Bow and Wave
The navigation center where ships are operated from is called the “wheelhouse,” also known as the “pilothouse” or “bridge” on larger vessels. Hence, to say someone is “in your wheelhouse” means that they are in a place which you control or feel comfortable in.
A very drunk person is often described as “three sheets to the wind.” Another great nautical idiom, the “sheets” here refer to the ropes which held the corners of a sail in place. Any ship with three untied corners of a square sail flapping in the wind had serious control and navigation issues, just as a big drunk might.
Boat speed is measured in knots, which means nautical miles per hour. This is similar to miles per hour in land speed, but not exactly; one knot = about 1.151 mph or 1.852 kph.
Oceangoing sailing ships operated with complicated systems of ropes and rigging, so to “show someone the ropes” originally meant to orient them with the ship’s workings.
When someone “shows their true colors,” a dark side is often revealed. This term started when ships (particularly 17th century Spanish ships) carried many countries’ flags with them to mislead their enemies at sea. “True colors” were those of the ship’s actual national flag, often only shown when the deceived nearby ship was attacked.
Someone in the doldrums may feel dispirited and unmotivated. The original doldrums are a band of calm and low-wind areas north of the equator in the Atlantic and Pacific Oceans where sailing ships often got stuck or substantially slowed without winds to push them.
“By and large” means “generally” or “on the whole” because it refers to the full range of ways ships could sail relative to the wind. “By” referred to sailing into the wind or perpendicular to its direction, and “large” meant enjoying the stronger push of the wind from behind.