A Dell Quay Dory is a small boat usually 13 to 22 foot in length.
This boat design has a Cathedral Hull

Cathedral hull

A cathedral hull is a hull shape used in modern boats, usually power-driven. It can be thought of as a kind of vestigial trimaran in which the center hull has two smaller side hulls which are so close to the main hull that there is no longer any open space. In fact a cathedral hull is a...

 which is very stable when stationary on the water.
The boat was manufactured by Dell Quay Marine in the UK between the 1980s and 90s.
Dell Quay Marine also brought out a Eurosport

Eurosport

Eurosport is a pan-European television sport network operated by French broadcaster TF1 Group. The network of channels are available in 59 countries, in 20 different languages providing viewers with European and international sporting events...

model that was designed to pull a skier.

A modern equivalent of the Dell Quay Dory is manufactured today by
Fletcher Boats.

The Dell Quay Dory has been described as a UK built copy of a 'Boston Whaler' from the US, but from heavier construction. Online articles have it that a British agent for Boston Whaler in the US returned to the UK and created the DellQuay brand after being denied permission to import the BW into the UK.
An 11 foot version was quite common as well as the popular 13 and 17 foot models.
These boats were built from the mid 1960s, with the DellQuay brand going through several ownerships.