Solid fiberglass or glass over wood for light bench seat box?

[lil' beaver]

I am making a 60" bench seat for the rear of my boat. It will be removable, so I need to keep the weight down as much as I can. I was curious if box made of 1/4 ply glassed over would be lighter than making a mold and laying up a solid glass box? I have tinkered with some mat over 1/4 ply and I believe with the right layup, it will be plenty strong. What do you all think?

 

[Woodonglass]

Upholstered or No??? If it's just gunna be solid wood then I'd use 3/4" solid Cedar and Soak it with the Old Timer's Recipe. It would be very light weight, strong and It'll last for decades and Look GREAT!!!!

Is this for a "Tinner" or a Glass Boat?? Got any Pics?? We LOVE Pics!!!:nod:

 

[KnottyBuoyz]

The glass over ply will be lighter than all glass given the same strength characteristics and most likely a lot cheaper to make. A 60" unsupported span of pure glass would have to be near 1/2" to 3/4" thick to give you the same sort of strength as glass over ply. The ply is only a core. To get maximum performance out of the products you're suggesting you should glass inside and outside so that one surface is in tension and one in compression under load (think I beam) that's where the strength comes from. Stick to biaxial fabrics for strength. If you need to go lighter look at some of the structural foam cores available. I think foam would be a better choice.

 

[lil' beaver]

I was thinking something like this. The backrest will be attached to the gunnel. Feet will be some 1" starboard I have laying around.

 

[DeepBlue2010]

So, you are talking about the frame for the seat not necessarily the upholstered base. In this case, here is a different approach for your consideration....

Go to Costco and buy the longest and the highest quality cooler you can find. Attach the upholstered base (the white one in the picture above) to the cooler's cover and you got your seat but also you got the cooler which you can use on the boat or convert it into a live well or even store things in it. The cooler is plenty strong and will end up much cheaper than you building from scratch when you consider the cost of material to build and finish (paint or gelcoat) the product. Just a thought.

 

[Scott Danforth]

if you want light weight, DeepBlue's suggestion of a cooler is spot on. infact the local marine surplus sells them with upholsterd tops on for that reason. However if you are bound and determined to make it yourself, the lightest commercially available reasonable cost core out there is nida core. it is a honeycombed fiberglass panel that you can put a layer of glass over the outside and inside and have a super-strong, super light weight box.

 

[Woodonglass]

Ahhh, Now I see what you have in mind. The cooler Idea is a Great one!!! But as stated, If you just HAVE to build one then, 1/4" ply banded at the edges with 3/4" cleats and then glassed or heck just epoxy coated should be plenty strong and light weight too. A Gallon of epoxy should do the trick. I'm thinkin' this thing could be build and upholstered for about $150 bucks. The largest ones my googling turned up were only 48" wide. Not sure they make 60" wide coolers but I've been wrong before.