Re: Prop Advice
rndn, even though the engine is not "that old"..it is 12 yr old technology.
A 21 on that rig is a lot of prop, and regardless of 4500-5500, or 5000-6000, we've found it best for the engine, fuel economy and performance-over-all, to shoot for at least 5800 with a normal load, and 6000 with a normal load will not hurt anything. 5800 would give you possibly the better top-end and still keep you in a very strong hole-shot mode...better than you have now, and beings the engine will only pull the 21P at 5100, I don't think you will lose any significant speed.
I use this as an example at times....I have a friend with an 1800 fisherman Lund with a 115 looper. I tested some new MWC designs on this boat specifically for MWC...very in-depth data. We ran 3 different aluminum props from MWC in 17P and to prove a point to the owner of the boat, I bolted on a Turbo1 in a 15P....the T1 was (as one would expect) faster out of the hole, better mid-range and a surprising higher top-end speed at the same RPM as the fastest of the 3 17P aluminums....about 2.5mph faster.
We "could" go back and raise the engine to the third hole and maybe run a 17P T1 and really make it fly, but he liked the trolling speed and yet was able to increase speed when headed across the lake at the same rpm so he just flat-out bought the T1.
The test props were not for sale, but after the test-run of the T1, he didn't care about the aluminum anymore.
3/4" less diameter, yet 2" less pitch than the fastest 17P alum.....my point??? don't let anyone tell you the diameter "Must" change with the pitch to work properly. Blade design is more important than size or pitch.
Sorry for the long hoop-la, but if you want the most from your rig, let's talk about the brand and style of 21P you have now, and I'll bet we can point you in a direction to get you maybe a bit more than you thought you could get.
