Trim Tabs Princess V39

[47GC]

Hi all,
I’ve got a question in trim tabs. What should the default positioning be on trim tabs when leaving marina etc. should they be all the way down, in the middle or all the way up.

I’m on legs, have those at -5, when leaving then adjust to 0 when I get onto plane. Then I start playing with tabs but never sure exactly what best practise is when trimming.

 

[Portofino]

They should be up .This is because they should be stored up in the interest of ram hygiene.

As you say trim the legs in when transitioning to getting up on the plane then trim the legs out once up .Watch the speed change as you set the best trim angle with the legs .


The trim tabs are for adjustment of the bow in a chop , you put them down to present the finer, sharper bow area to cut waves in a head sea .Conversely trim the bow up ( tabs up ) running in a following sea , ie waves on the stern .This is to prevent ,or lessen the chances of bow steer .You want the bow up and out of the waves .

In cross winds , the waves and wind on the sides you might use one side more down the lee side to correct a tilt and get the boat to run flat .

Your boat is powered correctly and not overweight with cruising stores , correctly balanced you should NOT need any tab to get it on the plane.
Sure use the leg trimmed in , that’s what it’s for .

Any shaft drive boat that needscjudicious use of trim tabs down to plane is basically under powered , incorrectly balanced or overweight, overweight being linked to under powered .
They ( hull designers ) have amongst other things a few little subtle details in there armamentarium to increase stern lift with out the need of the helmsman to use shed loads of tab down .Stuff like lifting pads at the stern , wider chine flats , wider more pronounced lifting strips , running further aft .etc etc .Careful weight distribution ie setting the the centre of lift and centre of gravity as close as poss together etc etc .This latter point is particularly evident with the engine positioning .

Anyhow you are stuck with what you have got !

They should when planning transitioning ideally just rise up pretty flat and level with a tad of bow rise then once up over the hump settle back to ideally a less than 5 degree hull angle to the water …..no trim tab needed ie left in position zero .
I know I will attract hate form a section a small section of the forum for saying this ^^^ .But I tell it as it is .

I see a lot do not run under 5 degrees .I hear a lot need zillions of tab to lift the stern.

Tabs as i say should be used to adjust the bow angle in waves or lateral balance in cross winds.
Trim tabs / flaps down all the time act as brakes and slow it and burn more fuel .

 

[47GC]

They should be up .This is because they should be stored up in the interest of ram hygiene.

As you say trim the legs in when transitioning to getting up on the plane then trim the legs out once up .Watch the speed change as you set the best trim angle with the legs .


The trim tabs are for adjustment of the bow in a chop , you put them down to present the finer, sharper bow area to cut waves in a head sea .Conversely trim the bow up ( tabs up ) running in a following sea , ie waves on the stern .This is to prevent ,or lessen the chances of bow steer .You want the bow up and out of the waves .

In cross winds , the waves and wind on the sides you might use one side more down the lee side to correct a tilt and get the boat to run flat .

Your boat is powered correctly and not overweight with cruising stores , correctly balanced you should NOT need any tab to get it on the plane.
Sure use the leg trimmed in , that’s what it’s for .

Any shaft drive boat that needscjudicious use of trim tabs down to plane is basically under powered , incorrectly balanced or overweight, overweight being linked to under powered .
They ( hull designers ) have amongst other things a few little subtle details in there armamentarium to increase stern lift with out the need of the helmsman to use shed loads of tab down .Stuff like lifting pads at the stern , wider chine flats , wider more pronounced lifting strips , running further aft .etc etc .Careful weight distribution ie setting the the centre of lift and centre of gravity as close as poss together etc etc .This latter point is particularly evident with the engine positioning .

Anyhow you are stuck with what you have got !

They should when planning transitioning ideally just rise up pretty flat and level with a tad of bow rise then once up over the hump settle back to ideally a less than 5 degree hull angle to the water …..no trim tab needed ie left in position zero .
I know I will attract hate form a section a small section of the forum for saying this ^^^ .But I tell it as it is .

I see a lot do not run under 5 degrees .I hear a lot need zillions of tab to lift the stern.

Tabs as i say should be used to adjust the bow angle in waves or lateral balance in cross winds.
Trim tabs / flaps down all the time act as brakes and slow it and burn more fuel .

Thanks. Makes sense to me now. I’ll try that next time we go out.

 

[Portofino]

Runs really well on this vid .They have a nice hull .

See how the bow spray rails morph into wider and ave lifting strips as they go back .

 

[jrudge]

Tabs should be up. Simple reason is that if you reverse with them down you are likely ( over time ) to rip them off as they will act as a speed brake.

You trim to keep the boat flat. You don't want a bow high boat.

With outdrives most of your trimming is going to be with the drives. The aim in the cruise is to have the prop pushing backward not up to down.

In a straight line trim the drive for best speed. Then see if the tabs will improve it. They may or they may not. On my boat I gain about a Knot and drop fuel consumption. Every boat is different. On yours it may make no difference or slow it down.

The main other reason it use them is to lower the bow if going into the waves. It stops it rearing up. Allegedly you can use one tab to right a list with a beam sea but I have never had a list to correct so whilst theoretically correct I am sure it has no apparent practical use

 

[47GC]

Thanks @jrudge. All set up. I’ll test next time we go out.

 

[marcochi76]

Runs really well on this vid .They have a nice hull .

See how the bow spray rails morph into wider and ave lifting strips as they go back .

Yes, I agree, wonderful boat
Here other pics of the hull, where we can clearly see the chines and strakes

 

[marcochi76]

and here we can see the different design, compared to similar sport-cruiser on the right.

 

[PowerYachtBlog]

Trim tabs always closed, stern drives all down as they tend to obey better in reverse if are all in the water.
Also for reduced stress to trim rams it is better to drop the drives down when minimizing speed to go down from the plane.

 

[PowerYachtBlog]

Runs really well on this vid .They have a nice hull .
See how the bow spray rails morph into wider and ave lifting strips as they go back .

She is running ok, but they are doing quite a few corrections in the last part of the video when the wave size is about one meter....

 

[MapisM]

and here we can see the different design, compared to similar sport-cruiser on the right.

Waddumean, exactly?
I don't think that 1 spray rail less on the Atlantis is going to make a day and night difference, neither for better nor worse.
As opposed to shafts vs. outdrives, which matter much more, obviously.

 

[MapisM]

She is running ok, but they are doing quite a few corrections in the last part of the video when the wave size is about one meter....

+1, and I don't think those waves were really 1m, anyway.
BTW, she appears to be running more bow high than I would like.
Though of course that might be due to sub-optimal trimming, so not necessarily a boat fault.

 

[MapisM]

On my boat I gain about a Knot and drop fuel consumption.

Out of idle curiosity, what flaps position works better for you, at say 20kts?
In mine, out of 12 degrees total downward excursion, at 20kts the boat still likes 8 deg or so.
Progressively reduced (=raised) to neutral at and above 25/26 kts.

 

[QBhoy]

Not sure I agree with some of the advice around the outdrive trim position. Not exactly anyway. When on plane and cruising or more.. you’d want the outdrives in a position of trim that allows the most efficient form. This often or mostly means that the trim of them would be positioned up a little from the 0 or neutral angle. This allows them to lift the hull…in suitable conditions of course. It’s a variable thing for sure though.

 

[Mr Googler]

In all the outdrive boats I’ve had (5 in total) , tabs are for roll balance

Use the outdrives for bow pitch

my experience anyway.

 

[Portofino]

In all the outdrive boats I’ve had (5 in total) , tabs are for roll balance

Use the outdrives for bow pitch

my experience anyway.

On a lardy 8/9 ton Porto 35 with KAD 300 s I found once up and I trimmed them out looking at the speed , you could hear the engine note change .It sounded laboured if the drives were wrong to the hull .

So to change the bow angle , lower it in head seas , or raise it in following tonking along at 26 knots I use the tabs .
Obviously I think we all agree to lateral balance it as well in X winds .


In hind sight the labouring noise was prob a sign of overloading .No EGT gauges or load gauges , but on a little lively outdrive boat you don’t need them as you, well I could hear the engine note changes .As said make drive trim adjustment s so they sounded better .


A modern CR engined stuffed to the gunwhales with electrotwackery like the D6 in the OP boat has probably has the computing power to adjust the fuelling and phaff with cam timing and other stuff. So maybe on todays outdrive sports cruisers you don’t hear such a distinct change of engine note ? They take the potential overload scenario in there stride .

 

[marcochi76]

with my V39 I have similar experience as Porto.
Once the boat is on plane (2800rpm, 25knots), if I raise the legs I see the efficiency decreases (nm/lt)

I tried to play with the tabs and I found that if I raise the legs I need to lower a little the tabs to compensate.
I am not certain this is the correct way of doing it...

I did this as I would prefer to run the legs horizontal (0°) instead than all negative to protect the transmission.

 

[47GC]

When it comes to the legs, yes arround 25 I normally lift the legs to 0. I haven’t tried further up. But 0 seems to make her run best all the way to 39 knots.

 

[marcochi76]

When it comes to the legs, yes arround 25 I normally lift the legs to 0. I haven’t tried further up. But 0 seems to make her run best all the way to 39 knots.

I have never seen 39knots with mine!!!
Yours is fast!

 

[47GC]

I have never seen 39knots with mine!!!
Yours is fast!

Small video from earlier this season.
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