Not sure about the term "Boat train"- if you mean what I'd call a ferry, try this:
You'd need to get from Glasgow to Ardrossan- around 30 miles. You could hire a car in Glasgow (perhaps cheaper), drive to Ardrossan and take it on the ferry- for more than GBP30 each way, though- and have the car for Arran and the return to Glasgow OR here's a link to some info about car hire on Arran itself:
Fantastic! At long last someone has the taste to go to Arran; it's lovely. If you bomb out on car hire on the island, you could try Adrossan itself. It's a small town but as a port may have car hire.
If you do hire in Glasgow or elsewhere on the mainland, make sure you ARE allowed to take the car off the mainland and on to the island; may or may not be an issue but best to be sure.
If you're going as a foot passenger, I don't think you need to book.
As an Arranphile...:-)
Yes - there's a garage on the pier that rents cars, although I've only ever seen Smart cars there.
Not entirely essential as there is a good bus service and walking/cycling are good ways to get around.
When are you going? Taking a car on the ferry is very expensive compared to being a foot passengers.
Any Arran questions, fire away. I'll be there in May. Counting the days....
Taking the car across on the ferry is really expensive and as suggested earlier there is a garage right at the ferry on Arran that does hire cars, but i'm pretty sure it only has 1 or 2 cars so may be worth tracking down in advance. You'll not need to book your train tickets in advance but do book the ferry as even as foot passengers it can get very busy depending on the time of year.
There is a very good bus service all around the island and for about 4 pounds you can buy a day-ticket, which gives you unlimited travel all day.
Whatever you do, do not hire a car on the mainland and take it over to Arran on the boat (expensive!!) as you would be cheaper travelling by taxi everywhere.
Is this mandatory advance booking for the train a new thing? When I went to Arran (God bless this island), all one had to do was to show up at the train station, buy the ticket, get off at Ardrossan HARBOUR station, then walk 2 minutes, buy the ticket for the ferry, and go.
Unless money is really not a problem with you, I concur with those suggesting not to hire a car on the continent: way too expensive to cross over. Either make prior arrangements with the small local agency in Brodick, or else use the bus: buses are waiting for you at the pier when you arrive. The essential timetables booklet is available on the buses and also at the Tourist Office at the same pier, you cannot miss it. During the week, at day time, you may also complement the regular buses by using the Post buses (which bring you to a few places the regular buses won't) - more infos on these in the same timetables pamphlet.
Car hire is available from the following companies on the island:
Alba car Hire, Whiting Bay Garage 01770 700345
Arran Transport, The Pier Brodick 01770 302121
Blackwaterfoot Garage 01770 860277
It is expensive to take a car over on the boat, and you would need to book ahead with calmac (site mentioned by previous posters). If travelling by public transport, you do not need to make bookings at all, for either the train or the boat.
It is handy, but not essential, to have a car on Arran. The bus service is fairly good for the main villages, Monday to Saturday.
Thanks for all this helpful information! I am taking my family of 5 to Arran in July. Not taking a car, and the only place we could afford to stay is at the Corrie Hotel. Please post any info you think we should know when you return. I'll do the same for the next traveler.