Who is correct?

[Tones]

I had a robust discussion with a boat dealer on how a boat was plumbed,a heat exchanger and Rolco manifolds with risers. The heat exchanger is plumbed so the raw water is at the cold end exiting at the hot end then going to the manifolds at the front (cold end) and from there continues to the risers and out. I said the whole raw system is wrong and should be plumbed so the water is cooling the hottest water/exhaust first.  Who is correct?

[Matthewf/Norbert/TuiDog]

Hi mate

Physics is correct, so the largest temperature differential is the most efficient heat transfer

[Keltik]

Seen it done both ways plenty of times. Don't think it makes much difference with a heat exchanger but with full raw water cooling - I'd want it going through the manifolds first

[Tones]

Matt, I've changed the raw water system so it's proper.
Keating, it matters heaps when you're boating in nearly 30 degrees of surface water temps was we do in QLD.

[Tones]

Keltik sorry about that, frign thing thinks it knows best. 

[Jimmy Jet]

I think you are correct, all advice I've had and read says to have the raw water against the flow of hot water/heat. I don't think the manifolds are as critical but I'd have the HX set up that way.

[Paul]

On raw cooled, send through the manifolds first, as it takes the chill off before it hits the block. The water coming out of a HX is probably 50-70?C, vs 10-30?C for whatever you're floating on if raw supply.

Re parallel-flow, vs contra-flow in the HX, it really depends on the relative flow rates, of the jet cooling supply vs water-pump flow.  Chances are, the cooling supply from the jet is several-fold the water-pump flow rate, in which case it really doesn't matter which way you choose, as the jet supply totally dominates the water-pump rate.  If you do contra-flow then you can get a lower temp coming out of HX (going back to water-pump/engine).  If you do parallel-flow, the best you can hope for (going back to water-pump/engine), is somewhere approx halfway between hot coolant temp and raw temp supply.

Mine is setup as contra-flow.
Jet supply > sand trap > water filter > HX > manifolds.


Discussed a few years ago too:
http://www.jbnz.co.nz/yabbse/index.php?topic=29225.msg211280#msg211280