Video

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


published on 12 May 2022 727 -

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

Article Finnish-Singaporean Maritime Innovation camp explored new ideas from the contrast between pilotage operations of both countries

published on 20 January 2023

In December 2022, a week-long innovation camp was organized in Turku Finland, in which 16 students from the University of Turku, Novia University of Applied Sciences and five different universities in Singapore participated. Pilotage operators Finnpilot from Finland and PSA Marine from Singapore acted as industry partners.

1

Article New app: Pilot´s Tug Assist Tool PTAT - Bollard Pull Calculation for Marine Pilots

by Capt. M. Baykal Yaylai - published on 19 February 2020

Required tug power and number of tugs needed in variable conditions of wind, current and waves isin most cases an assessment made by pilots based on their professional experience. However, assessments will raise questions by lawyers if something goes wrong. They will use tools to calculate what really is needed with respect to tug power and number of tugs. They have furthermore the advantage of time.

1

Video What Happened To The Napoli?

published on 22 October 2021

In this video, you can take a look at what happened when the Napoli broke her back and was run aground on the south coast of the UK.

0

Video Maritime Pilot Training VI - Pilot Ladder Training

published on 12 May 2021

Training video VI on the correct use of the pilot ladder

0

Video Pivot Point Demo - HS Wismar

published on 10 July 2020

SAMMON Lecturing Video describing
"Pivot Point Demonstration"
-------------------------------------------------------------
SAMMON - the IDEAL tool to identify manoeuvring capabilities of a ship - SAMMON - learning the EFFECTIVE way

0

Video Bellcraft pilot boat powered by Volvo Penta IPS

published on 23 March 2022

The busy Strait of Messina which separates the island of Sicily from the Italian mainland is now home to a new pilot boat, manufactured by Bellcraft and powered by Volvo Penta’s Inboard Performance System (IPS).

0

Video PILOT VESSEL SPINDLETOP

published on 19 March 2021

BREAUX'S BAY CRAFT 90' PILOT VESSEL

0