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[Pete25]

Hi
first of all im new to this and in the middle of building a 6ft long 1ft wide and about half ft tall battle ship. i have the hull built at the minute and now i need some advice on electric components to use and propeller size and so on.
here is a video of the hull iv built.couldn't seem to get good pictures so did HD video instead build it with no plans just looked at some hull designs and built the hull as i went along if that makes sense 

VIDEO HERE
http://youtu.be/Ee9wJpThPQ4

i have 2 Johnson 600 Motor's (brushed) at the minute and i want to run them at 12v. i will be using 2 12v motorbike batteries as the weight of these will aid in balancing the boat when its in the water
im buying my parts online and he said he recommends 5mm prop shaft for my model
will require 4 blade props
at least 60mm or 70mm diameter

is this correct anyone ? my budget is quit small so i need to do everything as cheap as possible would love to go brushless but that's £££££ as we all no plus ill be happy to get the hole thing up and running to have some fun with at my local boating lake :)

[brianB6]

Hi Pete
Hardly a battleship with those hard chines and deck lines.   Battleships were round bilge.
Why not try for a corvette or frigate but even then they should be round bilge.
I would keep your 600's rather than go brushless which are ok for fast electric boats but not much else on water.   Have you tried them on 12 volts under load since a lot of them are only 6 volt.
4 mm. prop shafts should be fine for that size motor but 5 mm. if you intend to get bigger motors, say 900's. Prop size depends on motor ratings and hull size and is often a matter of trial and error.   Try 50 mm. to start and work down.   Go for plastic to start with rather than metal in case you want to change them (and they are much cheaper)

[Pete25]

i was told there 6 and 12v motors. i haven't burgh them as of yet. can you recommend any 12v motors that i could buy in the uk and use baring in mind the price. i was thinking of cordless drill motors but unsure if they would work.

[tobyker]

Many of the cordless drill motors have a very high amp draw which forces up the cost of your ESCs. I'd be a bit wary of the Johnsons, as some of them are no good over 6v.The hull looks fine to me - Glynn Guest gets away with hard chine destroyers, so why shouldn't you. I think you will need some internal bulkheads as the material looks very thin and water pressure on the sides may well deform or rupture them with the weight of the batteries in. I'd have thought a couple of 500/540 motors would do, but make sure you get 12v rated ones, as many run too hot over 6v or just plain explode (gently) over 7.2v (many are made for cars with 7.2v nicad packs). See what motors ACTion do - his data sheets are useful.

[essex2visuvesi]

Many of the cordless drill motors have a very high amp draw which forces up the cost of your ESCs. I'd be a bit wary of the Johnsons, as some of them are no good over 6v.The hull looks fine to me - Glynn Guest gets away with hard chine destroyers, so why shouldn't you. I think you will need some internal bulkheads as the material looks very thin and water pressure on the sides may well deform or rupture them with the weight of the batteries in. I'd have thought a couple of 500/540 motors would do, but make sure you get 12v rated ones, as many run too hot over 6v or just plain explode (gently) over 7.2v (many are made for cars with 7.2v nicad packs). See what motors ACTion do - his data sheets are useful.

If going for 540s look up the high turn motors for rock crawlers
http://www.carson-modelsport.com/en/products/electronic/electricmotors/produktdetails.htm?sArtNr=500906023

[Shipmate60]

4 blade 60-70mm props will only require a max of about 5000 rpm so a motor that will deliver the torque is far more important that out and out speed.
Either gear down a faster motor or use a low speed high torque motor which will not be overloaded by these props.
I have used similar sized 3 bladed props with 2 x MFA 800 on 12 volts and it pushes a 6 foot Destroyer along very well.

Bob

[Pete25]

thankyou for everyone's reply and help. believe me i need it 
i am going to re inforce the inside of the hull as your right it is very thin and flexibble but nothing that cant be fixed with a skeleton of bolster wood  inside of it

arnt 60-70mm props abit over kill for this model ? i no its 6ft and 1ft wide but surly i don't need such big props. mind you im new to this so maybe that's what ill need :)


iv found MFA 800 for sale £25... and i need two  not cheap have to try and source them cheaper els were i guess of just accept it and spend.
so if i get 2  MFA 800 with 60mm prop. what side drive shaft should i go for ? 4mm should do it ?

thanks again for everyone's help 

[derekwarner]

Pete25.....one point of consideration is to try & understand an approximate scale [or stand off scale] that you are using   ....1:96?.....1:144?

From there you could compare & calculate the real vessel diameter props.....then scale down ....... ....

Lets work backwards for an example  

A battleship may have 18' [6000mm] diameter propellors...so if the scale were 1:96....[6000 divided by 96] = ~~~~ 69mm diameter which is pretty close to diameter offered by  shipmate60 as below  

Linear dimensions eg., "length/diameter" are simply divided by the scale.......however when we bring a second element  eg.,"speed or rotation" we divide by the square root of the scale ......

With respect to the prop shaft sizing.........the props themselves will have a nominal shaft size rating/requirement.........so try & match up your components prior to purchasing any individual item  & don't forget the shaft A frames....battleships may have two per shaft & all must be considered & match........ ....Derek