Several rudder and drive line questions

[Assocracer]

Got a few questions for a boat I'm building. I've picked out a rudder and a motor, it's a Turnigy 2000Kv motor (not worried about awesome quality or speed right now, just wanna get it built to see what I got). Motor shaft is 5mm. The hull is an old Dumas 42" shallow V-hull. Looks like it was at one time a nitro boat. What size shaft would suit this? would 3/16 cut it or do I need to go bigger. Also, what is the advantage to having the rudder offset from the center line of the boat, other than it might interfere with the prop? Thanks guys.

[Assocracer]

I should add that the boat is fiberglass, so heavier that the standard ABS plastic boats.

[Basstronics]

3/16" prop shaft is the electric norm unless you got a beast of a motor.

RPM wont tell us a lot, need to know the can size to have an idea of power. I would say you will probably be OK with a .150 flex cable, if your motor is a larger one you might want the 3/16" flex as well.

offset rudders will allow the boat to turn better in one direction while the other suffers. My attempts at inline rudders havent been the best.

[Assocracer]

It's a 40mm motor so it's gonna have some torque. Plan on running it on 4s.

[Basstronics]

You will probably want the assurance of the .187" flex then. Im sure its on the strong side but its the safe side.

[Fluid]

That is a 4S motor totally unsuited for a 42" mono. How long is the 40mm motor? You would want one at least 80mm long for a large boat like the Dumas. You would be far better off to get a larger motor with a much lower Kv and run 6S or 8S. You will need to run small props under 45mm with your current motor, and those are too small to be efficient with a large hull like that. Minimum 3/16" cable size unless you like replacing cables and buying new props. A large motor with a Kv around 800 on 8S would let you run a 55-60mm prop and get decent speed and run time out of the boat. Otherwise you are bound to be disappointed.


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[Assocracer]

Motor is 74mm long and 2000KV. At some point I'll upgrade to a bigger motor but right now I'm not looking for speed I'm just looking to get it on the water and make sure all is well. If it doesn't go hyper fast I'm not going to worry about it as I'm not racing it. Just something to play with when I'm out on my buddy's boat. I get more entertainment out of building it than running it really.

[Heaving Earth]

Motor is 74mm long and 2000KV. At some point I'll upgrade to a bigger motor but right now I'm not looking for speed I'm just looking to get it on the water and make sure all is well. If it doesn't go hyper fast I'm not going to worry about it as I'm not racing it. Just something to play with when I'm out on my buddy's boat. I get more entertainment out of building it than running it really.

Well I'm no racer, but my understanding is the ol turtle vs hare story. You don't need to be hyper fast when racing I think, just steady stable and able to finish. From what I can tell the hyper fast boats tend to end up upsideown halfway thru anyways

[Assocracer]

Yeah, same goes with cars. I race electric and nitro and I'm always faster with a less powerful motor or engine

[fas]

Assocarcer

I think what Jay is trying to say is ( Jay if I am full of it please let me know) it is a older nitro hull which = more weight which = more drag in the water( the more of the boat in the water the more drag) so running a boat slow (riding lower in the water) is harder in the motor and speedcontrol the when it is moving fast (on top of the water) because it = more drag= more power needed to keep it moving= higher amps=higher motor and control temps= bad things happen

when I came from running cars a wise man once told me to take everything I knew about setting up a car and leave it in my car box because a set up for a car and a boat are two different things as a car rolls on a surface=very little drag and a boat pushes water= much more drag ( that came from a national champ rc car driver Mr pags)

I would agree with Jay that motor is to small and the kv is to high for a boat that big a 28- 34" would be fine
you are trying to put a lawnmower engine in a full size truck will it work yes but it wont last long and your upgrade will come a lot sooner then you think

I am not trying to upset anybody, just don't want anybody to waste money on stuff I know will not work the way they want it to

Fred

[Assocracer]

Well, I'm not too worried about that. I do understand the physics of trying to push a boat thru water and move a car across the ground (I do hold a degree in engineering :) ) However, the boat hull really isn't as heavy as it looks. Probably weighs 3 lbs at the most. I know it'll weigh more that that once all of the hardware and motor is installed though.

[madmikepags]

Weight isn't the issue, if you're an engineer then you know the resistence of water on a hull is multi fold over that of a car on land, it's not so much the weight (that is an issue though) but the size of the hull on the water, (displacement) I tried this a couple of years ago with a 42" hull on a 4S setup and it was not what I was hoping for ( my entire boat RTR was 7-1/2 lbs) so it was light enuf and I had a Neu 1527 so I had the power, The 4 cells is not enuf to push it to an efficient speed. The boat would never get on plane, so the Batts motor and speedo all were super hot after just a minute or so of runtime, I tried a lot of stuff, props struts gearing!!!! I really wanted this to work but in the end the project was scrapped. Just to give you an example of how very different cars and boats are My very fast offshore boat runs for 4 minutes at 60+mph on 10,000mah My 1/8 scale GT car does 65mph for 18 minutes on 5000 mah, thats ovcer 8 times more power consumed to achieve the same speed There is nothing in RC that uses power like boats. By all means try it, good luck and let us know.