Trim tabs? Should I?

[Lancair]

IMHO There's so many mistaken ideas idea's about trim tabs and their correct use in this thread. A few people have the right idea with prop torque being a MAJOR culprit in causing a hull to lean, esp. to port.

The little trim tab on the underside of the anti ventilation plate plays a MAJOR role in getting your boat to perform best. If it's not set right, everything else is out and Trim Tabs are a band aid solution.

Before you start messing with the trim tab on the AV plate, make sure your boat floats perfectly level when normally loaded with fuel etc. and no one on board.
Basically the trim tab needs to be set, so that at WOT running speed with the motor trimmed to max rpm without venting (no cavitation as its commonly termed), you should feel no bias in the steering force to turn either way. Best tested and set in nill or very light wind situations. At this point the motor is at its most efficient. Anywhere from this point trimming up, you would hear ventilation. Trimming down, will bring the bow down, decrease in RPM and speed, an increase in force req'd to hold the steering straight in a tiller steer or an increase in force to turn to port and easier to turn to starboard in hydraulic steering, older cable etc. types should be easier to feel. With hydraulic steering it can be hard but not impossible to feel the torque. You will also notice the port side lowering as you increase down trim and hold a straight line. This is the prop torque. Once we have that sorted you'll that evenly loaded in light winds the boat will run true.
Once the AV trim tab is set at WOT, you'll be able to find the sweet spot at ANY speed.

Wind from the side of a boat tries to push the boat sideways, the rear end is pretty well fixed to its track in the water by the motor leg, so the bow moves easier. As wind pushes on the starboard side, the bow moves to port, so you turn more to stb. to counter that, effectively your boat is now in a slight stb. turn. What happens in a mono hull when you turn stb.? It rolls to stb. as well. Why? Because the prop not only turns the boats bow by changing the thrust line, but that thrust line to the stb. is below the centre of gravity of the boat, so it pushes it over or rolls to the starboard.

Here's where Trim Tabs like Bennets or Lencos etc. come into play.
When the boat is rolling into wind, its not cutting the water as the hull was designed to do, it's partially bashing a much shallower angled hull side making the ride uncomfortable and not very efficient. Use trim tabs to level the hull.
When pushing into chop or a sea, it's often more comfortable to have more of the front of the hull working, cutting the slop and smoothing the ride. As we saw, trimming down or in will lower the nose and smooth the ride, at the expense of a roll due to prop torque. Use the Trim Tabs to lower the bow but leave the engine trimmed at its most efficient spot.
As mentioned already, in a following sea you want Trim Tabs up and the motor trimmed at its most efficient spot for the speed, keeping the bow higher.
Of course trim tabs can also even up a poorly loaded boat, but at the expense of fuel consumption.

I hope this helps someone. I learnt so much from my first PTT equipped tinny.

[Volvo]

[QUOTE=Lancair;1514111]IMHO There's so many mistaken ideas idea's about trim tabs and their correct use in this thread. A few people have the right idea with prop torque being a MAJOR culprit in causing a hull to lean, esp. to port.

The little trim tab on the underside of the anti ventilation plate plays a MAJOR role in getting your boat to perform best. If it's not set right, everything else is out and Trim Tabs are a band aid solution.

Whats the chances of explaining how you adjust the little trim tab below the anti ventilation plate????.

[Vitamin Sea]

IMO 12 x 12's would be a vast overkill NLfiishing, simply not required. As has been suggested 9x9 's will more than do the job on that boat.

Trim tabs are great for correcting wind list and improving ride quality. I had 450mm QL tabs on the 19c haines i had, best money i ever spent on it. For the improved ride they cost me 1km/hr and .1 L/km., not worth considering.

cheers

VS

[Volvo]

Well I have a slight dilema with my trim tabs hence the quote. I do have the Lenco 12 x 9 and with a stiff breeze outside comming in from the starboard side I get a good list to that side.
In flat smooth waters the trim tab down on that side corrects the problemo fully but outside it only halfe corrects the problem and my rig is a 6 mtr platey.
So seems i have two options that i can think of, go 12 x12 plates or spacer under the rams give more surface area downwards to give more bum up lift??.
Though that would also effect the amount of plate out of the water when not using the tabs which from previouse threads would effect the boats performance in a following sea ??.
Having also read and viewed instalation guides to fitting trim tabs its been stated that 5/8ths inch plate clearance from hull level is ample ??.
Previousely had a 130HP evinrude with three bladedprop whereas now I have a 150HP Honda with four blade prop, hence more tourque n maybe why now more starboard list ??..
Also to make room for my trim tabs i had to have removed from the starboard side a small plate with a water pickup for live bait tank and think that may have acted as a small tab in itself , hence less list previousely..
So question is, which way to go ???.

[odes20]

So if your tabs are not mounted specs you should fix that first IMO. Your tabs are big enough. I only have 9x 9 on my 6 metre fiberglass and they have a tremendous impact.
It would be way easy to trial a spacer as you suggested .

[Chimo]

I too have 9 by 9 Lencos on a 6.2 Vag and they are plenty and are as recommended by Seafarer's Lindsay Fry.

Who fitted yours? Are they experienced in this task?

Given the issues your experiencing why would you not obtain input from a qualified, experience tradesman? How would you fix a broken heart?

Wonder if there's a chat-site for budding heart surgeons etc although I know they do go to M & G sessions (conferences) in places like Los Vegas etc which is a bit like Sth Stradbroke Island without the pokies

Cheers
Chimo

[Volvo]

I too have 9 by 9 Lencos on a 6.2 Vag and they are plenty and are as recommended by Seafarer's Lindsay Fry.

Who fitted yours? Are they experienced in this task?

Given the issues your experiencing why would you not obtain input from a qualified, experience tradesman? How would you fix a broken heart?

Wonder if there's a chat-site for budding heart surgeons etc although I know they do go to M & G sessions (conferences) in places like Los Vegas etc which is a bit like Sth Stradbroke Island without the pokies

Cheers
Chimo

Yep, just had another squizz at the pics you uploaded as well as did find some Forums regarding trim tabs and instalation and mine have been fitted outa kilta from recomended fittting instructions so as not to have to weld holes and redrill newies it appears the spacers will have to do the job.

[odes20]

good call Volvo. you will gain the travel and influence. Have the outer edge raised no more than 10 mm

[Andrew Wylie]

Hi Nilfishing,
just wondering how far you have progressed with your trim tabs ?

Regards
Wheelybin.

[Nslfishing]

There still on the list. Hydraulic steering first 😃.