Just another thought to throw into the mix
You might consider regarding a 'foriegn' stone as possible ballast, especially if your wooden posts represent some form of quay.
Basically, due to shallow daft, any boat designed to carry cargo is less stable/manuoverable if unladen, so if a boat was not carrying a cargo it would carry ballast in the form of stones to increase the draft.
However your stone may be a little to large for this purpose.