I have a 2010 Lund 1725 Rebel XL Sport with a Merc 90hp 4 Stroke. Everything seems good, but I am only getting 5100rpm and 40mph at WOT. Shouldn’t I be seeing about 5900-6000 rpm? I have the stock 21″ prop and mounted in the second hole from the top.
Thanks
I may be wrong here. But if you’re hitting 40 mph with that motor your tach might be off.
You are definitely on the low end of the 5000-6000 rpm range. It seems that many boats coming out of the marinas are overpropped and running very low in the RPM ranges for their motors. There is a sweet spot for every motor and it is usually a hundred or two rpms above the rpms listed for peak horsepower. I would guess that to be 5700-5800rpms. Be aware that tachometers at the helm are notorious for being inaccurate and even hooked up incorrectly. Verify your rpms with another method to be certain you are getting accurate information. Right now you are close to top speed but the engine is working too hard to get there and is not reaching max hp in doing so. I would find a dealer (hopefully the one you purchased the boat from) who will let you try a variety of props (without having to buy each one first) in order to get the best possible performance out of your boat/motor. Check out other Mercury or Lund forums since someone else may have solved your problem with the same setup.
do you have GPS for MPH?
if you wan’t more RPM’s dropping to a 19″ pitch will result in an average 300 to 400 RPM increase at full-throttle going to a 17″ pitch will result in an average 700 to 800 RPM increase at full-throttle.
also check out the Stiletto SS prop in a 19″ pitch. on that motor in the 2nd hole you should hit around 5800 to 5900 RPM 
You’re slinging to much prop, 17 or 19″ pitch is what you looking for.
My guess is the 17″ pitch is youre best choice.
Above posts are good comments. The Tach should be calibrated first to make sure it is reading the rpm correctly. Lund has a PDF with specifications for props that have been tested with certain boats listed on their website. Here is the link:
http://www.lundboats.com/pdfs/Lund-Red-Book-2012.pdf
The general rule of thumb is 1 degree of pitch will equal about a 200 rpm change. That is when you are staying with the same design of props. If you start changing different prop designs the rpm could vary alot. Test the props before you buy, if you can. With the 4 strokes I always run the motors close to the highest rpm listed in their rpm range. Granted I test the boats when they are not full of gear and people. When you add the gear and people it can at times drop the rpms of the motor some, but I still like it at the top for the 4 strokes. The 2 strokes are a different story they have a much narrower peak horsepower rpm band. A couple of hundred rpms can lose some serious horsepower. 
Thanks for the info. The speed is taken off of my HDS5 and the rpm is from my Smartcraft monitor, so I believe these to be pretty accurate numbers to deal with.
Quote:
I have a 2010 Lund 1725 Rebel XL Sport with a Merc 90hp 4 Stroke. Everything seems good, but I am only getting 5100rpm and 40mph at WOT. Shouldn’t I be seeing about 5900-6000 rpm? I have the stock 21″ prop and mounted in the second hole from the top.
Thanks
When talking a stock prop, are you saying the factory aluminum prop? The rpms are too low, I would diffinately change the prop out to get the rpms up close to the 6000 rpm range. This could get you better speed and a better hole shot, plus better fuel economy. Plus the Merc reps have told me in the past that lugging the 4 strokes is not a good thing to do, they have always said to get the rpms up.
I would keep the motor in the second hole. If you are running a large diameter stainless that is made for more bow lift then you could get away with raising the motor up one hole, but if you do this with out the right prop you will tend to blow out in the corners unless you trim the motor down alot.
The prop is the original aluminum 3 blade that came with the package. I am thinking of going from the 21 to a 17 and give that a try.
Yes I would go down to that and see how it goes. Either way the 21 is just to much for it. Post your results when you get a chance to run it with the 17.
OK, finally have some results to share. Talked to Ricky at Brainerd Prop and he hooked me up with a Quicksilver Nemesis 4 blade 17″ pitch prop.
Wow, is all I can say.
Old prop 21″ 3 blade I was seeing 5100 rpm and just under 41 mph, and slow out of the hole.
17″ 4 blade prop now seeing 6000 rpm with 41.5 mph and unbelievable hole shot, and holds like glue when cornering.
Gotta say that I am very pleased with this new 4 blade Nemesis prop!
Awesome
Quote:
OK, finally have some results to share. Talked to Ricky at Brainerd Prop and he hooked me up with a Quicksilver Nemesis 4 blade 17″ pitch prop.
Wow, is all I can say.
Old prop 21″ 3 blade I was seeing 5100 rpm and just under 41 mph, and slow out of the hole.
17″ 4 blade prop now seeing 6000 rpm with 41.5 mph and unbelievable hole shot, and holds like glue when cornering.
Gotta say that I am very pleased with this new 4 blade Nemesis prop!
Awesome..congrats. Just another positive story to hear about Ricky. He sure is on top of his business.
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