3 blade or 4 blade?

[waterdog55]

1986 Boston Whaler 18' center console
​2005 Mercury Optimax 150, 1.87 gear ratio, mounted two holes up (third hole)
​WOT range is 5250-5750

​Currently operating a Stiletto Advantage SS prop, 4.75 series, 14 1/4 x 17 pitch (E800317)

​The following was taken on salt water, 3' swell @ 15 seconds, 5-10 knots wind, ran the tests in the ditch. All speeds taken from GPS.

Current performance:
​time to plane, 5 seconds
2500 RPM, 11.5 knots, full trim, not on plane
3000 RPM, 21.8 knots, +2 up from full trim
3500 RPM, 27.4 knots, +2
​4000 RPM, 30.4 knots, +1.5
4500 RPM, 33.8 knots, +1.5
5000 RPM, 37.3 knots, 1
​WOT 5200 RPM, 39.1 knots, +1.5

primary concern, would prefer to get the WOT up near the top end of the range.
​secondary, would like to improve hole shot, lower the minimum planning speed and better performance in rough seas.

​It was suggested by a well known prop shop that I try a 15 pitch 4 blade prop. They suggest I would get all I was looking for and increase the RPM by about 400 RPM's. My understanding of 4 blade props is that the performance would increase because you have more blade in the water, ie more torque but not gain any RPM's? I know if I simply go to a 15 pitch the RPM's would go up but may not get the performance on the lower end? Also suggested to me that I stick with Mercury props, not sure why, they sell many brands.

​I would like to hear prop suggestions, manufacturer, pitch, number of blades. Any other feedback?

 

[Stingrayaxe]

Ok different motor different boat but when I made a switch from 3 blades to 4 I dropped 2 inches in pitch. I got exactly what you are looking for. Hit the higher end of the rpm range. Way better hole shot. Stayed on plane at lower rpm. Better low speed handling. Only down side is I lost about 4 mph on the top end. Hope this helps.

 

[rallyart]

Just the change to 15" pitch will help the bottom end and get your RPM up. It is not likely to lose you any MPH, as the increase in RPM will put you back up in speed. 4Blade will work well for hole shot and control near planing speeds at that pitch.

 

[porscheguy]

Quicksilver Q3 (same as mercury Enertia). Get one in a 15 pitch. It has a 15? diameter which means you?ve got extra blade surface area without the drag of a 4 blade. You may pick up speed (despite dropping pitch) with a q3.

A 4 blade has more surface area which moves more water and generates thrust. The downside is that it also has more drag. If you run heavy and need stern lift, go for a 4 blade like the q4/rev4 but be warned that you may not increase your rpm which is something you want to do.

Why use mercury props? Their development budget is almost limitless compared to most other prop manufacturers. In addition, mercury operates a state of the art foundry. This allows them to buy raw materials and produce the alloys they will use in prop production. Remember the corvette zr1 from the late 80s/early 90s with the aluminum 32 valve dohc small block? Mercury made those engines for gm because mercury was better equipped to build engines like that than GM.

 

[Texasmark]

Ok different motor different boat but when I made a switch from 3 blades to 4 I dropped 2 inches in pitch. I got exactly what you are looking for. Hit the higher end of the rpm range. Way better hole shot. Stayed on plane at lower rpm. Better low speed handling. Only down side is I lost about 4 mph on the top end. Hope this helps.

Totally agree. This is good info Waterdog; might take it under advisement. Reasons why this worked as it did could be forthcoming if necessary.

 

[batman99]

I use 4 blade (2 pitch below factory build) on my bow rider boat = that mostly does tubing and/or slow speed cruising the shorelines. Have my 3 blade (as per factory build) as onboard spare - in case it's needed. This works great for me. Although, I hear some folks like using 3 blade (at 1 pitch lower than factory build) for long distance cruising (and less tubing conditions). Remember that many factories size their boat based on 1 x 150 lbs driver and no gear. Reality outing if often 2 x 200 lbs adults (averaged together) with their 2.1 kids + onboard gear. Thus, I find less pitch compared to factory build in best (for reality).

 

[waterdog55]

Thanks for the replies everyone. OK, sounds like a 15 pitch four blade should be good for what I want. In looking at the Rev4 they are 14 5/8 diameter. Does the diameter play into how it will perform? The prop I have now is a 14 1/4 diameter. Going to four blades increases the amount of prop in the water but the diameter also really pushes that up. Because of that should I expect less gain in RPM?

 

[porscheguy]

I think you should look at a Q3/enertia. If you insist on the rev4 save some money and buy a quicksilver q4. They are the same prop.

The extra blade, like the extra diameter increases surface area. Heavy boats require more blade surface area because they need more thrust to get moving. The downside to the increased surface area is drag. On a heavy boat, the loss in performance from increased prop surface area is less than the performance losses you would suffer due to not making sufficient thrust.

I?ve got a Q4/rev4. My boat is less than 20?. I can run the q4 up to redline just like I can a mirage plus of the same pitch. The mirage is a faster prop. There?s really no benefit I get from the q4. If you had a 24?+ length I?d tell you to go for it.

The Quicksilver q3 is a mercury enertia. Cost is the same as a q4. With a 15? diameter, the q3 has a bit more surface area than what you?ve got, but not so much like a rev4. The enertia is also made from mercury?s In house X7 stainless alloy. The blades are thinner than most and stronger.

I?ll admit the rev4 looks badass, but I?ve got experience with it, and will tell you straight up, look at a q3 instead.

 

[waterdog55]

porscheguy, so if I understand you correctly, going with the enertia, dropping the pitch gives me some performance enhancement as well as the RPM change I want. Because of the larger diameter of that prop I will also gain more torque as a result? If I go to the rev4 I may not gain too much RPM's because of the volume of blade increase due both from four blades and the larger diameter.

 

[Leardriver]

More blade surface equals more traction. Think of it as four wheel drive. A twin prop Bravo 3 drive on a bigger boat helps convert the power into forward thrust rather than beating the water to a froth like a blender when trying to get moving.
​The penalty for more blade surface is drag. That is why the top end is usually lower. The manufacturers put three blade props on for cost savings and bragging rights so that they can claim higher top end speeds.

 

[QBhoy]

Going from a 3 blade to a 4 blade with same pitch will always be a compromise on top end performance.
It all depends on what you are after.
If you are willing to give up conventional performance characteristics of a 3 blade and benefit from low end grip and perhaps occasionally more grip in turns (if you don’t know how to trim down)...then go for the 4 blade. They certainly have their place...but will never be as efficient as a good stainless 3 blade.

 

[dingbat]

Your slow time to plane and the need to trim down with speed suggests a lack of lift at the transom.

A set of tabs would probably give you more bang for your buck.

 

[82rude]

porscheguy posts are all blank ?Whats up with that?

 

[porscheguy]

I’m working on getting it fixed. Been busy with the holidays. Once I sit down with a laptop, I’ll fix it.

 

[82rude]

Oh , I thought it might of been the site,it does tend to do wonky things at times.

 

[Bsw273]

What would be a good 4 Blade SS prop,to go with a 2100 maxum Sr2 5.7 mercruiser with alpha one gen 2 w/1:47r gears. As,far as better handling,fuel efficiency, hole shot? Had a 3 blade SS vengeance 14 3/4 19p. Poor handling, no acceleration over rev at top end. Just can’t decide on pitch and O.D for a 4 blade stainless steel prop...

 

[jbcurt00]

What would be a good 4 Blade SS prop,to go with a 2100 maxum Sr2 5.7 mercruiser with alpha one gen 2 w/1:47r gears......

BSW start a topic about re-propping your Maxum and ask there.

asking here is considered a hijack