Theory behind Turning dynamics of ships

published on 6 May 2020 1552

Found on YouTube. Created by
"ISSIMS GmbH - Marine Prediction Technology"

SAMMON Lecturing Video describing

"Theory behind turning dynamics of ships"

SAMMON - the IDEAL tool to identify manoeuvring capabilities of a ship - SAMMON - learning the EFFECTIVE way

Comment by Gunter Schütze via LinkedIn:
"Prof. Benedict a very interesting video by HS Wismar / Maritime Simulation Center Warnemünde ( MSCW) & Innovative Ship Simulation and Maritime Systems GmbH (ISSIMS). Excellent and understandable the dynamic effects of the forces and moments in turning circle explained. A really good illustration for students, nautical officer and Captains to lead them to the dynamic basics and to refresh the knowldege. I can only recommend this video. Thanks for sharing."
Germany, Wismar

Join the conversation...

Login or register to write comments and join the discussion!
Knud Benedict Germany
on 21 December 2020, 11:49 UTC

Thanks to Gunter for the recommendations and Michael for bringing in ideas and questions. To answer your questions, I like to explain the following:
1) The transverse force Y(ß) can be explained by two models:
a. Either it can be seen from its nature as a Lift force, i.e. the same force who lifts an airplane wing up in the air, works now horizontally on the ship hull due to the drift angle ß. It is generated by the uneven force distribution caused by an additional circular flow around the body (wing, or here the ship’s hull). This lift force has it maximum close to the wing nose – this means for the ship it is working more to the bow, so it turns the ship: I made an additional movie on that effect at out ISSIMS website on YouTube (“Effect of Drift Force and unstable moment”,
b. A second way is to look at the effect of the transverse speed along the ship length (This as named as “Slender body theory”). You are right that the transverse speed distribution is constant. However, the force due this inflow is not constant: because of the friction in the flow there is a boundary layer around the ship which is getting thicker to the stern and therefore the transverse forces are smaller at the stern than on the bow – this model also explains why the bow turns to increase the drift angle, which is called as unstable moment.
2) The "additional force at the stern" Y(r) is not just the aft component of the above evenly distributed drift force. The rotation /Rate of Turn creates a linear transverse speed distribution with maximum at bow / stern and minimum / zero at the ships center. This has an effect which can be explained by the wing/lift model under a) as curved centerline of the wind profile
3) You are right: A centripetal force is a force that makes a body follow a curved path. Its direction is always orthogonal to the motion of the body and towards the fixed point of the instantaneous center of curvature of the path - so in case of the ship motion on a circle these are the forces due to drift Y(ß) and turning Y(r). These forces are balanced by the centrifugal forces (which is Ycentrifugal in the movie). The ship is able to move in a steady state motion - This is also an equilibrium condition at constant speed and also constant rate of turn.
I do hope my explanations are of some help for professional as you are. And I should underline that these are attempts of us as humans to understand the nature – that’s why I mentioned two models (there are even more…). And they are not “Laws” - even the equations of Newton and Einstein are not Laws, but they represent our current views and approaches to describe the nature with our brain in order to think and plan ahead (– and have to be checked and approved continoulsy in daily life). In this way I made some comments in my movie about “digital twins” as key maritime innovations ( you can have I look if you like.
[show more]

Michael Nicholson Shipmove Ltd., United Kingdom
on 7 May 2020, 09:43 UTC

I either; don't fully understand, or disagree. 1) Why must the working force (transverse force) Y(B) be acting close to the bow. The rudder is providing a moment, I don't see why/how the ship also provides a turning moment. The drift angle of the ship to its bodily movement is uniform. Surely the forces would be distributed evenly?
2) Is the "additional force at the stern" Y(r) not just the the aft component of the above evenly distributed drift force.
3) The use of the term Equilibrium, is this correct? For an object to describe an arc or a circle requires an acceleration towards the centre, caused by centripetal force. This is not in equilibrium. Equilibrium would be a straight line at uniform speed.


Video Pivot Point Demo - HS Wismar

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


Video SAMMON Intro Ships Manoeuvring Predictions

SAMMON Introduction into Ships Manoeuvring Prediction
- newly made Video to display the principles of SAMMON


Video Knud Benedict Presentation on “Digital Twins” at IMLA SMU Seminar

This is the recording of the presentation with the title:
“Digital Twins" as Key Maritime Technology Innovations for MET - and for Operation of Intelligent Ships
It was held at the MET Training Course by Shanghai Maritime University on Oct 27 2020 on the occasion of IMLA 40th anniversary


Video Discussing video: Pilot Transfer to Ship by Helicopter

Let us see how a maritime pilot is transferred by helicopter to a ship. In this video, we discuss briefly some procedures in a helicopter/ship operation for the transfer of pilots.


Opinion Pilot Ladder - The Weakest Link in Marine Pilotage

by Capt. Santosha K Naya - published on 10 August 2020

Pilot transfer arrangement is a sensitive topic to be discussed among the pilot’s fraternity. Although ships are designed and operated with compliance to the SOLAS requirements in all respects including the pilot transfer arrangements, there has been numerous deficiencies observed related to pilot transfer arrangements. The small deficiencies from the part of ships cause life threatening accidents for pilots and sometimes to the ship staff themselves. There are many instances of defective ladder and complacency in proper rigging of ladders has been reported almost every day in different parts of the world. Many pilots lost their life, severely injured for life and face many minor to major accidents. The latest incident being the Capt. Timothy Murray of Sandy hooks Pilot.


Article What is a SWASH pilot boat? What's the difference to the SWATH technology?

by - published on 5 June 2020

At the A&R shipyard in Germany, the successful principle of SWATH boats was further developed in 2013: The SWASH principle allows sea-going, smaller and more economical boats.


Video Humber Maritime College Simulator Tour

At Humber Maritime College we have state-of-the-art marine simulators to teach our Merchant Navy cadets in an environment close to reality, preparing them for a career at sea.


Video How not to climb down a Pilot Ladder

The video was found on some social media channels in June 2020. When so many elementary mistakes are made and so many risks are taken, this is exactly what can happen! It's a demonstrative example of an unprofessional action: 1) Where is the life jacket? 2) No backpack on the shoulders. Use a rope to have the backpack lifted by the deck crew. 3) Where is the rest of the crew (on vessel / on the small boat) for safe assistance? What other mistakes have you discovered? We do not put videos...


Video ONE EAGLE ULCS coming in to Europoort

The 366 m long ultra large container ship ONE EAGLE entered Europoort at deep draft , backing into the Amazonehaven. She finally berthed to ECT DDE terminal, before partially discharging her cargo.


Article Danish Butter Cookies...

by Marine Pilot Luis Vale, Portugal - published on 17 July 2019

Why “Danish Butter Cookies” are a part of the standard navigational equipment…