How to "back" fittings used to route halyards to the cockpit?

Jul 10, 2018
Oday 20 Minneapolis
For my 1978 Oday 20, I am routing halyards to the cockpit using a lifting block, deck organizer, and line clutch. How do I "back" the through bolts on the inside of the cabin? There will be 12 through bolts. Will fender washers provide enough support or is there a better solution? Is the headliner an issue? There is no way to remove the headliner. Can I put the fender washers directly against the headliner without crushing, cracking, or punching through it.
Jan 1, 2006
Slickcraft 26 Greenport, NY
I'm assuming the headliner is a molded material that is hard. If it were an adherent material you could put backing plates or fender washers directly on it as was done for my Ranger 29 - probably similar vintages.
I would have a concern about a hard liner type. They don't always fit tightly to the underside of the deck. So punch thru could happen. You might be able to install access ports. Or cut an opening and use finished hardwood to be the backing and fill the opening. Either would take some careful planing to get an attractive result. A place to start is a pilot hole which would reveal what is between the liner and underside of the deck. On a 20 foot boat, I presume without standing headroom you want to make sure the bolt ends aren't noggin' knockers.
The answer to your question depends on the what the liner material is and how it is attached. Pictures would help.
Jul 10, 2018
Oday 20 Minneapolis
It is molded and hard. Fiberglass, I'm guessing. You are right about no headroom. No pictures at this time, maybe later. The bow pulpit, which is about 8' forward of the new hardware, has 9 through bolts. Nothing special about those nuts and washers. No backing plates on those either. Thanks for your comment.
Dec 28, 2015
Laser, Hunter H30 Cherubini Tacoma
Make plates out of starboard, one for the whole fixture. This will give you more than enough surface area for both the fixture support and will keep the liner:deck from crushing so easily. I made mine out of exotic hardwood because I like to be fancy.
May 23, 2016
O'Day 1984 23 Island Park, NY
PS has a great article on backing plates of various materials... I highly recommend buying G10 and bonding it to the fiberglass... fender washers are usually thinner than standard and have a tendency to go cone shaped and pull out.