props

[gimruis]

I don't quite understand the pitch thing when it comes to props.

 

I currently have a factory aluminum 4 blade prop for my Mercury 75 hp 4-stroke outboard but I would like to at least consider a SS prop for better top end speed and performance.  I am open to a 3 blade version too but I tried one in the past and was greatly disappointed with it.  I get a good hole shot and handling with my current 4 blade aluminum prop but I'd like to get more speed.

 

Maybe someone can explain the pitch thing here.  I don't want to just go buy another prop, put it on, and get worse performance like I did last time.

[DaubsNU1]

Great question @gimruis!  ** Following **

 

Factory aluminum 4 blade on my boat has a very good hole shot, and tops out between 38-39 MPH.

[Alex from GA]

A 19” pitch prop will push your boat 19” through the water with no slip.  If you want top speed select a prop that will turn the maximum rpm of your engine at WOT.  The best thing is to consult a good prop shop for the right one for your boat.  The pitch isn’t the only thing that will make your boat perform at its best.

[gimruis]

11 minutes ago, Alex from GA said:

A 19” pitch prop will push your boat 19” through the water with no slip.  If you want top speed select a prop that will turn the maximum rpm of your engine at WOT.  The best thing is to consult a good prop shop for the right one for your boat.  The pitch isn’t the only thing that will make your boat perform at its best.

 

I kind of got burned the last time I did this exact thing at the prop shop.  The tech was hell bent on selling me a 3 blade prop that would vastly outperform my current 4 blade version.  Unfortunately, it back fired.  Not only did it go slower, it took me forever to get on plane.  When I went back there with this information to the tech, he was flabbergasted.  I told him it was a massive failure in some choice words.

 

I haven't been back there since and have simply continued to use the 4 blade version that came with the boat/motor from the factory.

[Alex from GA]

Find another shop.  The weight of your boat fully loaded and where the weight is located are also factors in determining the right prop.  I have a stainless prop on my tin boat with a 50 and got very little speed increase and my hole shot is good.  You have to have a tach and know your maximum rpm to properly dial in a prop.

[A-Jay]

51 minutes ago, gimruis said:

I don't quite understand the pitch thing when it comes to props.

 

I currently have a factory aluminum 4 blade prop for my Mercury 75 hp 4-stroke outboard but I would like to at least consider a SS prop for better top end speed and performance.  I am open to a 3 blade version too but I tried one in the past and was greatly disappointed with it.  I get a good hole shot and handling with my current 4 blade aluminum prop but I'd like to get more speed.

 

Maybe someone can explain the pitch thing here.  I don't want to just go buy another prop, put it on, and get worse performance like I did last time.

What is the Max HP rating for your rig ?

A-Jay

 

[gimruis]

Its a 75 max HP rating, which is what I have on it.

 

I am unsure what the RPM is WOT.  I will check that next time.  The boat is 17 feet, 8 inches long.

 

I'm not in any tournaments and I don't need a speed demon.  I would just like to get a little more speed out of this thing.

[Way2slow]

Actually, props are very complicated and not many average boat owners really understand them.  

In the simple explanation, changing pitch is like changing the gear ratio so it's a tradeoff for what you want. 

As you go down in pitch, the boat launches harder and gets on plane easier but the RPM increases, and at WOT can be too small and to overrev the engine.  

As you go up in pitch, the boat launches slower and may run a little faster, but does not turn as many RPMs, so you generally want to prop one so with your normal load, live well full, gas in tank passenger and gear the motor turns within a couple hundred RPM of the manufactures max rating.

Three blade VS four blade.  Because of the drag created by extra blade surface, the four blade props tend to be a couple MPH slower than the same pitch in a three blade.   For heaver boats and underpowered boats, the four blade props tend to give a better hole shot because of that extra surface reduces slip.  

Because of the thinner blades and stranger material, Stainless props usually outperform aluminum props because the thinner blades cut the water better and the stronger metal does not flex back as much, creating a lot less slip.  

Then you get into the technical aspects of rake, blade shape and cupping.  I'm not goig to begin to try explaining all that but will just say you have to pick the prop that best matches what you hull design likes.  

This is why you DO NOT try saving a dollar and order props online.  Find a reputable dealer that has a try before you buy policy and knows props.  As long as you don't damage the prop in any way and just make a short test run, the let you try one, as long as you DO plan to buy one from him when you get the best match.  

In general, most people opt for the three-blade aluminum in a pitch that satisfies their needs because that's the cheapest way you can go.  A properly matched SS prop can be expensive.  

If you have a larger faster bass boat, and want max performance you order a custom tuned prop.  I never ran stock props on mine.  

 

One thing I forgot to mention, don't think you can just go to a higher pitch prop to get more speed, it don't work that way.  Once you start loading the motor more and dropping the RPM and it comes out of it's peak power band, you can actually loose a lot of speed versus what a smaller pitch prop was giving you.  Also, the cupping of the blades have a lot to do with the RPM.  

 

[A-Jay]

9 minutes ago, gimruis said:

Its a 75 max HP rating, which is what I have on it.

 

I am unsure what the RPM is WOT.  I will check that next time.  The boat is 17 feet, 8 inches long.

 

I'm not in any tournaments and I don't need a speed demon.  I would just like to get a little more speed out of this thing.

Got it, Thanks.

Well, you are about to head down a rabbit hole that has many twists & turns.

@Way2slow knows this deal far better than I.

However my limited experience is that the Reasons for 4 Blades:

The increased blade area afforded by the addition of the fourth blade can provide increased water displacement capability, lift, and grip, as compared to a 3-blade propeller.

In terms of actual boat performance, these characteristics can combine to enhance:

Handling

Hole Shot

Low-speed planing ability

Cruise efficiency

Fuel efficiency

Load-carrying capability

Performance in big or following seas

Ventilation/cavitation resistance

Motor-elevation capability

In short, a 4-blade propeller can improve all those characteristics vs a 3 blade

that make for practical, all-around boat performance.

 

This is what you have now, minus more speed. 

 

At 75 hp, the easiest way to get more speed IMO, is to lighten your load.

The lighter your rig is the more speed you can get with what you have.

But it's going to be a SMALL improvement.  It's not like you're going to get 10 knots out of whatever you decide to do.

HP is king and at 75 hp, you can only do so much. 

Going to a 3 Blade will probably reduce Most ALL of the handling characteristics listed above,

but MIGHT get you a little more speed.  But at the expense of what ?

Which is what I think you've already experienced at least once.

IMO, stand pat on the prop.

Good Luck.

A-Jay

 

 

[Way2slow]

Let me also ask, how bad do you want a little more speed.  More speed is usually gained with a little different weight distribution, engine height, engine setback and a prop properly matched to the hull.  

One your boat, you might gain a few more MPH, perfecting the setup, but you can easily spend $1,000 doing it.  It's not like you have a hydro-rocket to start with some more speed is not going to come cheaply.

[Tennessee Boy]

As a fellow member of the Under 100 HP Ranger Aluminum Club,  be careful what you ask for.  In my experience nothing is worse than a slow hole shot.  
 

My boat does 40 MPH at top speed.  A 10% increase would take me to 44 MPH.    If I was in a hurry I would buy an Allison.😏

[gimruis]

22 minutes ago, Way2slow said:

Let me also ask, how bad do you want a little more speed.  More speed is usually gained with a little different weight distribution, engine height, engine setback and a prop properly matched to the hull.  

One your boat, you might gain a few more MPH, perfecting the setup, but you can easily spend $1,000 doing it.  It's not like you have a hydro-rocket to start with some more speed is not going to come cheaply.

How bad or desperate do I want more speed? Not that much to be honest. I’ve read on other forums that the boat and HP outboard I have are getting up to 40 mph with theirs. I get about 32 with mine but I mostly cruise along at about 26-27. A jump to 40 seems fairly substantial.

 

Rabbit hole is accurate. Now my brain is over loaded.

[A-Jay]

18 minutes ago, gimruis said:

 I’ve read on other forums that the boat and HP outboard I have are getting up to 40 mph with theirs. I get about 32 with mine but I mostly cruise along at about 26-27. A jump to 40 seems fairly substantial.

Everyone's rig is ALWAYS faster on the interwebs . . .

A-Jay

[Alex from GA]

Remove the Talon and try it.  Do you have lead acid or lithium batteries for the trolling motor?

[Born 2 fish]

To be honest I would just keep the aluminum prop you have on it. A stainless prop is going to be expensive for the little bit of speed plus if you hit something with the aluminum prop it’s more likely to just break the prop and not damage the prop shaft. Like others have said take some weight out. Or rearrange the weight you have.  

[Way2slow]

I live by the old saying "Believe half what you see and nothing of what you hear".  I'm not saying a bass fisherman would lie but a whole lot of them seem to stretch the truth about the fish they caught and performance of their boat, A LOT!

 

I will also say, 32mph for that boat does seem a little slow, but I think 40 is a bit of an exaggeration with a fishing load in it. 

So here's some things you might want to check.  

First get an accurate RPM reading with the boat at WOT and trimmed to perfection.

Find the gear ratio for you lower unit and the size/pitch prop you have now.  Also inspect the prop for dings and bent blades.  It's very easy to roll the leading edge and not notice it.  Also note, the RPM should be close to the recommended max for that motor, or it may be over propped and damaged.

Find a good online prop slip calculator and fill in the blanks and get the percentage prop slip.  An average setup should be 11 to 13%.  Below that is high-performance, go-fast boats. much above that and you start getting into barges, but I have seen some as high as 18%, before working on them. 

Now, if the slippage is ok, and the rpm is up where it's supposed to be, then I would start looking at the motor's performance because it's highly likely it's down some.  

The first thing I would look at then would be to make sure the throttle is fully opening.  I have seen tons of low performance problems being as simple as the throttle cable needing adjusting.

This is as far as I can take you on checking your motor, I know diddly squat about your motor, so other than doing a compression test, I would not know anything about where you need to go from there.

 

 

[Woody B]

How is your boat balanced?   When wide open, or close to wide open trimmed up where does the spray come off the sides?   

 

I got a "fast one".   After break in with everything just as it came from Tracker I got a max gps speed of 37.9 mph.   (Tracker estimates top speed to be 32-35 mph)

 

I added storage, tackle, changed trolling motors, went to a bigger gas tank and went to lithium batteries.   After than I could "maybe" get 36 mph in excellent conditions.  Also, it was almost a different boat when the tank was full.   Basically I had added weight to the front, and removed weight from the rear.   When on plane, trimmed up the spray off the sides came from a little in front of my feet.   It also rode a little bit lower on the starboard side.  I usually fish alone so my weight as well as the console created an imbalance.   During all of this I ended up with a used SS prop, the same pitch as my original aluminum one.   I "think" the prop gave me a little better hole shot but that's about it.   My boat rode rough.  When the water was rough the ride was also wet.  As an experiment with my electronics I installed a Group 27 lead acid battery in the port side rear to separate my cranking and electronics batteries.  It didn't have any effect on my electronics, but it turned my boat into a different boat.   When planed and trimmed the spray is even with the back to my seat.   It's also balanced better side to side.   The ride is smoother in rough water, and I rarely get wet now.   Top speed?  I recorded 41.1 mph but it was 30 degrees with a tail wind.  That was at 6100 rpm.   In normal, and calm weather I can get 38 anytime, occasionally hitting 39.   (@ 5900 rpm).   I cruise around 30 mph just under 5000 rpm now.   I no longer have the battery connected, but won't remove it.  It turned my tub into a different boat.   I've since added 20 pounds under the passenger seat.  The side to side balance is good when I'm alone.  When someone is with me I either swap sides with the 20 pounds, or take it out.  

 

IIRC you have your batteries, or at least some of them toward the bow.   See where the spray comes from next time out.  I suspect you're riding with the bow low, basically plowing, instead of getting on top of the water.  

 

I've never had a 4 blade prop, or even a fast boat.   My last boat was 20 horsepower tiller steer.   

 

 

I need to add.  Keith mentioned motor performance.  A while back I was cruising around 30 mph.  A guy I see at the landing with the same model boat I have passed me and was waving like "come on".  I throttled down, trimmed up and passed him back.   When we got to the landing he was amazed.  He had changed the ECM and removed an intake restrictor on his 50 horsepower to make it a 60 but I was still able to pass him.  We popped his cowl off and inspected his throttle.  He wasn't getting anywhere near full throttle.   The next week he passed me, and drove away.   

 

Added screen shot from Navionics app to show my real top speed.  (I thought it was 41.1, it was 41.3)  If lake conditions permit I'll make a speed run for a few miles this weekend.  Top speed will probably be low to mid 38 range with normal weather.  

 

[Susky River Rat]

What’s a prop?

[gimruis]

Lots of good info here. Especially from @Way2slow and @Woody B.

 

I have brand new AGM size 27 deep cycle batteries (2) and one lead acid cranking/starting battery. What I might do is just try a 4 blade SS version that’s exactly the same as my current aluminum one. I think you guys talked me out of trying a 3 blade version. The handling and hole shot I get now is pretty optimum. I generally don’t fish in super rough water but I was on a decent chop last weekend on my way out and the boat performed well.

 

In the meantime, I will also check my WOT rpm and the pitch of my current prop.

[Bird]

I'd say boat weight is the biggest player here.

I have a 4 blade aluminum on a 17.5 aluminum boat " 60 HP " that consistently does 38 mph at 6100 rpms.

The lakes here aren't very large so speed isn't a priority.

I prefer to be on plane quickly and cruising at lower Rpms.

 

[Way2slow]

I'm not sure in your situation I would opt for the four blade over a three-blade prop.  On most bass boat hulls, I prefer a higher rake three blade SS prop.  There are high rake four blade props that perform pretty well and some even like something like the High Five, but if the setup is right, I generally get better all-around performance from a high rake three blade.  However, the trick to that is being able to get bow lift.  I have to admit though, I have little experience with aluminum hulls.  Glass boats with riser hulls are a totally different animal than what a tin boat has.  Aluminum hulls generally have a lot of flex so you get a lot of cupping affect that creates a lot more drag and they tend to run very wet in the first place.  That makes them very sensitive to weight and weight distribution so it's very easy to overload the hull with a Large TM on the bow, several heavy batteries and then if you have other accessories like Power Poles etc, it becomes extremely difficult to get the bow lift you need for good speed.  A good setup is going to have the water spray coming out behind the diver's seat.  If you have it coming out in front of the console, you are running too bow heavy, or just too heavy all together.  If that is the case, you might want to take as much weight out of the boat as you can.  Just the cranking battery, empty live well and even the TM off the bow if that's not a major challenge.  If this does not put the spray behind the drives seat, you have a significant setup problem to work out, or totally the wrong prop. 

A prop with more rake will help lift the bow, and deep cup will help lift the stern, helping lift the boat out of the water.  Just remember, watch the tach, because as the speed increases so will the rpm and you don't want to get more than 100-200 more than the max rated rpm .

Once you get that worked out, and have good lift, start putting it back together and trying it with each item added.  they you can see what and where the problem is.

[airshot]

4 hours ago, Way2slow said:

Actually, props are very complicated and not many average boat owners really understand them.  

In the simple explanation, changing pitch is like changing the gear ratio so it's a tradeoff for what you want. 

As you go down in pitch, the boat launches harder and gets on plane easier but the RPM increases, and at WOT can be too small and to overrev the engine.  

As you go up in pitch, the boat launches slower and may run a little faster, but does not turn as many RPMs, so you generally want to prop one so with your normal load, live well full, gas in tank passenger and gear the motor turns within a couple hundred RPM of the manufactures max rating.

Three blade VS four blade.  Because of the drag created by extra blade surface, the four blade props tend to be a couple MPH slower than the same pitch in a three blade.   For heaver boats and underpowered boats, the four blade props tend to give a better hole shot because of that extra surface reduces slip.  

Because of the thinner blades and stranger material, Stainless props usually outperform aluminum props because the thinner blades cut the water better and the stronger metal does not flex back as much, creating a lot less slip.  

Then you get into the technical aspects of rake, blade shape and cupping.  I'm not goig to begin to try explaining all that but will just say you have to pick the prop that best matches what you hull design likes.  

This is why you DO NOT try saving a dollar and order props online.  Find a reputable dealer that has a try before you buy policy and knows props.  As long as you don't damage the prop in any way and just make a short test run, the let you try one, as long as you DO plan to buy one from him when you get the best match.  

In general, most people opt for the three-blade aluminum in a pitch that satisfies their needs because that's the cheapest way you can go.  A properly matched SS prop can be expensive.  

If you have a larger faster bass boat, and want max performance you order a custom tuned prop.  I never ran stock props on mine.  

 

One thing I forgot to mention, don't think you can just go to a higher pitch prop to get more speed, it don't work that way.  Once you start loading the motor more and dropping the RPM and it comes out of it's peak power band, you can actually loose a lot of speed versus what a smaller pitch prop was giving you.  Also, the cupping of the blades have a lot to do with the RPM.  

 

Well stated !!

[Way2slow]

Well, props have always puzzled me.  A person will fork down thousands of dollars on a new boat and motor.  The ONLY thing that's applying that motors power to the water and how it's going to react with the hull is the prop.  Then because a good prop can be several hundreds of dollars, they buy a cheap**s aluminum prop.  

[WRB]

Mercury has a prop selection chart for boat type.

SST Merc props have venting whereas aluminum doesn’t.

What boat do you?

Tom

[K1500]

If you can’t hit redline when at WOT with your current prop, going up pitch won’t help. I have two props for my 20’ aluminum bay boat with a 115 pro XS ct, a 4 blade 17 pitch and the same prop in a 19 pitch.
 

The 19 pitch is what I use in the spring and fall for fishing. It takes a bit longer to get on plane but has a higher top speed and (more importantly) a lower rpm at the speed I want to cruise. This is with 1-3 people on the boat. As I add people/weight it is a noticeable difference in getting on plane. 
 

I put the 17 pitch on in the summer, when I am pulling a tube and tend to have more passengers in the boat. I’ve never even tried to pull the tube with the 19 pitch. 

Aluminum props can help save your lower if you do something boneheaded like strike a submerged rock jetty on plane. I’ve seen it save a boat lower once.