Chris

As someone will be able to tell you there are Graupner 600 of differing kinds. I have 2 600 Eco in a Tamar lifeboat running on 9.6 v, I did install 2 computer fans above the motors.. Another boat uses 2 Graupner 600 12v BB motors.

What size are the propellers.

Tim

That's all good advice, years ago I changed away from grease and had no problems, it's been a hot discussion point on here in the past.

If it were my model I'd buy a few cheap plastic props, 35 mm and 37.5 mm and do some testing. As Glynn says there is no substitute for measurement and numbers.

Chas.

Re grease, as I said this has been much discussed in the past, with some people being in favour of grease an many, probably a majority against. To stop water coming up the tube, a decent shaft and bearings, together with properly adjusted prop / locknut and coupling at the top should be fine. Any decent light oil is ok in my opinion.

Other ideas and opinions are readily available, but this has worked for me on over 60 models…….. I'm old!

Chas

Chris
The clue to the main problem is the word "Speed". The whole range of Graupner Speed 600 motors is essentially for electric flight – even the ECO 600 has a no-load speed in excess of 10,000 RPM at 7.2v. This being the case then they need to be combined with racing props in an appropriate hull when used in a model boat. Drumbeat is not an appropriate hull, and four-blade props of that diameter are far too much of a load. I wouldn't use them with anything less than a Speed 700 12v, and two of those would vastly overpower Drumbeat.
Your most cost-effective solution is to change the motors for two Mabuchi 555's – less than a tenner apiece . They have the same mounting holes as the Speed 600 range and the same diameter shafts. They will turn at about 3500RPM no load on 8.4v and should draw a low single-figure current on load, even with those big props. An alternative is the MFA 540LN, which is also a 5-pole motor and has similar performance. I have used both types and was very happy with their overall behaviour.
Links are here **LINK** and here **LINK**

Dave M

Chris

You can start with the current props but, as Ashley says, you might choose to experiment. I'd start at 40mm dia x 3-blade if the model was mine.
MFA and Component Shop can supply a suitable ali mount – it's the same for the 540LN and the 555 – and the Speed 600! You can also obtain a moulded glass-nylon mount. Model Boat Bits [Steve Tranter] can supply both types **LINK** I favour the glass-nylon type as it doesn't flex at the bend.
The motor mounting thread is M3. I buy all of my model boat fixings from this supplier **LINK**
The 540LN has a very short shaft so if that might be an issue with the length of the couplings – especially if you use a glass-nylon mount – then the 555 might be more suitable. There's not a great deal of different in performance. The links I posted should show these dimensions.
Finally here's my choice of watt-meter, although others are available **LINK**

Dave M