Power train for a fishing catamaran

[MARTIN BREWERParticipant @martinbrewer71680]

Hi – Please can I ask for some help – Ive been asked to fit out the hull in the pictures attached with electric motors, speed controllers, batteries, props, rudder etc. Although ive got absoloutely no experience of boat building I do have reasonable modelling/building skills – although all in the r/c aircraft field.

My plan is to use 2 x 600 graupner motors,2 x mtronics viper reversible speed controller – 2 x 6v graupner 4 amp hr gel cels as the basis of the power train – not sure of the prop shaft length yet – and also using a 30 or 35 mm prop but not sure of the pitch.

The hull is 28 inches long has a beam of 16 inches and a depth of 7 inches. as you can see from the pictures the hull is going to need some work as well – although that is well within my skills (I hope).

the intention – with regard to radio gear is to use the kiss principle and have one receiver driven by bec off of the speed controller – one channel off of the receiver driving two servos connected by a y lead for the rudders and y lead to the two speed controllers – thus making two channel operation possible.

The boat is for a young lad so it doesnt need to be ultra fast and does need to be easy to operate.

No doub there are going to be a lot more questions and I ill willingly accept any advice

[MARTIN BREWERParticipant @martinbrewer71680]

advice needed – please

[ashley needhamParticipant @ashleyneedham69188]

Martin.Nice to see another chap having a go, especially to get the youngsters involved.

A couple of things. Gel batteries of that size do not cope well with speed 600 motors..not enough capacity (as you do not want to run them flat as this ruins them), they do not give out the amps very well…and of course they are very heavy.

There are many types of 600 motor..for your application the Graupner 600 ECO motors will do. Best to get a NiMh pack, 7.2 or 8.4V in as large a capacity as is affordable. 35mm Props will be ok..3 blade brass or plastic twin blade (ordinary, S pitch, not an X pitch one).

If using the BEC facility on one ESC, the power output lead of the other one will need cutting..Not sure, may be the red wire.. best check with Mtronics.

On a hull like this, I would float it in the bath with the bits you are going to use, motors, controllers and batteries and see how level the boat is before glueing things in..you can move the bits around and get the best attitude, although it is quite big and you may not see a lot of difference. Make allowance for the superstructure. ALSO you will need access to the bits once in service, so this needs to be though of at the same time. Shaft length will obviously depend on where you decide to position the motors. Dont forget a longer shaft will enable the motors to be further forward and so get a shallower prop angle for better efficiancy.

Ashley

[MARTIN BREWERParticipant @martinbrewer71680]

Thanks for that Ashley – ive had a look at nimh batteries and 4700 mha batteries are within budget along with thegraupner eco 600 – what sort of run time can i expect on these batteries with one per motor ?.

the decking is going to be some what of a problem – im currently (although not by any means definate) of making a completely removable deck due to the design (will publish a drawing when ive done it) the plan (horrible word that) is to pu a fairly substantial wooden strip around the top of the hull and secure the deck using nylon bolts and blind nuts.

Also wondering wether actually using two receivers on the same channel may be a better option – ive got access to quite a lot of 27mhz radio gear so that wouldnt be a problem

do the props come with a different range of pitches or is it a fairly generic pitch/diameter combination – acceleration rather than top speed is probably what ill go for.

The original intention was to have independant throttles controlling each engine and then acombined rudder so that reverse thrust could be used to turn it but suspect that – given the lads abilities – this could be a problem. And would also need a four channel transmitter and the sticks modifying to remove the ratchet on the throttle. 

any thoughts on the above please – thanks

 

Edited By MARTIN BREWER on 24/09/2012 08:43:39

[ashley needhamParticipant @ashleyneedham69188]

Martin. I would have one reciever, a proportional splitter or Y lead for two ESC and the 2nd channel for rudders (linked). Run time….depends on your throttle style…so 10 mins to an hour, depending.. Marine ESC will have reverse of course, unlike car or plane ones (generally).

Boat, as wide, would benefit from a permanently glued on deck for stiffness. Check out the website as per the sticker on the side of your hull…interesting pictures and ideas for superstructures. Acess will take a bit of working out, and a pad of paper and sketches will provide inspiration. Rudder tillers i favour the nylon ones..use a seperate bolt and nyloc nut and these can be a tight fit and pushed onthe rudder post, and tweaked easily for adjustment..

OR consider a pair of "Z" drives, Graupner or Robbe, not very dear, looks the business. Bolts on the rear faces of the hulls…is its own rudder, and so the gear can be located under (for instance) a removeable cabin. Props…come with the Z drives, but the ECO motor will be quite suited to a two blade plastic prop (not an X pitch one). Z drives fantastic for going in reverse.

Ashley

[MARTIN BREWERParticipant @martinbrewer71680]

Thanks for getting back – think ill stick to the power train mentioned earlier – eco 600/nimh battery/prop etc.

Had a re think about the decking – what i think ill do – well the present idea anyway – is to put apermanently attached deck using internal framing around the edge and where the working area is – which is dropped – make that a fairly large hatch to give access to both hulls.

Im debating putting charging sockets in the wheelhouse so that the batteries can be charged in situ – any thoughts on that ???.

Will the hull need ballasting to get it to sit right – my father built a 51 inch Pinnace which he had to ballast with 15lb of lead to get it sitting right – not sure how the sit in the water will affect its sailing.

This is definately a trial and error build – just want to eliminate as much error before wood and glue meet hull and credit card meets t he suppliers.

Ive attached some photos of what its going to be based on – its the boat my youngest lad and the father of the boy work on so its got to be a reasonable replica although there will be some artistic licences involved to make the build easier.

i

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