Opinion

Bow Truster Effect on Ship's Headway


by Capt. Hugues Cauvier - published on 14 July 2022 2387 -

6
article courtesy of Hugues Cauvier & "The Pilot Magazin" (UKMPA)
Link to the original article below

To publish or not to publish

Usually, the reason to publish a technical essay is twofold. First you want to share findings with your peers. You hope that the ideas can be discussed and validated, that the added knowledge might one day play a part in improved professional acts. Secondly, you are seeking a date stamp, proving that you have expressed your ideas at a given moment. There is no patent for theories. The only retribution they bring is the recognition of authorship. If someone pretends that he or she figured it out before you, the burden of proof is on them and the date of issue of an article is a solid argument to back your position. My wife suggested a third reason to publish that was vaguely rhyming with self-glorification. I skilfully deflected that observation by telling her how beautiful she was and how I intended to wash the dishes and do the laundry for the rest of the month.
Capt. Hugues Cauvier, Pilote Corporation des Pilotes du St-Laurent Central. Source: LinkedIn
Capt. Hugues Cauvier, Pilote Corporation des Pilotes du St-Laurent Central. Source: LinkedIn
Capt. Hugues Cauvier, Pilote Corporation des Pilotes du St-Laurent Central. Source: LinkedIn
Capt. Hugues Cauvier, Pilote Corporation des Pilotes du St-Laurent Central. Source: LinkedIn
Promoting new views on a subject having a long history like ship behavior can be a slippery task. As convinced as you may be before writing, you can’t help wonder: why someone hasn’t come up with it already? Will it be shredded to pieces because key points were missed?

These thoughts are sure to wake the butterflies in the stomach, but the preparation of a technical demonstration remains a hrill. So, I’ll give it a go, and try to shed a different light on a ship handling phenomenon: why the use of bow thruster can ause ships to gain headway?

Bow Truster and Ship's Headway

It is common for pilots to realise, when the bow thruster has been in action for a while, that not only the ship turns but it also ains forward speed. A common explanation is that the low pressure created at the suction of the bow thruster would pull he ship ahead. This effect can also occur when turning the ship with the push of a tugboat or a rope pulling at 90° (on a small-scale vessel). In these cases, though, no area of low pressure is acting on the hull. The explanation has to lie somewhere else.
Here is a different approach. Apply a side force on a vessel. The resulting movement is the combination of two motions: the otation and the translation (lateral movement). In our case, the use of the bow thruster changes the position of the vessel as in figure 1. The bigger part of the vessel, including the centre of gravity, starts moving North. As the ship drifts with an angle, the water resists more on the side than at the bow, (fig. 2).
The direction of the centre of gravity is also more and more aligned with the ship’s heading (fig. 3). Those two factors help the buildup of forward speed.

In the case of a side force applied at the stern of a ship, the same principle applies. The azipod, the stern thruster or the pushing tug can, in addition to the desired swing, create sternway.

ABBENDUM

It has been a few years since the publishing of “The Pivot Point?” in The Pilot October 2008.

One of the consequences of the concept is a need to refresh the representation of the water pressure around the hull in ship handling books. The diagram showing positive pressure on the port bow when a ship turns to starboard is a classic. It was the cornerstone of the previous explanation for the shift of the pivot point. The bow is shown "leaning on” the compressed water, pushing the pivot point ahead. At ship handling speed, this pressure diagram makes little sense and should be corrected. The part of the ship ahead of the pivot point is moving to starboard and creates a void in the area of the port bow (fig. 4). So, negative signs should appear in that zone.
------------------------

A detailed animation and video of the above demonstration can be seen here:
Editor's note:
Opinion pieces reflect the personal opinion of individual authors. They do not allow any conclusions to be drawn about a prevailing opinion in the respective editorial department. Opinion pieces might be deliberately formulated in a pronounced or even explicit tone and may contain biased arguments. They might be intended to polarise and stimulate discussion. In this, they deliberately differ from the factual articles you typically find on this platform, written to present facts and opinions in as balanced a manner as possible.
Author: Capt. Hugues Cauvier
active marine pilot - Corporation des Pilotes du Saint-Laurent Central
Read more...

Video Bow thruster effect on ship's headway 1

by Capt. Hugues Cauvier - published on 14 July 2022

What is causing the forward motion of a stopped vessel using continous bow thruster action?
by Capt. H. Cauvier

4

Video Hugues Cauvier: Understanding the ship's pivot point (complete video)

by Capt. Hugues Cauvier - published on 3 September 2024

This video has been recut and edited by the creator Hugues Cauvier. Previously there were three episodes, which have now been combined into one.

1

Video How to Launch a Pilot Boat–Behind the Scenes at Point Hope Shipyard

published on 20 June 2025

Welcome to Point Hope Shipyard in Victoria, British Columbia, Canada. In this video, I follow the float off of the Pacific Navigator, a hardworking pilot boat that serves the Port of Victoria and Ogden Point. We watch as the vessel is pulled along the marine railway, rotated on the turntable, and positioned onto the cradle. Once secured, the cradle lowers to float-off depth, and the Pacific Navigator fires up her engines for a short harbour spin before returning to duty. Some segments,...

0

Article Study "Master (M. Eng.) Maritime Pilotage" in Germany

by Hochschule Wismar, University of Applied Sciences, Technology, Business and Design - published on 7 August 2024

Neuer Studiengang ab dem Wintersemester 2024/2025!
New degree programme from winter semester 2024/2025!

1

Video AIMPA’s Webinar on “Reconceptualising Indian Maritime Pilotage on 24th Oct 2020

published on 28 January 2021

The need to hold such a webinar was felt from the interaction over several months of AIMPA members through its President, Capt. Gajanan Karanjikar, with Capt Simon Meyjes and Capt.Ravi Nijjer - both instrumental in the thorough upgrade of pilotage operations Safety management systems in parts of Australia. From these interactions, AIMPA has come to the firm conclusion that a thorough upgrade of maritime pilotage management systems in India is necessary. Holding a webinar would be a good...

0

Video Route Planning With ECDIS

published on 11 July 2020

What is voyage planning, Who is responsible, how do we comply with the rules and how do we utilize the features and functions available in an ECDIS? Chart Projections and Chart Accuracy https://youtu.be/kOaWimnAN-U Principle Used For Creating Electronic Charts https://youtu.be/xY_MBubhUFs Display of Electronic Charts https://youtu.be/qnoFO0T-cLo Route Planning With ECDIS https://youtu.be/s5ebZQru7mg Sailing With ECDIS https://youtu.be/GZrmzE24K44 Whats is Electronic Chart Display? https://...

0

Video Curso Maritime Pilot AND Pilotage Transportation – Safety and Sea Survival Training

published on 12 March 2024

ANPRA y la Escuela Naval de Aviación Naval presentan el curso "Maritime Pilot AND Pilotage Transportation – Safety and Sea Survival Training (MP-SISST)".
Este programa integral está diseñado para preparar a profesionales de la navegación con las habilidades necesarias para enfrentar los desafíos del mar con confianza y seguridad. Desde técnicas avanzadas de pilotaje hasta protocolos de supervivencia en el mar, este curso ofrece un enfoque completo y práctico para garantizar la seguridad y...

0

Video SAMMON Demo Planning FtLauderdale Arrival with comments

published on 20 January 2021

This updated video shows how easy it is to develop an arrival plan with the SAMMON Planning Tool. As a sample the arrival from appraoch until the berth to Ft. Lauderdale is used under strong current of 2kn. At the simulator training courses where we used this tool for preparation of a manoeuvring plan during the briefing sessions all nautical officers involved stated afterwards: "Why don't we have this tool on our ships?"

0

Video Delaware River Pilots - 2013

published on 26 May 2020

A story I shot on the Delaware river pilots, very cool people who have a very important job. Every cargo ship that has to get anywhere up the Delaware River gets a pilot delivered to it while in the Delaware Bay, who guides it up through the narrow shoals

0

Article The BMA introduces inspection campaign for pilot transfer arrangements

published on 23 July 2021

The Bahamas Maritime Authority (BMA) once again demonstrates its commitment to seafarer safety by being the first registry to instigate a Concentrated Inspection Campaign (CIC) for pilot transfer arrangements. It will continue to run until the end of 2021.

1