I am fitting two tuna tubes on a trailer boat and trying to get my head around the pump requirements. 

Do I really need 3700GPH for this (pic below)?  That would be 14,000 litres per hour or 233 litres per minute??? (divided by two tubes). 

Keen to hear from those that have successfully kept tuna alive for the day and what they have? I see a few posts where people have used the 1600GPH Bronze Tournament Rule Pumps but cant find them online here (NZ).

There are other calculations that suggest that you will get close to enough flow velocity over the tune to keep them alive with only 600gph per tube, but in our warmer conditions (lower oxygen levels) my feeling is that you will probably soon be wishing you had bought the bigger pump.

You could go for maybe a single tube and run a skippy on one side and a big jack mac or Koheru on the other from a live bait tank. Still wouldn't want this off your engine battery though so would be looking at a largish house battery on a VSR setup knowing that it will get run down during the day but that you can charge it from the mains over night. Say you are drawing 8 amps for a single tube pump and can budget maybe 2 amps average from the alternator after running your electronics etc then you lose 6 amps per hour. Allow say 8 hours of tube running and you need ~50A/H and to stop that battery getting killed each day you need to double that so ~100A/H house battery. To be safe I would probably try and go a bit larger if you have the space.

If you really want two tubes you could up the battery size and run a larger pump or the other alternative is to put 2 tubes on the smaller pump as you initially asked about and have valves in the feeds so you can run just 1 tube if you have a big skippy or 2 tubes if you have smaller skippies or some other smaller baits (can drop big Jack macs & Koheru etc into the tubes also. Might not give hours and hours of life to a pair of Skippies but could be a workable solution for your constraints.

But you are not going to have much leeway.

Regards

Alan