A puzzle to be sure!!! !@#$%^&*

What does the fuel burn chart say. I am having some issues you say this is a 28.55 footer, yet it has a command bridge, full canvas and a dinghy on davits mounted on a swim grid? 28-20 m/hr sounds pretty good to me, now I have V-drives and this speed for me would be doing something with my 380.

So that being stated what is a swim grid and I am guessing the 28-30 m/hr is miles per hour, MPH. Now I know with my boat I have ben told one encounter performance issues or a speed reduction with too large of a dinghy mounted on the swim platform. What is your load for your question you posted,, water, fuel, passengers, provisions, tools etc.? I have never researched this, but I would say lets start with the fuel burn chart from Bayliner and then go from there.

My wide open rpm's is around 4400 rpm,'s max and I do not care to do that but for a minute or two at that. I typically cruise at 3200-3400 rpm's.
 
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Our 280 is roughly the same size, at 3400-3600 we are at 20 knots and 16 gph. At 4000 rpm we are at 31 knots and 28 gph. I rarely push it to WOT.

I agree prop pitch and or gear ratio is off. Running prolonged at 4700 is pushing it the envelope even for the 496 HO 425HP version.

Henry


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OMG!!!! My deepest appologies,VERY big mistake!! I am NOT cruiseing at 4700 rpm,but 3700.I am sorry for the mistake. At WOT I top out at 4400 rpm,and 42 mph,which indicates a proper gear/prop match.
 
As for the load weight,all the gear...tools,cloths,water,dishes, fishing gear,food ect would be in the 2000 pound range with 3 passengers.The dingy is aprox.80 pounds.I have stripped the gear and taken her for a run,thinking this is the problem,but the best that I could do was 77 litres/hr,even with no canvas up. During the 2 test runs in which I got great mileage: 50-55 litres/hr I had all necessary gear onboard,except for food,water,cloths,and had only 1 passenger. I have already had a mercury tech take a look at this issue.He stated that I should be burning no more than 60 litres/hr. The boat is a 2858 bayliner sierra as I stated before,if I had never gotten such great economy before,not to mention unbelievable performance...she jumped out of the hole...for a big boat,i was surprised! i would just accept the fact that I burn a lot of fuel. Again sorry for the rpm mistake.
 
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