Practical Boat Owner, a magazine, reports [in its June 2013 issue, published in April] that the British Marine Federation surveyed its members in February and March 2013 to ask about gross capacity and actual occupancy of their marinas in January 2013. The BMF press release is here.
It got 145 valid responses, a 56% response rate; it reckons that that means 31% of all UK marinas and 38% of all UK marina berths.
The total capacity of the marinas was 29118 and the occupancy 23462, which the BMF says is an 80.5% occupancy rate and a 19.5% vacancy rate.
Of those marinas, 69 [or perhaps 68] were tidal or coastal, with a total capacity of 17604 berths and the occupancy 14227 berths: an 80.8% occupancy rate and a 19.2% vacancy rate.
There were 53 responses from marinas on C&RT waterways; they had 7710 berths, 6122 of them occupied: 79.4% occupancy and 20.6% vacancy.
There were 23 responses from marinas on the waters of other navigation authorities, including the Environment Agency, the Broads Authority and some national authorities responsible for lakes. They had 3804 berths, 3113 occupied: 81.8% occupancy and 18.2% vacancy.
I don’t know what difference it would have made if the survey had been conducted at some other time of year. Should we assume that British boaters all book marina berths for the full year?
I don’t know whether the Irish Marine Federation or its associate group, the Irish Marina Operators Association, has published anything similar. While the IMOA has members on coastal and estuarial waters, it doesn’t seem to have any on non-tidal waterways. It would be interesting to know the vacancy rate on inland marinas, although there are definitional problems (does a block of flats with some moorings constitute a marina?). Maybe the only way to find out is to get HarbourAir to take aerial photos on one of their flights.
Irish waterways history 
‘Should we assume that British boaters all book marina berths for the full year?’
If we’re talking about the inland system then the vast majority do pay for a full year – there are a number of boaters who like to take a winter only mooring and shift about during the season, but this survey was done out of season, and their numbers are not high anyway.
To be honest the way the figures are presented it’s easy to get the impression that all the marinas are about one fifth vacant, while the likelihood is that some are jammed solid and others only a third full.
What’s striking is the near exactness of vacancy percentages across the range of mooring suppliers. You’d need to know the occupancy percentages of those not in the survey to really make sense of what’s going on.
And what was it Mark Twain said about statistics…?
Giles