The shockingly scanty yet amazingly noisy little box-ticker blower (fan, actually, sadly) on our SO39ip was one of the first things I gave the boot when we took her over.
An axial fan (OEM) is a misapplication when working against high static pressure, such as with a long exhaust hose, for starters. That's partly why the little things supplied for box-ticking purposes are so noisy; the blades are in aerodynamic stall 100% of the time. A centrifugal "squirrel cage" is much better suited for operating against static pressure and is inherently more quiet. The choice of axial is tilted far too strongly to cost containment.
Meanwhile, let alone acoustics, decent CFM actually delivered is important for long-term alternator health, particularly when big depleted battery banks are a regular feature of life.
Finally, longevity is a distinct plus.
So, a centrifugal blower with ball bearings, high surplus capacity and then derated for extra long life is a productive alternative.
I combined a Delta T 500-304121 IP "LIL Champ," which ticks all the above better boxes with a PWM controller to replace the failed concept of the OEM blower. This unit delivers 350 CFM nominal, 200 CFM against extreme static pressure of 2". By comparison, the OEM box-ticker is rated at 130 CFM but in reality will deliver a fraction of that due to static pressure from the long and rough exhaust hose (with upward/downward sweep at transom and finally a hard right-angle as final performance-killing insult).
The PWM controller is adjusted to run the Delta T at 2/3 nominal RPM, extending lifespan. This still moves a copious amount of air down the hose and out the back, even with all the bendy bits.
At 5 years and ~1,800 hours after installation, the blower is still perfectly healthy. Not least it's extremely quiet, so there is no fan howl added to the already loud-enough diesel. Previous blowers were lasting about 2 years while making a hell of a racket and not accomplishing much else.
Blower spec sheet: Specification PDF
PWM controller is this one from Amazon, still available, does need to be put in a plastic box for reasonable splash protection and easy mounting: Rio Rand Switch Controller
Photo (somewhat lousy) shows installation, upper left. Blower sits on a fabricated pedestal mounted to engine casing. The PWM controller is attached to the side of the blower scroll, with bleed port to push air through the controller for cooling MOSFETs (which is also massively derated so this is probably overkill).
Should add: heat soak-back and diesel stink is a factor in aft cabins, particularly in summer. The year after adding this blower, I added a thermostat switch and manual control along with another PWM controller and relay, so that if the engine compartment temperature rises above 115 degrees F after shutdown, the blower will run at highly reduced speed until compartment temperature falls to 105 degrees F.
In practice, this feature runs rarely, but when it does, it's on a day when more heat down below is definitely not desirable.
Crew may manually select this to "on" for stink control. The blower at this low speed still effectively creates negative pressure in the engine compartment (and entire void area for that matter), ending the stink problem for those bothered by it. This has proven quite popular.
Power consumption in this mode is reasonably negligible unless the crew use the feature a lot. About 2A.
Added rubber isolation mounts for vibration control with this change, to avoid motor vibration coupling to woodwork and being annoying, when the engine doesn't mask this. This style:
Article from this Jeanneau Owners Forum post