Mercury 50 fuel consumption & Speedo connection

[mikewallis]

Having recently aquired a UK Norman 20ft cabin cruiser with a recently serviced Mercury 50 2 stroke, I am interested in approx fuel consumption for inshore cruising. It was suggested that my two most economic speeds were 'displacement' just before the stern digs in, approx 5 MPH, and when planing, the minimum planing speed of approx 18MPH. I was also advised that economical consumption would be approx 1 Litre per Nautical Mile and would welcome a second (or more !) opinion on this. Also, I have a speedo on the dash but was told that there was a "bit missing in the engine that it connects to" , can anyone advise. Many Thanks, Mike.

 

[steelespike]

Re: Mercury 50 fuel consumption & Speedo connection

You don't say what year your motor is.<br /> At 20ft and 50 hp.your motor will be working pretty hard at planing speed.Not knowing what type hull you are pushing,semi V,Deep V, rounded bottom or displacement type. it's difficult to be too specific.But at about 4 miles per gallon at planing speed I would think your pretty close.<br /> A set of trim tabs would surely help get on plane and save a little gas.I can't help much with the speedo but most speedometers are<br />pretty inaccurate a GPS will do a better job.

 

[Silvertip]

Re: Mercury 50 fuel consumption & Speedo connection

I'm not sure if that engine has a built-in speedo pitot. Any marine shop can provide you with a universal speedometer pitot. It's a plastic device mounted on the stern. It protrudes into the water just below the hull and has a tiny hole in it. A tube attaches to it and the speedometer head. Pressure in the tube is relative to boat speed. That pressure is translated (rather loosely) into speed.