Splashboard (coaming) problem


I recently acquired a 1980 Sunfish in nice shape except for the splashboard (coaming), which seems to be warping and pulling itself up off the deck on the two ends. On one end the OEM pop rivets (Rivnuts) have pulled out of the deck and are loose. The deck seems to be in great shape, with no spider cracks, etc., except at the ends of the coaming. Is this a common problem? I suppose I could drill out the loose rivets on the ends and replace them but I wonder if the splashboard warpage would cause undesired pressure on the deck. Any ideas on how to accomplish proper repair? Should I use another (better) type of fastener?


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"Regular" aluminum pop-rivets are easy to drill out, so use drill bits to determine the correct size to reinforce/expand the existing (three?) riv-nuts.

If that doesn't work, drill out the "try" pop-rivet(s), clamp or weight the splashguard, apply a minimal layer of petroleum jelly underneath the splashguard (as a separation layer), inject THIXO or Marine-Tex into the void*, let it set overnight, countersink the splashguard minimally and drill to fit new rivets. (Minimally, because a permanent bond isn't wanted!) :confused:

*The "void" may be backed by a large Styrofoam block if clamped tightly, and won't stick to it.

If riv-nuts are missing, there's enough space molded under the splashguard to invisibly bond coin-sized scraps of cured fiberglass to the deck. (Drill to fit new rivets).

If replacing all the riv-nuts, a variety of riv-nut tools are available from AliExpress from about $30 up. With the tool, AliExpress includes a large variety of riv-nuts in metric sizes. (Rental tools may be available at your local hardware store). However, members here have reported difficulty in aligning new riv-nuts. :(

A few years ago, I posted a video showing how one's partially attached splashguard flexes inches as one sails, so there's strength in fastening it firmly to the deck. (And fewer occasions of spider-cracking).

OK, I think I'm done here....;)
Could a person drill out the rivets, pre-make assemblies with rivnuts and small fiberglass disks, and then bolt those to a properly masked coaming and then epoxy the disk assemblies into place on the deck?
That might work, but there's not much room between the big Styrofoam blocks and the end-three rivets in the underside of the deck.

:oops: Now I see you mean to attach the assembly ON TOP of the deck :rolleyes: . I'd measure twice, do one side then the other, but that's a great suggestion IMHO. :cool:
Yes, was thinking from top. I thought if all were bolted to the coaming and glued to the hull at the same time the alignment issues go away. I suppose a person would want to wax or grease the bolts, so they are not accidentally glued into the rivnuts. I did not consider any spring back or clamping. forces required.

Have you ever seen the Allen key trick for removing foam or core from underneath a glassed surface? Short end of an Allen key or bent nail goes in the hole and is spun with a drill to grind up and clear out the core material. On bigger boats these holes get taped off and filled with resin and then are re-drilled for mounting hardware to prevent a path for water intrusion into the core. One still needs mastic or sealant to finish the job. This could be used to shave out a pocket in the foam for the rivnut.s if needed.

My boat leaked out of several rivet locations on the deck when I rolled it over, so I see some sort of repair in my future...
Interesting thought regarding the Allen wrench type fix procedure. Pretty much anything that I’d be wanting to attach over a repair would originally have had a backer block, I would think. Now I’m curious enough to go see if I have any boats with rivnuts on coaming, then throw my endoscope camera in and see if there was foam or blocks under there.
The Allen key approach is good for boats with "cores" made of balsa wood, nomex, Styrofoam, etc., but the Styrofoam in older Sunfish isn't structural in the same sense. (Not by a 1/2-inch). There's plenty of clearance for riv-nuts as you intend to afix them, but assure clearance under the splashguard. :oops: Your "discs" may turn out to be rectangles.

To protect the bolts, put a wrap of [inexpensive] whiteTeflon tape around them. They're protected where they take the white color, and the bolts will readily screw into the riv-nuts.
I am still concerned about why the only spider cracks on this deck are at the two ends of the coaming and the first 3 rivets on one end have broken free, leaving a gap. I think I will go sailing.
That is a good balancing point. (Either side of the daggerboard!)

Two people might think to carry it that way.