Help with propeller assembly
 

Hello,
i want some help with the propeller assembly to my rc boat. I don't know anything about mechanics, i have knowledge only in electronics and programming so i don't know which mechanic parts and what dimensions should i buy. From what i found after a long extensive search on tutorials (videos/articles), i need 2 shafts one small and one long which they need to be the same diameter as the motor shaft, 2 couplers one joint and one brass coupler solid which they need to match shaft diameter, one tube which i don't know how much diameter, 2 bushings again i don't know diameter and the propeller. If i forget something correct me. So specifically i need to know the exact diameters if have a motor with 4mm shaft and how and why i stuff the tube. Furthermore how i attach the tube to the long shaft and how i attach the propeller to the end of the shaft

You are missing a lot of information that we would need to help you. For example:
1) What boat are you dealing with and is it a kit build or a premade hull
2) You already said it has an electric motor but what other electronics do you have for it
3) What motor does it have? 4mm is pretty much a standard size, what about KV/RPM
4) Do you have the parts to steer it with yet and, if so, what do you have?
As you can probably tell, there's a lot more to setting up an electric boat than just adding parts to the motor output shaft

Thank you for replying. My boat is going to be an autonomous low speed boat so I want to keep it as simple as possible. No preferences, even a tanker like boat from a light material would do. Now my electronics are an arduino board, a gps module, an antenna module, a brushless motor, a servo motor, an esc and a lipo battery. The motor is a 750 kv 28/36 brushless 800g thrust.
I don’t have the parts to steer it yet that’s another issue. When I find out how to assembly the motor with the propeller I’ll search a way to attach the servo motor with a rudder that it will go at the center after the propeller.

To find out about parts needed, look at Hulls and click the "shafts" tab. Although it describes scratch building, the principles and part names are the same.
When you buy a prop shaft, you normally get the actual shaft along with an outer tube fitted with bushings. The propeller fits on one end and SHOULD BE SECURED WITH A LOCKNUT. At the inner end, you usually fit a universal joint which goes between the inner shaft end and the motor shaft. Most makers have options to give the appropriate sizes of hole for the shafts.

I am looking more like a how to article that explains the procedure and why we do that. I already know what to buy (mostly)but not exact dimensions except for shaft and propeller. I just don't know how to assemble it. How to attach bearings, locknut, how to stuff the tube etc.

Google can be your friend for most of what you need to know, but has a weak spot with "locknuts". It only finds self locking nuts, which are unanted here. Look for "double nut".. Locking the prop to the shaft prevents the tendency of the prop to either wind itself ever tighter on the shaft, or off the end of the shaft, depending on thread and direction of rotation.
Shaft bearings are ready fitted in the prop shaft tube, sometimes called a "stuffing box", since on some real boats the shaft passed through a box with a bearing each end that was stuffed with grease to keep water out.
Follow the link I offered earlier (autocorrected by the site to "hulls" ) and read it. It tells you a lot about how you do stuff and why.

Thank you for the information but i finally ended up just buying the couplers and an already assembled stuffing box. My only concern now is that my motor specs define that my motor have a max pull of 800g. Does this mean that the hull and the components inside (including the motor) cant exceed 800g or else the boat wont move?
the motor will be assembled with a Φ40 pace 21 shaft M4 propeller and a Μ4 x 210 mm MPJ stuffing kit
motor specs:
Turnigy D2836/11 750KV Brushless Outrunner Motor
Battery: 2~3 Cell /7.4~11.1V
RPM: 750kv
Max current: 14A
No load current: 0.8A
Max power: 210W
Internal resistance: 0.160 ohm
Weight: 71g (including connectors)
Diameter of shaft: 4mm
Dimensions: 28x36m
Prop size: 7.4V/12x6 11.1V/9x6
Max thrust: 800g

Ignore the "thust" figure for boat power. Everbody else does, and their boats work fine. Thrust of motor (whatever that actually means in useful terms) and weight of boat are totally unconnected. It "might" be a useful figure if trying to power, say, a helicopter if it is to go upwards and not just whirl that fan thing on the top around.
For moving a displacement boat, you have to overcome the inertia of the water, and to go forward by one boat length in a given length of time the propeller needs to move at least the volume (and therefore that weight) of the displaced water by at least that distance. I say "at least" because there are a lot of other variables involving propeller design and hull shape.