what props

[Eric HoareParticipant @erichoare71058]

Hi William, I had a few problems choosing motors for my really heavy 2 metre boat (which you can see on Albums page) As the two engines each have a 12v lead acid battery to drive them I was told that the Johnson 600 motors would be ok, these motors have a 3.2mm shaft so you need the coupling to match. The motors are made for Black and Decker drills so have a huge torque and spin at 22000 revs at maximum power. You can reverse the motor by reversing the power input eg; positive from speed control to Negative to motor. Ensure each prop turns outwards (looking at the top of the prop) There has been a lot of controversy about which way props turn but in a new study they found that outward turning props draw the water up from the keel unlike inward turning props draw the water from the edges of the boat which pulls in air from the wash, this reduces speed. Hope all this helps a little.

Regards, Eric

[Dave MilbournParticipant @davemilbourn48782]

I'm sorry but I have to disagree. No 500/600 sized motor would be able to power a model the size of Mr Hoare's, even in a pair. To power that big model he needs either two large car blower motors or two suitable brushless motors of at least 600W each. You might get two MFA 850's to move the boat but I doubt it would be at any significant speed. These particular motors are likely to be those he has described and recommended , although I note that he hasn't actually installed or tried them in his model yet. They were manufactured to be run through 9:1 or even 10:1 gearboxes and are totally unsuitable for operating model boats when coupled direct to the props (i.e. without gearing). The following is lifted from Model Boat Mayhem main site and was written by yours truly some time ago. Unfortunately the motors are still being sold as suitable for model boats. In a big model on 12v they would have a similar effect to putting a Formula One engine into a quarry dumper truck.

Bad 540 Motors!!

These are pictures of the rogue 550 fan-cooled motors which have caused several members some grief over the last year. They are available on E-Bay as well as at shows and from certain retailers. The legend on the can says simply “Johnson”; there is no further ID except the numbers around the flux rings (which mean nothing to me). These are three-pole motors with an internal plastic cooling fan which can be seen through the slots in the case just in front of the brushes. The backplate is a dark grey metal casting as opposed to the usual 540-style white plastic moulding or silver-coloured steel pressing. The case is substantially longer than a stock 540 – some 65mm from end to end, and the motors have two steel flux rings pressed around the forward half of the case.

We have found that the motors are not suitable for “normal” scale models if run at anything over 6 volts. For example, one member has two of these things fitted into a Graemsay ferry and has discovered that he has “low speed handling difficulties running from 12 volts” – probably the understatement of 2006. Another member reports that the stalling current is astronomical and I can personally vouch for the high current consumption, even at relatively low speed on 7.2 volts. They also get very hot very quickly and should be water-cooled for all installations.

In short I wouldn’t recommend anyone to buy one of these unless they are very familiar with all aspects of operating high-speed DC motors. Indeed, the only reason I have one to photograph is that it was given to me. Personally I wouldn’t install it in anything but a wheelie bin………but what do I know!

William

I think that the 9.6v packs will be too heavy and too powerful for Sentinel when used with those motors. This is not speculative – I designed the kit of HMCC Sentinel and have built two of them, and we used to sell the MFA 540/1 motors when I ran ACTion RC Electronics.

Dave M

[Paul TParticipant @pault84577]

I don't know if this will be of any help.

For my larger model boats I use the motors and control equipment from mobility scooters and for my smaller models I use golf cart motors and control equipment, lots of these on ebay and sometimes at car boot sales.

For my really small models I use 550s / 600s (which are as rare as hens teeth but I know a very good chap) or the ever faithful MFA 800 / 850.

I do miss the petrol engines though.

Paul

[harry smith 1Participant @harrysmith1]

Hi Paul

I miss my old OS40FSR, but, engine motors start easier!!!!

[BRYAN ASTONParticipant @bryanaston57723]

Greetings all

I am building an Aronuat Victoria boat kit, would an eight blade prop be suitable to use in this boat ??.

Regards Bryan

[Dodgy Geezer 1Participant @dodgygeezer1]

If you're talking about the Aeronaut Victoria, the more normal prop is a 2 or 3 blade.

Of course, any prop CAN be used on a boat, and any given prop design can be optimised for a boat/motor combination – but you would usually think of a 2-3 blade, perhaps 40-50mm diameter prop for that. Purely on cost grounds. An 8-bladed prop is going to be unusual, and VERY costly…

[BRYAN ASTONParticipant @bryanaston57723]

Greeting Dodgy

Thank you for your reply, I take your suggestion, by the way a graupner eight bladed is only £7.50 on eBay .

Regards

[Colin BishopModerator @colinbishop34627]

Never heard of an 8 blade model prop, 5 is usually the maximum. Can you post the link so we can see what this beast looks like?

Colin

[BRYAN ASTONParticipant @bryanaston57723]

Colin

I missread the add it was for a five blade prop, perhaps I should clean my glasses more often, my apologies , my only excuse is I'm getting old

Bryan

[Dodgy Geezer 1Participant @dodgygeezer1]

Posted by BRYAN ASTON on 30/08/2017 16:24:00:

Greeting Dodgy

Thank you for your reply, I take your suggestion, by the way a graupner eight bladed is only £7.50 on eBay .

Regards

 

…and £3.30 from Cornwall Model Boats – though you have to pay postage on top of that….  http://www.cornwallmodelboats.co.uk/acatalog/graupner_propellers.html

I quite like the prices here – **LINK**

Edited By Dodgy Geezer on 30/08/2017 22:52:29

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