Adding chocks for tender to sun deck top

Hi,
Looking for a little help. We own a 1988 46 Jefferson Sundeck MY, it has the davit system on the hardtop over the aft deck, but does not have the chocks/cradle for the dink. I have built a cradle our tender and want to attach it permanently via lag bolts. the problem is that I don't know where in the fiberglass top the solid supports are located. Any help on techniques to find the joists or from someone with the me boat with chocks in place would be greatly appreciated.

Thanks,
the Real Esc...

P.s. Yes, through bolting with backing plates will work, but I'd rather not ruin the astetics of the underside of the roof with backing plates. We are in relatively calm waters in the Midwest. ( for now)

You should be able to find the support by rapping and tapping like they surveyor's due.* At the hardware stores they sell electronic stud sensors ranging from 10 buck to 50 bucks.* I had one that worked great until my step son borrowed it!***

If you do not want to drill any holes in the roof,* then you might want to epoxy it to the roof, and then calking to seal the edges.* I hate drilling holes in the roof and/or below the water line.* *

*


-- Edited by Phil Fill on Monday 27th of February 2012 03:07:50 PM

I*wouldn't worry about finding joists or using backing plates.* Your chocks should have a large*enough foot print to distribute the load.* Your loads will be*horizontal (shear) and vertical (weight of the dinghy).* Ours is just through bolted with 4200 and fender washers on the inside.* We just*re-beaded everything on the boat deck*after 25 years.* What a PIA to remove the chocks*to find out they were fine.*

As another option, may or may not work for you. I used high density foam chocks for a v hull 10 foot hard bottom rib. I then put three stainless tie downs on the deck where the ring is flat when not used. This gives me the ability to use the deck space when needed without the chocks taking space. I have not had any problems with the boat shifting since the foam and deck grip with the weight of the boat, keep it in place. As mentioned, may not be the nest solution but another possible one, depending on your boat, requirements and value of desk reuse vs perm dingy placement.

Phil Fill - good idea on the surveyor method, and the stud finders. Non invasive.
Old Stone - the top is about 3.5 to 4 inches thick. 5200 is great stuff, but bolts and 5200 would be less worrisome in a seaway. Definitely plan to goop up any holes liberally. Would like to find the ribs so that I do not have to trough bolt.
Larry, great pics! If I get in and find I missed a joist or there are none, I'll plan on through bolting w/o the big backing plate, just washers - very cool.
Coast Guard Dave - nice idea. We don't really use this deck for anything else...haven't had the chance yet, but will post pics of the boat.
These are all good ideas and every one helpful. Thanks!! I'll try to let everyone know how it turns out.

Jeff4688