Power system advice?

[Forester]

I just tonight finished building the hull for my moon mist. It is a 21" long 6" wide boat. I would like to be able to move it around at about 15-20 mph. How many watts will I need to do this? Just a ball park figure is fine. I am thinking that a brushless motor putting out ~110 watts isn't going to be enough. Would 350-500 be too much? I don't think that this boat can take a whole lot of weight and I am already going to be using either 1 or 2 10 cell nimh packs depending on motor.

Any ideas?

[Massey]

Alot of what you are wanting is going to depend on the type of hull you are building. A hydroplane hull will need less power to move 15-20 MPH than a tug or a tanker will because of the shape of the hull. So your question really cannot be answered without a little more info. In general tho a 21" V type hull should be able to achieve what you want with a 500 sized brushless and 12V. It may take a little to get the proper ballance but 15-20 MPH out of a "cruiser" type boat would be pretty easy.

Massey

[Forester]

Sorry, yeah it is a v hull type. I can post a picture if necessary. Not a tanker, hydroplane, tug, warship. I was actually looking at a 600 sized brushless motor pulling 35-40 amps. Do you think that size motor would be overkill?

[Massey]

It would prolly be a little too much but you dont have to always run at full throttle. So if you do put the 600 in the boat you will have all the power you need and a little more just in case.

Massey

[MumblinAviator]

You dont have to always run at full throttle.


New Concept....I'm not sure I fully understand....



;)

[Ghost 2501]

forrester, what you have to remember is if you put TOO much power through the prop you will cavitate and get nowhere, the trick is to ballance the power to start off. once moving you will be able to get to faster speeds easier than simply whacking power to the throttle stop!

[Shaun Hendricks]

Too much power at start up? Sound like he needs one of them handy-dandy 3 speed transmissions! LOL! :D

(The irony kills me....)

[fleetmaster]

Be careful,as a lot of brushless esc's will burn out if you use partial throttle a lot.
I am led to believe that they run cooler and safer at WOT.

[CG Bob]

New Concept....I'm not sure I fully understand....



;)Full size ships, especially military ships, will usually have several different speeds listed in books like Janes, Ships & Aircraft of the U.S. Fleet, et al. The speeds are usually listed as full or top speed, and cruising or best economical speed. One of the USCG cutters I sereved on originally had Diesel and gas turbine engines. Full speed on Diesels was about 17 knots; full speed on turbines was 18 knots and about 3 time the fuel consumption. The gas turbines had been removed before I served on that cutter, our top speed was about 17.5 knots because we didn't have the extra weight of the turbines.

The size and type of hull has a lot of influence on the ships speed - not just the powerplant. Long narrow hulls (destroyers, frigates, cigarette go-fast, etc) have a much higher speed than cargo ships, tugboats, and fishing boats.