hi ya there Ray
I think you have reached a point now, where you need to decide what motor you are going to power this model with. Are you going to go with the same power unit as in the build I did? or, are you going to direct drive this?
1. MFA have stopped producing the belt-drive gearbox which I have used - but - I do know there are still several available from MFA commo drills. The item number for the gearbox (without motor) is 1092/4. Their contact telephone number is 0130 461 2132.
Failing this, if they have none left in stock - there is a model shop which is called Phills Model shop (they have a website) they are based in North Tyneside (North Shields) and have a few in stock. With this belt-drive gearbox, it would be adviseable for you to shorten the length of your prop-shaft tube - to say, about 6 inches in length. Doing this will give you a bit extra space inside the hull for batteries etc.
2. The next option you have is to use direct drive. Here you would have to source a favourable motor, for the size of prop (I think the prop is approximately 40-45 mm diameter) x 3 blade. FLJ (ACTion) sell / may still sell a 12 volt motor - classed as a 555 motor, which is physically the same as a 540 motor in size - about 33 mm diameter by about 56 mm long. This would be ample to power this model.
As I say, it is classed as a 12 volt motor, I think 12 volts driving a 40 mm prop, would give you a 'very-over-scaled' top-end speed. But, that is why we have speed controllers - plenty power in reserve.
The thing though with using direct-drive is that you will have to check the clearance between the centre of your prop shaft to the top of the keel this will ensure you have enough clearance to fit the motor, without it fouling anywhere. Also, do not forget one has to allow for fitting a coupling between your motor and prop shaft.
So. basically, before you fit the prop shaft, decide how you are going to power the model.
Another thought with regard to motors, when Billy Ruffin built the Cervia Tug, he used the motor from (I believe it may have been Model Motors) it would be a good idea to send Billy a personal message to find out what motors he used for his model, as the Cervia Tug is basically the same size.
Billy Ruffin is known as Cyril on this forum.
Hope this helps.
Aye
John
Bluebird.