What does this Excel app do?
This Excel sheet helps you calculate the following:
1. Required Static Bollard pull of a Tug used for towing a Ship-shaped vessel
2. For a given environment, it calculates the limiting towing speed possible for the tow
This app calculates each of the following components separately and adds them to give the final Total Force and the required Bollard Pull
Following are the bases for calculation of different components
1. Calm Water Resistance: Ref 5 below
2. Wind Resistance: Ref 2 below
3. Wave Drift Resistance : from ref 1 and ref 6 below
4. Propeller Resistance and Hawser Resistance: Ref 4 below
5. Limiting Speed: It further goes on to predict the limiting speed when the tow route environment details are provided by the user
It creates a curve of the resistance vs tow speed, and predicts the limiting tow speed from the curve
How to use this App
The user is asked for some inputs for the Vessel, Cargo and Environment and Appendages. The Input cells are highlighted in blue.
The user has to provide all the inputs highlighted in blue.
For some inputs, Tables and charts are required to be referred. These Tables and charts are provided alongwith for the user to enter these inputs.
Once all inputs are provided, the components of required bollard pull are calculated and added up to give the Static Bollard Pull required.
The towing environmental parameters are then utilised to calculate required pull at different towing speeds,
which is matched against the tug’s performance curve to give the limiting towing speed
1. DNVGL ST-N001 Marine Operations and Marine Warranty
2. Principles of Naval Architecture, published by the Society of Naval Architects and Marine Engineers, 1988.
3. ABS Rules for Building and Classing Mobile Offshore Drilling Units, 2019, C 3-1-2/1.3.2
4. US Navy Towing Manual SL740-AA-MAN-010, Rev 3, Appendix G
5. An Approximate Power Prediction Method, J. Holtrop and G.G.J.Mennen, 1982
6. Sea Loads on Ships and Offshore Structures, Faltinsen 1990
JOSEPH LOMBARDI (verified owner) –
Clear, simple and well thought out program. I use it on my dead ship tows and it works.