TheOneToGo
On the Tagus, the light turns the water copper and the 25 de Abril bridge drops to silhouette, so the boat you choose matters less than having a glass in hand when it happens.
Our pick
This one puts you on a proper sailboat rather than a packed motor cruiser, which means quiet under sail instead of an engine drone the whole way. Two hours, wine poured from the start, and a crew that names the monuments as you slide past Belem and under the bridge. It is the right length to settle into and not so long that it drags, and the timing is built around the sunset rather than just happening to overlap it.
If our pick doesn't fit
A more upscale vessel with fewer passengers per deck; costs more but feels noticeably less crowded and more intimate.
Notably cheaper and shorter, on a catamaran rather than a sailboat, good if you just want the sunset views on the water.