If you were on the open ocean on a large ship, how could you determine the height of a wave?

If I were on the open ocean on a large ship, the way on how I can determine the height of a wave would be simply looking at the marks it leaves on the sides of the ship as it hits it. The wet part can be an estimate on the height of the wave.

The horse latitudes-high-pressure zones about 30 degrees north and 30 degrees south of the equator.-warm air traveling away from the equator cools and sinks-weather tends to be clear and drythe doldrums-low-pressure near equator-air rises and spreads out toward the poles-rising moist air produces clouds and heavy rainthe westerlies-blow from the west-move from the horse latitudes toward the poles.-bring storms across much of the united statesthe tradewinds-blow from the east-move from the horse latitudes toward the equator  -strong, steady winds