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Author Topic:   Smart Tabs - gas shock trim tabs
wetdogsoup posted 02-19-2004 11:18 AM ET (US)   Profile for wetdogsoup   Send Email to wetdogsoup  
Has anyone used or seen these in action?

Sounds like an automatic trimming, affordable trim tab solution for the small boat (under 21')


JohnJ80 posted 02-19-2004 03:51 PM ET (US)     Profile for JohnJ80  Send Email to JohnJ80     
I have seen them, but never owned them. I do have trim tabs on my boat and love them.

I can also tell you that how I use my tabs is widely different depending on conditions and loading in the boat. These tabs don't know anything about that except the force of the water moving them up and down. So, you would have a hard time optimizing the trim of the boat and the efficiency because of the variability of conditions.


wetdogsoup posted 02-19-2004 08:58 PM ET (US)     Profile for wetdogsoup  Send Email to wetdogsoup     

Do you really fine tune your tabs that much to the conditions (this might be a stupid ? since you are an engineer :)!


Moe posted 02-20-2004 12:11 PM ET (US)     Profile for Moe  Send Email to Moe     
You guys are the engineers, but here's where I see the difference. Feel free to point out any error in my thought process. I'll learn from it.

The amount of lift, and hence drag, of tabs is dependent on angle of attack and speed, right?

At some point, as speed goes up, the springs in the SmartTab gas struts begin compressing, causing the angle of attack to decrease. Whether total lift, and hence total drag, then remains constant as speed increases (and angle of attack decreases), or whether it still increases at a lower rate, can't be determined without a lot more info.

If the total lift and drag being generated by the SmartTabs is remaining constant as the springs increasingly compress (and the angle of attack decreases) with increasing speed, the portion of the lift applied to the boat has to be decreasing. And that could be okay, with the hull providing additional lift as speed increases.

But the point is, the SmartTabs have to be providing lift, and hence be creating drag, whether that lift is being applied to the hull or it's being applied to compress the springs.

The SmartTabs are always creating lift and drag, where electric or hydraulic tabs can be set not to do so.



kingfish posted 02-20-2004 03:02 PM ET (US)     Profile for kingfish  Send Email to kingfish     
Right - and additionally, full grown trim tabs can be trimmed differentially from one side to the other, to accomodate balast, prop torque, wind lean, etc.
andygere posted 02-20-2004 03:41 PM ET (US)     Profile for andygere  Send Email to andygere     
It seems to me that if you are going to go through the trouble of drilling your transom and mounting tabs on it, you may as well get the real thing and be able to adjust them to optimize performance. If you are just looking for a low cost way to improve holeshot and lower planing speed, I'd go with an anti-cav plate fin like the Doel Fin or Whale Tail.
JohnJ80 posted 02-20-2004 07:31 PM ET (US)     Profile for JohnJ80  Send Email to JohnJ80     
I agree with what Moe says. Let me give you a practical example:

light breeze (10kn or so). For a full power run down wind (WOT), no tabs will be required. The boat has enough power to hold itself very flat, and the tail wind doesn't force a lot of air under the boat (quite the opposite). When I turn around and run into the wind and light chop, the ride will be different and may require a touch of tab to keep the bow down a bit.

The other example is take that same run downwind. Suddenly I see a large set of boat wakes heading toward me. I would put a bunch of tab in to bring the bow down for its fine entry to get through the waves. Then after I was through them, i would take the tab off again (raise). So, I only needed the drag for a bit to adjust trim. The smart tabs would have the drag there all the time - even when I don't want it.

The tabs do make a substantial and significant change to the attitude and ride of the boat. You can feel it in the steering and hear it in the loading on the motor. I think the bigger the water you are on (chop and conditions) the more you will appreciate what they do. For small inland lakes, probably not a big deal.

So, I don't have to adjust the tabs that much (engineering geek factor aside), but unless the conditions are identical, loading of the boat is identical, then there are different tab settings (more or less lift/drag). The result is that I think you would have a very narrow window of performance where the smart tabs are properly adjusting the trim of the boat.

The tab manufacturers all tell you to run your boat at WOT (usually maximum hull efficiency through the water) and try to replicate that trim position with the tabs. At that position, you usually don't need tabs anymore. These smart tabs will still be pressing on the water in exactly the scenario that Moe describes.

These things (Smart Tabs) are not all that cheap either ($190 for 12x9 Smarta tabs vs $450 for Lenco 12x9s). If you are going to drill the holes, I'd just install the real thing. They are easy to install (Lencos, can't speak for Bennetts, don't have 'em).


Lars Simonsen posted 02-20-2004 09:22 PM ET (US)     Profile for Lars Simonsen  Send Email to Lars Simonsen     
I thought briefly about getting the smart tabs for my boat, but, like andygere said, I figured that if I was going to drill holes in my transom, I wanted something I was certain I'd be happy with. So I just recently got the Bennett M80 sport tabs for my Dauntless 18. They cost me $400 delivered to my doorstep (I got them at The installation was pretty easy. My neighbor and I installed them over the course of two weeknights. Total time was about 4 hours. The hardest part was drilling two 3/4 inch holes in the transom for the hydraulic hoses. Drilling the holes was itself not hard, but overcoming the aversion to putting holes in my boat was difficult. I used plenty of sealant and everything fit together like a puzzle. I'm real pleased with the installation.

The trim tabs look extremely well built. I haven't had the opportunity yet to take the boat out in any conditions that would really test the tabs (I just put them on two weeks ago). I'm taking the boat out tomorrow to do a little striper fishing, and I'm anticipating that it will be a bit windy. So hopefully I'll get to really try them tomorrow.


wetdogsoup posted 02-21-2004 10:51 PM ET (US)     Profile for wetdogsoup  Send Email to wetdogsoup     
Ok, Ok!

Much wisdom have I seen in this thread, so I'll stop trying to be frugal and pony up for the real trim tabs.....

that said, do you guys use a console mounted trim tab position indicator, or just go by feel?


Lars Simonsen posted 02-22-2004 05:43 PM ET (US)     Profile for Lars Simonsen  Send Email to Lars Simonsen     
I don't have an indicator on mine. So I'm going by feel for now, and it's immediately obvious when you have them out of whack (i.e. one down more than the other). You can also feel when you pull them flush with the hull or out of the water (by the reduced drag, if nothing else). An indicator would be nice, but I suspect that adds a fairly significant amount of cost. I don't think an indicator is necessary, just an "added luxury."


Lars Simonsen posted 02-22-2004 05:45 PM ET (US)     Profile for Lars Simonsen  Send Email to Lars Simonsen     
Also, I would highly recommend (I think that's the right web address). They had the best prices anywhere for the Bennett Sport tabs (which are specifically designed for the smaller, trailerable boats), and they shipped immediately. I ordered them and had them delivered within 4 days. I was very impressed.


kingfish posted 02-22-2004 07:20 PM ET (US)     Profile for kingfish  Send Email to kingfish     
Bennett is not the only mfr. that provides trim tabs for smaller trailerable boats - Lenco does too, and Lenco has the added advantage of having less hardware so they are easier to install, and being electric you don't have to give up space on a small boat for the hydraulic pump. Lencos are currently what Whaler is installing at the factory, and I can personally attest to their good performance, although on larger boats than being discussed here (22' and 25").

I don't think you'll find any need for the extra expense of an indicator, unless you're just gadget-oriented (like me); they're not necessary.

JohnJ80 posted 02-22-2004 08:05 PM ET (US)     Profile for JohnJ80  Send Email to JohnJ80     
I don't think that you need an indicator - especially for what both companies are asking for them ($200+). The feel is immediately obvious, you can glance back and see your wake to see as well. More importantly, you just trim until you get the results that you are looking for in boat attitude.

I thought long and hard about installation on these. What came down to it for me was the ease of the Lenco tabs and the lack of hyrdaulics. The hydraulics mean adding an additional component (pump and resevoir), having another fluid level to monitor, and the potential for another fluid spill. Because the Dauntless doesn't have a lot of room for mounting things when you get right down to it, that was a big factor for me. With the Lencos, all you have to do is to pull the control lines through the tunnel and your done.

It took me 2 hours to install the Lenco tabs. I was able to do it all with my Leatherman, a fish tape, and a power drill with hole saw (so pretty simple overall). The expectation of time for Bennetts is somewhat longer from what I have read and there is more fooling around.

In construction, I prefer the metal construction of the Lenco jack screws vs Bennett's plastic pistons. I also like the idea that the jack screws will hold position if they fail. The hyrdaulic cylinders will release if pressure is lost.

I also liked the more finished appearrance of the Lenco tabs (but that is just esthetics).

Arguing against that was Bennett's reputation and long standing customer service. That all being said, I broke a part intalling my Lencos and Lenco Fed Exed P1 the part to me next day. Their tech support has been just as knowledgeable as Bennett and just as available.

Others have had equally good luck with their Bennett's so I think this is probably not an place where you can really go wrong. I think if you can get past the Bennett mounting issue then it is probably a horse a piece.

Anyhow, I'm not trying to start a B Vs L war here (because both are great companies) just telling you how I made my selection.


wetdogsoup posted 02-23-2004 10:28 AM ET (US)     Profile for wetdogsoup  Send Email to wetdogsoup     
Thanks all for the input!

I'll take a look at both the Lenco and Bennett's before installing in the spring.

PS what a nice difference in ride/rpms/top end speed raising the motor all the way to the top hole made - just a matter of caulk and time:-)


JohnJ80 posted 02-24-2004 05:43 PM ET (US)     Profile for JohnJ80  Send Email to JohnJ80     
Raising the motor is a huge deal. For me it was like I got a new boat.

Dealers almost always mount them all the way down or at least too low. makes you wonder if they ever got out and use the products they sell!


acseatsri posted 02-27-2004 07:07 PM ET (US)     Profile for acseatsri  Send Email to acseatsri     
I just found this thread- does anyone have them on an Outrage 18, and if so, did you mount them closer to sides of the boat where the transom steps in about an inch? Was there wood to screw into? I presume you would use 3M 5200 to seal everything up?
JohnJ80 posted 04-15-2004 01:09 PM ET (US)     Profile for JohnJ80  Send Email to JohnJ80     
I assume the Outrage construction is similiar to most of BW's other boats in terms of layup etc...

There is probably wood on one side (port) for mounting a ladder or kicker motor. However, where the tabs mount at the bottom of the hull is where there is a whole lot of fiberglass from mating the hull and the transom. More than enough to mount the tabs. THis is especially true since the forces are in shear to the surface of the transom and not along the long axis of the boat.

Yes, you seal it all up with 5200.

I would call up Bennett or Lenco and ask them about this mounting. In my experience, they have big experience with mounting these on whalers of all models and will be able to tell you the issues. Both are very honest and upfront with the problems and benefits.


rbruce posted 04-25-2004 02:20 PM ET (US)     Profile for rbruce  Send Email to rbruce     
Being a Sport 11 owner, planning seems to be a bit elusive even with my 20 HP motor at WOT. Therefore, has any one of you used these "smart tabs" in such a boat?
JohnJ80 posted 04-25-2004 09:27 PM ET (US)     Profile for JohnJ80  Send Email to JohnJ80     
I think that any of the tabs made are probably too big for a boat that size. Much else to try first.

Have you tried adjusting the vertical height of the motor? How about the angle of the motor to the transom (really easy)? What happens when you move weight forward in the boat, does that help? Does your motor have a fin on it?

I would think you would have no problem making that boat plane with a 20HP motor set up correctly.


Moe posted 04-26-2004 01:15 PM ET (US)     Profile for Moe  Send Email to Moe     
Looking at your pictures at , it appears you have a coupla things working against you for planing.

It's hard to tell, but it appears the motor's anti-ventilation plate is 1.5-2" or more below the bottom of the boat. This is going to push the bow up pretty high on take-off.

It also looks like most of the weight is in the stern of the boat, which doesn't help keep the bow down. Can you remount the battery up under the forward seat and extend the fuel line to get the tank up ahead of it?


rbruce posted 04-26-2004 05:20 PM ET (US)     Profile for rbruce  Send Email to rbruce     
JohnJ80 and Moe:

Thanks for taking your time. The antiventilation plate is level with the hull of the boat. it is a matter of perspective. However, the tank and myself at 85 Kg are in the back. My brother at 85 Kg is in the front and this helped. It takes a while to plane as the motor doesn't seem to be powerful enough. I will try placing the tank beneath the front bunk.



rbruce posted 04-26-2004 05:23 PM ET (US)     Profile for rbruce  Send Email to rbruce     

Do you thing a whale tail would help my motor? The boat only planes at WOT.

Lars Simonsen posted 04-26-2004 08:39 PM ET (US)     Profile for Lars Simonsen  Send Email to Lars Simonsen     
If the antiventilation plate is even with the bottom of the hull, you can probably stand to raise the motor one hole.

I would bet that a hydrofoil would help you get on plane more quickly. I put one on my motor (I've removed it since installing trim tabs) and it did help.

JohnJ80 posted 04-26-2004 09:19 PM ET (US)     Profile for JohnJ80  Send Email to JohnJ80     
Its critical to get the motor mounted at the proper height BEFORE you get the fin installed. If the fin is too low, you make the problem worse since you are dragging even more surface area around under the water. Remember the drag (IIRC) is proportional to the square of the speed. So a little extra can turn into a huge drag. This is going to be even more important the smaller the boat (less waterline to help you out).

When the fin is operating properly, and the boat is on a plane, then the fin ideally should be riding pretty much at the water air interface. It can be a little lower since the water is disturbed by the leg of the motor passing through it. However, it needs to ride on top of the 'solid' water.

I'm not sure about the 11' boat, but whaler recommends on the Dauntless series that the AV plate be 3/4" ABOVE the bottom of the hull. In point of fact, it seems on most boats here that the common knowledge is that this be at 1.5" or so above the bottom of the boat. On mine, (Dauntless 15), that means all the way up.

What you want to do is to move the motor up as high as you can and still keep cooling water and not have the prop blow out in a turn.

Since two guys and gear in the boat is probably a pretty good load, the boat is going to want to sit lower anyhow. So, that also argues for raising the motor higher.

If this doesn't work and the motor is developing full revs, then you might need to look at putting a different prop on the motor. My bet is that this is also probably not right and you might want to get Sal (the prop expert) to comment on the proper selection. If Sal doesn't bite, then call Stiletto Props (they are on the internet) and they can give you a good recommendation about the right prop for that boat and motor.

In parallel, you might want to have the motor tested for leakdown to make sure the rings and valves are ok. If they leak, you can get full revs but not full power.

Looks like a nice boat. I'm sure you are going to have a good time with her once you get this all figured out. When I was growing up, our first boat was a 14' fiberglass boat with a 1969 or so 25HP Montgomery Wards motor (actually, a Johnson I believe) on it. We all used to water ski behind that boat for years. So, I'm thinking that with a 20HP on your 11' boat, it ought to just fly with it all set up properly.

Sounds like a fun project.


keltonkrew posted 04-27-2004 08:40 AM ET (US)     Profile for keltonkrew  Send Email to keltonkrew     
I have a 13'.

at first, my motor was sitting low, with the whale tail.

poor, poor performance.

I've raised my motor, got rid of the whale tail. it is much more responsive although it is nose up for a little bit...much better with 2 people than one.

I just received the smart tabs and will be putting on my 13'. Hopefully mid May I'll be back at the lake and test them and I'll post how it works for my 13'

good luck

JohnJ80 posted 04-28-2004 09:51 PM ET (US)     Profile for JohnJ80  Send Email to JohnJ80     
Since it would be pretty easy, why don't you install the whale tail again now that the motor is moved up? That would be easy to try before you drill any holes.

Bet it helps too.


keltonkrew posted 04-29-2004 08:28 AM ET (US)     Profile for keltonkrew  Send Email to keltonkrew     
because I've filled the holes and painted the lower unit.

From my research, the whale tail keeps creating lift, whereas the smart tabs create lift at slow speeds, then once the pressure of the water equalizes with the hull, they are not creating lift.

There were a bunch of threads on iboats about this very subject and I've done a lot of research, so the whale tail stays off.

kingfish posted 04-29-2004 09:18 AM ET (US)     Profile for kingfish  Send Email to kingfish     
When a motor is mounted at the optimum transom height, the anti-ventilation plate is above the surface of the water and therefore so is a hydrofoil like a Doel-Fin at medium to high planing speeds. That means there is NO effect from the hydrofoil at these speeds; only at displacement and low planing speeds, where it is needed. Maybe a Whaletail is somehow different - I'm simply not familiar with them.

I am unable to to comprehend how Smart Tabs are not creating lift (perhaps a relatively small amount) at high speeds, unless somehow the preloaded springs are released. Are they somehow clear of the water at medium and high planing speeds?

keltonkrew posted 04-29-2004 10:20 AM ET (US)     Profile for keltonkrew  Send Email to keltonkrew     
go here

if you want an in depth conversation on them, call John (number is listed in the site). He will take whatever time is needed for you to understand the concept.

take a look at this post from another forum where someone just put them on;action=display;num=1083178525

cut planing time in 1/2, reduced slow plane speed from 25mhp to 15mhp, gained 1mph....

skred posted 04-29-2004 04:33 PM ET (US)     Profile for skred  Send Email to skred     
KeltonKrew, I raised an inquiry about these tabs a while back and was literally blown out of the place by all the "informed" responses attempting to prove that these couldn't possibly do what they say. I figured to buy a set for my Dauntless 16, install a piece of whalerboard with two (2) screws on each mounting location on the transom, and then mount the tabs on the whalerboard. That way, if they didn't work as advertised/predicted, I only had 4 holes to deal with instead of 14... I think that if they offer a return policy if the buyer isn't satisfied, they'd be worth a try. S'pose I ought to call this John guy?

JohnJ80 posted 04-30-2004 12:01 AM ET (US)     Profile for JohnJ80  Send Email to JohnJ80     
I absolutely don't doubt that they work but they are a broad brush sort of solution and not a fine tune as a trim tab is - i.e. they are a set and forget sort of solution. There is no adjustment on them underway as there is with trim tabs or with fins (if trim and tilt is installed). I'm interested to hear your experiences with them and it would be fun to compare that to other solutions.

What you can't do with these is remove them from the boat trim equation at all like you can do with conventional tabs. For example, if you are going downwind at full tilt, you don't need tabs. But if you turn around and go upwind on the opposite course, in order to maintain the same boat attitude, you probably will. The wind speed added to the boat speed, helps get air under the boat and raise the bow. So, it is common in a boat that porpoises to need tabs to take out the porpoising going upwind in this example, but not on the opposite downwind run. Regular tabs can adjust for this as you can with a fin and trim and tilt. The Smart Tabs obviously cannot be adjusted. The real question, is does it matter and is there a significant performance hit in this case? I don't know and it would be very interesting to know.

If the Smart Tabs are in contact with the water and they are trying to push down, then they are providing lift and drag. My guess is that this lift and drag is nonlinear. The most lift and drag are provided at the lowest speeds since the strength of the spring is a larger fraction of the force provided by the moving water. As the boat speed increases, this force of the water (IIRC) increases as the square of the speed but the spring force provided is a constant. So at high speed, the force of the moving water has to be far higher than the spring force opposing it - i.e. lower lift and drag as a percentage. So, at WOT or high speed there probably is little performance or economy (gas) savings but I would think that if there were an effect it would be in the range just after achieving a plane slow planing speeds. In this range the Smart Tabs would be achieving a higher deflection than may be needed. Again, it would be interesting to know if this matters.

If I am understanding what is being said here about the adjustments that were made , is that you have changed two things (at least from what has been written) at the same time - the motor was raised AND the fin removed. In order to say that the fin didn't work or the motor being raised didn't work, just one of those things would need to be done at one time. It is impossible to tell if the raising the motor or the removing the fin brought the performance change or what the impact of either was.

So before it can be said that a fin would not work here, it would be necessary to raise the motor with the fin and observe the change. Then remove the fin and observe again. Additionally, since the fin and height are not independent, this is even more important to prove that the tail doesn't work.

From an economic perspective this could conceivably lead to a considerably cheaper solution - $105-210 for Smart Tabs and $25-$100 for fins depending on boat and application. Although, heaven knows, if we were all worried about economical solutions we probably wouldn't own Whalers or perhaps even boats at all!

My experience has been that a fin mounted too low - so that it is under the water all the time does significantly hurt the performance and ride. Under water it presents a very significant amount of drag and probably inconsistent lift depending on the pitch and attitude it presents to the water coming at it. A fin mounted at the right height so it planes at the surface on a plane does work pretty well in most applications.

Good luck with your Smart Tabs. Let us know how they work.


keltonkrew posted 04-30-2004 07:58 AM ET (US)     Profile for keltonkrew  Send Email to keltonkrew     
I will be installing and testing mine next weekend (mother's day). I'll post my results. Worse case scenario I get my money back and have to fix several holes - not a problem, I know what I'm doing now :)

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