Trim tabs

[wayno60]

Ive noticed that the Bennett trim tabs have two rocker switches. Im taking that means you can adjust each tab separately??
For those that have them how often do you have them set at different heights? why would you have them at different heights???

cheers

[tenzing]

Yep , each tab separately.
Almost always at different heights to compensate for a lean side to side of the boat due to weight distribution , leaning into the wind, your sons fat arsed mates all in one rear corner etc.
Wouldnt work with just one switch
Cheers
Brendan

[johncar]

Wayno, I and many others use their tabs for keeping the boat level while underway to achieve the best hull performance. When my boat is running level then I tend to just use the engine leg trim to achieve bow up or down. In extreme conditions I may use the tabs to aid in some more bow down but they can still often be set at different levels to each other to get best results depending on sea and wind conditions.

[wayno60]

cool thanks guys.

[Lancair]

Im going to chime in and say put them on your boat.
I love mine on a 5.65m boat and use them almost every trip, like Johncar and others have posted, to keep the boat level and the hull working as it should. I dont think Ive ever used both of mine to keep the bow down, motor trim will do that better. The only time Ive had both full down was when trying to maintain a fast troll speed, like 9-10kts, they helped lift the stern and I could back off a tad to maintain the speed.

Lancair

[Smithy]

I adjust mine about every 4-5 mins on average. Any little wind gust or customers moving about, whatever to upset the trim.

[wayno60]

I suppose i do the same thing in the little tinnie. I look at how the wash is coming out from under the boat and it might only be that i have to move my butt an inch or two to get it coming out even.

[gofishin]

.... I dont think Ive ever used both of mine to keep the bow down, motor trim will do that better....

Actually, that is not quite correct. There is a saying commonly used; “motor trim is to trim the prop, trim tabs are to trim the boat”. It’s all about the physics/hydrodynamics and what is most efficient to use in what case/situation…


For the greatest efficiency for a ‘bow down’ requirement, the prop is best trimmed (by motor trim) to the ‘sweet-spot’ for the conditions (i.e. parallel to, or slightly below, the horizontal), and tabs used for any lateral levelling AND bow down requirements of the hull.

Obviously tabs can’t raise the bow any further once they’re fully retracted, so prop thrust must be used for this scenario. However using propeller thrust ‘off-line’ to trim the bow down is a less efficient means of achieving this outcome compared to using tabs – assuming the tabs are correctly sized for and installed properly on the hull etc.

However, there may be times (especially with as$e heavy boats/loads), when you may just need to use both.

If a foil is involved I guess this theory is muddied a bit, is it acts like a trim tab too when the motor/prop is trimmed off-line/down/in, but let's not go there.
Cheers
Brendon

[Fed]

What gets me is that it seems only big boats need tabs, they must all be dogs to start with. Meanwhile there's 1,000s & 1,000s of smaller boats buzzing around that don't even think about these things.
What about bow lifting & stern lifting props, have you ever heard anything so silly.

[gofishin]

What gets me is that it seems only big boats need tabs, they must all be dogs to start with. Meanwhile there's 1,000s & 1,000s of smaller boats buzzing around that don't even think about these things.
What about bow lifting & stern lifting props, have you ever heard anything so silly.

No not at all silly! My use of tabs to provide a bow-down trim when it gets a bit lumpy has probably halved since going to stern lifting props (4 blade). Performance benefit was huge, just because of the better normal trim and not wanting to bog/squat down when it gets real lumpy - amongst other things.

And yes, even sub 6m boats can benefit immensely from tabs, so I agree with Lancair and the others 100% in that regard. Tabs would be the first option I would tick no matter what the boat - well 5m + anyway! when you have had tabs you can't go back

[FordGT]

what about on a 5m boat? any benefit there?

[Chimo]

Hi FordGT

I fitted tabs to a five and a half M alli and they were good value. Planned slower, stayed level, bow down if desired, improved ride thru chop etc. etc

In short, all the usual benefits.

Cheers
Chimo

" when you have had tabs you can't go back " so true "Gofishin"

[Lancair]

Gofishin, I agree with you re correct trim procedure and the usefullness of trim tabs to do this. I guess I say the motor will do t it better because its one switch to move and with hydraulic steering I dont really notice any adverse helm force.

[Smithy]

They should be on every boat! If you want to see little boats with tabs look at all the American flats boats. They have them in all their 4.5-5.0-5.5-6.0m boats. The thing with boats up to say 5.5-5.8m is you can trim them easily by moving an esky here or there or moving your bum 2" in the case of a small tinny but once you get up in size it takes more effort and you would have to move a person or move an esky from east-west to north-south on one side or the other etc. In my case with customers, they sit all over the place and instead of saying you sit here and don't move and you stand there and don't move I let them do their thing up to a point and just use my tabs to tab it out. Easy!

[julian1]

every mono hull will benefit from Trim tabs, the old myth that if a boat needs them then its a dog of a hull is total BS