Mspc 2018 buet name

1. Md. Ashifur Rahaman
Dept. of Naval Architecture and Marine Engineering , BUET
Organizer , MSPC-2018

2. Confidential Customized for Lorem Ipsum LLC Version 1.0
Topics :
Propeller basics
Cavitation & Vibration control
Shaft Arrangement
Rudder basics
Water Tightness
BLDC vs DC motor
ESC
Workshop
INTER UNIVERSITY MSPC 2018

3. What is Propeller ?
Rotating hydro or airfoil to converts rotational power from the
engine into thrust
Lower pressure zone
/ Lift force
Workshop
• INTER UNIVERSITY MSPC 2018

4. Terms related to Propeller :
Workshop
• INTER UNIVERSITY MSPC 2018

5. Propeller Pitch :
• The higher the pitch, the faster the top end speed but the lower the rev's.
• The lower the pitch the faster the acceleration and the higher the rev's
• The angle of attack the greater the pitch.
• Effect the propeller efficiency.
Workshop
• INTER UNIVERSITY MSPC 2018

6. Propeller Pitch Vs Efficiency
Workshop
• INTER UNIVERSITY MSPC 2018

7. Propeller Slip :
● Due to prop slip we are going approximately 10-20% slower at top speed on high
speed craft.
● If the boat had zero drag and the prop operated with zero slip
Workshop
• INTER UNIVERSITY MSPC 2018

8. Workshop
• INTER UNIVERSITY MSPC 2018
Propeller-hull Clearances :
● Source : http://www.ricepropulsion.com/cartas/TNL48/TNL48.htm
(NOTE) These clearances are closely associated with the number of blades and can be estimated by :
(1) % = 0.23 - (0.02 x n)
(2) % = 0.33 - (0.02x n)
where: n = the number of blades on the propeller

9. Basic ideas about propeller :
● Submerged in water
● Zero degree angled with water surface horizontally
● Aliened with ship centerline
● Set before Rudder
● Keep 90 degree angle Rudder stock centerline with propeller centerline etc …..
Workshop
• INTER UNIVERSITY MSPC 2018

10. Cavitation :
Reduced pressure & Cavity creates
Workshop
• INTER UNIVERSITY MSPC 2018

11. Workshop
• INTER UNIVERSITY MSPC 2018
Types of cavitation in propeller :
Hub Cavitation Tip Cavitation
Face Cavitation Root Cavitation

12. Cavitation control :
Workshop
• INTER UNIVERSITY MSPC 2018
Effects of Cavitation :
● Low propeller efficiency (Thrust reduction)
● Propeller erosion (mechanical erosion as bubbles collapse)
● Vibration due to uneven loading
● Cavitation noise due to impulsion by the bubble collapse

13. Workshop
• INTER UNIVERSITY MSPC 2018
Ways to Control Cavitation :
● Remove fouling, nicks and scratch.
● Increase or decrease the engine RPM smoothly to avoid an abrupt change in thrust
● Keep gradual pitch setting for controllable pitch propeller
● prevent ventilation of propeller

14. Source : https://www.youtube.com/watch?v=8FItnysLHCA
Workshop
• INTER UNIVERSITY MSPC 2018

15. Shaft arrangement :
Considerations:
• Lower Mass (stability)
• 100% straight (vibration)
• Smooth surface (friction)
Workshop
• INTER UNIVERSITY MSPC 2018
Approximate bare shaft length should not exceed 4 times of shaft dia.

16. Rudder :
● From the reference book Applied Naval Architecture by Munroe Smith the
rudder area can be determined by,
A =
𝐿 𝑚 ×𝑇(𝑚)
60
● Setting Rudder after propeller is better
● Submerged fully or larger portion to water
● Hydrofoil shape to higher efficiency
Workshop
• INTER UNIVERSITY MSPC 2018

17. Source : https://www.youtube.com/watch?v=cOX4X7duDvo
Workshop
• INTER UNIVERSITY MSPC 2018

18. Water tightness :
● Water kills Arduino & ESC
● Increased mass of ship & Loss in stability
● Main consideration is motor position
● If motor is set at outside of hull (less fear of
leakage but loss of stability & cavitation )
● So motor should be set at inside of hull ( recommended )
Source : http://www.eugeneleeslover.com/ENGINEERING/CHAPTER-7.html
Workshop
• INTER UNIVERSITY MSPC 2018

19. • Glue sticks can create good water tight bond but gapes may created when glue gun used.
• Super Glue also water resistant but brittle & not recommended when gapes are need to
fill .
• Araldite or epoxy is not so brittle , good for filling gapes & good for water resistance.
Workshop
• INTER UNIVERSITY MSPC 2018

20. BLDC VS BDC
• Higher Torque
• Lower response time (high RPM)
• ESC needed to operate
• Lower Torque
• Higher response time (Low RPM)
• ESC not needed to operate
Workshop
• INTER UNIVERSITY MSPC 2018

21. Why BLDC need ESC ?
Workshop
• INTER UNIVERSITY MSPC 2018

22. PWM / signal & 5V
Battery connection (Main Battery)
PWM / signal
Battery (Ground/ + ve)
Battery (VCC / - ve)
 Generally ESC should be able to supply 1.2 or
1.3 times current to DLDC rating current (But
heat generated in ESC so 1.5 times instead of
1.3 times recommended )
Workshop
• INTER UNIVERSITY MSPC 2018

23. Servo motor :
• To control or steer the rudder.
• Must be able to keep rudder in fixed
position against forces from water.
PWM / signal
Battery (Ground / + ve)
Battery (VCC / - ve / 5V)
Workshop
• INTER UNIVERSITY MSPC 2018