They were of a double diagonal oak plank over lightweight teak frames hull construction (the diagonals of the inner and outer skins running in opposite directions & separated by a skin of oiled calico cloth), as were RNLI lifeboats of the era, making for an extremely light but strong construction.

The first were built in the 1850s with the advent of the steam engine and were originally designated harbour service launches.

The earliest vessels also had a fully round bilge, compared to later designs.

On later models they were moved slightly aft, being positioned over the front section of the forward cabin, before finally settling down to a midships position, allowing good all round visibility.

Conversely, many early diesel boats have straight prows, either fitted from new, or retrofitted when the original steam plant was replaced.