Density of fiberglass used in boat construction?

All CSM and resin laminate = about 1550kg/m cubic for what its worth....

 

The implication of my calculations is that the bottom, which is the part that holds more pressure, should be 6,527 mm thick. The rest could be thinner but think it is not worth, for now, refine.
To give you an idea, the last boat I designed a 15-meter catamaran passage, about 40 tons, was 16.98 mm thick at the keel. 6,527 mm therefore not surprising.
Estimates say that one square meter of a panel of 6,527 mm thick, weights 10.318 kg. If you add the weight of the resin, you can estimate a total of 20 kg/m2. The total external surface, multiplied by 20 will give the weight of the laminate. Increases, to that total, 25% to take into account the weight of the reinforcements, and get the total weight.
If you have weight problems, it will take a more detailed calculation, taking into account the actual internal structure of the device, and in more detail by calculating the thickness of the sides and deck.
I believe what you call "fiberglass cloth + resin" is the same as "fiberglass laminates". In my study, at the end, you'll see the layers that I intend to apply to get the thickness required by the Regulations of Lloyd's

 

It is generally accepted that the total weight of a dry finished laminate, is 65% the fiber and 35% resin. Normal (but no good) practice when laminated by hand, it's 50-50 or worse. The infusion lamination results in a much smaller percentage of resin, up to 25%.
In a project like yours, handmade, of small size, the resin percentage increase much. So I am saying that the ratio is 50-50.
But here there are plenty of opinions. I tell you what is my experience.

 

The original poster should clarify the boat.

The small Harbour trash skimmers working locally are VERY robust boats, very heavly fendered, powerful for their small size and take a beating in the harbor.

They frequently run aground on the breakwater rip rap stones when chasing schools of condoms and Big Mac wrappers.

 

Thank you!

We redesigned.
https://www.dropbox.com/s/2pngeuvznqhid36/rede+apoio.JPG

The middle part is an aluminum structure, with 28m total length(if you take each individual aluminum tube and place them in a straight line), at 0.67kg/m (4cm diameter with 2mm thickness), we estimate around 15kg worth of aluminum.

Now we changed the design to this:

https://www.dropbox.com/s/2pngeuvznqhid36/rede+apoio.JPG

each yellow piece is 4m long x 0.56m wide x 1m tall
Total surface area of 2x13.6m2=27.2m2


https://www.dropbox.com/s/alcq0mn17ywcaml/tcharam V2.JPG

The middle part holding the solar panel and the lights is 2 x 1.7 x 0.4 = 9.6m2 surface area.
It has to hold a 10kg solar panel (top part)

Maybe it doesn't need 6.7mm, but maybe 5mm would suffice?

9.6+27.2=36.8m2 surface area.
at 20kg/m2 that will give us 736kg total...

We wanted 350kg max, I guess the only way is to either cut the volume in half, or reduce thickness.

You are absolutely sure on the 20kg/m2 value?

 

I can not be absolutely sure. When working with heterogeneous materials, the handling significantly influences the final product, one can not be sure of anything. I'm sure, only, that the fiber that I have planned, the layers provided, WITHOUT resin, weigh what I indicate.
If you need some other calculation, that you think I can do, I'll be happy to help.

 

a250004: As an engineer or businessman you will be required to be sure of your calculations and designs. You will be required to be sure to the point of writing a contract that binds you to the calculations and design. Experienced designers take into account errors and variations that occur during construction. That is something that takes time and experience. Also, if you work with a particular crew and know their capabilities, that enters into the calculations and design. Looking at the design you posted, aluminum or steel are your best options. It is an easily developable surface which makes it fast and easy to build.

 

For the same surface area, using aluminum or steel are going to have higher density, more kg in the same square meter area, making it heavier :/

We reduced the volume calculations by 30%, and changed the design, so we have less surface area.
We are getting 500kg total now (With electronics and everything).

I am quite pleased with the actual results.

Thank you all for your help, and thank you gonzo for your words, they motivate me to study to become a great engineer!
I wish you all the best

 

As an example, look at the weight of aluminum canoes vs fiberglass. That will give a good idea of weight differences, if any.

 

For a boat that size, a hull thickness of 4mm could be considered "normal" by recreational boat building standards...

As to the density, of course it varies, but typical fibre volume fractions of 50% are typical and widely accepted realistic ratios for a hand laid laminate. So take the surface area * thickness * density of chosen resin. Repeat with density of e-glass, add both and then divide the total by 2.

Density of e-glass is ~2540kg/m^3
Density of a typical epoxy resin is very close to 1000kg/m^3 not sure on exact figures, but densities of composite resins and fibers are well published by the manufacturers online... download the data sheets of your chosen products and then you have accurate numbers which also prove where you got your figures from...

 

It's risky, if not wrong, determine the scantlings of a vessel only considering her size.
On the other hand, it is a working boat, not a pleasure boat, therefore, standards for recreational boats are not applicable.