physics of QL Trim (Tab) System – how does it work ???

[uripper]

Was considering Bennett trim tabs for my old Haines 560SL but it has a custom made pod & modified transom, so am very restricted with transom space / aft mounting options. Can be done but it will be a real pain in the ar$e. So am now looking at the QL Trim System as they seem much easier to fit – no hydraulic lines, pumps etc – all electric.

Have tried internet research on the QL’s but coming up with bugger all other than general blurb (Google /Ausfish /Fishnet/ US boating sites etc etc). Even the Volvo Penta distributor sites have very limited explanation – other than that they are the next best thing to sliced bread. Like to find some commentary /research on the “aerodynamics’ of how they create lift, performance comparisons etc etc. The lift /drag principles of a Bennett or other plate type trim tab seem fairly obvious but the QL’s are simply vertical blades that lower into the water approx 25mm at the transom & ‘muggins’ here just can fathom the physics of it. … “they are counterintuitive to a layman, but if you understand something about fluid dynamics, they make a lot of sense” ... yeah, well I sure don’t get it – yet, but am keen to learn more.

It seems the QL system has been around for a while … Aug2005 : “The newly launched QL Boat Trim System has been awarded a prestigious innovation award in the US. The trade association for marine manufacturers, NMMA (National Marine Manufacturers Association), jointly with a jury of international boating journalists, selected the QL Boat Trim System as the best innovation in the propulsion category”. Gees, we seem to be slow in AUS to catch on to new innovative boating /fishing techniques – (e.g. the yanks have been using plastic lures in various forms for over 20 years)

Fisher boats (awesome machines) offer QL’s as part of the package & feedback from Fisher owners with them on seems very positive. It appears other boat manufacturers (incl Boston Whaler USA, Quintrex, Mustang ) are accommodating them as well.

This is an interesting discussion … “Shitcan the Lencos, sell the Bennetts and buy the Volvo QL Trim System. Easy to install, simple to use, almost intuitive and they work beautifully” ... http://www.sportfishermen.com/board/f27/trim-tabs-electric-vs-hydraulic-34921.html (http://www.sportfishermen.com/board/f27/trim-tabs-electric-vs-hydraulic-34921.html) - seen this website format before ??

So …. if there is anyone out there in Ausfish cyberspace that “steer” me in the right direction (pun intended), then would greatly appreciate any “learned” advice – thanks again in advance - MalM

[ozbee]

In the ideal conditions yes personally they may be fine but conventional tabs have the effect of extending the length of the boat as the water is pushed over a longer period it is more likely to hold a boat better if a wave drops out under you as in a side on sea. In deep v monos many people think the most important thing is holding the nose down. yes it does but very important is the ability to tab down on the side leaning down to raise the v to be dead straight up an down so as to create best ride . The idea seems to come and go over the years so i feel they ain't the ducks nuts .It would be interesting if someone who has had both on the same hull to reply.

[Angla]

I would think that from the picture it could be assumed the effectiveness is the same as a conventional trim tab as we know them, in a forward motion. Maybe there are other positive effects like imagine when reversing the boat it would stop the boat from digging down at the stern due to the angle of the tabs or even when a wave hits on the stern of the vessel it cannot pressure the tabs downwards

Chris

[Chimo]

Hi uripper

I didn't bother registering on the other site to read the thread re the Lencos but I have a set of them on my Vagabond and have had no issues.

They work well and level the boat side to side which keeps the bow cutting rather than smacking on the shoulder as one cuts thru chop.

They also do create a "longer boat" and one can lift the bow or shove it "in" if thats whats required. Have had no problems in reverse but I dont try to back up so fast to see if I can drown the tailend.

No hydraulics so fairly simple instalation.

To each his own I say!

So whats the problem with them?

Cheers
Chimo

[ozlongboarder]

I have a set 300's on my Bertram 25 for over 6 months now. They level the boat port to starboard with ease when the wind or passengers cause the boat to lean. Easy to operate, auto retract when engine switched off. Easy to install. My boat lives on a mooring. I just give them a wipe over every few weeks to knock off any growth.

I have not had any other tabs but these work well. I believe Riviera are now fitting them as standard on there cruisers. Time will tell how they last submerged in salt water all year round.

[Greg P]

Mal - I had M80 Bennets on my Sportfish. Now with QLs on the Fisher and I would never consider Bennets or Lencos again for future boats.

With the Fisher I only need them for wind heel and the response is great and they are far easier to set than Bennets especially with the control panel. One huge advantage is if you are in a wind heel situation and you want to lower the bow, the control panel maintains the initial setting to keep the knife straight.

I dont know about the extra length thing regarding the bennets/lenco wings - maybe true for some hulls but personally I would rather have a clean transom than have something for line to cut on or people to stand on.


Cheers

Greg

[uripper]

thanks all

ozlongboarder & Greg P

do the QL's allow your hulls to plane at slower speed??
do you have fuel flow meters?? - any improvement in fuel consumption??
do you think the drag created is more than compensated by less drag from the hull & motor??

MalM

[ozlongboarder]

Yes maybe a knot or two slower and still be on the plane.

I have not installed my fuel flow meter yet...its siting on the bench along with a few other jobs to do.

As for drag its hard to tell really until the flow meter is installed. Logically you would think its going to create more drag then a regular tab but it creates a pressure wave in front of the unit under the hull so it may not be creating as much drag as what you think.

The ultimate test would be to fit QL's then Bennets/Lencos to the same boat and run some tests on speed and consumption.

[Chine]

Interesting discussion considering so many people have inherent trim problems owing to heavy four strokes, inability to move weight forward, short waterplane areas etc, etc.

Far from being an expert on hydrodynamics it would appear to be a similar concept to the aircraft wing. At lower speeds the shape and surface area of the aerofoil section is altered using slats and flaps to increase lift. To achieve this the air molecules passing over the top of the section are faster than those below resulting in a pressure differential......hence lift.

It may be drawing a long bow but looking at the diagram detailing the vertical blade indicates that it slows the water velocity under that section of the waterplane and induces lift. That appears to be represented by the concentrated high pressure just for'd of the blade.

A very amateurish attempt at some sort of explanation. I will put it up for discussion.;D

[Getout]

I still reckon that some of the effect of trim tabs is due to the drag produced by the tab. This causes a corresponding opposite helm reaction to maintain heading. Effectively the boat is being heeled by engine angle whilst travelling in a straight line.
Try taking your hands off the wheel and then trimming down one tab. The boat slews to that direction.

[Lucky_Phill]

I believe AMM are fitting them to their larger range of boats, maybe worth a try contacting them locally.

Phill

[Reefmaster]

You will find a huge percentage of boat builders are now using these tabs and there simple but yet effective operation soon made them the number one trim system around. After using various systems I would never consider using anything but the Volvo QL trim system and although it was hard to workout how these tabs can be so effective being that there a vertical blade it soon proved that this product was a step a head of the rest. They have become extremely popular overseas and with large boating manufactures like Riviera, Quintrex and many other builders now fitting them you can feel confident that these are a great choice.

I called Volvo about these tabs when I was first looking around for a system and received some great information and explanations about the Volvo trim system from Paul Nebauer who is the national sales manager for Volvo. His informative conversation and detailed email of the trim system was enough to convince me that this would certainly be a perfect choice.

Mal if you would like some detailed info on the Volvo trim system then just PM your email address and I will email it through. It's a very large file size so I can't send it if you have a dail up internet connection.


Just another note - In all the cases I have seen, these volvo tabs only have to be put down a fraction to get the required trim you need and most find they don't lower them down more then level 2 to 3 on the gauge. (has 7 levels) Extremely effective.

Regards,
Greg

[Reefmaster]

Here's some info but unfortunately I was unable to attach the 2 diagrams that go with the following info but you will get the idea with out them.

Why does the QL Boat Trim System cause less drag than conventional trim tab systems?

Background

Two types of drag, the wave drag and the frictional drag, affect a boat hull moving forward in water. At planing and semi-planing speed, the two types of drag are about equal in size for most types of boats, and the aim is to quickly reduce the wave drag (can be seen as a hill or hump to overcome), in order to reach the desired attitude, resulting in comfortable, safe and economiccruising.

How it works

The QL Boat Trim System and also the conventional trim tabs are used as a lifting aid at the boat’s stern, in order to quickly overcome that wave drag. The fundamental working principle of QL Boat Trim System is similar to that of trim tabs, although there are several important differences.
The QL system generates a high lifting force to a planing or semi-planing boat, by intercepting the water flow at the transom with a blade - the interceptor, see figure 2. Even when this blade is just projected a small distance below the transom edge, the upstream effect of the water flow is substantial and the centre of the pressure acts more aft on the hull, compared to that of conventional trim tab. This provides a larger actuating trimming moment to the boat.

Conclusion

The projection or depth of the trailing edge of the flap of the conventional trim tab system is several times the corresponding depth of the interceptor blade, when producing the same lifting force (see figure1 and figure 2). This means that the QL Boat Trim System provides reduced frictional drag compared to that of conventional trim tabs.

[chop duster]

What are peoples thoughts about these tabs on a high speed vessel?
Haven't seen or heard of any being used on racing or high performance applications?

[uripper]

Thanks to eveyone for input on this - please keep it coming. As has been said, I too think it is likley that many more boaties will be contemplating these issues with the inexorable growth in 4stroke popularity - particularly for those repowering.

Regardless of which system, most manufacturers claims seem to include :
*Correct listing (caused by wind /wave action, uneven weight, prop torque etc)
* Get out of the hole and on plane quicker
* Plane at slower speed
* Better fuel efficency
* Tow heavier weight (skiers /tubes)

Think that boats with with good pitch & attitude (eg Fisher) will greatly benefit from QLs to correct list tendancies of deep V hull. My old girl however has a heavy rear end = bad attitude. She really needs rear lift, particularly at lower speeds. For the moment, can't see how QLs are going to deliver that.

Guess the bottom line is what system suits a particular hull /motor combination. More importantly ... will the drag imarted by the system (they all do it) be significantly repaid by the decreased drag of hull & motor at a higher attitude & more level pitch ??


A propeller is designed to force the boat forward. When trimming the boat with the prop, the prop must not only push the boat forward but alter the pitch as well (bow and/or stern up - down). In this situation, prop slippage is greatly increased thereby wasting energy. Trim tab systems can facilitate the hull and motor to travel at a more level pitch and higher-in-water attitude, thus imparting prop thrust more horizontally & effectively.

MalM :-/

[ozscott]

I considered Lencos, Volvos etc and settled on Bennett 120 sport tabs for the Vagabond. I liked the idea of hydraulic and stainless steel. I also liked the idea of extending the waterline length (even at rest) for some extra hydrodynamic lift in particular on the plane. I have found that these tabs have transformed the old girl and makes her glue down to the sea - it literally feels like its glued to bigger chop and swell compared to the old state. Having said that the Volvos might have done the same I dont know, but having read the basics of hydrodynamic lift for fast boats I think there is something in having extra lifting area and the 2 sizeable lumps of stainless do provide that..

Cheers and good luck - looks like and sounds like its going to be a nice rig Uni'

[Nowahh]

Hi Guys. A very interesting conversation. I too am looking at the QL trim tabs and have found argument both for and against. Some suggest a reliability problem but as has been pointed out above, many of the large boat manufacturers are fitting them as standard.
Can anyone tell me the cost for a set?
Thanks.

[Hell Boy]

Hi Nowahh,

I had a look at them last week at leisure marine, the price i think was just over $1200 from memory.






Hi Guys. A very interesting conversation. I too am looking at the QL trim tabs and have found argument both for and against. Some suggest a reliability problem but as has been pointed out above, many of the large boat manufacturers are fitting them as standard.
Can anyone tell me the cost for a set?
Thanks.