Chris
On Sea Eagle we never use the speed log / paddle wheel !
reason a) has no benefit or use !
reason b) bungs up with weed so unreliably
reason c) why make a hole in the bottom of the boat ?
reason d) needs to be removed on lift out !
reason e) survived sailing nearly 30 years without !
Normally half a litre of sea water enters before placing the dummy bung, and the same to replace. so nearly a litre of briny to be removed and dried out !
Speed over the ground via GPS is all thats required, as speed thru the water has no real relevance.
Sure someone will contradict, but the tide conditions, times, ranges etc is all available without making an un-necessary hole !
regards
Kev