Hello fellow Cat people,
My TheMightyHobie18 is a 1977, maybe one of the first TheMightyHobie18's made. On the underside of the deck flange, there is some kind of waterproofing that looks like some kind of rubber paint. Some of this is peeling off. What should I use to repair this? Would coating the affected area with Krazy Glue (R) work?
Fair winds,
David Ho
TheMightyHobie18 1067
3M-5200 is what I think would be a suitable replacement. It is waterproof and remains flexible. You can get it in various sizes including large tubes to fit a caulking gun.
I had the same issue with my older H-18. 5200 worked like a charm.
On early (pre-'81) boats, make sure it has be retrofitted with the shroud plates that bolt into the hull just beneath the flange. Otherwise, you will be pulling the deck off the hull one fine day. Been there, done that!
I think Hobie did run a free-retrofit kit at one time...contact a dealer to see if you can get the plates if needed. Retail price is quite steep for all 4 or 6 plates (two per beam (both fore & aft?), two for the shrouds.
What I did a long time ago was epoxy two layers of 1" Carbon tape on the underside (bottom side) of the lip all around the boat (NOT THE EDGE/glue seam), since it was cracking/spiderwebbing and leaking everywhere. (If you question the legality of this the 1989 Worlds TheMightyHobie18's where carbon reinforced.)
In addition, As I recall, I took old aluminum rudder pins and West System'ed them
under the lip at all four beam beam attachment points. (Aluminum is 10X fibreglass?)
At first I only did this at the main beam, but then the ream beam area cracked/split and the boat would again mysteriously fill up with water. (shear & tension between the lip and beam bolts area?)
Websites for carbon materials:
http://www.acp-composites.com/
Waterproofing?
The original boats had silicone wiped all along the glue seam. On Hobie 16s we now pour a resin bead to seep into and seal the lips. That would work on older boats if you clean out all of the old silicone. Otherwise… 5200, as mentioned already, is great stuff. You could do a “soapy-water bubble” leak test to see if there is even a reason to seal the lip.
Yep, be sure there are shroud reinforcement plates, but there are no more free upgrades for shroud plates on boats that old.
I own a 89 Worlds Hobie 18. 
The anchor plates are at the shrouds, and the inside and outside of the front beam. The best thing to do is to find used anchor plates (on the web)and install them as soon as possible. I plan to add ports aft of the rear beam and four anchor plates to the rear beam next winter as I have found some magnum wings to install for crusing.
I also helped my crew fix the seam on his Hobie 16, it had come unglued in some areas. Here is how we did it. Flip the boat upside down, grind the silcone off the edge of the seam. (Hold a piece of cardboard against the hull so if you arn't careful the cardboard takes the grind marks not the hull). Vaccume the seam out. Tape the gelcoat on the "deck" letting it hang down. Mix up some thickened epoxy, pour it into the seam while someone holds a vaccume against the drain plugs. After enough epoxy gets sucked into the seam, turn off the vaccume and clamp the seam shut with spring clamps. After a day cure remove the spring clamps clean up the hull & deck and check the hull for any leaks. Repeat if necessary.
I did about the same thing to the front seam of my comptip, it worked great.
I did a similar repair to a late model Hobie 18. The seam had started to split open and let in plenty of water. We turned the boat upside down and raked out all the old silicon. Then we poured in epoxy resin (without thickener) and clamped the lip with strips of aluminium secured by visegrips.
Worked a treat - we did 100 miles in the gulf the next day without taking on a drop of water.
The anchor plates are a very worthwhile upgrade - my suggested priority would be:
- At the side shrouds
- At the front Cross bar
- On the outside at the back crossbar if you have wings (you will need to cut in a port behind the cross bar)
Chris.
I have helped several new owners with early used TheMightyHobie18 Magnums: Both had broken-through 9 inch long cracks under the front stbd and port rear crossbars. (none had ever had stainless steel reinforcing plates). If this bad, the clean-up and repairs must be done from inside, hulls inverted.
Big job, but doable.
Wrong!
The stress on the wings came from the earlier design without the rear stress bars. They've since corrected it, so just go look up the current parts catelog and add the aft bars and brackets; it'll cost you under $30.
Stop the flexing and you'll stop the cracking!
Wyatt 