3-blade vs 4-blade

[Nfowler]

So, I have a 23’ Rinker Cuddy. 5.7, Alpha One. Currently I have a 19p 3-blade aluminum and a 20p 3-blade stainless. I like the performance of the 19, however I would like to improve my boats ability to hold speed and maybe plane out at a lower speed. That being said I was thinking of switching to a 4-blade prop I’m just unsure of what pitch to go with. I’ve been told to pitch up 2” and I’ve been told to go down “ 1” or more”. Which one is right?? Help, I hate when I trust both sources and the answers are totally opposite.

 

[alldodge]

Have the same boat with a 7.4 B1, and have talked to owners of the same boat with 5.7 and B3 drives.

Changing to a 4 blade will create more load and that is the last thing needed. If you go to 4 blade you need to lower pitch by 2 inches to equal the 19 (17 pitch). Going up in pitch is bad news because the boat will have even more trouble getting up.

The 4 blade will reduce slip, but also takes more power to turn, and you don't need anything else taking power. You really need more motor, but that is another topic

 

[Sea Rider]

What's the min-max wot rpm range factory stated for that motor ? Make a wot test on flat, calm water cond and report max wot rpm achieved to know what to improve with a prop.

Happy Boating

 

[Nfowler]

Yeah, more motor would be nice, but I may as well get a new boat for that kind of cost. Even a 383 stroker kit would be more than I want to spend (counting my own labor).. thanks for the input!

 

[jimmbo]

If you want the boat to plane quicker and stay on plane at lower speeds, I suggest you add Hydraulic Trim Tabs.

 

[Scott Danforth]

if you go up in blades, you need to go down in pitch

trim tabs help stay on plane at lower speeds.

 

[fishrdan]

It's recommended to drop 1" of pitch going from a 3-blade to a 4-blade prop pf the same material.

The 4 blade will reduce slip, but also takes more power to turn, and you don't need anything else taking power.

I had the opposite experience on my 18'er with a 140HP Mercruiser, which is no power house. I was running a 19P 3-blade MW aluminum prop and swapped for a 18P 4-blade Alpha4 prop. Everything about the boat's performance changed for the better, except top end speed where I lost 1-2 MPH. The boat planes in 3 seconds, lifts the stern to help get out of the hole, holds plane at a lower speed. Mercury no longer makes the Alpha4, with their Spitfire prop being it's replacement.

I also use a Michigan Wheel 16P 4-blade for heavy loads or power sports. I hate that prop as it doesn't lift the stern and it brings the bow high climbing on plane.

Of course this is an apples to oranges comparison of my 18'er to a 23'er.

 

[QBhoy]

As said. Normally, if your set up is spot on with the 3 blade and want to change to a 4 blade, ideally you go down an inch, if possible. The main reason for which is that generally the 4 blade has a much larger diameter to swing. Especially if you refer to a rev 4 or something. Some really struggle to turn these things.
Personally I much prefer to get the right 3 blade. So much more efficient and better too end. You will lose top end performance going from 3 to 4 generally.
If you not bothered about efficiency and top end. Go to a hi 5 prop of the same pitch as your 3 blade (all being well with rpm etc I’m the first place). They defo sit on the plane at a slower speed and will accelerate better than the equivalent 3 blade. Tried and tested here.

 

[Faztbullet]

You be happier with tabs.....

 

[Sea Rider]

How can someone blindly recommend to go per a less pitch 4 blade prop if owner doesn't know which rpm his motor is revving at wot with current 19 & 20 3 blade props. Knowing which is the min-max factory rpm range of his motor along current load on the boat when tested will be good to know when going for a prop maximization from current ones. That's if wot rpm and load does not matter at all and were excluded out of the water party..

Happy Boating..

 

[porscheguy]

I concur with the statement how can you know how much you need to reduce pitch if you don’t know your current rpm. i can hit redline in my boat with a cupped mirage+ 21p, a rev4 21p, and an enertia 22p. Of these, the mirage+ is my prop of choice. All of the stainless, high performance props produce some lift. Aluminum props will provide propulsion, but don’t expect much more out of them.

A few people have suggested hydraulic trim tabs and I’ll add my vote to that as well. They’ll provide the benefits you’re looking for way more than any prop.

 

[alldodge]

Your all correct, but if we make an assumption (I know assume, makes a something out of U and ME) that the owner knows his boat (max rpm, planing rpm, etc) and just was looking for the answer to the question

 

[Nfowler]

It’s really not a matter of finding the optimum prop for my boat. I have that. I bought this boat from a former formula boat racer Lynn Simburger. The stainless prop is exactly what I need for maximizing wot operation. My max rpm is 4200-4600, the 19 turns 4600 and the 20 hits around 4400, But that isn’t relevant to my question. I was looking for input on the idea of switching to a 4-blade in order to hold cruising speed better like 20-25mph. That’s all, I rarely run wide open

 

[fishrdan]

Are you looking to buy an aluminum or SS 4-blade prop?

 

[Nfowler]

I go back and forth, but I would like to find a stainless 4-blade prop that will give me that improved grip at that lower speed.

 

[dingbat]

I was looking for input on the idea of switching to a 4-blade in order to hold cruising speed better like 20-25mph. That’s all, I rarely run wide open

You might want to try a Merc Enertia prop. Pretty wild looking prop with tons of lift.

I ran a 4 blade for a number of years. Good improvement in hole shot and didn’t break loose near as much in the slop as the aluminum 3 blade it replaced.

At the recomendation of a friend I tried the Enertia 3 blade. A day and night transition. It’s quicker out of the hole. My top end speed increased by 2 knots and my fuel consumption at cruise (27 kts.) decreased by 10%

The downside....they are not cheap

They now make an Enertia Eco geared towards cruise mileage.

 

[porscheguy]

Mercury stainless 4 blade props are limited to the rev4 and the trophy plus. There’s such high demand at this point mercury isn’t even making Quicksilver variants. So you’re looking at between $600-$700 through discount retailers and $700-$800 through most local dealers.

At that price point, for what you want to do, you could put on a set of Bennett m120 hydraulic trim tabs. If you’re handy with tools, you could get them installed in an afternoon. They’ll provide more lift and much lower planing speeds than any 4 blade prop.

 

[alldodge]

I also think tabs would help very much, but as a current owner of a 232, installing tabs would not gain much benefit IMO. The reason being is there is no room to place them where they would be needed close to the outside. Installing them close to the drive would bring its own problems and don't think would work either.

Pic of a 232, not mine

Edit: I do have the Stingray dole fin on mine which allows for slower planning speed, and I can still hit 60mph. Would probably get a tad more without it.

 

[QBhoy]

Hi

hopefully the previous comments about “blindly recommending” don’t refer to my post, haha. I’ve clearly stated that you should only go down in pitch in relevance to the current prop set up being ideal.
Probably not aimed at me...but just in case. My point still stands...should the current 3 blade prop see ideal results in terms of being within the rev range etc...generally you’d need to go down an inch going to a 4 blade...to see similar rpm data. Speaking from experience...so far from blindly recommending.
Happy boating.

 

[Sea Rider]

QBoy, was just a blind shot to no one in particular. The OP's starting post did not provide the max wot rpm achieved with both props. To play safely with proips, pitches, number of blade must start with that data along load, number of passengers and then go from there maximizing a prop.

Happy Boating