Had a boatbuilder look at it and he suggested leaving it for the season - 4 litres a week is good for any boat. Then he suggests dropping the bolts over the winter and getting the yard to leave it in slings over the weekend. He says the there is a strong chance the bolts can break (being only 1/2 inch) making a right mess of things and damage the oak deadwood considerably. Any suggestions on the tried and tested method of bolt removal through the deadwood?