There are no benefits to other than the integral motor mounting and connection for interference suppression.

Apart from special ingredients that would permit higher operational temperatures (bearings,insulation and magnets) all these motors conform to the same laws of GCSE level physics.

If you search the internet for PDF files for small low power dc motors you may get the Torque Vs Current, Speed Vs Torque ,Efficiency Vs Torque graphs.Once you understand these then you’ve learned the black arts and have an advantage over salespeople.

The shaft diameter of a 550 is 3.2 mm nominal and the monoperm is a 2.3 ,I think.

A 550 is not a similar match to a monoperm. (see speed/torque performance curve)

Running time better on a monoperm than a 550? ..Yes, only because mick has a small prop which equates to a light load on the monoperm motor…. It would be the other way round with a large prop where the 550 would be giving more power and the smaller monoperm would be near to stall and red hot ..

http://www.mellorelectrics.co.uk/English/HTML/E_RSDC.html The 555 on this link would be closer to a monoperm although that is not the point Allan is trying to establish.? What I tried to clear up in my reply post is that one brand of motor is no better or more efficient than another.

http://docs-europe.electrocomponents.com/webdocs/002e/0900766b8002ed31.pdf is a link to a typical small dc motor data sheet which has both tabular and graphical data on page 2….

The motor output power curve is missing but it can be plotted because….

 Output Power, P (watts) =  ang speed (Radians per second) x Torque (Newtonmetre)

or                        P (watts) = 0.105 x R.P.M. x Torque (Nm)

The output power curve starts at zero at the origin,peaks out at the 50% load and falls back to zero at stall point. So if you start with a 5mm prop and gradually increase load torque with a 100 mm prop you pass the point where increasing prop size increases power .SAME GOES FOR ALL SIMILAR MOTORS.

If you have (at a given voltage) graphs or such monoperm parameters as

1. stall torque and current OR motor constant (Nm per amp)
2. no load speed

You can pick a cheaper replacement.

David. I rather think the question should be… I have a hull so and so big, what size motor should I put in it?    I am not sure building a hull to suit your motor is wise, as there are too many  variables to consider, notwithstanding certain types of hull have to have certain sizes and shapes of propeller to suit them and in turn these may not suit your motor. Ashley

I tend to agree with that, they do seem to be very expensive and have little benefit, if any, over a cheap motor. I like 385`s, I have several boats propelled by them, all motors brought from Maplins. They turn 40mm props nicely on 6v and will propel even largish boats, destroyers etc on 12v. MFA motors all come pre-suppressed and with mounts and leads on . Bargain. Ashley