All hands to dance and skylark!
Although work on a tall ship must have been hard at times, this command was given to the crew to let off energy and have fun.  Skylark means frolic, play tricks and scramble about in the rigging (The Oxford Concise Dictionary was of assistance here.)

Splice the mainbrace! is another command on a ship.  The mainbrace is part of the structure around the main sail.  Until I looked it up in the dictionary, I had no idea that it meant serve an extra rum ration!  Splice means join.

I wouldn’t touch that with a barge-pole.
This nautical image has passed into everyday speech.  A barge-pole would have been used for pushing the barge away from the bank of the canal or from another vessel.  It was long.  The idiom means that the person would avoid whatever was being discussed.

Clear the decks!  Another command, perhaps before battle at sea.  It can be used (often in the form Let’s clear the decks! about any surfaces, whether in the kitchen, the dining room or the office.

Stoke the boilers needs to be done on a steam-ship or steam engine.  Sometimes it is used about eating in the form stoke up.

Walk the plank!  Pirates and other criminals were disposed of at sea by being made to walk along a plank leading overboard.  The chances were that they drowned.

Hit rock bottom is an idiom about reaching the lowest point financially or emotionally.  A ship which did this might be wrecked.

Shifting sands are moved about by the sea.  They do not provide a firm foundation.

The seafront may have a promenade and gardens for the summer visitors.

Throw a lifeline means rescue.  Near water there are often lifebelts to be thrown to rescue anyone in danger of drowning.  Of course, one end has to be held onto by the person on the shore!

Battening down the hatches is necessary before a storm.  The expression has transferred to land-lubbers, who may well secure all loose items in their gardens before a storm.

On the rocks can mean a drink with ice.

All hands to the pump!  Yet another command.  In a storm a priority on ships was to pump out the water which threatened to sink the ship.  Before steam and electricity man-power was required.

Press-ganged means forced to do something against one’s will.  Press-gangs used to roam ports looking for people to join the crew.

Shanghaied meant someone was shipped as a sailor after being made unconscious through drink or drugs.  Shanghai in China was a possible destination.  They were tricked.  This meaning persists.

Four of Jesus twelve disciples were fishermen.  He sometimes went in their boats.  Here is a story about one of the times they were on Lake Galilee.  Matthew 8:23-27