Video

Pivot Point Specials 2 - position for ship moving ahead or astern


published on 12 May 2022 714 -

Found on YouTube. Created by "ISSIMS - Innovative Ship Simulation". Originally published on 2020-07-11.
In my view the old conventional opinion from seamanship books and even the mentioned earlier discussions (e.g. Cummins, Seon-Gi Seo,…) are limited and not very helpful – in the following I tried some samples for clarification:
1. What is the Pivot Point (PP): The pivot point is per definition the point where the ship is turning around momentarily – it is the point where the transverse speed component of a rigid body like a ship is zero; before and behind this point the transverse speed components have opposite directions. So it is real - and not “a trick of the eye” or “virtual point of rotation” etc. (The only thing what should be pointed out: Under the effect of current there will be a difference between the Pivot Point through water and PP over ground!).
2. What is the PP positon depending on? – The position of the PP is depending on the ratio of drift motion (transverse peed) and the turning motion Rate of Turn:
a. If there is pure turning then the PP is at the middle of the ship length - the transverse speed components at bow and stern are equal but with opposite directions.
b. When drift speed is added to turning motion then the turning point moves out of the centre to bow or stern – it is still on the ship lengths when the transverse speed components at bow and stern are different but with opposite directions.
c. If the drift speed is higher than the rotational speed at bow or stern then the PP moves in front of the bow or behind the stern.
d. For pure drifting motion and no turning the PP is in infinite distance.
3. Is the PP applicable as a reference Point or even fulcrum to use the distance to the PP as lever for creating a turning moment by a force? - No, not at all: Because due to the effect of the force mostly the PP will immediately move to another position! Therefore in all simulation systems normally the Centre of Gravity is being used as origin of the coordinate system where the balance of all forces and moments will be used to calculate the future motion of the ship – and there are more effects to take into account than the lateral resistance and the centre of this force…
4. So where we can finally expect the PP to be under the effect of control forces or external effects: to say the truth: simulation would help to find the answer therefore we set out to develop the Fast Time Simulation system SAMMON to support training and even more the conning of ships in future. However, some trends can be concluded from sample simulations:
a. When the ship is moving ahead then
· the PP is close to the bow if the rudder or thruster at the stern is used, there is a considerable drift speed and the swept path is high
· the PP is moving into the midship or stern direction if the bow thruster or bow rudder is used – then the drift is decreasing and the swept path is smaller
b. When the ship is moving astern you get the opposite effects when control forces are applied at bow or stern…
These trends are shown in the movies for PP position for stopped ship and another for the moving ship. You might also have a look into the movie “Theory behind turning…” for an overall understanding…
Please enjoy!
Knud Benedict

Join the conversation...

Login or register to write comments and join the discussion!
RC
Ricardo Caballero Vega Panama Canal Pilots Association, Panama
on 12 May 2022, 14:25 UTC

A thorough an wonderful, easy to understand explanation of one of the most important fundamentals of piloting. Great job, and thanks for posting.
0

Read more...

Video How Ship Anchor Works? - Procedure For Anchoring a Ship at Sea

published on 11 July 2020

#Anchor #shipanchor #windlass Anchoring is one of the very frequent operations onboard ships. A number of variables and external factors influence the duration and location of an anchoring operation. While the type of seabed is of utmost importance during anchoring, soft muddy grounds or clay bottoms are best preferred. It should be taken care that the anchoring bottom is free of power lines, submarine cables, pipelines or rocks. Various methods on anchoring include consideration of...

1

Video How port pilot sail out ship from the port? Grimaldi lines catania roro ship

published on 22 April 2022

In this video I will show you Grimaldi Lines Catania RoRo Ship

0

Video Physical Pilot Ladder Simulator (Chile)

published on 2 January 2020

This video has already been published for the first time in 2020. Please also note the second, more recent video in the appendix. This physical ladder simulator was designed for crew training in the ladder arrangement and for all the users especially for pilots.

0

Video Yaw Stability of Ships - Basic Principles by Knud Benedict

published on 18 November 2021

Another very good explanatory video by Knud Benedict. Absolutely worth seeing.
Yaw Stability is an important element of Ships Manoeuvrability - both for course keeping and turning ability. This first video in a series explains the Basic Principles of stability in steady state equilibrium conditions and the forces / moments involved

1

Article GPS (Part 2), physical and technical errors of GNSS - an error analysis

by Capt. Gunter Schütze, Thailand/Germany - published on 26 February 2020

In my announced sequel, the second part of GPS, it is primarily about the technical and physical operational and functional limitations to which GPS is subject. These limitations, in part, have serious implications for the accuracy of GPS, and even go as far as limiting the functionality of GPS in its functions or even making it impossible. In doing so,

0

Video 2021 SAFETY4SEA Virtual Forum – DAY 3

published on 1 September 2022

Welcome to the #2021SAFETY4SEA Virtual Forum! On DAY 3 we are navigating through… Forum Agenda 0:00 - Intro 0:06:38 - Panel #7 Ship Safety – Dry Bulk 1:10:38 - PPT: Loss Prevention, Capt. Konstantinos G. Karavasilis 1:23:20 - PPT: Digital Loss Prevention, Capt. Martti Simojoki 1:36:35 - Panel #8 Ship Safety – Tankers 2:38:02 - PPT: Balancing between automation and people: the Future of Maritime Training, Mrs. Joanna Eugenia Bakouni 2:47:16 - PPT: Training & Development: Lessons Learned from...

0

Article The continuum of simulator-based maritime training and education

published on 23 November 2021

The COVID-19 pandemic has brought unprecedented challenges to the maritime supply chain and called for accelerated adoption of digital technologies in various aspects of maritime operations, including the area of maritime education and training (MET).

0

Video Pilot transfer by helicopter is a demanding task

published on 8 December 2021

transfer of Marine Ship's Pilots by helicopter hoist is a demanding task.
Berthing means bringing a vessel to her berth until the ship is made fast. ... The berthing and unberthing manoeuvres require great knowledge and skill by the master, officers and the crew, as well as an excellent team-work with the rope-runners and the mooring party ashore

0

Video Eden Pilot Station & it's Harbour Masters-Pilots

published on 17 August 2020

Created by Eden Killer Whale Museum in association with a display, 'Navigating the way' looking back at the 160 years of history of Eden's Pilot Station and its harbour masters-pilots.
'Navigating the way' was on display from 19 August 2020.

0