Talbot's recommendation will do the job, but I found the price a bit steep, went for 2.5 litres of Dilunett from rod@shipshaperamsgate.co.uk £26.10 including postage, that was the cheapest price I found after a long search.
Thats exactly how I have just stripped 3 coats off my 24 footer. Slow, - 3 weekends - but much kinder to the GRP than those chemical strippers.
Rab. /forums/images/graemlins/cool.gif