I thought it would be interesting to delve in to this and see how many of these you were aware of, and it also sets off my naval theme leading in to October.
Starting with the above, 'batten down the hatches' is usually used on land when we have a storm coming and we need to prepare. At sea? The openings on board the deck were known as hatchways and the cover was known as the hatch. These would be shut and covered with canvas secured by a batten (piece of wood) to prevent water finding its way in to the ship.
Shipshape and Bristol Fashion
Learn the ropes
Tall ships have miles of ropes, used to adjust and hoist the sails as well as supporting the masts. All of these had different names, and so when a young seaman had managed to remember all of these, it was said that he had 'learned the ropes'.
Not enough room to swing a cat
The 'cat' was a 'cat o' nine tails' - a lash with a 2 foot rope handle and nine 2 foot 'tails' with 2-3 knots tied on each.
The space between decks on a naval warship at the time was very small and cramped (which you will be aware of if you've ever set foot on HMS Victory). This punishment of a flogging with a cat o' nine tails was undertaken on deck, as below there was 'not enough room to swing a cat'
This leads me nicely on to my next phrase...
A Square Meal
A Loose Cannon
Out of control or 'loose' these cannons, often weighing upwards of 6000lbs would cause a lot of damage.
The sun's over the yardarm
In the navy, sailor's used to be given a ration of around 8 pints of beer a day. Officers did not generally drink beer and so they had to wait for their rum ration, usually given between 1000 and noon. In the northern hemisphere this was at around the same time as the sun passed the top yardarm.
Give them a wide berth
With tall ships, a ship was seen to be berthed when at anchor, preferably far enough away from shore and the harbour mouth. Tall ships used the tide and wind to their advantage when berthing and so to avoid other ships already at anchor they gave them a 'wide berth' thereby avoiding a collision.
Which phrases did you realise had a nautical background?