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Old    Adam Clark (adam1680)      Join Date: Jun 2008       07-07-2012, 12:06 PM Reply   
Someone in our private community stated that boats with heavy ballast destroy the lakebed, fish, and wildlife. Can anyone speak intelligently about this? I know it erodes the shore some, but I'm definitely not educated enough to speak of sonic waves that kill fish, lol..

Sounds like bull to me, but if anyone would know, it would be you guys.

Thanks for the responses!
Old    Cobra Rob (CobraRob)      Join Date: Aug 2010       07-07-2012, 12:22 PM Reply   
That pressure gets damped VERY quickly it goes down at an exponential rate so if you are more than 20ft deep. I doubt it is even barely measurable at the bottom..
Old    Dan (hco)      Join Date: Jun 2006       07-07-2012, 12:32 PM Reply   
Well if that's how they feel ask them to prove the damage with some physics and science.
Old     (pprior)      Join Date: Jan 2012       07-07-2012, 2:13 PM Reply   
That is the most inane thing I've heard in a long time. Ask anyone who's ever been scuba diving - the effects of a "wake" diminish rapidly in the water. Shoreline, yes it's an issue, but down underneath - not a chance.
Old    Greg Wasson (lhlocal)      Join Date: Jun 2003       07-08-2012, 8:00 AM Reply   
Im a board member for our private lake community. For a long time the fisherman have had a great influence over the board and its policy. About five years ago there was a push to ban wakeboard boats based on erosion. It was quickly shown that a moderate wind does far more damage to a shoreline than a boat wake. Think about a 12 mph wind hitting the shore for hours compared to a series of six waves from a boat.

After that they shifted their focus to disturbing the lake bottom. Our lake averages 5 to 16 ft so we do have to be careful. However your average deck boat with its lower unit is much more likely to disturb the bottom. Think about whats sitting lower in the water. Also a wakeboard boat is up on plane in seconds compared to an underpowered I/O chugging down the lake trying to pull someone out of the water who use to be able to get thru the course 20 years ago.

Good luck, if it's like our lake they will move onto the next thing after you shoot this one down.

A quick search online will confirm the effects of wind on shoreline erosion.
Old    Adam Clark (adam1680)      Join Date: Jun 2008       07-08-2012, 10:56 AM Reply   
Thanks Greg.. It's just a few kooks who are bringing this up. Our lake sounds like yours.. It goes to beach all the way to around 20 feet at the middle.
Old    Karl De Looff (boarditup)      Join Date: Jan 2004       07-09-2012, 12:30 PM Reply   
You can erode the bottom through a process called "squat." It is when the hull is sucked down to the bottom is a shallow water situation - typically less than 6" of water below the prop. The water in front of the prop is evacuated so quickly that the boat will sink down into a hole that the waterflow into the prop creates. This will typically stop the boat as the running gear will strike the bottom. This is really bad with an I/O trimmed up.

Under normal conditions with decent wake that you can ride on, the interaction with the bottom will result in hull rise - actually making the boat rise out of the water. This will occur with about 18" of water until about 4' or so, depending upon hull and speed. This actually gets the hull away from the bottom in these relatively shallow conditions. After 12' of water, the interaction with the bottom is irrelevant.

So, erosion can occur rapidly at very shallow water depths at speed - prop depth to 18" below prop depth. An inboard has shallower prop depth than any I/O, event with most ballast conditions. In any conditions that a wakeboat could provide a decently shaped wake, the boat cannot cause bottom erosion due to the physics of fluid dynamics as it interacts with the hull. Most of the time, wakeboarders need at least 8' of water to have a decent wake to ride.

Shore erosion will not happen at a "natural slope." The natural slope of sand it about 16:1. All wave action will work to get to a natural slope. You cannot stop it - it is the physics of fluid dynamics as it relates to the particle size of the soils on the shore line.

If you need more expert testimony, please let me know.
Old    N L (drnate)      Join Date: Jul 2006       07-09-2012, 1:33 PM Reply   
Quote:
Originally Posted by boarditup View Post
You can erode the bottom through a process called "squat." It is when the hull is sucked down to the bottom is a shallow water situation - typically less than 6" of water below the prop. The water in front of the prop is evacuated so quickly that the boat will sink down into a hole that the waterflow into the prop creates. This will typically stop the boat as the running gear will strike the bottom. This is really bad with an I/O trimmed up.

Under normal conditions with decent wake that you can ride on, the interaction with the bottom will result in hull rise - actually making the boat rise out of the water. This will occur with about 18" of water until about 4' or so, depending upon hull and speed. This actually gets the hull away from the bottom in these relatively shallow conditions. After 12' of water, the interaction with the bottom is irrelevant.

So, erosion can occur rapidly at very shallow water depths at speed - prop depth to 18" below prop depth. An inboard has shallower prop depth than any I/O, event with most ballast conditions. In any conditions that a wakeboat could provide a decently shaped wake, the boat cannot cause bottom erosion due to the physics of fluid dynamics as it interacts with the hull. Most of the time, wakeboarders need at least 8' of water to have a decent wake to ride.

Shore erosion will not happen at a "natural slope." The natural slope of sand it about 16:1. All wave action will work to get to a natural slope. You cannot stop it - it is the physics of fluid dynamics as it relates to the particle size of the soils on the shore line.

If you need more expert testimony, please let me know.

Wow, this is highly insightful and by far the best explanation I have ever heard. I tried to wakesurf on a private lake once that was only 5-6 feet deep. Didn't work, wave was too small because the lake was so shallow. I too have found that 12ft+ is ideal
Old    KDA (idaho_hillbilly)      Join Date: Jun 2009       07-09-2012, 2:26 PM Reply   
Sounds like a couple people don't like you hooligans playing your loud music in your fancy boat and making those big waves that spill their beer while they fish.

I can't image boating in boat that shallow! I kind of get freaked out when we are boating in water less than 20'!
Old    Greg Wasson (lhlocal)      Join Date: Jun 2003       07-09-2012, 3:36 PM Reply   
Karl

If you can point me in the direction of something I can print that speaks to the bottom disturbance I would be forever grateful. Im dealing with a lot of observational expertise. Would be nice to shut their pie holes for a while.
Old    Karl De Looff (boarditup)      Join Date: Jan 2004       07-10-2012, 2:24 PM Reply   
I wish I could. Unfortunately, I am the expert on this and have not published formally. Getting a peer review on this would be difficult, as well. There just is no money to support a full study on this. The ACOE has a program that calculates surge (the bow wave resulting from a displacement hull through a constricted channel) that I used to model various hull configurations and water depths while designing my lake. Yes, I have the first lake designed for wakeboarding based on real data and engineering.

So, let me know what I can do to provide expert testimony for you. Of course, if they don't want to discuss the physics of a wakeboat on the bottom, there is nothing I can do.

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