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 TB 55-1900-232-10
TABLE 5-4. Safety Factors for Good Towing Practice.
Minimum Factors of Safety*
Wire-
Wire-
Chain
Bitts
Towing Mode for Tug
Rope
Rope
Penda
Synth
Detacha
Shac
Padeyes,
Hawse
Penda
nt
etic
ble
kles
etc.
r
nt
or
Line
Links
Bridle
Note
1
1
2
4
2
2
3
Long-Scope Wire Rope
Hawser
On Automatic
Tension Control
3
4
4
-
3
3
3
On the Brake
5
6
6
-
5
5
5
On the Pawl (Dog)
7
8
8
-
7
7
7
On the Hook
(Bitt, Pad, etc.)
7
8
8
-
7
7
7
On the Hook with
Chain Pendant
4
5
6
-
4
4
4
On the Hook with
Synthetic Spring
4
5
5
14**
4
4
4
Chain
Long-Scope
Synthetic
Hawser
Bridle
with Wire Rope Pendant
On Automatic
Tension Control
-
4
4
10
3
3
3
On the Brake
-
6
6
12
4
4
4
On the Pawl (Dog)
-
8
8
12
4
4
4
On the Hook
-
8
8
12
4
4
4
(Bitt, Pad, etc.)
NOTES
1. Based on Minimum Breaking Strength
2. Based on Proof Load ***
3. Based on Material Yield Strength
4 Based on Minimum New Dry Breaking Strength (for nylon only, reduced by 15% for wet strength).
*"Minimum" applies only to new components, good weather, short duration, or emergency conditions
Old components, possible heavy weather, long-duration use, etc., may impose uncertainties which
require use of safety factors greater than the listed minimum safety factors.
**For synthetic line used in a grommet.
***Navy safety shackles (see appendix D) have a Safe Working Load (SWL) that is 50% of proof load
for Grade A shackles and 40% of proof for Grade B (high strength) shackles. Do not confuse SWL
with factors of safety See Section D-14.
****When pendant is used as a deliberate "fuse" (i.e., weak link), use the same factor of safety as for the
hawser but applied to the breaking strength of the pendant.
5-25
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