Could someone help please?

I'm trying to sort out travel to Bournemouth for August. But the day I have to travel doesn't have any flights from Dublin to Bournemouth

So I'm going to have to fly somewhere else and get a train there. Anyone know how long it a train journey would be from London(Central) to Bournemouth? London would be best cos it's the only city I really know but it looks so far away on the map!
Thank ya!