Actually, Swamphen, ship's boats aren't exactly in the "Lifeboat" category. They perform a number of duties, not the lest of which is connecting the ship to the shore in areas without developed piers, quays or harbor facilities. Also, in crowded harbors, where a ship cannot tie up at a quay because of space, they do the same. There were usually rowed and powered ships boats, powered could be gasoline, diesel or steam powered.
In the RN, with the rise of carriers and the numerous use of US built escort carriers, the removal of aircraft form capital ships saw the former catapult area returned to ship's boats. With numerous bases, ships boats were an important part of any RN ship.
If you look at the original designs of Iowa, North Carolina and South Dakota, even Montana you see they still have ship's boats as part of the design.
North Carolina and Washington actually took theirs to sea. That's why they have the cranes abreast of their after funnel. Here's a pic of Washington. If you can make them out, they are in the mess between the after 5" turret and the after 16" turret.
http://www.history.navy.mil/photos/images/n20000/n24148.jpg
And here's a builder's model of Montana, with the ship's boats clearly visible between the funnels:
http://www.history.navy.mil/photos/images/h44000/h44529.jpg
They were abandoned in WWII because of the priority to have AA guns. That's why you see the rise of the mats and floats tied to nearly every verticle surface, while ships boats gave way to guns.
On a final note, when the Iowas were taken in hand to be modifed for service in the 80's, the ship's boat's rails were found underneath where the 40mm gun tubs were placed.
Regards,
Big Rich