Second Tri and second time calf cramped on bike

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I'm dealing with cramping lately as well and think it has to do with hydration. Stay well hydrated, eat a banana or two each day, limit alcohol consumption (that was directed towards me), and train more.

That sounds like a bike fitness issue. You are probably pushing much harder in races than during training.
I doubt it is a hydration issue so soon into a race.
Go a little harder in training and pace a bit more in the next race.

+1 on "pushing too hard for level of fitness". That is typically the cause, especially in shorter races. Especially with it being a calf cramp...in the bike. Back it down just a bit, and you will be fine. Happens to me all the time...sort of a good thing as you know you are really putting it out there

I know it was hot on the Sunday for the OD but not sure the weather Saturday which may have attributes to sweating more.
I found the hills on the OD (to Billingsgate and Westminster) unexpected so had to work hardest than expected.
I then got a twing of cramp in my thigh on the run which stayed for sometime but managed to get rid of it with a couple of gels and gatorade.
Because of getting there late I hadnt prepared correctly so didnt take my usual powergel with added sodium. 

My legs felt fine running apart from the twing so Im putting mine down to hydration and electrolyte intake.

You could always try a thigh compression guard (compressport.uk.com), I have used them for longer distance events.