Tugs General - Shiphandling Facts and Rules Flashcards
Tugs General - HP to BP
(MacElrevey)
100 HP = 1 ton bollard pull (MacElrevey)
Tugs General - BP to 100BHP by tug
(Henson)
VS: 1.0 tons / 100bhp
ASD: 1.3 tons / 100bhp
Conventional:
- w/ nozzles: 1.5 tons / 100bhp
- w/ open prop: 1.1 / 100bhp
(Henson pg 79)
Tugs General - ship speed for conventional tug
maximum 3 kt ship speed
Tugs General - negatives for pulling
- may part line
- poor lead for ships in ballast
- wave surge puts shock load on line (Hooyer pg 60)
Tugs General - tug position in turn
tug pushing forward on shoulder less effective than on quarter because of pivot point and hydrodynamic forces forward opposing the turn
Tugs General - Conventional and Omni positioning
use conventional forward and omni aft
Tugs General - VS and ASD positioning
use ASD forward and VS aft (except if more braking force is needed)
Tugs General - bow in maneuver tug position - same type
1 or 2 tugs same type - use stronger tug forward
Tugs General - stern in maneuver tug position - same type
1 or 2 tugs same type - use stronger tug forward
Tug Use in Port - AST / Voith tractor assist
(Henson)
- Voith better at stern indirect towing at higher speeds
- ASD better as forward tug and at stern direct towing at speed (100% thrust any direction)
Tug Use in Port - main types of tug assistance
(Henson)
- tugs towing on a line, usually 1.5x length of tug
- tugs operating at the ship’s side made fast with 1, 2, or 3 lines
Tug Use in Port - Voith assist towing/pushing switch
(Henson)
can switch from towing on line to pushing, forward or aft, at ship speed of 2 kts or less
Tug Use in Port - IMO escort heeling regs
(Henson)
requires tugs engaged in escort operations with the max heeling lever in an equilibrium situation, heeling angle 15º or less
Tug Use in Port - line pull relationship to bollard pull
(Henson)
- if prop RPMs double, then line force will increase by a factor of 4 and required engine power will increase by a factor of 8
- applies to most tug ops
Tug Use in Port - towline length
(Henson)
- should be as long as possible
- tugs lose 40-60% on short towline
- in heavy wave conditions could lose up to 90%