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Mastercraft experiment part two


eleeski
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Inspired by the cool Americas cup foiling sailboats, the experiment continues! The purpose of this experiment is to enhance the trick wake. But it may be of interest to you slalom only types.

 

Trick wake: bigger? Maybe. Slalom wake frothy?

 

I need to ski it.

 

Upside down photo, sorry.

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@EleeSki as long as you keep out tricking @Horton I will help you out..

A little edit here, a little edit there and all your images should be good to go.

You should post some side by side video with and without the plate.

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This was a fun project. A lot of work! I have a newfound respect for boat designers.

 

The plate was set about 10cm below the hull bottom at varying angles from ~15 degrees down, ~5 degrees down, ~5 degrees up to ~15 degrees up. You .001 fin adjusters will have to wait for exact measurements. The plate impacted the propwash. It seemed to affect the rooster tail most making it softer no matter what.

 

Maybe I should have done this a couple years ago - Mastercraft might not have obsoleted my boat. Sorry about no ski reviews - but the doc still wants me off the water for a bit longer. I'll get some others to try it next week?

 

Eric

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That thing's huge! CC's on the 196 only drops 3/4 of an inch below and has a major effect on the wake. I think one as big as yours could make a big difference mounted the same way. I'm sure you can find some test skiers in the area....where are ya?
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@eleeski: check out the Scarpa Barefoot Plate used on some Malibu's. Same concept as your plate. A very effective tool for the footing wake. It tends to be set level with the water surface. Keep tuning, you will find a sweet spot for it!
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So was the idea to semi- hydroplane the boat for a smaller wake? Why did you chose a single plate vs two plates on each side of the exhoist ports? Would that have made it more drivable? Do I see notches in the plate? What are those for?
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@Wish and @eleeski, conerning the notches - it appears as though they are only on the driver's side and the plate is not symmetrical. This would decrease lift on the driver's side and increase lift on the passenger side. So not only are you introducing a lift or drag on the rear of the boat, but also a degree of twist. If the notches are intentional, it seems to me that they would be on the passenger side of the plate to produce a torque on the boat to counter act the rotation of the prop and the weight of the driver.

 

Another thought would be that perhaps the notches are to soften the wakes on the driver side since the boat isn't typically balanced during most practice sets. to combine this with the previous idea, I would offset the plate to the driver side while keeping the notches only on the driver side. This would help with leveling the boat and softening the 1,3,5 wake with only a driver in the boat.

 

Maybe I took way too much of an engineering approach to that, but just my .02...

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The wedge definitly would not yield a better slalom wake, but it does work great for a wakeboard wake. If you are actually trying to shape the slalom wake then maybe take a look at the multisport plate that Moomba uses. It is like a giant trim tab in the middle of the transom, and it is one of the ways that they get the Outback V to have an acceptable slalom and wakeboard wake.

 

A single big Bennet trim tab might work for what you are trying to accomplish.

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I'm guessing he's not driving at a trim tab or a wing to weight down the back but to hydroplane the boat somewhat. Thus eliminating the wake all together.

 

It's been done on a much bigger scale since 1963

ABOUT 12:52 into it you can see the wake OR LACK OF. And again at 13:12 WOW! Bet that has more then adequate tracking.

 

.

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This experiment had many areas of research. First, my lake is shallow - many tournament sites are deep and the wake is a lot bigger in a deep lake for tricks. I would like to simulate the deep lakes for practice at my lake.

 

Second, my particular boat's slalom wake sucks at the slower speeds (for me it is every bit as good as anything else but others do use my boat). Perhaps I could "tune" the slalom wake to make it friendlier for Lisa.

 

Third, Marcus is concerned that the trick wake on the new MC is a bit small. He invited me to ski with him late October and maybe try some ideas to improve his wake.

 

This is a quick and dirty weld up to test proof of concept. The size was generally set by dimensions on the transom. A piece of scrap steel off an old bulldozer was used (hence the holes). Marcus had tried the wedge and found that it didn't have enough effect - so a copy of the wedge was ruled out. Trim plates were on the agenda for my boat but I was unsure they could augment the wake size so I pushed that test back. The Americas Cup boat's foils were cool so I started thinking on those lines. I dropped the plate about as far into the water without generating huge structural loads on the transom. Since it impinged a bit on the propwash, several interesting side effects were generated. I really need to ski this to see how it feels. At least I have narrowed it down to two settings worthy of skiing.

 

But the experiment continues!

 

I wonder if Marcus will recind his invite now?

 

Eric

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Man, they got this one to run with a dinky little outboard. Certainly would have lateral stability. No short course balls could be used and a bit of a bitch around the turn island.

.

.http://youtu.be/-4IUiIqz3Gw

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@eleeski Did you attempt any maneuvers at 34/36mph with the plate at a negative trim angle? The fact that you state it got loud and rattly at those speeds would indicate to me either you were able to ventilate the prop/rudder or that flat plate had a lot of cavitation occurring.
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@MCskiFreak At low angles, the boat appeared to handle normally. The wake differences were subtle but real. I didn't have a formal test card to run - I just drove, looked and turned around at both trick and slalom speeds. At high angles, the plate dragged and cavitated. The test was somewhat aborted to protect me and the boat.

 

I need to pull some skiers to see if there is a significant handling effect.

 

Eric

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OK, the doctor cleared me to ski so I got to test the foil today! Lisa wanted to slalom so I set it to slalom lift. She normally hates the slow speed 15off wake of my boat. Today - no trouble at all. For the first time in a while, she was excited and happy with a slalom set.

 

So I try it. 30mph 15off. The hip is still quite sore so that might be my limit physically and safety wise. Hardly any wake at all! (And I made the pass!) Now I did try 30/15 earlier when she first complained about the wake - and it honestly was quite brutal. The foil did make a substantial difference in the low speed slalom wake.

 

Kirk had tried this setup earlier. He felt the 30/15 wake was tiny but couldn't run a 36/15. Said he hit a wall at the wake. Interesting, perhaps the propwash is directed down and bounces back up at faster speeds. There is probably an optimum angle for each speed. I need to try skiing 34 and 36 - when I get healthier and try some other angles.

 

At trick speeds, the wake was a bit smaller. Not out of the realm of depth, balance and loading variables. Still a nice shape but just not as high. The table was smoother - that tiny phantom wake in the table was gone. And the rooster tail that makes it a bit hard to see the ski was much lower. The boat was more sensitive to balance. Both Lisa and I adapted in less than a pass. Overall the trick wake was not as good as the stock wake - but I may end up training with something along those lines to closer simulate tournament boats.

 

Still lots more work to turn this boat into the new MC with just a tiny mod...

 

Eric

 

PS @MarcusBrown This is not why we need to meet!

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Dee Johnson was my tester yesterday. Santa Ana winds at the end of a long work day made conditions a challenge. Dee started at 34, 22off. I watched him almost trip on the wake on the way to one ball. At the end, Dee said the rooster tail was a bit firm - an understatement but he did make the pass. 28 was tough also. 32 felt good to him - almost as good as the stock wake which is really good on my boat. 35 was sweet and he rocked the pass despite the conditions. At 38 there was an uncomfortable bit of spray.

 

He preferred the stock boat overall at his skiing level. But even the 22off hard rooster tail was skiable and he did like the 35off wake a lot.

 

I need to redesign the mechanism for attaching and adjusting the plate. An easy configuration setting from trick to slow slalom to nothing would be cool!

 

Eric

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@Eric: ala Hydrogate or a cockpit adjustable anti roll bar on a race car, you should be able to set up a cable and slotted adjuster to allow position adjustments on the fly. Then it would be a matter of marking the position for optimum wake per given speed. Instead of holes, you have slots and the cable stops set the position. Heck, if you really want to high tech you could set up a controller to adjust it from the GPS sensor.
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One thought you might consider...in the old Supra boats the slalom wake was enhanced - flattened and softened by a trim plate the was attached to and flush with the bottom of the hull. It extended out about 10-11 inches and was about 15-16 inches wide (or so). There were adjustable supports (working much like a turnbuckle) that connected from the outboard corners back to the transom. Just a 1/4 inch or less of lowering or raising of the outboard edge would make noticeable changes to the wake. To improve the slalom wake, you would adjust the plate downward to create a little lift in the back, and drive the modified V bow downward into the water. The basic design of the Supra hull was that more speed drove the bow down more. This could be increased, or somewhat lessened by adjusting the trim plate down or up. Old MC hulls may be somewhat similar.
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I have pondered for years a rudder with horizontal wings that came out of the sides of the rudder. These wings would be adjustable, such that you could change the angle of the wings in a small range; up and down.

 

The idea is that it could go from providing a small amount of lift at the transom for slalom to providing a downward pull at the transom to enhance the wake for tricks and wakeboard.

 

I imagine it working by the rear of the wings being connected to each other by a rod going through the rudder, making a hinge point. And the fronts of the wings being able to move up and down by being connected to a vertical threaded rod that would operate as a screw drive.

 

Ideally this threaded screw drive would run in a passage way inside the rudder, up into the boat, and be driven by a small motor.

 

 

Of course this idea could make steering unbearable.

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@DW @Zman @Jordan The hope was a very simple mod would do everything. And for world peace. Practical reality has its own agenda.

DW, the plate is under a lot of load. I'm not sure a cable could carry the load. A three pin locking mechanism gets very complex. The GPS automatic setting is most desirable but out of the scale of my project.

Zman, there may be better ways to alter the wakes. I'm not unhappy with the results of this particular experiment, just the complexity of the mechanism needed to make it work best.

Jordan, I believe that a rudder wing has been tried. While the one I heard of was not adjustable, I think it worked but wasn't worth the hassle. Adjustable on the fly gets really complex. GPS auto adjust - NOOOO!

Eric

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@eleeski: first, just having some fun but my thought was not to have the cable actually be loaded, you would have a series of notches that would lock the plate and the cable would simply move the mechanism from one notch to another. An anti roll bar is the same, heavily loaded in corners, but unloaded on straight sections thus allowing an adjustment to be made. For you application, you would adjust at rest since the skier most likely stops between speed changes.
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