Should I have a survey?

It is ultimately your choice but with a few exceptions I would recommend that you do so. Firstly, a boat is a substantial purchase and it will help to give you peace of mind. Secondly, should any material defects come to light ( and I emphasise "material") then a professional surveyor may be liable for the cost of putting them right if s/he failed to spot them in the survey.

How much will a survey cost?

Typically a full out-of -the-water survey will cost between £450 and £600, plus the cost of taking the boat out of the water. Depending on whether the method is a dry dock, a slipway or a crane it will cost from £125 - £250 - a crane usually being the most expensive method. Which means of removing the boat from water is used will usually depend upon what facilities lie nearest to the boat's location.

Can I have the hull blacked at the same time?

I include this because I have been asked this question on countless occasions. Usually the answer is no, for the following reason. Dry docks and slipways (the commonest means of taking a boat out of the water) are usually booked some way in advance for longer term work such as hull blacking. For a hull blacking to be done properly the boat should be out of the water for 4 days (possibly 3 if the weather is particularly warm and dry). Survey boats are only out of the water for 2 hours or less, and are docked/slipped between a long term booking changeover. In any case, although I can't imagine the owner objecting to a free blacking, the boat is not yours at this point.