Just got a Hobie 18 with really soft decks, I sure somebody here has gone through it before, and I'm searching, but any quick tips? Remove the decks and glass underneath? Glass over the tops and paint them?
There is no quick fix. There are temporary solutions that may acutally be dangerous, the whole thing can fold up on you!
The oldest remedy is to drill many small holes through the outer layer of glass but NOT the inner layer. Then use a squeeze bottle to "inject" polyester resin into the foam between the two layers of glass. Generally, the more holes the better, the closer together the better.
This is only a temporary fix, it will not last and all such repairs I have done personally, or seen done are ugly!
If there is any way possible, dump this boat! If you continue, lots of frustration awaits!
Your best bet is to go to the Hobie forum on thier website www dot hobiecat dot com and do a search there. There is actually a FAQ about how to do it with diagrams and everything. I hve repaired small delamination areas on my decks and that has lasted for years. If done properly you will be fine. If the areas encompass the entire deck, then you really should look at replacing the hulls. Do not do any exterior or interior glassing as this will not solve the problem.
As for your repair, if you follow the directions and advice all you need to do is cover teh epoxy filled holes with some Marince Tex that matches your hull color. Depending on how much time you put into it will determine how pretty the repair is.
Do not sail with delaminated decks as the hull structure is seriously compromised. Do the repair before you sail and, as long as you completed it properly, you will be fine. If you have any more indepth questions, feel free to pm or email me.
You may well be able to find a sound hull. Check "Catamarn Sailors" classifieds, ya' never know!
Insurance, petrol, and a match, all come to mind.
You guys in SA seem to have a fasination with blowing stuff up! Rumour has it that a South Australian was the first person known to blow a tiger up (literally!) & now you want to do it again! 
My personal fave is find a good stiff day, point the boat at a pier and jump off before the collision. You don't even have to be going particularly fast - the waves pushing the boat underneith the pylons should take care of most of your issues.
Tiger Mike
...insurance services google-bot has now visited this thread...
Don't give up on the project just yet. Delamination is often completely fixable and depending on where on the boat it is...may be somewhat harmless, but still should be fixed.
Delamination on a Hobie 18s bow / deck is far less common, so I will assume this delamination is in the seating area between the crossbars. Try the delam fix shown on the Hobie Cat support page. I have personally done this with excellent success on several occasions.
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I looked here and at the Hobiepage recently: please Use EPOXY resin for injection into multiple holes, do not use polyester resin. I have fixed several of these- usually with impact/physical damage that came out ok.
Again- usually this is the sad result of neglect- leaving cats built of fiberglass/polyester resin/foam sandwich uncovered in the hot sun & full of water- its a mean trick. When in unrecoverably bad condition, the inner glass layer has come totally loose and is hanging down: The foam has turned to sawdust-like crumbles. Sorry but Botox won't help anymore
"Blowing it up" is much more fun! But seriously, the foam laminate that was used in most early TheMightyHobie18's decks is low-density polyurethane, which has a few "poor" qualities for a foam core laminate. 1. It does not take any impact well (it will crush and delaminate). 2. It has a relatively low thermal capacity so that if exposed for long periods of time in a hot sun the thermal capacity of the foam can be exceeded and it will once again delaminate. 3. Although it is promoted as a "non interconnected cellular structure" it will absorb and hold moisture within it's structure, even at times drawing it from out of the air, if it is not permanently and completely "sealed" (and as shown over many years in many types of boats, to permanently seal it is almost impossible). The biggest problems with “injecting” resin back into the delamination are 1. Ensuring that the whole area of delamination is covered, and 2. If the foam is wet, the resin injected will not bond with the foam and/or the laminations. When polyurethane is internally “wet” it is difficult to impossible to dry it out.
We have successfully repaired delaminated TheMightyHobie18 decks in the past, but the only guaranteed way to ensure that the repair worked correctly was to cut the deck at the middle of the front and rear beam mounting points (this was so that after the repair the cuts were supported and hidden by the beams), then lift the decks between the cuts off, grind off the inner laminate and the foam, vacuum bag new “semi rigid PVC foam” and vacuum bag a new inner laminate. We would then join the deck back to the hulls. This repair has stood up until today on boats that we repaired as far back as the early eighties with no sign of any recurrence of the problem.
