darynxbcoupe Posted April 8, 2016 Share Posted April 8, 2016 Hi All, I have a f115A coming up 2 years old now with 150 hours on it, when I first bought my boat the top speed was around 31-33 knots, now I only seem to be getting 27-29 knots. I am running the same prop. Does this sound like something wrong with the engine? Link to comment Share on other sites More sharing options...
SquidMarks Posted April 9, 2016 Share Posted April 9, 2016 before you blame the engine, maybe think about the boat itsself. Have you added any extra weight to the boat? (such as additional batteries, anchors and chains, taking extra eskies full of ice, taking more mates on board lately etc). All of these will affect top speed and your ability to get on the plane. once you have ruled that out, then you can start looking at other factors (one of them maybe being the outboard). Link to comment Share on other sites More sharing options...
Ric001 Posted April 9, 2016 Share Posted April 9, 2016 (edited) Wind, tide, trim settings, Bimini up or down. Speed is a factor of thrust versus drag and is affected by how deep the hull is in the water and how much air resistance you have. Any nicks in the prop will also reduce your effective thrust because of cavitation. 2-4 knots off top speed isn't bad. 10-15 and I'd be really worried. Sent from my iPhone using Tapatalk Edited April 9, 2016 by Ric001 Link to comment Share on other sites More sharing options...
darynxbcoupe Posted April 9, 2016 Author Share Posted April 9, 2016 before you blame the engine, maybe think about the boat itsself. Have you added any extra weight to the boat? (such as additional batteries, anchors and chains, taking extra eskies full of ice, taking more mates on board lately etc). All of these will affect top speed and your ability to get on the plane. once you have ruled that out, then you can start looking at other factors (one of them maybe being the outboard). Yeh Na no extra weight like batteries or big eskies, or extra mates.. so it is defanitly same weight if not lighter than when first tested and used. The prop is in good working order and the condition as wind etc much the same most time I go out Link to comment Share on other sites More sharing options...
SquidMarks Posted April 9, 2016 Share Posted April 9, 2016 Could the speedometer hole on the outboard leg be blocked? that is another possibility. Link to comment Share on other sites More sharing options...
squidboy Posted April 9, 2016 Share Posted April 9, 2016 Agree with SquidMarks. Try getting some 100lb mono line and clear out the speedo inlet hole. It is in front of the dog leg of the motor. There maybe a small price of junk in the inlet so less water passes through. Make sure when you do this you get the line all the way to the bottom of the motor cause there is a 90 degree turn about 10cm into the motor. Good luck Link to comment Share on other sites More sharing options...
darynxbcoupe Posted April 10, 2016 Author Share Posted April 10, 2016 The speed is coming through the GPS Link to comment Share on other sites More sharing options...
squidboy Posted April 10, 2016 Share Posted April 10, 2016 Few other things then: 1. Is your hull clean like new? This creates drag if not 2. Is the motor serviced and the oil is at the right amount? 3. Have they changed the plugs lately and did they fit the correct plug number? Link to comment Share on other sites More sharing options...
darynxbcoupe Posted April 10, 2016 Author Share Posted April 10, 2016 Going to have to check these points, the hull is very clean so maybe plugs Link to comment Share on other sites More sharing options...
tackleberry Posted April 10, 2016 Share Posted April 10, 2016 and how old is the fuel Link to comment Share on other sites More sharing options...
darynxbcoupe Posted April 10, 2016 Author Share Posted April 10, 2016 and how old is the fuel Fuel is always fresh as I use it all the time Link to comment Share on other sites More sharing options...
tackleberry Posted April 11, 2016 Share Posted April 11, 2016 Link to comment Share on other sites More sharing options...
jeffb5.8 Posted April 21, 2016 Share Posted April 21, 2016 How did you go with this issue any findings or fixes? Link to comment Share on other sites More sharing options...
Guest Posted April 21, 2016 Share Posted April 21, 2016 You may even have water in the hull from rain or washing the boat and that adds heaps of weight you cannot see Link to comment Share on other sites More sharing options...
darynxbcoupe Posted May 9, 2016 Author Share Posted May 9, 2016 How did you go with this issue any findings or fixes? I have had the boat back on the water a couple times, last time conditions were very flat and only had 50 litres of fuel on board. Just my mate and I and still could only get 28 knots. The boat doesn't take any water in the hull from rain and hull is a dry hull Link to comment Share on other sites More sharing options...
Guest Posted May 9, 2016 Share Posted May 9, 2016 a couple of knots can be in the trimming as well and if the motor is going well I wouldn't worry Link to comment Share on other sites More sharing options...
sydney south Posted May 9, 2016 Share Posted May 9, 2016 Have you changed the grade of fuel that you use. Maybe new spark plugs....... Link to comment Share on other sites More sharing options...
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