Welcome aboard Jason! Ask away here as needed, as there are many, many helpful people here, but also realize that while there's usually 1 really
wrong way, there could be 3 or more good to better, but quite different, ways one could do something. So always keep YOUR needs and budget in mind! It's also far too easy to go overboard and add significant weight to a small boat - so go slowly. I always advise adding the least weight needed and keeping it low (for stability), less if only using it floating on small ponds with not much wave action.
To your question - honestly, tin boats are designed to flex so that they don't crack. Keep in mind and look at T-Tops for offshore vessels, the structure is made out of aluminum - as it moves and flexes - but it is not stainless steel tubing. SS tubing and structures is sooooo rigid it that it doesn't flex and that can cause cracks quickly on new items. Even where SS is used, there are wear components of other materials built-in to absorb the stresses or send it to another place designed to handle that force.
Now yes, with an older tin boat flexing, flexing, and flexing ... over time and age it could develop a crack, akin to taking a steel paperclip and bending it back and forth, sooner or later it's going to crack and break. Those grooves in the extrusions going from fore to aft in your hull are designed to give rigidity and strength, but it will also allow it to flex from side to side - as tin has to move. Think of an archery bow, pull the string and let it go - it vibrates, that's due to the force. Also think of an airplane wing, ever sit looking at one outside the window and see that wing tip moving up & down, and a lot? It's designed to moved - if too rigid it would break :shock: . On a tin boat, the large tin panels between riveted structures are designed to vibrate/flex to absorb
and dissipate those forces and stress. Also for tin boats, think of the
entire hull being tied together that gives it the 'toughness' needed. It's not the '1 rivet', it is the 100s of them that give it the toughness.
For you, if/as needed, check all pieces in that area and even re-buck any rivets that may look suspect. My mind immediately went to a simple idea like adding a small indoor/outdoor rubber matt in that area - if the flexing really bothers you - but note you could then be causing all that force and stress to then be localized in a riveted area. Do you get the concept here?
The bigger tin panels indeed are designed to flex, so as to absorb the force/stress through the flexing, to keep it away or from being absorbed into the riveted areas.
Now clearly if the hull is wicked old and suffered some kind of structural damage already, well that changes the situation. But from where I'm sitting and advising via cyberspace ... I'd say
just use it! Watch it - yes, but use it. FYI, one of the 16' rebuilds in my signature had the floor between the middle seat and front seat flex and move like Courtney Love on crack at a Dead Concert ... it bothered me at some level, as it is somewhat disconcerting to see it whilst running an inlet (saltwater boat w/ a 40hp on it) with standing waves, and yet that hulll never leaked nor cracked.
I hope this gives you some perspective ...
....