I think that the OP does not realise the scale of the operation of a prison.
Let’s get to numbers of bodies, US prisons are generally much larger than their UK counterpart but I will stay with the UK anyway.
You are looking at between 900-1500 prisoners. Add in around 400 staff.
Then add in the visitors who require reasonable access and facilities such as car parking - that’s going to be around 400-500 of whom maybe 100-200 might be present during day time.
The reality is that we need around 400 parking spaces.
So now we have to heat, water, air con, feed and supply electricity to around 2000 people at any given time.
This is extremely high density accommodation, and has high density services usage. This prison will likely require as much in services as perhaps 1000 to 2000 homes.
Actually this service usage is probably more than that, due to the fact that what we have is something between an industrial complex and a domestic setting.
So how are we going to manage an influx of 500 people in and out each and every day if we are on a ship offshore? transport costs would be immense. Its either by ship or by flight and both are extremely expensive.
If we have the prison ship alongside a jetty, access would still need to cater for vehicles right up to lorries.
How are we going to supply all that water, prisons use huge amounts of it.
How are we going to dispose of all that sewage? What about the garbage, I can personally attest that a prison will accumulate garbage of at least 3-4 tons a day - I know because I have to haul it. This is just ordinary garbage, we also have massive amounts of office equipment, loads of wood and metal - I mean by the tens of tons per month - I know because I have to haul it.
We have confidential waste that has to be security shredded, we also absolutely must have IT and internet access, its essential that we can communicate with the many other agencies involved in offender management, including other prisons, social welfare agencies, probation services, legal services.
We need to move prisoners to and from courts securely - how will we do this on a prison ship?
We also need radio nets, on ships radio systems are notorious for having dead spots - not a great idea when you need radios to summon and direct emergency assistance.
Fire fighting on ships is a real problem, there is no where to run and smoke can and will cause immense problems, whereas you can separate out buildings in a prison so that only one area is affected at a time in the vent of a fire - did I mention how common fires are in prisons? Well in your prison ship you are going to get at least 5 or so serious cell fires a year plus a couple fires in other locations. Fire is one of the biggest mass death risks in prison.
In a ship, who will fight the fire, because the fire brigade isn’t going to get there - that means you now need an additional number of staff on call - all trained up - that’s incredibly expensive - having done fire fighting using Breathing apparatus, the obstacles to implementing a fire fighting team that uses this types of equipment are considerable - not least the physical fitness of staff.
What are we going to do with all these ship borne prisoners during the day? We have to put them on exercise yards - its a legal requirement that prisoners are given a certain amount of cell release exercise time. Ships do not tend to have areas large enough for such a purpose.
We are also going to need a fence around all the upper decks, just like a shore based prison - we can’t have prisoners making escape attempts
Suring the day we need to put prisoners to work, or education or rehab courses. All these need facilities, from simple classrooms right through to full on industrial facilities for welding, woodmills, plastic injection moulding or the other hundred or so choice of occupations that are used to keep prisoners working - all those industrial facilities will need materials to be delivered and completed products to be removed.
That could easily mean 20 large lorries a day coming and going.
All this will need fuel, we have to move this ship, or we have to run generators, or we have to be alongside a jetty drawing power through vulnerable shore cables, and if this latter were chosen, we’d probably also connect to shore side steam supplies too.
This is just for starters, I have not covered other emergency services such as medical and yes we also need the police to attend for various reasons. There are a myriad of other functions and services that prisons have to be able to access, just think of a small town, all the goods it will import, all the money moving in and out all the communications to the rest of the world.
We did have one prison ship in the last 20 years called HMP Weare - this really was a last resort and a stopgap - it was not all that successful it cost too much to run and the regime was very limited in scope. Prisoners were very carefully selected - not much use for the general prisoner population.
Summary, it costs huge amounts more, yet it cannot provide the services and facilities that a modern prison facility requires - and is likely to consume a lot more resources than a land based facility.
