Most sunset photographs taken from boats are disappointing, and it is almost never the camera. It is that a boat introduces three problems a tripod on a beach does not have, and nobody warns you about any of them until you are looking at the results.
The Best Light Arrives Before the Sun Leaves
The window people are actually chasing is the twenty to thirty minutes before the sun reaches the horizon, when it is low enough to go warm but still bright enough to light a face. Turn up as the sun touches the water and you have missed most of it.
There is a second window afterwards that gets abandoned constantly. Maritime haze over the Peconics scatters light in a way that keeps colour in the clouds well after the sun has gone, and the sky often peaks ten or fifteen minutes into what feels like the end of the show. The boats that fire up and leave at the moment of sunset miss it every single time.
A Boat at Anchor Is Not a Tripod
Even with the engines off and no wind, a hull swings and rolls slowly. Long exposures are out. Push the ISO higher than you would ashore, keep the shutter faster than you think you need, and take three of everything, because one of them will be the sharp one.
Horizons are the other giveaway. On land your brain levels the frame automatically. On a moving deck it does not, and a tilted sea line ruins an otherwise good photograph. The water gives you a perfectly straight reference across the whole frame, so use it, and turn on the electronic level if your camera has one.
Choose the Water, Not the Landmark
The single biggest factor is what sits between you and the horizon. Looking west from the Shelter Island side you are seeing across miles of open bay with nothing interrupting the sightline, so the sun actually sets into water rather than behind a treeline. Most of the East End does not offer that.
The second factor is who else is there. The famous anchorages fill up on summer evenings, and a raft of boats leaving at once puts wake through every frame you take for the next five minutes. Quieter water on the south and east of the island gives you the same sky without the chop. If you want to learn more about how those spots get chosen on the day, the short version is that a captain reads the evening breeze and picks accordingly.
Expose for the Sky and Let Everything Else Go Dark
Meter on the brightest part of the sky and accept that the foreground drops to silhouette. Trying to hold detail in both will flatten the sky, which was the reason you were out there.
If you want people in the shot, put them between you and the light rather than lit by it. Silhouettes against a coloured sky are far more forgiving on a moving boat than a properly exposed portrait, and they tend to be the frames people actually keep.
Things That Ruin Evenings
Salt spray dries on the front element and it is invisible until you review the files. Carry a microfibre cloth and check the glass before the light turns, not after.
The temperature falls quickly on the water once the sun is down, and cold hands make for shaky frames and short patience. Bring more layers than the afternoon suggests.
The run home in the dark is worth staying alert for. Harbour lights, lit ferries crossing, and a very dark sky over the bay because there is almost no light pollution out there. Long exposures will not work from a moving hull, so lean on high ISO and accept the grain.
The Month Matters
September is the strongest month for this. The sun sets early enough that you are not shooting at nine at night, the air is cleaner than midsummer, and after Labor Day the anchorages empty out so you have the water to yourself. Discover Long Island’s Shelter Island guide covers what else is worth doing on the island if you are building a trip around it rather than an evening.