Stress (stiffness) testing a small tri hull

What is it you're trying to learn?

Unless you have a composites engineer design the laminate schedule with the exact basalt and epoxy, plus understand the exact design, and understand small triameran stress loads to get the number, you don't end up with any useful information.

 

It seems like hull deflection will be very small compared to beam deflection and not worth measuring.

For catamarans Richard Woods says the beam deflection should be 1-2% when opposite corners are on blocks and the other two corners are floating. Even without any mass added he calls this an "extreme" load that you wouldn't see at sea.

I'l don't know if it makes sense to apply this to a small tri. If you did, the most mass would would want to add is the load of the crew, not 500kg.

Also the goal is stiffness, not strength, so "not breaking" isn't necessarily sufficient.

Sailing Catamarans - Crossbeam Design https://sailingcatamarans.com/index.php/faqs/15-general-questions/88-crossbeam-design

 

Thanks for that - something to think about. I prioritised toughness and simplicity over strength or stiffness with the beams. (not yet built)
The above sounds like a good test.