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Question for those familiar with coosa board. I am thinking of building a hard top for the boat using coosa, is the product flexable at all? I would want the top to have a slight arch to it. If not can I groove the under side , jig , then back fill to achieve the arch? Thanks for any input.

Coosa is stiff as a board! It would be very difficult, I think, to kerf this and get much of a bend. It contains fiberglass sheets near the surfaces. Might be possible with the lower grade version, but still difficult. It's also heavier than divinicell or other foam boards used for cores. Coosa would be good in spots where you need more strength, i.e. thru- bolting locations

I would be interested in following your project, as I plan the same for my B25. The "traditional" method of construction uses a pre-made jig form to obtain the shape.

Cam

Got it Thanks. Looks like divinicell then and probably lighter with coosa inserts for mounting areas.

A guy right next to my boat, with a 28 too, did the following:

He took two or three of those 2-3 cm thick insulation boards from Dow that they use in construction, can be either light blue or green depending on thickness or specs.
He then measured the curve of the fb floor, and copied the same curve for the top (secured the dow boards with wedges and clamps and applied a few layers of glass on both sides). The dow boards can take that slight curve fairly easily. The rest was easy, he gave the whole surface its final form and dimensions and finalized the trim around it as well as gel coated it. He also inserted pieces of plywood where he would hang the instruments from. The result is beautiful. He told me if I wanted he could do the same for me, but I don't have the proper structure to mount it on (I have a bimini with SS tubing) so I hesitated. Otherwise a pretty straightforward and quality result.

Yannis

that works, makes a supper light structure. Only issue would be you probably can not put any weight on it. So if you have to go up there for some reason I think it would be questionable.

Tony,

What would one want to do up there? The 28 rolls enough down below, I hate to think you’d build a tower in a 28...
Besides, like you said, its super light and you can mount all sorts of things on it, like even solar panels that would look much better being flush on a rigid surface like this one, as opposed to being mounted over a bimini like I have them now.
For me, it would have been a huge improvement over a canvass bimini, only I’d need to install all that tubing all around the boat which is super expensive, heavy and cumbersome.
I’m not too sure it protects you from the sun like a canvass bimini does that curves down around the sides.
The rigid top is better for mounting things on it and under it, less if you also want it for sun protection like I do.

Around here we mount radar on them then when the snow fly's we cover everything up. That usually requires climbing up there to pull the canvas over the top.

A ha, that explains it.
I’m sure what I described can take the load of a person up there.
Next time I’m down at the boat, I’ll take a pic of my neighbor’s rigid top.

https://imgur.com/dLrpYzr

https://imgur.com/XnNIAVz

Yannis

That looks thick enough, it should hold a person's weight. Maybe an average person, we would not want a large person testing it out.

Tony,

I assure you this particular one can even hold me, being 105 kg.
The problem with these rigid tops is the burden and weight of the metal frame.
I find it too cumbersome to carry onboard and too heavy/top heavy for the size of our boats.
It's also too d@mn expensive.
But it would certainly accommodate with extra care my solar panels, that's why I still contemplate putting one!

Big difference is here our structure for these tops is all aluminum tubing.
It's a huge weight difference with a hardtop like shown.

SS is really only and option with soft Bimini tops.

Carl,

The alu tubes have to be much thicker than their ss equivalent.
Do you still believe that they are lighter?

My buddy with an Albemarle that has a stock rigid top which is very sturdy, is made in the usa and is all alu.
It’s much wider in dia. and I also wonder if they are not also thicker as tubes.

Edit: I just looked up the rel.weights of SS vs AL. Its a bold 3 to 1. I still believe the vol. of alu required, is close to 3 times more.

Had a stainless steel radar tower on my old Formula. It needed support to stop the side to side motion. Aluminum does not sway as much.