Your experience in flaps/trims settings

[marcochi76]

Hello,
I would like to receive your experience concerning the usage of flaps and trims, preferably on a motor yacht on outboards.
I have a Princess V39 with outboards. I mainly use the flaps to correct the lateral angle of the boat when on plane.
I have never used the flaps to help me go on plane. I just use engine torque.
I usually navigate either at displacement speed (approx 8 knots) or at full plane (> 24 knots), with flaps fully flat (except for fixing lateral angle).

But I have friends me who suggest me to use flaps to allow me to navigate at intermediate speeds (16-20 knots range) and also to help the boat do easier on plane.
That might be interesting when sea does not allow to run at full plane speed.
But I have never really done it fearing to stress the engines/propellers.

What are your experiences?
Do you also combine flaps with trim?

THanks

 

[Portofino]

I think you mean outdrives ?
I just used trim to achieve max speed @ a particular rpm .
I had a Portofino 35 ( 37 ft - 11.7 M Loa ) with KAD 300 circa 2003 modal
The 3200 rpm made about 26/ 27 knots cruise .
Trimmed in about -4 and just left them there .As you say it just got up on the plane regardless of the leg trim .

A cross wind , beam sea the boat used to lean because of the wind pressure .In this case I used the flaps , usually one side to correct the tip .
Also in a head sea ( big waves ) I used the flaps to lower the bow , to get more deeper forward V cutting the sea ahead .
It worked a bit but the hull was inherently a bit of a slammer going fast in a head seas .Often I had to throttle back down to 20 knots .
The annoying superchargers kicking in / out used to occur under 3000 rpm .Approx 28/2900 rpm , a big wave could knock it under .Urgh!
I never went between 8-18 knots superchargers on permanently on supercharger territory.Those Ogura SC s are for short bursts only - clutch engagement between a pre defined rpm range , because they are lightweight low inertia .I only used them to see past 18 knots when they cut out .

Down wind in a big sea I put the flaps all the way up to get the bow up .Sensible anti broaching practice .
Although the boat felt fine , just habit .
I only had 2x 285 Hp ish back in the day for a 9000 kg ++
boat .
Fully loaded I remember using say 1/3 rd down flaps to assist it getting up on the plane .As the fuel burned off I eased the flaps up .
We went all over in it ( weather permitting) CdA to Corsica/ Elba / Italy many times .

It was a bit of a fair weather boat , too flat aft to go fast in big wave.
After a while watching other boats in the same conditions I wanted a better riding boat .Plus the volvo Penta outdrive anxiety started to creep in , increase year by year .I got out before a big bill arrived .

 

[marcochi76]

Thanks Porto for your feedback.
On the user manuel of my boat, it is suggested to keep the outdrives all down (-5°) to help the boat go on plane, and then to rise them to 0 when on plane.
I think this is to have the transmission working straight.

Issue is: when I rise the outdrives even just to -3 or -2, I see the consumption rising. THus I understand the motor is making more effort and cruise is less efficient.
So I keep the outdrives at -5 or -4.
But Is this safe long term for the transmission?

Or maybe I should rise them to 0 and help with the flaps? Never tried to be honest...

 

[Portofino]

Thanks Porto for your feedback.
On the user manuel of my boat, it is suggested to keep the outdrives all down (-5°) to help the boat go on plane, and then to rise them to 0 when on plane.
I think this is to have the transmission working straight.

Issue is: when I rise the outdrives even just to -3 or -2, I see the consumption rising. THus I understand the motor is making more effort and cruise is less efficient.
So I keep the outdrives at -5 or -4.
But Is this safe long term for the transmission?

Or maybe I should rise them to 0 and help with the flaps? Never tried to be honest...

Snap !
I think you are over worrying a little .

No exact “do not do this or that “ in the S/Sker book , just trim them to best performance.
Best performance for a set rpm ( for me 3200 rpm ) was - 4 . I used speed .
As you say if I went to 0 the boat slowed down and maybe the rpm by a fraction .This means more load and thus more fuel burn and strain on the engines .
I would not worry about the UJ joints. Every 2 years when I had my bellows changed by authorised VP tech s they actually removed the whole outdrives , took them into the engine shed , lay them on a table and stripped them over 3 days , used a micrometer the measure stuff , to see if within spec .
Then replaced stuff that failed to meet this spec .As well as pressure tested them .
I had a couple of UJ joints , not a lot €80 + tax + Labour to fit .Plus a few other bits + bats .
But they never broke down over 9 years , just cost a lot of € .
The VP techs at Arie d Boom la Rague looked after mine , same guy Franc, that’s all he did all day remove , strip and test test outdrives . An employee.

Often they would sea trail after refitting as well .

 

[marcochi76]

Got it Porto!
Another question:
Always in the Princess book, it is mentioned to not travel long with the flaps full down, as that would damage the propellers/ legs.
How dangerous is that?

 

[jon and michie]

I adjust the trim tabs to get the boat onto the plane as quick as possible then once on the plane I can back off / retract the tabs to increase the speed because of the less drag caused by the tabs - I can then adjust the drive leg trim to +2 and get an extra 100 rpm

 

[Portofino]

Vaguely remember something about trimming the drives out if the bow was down from full flaps .
Flaps full down increase drag and the slower boat through the water at the same rpm spinning props might lead to more cavitation , as the water flow that cools is decreasing = more likely more surface now getting hotter = cavition risk increases.

But as said in big waves on the bow you needs some flap to lower the bow , perhaps not full down .But then presume the rpm .throttles and boat speeds dropped down to prevent slamming anyhow .

 

[DavidJ]

Hello,
I would like to receive your experience concerning the usage of flaps and trims, preferably on a motor yacht on outboards.
I have a Princess V39 with outboards. I mainly use the flaps to correct the lateral angle of the boat when on plane.
I have never used the flaps to help me go on plane. I just use engine torque.
I usually navigate either at displacement speed (approx 8 knots) or at full plane (> 24 knots), with flaps fully flat (except for fixing lateral angle).

But I have friends me who suggest me to use flaps to allow me to navigate at intermediate speeds (16-20 knots range) and also to help the boat do easier on plane.
That might be interesting when sea does not allow to run at full plane speed.
But I have never really done it fearing to stress the engines/propellers.

What are your experiences?
Do you also combine flaps with trim?

THanks

Your characteristics are identical to my experience with my Sealine S37 and it’s been running without problems for 20 years.
ie outdrives always at -5 and trim tabs just for lateral angle (due to wind or guests in the wrong place)
So don’t worry and enjoy your boating in a very nice boat.