Hi, I have a 31aft cabin and am going to install a bow thruster. I am considering a 75kpf with 180mm tunnel or a 55kpf with 150mm tunnel. I would prefer the smaller one but want to check if someone can advice based on what you have? feel free to reply in English or your preferred nordic language. Thank you in advance

I have 75kpf (Vetus) in my 32 Oceanfarer. It works fine, I have never been in a situation where its not enough. I guess a smaller one would work in most situations.

I have created a formula, which i cannot share since it belongs to a company now, but I can share som output rendered from the 31 aft cabin. Based on 10m hull length, 1,5 meter average wind appendage above wl, and thruster mounted ca. 1 meter from the bow.
Winds up to (value) : kgf
8 m/s : 33 kgf
11 m/s : 60 kgf
14 m/s : 100 kgf
This does not mean that the 75 kgf won´t give any assistance at 14 m/s wind or that the 50 kgf wont help at 11 m/s. But it gives an indication.

Thanks for great answers, I have swapped for the 55kpf Vetus with 150mm tunnel as it was almost half price. Adrian, if you have a setting in your formula to also take the smaller dimension of tunnel into account and a tunnel length of 1000mm, would that make a difference?

Well, the performance should not be compromised by the fact that the diameter is 150 mm since that already renders the 55 kgf output. However, the general guidance is to have no longer tunnel than 6x the diameter = you should prepare for some generous fairing to shorten the effective tunnel length by a good few cm.