Hi Visje,
Please do not misunderstand. I am not trying to discourage you from posting here, but a word of constructive critizism might be in order. This is a technical forum, and your posting above is so vague, that it does not meet the friendliest minimum standard of a factual answer. I do not believe you thought much about the question when giving your answer.
How abt. something like this:
On the type 9 top of old ball valve snort was 5.10m above top edge of conning twr, abt. 20cm below periscope lens at max. extension. Cdrs tried to keep upper edge of twr abt 3m below, which allowed for abt 1.5m swell/waves. Actual depth depended on sea state.
The only reason why any cdr without a suicidal bent would NOT attack a convoy while snorting is selfevident. With diesels running the racket would have alerted every escort\'s sonar operator about the boat\'s position, before it\'s cdr would have seen anything of the convoy.
Cheers, RB