With a 4.5 metre you will need to choose your day; it can get quite lumpy around the southern side of the island. When I measured it I made it about 73 miles, but this is not exact as I did have to allow for one or two diversions
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I remember Bedajim doing it in a similar size boat, he and his other half did seem to be taking some punishment
, come to that so were we in a 5.5 metre XS