Advice from the RNLI - applies to all boats not just fishing boats - the negative affects of free surface water and watertight integrity.

Loose kit, fish and excess water on or below deck can all shift and raise your boat’s centre of gravity. If left unchecked, the effect of their movement can capsize your boat within minutes. Find out how to avoid the problem before it develops. 

Next time you’re on your boat make sure you: check all scuppers/freeing ports are open and clear stow catch and loose gear securely at all times, preferably below deck keep it watertight: check critical pipework, stern and rudder glands before each trip and check bilge alarms regularly.