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[n33h]

i've got a scratch built oil rig support vessel, over all weight is 10.5lb

the motor gets hot (i know its struggling against the weight of the boat so hence the heat)

do i swap out for a bigger motor (600 size or so)

or

do i put in a gear box (if so, what ratio shall i use ? i want the prop spinning slowly for fairly scale speed)

thanks nick

[nick_75au]

Gear it or lower voltage or slower motor,
 what size prop are you using?

Nick

[n33h]

its spinning a plastic 35mm, 3 blade prop, the motors a 500 size, what size motor shall i use ?? a smaller prop and lower voltage will not move it

[malcolmfrary]

the motor gets hot (i know its struggling against the weight of the boat so hence the heat)

The motor never struggles against the size or weight of the boat.  It does struggle against the size and/or pitch and/or number of blades on the prop.
A 35mm prop seems a bit small for a 10lb boat, a larger prop would need either gearing down or a larger motor, preferably one wound for torque rather than revs.

[n33h]

its a pre-built hull by some one else, 35mm is the most size prop i can get on there without ripping all apart again, so i'm left with gear reduction (2.5:1 maybe) or going upto a 600 size motor, the prop is also the least pitch (1.2) prop i have

[n33h]

what if i try a rock crawler motor, are'nt they high torque, low rpm motors ??

[nemesis]

Hello, I always gear down 3 to 1, Nemesis

[Martin (Admin)]

Hi Nick,

Out of the water, does the motor scream at full power?
 If so, you may just need a "slower" 500, or a 5 pole motor.

I always prefer to 'go bigger' and throttle back, ideally, I like a boat that rull a full scale speed at about half throttle...
... not sure how that helps you but you never know!

I've used these with some success! - http://www.mfacomodrills.com/motors/540ln.html
 ACTion and MMB useed to do some nice slow motors but they sold out of those pretty quick....

[Martin (Admin)]

Just seen these: 

RS 555 MT  5 POLE MOTOR
RS 555 MT  5 POLE MOTOR
6- 12 volts
No load speed 4900 rpm on 12 volts
No load current 0.3 amps
Length 70mm
Dia. 35mm
Shaft dia. 3.2mm
 
Medium torque motor suitable for tugs, trawlers, cargo boats and warships with props up to 40mm diameter. -

http://marksmodelbits.ieasysite.com/mmb_site_013.htm