I think my biggest hang up is I haven’t really been able to rationalize the difference between what a wave is versus a swell.
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Peak to trough? I’m no sailor but that seems pretty rough
Here is good explanation of wave vs swell:
[https://www.hko.gov.hk/en/wservice/tsheet/pms/files/Wave_observations-final.pdf](https://www.hko.gov.hk/en/wservice/tsheet/pms/files/Wave_observations-final.pdf)
Imagine your standing atop a hill where there is only room for you. In every direction, the hill slopes downward into a valley which slopes up to another hill like your own.
Suddenly, the place where you are standing lowers towards the center of the earth and becomes a valley. What were valleys are now the hilltops.
Repeat that cycle of raising up and lowering down every few seconds and that’s a swell. If the distance between the hilltop and the valley is 30 feet. You’re in the land equivalent of 30 foot seas.
Trade the land for a deep body of water and things become quite sloppy. If you’re in a boat in 30 foot seas, better hope it’s a big boat.
When you are in the ocean, 30′ seas indicates huge waves. Think of an average car is a little under 20 feet. Imagine a boat twice that long on the sea. The height of this 40′ boat’s sides from the water line up to the deck is about 4 to 8 feet. If the 30′ sea has these waves close together they would be crashing over this 40′ boat. Now let’s increase this boat to a large ship, say 120′, like a supply boat to offshore oil wells. The Bow (front) of this ship is probably 20′ tall, and if these 30′ seas / waves are spaced out, this larger ship could manage. One scenerio where it gets risky is when either the depth gets shallow, or a sudden increase in wind speed, like over shoals or in straights, or around storms, because that changes spread out 30′ spread out swells to get really close and steep. I personally would not want to be in 30′ seas in anything smaller than 500′ like my Navy ship. And even then, would want to be heading directly into or away from the waves. Traveling in a direction where the hit directly on you side causes significant sideways rocking. Had hurricane storms break welded equipment when our ships rolled hard. In a giant room aboard a ship, having a 300lb motor sliding into everything inside a compartment over and over is terrible dangerous.
Swell and waves are two different things as you mentioned. The height of the seas is the swells+the waves.
Swell is like the hills, its the main topography of the ocean surface caused by longer term winds over a very large distance. Waves are caused by local winds and ride ontop of the swell like grass on a hill.
So a 30ft sea can actually mean a couple different things (usually it’s reported alongside a wave period) it can mean a hurricane passed 100nm south of you and so there 30ft swell but local conditions created little to no waves. That’s actually a relatively gentle ride with swells often being 50′-100′ wide
Or
A hurricane is chilling in the mouth of the harbor and your heading into it. Now your looking at 30ft waves that are 10-15′ wide making for a very very rough ride
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