Bollard Pull Calculator: Tow Resistance, Tug Requirement & Towing Gear Capacity Tool | ShipUniverse
Harbour Towage • Dead-Ship Assist • Environmental Resistance • Effective Bollard Pull • TOW / Towline Capacity • Tug Package

Bollard Pull Calculator: Tow Resistance, Tug Requirement & Towing Gear Capacity Tool

Estimate the force needed to control or tow a vessel under wind, current, tow-speed and user-entered wave/interaction loads. Convert certified static bollard pull into effective operating pull, check tug count and reserve, screen towline and shipboard towing fittings, and solve the environmental envelope before the operation starts.

Engineering screen only. Port, pilot, tow master, tug operator and approved shipboard TOW limits control.

Operation & Vessel

m.
m.
m.
tonnes. Context only unless used in external approved methods.
Used only for the entered shallow-water / wash derating screen.

Projected Areas & Drag Inputs

Use vessel-specific wind/current coefficients when available. The drag-force calculation is a planning screen and should not replace model tests, pilot/tug-assist studies or tow-engineering analysis.

m² broadside projected area.
m² head-on projected area.
m² side projected submerged area.
m² transverse submerged area.

Wind, Current & Tow-Speed Resistance

knots. Use gust / operational design wind appropriate to the towage plan.
0° ahead/astern axis, 90° beam.
knots.
degrees.
knots. Zero is appropriate for a static harbour hold/control case.
kN. Enter approved/model/test value; 0 uses the screening coefficient below.
m².
Screening C only. Replace with tow-test/model resistance where available.
kN from tow study, pilot guidance or conservative engineering allowance.
kN.
% applied to hydrodynamic current + tow-speed components.
% added after steady environmental resistance. User-entered project margin, not an IMO universal factor.

Selected Tug Package

tonnes-force from the tug's current certificate.
% of static BP retained at the entered vessel/tow speed.
%.
% after towline geometry and tug working position.
%.
% of theoretical summed effective pull that is usefully combined.

Advanced Tug Fleet Register

Each tug is derated independently. Enter certified bollard pull, current availability and the expected effectiveness at the actual speed, sea state and working geometry.

Tug Type BP tf Available Speed % Weather % Angle % Wash % Max line tf Line MBL tf Hire $/h

Towline, Chock & Shipboard Towing Fittings

For normal towing, use the marked TOW and approved towing/mooring arrangement plan. Do not substitute mooring SWL for a towing rating unless the approved plan explicitly permits that use.

tonnes-force.
tonnes-force.
tonnes-force for the controlling tug load path.
tonnes-force.
% used as an operational screen. Use approved tug/operator value.
tonnes-force from approved towing/mooring arrangement plan where known.

Port / Tow Plan Requirements

Enter port / pilot / terminal requirement. 0 means none entered.
tonnes-force. 0 means none entered.
% above design towing force.
hours for tug-hire illustration.
USD per tug-hour.
Operational limitation: Static bollard pull is not the same as useful tow force in motion. Tug propulsion type, vessel speed, towline angle, interaction, sea state, current, UKC and tug working position can materially reduce or alter the force delivered to the assisted ship. Escort towing can generate indirect hydrodynamic steering/braking forces and requires separate approved evaluation. This tool does not replace port rules, pilot/tow-master judgment, tug manuals, towing certificates, approved towing arrangements, class/flag requirements or a tow engineering study.
Regulatory / guidance basis: SOLAS II-1/3-8 and IMO shipboard towing/mooring guidance distinguish normal harbour towing from other towing services. MSC.1/Circ.1175/Rev.1 applies to ships constructed from 1 January 2024 through 31 December 2027; MSC.1/Circ.1175/Rev.2, approved in 2025, applies to ships constructed on or after 1 January 2028. For normal towing, the guidance uses 1.25 times the intended maximum towing load as the minimum design load applied to supporting hull structures, and the marked safe towing load TOW and approved towing/mooring arrangement plan control use. IMO MSC.1/Circ.1101/Rev.3 points port authorities and operators to current tug-assistance guidance covering total bollard pull, environmental limits, tug capability, interaction and towing equipment.
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