Coring Floor Hatch with Foam

[DennisG01]

I'm recoring the floor of the Grady and I thought I would try something different for the floor hatch. Given that it's easy enough to rectify, either now or even when it's in the water, I thought it might be fun to try something that hasn't (to my knowledge) been used before. There are obviously foam coring materials available (Divinycell, for example) so the idea of using foam is not at all new. What I'm going to experiment with is the inexpensive pink/purple foam-board insulation that you can get at Home Depot. I've got some leftover pieces of 3/4" board that I'm experimenting with right now. The picture below is of an unaltered piece of foam and one that I (very) quickly put a layer of glass on the top and bottom with epoxy resin.

The amount that it stiffened up is amazing. I'm going to do some weight tests to help quantify this. The only thing that concerns me a little bit is that, while the epoxy seems to bond extremely well with the foam board it does not soak in very far. Meaning, if I pull hard enough, I can rip the layer of fiberglass off the foam. I'm going to try using a star-wheel tool and poke a whole bunch of holes in the foam board and see if that makes a difference. Ultimately, I don't know if this will pose a problem or not since everything will be completely encapsulated with fiberglass. I'm open to opinions and discussions on this!

 

[gw204]

Curious to hear how this works out for you. I think you are going to have problems with the glass separating from the foam.

I may try something like this in a non-structural area like insulating the forward tank compartment in my 227, but for a deck panel, I will always use a structural foam or plywood.


I have also heard/read that this type of foam does not work with poly or vinylester resin. The styrene in them dissolves the foam.

 

[DennisG01]

The separation, or delamination, is my concern as well. But not in the typical sense that we deal with. In other words, I don't see the glass delaminating from the foam. Instead the foam will delaminate from itself. But, in order for this to happen, there's going to have to be significant flex and once the the "sides" of the foam are glassed, that will cut down (even more so) on any flex. Once I add the holes to the foam, I'm hoping that may cut down tremendously on the possibility of delaminating, too. Either way, since it's on an easily removable hatch, if a problem does arise I can just take the hatch home with me and redo it with wood in a few hours. I'm looking at this as a fun experiment, but there's no way I would do this on the main sections of the floor.

The other night, I also epoxied a piece of the foam to the old "underside skin" of the hatch locker and also a piece of scrap plywood. As hard as I try, I can not pull the foam off. Honestly, I was expecting to be able to pull it off via ripping the foam, but I cannot. As I somewhat mentioned in the first post, the way that I was able to get the glass to delaminate from the foam (but it took a layer of foam with it) was peeling the glass off like you would rip a page out of a notebook. Obviously, that type of stress is not going to be seen when the piece is in the boat.

 

[onoahimahi]

Interesting experiment. The holes though the foam will be key I think. I'll bet it would work if you cut it up into 6" blocks like the original plywood, left some space between the blocks, and used a layer of mat on both sides. It will essentially be a torsion box which are very strong.

 

[DennisG01]

Interesting idea on cutting it into squares. I might stick with a large piece - but more for the experimental aspect. Not because I think the squares would be in any way inferior. It'd be so easy to come back and redo this down the road, I'm in no way concerned about that part of things.

What's the reasoning behind adding another layer of glass between the foam and the hatch? I mean, the hatch is already glass. Is it just to beef it up a little more?

 

[onoahimahi]

What's the reasoning behind adding another layer of glass between the foam and the hatch? I mean, the hatch is already glass. Is it just to beef it up a little more?

I don't know exactly - someone who has been "building boats for 35 years" told me to do it that way so I did. I would guess it has to do with improving the bond and helping to assure there are no voids between the hatch and the plywood. Maybe you won't need to since the foam won't absorb resin the way plywood does. The discussion is here and the posts from FX10 describe it:

http://www.thehulltruth.com/boating-for ... panel.html

 

[DennisG01]

That sounds reasonable. I suppose thickened resin could do the same thing, but the thin glass would add one more layer and also be cheaper.

 

[DennisG01]

Crazy couple of weeks. Finally got around to seeing how much weight these little scraps of styrofoam can hold.

This one is how I balanced the weights on each piece of foam:



This is 15lbs on bare foam:



This is 25lbs on bare foam. The weights are now contacting the foam, keeping the foam from sagging any further.



This is 25lbs of reinforced foam. The reinforcement is only a thin layer of fiberglass cloth on each side:



This is 75lbs on reinforced foam, very slight bend:



At 85lbs, it failed and the weight contacted the foam. I believe it actually could of held more, but I think I failed to evenly the support the weight on the piece of small wood and the edge of the wood "point loaded" the foam, creating a crease and cracking the fiberglass.








However, I was happy to see that the fiberglass never sheared away from the foam, even when bending it numerous times. I'm pretty satisfied that it's at least worth the effort to use this cheap stuff and see how it holds up. To stay with the "experimental" theme of this project, I'm not going to poke any holes (was actually thinking of 1/4" holes all the way through) in the foam or cut it up. I am 100% confident that either one of those ways would be superior, but that defeats the purpose of what I want to try. BUT, I want to point out, that I am doing this STRICTLY as an experiment and for the "fun" factor. I DO NOT recommend anyone using styrofoam for anything more permanent/structural than an easily accessible hatch. Even then, as they say, proceed at your own risk! There is NO WAY that I will be using this foam for the main parts of my floor. If this styrofoam fails, it's only a couple hour job to redo it with plywood or something like Divinycell.

 

[onoahimahi]

That's impressive - especially when considering the foam block was only about 2" wide. I'll bet the normal deck forces from people's feet will not exceed the PSI of that test. (I don't think I'll be squirting Great Stuff into my transom anytime soon, however :lol:

 

[DennisG01]

So, time has been my enemy here. Between two work schedules, the kid's after school stuff and normal "honey do" stuff, I haven't had a whole lot of extra time. I've also been working out in the boat on various things, too. Structurally, though, the hatch is done and I'm very happy with the results. Could not detect any deflection when I stood on it with one foot. For good measure, I even jumped on it. I'm confident reinstalling it in the boat. We'll see how long it lasts!

I had to rebuild the one edge of the hatch since it had been cutoff by the previous owner. I used fiberglass "L" channel for this. I notched it to fit in and then epoxied and glassed it in place. I'll come back later and trim it flush with the other edges. For extra support, I added a single layer of fiberglass mat between the hatch and the foam. I also reinforced the edges/lips. It's rough looking right now, but it will be nice in the end. Although this is going to be a "work boat" and doesn't really need to be super pretty - just functional and reliable.



Since this hatch will be on hinges, there was no need to reuse the deck plate. So I filled in the hole.









With a layer of 1708 bi-axial...


Last step was to fill the topside level with epoxy. I'll be painting the floor when I'm done, so it allows me some leeway on this step to not have to worry too much about "prettiness". I'm also going to use this hatch as a mold to make another hatch for the boat - which will cover the area that the stern drive used to be.

 

[dale1]

Dennis, man i cant believe i havent seen this post before now. Ive been using that type of foam for some time. i did not use foam for whole piece but did use it to close the round hatch, and also for the stringer on my hatch project. it works great. I used it to bief up the nose on my carolina skiff to mount a windlass motor. its been used many times since.

viewtopic.php?f=2&t=21435

the testing was great. thanks for sharing.

dale

 

[DennisG01]

Cool - thanks for the reassurance, Dale. The only thing I don't like is that the foam doesn't have (if I'm explaining this correctly) the resistance to "de-layering" that plywood or Divinycell would have. Which is why I don't want to take a chance and use this with the floor. But for this area, especially since this is primarily acting as a separator between the two layers of glass, I'm good with it.