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The strange approaches Volvo often takes when introducing new products could well be called innovative, but after seeing their " sort of trim tab product" I am forced to believe that there has to be something wrong with them, like Citroen french cars well known to be ugly and strange for the sake of it.
Not only did Volvo designers decide to point their propellers forward in their pod drives against every humane logical approach considering the probabilty of encountering objects in the direction of the movement, not happy enough with THAT, they introduce a trim tab system that works by the principle of introducing a blade perpendicularly into the water flow.
I find this, despite they doing their intended job or not an umbelievable approach since it is well known that any block shaped trailing edge will surely produce a lot of drag due to the vortices and turbulences created, stealing a lot of energy during the process which considering the actual prices of fuel I regard it as an insult to the intelligence of boaters because it is a well known fact that it is exactly the working principle of airbrakes in aeroplanes which main job is to dissipate nergy and slow down planes when landing ( or whenever necessary), so if the system works something I do not dare to doubt it has neccessarily have to be paying a higher price in the form of fuel consumtion that conventional trimming tabs so where are the benefits ?? only in a more compact design ?? at the price of waisting fuel ???
I find this comparable to someone trying to sell me a wheel that is not round pretending that it has some obscure benefits.......
Maybe MR Oreely and MR Darbikrash among many other educated memebers of THT would be so kind as to throw some light with their educated opinions about this ........
When the trailing edge of a conventional tab extends BELOW (perpendicular) the bottom of the hull it causes DRAG and you get the adjustment you were aiming for. (yes, your conventional tabs cause drag ,turbulence and increased fuel use too)
Most here who have them (qtabs) are very happy and report no loss of performance. They also are easy to install, simple in design and far less prone to damage.
Years ago someone somewhere probably said "Why would they make boats out of fiberglass."
I agree with canarianfisher on this one because conventional trim tabs especially ones that extend beyond the transom provide lift by increasing the surface area of the hull, whereas like you said the volvo tabs simply create drag. even conventional recessed tabs push the bow down but are more streamlined shaped than the volvos.
I have a boat with the volvo Qtabs. As an engineer it annoys me. CFISHER is right on. I would much prefer conventional tabs. The Qtabs are adjusted by a stepper motor, quite often I am cycling one side up and down one step with the perfect spot in between the "steps" and not attainable. Give me infinitely adjustable elect/hyd. Also, my boat is small so I would appreciate the small increase in hull area provided by the plate tabs. AND, I cringe at the thought of the drag introduced when I do use the Qtabs. Oh well, I will live with it.
It "looks" interesting? I had the same concerns, what about the forces on the transom when that "blade" extends down into the water? surprised it doesn't tear right off the transom.......
Not only did Volvo designers decide to point their propellers forward in their pod drives against every humane logical approach considering the probabilty of encountering objects in the direction of the movement, not happy enough with THAT, they introduce a trim tab system that works by the principle of introducing a blade perpendicularly into the water flow.
Maybe MR Oreely and MR Darbikrash among many other educated memebers of THT would be so kind as to throw some light with their educated opinions about this ........
I am not Oreely or Darbikrash, but have you ever noticed that 99.999% or propeller driven airplanes use the tractor configuration and not the pusher configuration? Yes, the props are the first things to get struck but one usually assumes that nothing is going to get struck, even though this sometimes happens. From a design standpoint the tractor config is much more efficient than the pusher configuration since the props are in clean air/water.
I am old enough to remember when turbo jets became turbo fans (with the addition of additional fan blades within a shroud) and people accused the designers of being "nuts". Now look at almost every jet engine made. It will be a turbo fan.
I am going now to study their trim tabls to see what the fuss is all about.
I am not Oreely or Darbikrash, but have you ever noticed that 99.999% or propeller driven airplanes use the tractor configuration and not the pusher configuration? Yes, the props are the first things to get struck but one usually assumes that nothing is going to get struck, even though this sometimes happens. From a design standpoint the tractor config is much more efficient than the pusher configuration since the props are in clean air/water.
I am old enough to remember when turbo jets became turbo fans (with the addition of additional fan blades within a shroud) and people accused the designers of being "nuts". Now look at almost every jet engine made. It will be a turbo fan.
I am going now to study their trim tabls to see what the fuss is all about.
jethro1 I'm not going to debate the technology here but your analogy ,you don't see a lot of stuff floating around mid air , like tree branches ,pallets ,or even shipping containers barely skimming the surface ,that are going to run into the forward facing turbo prop ,like you will run into with the boat .
Both types of trimimmng devices cause drag, there is no question about it, but also there is also no question about the fact that the more abrupt change in the direction of the flow of any liquid you introduce, the more looses of energy you produce and I suppose that this is why no one but Volvo was as cheeky as to try to sell that.
And in regards to drag, If the system caused less drag than conventional trim tabs how come that not even one competition boat uses them ?? is it that the racing boys do not want less drag ??
And the reason for saying it now is that it was ABOUT TIME that someone says it.
About what Mr Jethro said about the abundance or not of objects in mid air not being comparable to the probability to find them floating, I could have not said any better ...... they are not comparable if you want Drive pods there is a better and more logical way: propellers facing backwards, the ZEUS way ( and I am not American )I'm not going to debate the technology here but your analogy ,you don't see a lot of stuff floating around mid air , like tree branches ,pallets ,or even shipping containers barely skimming the surface ,that are going to run into the forward facing turbo prop ,like you will run into with the boat . jethro1 I'm not going to debate the technology here but your analogy ,you don't see a lot of stuff floating around mid air , like tree branches ,pallets ,or even shipping containers barely skimming the surface ,that are going to run into the forward facing turbo prop ,like you will run into with the boat .
There are no aeronautic engineers in this forum to commento on this ??
Last edited by CANARIANFISHER; 11-01-2009 at 01:11 AM.
Reason: mistakes
uses them ?? is it that the racing boys do not want less drag ??
And the reason for saying it now is that it was ABOUT TIME that someone says it.
I could have not said any better ...... they are not comparable if you want Drive pods there is a better and more logical way: propellers facing backwards, the ZEUS way ( and I am jethro1
There are no aeronautic engineers in this forum to commento on this ??
Holy Cow Canary...Your a little late with your nonsense, and even more deranged.
The Interceptor style tab has been around for years, and except for some issues with certain stepped hulls, has had favorable reviews from OEMS & users alike.
(See Humphree's)....Right, like their engineers are dumber than you too
Maybe the Engineers on here realize your head is somewhere that they cant sink too, and find it pointless to send a message.
Better & Logical? I'm going to go way out on a limb here Canary, The Zeus Pod is the ONLY Pod I can find with rear facing props. Please show me another, ...must be those crazy engineers building cruise ships that are dumber than you.
As long as its time, or "About Time" that we start bringing up the dirt, lets take a stab at:
Indoor Plumbing- Whoever thought of this had to be crazy. Take the Poop outside where it belongs.
Leaf Blowers- Give me a rake anyday. Now your controlling the leaves..
The Internet- These people are crazy....it will never last.
__________________ It's always a Minivan.
Last edited by High Cetane; 11-01-2009 at 06:34 AM.
If this concept did not work it would not end up on mega yachts, high speed ferries, etc. etc.
From a hydrodynamic view there is no argument - Interceptors are more efficient and adds less drag than a conventional tab system.
Draw back ? They provide no "hull extension". This would be a relevant draw back in a small (short) boat - say below 25' or so - or in a boat with an inherent cgl problem.
Location: Boat,Town Cove, Cape Cod. Live south of Boston.
Posts: 815
This would be a ideal subject for a boating mag to do a story on, take the same boat, motor and publish the performance results of the Q-tabs and conventional tabs.
This would be a ideal subject for a boating mag to do a story on, take the same boat, motor and publish the performance results of the Q-tabs and conventional tabs.
Yes, but that would require an actual test between two boats and these days, most boating mags would much rather just write up a "review" based off of their advertisers, (cough, cough) I mean the boat MFG's supplied information...
This should help explain their theory. That actually looks like less drag than standard planes to me
Well, that is a snazzy illustration you got there and no doubt published by the MFG of the gadget in question. And yes, they are already getting long in the tooth. Nothing "new" here...
But in all of my years of boating with trim tabs, I have NEVER had to lower them to the position shown in the diagram to obtain a proper plane.
It's an obvious exaggeration of the (supposed) facts surrounding the "drag" scenario. And the fact that the MFG has to promote over-exaggerated comparisons, proves to me that they are pushing the limits of snake oil salesmen.
No thanks. I'll stick with my Bennett's or Lenco's...
Unfortunately in this forum lurks Mr Cetone Who is probably "high on something" and so can only write stupiditys ....... God forgive him for being like he is ... he canīt see any farther .. so he only sees that if someone sells something it has to be good ........ like if there were not enough examples on the contrary .......
...lotta' bloodpressure going on here, for a subject like 'trimtabs'.
Never owned anything but the traditional tab, but: the shorter extension/ wider span (aspect ratio?) appeals to me. A high-pressure area is going to form in front of the QL-style tab, effectively forming a 'water ramp' just ahead of it. I don't see that drag will be significantly worse; looks like it could be less, to me.
Unfortunately in this forum lurks Mr Cetone Who is probably "high on something" and so can only write stupiditys ....... God forgive him for being like he is ... he canīt see any farther .. so he only sees that if someone sells something it has to be good ........ like if there were not enough examples on the contrary .......
Its Cetane.
"Stupiditys" ? I didnt even know that was a word.
Me & God are okay.
I can see much further than you. You are the one questioning proven technology thats been out for years. You bring no facts, only your uneducated opinion.
I asked you to show me these "examples" of rear prop pods. You bring more drival instead.
I question your ability to hold a lucid thought Canary.
Strange Volvo approach indeed .. 
