Mato,
Good to hear from you (we met at Brancaster in 2007). Hope you are well.
The torch is just a fairly cheap high power thing I bought for about £10 at a garage in UK. It gives a high intensity beam (hence “1 million candlepower”). The point I was making was that although some materials (like GRP) are opaque to normal light levels, bright light will get through. I put the torch inside the rear buoyancy compartment and was able to trace with a pencil – on the outsde of the transom – the outline of the plywood reinforcement. Any bright light would do.
Regards,
David Smillie