Boat, aka traditional American car. Like six passenger, V-8, four door sedan. There was a time then that was all Detroit made. Then they started confusing the issue with station wagons, compact cars, intermediate cars, pony cars, mini vans, SUV's and crossover SUV's. The breed has been thinned down a lot, and there are just two survivors, Cadillac DeVille, and the Ford Crown Vic/Mercury Marquis/Lincoln.
My beloved '99 Cadillac DeVille bit the dust a few weeks ago. I just replaced it with an '03 Mercury Grand Marquis. The two survivors are an interesting contrast. The Caddy has better styling and more groovy gadgets then the Merc. Caddy's have, in addition to the standard electric seats and power door locks, power antenna, power trunk lid latch, power gas filler door, hands-off air conditioning & heating, all digital dashboard. Caddy engine is the magnificent all aluminum, double overhead cam, 4.6 liter Northstar. It's lighter and more powerful than the Merc's plain jane cast iron V8. Step on the Caddy and the Northstar would launch the car into orbit. Step on the Merc and it does accelerate, but it is modest. The advanced engine bought Caddy better gas mileage, 27 on the highway where as the Merc only gets 20.
The Merc is built stronger. The Caddy got scrapped because the rear axle loosened up and nearly came off the car. The combination of New Hampshire potholes and road salt caused the fasteners holding on the axle to loosen up and make an unnerving banging noise over bumps (of which NH has plenty). Two different body shops opined that 1. It couldn't be fixed; and 2. It wasn't long for this world. Caddys have also have heat gasket problems because you cannot torque up the head bolts enough to keep the head gasket in place with stripping the threads out of the aluminum block.
At 125K miles the drivers seat upholstery in the Caddy was sagging.
The Merc has a reputation for longevity, and long hard service as police car, taxi cab, airport limo, doesn't faze it. It has a better radio than the Caddy. Signal seek actually finds stations out here in the deep fringe area, the bass is stronger and it will play CD's AND tapes. The Merc does the plain car things well. It feels better charging thru a narrow slot between the Jersey barrier and the 18 wheeler at 80 mph. Ride on the interstates is smooth and solid, ride over bumpy back roads is confidence building. It doesn't bounce up and down.
In short, Caddy is a more advanced design, but the Merc is more rugged.