Best Extractor Fan/Grill Solution for windy wall vent

[pldaveo]

We have an existing bathroom 100m duct extractor fan which travels through the wall to a very exposed elevation that lets in a howling gale.

When we moved in the extractor fan was fairly standard and has a Gravity Ducting Vent grill to stop backdraught. Unfortunately, this grill keeps getting wedged open and is in a really inaccessible place.

So I have just replaced the fan with a Manrose QT100S because it has a integrated backdraught shutter thinking this would solve the problem from the inside.
However, I think I was expecting too much from the very flimsy backdraught shutters which, 1. clack around loudly in the wind, 2. don't really cut down the backdraught that much (you can still see daylight through it then closed).

So, I wanted to ask if there is a particular fan/vent-grill combination which is particularly recommended for a windy location?

Would an external cowl like the attached make a bid difference in addition to the integrated backdraught shutter?

 

[foxhole]

Cowl is best , manrose are pants

 

[SithLordHood]

Could go for one of these:

110mm Mushroom Vent Cowl

Aquaflow’s 110 mm mushroom vent cowl allows air to be released from the top of a soil stack without letting rainwater, debris like leaves or litter, or even small animals enter the plumbing. These nifty devices can be used anywhere a pipe runs outside of the building to allow for nasty plumbing...

www.toolstation.com

 

[chirpychippy]

You could try this, it is for 150mm duct but seems to screw flat to the wall, use rubber to seal the gaps.

 

[StephenStephen]

murdochcat recommended an ICON 30 - it's not arrived yet, but looks like it would solve your problem.