HI its actually an old MFA Avenger which has been rubbish since the original MFA motor failed.Even a new modern type but with non replaceable brushes was no use. Tried all sorts to get speed up. Recently put in 2 Graupner speed race 500's with 2:1 gearbox, and it runs nice now on 8.4v. But in the quest for more speed, thought I would try 9.6v. Hence the water cooling. ifsucessfull I will split the water as you said.
This is the actual model that featured in the Model Boat mag review in the mid 1990's. I am under pressure from club members to go to brushless, but resisting.
Thanks for idea's

I would not advise putting both outlet hoses togeto a "T" piece. Do yourself a favour and run seperate outlets. Reason is, if one outlet blocks, you dont burn out both motors due to total loss of cooling.
Any form of restriction in the water exits and it reduces the flow rate and the water stops in the coil too long and the water gets too hot as its taking longer to exite the water system.
Its far better to have a exit outlet on either side of the hull, in line with the cooling coils, so this hose is a short and straight as possible.

Thanks for that, after a bit of thought I used larger tube to the "T" in. reduced to cooling coil size.Then back up after "T" out to drain. Now going to up the battery cells ?????

NO !

if you do this then the second of the motors is going to get HOT water thats already been through the first motor, thuis reducing its efficiency and not giving the cooling effect you desire.

Its far better to supply each motor with its own water supply, be it from a single input [but may reduce flow] and "T" piece but you definately must have seperate outlets to move as much water as possible to keep the motors cool and reduce risk of overheating/burnout.