Build your frame like all the big manufacturers using square U bolts the U bolts allow the frame flex a little it may be micro measurement but it flexs so it wont crack
Me im a silly bugger i bolted all my frame together using 12mm bolts its all bolted hard and tightly together so i will likely have problems
Just what i observed bending the 101mm i beam in my hydraulic press u shouldnt have any worries carrying a 4.1m hull
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