Prop Pitch vs. Wake Size/Shape

I've heard that when switching to a different pitch prop, it's possible for the size and shape of the wake to change. Has anybody experienced this? If so, tell us about it.

I do not believe this to be true...

dave,

i heard it was true.... i will be switching out my prop this week and will let you know (acme 1234 replacing 644)

I would think that pitch would directly affect the wake - I do know that by trimming the motor, you can dramatically change the wake. When my friends added a bladder and trimmed up the motor on their boat, you coulda surfed behind it with the wake it created!

I think that changing the pitch f the prop will have some effect but not a hug amount. It makes a big difference on outboards but not sure how much change on direct or v-drives. I would think trimming it out would have more of an effect.

There MAY be a subtle change, but nothing dramatic. In most inboards, the running attitude is fixed by the hull and weight distribution. The prop, provides the propulsion. If you make a dramatic difference in the prop, dramatically dropping pitch, the boat will get on plane much easier and hold speed much better. This makes it so that the boat does not change attack angle when a rider cuts hard. During that time, the wake will be constant and firmer. Slowing down the boat, depending upon timing, will make the wake feel soft. This is more from boat speed than wake dynamics, but it can be felt. The same can be said about firmer PP settings, if you have the motor and prop to hold it.

If you are in the table (prop wash, between the wakes) you will notice a difference in the firmness of the prop wash from prop to prop. Big deal for trick skiers and barefooters, but not for us.

Prop selection should be based upon how you want the boat to perform from a speed and speed holding perspective. The effect on the wake is minimal and the percieved feel is more a boat speed issue than a wake size or wake shape issue.

I sell Acme an OJ props and have tested various props in many conditions. These are observations of my customers and my observations. This is unscientific. We would have to perform a double blind experiment with several riders and several hull/prop configurations to be exact. I am willing, any funding?

Karl is correct. It wont change anything but effort. IMO, you need to look at everything you do with your boat and determine which prop will be best for you. If all you do is wakeboard, and ride close to where you put in, getting the lower pitch will be easier on the engine, and more powerful for wakeboarding. However, if you usually put in, and have to haul a$$ across the lake to get to your spot, you may want to reconsider changing to a lower pitch as you will wrap out at 30mph or so. Also if you do any slalom or footing at high speed, you will want to avoid changing as well.

Some of the engine guys might be able to help with explaining this one, but it does affect the rev of the engine. I dont know what newer boats have for rev protection, but in older boats I was always told to adjust rev-limiter and be weary of over-rev risk with the lower pitch props.

I just upgraded to and ACME prop on my Malibu VLS and expect what Karl decribed....faster planing, hold speed better etc. After the prop was changed all of the people that ride behind my boat thought the wake was noticeably steeper. This was very noticeable at surfing speeds. It does also appear that the boat runs with a little more nose up. Anyway I can't explain it but those are my observations.

Driving a newer wakeboard boat these days is like driving the freeway with your car in first gear.

Ray, what year is your VLX and what prop did you go with?

I have an 05 VLX and can't imagine going with ay less pitch. Also what does less pitch due for gas consumption? (Can it get any worse LOL)

We changed our prop from a 17 pitch to 15.5
No difference in shape or size. Just the well needed better hole shot when sacked out.

Decreasing pitch gives you more pull out of the hole and on plane faster but increases your rpm at speed. For example our prop had a pitch of 18 we repitched it to 17 so we can pull heavier riders easier it made us plane out faster and also increased our rpm by 200 once on plane.

I've got the 13.5 X 16 now which evidently is the stock prop. It looks like they sell a 13.25 X 15.5 (the 857). We're running stock ballast (including front tank), wedge and about 300 lbs of lead in front of the driver and in main compartment but I also have the std motor and it struggles with a lot of passengers and/or when going into the currents we have here at the Delta.

Anyone with an 05 or later VLX tried the 857? I'm curious what it does to your RPM (and in turn milage). Jason G made a good point in that normally we don't have to drive too far before we start riding so I'm not concerned with top end. And if the wake get's steeper or bigger - well that's good as well.

I had the same experience as Daniel. I went from a 23p 3 blade to a 18p 4 blade. A lot more pull but you sacrifice cruising speed because of the RPM factor. It didn't seem to have a huge impact on the wake though.

here is a thread that supports the idea that prop pitch has a noticeable effect on wake size and shape

http://www.wakeworld.com/cgi-bin/Discus4/discus.cgi?pg=topics

my explanation (as stated in the above thread):
My theory is based on the fact that energy in equals energy out. Energy in is the engine, which turns a higher RPM with a lower pitch prop for the same speed. Therefore, the amount of energy in is greater with a lower pitch prop for the same speed. Energy out is put into the speed of the boat and the water. The speed of the boat is the same therefore the amount of energy to move the boat with either prop is the same. Thus, the amount of energy put into the the water is greater with a lower pitch prop. Hence, more energy left behind in the wake.

I'm not sure I understand your theory that a lower pitch prop puts more energy into the water at a constant speed.

The amount of energy required to move a mass (boat) at a constant velocity is constant by formula. Energy = mass times velocity.

In the case of a boat (given that different pitched props are equal from an efficiency standpoint) the formula is better represented as power (energy) = torque times angular speed. So if there is more angular speed (which is the case with a lower pitch prop) the torque required has to go down in value to make the equation true. So given a totally efficient system as rotational leverage goes up the required torque has to be less.

The unknown here is how much energy is bled off into the prop wash with a faster spinning (lower pitched) prop and in what way (if any) does does that energy affect the wake.

If your theory about prop pitch affecting the wake is correct I would think it would have to be because of that.

Well I will say there is no doubt in my mind changing the pitch affected the wake on MY boat. I'm sure my son Blabel will say the same thing, the whole shot was great but the end result compromised the wake in shape, size and how hard the wake was.

I run the stock prop on my boat with 1800lbs + and don't mind what little extra time it may take to plane out.

Those props were put on by the manufacturer to MAXIMIZE performance, gas and engine longevity in my mind so why change.

I haven't had any complaints about the wake or time to get to running speed since I have had the boat.

Gramps

This is s slightly related post. I just replaced my ACME 380 with an ACME 644 on my SAN. There is, as most have noted, a noticeably better hole shot, but at the sacrifice of about 4 Mph top end, and several hundred more RPM. previously, my top speed (I know, who cares)was around 44, now it is 39-40. All that being said, another somewhat frustrating situation is taking place. When I am fully weighted (sacks + stock ballast), and I cut out to the port side of the boat (heelside for me) the wake is awesome. PP holds speed, and the wake is clean. However, when I cut out to the starboard side (toeside for me), the boat seems to drag, PP searches within several MPH, and the wake softens and becomes very peaky. Still clean, but there is a noticeable speed decrease. This happens with any rider, and on several different days, and the boat is perfectly balanced out, side to side. My theory so far is that somehow, I am getting a cavitation effect that is screwing up PP. Don't know how a new prop could affect this, but that is the only variable that is different. Any ideas?

Chad