Hi, thanks for the advice.
I also contacted Uncle Al in Canada, who asked Mike Porter for his assistance.
Mike confirmed that the bow is only made of laminate and not strong enough on its own to attach a heavy duty U Bolt.
For info, his very helpful reply posted below.
Uncle Al has forwarded your email to me.
It sounds as though you have a Mark II GRP boat, in which case the standard laminate is not sufficient to take the U bolt. If we used to fit them, which from time to time we did, we always moulded a wooden pad onto the reverse face (shaped of course to go in to the bow as snugly as possible). This can be overlaminated into place for additional stringth, or just glued in on epoxy.
The standard glass laminate is certainly not sufficient to take the load!
The only thing I would say is that, depending on how you intend to use the eye, we always felt that an eye fitted above the forward tank was at the wrong height for winching etc; it really was better positioned just above the waterline, and fitting that is a real problem!!
Mike also said that his brother Ian is still in the business and excellent at all things technical, which I welcome.
But at this point, I feel enough is enough and I shall fill the holes I have drilled and use my previous (even if not as cosmetically pretty) arrangement to attach the winch to a rope / bridle which spreads the load.
Thanks for your help