inkaboat

Hi, I'm new here but the site looks pretty good from here! My last model was steam driven but I've acquired a 1300mm x 300mm glass hull, looks like a Perkasa type. I need some guidance on drive unit selection and weight distribution. I have three 'rogue' Johnson motors which the media doesn't like but I can live with them! Can anyone help please?
Thanks
John

Bunkerbarge

Hi John and welcome to the forum. I used to live at Locks Heath for a couple of years so I know what a nice part of the country you are in.

As with so many of these questions there really is no easy answer so all we can do is offer a guidance along a path that you must ultimately follow and come to your own conclusions.

I think the first decision has to be whether you want all three props driving closely followed by which ones do you want to independently control. This will help you to decide what size of motors would be required.

I was looking inside a Perkasa only this morning of round about this size and it had a single motor through a gearbox driven by a 12 v gel cell motorcycle type battery sat flat in the middle. I would have guessed the motor to be in the range of a 550 but the boat didn't plane or even significantly rise so I think it could have done with a bit more.

The only way to be sure is first decide on you choice of drive preferences then experiment on the pond with a ballasted open hull and everything free to be temporarily located.

I always prefer scale so if it was me I would go for all three props driving and maybe the two that rotate the same way being on one speed controller and the other one on its own. You can then play with maneouvring the boat as well. Another more balanced arrangement would be to have the centre one a dummy and the two outer ones on thier own speed controller.

If you were looking at three motors you may even have enough with three 385's but if you were going for two I would think you may need a couple of 500's.

You will need a 12 v gell cell for any sort of duration on the water and I would tend to have it slightly aft of midships as you want the bow to at least rise under power

__________________

“Dirty British coaster with a salt-caked smoke stack, Butting through the Channel in the mad March days"

inkaboat

Thanks for the advice, really helpful. I see model boats as an opportunity for naive experimentation and then move on: for example I made a variable pitch prop for my 1 metre steam lake launch (my avatar) which made for some great handling and lots of interest! Once I'd proved the design I put the boat on ebay and to my surprise someone paid over a thousand pounds for it! Back to the Perkasa I rather like the idea of two 600 type motors (now I'm talking out of my A**) driving contra-rotating props with a third motor on a microswitch to get the boat over the 'hump' onto the plane, then feathered to conserve power. I'll post info as to how I get on !
Cheers
John