| 
		        
                
 
 
	Group: Forum Members 	        
    Posts: 48, 
    Visits: 15 
    
 
          
		     | 
				                       
                 
                
                    
			            I had an Airmar ultrasonic log the whole of our circumnavigation. The advantage of ultrasound is that it doesn't need to be raised and cleaned all the time - is maintenance free. You often learn that the  paddle wheel needs cleaning when you most need to know your speed - particularly if you have been stationary for a week or so.   The disadvantage of ultrasound is that it is very sensitive - it measures the speed of the boat as it hunts on its anchor -  even a light cross current. 0.1-0.2 knots.  If you spend a week at anchor you can easily find the boat has measured a 50-100 mile passage. Switching the depth sounder instrument display off may stop the system logging the distance - or not - depending on how it is set up.
  Eventually, I gave up and fitted an Airmar paddle wheel. However, 4 years on and I am thinking of returning to the ultrasound because i am fed up with cleaning the crud off!
                   
			            				
			                                 
                     
                                            
                         
                    
                  
             |