Do swell waves really travel in sets of 7?

Hello again, on rocky coast around the great Lakes, swell can make launching difficult.
offshore, these waves were visible spaced on a period of 6 seconds. While on shore i spent 30min timing the sequences of calm/small & big waves with a stopwatch. i could see no obvious pattern.

Dispite all this data, choosing the moment to launch my kayak still ended up based on luck (& i nearly got swamped).

Can you predict when the next wave, or calm is due, even if you cant see whats coming in from offshore, due to being in a cove, behind a pier etc

Sets of 7, no. Can you predict the large set waves, maybe. Depends on the dominant period, conditions by which larger waves were created. On the Great Lakes you can probably only predict the large sets coming from very long fetch over the water. Local knowledge and experience will help you judge when to launch. Experienced paddlers seeing the height and direction of smaller waves can make a good guess about when to hold and when to sprint out. Look for features that create channels in the waves, usually rips where the water from waves piles up and runs back out into deeper water.

Were you trying to launch bow or stern first?

I often have more luck especially if anything is breaking going out stern first. You can limit a fair amount of water getting in with the skirt only snugged on in back and along some of the side. Your body will shield things so not so much comes into the boat in front of you if you boogie out beyond the break fast enough. Then clean up and slap the skirt on in front when you are in the swells.

Plus I find it easier to keep heading into the wave going backwards than if the waves have my bow to mess with. I win the argument more often going out backwards.

I used to surf a lot when I was younger. Sure sets come in sevens. But they also show up in sets with lots of other numbers.

In a word, sometimes.