A few years ago, WS changed the tsunami by making it lighter. They did this by reducing thickness of the hull.
Does anyone know when this happened?
I’m looking for an older model when it was still heavy and thick.
temporary change
Those lightweight Tsunami’s were not made for a long period of time. They had additional foam pillars along the centerline of the boat between the footpegs, and behind the seat, in order to help offset the flex potential of the thiner plastic. I haven’t seen too many of them around.
I think it would be easy to determine the style of a Tsunami by looking at it. Or just pour water into the rear hatch - if the water flows freely into the cockpit it is probably one of the lightweight ones 
Duralite
probably referring to the Duralite models – it wasn’t a change, it was an optional model, made of a different PE with a slightly thinner hull and foam pillars & keelson to stiffen it up. I have a 140 DL and it’s great, have had no issues with it and it doesn’t seem flexier; but IIRC they had various production issues/too many 2nds and low demand so it was discontinued in 2008.
If it doesn’t say Duralite on it and lacks the extra structural members then it’s the standard model.
thanks
That answers my concerns.
I tend to NOT buy nay boat that needs a styrofoam block to keep it in shape or which will deform with the pressure of a thumb.
I like the 125 as it has space under the deck for my daughter’s dog, but also has that front bulkhead to prevent him getting lost in the bow.