What is KDW???

[Rye]

I was wondering if anyone knew what KDW stood for? When you program a rider in B.I.G. with their settings it asks for you to enter an KDW amount to contour the way the boat responds to you??? Any thoughts???

[bobx1]

Not sure of what it stands for but it is associated with throttle pull rate (Perfect pass and I assume other use this terminology). The Big Screen MC web site (http://www.mastercraft.com/bigscreen/rider) says:

"Enter in a KDW number within the range of 50 to 400. This gain allows the driver to tailor the pull characteristics (higher numbers result in more throttle)."

[Rye]

Yea I saw that, what does that mean?? Does it mean the throttle responds quicker in turns or something?

[bobx1]

Others with experience will chime in (I dont have PP - Mastercruise for me) but from what I have been told, it is the response level. More passive/gradual the lower the setting, more responsive (i.e. rip it out of your hand) the higher the setting.

If you google "Perfectpass KDW" you will see topics on various boards (i.e. Mailbu Crew, Planet Nautique, etc.) that have to do with surging and most suggest you adjust the KDW setting.

That is about all I have to offer - sorry.

[kdr]

It's basically a variable in a feedback control equation. I don't remember all the details from control theory in college, but there is an input (throttle position), output (speed), and a reference value (perfect pass setting). The equation compares the speed to the reference and adjusts the input accordingly. The greater the difference between the output and the reference, the greater the throttle response.

There are three variables, KDW, KP and KI are the constants for the proportional, integral, and derivative control portions of the functions. The proportional function is the part that says I've got a large difference between the output and the reference, so I need need more throttle. The integral part is used to ignore spikes in the feedback loop, it basically averages out the signal to make it smooth. The derivative part is used to control the feedback response. This is crucial because one of three things will happen. 1) an overdamped response - the desired speed will never quite be reached, 2) underdamped - the response will be very fast, but it will be so fast that the speed will overshoot the desired speed so much that it will cause the throttle to drop out and then it fall under the desired speed greatly. This process will continue and the speed will never settle down. 3) desired response - the throttle will respond quickly but the speed will only overshoot the setpoint by a little bit then it will settle down to the setpoint. The KDW setting has a great effect on this response.

This is mostly from memory and it was ten years ago that I studied this stuff So just remember that its a variable in an equation.

[swatguy]

Ok I will break it down in "wakeboarding/pull" terms. The KDW is the "aggressiveness" in which the engine makes adjustments to you speed. The lower the KDW the less throttle is used to get you speed up to par. If you ride with very little weight in the boat you will run a low KDW rating probably around 100-75.


The higher the KDW the more "aggressive" the engine will surge to control the speed. Usually boats with lots of weight will require a higher KDW setting. I don't know anyone who runs a KDW setting above 250. However I have never spent a ton of time in an X45 or something that loaded down. Most 21-22ft boats that that I spend a ton of time in , that are weighted down , are running 150-250 KDW's A ton depends on the engine. Also heavier more aggressive riders will require higher KDW's because their edging will be felt.



Now the NN value is also a huge factor and a also effects your KDW setting as well. The higher the NN value the more time it takes your pp to adjust. When the NN is higher the pp module lets the paddle wheel rotate more times before it adjusts. When you lower the NN value the less time it takes before the boat adjusts. Normally the NN value isn't never changed too much from factory setting. If I recall correctly your NN value from the factory is around 80. Now usually if you lower you NN values you need to lower you KDW setting as well or the boat will feel like it is surging/ hunting to keep a constant speed. The NN value is not altered too far from factory. 60 on the low end and 100 on the high end from my experiences.


So in order to get you around the right number what kind of boat, weight, speed and rope length are you riding and how big of a crew? Good start point is 150 KDW though.

[swatguy]

Also another way to kind of feel the system out is if when the pp makes adjustments it surges past the desired speed too much when it adjusts that's usually a good indicator your KDW is set a little high. If it takes to long for it to get back up to speed when it is adjusting it's usually too low of a kdw value.

I run 2200lbs in my 2000 Xstar and my KDW is set at 180.

For my wife who only runs the bow sac filled, no weight in the rear bags, and no weight in the center sac her KDW value is 90.

[Rye]

Wow very informative, Thanks!!
I guess I want to program riders just for the fact of keeping track of rider
time. I think it would be cool to see how many hours I actually rode in a summer.

As far as the PP, I want it to respond just like it does now. I turn it on wakeboard, put 21.6
and ride. So, I want the kdw to respond just like it does now. I have 2010 X2 with stock ballast plus custom bow sac with 100 pounds of sand in bow, and custom X2 side sacks in the lockers on hard tanks. I pretty much ride with full tank of gas and 3 people on boat.

[swatguy]

KDW from the factory I think used to be 140-160 so stick there if it's working fine on your original setpoint.

Your weighted down pretty good so stay above the 140 for sure.
Weighted down you are able to keep the wake clean at 21mph?

[Rye]

Yes with all the weight I can have clean crisp wake at 21.6, of course more people in boat requires proper placement of body weight... What speed do you ride at for a clean wake?

[swatguy]

I have the X1 hull and have to pull at least 23.5 with 2200lbs. With an 80ft line.