Talk to me about Amp Hours

[2Xtreme]

I?ve done a considerable amount of research regarding amp hour calculations, but I?m still stumped.
Hoping someone here can shed some light on this for me.

Using round numbers and assumptions:
If I have a trolling motor that draws 40 amps (max) on my kayak with a 100 Ah battery, I should expect approx. 2.5 hr of use out of the battery. (I know it's actually less, but for the sake of this question, let's go with that)

If I put that same motor and battery on my 10? pontoon with 2 people fishing from it, in my mind there is no way I can expect that same usage.

So, what am I missing, here?
Are amp draw ratings of components (trolling motor) based on zero load??

I guess my real question is- how can Ah be calculated by the manufacturers without knowing how much 'work' is going to be done by the component(s) a battery is powering?

Thanks in advance!
2X

[redidbull]

Using your numbers. I believe that if the motor draws 40 amps when wide open that is what it will draw no matter what the load is. A small boat with 1 person will go faster and you will get physically farther than with a larger boat. The motor has no idea what it is pushing just that it is at max. Jim