Towline Forces Diagram 2 3 18



Types of markings stamped on ship’s fittings:

SWL = The safe working load for mooring lines.

TOW = The safe working load for a tug’s towline.

ETB = Emergency Towing Bitts (usually found on tankers & LNG Carriers)

kN = Rule of thump is insert one decimal place to convert to Tonnes: 1000kN = 100 tonne


If the tug’s towline is placed over a set of Bitts so the eye of the towline is near the base of the ship’s Bitts then the stated SWL on the Bitts can be doubled.

  • NB: This does not apply to the ship’s other fittings: Fairleads, Roller Leads etc.



The construction age of a ship should to be considered when estimating the towline force that can be safely applied to or through its deck fittings.

  • For ships built prior to 2007 there is possibly no Class notations for deck fittings.
  • For ships built prior to 2012 there is possibly no Class notations for the underpinning structure the deck fittings are connected to.
  • For ships with rated Emergency Towing Bitts (ETB) the deck fittings SWL are likely more trustworthy.



  • When the towline leads at a steep angle down from the ship’s Fairlead this equates to a crushing force, hence more destructive force is applied to the Bitts than the Fairlead; So focus on the Bitts SWL than the Fairleads SWL.
  • When the towline force is near horizonal to waterline there is virtually no towline angle multiple factor to be applied to the force the towline is generating.
  • If the towline leads at an obtuse (soft) angle from the Bitts through the Fairlead to the tug less force will be applied onto the ship’s Fairleads. Hence focus on Bitt’s SWL.
  • If the towline leads at an acute (sharp) angle from the Bitts through the Fairlead to the tug more force will be applied to the Fairlead. Hence focus on the Fairlead’s SWL.
  • For tugs with towline tonnage Load Cell measure-ment equipment the readout includes the factor for towline angle up to the ship and the actual bollard pull the tug is creating. But the readout does not make allowance for the fiction percentage caused by the towline leading around the tug’s towing staple or ship’s fairlead. This can be + 10% to the Load Cell readout.
  • The % Factor to apply to the tug’s Bollard Pull a is guidance for a worst case possibility for tugs without towline Load Cell measuring equipment. It takes into account estimates for snatch loadings due to sea state, steep towline angles and acute angles from the CLA to the ship’s bitts.
  • The Pilot should always inform the tug as to the SWL of both the Bitts & Fairlead the tug is to attached it’s towline to. Note: The SWL could be rated at different tonnages.


PB Towage consider SeaWays Tug Master training a significant competitive advantage, the same objective competency based standard delivering optimal safety and efficiency outcomes across their growing fleet. While the towage industry is seeing the power of tugs go up around the coast, it is not just bollard pull that Marine Pilots are looking for. Quality training, in particular of the Tug Master in conjunction with the Pilot is the key to the effective use of a modern, omni-directional tug.

It normally takes in the order of three months to train a new Tug Master. Even if you have a good training system, the cost of “live” training is prohibitive taking wages, fuel, weather and opportunity into account. The ability to replicate maneuvers in an advanced, well calibrated simulator, configured for specific port and vessel condition, allows the trainee to achieve the required level of competency in a fraction of the time.

Full mission simulation is the future of Tug Master Training and PB Towage recognise SeaWays as an international leader in the field.

Tony Cousins

Managing Director, PB Towage

The course content, structure and materials is all a credit to Seaways and the facility for the course is just fantastic.

The trainers experience and professionalism is unequaled and their complete understanding of our requirements at Barrow Island made the training so much easier.

I found the structure of the training very easy to understand with more hands on training than sitting in the class room, I for one adapted well to this environment.

Each trainer took time to ensure we fully understood each maneuver and spent extra time with us when required and allowed us free time alone to hone our skills on the controls, we all found this very beneficial.

A special mention must go to Steve Sandy, I can’t speak highly enough of this guy, his presentation and explanations of each section of the course was extremely easy to follow and watching him operate the tug controls was just incredible. He is quite a remarkable chap and an excellent trainer and of course his easy going nature makes him very approachable.

I highly recommend this training to all new and used tug Masters and would urge all Tug owners to put their Masters forward for this training.

Steve Linton

Tug Master OMSA

“The seaways training course modules one and two is without doubt the most frustrating but yet rewarding courses I have attended.

I found an excellent balance between theory and practical. The training was delivered by a number of professional, dedicated and enthusiastic instructors, each of them leaders in the field of ASD and Harbour towage.

The training had a strong focus on ASD/Towage safety and provides you with the tools to respond positively to emergency situations”

Steve Wall

OMSA Tugmaster on Chevron’s Gorgon Project

I completed my Azimuth training with Seaways and cannot thank Arie enough for the knowledge he passed to me at that time.

Not only did we complete the hands on ASD training but covered aspects of professional development that still assist me in everyday operations.

We covered items like our company safety management system, which was still in its infancy, crew and client management, personnel management and of course the mantra of Authority, Control and Finesse.

I still refer to my training almost daily and always have my training manual at hand. I would highly recommend the Seaways training to any of my officers or anyone who was serious about becoming a professional ASD Tugmaster.

Capt Jayne Hogarth FITA

Master “Mermaid Sound”

For anyone who has not had this brilliant training package, then I suggest you contact your Company and ask if this package could be made available to you, the booklets on the Modules alone are worth their weight in gold and something that you can refer to at anytime you like, like we say, you can never stop learning.

There are three principles that Seaways drum into you and if you remember them you will not go far wrong, they are as follows:- Authority, Total Control and Finesse. So once you have mastered the rudiments of the Training package you will drive with AUTHORITY, have TOTAL CONTROL of the VESSEL and the Situation and with that YOU will drive with FINESSE, what a lovely feeling and your Crew will feel safe as well, that’s all we/they want, to know they come and go home from work safely and Seaways Training does this by the bucket load.

Ps:- Happy Tugging.

Capt. Alan Preston

Serco Tugmaster