Opinion

Bow Truster Effect on Ship's Headway


by Capt. Hugues Cauvier - published on 14 July 2022 2153 -

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 What really happened at the Suez Canal?

published on 5 July 2021

Exploring the engineering principles behind the recent obstruction of the Suez Canal, which caused a weeklong disruption in global shipping traffic.

2

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

published on 12 May 2022

Another worthful video by Knud Benedict, Germany

0

Article Winter Edition of "The Master, Mates & Pilot" available

published on 22 December 2021

The Winter Edition of "The Mastes, Mates & Pilot" by the International Organization of Masters, Mates & Pilots (MM&P) has been released.

0

Video Loud & Clear COMM while berthing vessels

by Nasir Khan - published on 25 April 2022

A video by Capt. Pilot Nasir Khan, Pakistan
Why loud and clear communication is very important.

1

Video SIMULATION / MANEUVER OF APPROACH AND MOORING to "TIMBUES" HARBOUR" (BRM - P) BRM Course for #Pilots

published on 4 July 2019

These images show a Navigation drill (SIMULATION) of approach and mooring to one of the Harbours of the Paraná River - "TIMBUES" Harbour (Management and Resources of the Navigation Bridge for Pilots) - (BRM - P) in charge of the Paraná Harbours Pilot, Captain Mr. Diego SCHOTTENHEIM. Exercise carried out in the Navigation Bridge Simulator of the Maritime and Riverine Research and Training Canter (MRRTC), Autonomous City of Buenos Aires #Argentine on March 12, 2019, since 14:50 till 15:55...

0

Video GIDAS - GNSS Interference Detection & Analysis System

published on 29 April 2021

OHB Digital Solutions GmbH develops systems for monitoring the GNSS frequency bands as well as detection, classification and localization of intentional or unintentional interference sources. Many stakeholders and applications as well as critical infrastructure providers are relying on GNSS to provide their services. Since Global Navigation Satellite Systems (GNSS) are widely used in safety and value critical applications, GIDAS detects, classifies and localizes any GNSS interference...

0

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 Pilot Vessel SKUA Returning To Hawes Pier On Visit To South Queensferry Scotland

published on 17 February 2022

Tour Scotland 4K Winter travel video of the Pilot Vessel SKUA returning to Hawes Pier below the Forth Railway Bridge on visit to South Queensferry near Edinburgh.

0