My daughter and I acquired a 1970's 16 and one of the hulls has serious soft spots from the rear trapeze post almost to the bow. It is my understanding that there is a sandwich of fiberglass, foam and fiberglass including gelcoat that is about 3/4" thick. Rather than using the process of drilling numerous holes and injecting epoxy, howabout drilling a series of 1/2" holes about four inchs on center all over the soft area. Then take a drill with a piece of coat hanger in the dril and bent at 90 degrees for about 2 1/2 inches and "beat out the foam between the fiberglass using compressed air to blow out the pieces. Then, instead of using epoxy, use low expansion foam sold at home supply centers for insulation to fill the void. Unlike heaver fiberglass epoxy, the foam adds very little weight and, like epoxy, is very sticky. With enough holes drilled the foam excess could escape instead of distorting the top deck and still be strong and solid. After filling, simply feather out the holes and lay up fiberglass cloth and fair out each to the deck before refinishing.
Also, foam can be melted with Acetone. Instead of trying to remove the foam could Acetone be poured in the holes in moderation to remove the foam? Of course if there isn't a water tight fiberglass connection between the lower layer of the top of the hull and the flotation blocks, severe damage to the flotation could happen.
Any thoughts?
Interesting idea, but I don't think it'd fix the softness. Here's why: As you may know, the foam doesn't provide any structural strength to the boat. It simply acts as a base over which to lay glass and epoxy. The weakness in soft hulls (I believe is that the layers of glass become separated from one another (and the foam). You can certainly remove the old foam, but adding new foam will not cause the layers of glass to re-laminate. The point of injecting epoxy is to have it fill in all the voids and thus provide compression strength to the structure, giving the layers of fiberglass something to "push against."
Even this is not as strong as the original laminated fiberglass layup where all the strength comes from the laminated fiberglass & epoxy.
Dunno if that made sense. Heh.
I've installed deck ports in my H16 and the overall thickness of the top deck is about 7/16". There is no contact between the fiberglass layers, so the foam is an integral part of the sandwich which creates the strength of the hull. Your idea of using spray foam has been discussed before, but I've never heard of anyone following through with the idea. If your boat is as bad as you say, I don't think you can hurt anything to try it out. I think the key will be to get a clean surface for the new foam to adhere to.
Another idea is to pick up another Hobie that has good hulls, but is missing other parts. It might be cheaper in the long run, if you consider all the work and swearing that you'll be undertaking.
Good luck. Keep us posted on your progress,
Jack
Well, Jack and I seem to disagree and I will readily admit I may be wrong. Hope everything turns out okay for you, and do let us know your results!
Here's a photo of the plug that I removed from my H16 hull when I put the deck ports in. Notice that the gelcoat is almost as thick as the fiberglass.
I think I might of misunderstood what Jim was saying earlier. I assumed that when he mentioned the layers of fiberglass coming apart, he was talking about the inside and outside layers. I think he was referring to the actual thin layers of fiberglass that make up the outer shell of the hull. If that is indeed the problem, I understand his worries about this repair method working out.
![[Linked Image]](http://users.adelphia.net/~jmhoying/hull.jpg)
Jack
NOW we're on the same page, Jack. 
If the only problem with his boat is that the foam in the middle has broken down, then injecting new foam should be satisfactory, unless the subsequent weakened state of the hull caused damage to the glass.
If, however, the problem is with the individual layers of fiberglass delaminating, then the foam will do nothing to help.
My knowledge of fiberglass sandwich constructions is limited. There is some good literature on composite materials and their use in marine / recreational applications. They are available in form of many pdf’s and written in an understandable way. I will try to locate them and post a link.
Contrary to a previous post I belief that the core (foam, balsa, hex cell,…) in a well constructed sandwich construction is an essential part of this construction that provides strength and weight reduction. If it would be solely the basis to place layers of composite material (fiberglass, Kevlar, or carbon fiber) separation issues like with Hobie hulls would not result in soft spots. (Jim IIRC you build rudder blades as a sandwich construction – I might confuse you with some one else)
From what I have learned in the past and from pictures I have seen the more common failure among Hobie hulls seems to be the separation between foam core and the inner and outer hull shell. According to what I have seen so far the individual layers of fiberglass are less likely to separate (delaminate). Here in TX al lot of older (pre 80’s) Hobie’s have this issue. Some people claim that this type of separation between hull composite material and foam core might be due to high outside temperatures, water that remained in the hull for extended periods of time, pressure / loads put on areas of the hull which compressed the foam core to much, …
Fscot… I think your approaches to the issue are pretty good. I never liked the idea of filling the voids between foam core and fiberglass shell with epoxy (weight issues – especially when the separation extends over half of the deck. Removing and replacing the core is a good idea
The “drilling out” method…it might be difficult to monitor if you removed the foam in all areas that required to be removed. It might be difficult to blow or vacuum all the bits and pieces and dust out before you fill in the new foam.
The “Acetone” method… It will be difficult to monitor where the acetone will dissolve the foam and I am not sure what happens with the dissolved foam… I do not know if the residue of the dissolved foam is a good basis for the new foam to adhere to.
Please keep us posted. In case you decide to replace the foam core rather than trying to glue them back together – please take lots of pics and post them.
Patrick
You remember the rudder correctly. In that case, the foam simply provided a form over which to lay the glass. I'm not positive, but I strongly suspect that if now through some magic I could go remove the foam, the strength would be undiminished.
I *can* see where the foam between the thin layers of glass would transfer some load from one layer to another and add some strength that way, in which case the expanding foam would probably be effective... Somebody should take a trashed hull and try both methods to see if they can discern a difference.
O.K. here is the link to the book I mentioned befor
http://www.marinecomposites.com/
The book is available in small PDF files that total somewhow 20Mb. Materials and Fabrication might be the highlights of the book. Thanks to Eric Greene, who is making this book available for free!
Patrick
i say junk it. i got a decent hull thru this website for $150, hard and smooth. sounds like you are trying to retread a worn out tire. by the time you get through with that extensive repair a replacement hull might be looking very attractive. so what if my boat has one yellow hull and one thats white? paint is a lot easier than the repair.
Marsh Hawk
Believe me, if I could find a good solid port hull for a reasonable price I would jump on it. I have been watching Ebay for four - six months. Only ones I have found are four to five hundred dollars and pick up only which is usually half way across the U S.
Anyone got a good solid port hull for a reasonable price?
fscot
fscot... where are you located???
Patrick
I have actually tried to use aftermarket foam like you suggested in the first post. I had a soft spot on the inside of a 16 hull that was about 3 feet long, discovered it one day after we ventured into 45 mph winds (go figure). Anyways I cleared out the foam and shot this stuff called Great Stuff into it. It worked pretty well. I then sanded down the excess, and put a couple layers of glass over it. I must say that now it's hard as a rock and although we dont' sail that boat anymore we never had any problems with it.