Reality is that you purchased a Nitro that has been factory rigged with a engine that meets the bare minimum HP needed to adequately push the boat. That very same engine is usually over propped and occasionally incorrectly propped. Advertised speeds, fuel mileage, acceleration, etc. are usually achieved under ideal conditions, lite chop on water, no gear, minimal fuel, and a driver that weighs the equivalent of a equestrian jockey.
Lets face it, few fisherman want to accept that they may be substantially overweight, carry way to much tackle and gear in the boat, as well as insisting on keeping the fuel tank topped off. Lets also call out the guys that flood their livewells seconds from the launch ramp. And if you just got the boat, you definitely don't want to hear that the Nitro hulls themselves are inherently slow and feel like they drag through the water.
Note: Nitro hulls seem to have a 'speed' threshold that needs to be met before it will get completely on pad. If you don't surpass that threshold, the hull drag will prevent the vessel from truly getting on pad and reaching the its true top speed. Sadly many Nitro's I have seen and read about are factory rigged in such a manner that often puts them 2 or 3 MPH short of hitting that threshold.
Below is some self help information that you can perform yourself. Its true; in just a few simple steps you can gather enough factual information on your own, info that you will get very close to the actual source of the problem.
Verify a problem actually exists: This will also aid in determining which general area your boat is deficient in, you will want to start your diagnosis with some factual info. Look at the engine tag and what the max RPM is for your engine. After you have done that, take the boat with a tournament load to the water, get it on pad and document what speed on the ground (SOG) your GPS indicates and document the RPM it is currently operating at under full throttle.
Note: if during your water test you observe smoke or hear strange noises such as warning alarms, knocking or ignition misfires, immediately take your boat to a good outboard mechanic.
Lets say your boat is achieving the recommended RPM range: If your complaint was a poor hole shot and not top end related, there are a few low cost things you can try. Most modern Merc props utilize PVS® (Performance Vent System).
When you punch the throttle they essentially vent exhaust gases around the prop blades, causing prop slippage from a standstill or low speed launch, the slippage allows the motor to rev slightly quicker thus improving the holeshot. However they have zero effect on the boats mid and upper range performance. You can experiment with different size plugs which are readily available online
Re-evaluate the weight you carry and how its distributed throughout the boat. Do you really need to haul around 50 bags of Senkos and all of the tackle you have ever purchased? Probably not, so consider packing just the quantity items you need for the duration of that particular trip or a putting together a seasonal bag of gear.
Don't flood your livewell until you actually have fish to put in it. A US liquid gallon of water weighs about 8.34 pounds, with some livewells capacity ranging between 36 and 40 gallons, the additional weight can be staggering.
Do you really need to drive around with 40 to 50 gallons of fuel? Weighing 6.3 pounds a gallon, a full tank of gasoline can further add to your hull drag. I usually don't burn more than 6-10 gallons in a tourney, so I am more than comfortable running with half a tank.
Put your heavier items/baits like soft plastics in the stern compartments. Bow forward weight will momentarily aid you in getting on pad quicker, but that same weight will also kill your top end performance once you are actually on pad.
Jack plates. Nitro's have a setback transom per se, which is part of their rapid planning system. The idea was to put the prop farther back from the pad via moving the pad forward of the transom plate and theoretically placing the prop into less turbulent water, thus allowing the blades better grip on the water. Jack plates move the engine even farther back from the pad, as well as allow for lifting and lowering the motor. Some jack plates even offer tilt /trim.
Jack plates, according to most forum posters, offer a few MPH increase, as well as allowing the driver to make on demand adjustments to engine height. But can the factory installed jack plate cause a severe decrease in performance? Under most circumstance its doubtful that the jack plate is at fault.
You may have ran across chatter pertaining to prop to pad (P2P) distance. Unless you or a prior owner have been screwing around with the factory engine height that the P2P was originally set to, there is probably no reason to even measure it. My Nitro Z7 boat has a factory measurement of 4" prop to pad (engine is set to the middle mounting holes).
Also consider that the boat may be giving you all it has to offer, at least as it is currently rigged/loaded. Try the same water test with only half a tank of fuel, empty livewells and just yourself. Its possible that you may simply be out of horsepower for your load/application.
That's all dandy, but your main concern is only improving your hole shot: Ok you have concluded that you don't care if your top end suffers and only want a better hole shot without addressing any of the issues above. That brings us to a discussion on 4 blade props for bass boats. The bottom line, according to the guys at Mercury Racing, is that you can count on the boat having a lower SOG (because 4 blades will drag more than 3), but stability and hole shot will be noticeably improved.
4 blade props are also narrower in diameter than the 3 blade props, so you are going to have to experiment with pitches, mainly because you will still need more horsepower to turn a 4 blade at the same rpm you were turning with a 3 blade of the same pitch. I removed my 23 pitch 3 blade and personally tried a 4 blade with a 21 pitch on my Nitro Z7 and it provided a solid hole shot nor did it blow out making sharp turns under power. On the downside, with so much emphasis on lifting the stern, it was not able to offer much in the line of bow lift, the boat ran 3 MPH slower. Additionally my full throttle rpm dropped an additional 150 RPM when compared to my 23 pitch 3 blade coupled to a Merc 150 4S
Your boat fell considerably short of the recommended RPMs, oh the horror: As a talking point, lets say your engine is rated for 5800 RPM yet it only runs at 5250 with a 23 pitch prop at full throttle, where do you start? This is where your focus shifts almost exclusively to the propeller. You want the engine running close to the max RPM. Generally each inch in propeller pitch changes the RPM by about 200 RPM, so in this case you subtract 5250 from 5800 which leaves you with a 550 RPM difference.
So the course of correction in this case would be for you to raise the RPM by going down 2" to a 21 pitch prop, I would recommend staying with the same make / model / style prop when you make the change. Of course going down to much in pitch will cause you to consistently activate the rev limiter, that should be avoided.
I had a personal experience that was very similar to what was described above. In my case, my Nitro's RPM advanced to 5750 and SOG went from 42 to 54 with a just a prop change! The hole shot was also noticeably better, even with a full tourney load.
Tools: When it comes to diagnosing performance issues in a boat, you really don't have a lot of tools at your disposal. Below are a couple personal recomendations that could possibly help you.
Mercury Prop Selector This is a good tool for determining if your boat even has the recommended prop. Believe it or not I have seen some Rangers specked out with 4 blade props that are recommended for pontoon boats. Don't take Mercury's prop recommendation as gospel, they are factoring their recommendations on ideal conditions with ideal boats. Every make of boat / load is different so expect some trial and error.
Prop Slip Calculator This calculator is pretty straight forward, enter all of the data for everything except for the Propeller Slip field, then click the Calculate button under the Propeller Slip field. The consensus is that anything under 14 is acceptable. You will have to crunch numbers and do some hypothetical math to figure out how to re-prop your boat based on prop slip data. You can also call Mercury Racing for their opinion.
Propeller / Speed Calculator This will give you a good idea of what SOG you can expect from your configuration, as well as reaffirming the accuracy of your acquired data, as well as your GPS SOG and Water speedo accuracy.
Reynolds Racing Marine They have a propeller demo program that's worth its weight in gold.
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