Apologies for a pretty basic question. I plan to fit my pulpit rail by drilling through the deck, countersinking the holes slightly, and bedding the bolts in with cones of butyl tape wrapped round them that will compress into the countersinks and holes. Inside, I plan to use washers and nuts. My question is - would you put the washers and nuts straight onto the inside of the deck, or would you use blocks of wood, too? I've seen it done both ways.
My pulpit rail had 10mm ply rectangles inside with the bolts through and large washers. Then whoever had done it fibreglassed over the lot inside. Don't reccommend the fibreglassing as if they need re-sealing it makes the job difficult.
You need to honestly answer the question - "am I a skinny or a fatty" for yourself and those who ship with you. If you are all the size of a 13 year old anorexic schoolgirl then bolts and washers is fine, but if Nelly the Elephant is likely to fall against the pulpit then a nice spreader of 18mm plywood will keep fatty aboard and pulpit still attached.
So I'd say that as there could be occasions when the pulpit needs keep you aboard and safe and is also quite often the towing or handling point in emergencies the strongest fastening method is preferable. BUT can I advise bedding the plywood pattresses on a dob of P.38 polyester body filler and making it around 10cm square minimum as this should avoid future "spider-web" cracking around the pulpit stanchion bases.
One last point - use "penny-washers" under the nuts so the nuts don't crunch through the plywood and if possible use a hardwood WBP plywood and not the soft Elliottis shuttering plywood.