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[rathikrishna]

Friends, i am going to make a Tamar life boat, lengths in to a 3 feet,10 inches wide, and sure i am willing to fix two motors in it..some personal told me that , there's some problems,while using two motors in a same craft...is it true..?  what are the things that must carry in our mind, while fixing two motors in a same craft..? is it need to rotate in oppose direction...?or within a 10 inch wide craft, how much width is needed from each props..?  please advice me....

[triumphjon]

in order to prevent prop walking , it is normal practice to contra rotate the props on twin shafted vessels !

[Prophet]

get a p40 mixer from action and then just dont worry about 2 props 
http://www.action-electronics.co.uk/mixers.php

[triumphjon]

even with a mixer , the shafts still need to contra rotate ?

[Pirate]

If you were to 'Google' images of the vessel you were making there is sure to be an image of the props (twin) and you can guess/estimate the distance apart they are in scale with your model. In general, viewed from the stern (back) the left hand prop should spin anti clockwise and the right hand prop clockwise. So it is necessary to get a pair of props where one is right handed and the other left handed (one when turned clockwise will give thrust and the other anticlockwise will give thrust) this prevents prop walk where both props act as paddles and steer the vessel sideways a little whilst going forward or astern. As regards the use of two motors; it is possible to link both prop shafts to one motor using a band and pulleys. This simplifies things. But should you use two motors you need to power them with a high amperage speed controller (esc) together or two speed controllers (one per motor) if you should want to steer the vessel using independent motor control (like a tank steers). This last suggestion is one that has been alluded to (action speed controller) this unit tis two speed controllers and a mixer,r whereby you can steer the vessel by rudder control that also sends a signal to the mixer and it tells the speed controllers to alter the power to either motor. Very clever stuff, but perhaps unavailable to you. So if it was me I would link the two props to one motor and one speed controller and steer using either one or two rudders. Remember that this motor would have to be the equivalent of two smaller motors in power.
 I am sure other modelers will be able to give there ideas and links to images and diagrams that may help you keep up the most excellent standard of work you have shown us so far. Maybe some good hearted modeller may even contribute someparts towards this project, If you were to suggest your requirements!!!

Keep up the magnificent work
Pirate

[rathikrishna]

Good morning and i am back, after my heavy duty, as our independance day progs finishes...and thank you all for the suggestions and links, and i am back in my work with this boat...i have collected two motors, from car fan, rated at 1.4 amps, at 12 volts...soon i can finish my work.

[FullLeatherJacket]

(action speed controller) Very clever stuff, but perhaps unavailable to you.

Nope - we can ship to practically anywhere.
FLJ

[Perkasaman2]

Hi Rathi, this build thread has plenty of useful photos:

http://www.modelboatmayhem.co.uk/forum/index.php?topic=22458.0

Ideally, the props should spin/rotate in opposite directions (be 'handed'...................You can choose INWARDS (towards each other) or OUTWARDS (away from each other). Either choice is OK. There are many hull shapes and designs and prop direction is a feature of many designs because INWARDS can give better steering, but OUTWARD spinning props can give extra speed. Handed props give balanced thrust and more neutral handling/steering because twin props spinning in the same direction will generate some degree of sideways thrust, left or right, depending on spin direction and also exert some torque/twisting rotation of the hull.  


The coast of UK is very dangerous and these hull designs give protection to the props in 2 ways.
1) The props are spinning/placed  in 'tunnels' or channels.
2) The hull also has 2 'bilge keels' which also help in preventing damage to the props from underwater obstructions  or  'grounding' in shallow water. The  risks of grounding are very real:

http://www.youtube.com/watch?v=S7_HnG-PgTo&feature=related

Many models don't  need to use handed props and setup issues are avoided (some electric motors don't run/rev equally in either direction).