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Aurelia



Joined: 21 Aug 2009
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City/Region: Gig Harbor
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PostPosted: Tue Dec 28, 2010 3:43 pm    Post subject: Reply with quote

And this is why I started this thread in the first place. Thanks for all the comments and input so far. I am still not convinced one way or the other and I am still searching for more info. I too can't believe there is not a comparative test already documented somewhere. Why wouldn't Volvo have funded such a test themselves? I found a few articles in different languages but after translation they make too little sense to me.

I will keep watching for more info until my boat is on the hard stuff and I will post it here if I find proof. I do think the counter-intuitive design of the product is the primary problem with it.

Not small boat related but a good comparison none the less is here:

http://maritimedynamics.com/interceptor.pdf

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Aurelia - 25 Cruiser sold 2012
Ari - 19 Cruiser sold 2023
currently exploring with "Lia", 17 ft Bullfrog Supersport Pilothouse
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starcrafttom



Joined: 07 Nov 2003
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PostPosted: Tue Dec 28, 2010 3:57 pm    Post subject: Reply with quote

ok guys enough of the in fighting... I seem to stir the pot even when I'm not trying to , and I try to enough as it is.

After reading all the links, post comments and info listed above and then some i noticed a few thing.

1) everyone that hates denounces or does not believe in this produce has never USED IT. sorry but theories are for class rooms and I like to see how things work in the real world. remember bumble bees can not fly if they did math. Lucky for the bees they cant do math and go around flying anyhow. told to me by my high school biology and math teacher.

2. As pointed out in other forums. comparing water to air in like comparing air to ground. it's just not the same. as for the use flaps on a plane compared to speed brakes. both slow the plane down but flaps change the direction of the plane. Most flaps on planes EXTEND the surface area of the wing causing more lift but less speed or the same lift at slower speed. they do not cause you to go faster. Speed Brakes on a plane are not on the tail edge of the wind but in the middle area of the wing so are not a comparison to the trim taps in question.

3) everyone that has the tab LOVES them. only one guy replaced them after a faulty install by a bone head. and after they got them reinstalled he liked them. I think he was trying them on to much boat.

4) No one complains of loss of speed at top end or increase of fuel use. if it was a problem then someone would be complaining about it.

As to the "Why do you need them, just move stuff around " folks. Its not easy to move things around every time some one in the boat moves. and my wife likes to move around the boat a lot while we are under way. I also have a tilt to port due to engine torque. It does not go way until the port 50 gallon fuel tank is empty, and even then it comes back with a port side swell. if I did not need them i would not be getting them.

now as to mounting? I have a alum bracket for my motor and at the bottom I have a 1 to 2 inch stand off for the trim tabs to be mounted on. So depending on the wiring coming off the back of the unit I may not have to drill a hole into the hull. If I go with the lenco's, which is my other choice and preferable to me over the Bennett's, then i don't have to drill any holes in the hull but may have to weld another stand off of aluminum for the top part of the actuator so it is the same distance form the hull. with the Volvo produce I would not have to worry about that at all.

So i may drink the cool aid like others in the past and see if it works out as well as the whole earth is round thing did for Galileo. what i would really like to do is go for a ride on a 20 to 30 ft boat with this system.


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Aurelia



Joined: 21 Aug 2009
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City/Region: Gig Harbor
State or Province: WA
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PostPosted: Tue Dec 28, 2010 4:23 pm    Post subject: Reply with quote

Tom, It looks like the drive unit recesses into the transom 3.5 inches so it would have to be inside your bracket housing unless you welded on a much larger mounting extension. Can you easily get inside that motor bracket?
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Tug



Joined: 22 Jun 2007
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PostPosted: Tue Dec 28, 2010 5:05 pm    Post subject: Reply with quote

I would like to correct the description of the trim tabs i had seen years ago that i thought were great.After some thought i remember them as looking like this: i posted a picture ( drawing Sad ) in my photo album.I was not able to link it to this post.They should also work just as well for hole shots as Bennet Trim tabs. Tug
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starcrafttom



Joined: 07 Nov 2003
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PostPosted: Tue Dec 28, 2010 6:07 pm    Post subject: Reply with quote

I see what you are talking about. the back of the units plug and connection call for 3/12 inches. I don't thing that I would need that much if I changed the plug around. I would need the unit in my hand to see. I'm thinking about soldiering the connection together and then encasing it in epoxy or 5200 between the back of the stand off and the hull. Then run the wires up the back of the transom with the down-rigger cables and follow those up and in.

My main goal is to not drill threw the outboard bracket at all. More question more research. we will see.
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Sea Wolf



Joined: 01 Nov 2003
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PostPosted: Tue Dec 28, 2010 6:26 pm    Post subject: Reply with quote

This is and has been a fun topic, a little controversy notwithstanding!

This time/ this year, its all in good natured fun, and good for our C-Brats Forum.

Usually by December, we've all got such cabin fever that something turns controversial, but in the past, political threads have caused some hard feelings.

This is good, clean fun!

Thanks, everybody!

Joe. Teeth Thumbs Up

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journey on



Joined: 03 Mar 2005
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PostPosted: Tue Dec 28, 2010 6:34 pm    Post subject: Reply with quote

Tom,

Just a minor thought, and guess what, not on trim tabs. The analysis of compressible fluids (gas) and non-compressible fluids (liquids) uses the same theory. Yes, one is a gas and another is a liquid, but when you make the corrections for the compression of gas (changes due to heat and pressure,) the equations are derived from the same source. Reynolds Number is as applicable to gas as to liquid as an example. Boat propellers and airplane propellers use the same theory. The Wright Brothers spent many an hour in the laboratory to make sure their airplanes flew, along the way figuring out their propeller was a moving airfoil. Bernoulli's law applies to both liquid and gas.

The point of this blog is to point out that things do not "just happen", but there is a reason for it. One can back into that reason, as the Wright Bros did, but there is logic in this world. Except with politicians, and I think there's logic there, they just don't admit the real thought.

So when there's a device that defies logic, one ought to be able to find the logic (think bumble bee) or admit that we're always learning. I hope I'm in the last category and I also hope that I'm willing to listen. For the bumble bee, here's an answer: Bumblebee . Scroll down to Myth which gives an explanation. And maybe that's how those trim tabs work.

Boris
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tpbrady



Joined: 08 Feb 2005
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PostPosted: Wed Dec 29, 2010 12:12 am    Post subject: Reply with quote

I've read the story of the Wright brothers several times, and trying to work out the equations on propeller design confounded them for weeks. They thought they could find a body of propeller knowledge in the marine industry and found that propeller design there was a matter of trial and error. To some extent, I am not sure we have progressed much further since then given all the posts on props.
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Tom
22 Cruiser Bidarka 2004-2009
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38 Trawler Mia Terra 2012-2015
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starcrafttom



Joined: 07 Nov 2003
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PostPosted: Wed Dec 29, 2010 2:21 am    Post subject: Reply with quote

Greg thank you for this report.
http://maritimedynamics.com/interceptor.pdf

After reading it thru I learned a few things. 1) their test boat is the size of a cdory. 2) there was no difference in drag at all, NONE. 3) that the amount of lift was the same up to 55% of deployment of either system AND after that point the QL style tabs stopped producing additional lift while the lenco style tabs continued to produce additional lift up to 100% deployment. Now that is a big surprise to me. ( and is it lift or trim?)

Everyone go read that and then tell me what you think.
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Will-C



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PostPosted: Wed Dec 29, 2010 10:18 am    Post subject: QL trim system Reply with quote

I didn't see any in fighting, just comments, maybe a little good natured chain pulling which is what makes this site so great. Most folks try and defend their purchases. I said what works for me. My wife walks around the boat and for me that doesn't require the use of my trim tabs. I thought I read something about a pressure wave created in front of the deployed GL gizmo causes the lift. I also thought someone mentioned that unlike trim tabs the QL are deployed in increments and you could not stop them anywhere as you can other devices such as permatrims and trim tabs. I'm sure Lenco and Bennett which will work on almost any kind of transom are not all that worried yet. Everything in print is not always true. I wonder what the long term service history on the QL System will turn out to be. Far be it from me to try and stop the experiment. Have at men! Enough from me. Laughing
D.D.

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tpbrady



Joined: 08 Feb 2005
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PostPosted: Wed Dec 29, 2010 11:04 am    Post subject: Reply with quote

One observation on my CD25 is that at lower speeds, 12-20 mph, I generally use 60-80% of my Lenco tab bow down deflection. The boat is essentially stern heavy and drag not withstanding, gets best fuel economy with a lot of trim tab. Sometimes I wish they were bigger. I am not sure the Q/L system would generate enough stern lift across the operating range to make them a suitable replacement for tabs.
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Aurelia



Joined: 21 Aug 2009
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PostPosted: Wed Dec 29, 2010 11:24 am    Post subject: Reply with quote

I guess your tab indicators work better than mine. I could never tell you a percentage of "tab down" with my Bennetts. The indicator has been replaced once already and is nearly as flaky as the first one. They operate fine but have never really indicated what they are doing. Took me some practice to get the feel of it but now I use them all the time for to correct for loading/movement of passengers.

Do you have a Permatrim or two on your boat? I use much less tab with our permatrims than I did before they were installed.
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Sea Wolf



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PostPosted: Wed Dec 29, 2010 11:48 am    Post subject: Reply with quote

starcrafttom wrote:
Greg thank you for this report.
http://maritimedynamics.com/interceptor.pdf

After reading it thru I learned a few things. 1) their test boat is the size of a cdory. 2) there was no difference in drag at all, NONE. 3) that the amount of lift was the same up to 55% of deployment of either system AND after that point the QL style tabs stopped producing additional lift while the lenco style tabs continued to produce additional lift up to 100% deployment. Now that is a big surprise to me. ( and is it lift or trim?)

Everyone go read that and then tell me what you think.


Tom, Greg, and all-

This article is very interesting and revealing.

Actually, Tom, the boat used is " a 7-meter monohull model", not a full sized to scale boat, and one hopes the model performs as does the real boat, which is always something to keep in mind, or account for. Modeling is done a lot in aero and marine studies, and the tests and results have to consider any differences in scale and how i t would effect test results.

The measurements and performance results seem to indicate the following to me:

The interceptor type plate works OK at planing speeds up to that 55% deployment point, as mentioned.

This is because (theorizing now) the vertical plate acts as a flow "dam", creating stalled flow in front of it , and the water flow along the hull flows over this wedge shaped stalled flow, pushing upward on it and causing "lift", which is upward pressure (not to be confused with aerodynamic lift, as on a wing, but more "kite effect" like.)

I thought this might be true earlier, but nowhere was their any mention of this "how it might work" theory, and the 55% figure is an interesting determination.

While up to the 55% point the drag and lift effects are similar, past that point, the interceptor plate does not produce more gains, while incurring similar drag increases like the trim tabs, but without benefit. This, in itself, defines the limits of good performance with the interceptor plates.

The trim tabs have several advantages: 1) they work over a longer range of deployment without loosing their effectiveness ("up to 66% more lift at maximum deployment", 2) they also add increased planing area (similar to that added by a hydrofoil), resulting in A) increased control over pitching (longer hull effect) and B) quicker/earlier planning during acceleration. (The last two conclusions are not from the article, but generally accepted understanding.)

There are a lot of other practical/employment considerations discussed in the article, which is aimed at large boat/ferry/ and even jet boat considerations, most of which don't apply to our situation.

So it's up to you, individually, to choose, but I think mine would be for trim tabs, and hydraulic ones at that, considering the electric motor/salt water/seals/corrosion issues. I've got Bennetts on my 22 year old Sea Ray, and they still work well.

Joe. Teeth Thumbs Up
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tpbrady



Joined: 08 Feb 2005
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PostPosted: Wed Dec 29, 2010 12:31 pm    Post subject: Reply with quote

I have a Permatrim on my single Yamaha 150. It reduced the amount of trim tabs I use by about 15%, and also helps the boat track straighter at low speed. Together I can get the bow down as low as I need to go in chop. As speed goes up, I back off tabs and bring the motor up some to where at about 24-26 mph I have no tabs down and the motor more or less parallel to the bottom. At the top end, I can hit 32-33 mph with a light boat, but it is starting to get squirrelly and even with the Permatrim, the boat starts to porpoise. I have a little throttle left but can't use it due to the porpoising, but 30 is plenty fast enough. My most economical cruise in my current configuration is at 22-24 mph.
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starcrafttom



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PostPosted: Wed Dec 29, 2010 1:57 pm    Post subject: Reply with quote

Joe, that's what I said. and I was very surprised at the results. This is the first good reason for me to change my mind about installing these tabs. It was the proof I was looking for. That said I may still get the QL tabs. The amount of lift at 55% deployment may very well be more then enough for my boat and use and I would never need the extra lift of the other tabs. I do know that I never use the last 20% of tab deployment on my 22. Its not needed to get the bow down and in fact if I fully deploy my 22's tabs it cause's bow steer. So now I have to decide if its enough.

My need is mainly trim from side to side. I can control my bow angle with the motor trim just fine at any speed. My time to plane is great and my top speed is 40 mph which I like to have but rarely use. its the side to side that I have to correct and to tell the truth I really just need one as I always tilt to the port. but they sell them in sets so that's what I will get.
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