Mac x '2001 " Diabolo" with mercury 50 BF

[marsanden]

At the end of the season i received the '2001 i bought in France in July.
The engine is a Mercury 50 BF, with a 14x10 prop.
The boat is in a wery good shape , same the engine ( only 110 hours ).
The boat is equiped with a roller jib and the main sail.
I tested the boat in light wind : wery easy sailing with good speed ( 4,5 - 5 mph ).
Underpower with ballast full: 15 mph at 5300 rpm
With ballast empty and my family : 17,5 mph at 5300 rpm.
With boat empty: 18,5 mph at 5300 rpm.
The bottom is painted.

The only trouble i have is: i read on the engine istruction that it can run till 6000 rpm.
Mine doesnt run over 5300.I cecked every trim position: always the same. no more than 5300 rpm.
i asked to the mercury dealer , he told me it depends on the boat shape.....i think this answer is not correct.

[Dimitri-2000X-Tampa]

Maybe your tach is broken (hitting a limit and stopping)? You should see a difference in RPM with the difference in top speed. I have the 14X10 on my 2000X and if I fill the ballast, and put 7 people in, then I can't get over about 13-14mph and the RPM would be about 5500 or so. With a very light load (just me), I can hit about 19mph but now the RPM is more like about 5900. With the family aboard but with empty ballast, I get about 17mph which is about 5750 RPM. The point is that the RPM varies proportionately with the top speed and all your examples show a fixed RPM regardless of speed.

[ChrisNorton]

I have almost the same setup as you. 99 x with 50hp BF with bottom paint. I only get about 5300-5500 RPM max under any circumstance (with ballast, without, 1 person, many. Speed changes obviously but top RPM doesn't. My top speeds are about the same for what you indicate. Chop and tides also impact my speeds.

With the boat on the trailer and a hose hooked up to it, I can hit 6000 rpm but that's the only time.

[Gemini]

I don't have the same set up, I have a 2005 M with a Suzuki 50HP 4 stroke EFI.

My speed varies with load, but my WOT is always 6400 RPMs. I thought the WOT RPM was due to the prop pitch and size. And that you want to be in the WOT range of RPMs recommended by the motor manufaturer?

[Dimitri-2000X-Tampa]

Well, I'm no prop expert (and I know we have some on this board), but it would seem that if you were always turning the exact same RPM and your speed was varying, that your prop could be slipping a bit. I would think the RPM would vary if the prop has a good firm hold on the water.