A Simple Slip Vs. Roll Wake Enhancement Experiment

On the X-9 thread Matt says he’s having difficulty making a good “darkside” wake. This thread is an attempt to help Matt from afar. I think that slip is an important element for generating a good surf wake, at least it is on my boat it seems to be. I first stumbled on the idea when one of my goofy stance riders got up on the darkside when we were rigged for normal. He rode with the rope for a while eventually pulling on the rope. Every time he pulled on the rope the wake peaked up and looked great.

The rope was tide high on the tower so two things were happening. First he made the boat slip or dog track and second he decreased the roll of the boat. When we weight a boat we weight the surfing side. Pulling on a rope mounted high on the tower partly negates that effect. That suggests that slip is more important than roll.

Next time your out surfing tie off one rope on the tower and another at the lower eye at the stern. Pulling on the tower rope will flatten out your list and add some midship slip. Pulling on the stern rope will have more effect on slip than roll. Have a surfer get up on the wrong side and pull on the tower rope and then the stern rope. You can also have your surfer get up on the surf side and pull for a comparison. Which one works best for you? Do you need more slip or more roll?

It didn’t take a lot of force to have a noticeable impact. If you consider that a 160 pound man might be able to pull with a force of 160 pounds that should get you in the ball park. Note the tower gave a mechanical advantage. I’m sure that my surfer wasn’t pulling with all of his might. I removed the tracking fins on my boat to make the boat slip more easily. The fins were on when we made our first observation of this effect.

If roll helps then it seems like trim tabs mounted on either side of the boat should help build a better wake. Set one trim tab up the other down for more list or roll. If slip helps then remove tracking fins and add a canted fin, maybe on a trim tab that increases you slip. Make sure that you replace the tracking fin with something that plugs the fin bolt holes or you’ll end up bailing water.

I did notice that we once had the darkside really good. The one thing I remember about that day (it was in August) was that we had about 1300 pounds in ballast along the starboard side. We also had my 230 lb buddy who 6'3 hanging off the side. I remember that wake being nice, the sweet spot fairly long. We also had a few more people in my boat as well. I will try the rope trick you mentioned above. We will see.

Ed, I thought I was following you until I got to this:

"If slip helps then remove tracking fins and add a canted fin, maybe on a trim tab that increases you slip. "

What?

If slip works then you don’t want to track, so remove tracking fins. If removing tracking fins doesn’t provide enough slip that you need another fin someplace to push against the rudder. My in my 2006 experiment I replaced tracking fins with canted fins. That’s not practical. Mounting fins on an outboard mounted trim tab might do the trick. I’ll make a cartoon after work.

I love cartoons.

By changing the locating of the rope from the top of the tower to the bottom of the tower you change the effect you have on slip and what I'll call roll.

Here Jeff is pulling one a rope that is high on the tower. He's reducing the roll that the weight is creating. Let's say that he reduced the roll from 15 degrees down to 10 degrees. Jeff is also pulling the boat off course, the boat is slipping its dog tracking.


Here Jeff is pulling on a rope that is lower on the tower. He's not changing the roll, the roll is still 15 degrees. He is still pulling the boat off course.


Oh, and I have Jeff riding a Yellow Loogey.

More on tracking fins and trim tabs...

OK, suppose that you only want to add roll. Adding trim tabs should do it.

Suppose you wanted to add roll and change the slip angle. If you put fins on the trim tab I think that would change slip angle.

Just roll


Roll and slip fins


Top view of roll and slip fins

The latter makes sense to me

By adding the fins on the trim tabs, not only would the roll be increased, but also the slip ?

Right, the trim tab only provides roll. In fact it causes drag and may undo some slip. Putting fins on the trim tab should alter slip. You could put simple manually adjustable fins on a trim tab.

Will this have the effect that we want? Don't know. I don't want to put trim tabs on the Lightning. If I buy a new boat I'll probably add trim tabs on her.

With two trim tabs, the fins could be mounted respectively to give you your port/darkside wake with the flip of a switch. Not sure how much of an effect it would have, but it could be a step towards switching between wakes without much effort...

(Message edited by wakesurf_ohio on February 11, 2008)

Right, simply retracting the trim tab and deploying the other could give port and starboard wakes.

Suppose you 1,500 evenly in two back lockers. Would this system provide a good surfing wake on both sides with a flip of a switch. Don't know, haven't tried it. It would be even better if it worked with a switch blade.

Just read this topic and it was something I was considering doing to our boat, it just makes sense plus what a few hole in a boat right? My question would be what side plate to use?

Side plate? You mean trim tabs?

I think I'd measure the transon and look at an Overton's catalog.

My bad I was typing from my phone. What size plate, trim etc. This past summer I contemplated doing this but was talked out of it.

First off this idea is speculation. It would be nice to test before investing in equipement. Again, I would look at the stern of your boat inside and out. What obstructions are in place.

If you mount trim tabs too far outboard and if you use a lot of weight the trim tabs might not even come in contact with the water.

I think a rectangular shape would be OK, maybe good. I'd start there but I'd also consider a trim tab that is shorter near the centerline of the boat and longer as you go outboard.

You’re asking how wide. Now ask how deep, how much angle, and how strong. I don't know the answer on that either. I think this idea would take some experimentation.

Intereting concept - Ed, have you talked with JL yet? I swear that the Wakesurfing Magazine Calabria - several years ago now - had 4 or 5 trim tabs across the transom. No fins on the tabs but it would be interesting to get their input.

What if you angled the fins on the trim tab the other way? Would that force more water to go under the boat and come back out on the desired side? Wouldn't that displace more water to make the wake bigger? What i am thinking is how when you turn whichever way you are surfing on your wake swells, and when you turn away it shrinks. I don't know though, just a thought.. I guess someone will just have to test these theories ..

I tried the running the tracking fin experiment with the fins working with weight-generated-list and against weight-generated-list. On my boat it was better working with the list.

I'm not sure I understand Robbie’s question. If you make the boat slip too much the wake gets wide and shallow, but smooth. Plus the rooster tail gets huge. The extreme case would be so much slip that the boat would be dragged (or pushed) through the water sideways. I see the slip factor as a trim tab to correct for prop rotation.

Say you're surfing on the port side. When you turn the boat left, the wake size increases. When you turn the boat right, you lose you wave. So, wouldn't you want your boat to have slip towards the side you are on?

(Message edited by wakesurf_ohio on February 12, 2008)

This makes sense to me, but i don't know.. I'm not the engineer here ...yet

Thought you were going to be a doctor.

When surfing on the port side, the regular side, the propeller makes the boat is slip as though the boat was turning left, not right. If you increase the slip to the left I think the boat wake will clean up and improve, but only to a limit.

Thats the plan.. but via engineering school

So adjusting the slip is more for the shape/cleanliness than size?

I hear you’re a good student, you'll do well.

I think displacement is the key to size. That's all about horse power and ballast.

You know that shape is more important. The problem I'm fix the bad wake on one side problem. I think that at a particular slip angle the bow will trap more water and scoop out a bigger divot than others. That’s the only way that I see slip improving wake size.

Change the slip angle too far and the broad side of the boat is exposed to the water and comes up on plane making a smaller wake. Bring the slip back to neutral and the wake evens out, resistance to the hull falls both wakes even out, and become smaller. Go further in the other direction and the other broad side is exposed and the other side of wake improves. Go too far and the other broad side of the hull comes on plane and the wake gets smaller.

If there's a wake size increase it would be from setting the slip angle so the boat builds a bigger bow wake. This is my speculation and not supported by a lot of research.

Thanks!

I was thinking of it from just a size approach.. Hopefully you'll be getting a new boat soon so you can experiment!

Corroboration that is "real" is that manufacturers do not necessarily mount the tracking fins dead straight under the keel. Centurion tracking fins are angled slightly from the factory.