch speeds will be quite low.

Are these Dewalt cells NiMh 2200mAh? Is the Novak ESC brushed and you wish to stick with this throughout the build? What is the RTR weight?

Ryan

RE: How much power is needed ?
 

Thanks for helping out as I have no experience or anyone to go to on this size. The cells are Dewalt LIFEPO4's. Loafing at 20 C. No fires under any loads or charges.
RTR will be 10 to 11 # .
Novak is a brushed unit.
It handles accidental reversed hookups very well. 2 X.
What a flash the poor circuit breaker must have endured.
I have some Prop Shop props from England. They are 5 bladed bronzes of about 4 x 4.5" pitch.

2 lift my 72" WW II PTB in about 30' after WOT, from a dead stop. It weighs 60 lbs.

My boat experiences are useless on the hydros.....Try to post the props

RE: How much power is needed ?
 

I am trying to do them electrically because of the noise problems in places with gas or Nitro's.

6 of these battery & drives is a wallet drainer. Gas is cheapest. Brush could be a close 2nd if I knew how many watts & RPM's are needed. I have used BIG Octura props.

Rich

RE: How much power is needed ?
 

Being brushed it will be very tough to find a motor that would be most optimum. For scale boats they still work very well but for FE boats they just can't be matched up as easily.

I would aim for something around 1200+ watts. What motors do you have available?

Usually a boat this size would run on 10s LiPo, at around 100amps or so.

Ryan

RE: How much power is needed ?
 

What is a F E boat ? style ?

If I use the complete 36 volt Dewalt pack and divide that into the 1200 watts, I come out with 33 amps. Which is way over 1 electrical HP even with losses. that would also keep the amp draw well under 20 C also.
20 to 30 mph maximum.

I can use the 36 volt motor from a Dewalt drill. Will check it out for rpm. If it is only 3000 rpm the 4.5" pitch gives a prop speed of 12 mph. [:o]

RE: How much power is needed ?
 

Isn't the drill geared and the motor spins far more RPM than than the output shaft at the chuck?

This might be your cheapest possible route. Once you give it a try you may find out you could get away with less power reducing the cell count.

Not too many people build a boat that large and aim for just 30mph. I have never done this myself so I can not be certain on wattage figures. I do know that you should not need unloaded RPM speeds higher than 20 000RPM. If you go as low as even 13 000RPM you still should be fine. You will probably want to spin either a 2 or 3 bladed prop over 65mm in diameter. The kv and cell count will determine what prop can be used.

When I said 1200 watts, this was said assuming the brushed motor is around 60% efficient. This is a figure I used back in my brushed days. I never used high voltage setups so maybe perhaps in your case the efficiency is much greater? In other words final mechanical hp after electrical efficiency should be about 3/4 - 1hp.

FE is Fast Electric. Your boat will be considered a Fast Electric even at 30mph! :)

Ryan

RE: How much power is needed ?
 

I feel another learning curve coming.:D

I do have a left over 18 # thrust trolling motor that ran on 12 vdc. I could start with that and some left over 1 : 2 step up timing belts I have from the big PTB. ??????

When is bigger not a lot of work ?

RE: How much power is needed ?
 

I don't think a trolling motor will give you the results you are looking for. I always thought the small 25lb thrust motors were less than 1/2 hp. You can give it a try and let us know the results.

Ryan

RE: How much power is needed ?
 

Ryan. I just read your thought at the bottom of your posts.

It fits me perfectly !

I checked out Home Depot & their leaf blowers. Cordless. All are 18 vdc at 7 amps. 120 mph @ 130 watts rated. The PTB only pulls 480 watts WOT & chained to the pier.

Dc motors are never pushed until we get them. :D
It will take a week to make a pulley setup.