Main
Particulars
Stern
drive tugs intended for harbour duty and ship handling
should be dimensioned according to the local requirements,
assisted vessel size, environment (wind, current,
tide
), type of jetties, manoeuvring space etc.
Typical
maximum length of a harbour/ship-handling
tug is approximately 33 m (LOA). Correspondingly,
maximum bollard pull that normally reasonably can
be accommodated is 60
65 tons.
Nevertheless,
some recent designs indicate even much higher power/length
ratio.
Main
Dimension Ratios
Typical main dimension ratios for stern drive tugs
are
L/B
= 2.7
3.0
B/T = 2.3
2.6
CB = 0.48
0.52
Estimation of Main Particulars
Tug designs are normally based on a certain bollard
pull requirement, from which the necessary engine
power can be determined. Once this is assessed the
correct azimuth propulsor and propeller diameter
can be chosen. The required minimum draft of the
tug can then be set to 1.6
1.75 x propeller diameter.
For
the first estimate of main particulars the lightweight
of the tug can be approximated to 200
250 kg/m3
(LBH). Ice class and other special requirements
are not accounted for and should be considered separately.
Dead
weight capacity is depending on vessel purpose and
may vary from less than 60 ton to more than 400
tons for "same size" tugs.
Check
space and height requirements for the main components,
propulsor and main engines to determine required
hull height.
