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Message board > Engines > Should I trim the outboard first, i.e. as well as the tabs?

Message 9 of 9
Posted by member Kelvin on Monday 30 July 2012

Hi Tim, I have been otherwise engaged for some months attempting to get engine issues and other stuff sorted. You have made the discovery yourself (and there is no substitute for it) that hydrafoil wings on the engine can and often do give handling problems with or without the presence of trim tabs. In my opinion hydrofoil wings should not be fitted as they are capable of severely affecting steering especially at speed and can lead to accidents. Also if the enging is over-trimmed at speed, especially in a following sea you can experience some nasty surprises as our friend Marwin has previously pointed out. So to sumarise tabs plus hydrafoil wings are, in my opinion, a potentially leathal combination and you have done exactly the right thing in removing them. Sorry about the 10mm socket. kind regards Kelvin

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Message 8 of 9
Posted by member Tim Guest on Friday 13 July 2012

No takers then...! However, I can answer my own question, which may be useful info for someone. Due to the terrible weather this year, it's taken me a while to do some tests. On a fast run with the foils still attached, I found that the boat became dangerously unstable while crossing some wakes - even without much bow-down trim, she bow-steered hard right while banking left, and the only solution was to chop the throttle. The wheel had no effect. As soon as I could, I removed the fins on the pontoon (dropping one fin, several washers, and my 10mm socket into the briny in the process!) On a test today - transformation! Beautifully stable in a straight line and in turns, smoother than she's ever been, on the plane instantly, faster, and with lower fuel flows in all conditions. My conclusion is that the fins caused interference with the tabs. They are Bennett sport tabs, which have to be fitted inset somewhat on the transom due to the kink of the modified transom angle of the Pilot SE. I also believe that the fins were always draggy, as with the correct fin trim, the prop was at the wrong angle, and vice-versa. Also, the fact that the fin lift was all in the centre made the boat prone to some lateral instability. I'm no expert, and it's not at all scientific, and no doubt someone will correct me. However, my advice is, for what it's worth - if you have a Pilot, get tabs, bin fins! Tim.

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Message 7 of 9
Posted by member Tim Guest on Wednesday 28 March 2012

I'm starting the new season with trim tabs (hydraulic) so this is all useful info. My O/B has had hydrofoil fins attached, which have been good for getting on the plane quickly, but may not be helpful with tabs. I'll no doubt find out from experience, and I have replaced the attachment bolts so that I know I can easily remove the fins on the pontoon to test performance without. BUT - I'd be grateful for any advice up front from others' experience.

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Message 6 of 9
Posted by member Marwin In Norway on Wednesday 16 November 2011

An important factor is the size of the trim tabs. If they are big, the boat is very sensitive to the position of the tabs. And again: If you are running with tabs and engine in the lower position and NOT adjusting up by increasing the speed, you can get a very unpleasant surprise!

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Message 5 of 9
Posted by member Peterboo on Wednesday 9 November 2011

in a chopy sea can get it so its slicing through the chop with just the occasional bang

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Message 4 of 9
Posted by member Peterboo on Wednesday 9 November 2011

tabs down engine down ,when its getting up on the plane, engine level off then adjust the tabs the stop the banging ,if bad engine down a tad as well, then if the bow digs in a bit tabs a touch up...if that makes sense to you lol

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Message 3 of 9
Posted by member Marwin In Norway on Tuesday 21 June 2011

I start with motor and tabs down. As planing speed comming up, I regulate the flaps up. Then I regulate the motor up until the propeller starts to cavitate, then the motor a little down. And, as Simon says: "If the ride gets hard and bouncey, trim the engine down, and then if still bad, slow down and push the trim tabs down to soften the ride and hold her on the plane at a slower speed." What you NOT should do is: Full motor trottle, and motor + tabs down when the speed is comming up. Very important to reduce tabs as speed is rising.

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Message 2 of 9
Posted by member Keith on Monday 20 June 2011

Hi, I am a relatively new boat owner: Hardy 20 Fisher, Mercury 80 outboard and trim tabs. Should I trim the engine prior to trimming the tabs? To date I have been leaving the outboard 'fully down' and totally ignoring the dedicated Mercury engine trim gauge and trimming as far as possible on the tabs alone. The engine is apparently set up correctly. Many thanks in advance, Keith

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Message 1 of 9
Posted by member Simon Kidd on Monday 20 June 2011

Keith, I think best to experiment with your set up and see what works best for you. On my boats i've always trimmed with the outboard (or sterndrive) first as this is more efficent. I.e. drive right down and then get on the plane. If she's slow to plane, use the tabs to help and then retract them. Then once happliy on the plane, trim the engine out slightly to reduce wetted area (revs should increase a little). If the ride gets hard and bouncey, trim the engine down, and then if still bad, slow down and push the trim tabs down to soften the ride and hold her on the plane at a slower speed. At the end of the day it does depend on your setup, your load on board, the sea conditions etc. I've run 5 or so power boats of different sizes and types over the last few years and they've all responded slightly differently. Hope that helps. Best Regards Simon.

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