What are factors that cause squat? By which signs it may be identified and what actions to be taken?
Squat is an increase in draught caused by a vessel traveling through the water at a significant speed with a limited under keel clearance.
Whilst it can occur in relating deep water, it is more pronounced when the depth of the water is less than twice the draft in other words, the under-keel clearance is less than the v/l’s draught.
There is also likely to be a change in trim since the LCB is likely to change with a change of draught, thereby creating a trimming moment.
Factors increasing squat
- High speed ( squat α speed²)
- High propeller speed
- Deep draught
- Shallow depth of water
- High block co-efficient
- Broad beam
- Narrow channel
- Large trim
Sign that the vessel is experiencing shallow water effect
- Speed decrease
- R.P.M. decrease
- vibration may occur
- Steering may be affected, vessel becomes sluggish to manoeuvre.
- Ship made waves increase in amplitude.
- Ship wake changes colour / become muddy.
Reduce speed if squat is suspected until mentioned effects ceased.
