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[shadysadie]

Please can you tell me if four 385 motors will be sufficient to power my 55" Fairmile LRRL. The hull is from Kingston Mouldings , the props. are 30mm brass and I seek good (not high) speed and endurance.

Thanks, David

[Tug-Kenny RIP]

They might be a little small.

I tried 600's in mine and 4 of them were too much.  High battery use and very noisy.

Maybe for you to go up to 400's or maybe 500's.

Cheers

ken

[morley bill 1]

Ive had low drain 500s 6 volt from the component shop very smooth runners four of these should push the D ok   Bill.....

[shadysadie]

Thanks folks. I also have 4 low drain 545's but fear that these may be a tad too much?

[shadysadie]

Another thought has crossed my mind. As I shall be powering the motors through an Action P94 mixer, do both pairs of motor have to be the same or could I run a 545 (outer) paired with a 385 (inner) on each side? This should give me more than enough power with reasonable economy but is this technically feasible?                                                                     

[john44]

Hi, I am going to try 545s on mine and have only mixed the 2 inner motors/nearest the rudders,they run on L/hand throttle stick, for general sailing.I have put the 2 outer motors on the R/stick for when I want a bit of speed I will just push both sticks up at the same
time. I am just waiting for my 35mm props and I will let you know how it goes.
I will be running on 12 PB.

john

[morley bill 1]

 The 545/s should be ok you don/t have to use full power but it/s nice to have a little spare power when needed  Bill.....

[malcolmfrary]

Another thought has crossed my mind. As I shall be powering the motors through an Action P94 mixer, do both pairs of motor have to be the same or could I run a 545 (outer) paired with a 385 (inner) on each side? This should give me more than enough power with reasonable economy but is this technically feasible?                                                                     

Not a common arrangement, but as long as the props are matched to their respective motors it should work OK-ish.  Since both motors in each pair will be offered the same voltage at any given throttle setting, the load that they take will depend on that motors prop.  I can't really see any advantage in run time from the arrangement since the only time that the "cruising" arrangement of one running, one not would be at very low throttle settings, when one has started and the other is still making its mind up.  Anybodys guess as to which would be which.

[thunderchild]

Good Day David


I have the Kingston Mouldings Fairmile "D" MTB (I've only just started building her, and I've got the rudder posts in), I've spoken to Robin, the one in the videos on his website are fitted with Graupner Speed 500E's (unfortunately no longer available), I suppose any economy 540 size motor with low current drain would work well. I'm pretty sure he said that they were running on 6 volts.

[shadysadie]

Thanks again for all the help. I am going to use the 545's although it is going to be a bit of a tight squeeze for the centre pair - I measured carefully (or so I thought!) but still managed to make a slight faux-pas with the lateral spacing of the prop shafts. A slight (!) modification to the mounting brackets should do the trick but if this fails I shall have to turn them through 90 degrees and devise a vertical central mounting board.

Regards, David.                                                                                               

[shadysadie]

Hello again folks. I have managed to fit the 4 low drain 545 motors to the Fairmile but now need your advice on batteries.

My previous models have all been tugs, drifters and coasters so sealed lead-acid batteries have always sufficed but this is my first "speedboat" so I am thinking that I must go NiMH to minimise weight.  This is all new to me so please advise on the capacity and number of cell packs I shall require to obtain a duration of 40mins. or so cruising with the occasional burst of speed - if this is indeed attainable?

Thanks, David

[rnli12]

Hi David,
I had the same motor/prop set up and used 4 x 7.6v NiMH 3600 packs and just one on each motor also tried 6v 4 ah sealed gel but was heavier. The running time pottering was about 30 mins with the occasional bursts getting the model on the plane was difficult but get the weight right and power right it looked smart. You could drive either set of motors (Inb/Out) independently until mid throttle then all four kick in. Plenty of options....
Rich
 

[shadysadie]

Thanks rnli12 for pointing me in the right direction. I suppose  that I must now experiment with battery positioning in order to find the optimum centre of gravity for planing performance. Should be fun!

Thanks again to all of you for your advice.

Regards, David.