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[lockerrr]

Hi all,

After many years of RC car racing, i do a lot of fishing and am building a bait boat.

I am unfamiliar with the amps rating and engine sizes as i'm only used to using 540's,

I just have a couple of quick questions

1) if i was to use a johnson 540 motor off a 6v lead acid cell, how long would it last and what ampage speed controller would I need?

2) I am making a catamaran about 18" long and 12" wide, would 2 540's be too much?

Much thanks

Paul

[lockerrr]

Sorry meant 12v 3A lead acid

[Shipmate60]

2 x 540's on that battery will last less than 6 minutes.
540's will happily pull 11 amps each.

Bob

[lockerrr]

Thankyou for the reply,

I don't need speed really, what about if I wired 2 batt's in parallel and curbed down the motors, want a good hour really.

What motors would you recommend for small catamaran?

Thanks

[Shipmate60]

Lets get right back to basics.
Even if you use 2 x 3AH batteries for the hour run time required you will need motors pulling no more than 2 1/2 amps under load.
They would have to be very low powered motors.
For Bait Boats it is usual to use at least 1 x 12 volt 7 AH battery, and this can have a restricted run time.
For a Cat you will need some power to overcome wind and currents.
380 motors on 6 volts driving a 35mm brass prop should power her well with the option on faster flowing rivers of using 12 volts (batteries in parallel)

spec CLICK HERE

The specified current draw will increase while driving a prop.

Have you considered 7.2 MiNim Battery packs.

Bob

[tjones27]

check out these motors. http://www.cornwallmodelboats.co.uk/acatalog/graupner_1788.html
reasonably priced, low current and can pack a punch froma  12V pack.

[lockerrr]

Bob

I considered using lead acid as it was heavy, need a quite heavy boat as it lessens the overall weight distribution effect of carrying bait and dropping it hanging over the back.

I have attached my sketch of what i'm going for.





So if I added 2 6v 7ah gel cells, one to drive each motor with 2 speed controllers and anMtroniks mixer im looking at 3kg ish, does this mean water displacement of 3l, hence 1.5l per side?

Thanks

Paul

[tjones27]

nice design. i couldnt tell you about the displacement with weight. i think its inderectly proportional, try pushing a hull into the water, its easy at first, but the further the hull goes into the water, the more force is needed. action electronics do the P94 which is a dual motor ESC and mixer all in one. http://www.action-electronics.co.uk/mixers.php
do you know which motors you are going for yet? just being curious, have you thought about mounting the props inside the hull and having a tube running through each pontoon if that makes sense? although thinking about it that would decrease the buoyancy. would be interesting though.

[tjones27]

nice design. i couldnt tell you about the displacement with weight. i think its inderectly proportional, try pushing a hull into the water, its easy at first, but the further the hull goes into the water, the more force is needed. action electronics do the P94 which is a dual motor ESC and mixer all in one. http://www.action-electronics.co.uk/mixers.php
do you know which motors you are going for yet? just being curious, have you thought about mounting the props inside the hull and having a tube running through each pontoon if that makes sense? although thinking about it that would decrease the buoyancy. would be interesting though.

sorry as far as i can understand, if your boat weighs 3Kg, then it will Displace 3Kg of water which in turn should be close to 3L of water.

[Shipmate60]

If you are using that design of hull you will need to measure the prop tubes.
I assume that there is a water inlet towards the bow.
If this is the case simple "Tank Steering" will be fine but for ease of use a 4 channel transmitter would be better.
This will allow the use of the vertical sticks for throttle control and the horizontal sticks for the bait.
Something like the GiantCod 2.4 Ghz is only about £30.

http://www.giantcod.co.uk/gianitcod-24ghz-4channel-mode2-transmitter-p-403779.html

Bob

[dodgy geezer]

http://www.giantcod.co.uk/gianitcod-24ghz-4channel-mode2-transmitter-p-403779.htm

Missed the 'l' off the end - try this: http://www.giantcod.co.uk/gianitcod-24ghz-4channel-mode2-transmitter-p-403779.html

[lockerrr]

Hi

You have confused me with the prop tubes and water inlet, I was just going to taper the back of the hull to a point and have the prop out of that, hard to draw a prop on cad.

I have a 6 channel radio so no of channels is not really an issue, think I'm going to have to redesign now as think underestimated weight of hull. Prob looking at 6kg.

6l of hull is quite a headon displacement for travelling through water, am looking at graupner 500E motors with 6v 7Ah lead batts, but don't know if this will give me enough time as I fish for 24hrs a time.

Back to the hull drawing board I think, that seems to set the most amount of variables.

Paul

[ZZ56]

Amp draw depends on the load and the torque rating.  There is no way a 540-size motor with the correctly sized prop for its torque output will ever draw 11 amps. 

It would help if we could know the maximum prop size you intend to fit, as this determines top-end RPM for the motor and narrows the choices down.  I would look for some sort of gear reduction regardless of your prop size, as this would allow you to use a typical high-rpm low-torque motor without the high amp draw.

[dodgy geezer]

Back to the hull drawing board I think, that seems to set the most amount of variables.

Another approach to the issue of design might be to look at the boats which are on the market, pick the one closest to your requirements, and then read the specs for it. If you really like one boat, but need to increase its payload or duration, just adjust the specs accordingly....

[Shipmate60]

ZZ56
540 motors as used in fast boats and cars will stall at about 90 amps (roughly 20 turns) so 11 amps running isn't excessive.
They rev at 12000 on 7.2 volts (generic).
My 540 on a 38 mm 2 blade racing prop will pull over 7 amps (which I consider low).
Perhaps you mis read the text, not a 540 SIZED motor, a 540 motor.

Bob

[lockerrr]

These are the final dimensions of the boat based on a final weight of 3.7kg loaded with bait.





Sorry for my lack of knowledge with motors i'm still really non the wiser, I only deal in turns, I understand winds but have no clue on size, are all boat motors single wind or are there double, triple, quad and quint varieties?

confused 

[ZZ56]

ZZ56
540 motors as used in fast boats and cars will stall at about 90 amps (roughly 20 turns) so 11 amps running isn't excessive.
They rev at 12000 on 7.2 volts (generic).
My 540 on a 38 mm 2 blade racing prop will pull over 7 amps (which I consider low).
Perhaps you mis read the text, not a 540 SIZED motor, a 540 motor.

Bob

I must've misread the text.  I know Johnson makes a number of 500-sized motors.

[tjones27]

Hi, like i say, im not an expert, but if this was my bait boat my setup would be as follows.

http://www.component-shop.co.uk/html/body_lead-acid.html
12V 7.5Ah Sealed Lead-Acid Battery
Weight: 2.6kg
 Recommended 1st charge max current:  2.3A (2,300mA)
Dimensions: 151 x 65 x 94mm

http://www.action-electronics.co.uk/mixers.php
with action electronics P93/P94 ESC and Mixer-tank steering

http://www.cornwallmodelboats.co.uk/acatalog/graupner_1788.html
with two Graupner speed 500E 12V (1788)

driving maybe a 30-40mm prop

with it being a bait boat you wont be running full throttle for 3hours straight, so although at max eff. the motor is rated to draw 2A which on that battery would give you a running time of 3Hrs 45Mins.

thats what i would use, but its your design and you can use what you feel best.

[lockerrr]

Thankyou for your advice, I am not on with building the hull mould, I will keep you posted and prob ask for advice when I get stuck!!

 

Paul

[lockerrr]

Hi

I have now finished the mould, what weight fibreglass should I use for the hull?

Thanks

Paul

[wartsilaone]

Going back to the motors. I am using A12v 7 amp battery to drive two 530 motors using 20 amp speed controllers on each, plus this battery also powers the reciever. I haven't run out of power yet. It may be worth having a spare.

[lockerrr]

Thankyou that is reassuring to know, I am using 2 6v 7ah batteries for weight distribution, in series will give the same effect.

[lockerrr]

Hi All

Here are a few pics of my progress, all comments are welcome of my errors!

[lockerrr]

pics

[lockerrr]

bank holiday has given me some time to work on the boat, sorry been quiet for a bit.

Hull with inclueded ballast, apt amount of beer!! Should be able to get my twin 6v 7ah batteries in the end 




Also made progress on rear hopper, colour even follows drawing.



Comments welcome.