Proper use of trim tabs ...opinions please?

[rumy1]

When you have trim tabs fitted does that mean you no longer need to trim your motor? Or do you get up on the plane and then your motor is trimmed correctly, then adjust trim tabs down to level the boat? Or do you use both trim tabs and motor to get and stay on the plane?

I understand if you are travelling along and the boat is leaning to one side then you drop a trim tab down to level the boat. What I don't understand is the use of trim tabs when getting up and onto the plane.

Any experienced boating out there have any advice please?

[Smithy]

I'd still fully tuck in my motor to get on the plane. I'd then be trimming out my motor the same time as tabbing down. I'd get to my downsea trim position on the gauge and then trim with the tabs. If you are still bouncy in the nose like when you head out into a headsea you might have to use a bit of engine trim too. Some days in the Stabi punching a sea I would be full tuck in plus a heap of tab. Fuel economy wise you are best with your prop level with the keel and if the waves are tossing your nose around too much, use your tabs. A fuel flow sensor will confirm this.

[johncar]

Yeah what Smithy said. If your boat is well balanced and designed the engine can be enough to trim the boat and even punch into a head sea but the tabs can be used to assist little when needed. I don't tend to use the tabs much for that purpose and just use the engine trim unless it really gets heavy going. I do however use the tabs extensively for keeping the boat level from side to side counteracting and wind and current effects because I want to use every bit of that deep vee to cut through those waves and not pound sideways onto them.
For most typical trailer boats one thing with your tabs is to have both fully up out of use when travelling in a decent following sea, in this case trim your engine out as far as you can too without cavitation is the safest way. If you have to level up a bit in a following sea only use the minimal amount of tab to correct or not at all may be best.

[The Woo]

Rumy1, you'll learn the best way to use your tabs by experimenting mate. Every boat responds to tab use in a different way.

But basically, try to think of it this way;

1. Your engine trim is used to adjust longtitudinal trim, ie, how far the bow points to the sky. If you find you need excessive down engine trim to attain a nice running attitude, use the tabs instead of really burying the engine down.

2. Your trim tabs predominantly control your lateral trim, and your aim is to keep your boat on an "even keel", ie, as John said, using the V shape of your hull to carve the waves.

In extreme conditions when your want to plane very slowly into heavy chop, the trim tabs can ASSIST the engine's down trim to push the bow down and carve the waves using the sharp entry of your boat.

Just experiment, and you'll quickly see their benefits. In my opinion, all monohulls benefit from tab use in some way, budget is the only reason why you wouldn't run them.
At risk of looking like a cock, try to think of the tabs as a bird's wings, and how they alter your trim as you move.

[Chimo]

Hi rumy 1

On the other side of the coin I find my 9 by 9 tabs do allow me to not tuck the motors right in and the boat gets on the plane more quickly even with the tabs fully up. They certainly do level the boat against wind and side waves and as a result in the Vagabond they make the deep vee work better too and that results in a softer ride with little or no shoulder slap and bang.

Try them at different settings and speeds and you will soon appreciate the affect and benefits.

Cheers
Chimo

[rumy1]

The bird image in my head is a good one for imagining how they work. I do understand how they work though but I don't understand why people are using them to get on the plane? I would think if you need them to get on the plane then you maybe need a larger motor??? Just a thought!!! My boat leans to the left for some reason, maybe due to the full length canopy I have on it, I am not sure but this is why I am asking about trim tabs. This would correct that problem for me. I have no troubles getting up on the plane so I think I would skip using tabs for that reason. My boat is loaded correctly, I have no huge weight to the left side. I haven't had the boat long so I will use it more when I get the chance and see what maybe causing this leaning problem. I went offshore 30km and back, it was getting uncomfortable to be in the skippers seat due to the constant leaning and having to hold on so I didn't slide to the left. I had to tighten the seat base as the seat kept swivelling around to the left. Is there something in the way the motor maybe set up that could cause this?

[rumy1]

Thanks for the replies , keep them coming !!!

[The Woo]

Mono hulls typically lean into a side wind. Tabs can correct that.

And yes, I'm of the opinion if you need tabs to get on the plane without aiming to Mars, then you're either overloaded, VERY poorly balanced (stern heavy), or just don't have enough power.

[Smithy]

If you have fuel flow you will find that you get better economy keeping the nose down with trim tabs rather than in trim on the engine.

Forgot to ad last night, on the US flats boats they are big ones for using trim tabs. It lets them get on the plane quicker. When they are in 2' of water in those 16-18' sort of flats boats with the 115-150s I believe they go full tab down, full in trim and full lock, they gas them up onto the plane with the throttle in a couple of boat lengths then steer and trim accordingly to keep them running on the plane in such shallow water. We all know how much boats bog in getting onto the plane so this might counteract it. Some of the flyfishing gurus might elaborate if they have been on those sorts of boats chasing tarpon or bones or whatever. I might have it a bit wrong but you get the idea. Certainly for smallish boats they all sport tabs so it is important to these guys and the sorts of fishing they do.

[odes20]

The bird image in my head is a good one for imagining how they work. I do understand how they work though but I don't understand why people are using them to get on the plane? I would think if you need them to get on the plane then you maybe need a larger motor??? Just a thought!!! My boat leans to the left for some reason, maybe due to the full length canopy I have on it, I am not sure but this is why I am asking about trim tabs. This would correct that problem for me. I have no troubles getting up on the plane so I think I would skip using tabs for that reason. My boat is loaded correctly, I have no huge weight to the left side. I haven't had the boat long so I will use it more when I get the chance and see what maybe causing this leaning problem. I went offshore 30km and back, it was getting uncomfortable to be in the skippers seat due to the constant leaning and having to hold on so I didn't slide to the left. I had to tighten the seat base as the seat kept swivelling around to the left. Is there something in the way the motor maybe set up that could cause this?

If I ever heard a description of a boat needing tabs your description is it rumy1 !!
Mate I put tabs on mine last year after 20 years of boating and am still kickin myself I didnt earlier! Without doubt you wont ever regret it!
I too have a big canopy and its just so easy to rectify with the tabs.

[johncar]

many boats will have a tendancy to lean down on the port side, which I believe is more often due the boats opposite reaction to the propellors clockwise rotation. This will be more noticable with narrower beam deeper Vee boats as they have less natural lateral stability while on the plane. Also bigger pitch props and possibly 4 blade props can be worse.
If your boat sits nice and level at rest with nobody aboard but leans while under way it is most likely caused by the props rotation. Hull warps can also cause it even if very slight but that is rare. Just my thoughts as to the cause, have no science to back this up.
But I figure if you could hold the prop solidly while powering on the engine would try and turn the boat over in an anti clockwise direction hence down to port. The water friction acts as partial hold on the prop as she pushes foward so you get a partial lean.
Tabs are the easiest way to manage this I think, but I have heard of owners having a permanent mod to the hulls portside to compensate.
Most deep vee boats I have ever owned have done this and even in calm conditions often having to apply some lift to the port side.
Wind and current is another thing that of course varies on any day and tabs are just so useful to get the best out of the hull.

As far as getting on the plane easier, it would be just the same principal as a aeroplane taking off with it's flaps down, giving it more lift.

[bigjimg]

many boats will have a tendancy to lean down on the port side, which I believe is more often due the boats opposite reaction to the propellors clockwise rotation. This will be more noticable with narrower beam deeper Vee boats as they have less natural lateral stability while on the plane. Also bigger pitch props and possibly 4 blade props can be worse.
If your boat sits nice and level at rest with nobody aboard but leans while under way it is most likely caused by the props rotation. Hull warps can also cause it even if very slight but that is rare. Just my thoughts as to the cause, have no science to back this up.
But I figure if you could hold the prop solidly while powering on the engine would try and turn the boat over in an anti clockwise direction hence down to port. The water friction acts as partial hold on the prop as she pushes foward so you get a partial lean.
Tabs are the easiest way to manage this I think, but I have heard of owners having a permanent mod to the hulls portside to compensate.
Most deep vee boats I have ever owned have done this and even in calm conditions often having to apply some lift to the port side.
Wind and current is another thing that of course varies on any day and tabs are just so useful to get the best out of the hull.

As far as getting on the plane easier, it would be just the same principal as a aeroplane taking off with it's flaps down, giving it more lift.

What John has been saying is basically correct,Transverse and Axial thrust will pull your stern around in differing directions.very noticable on larger single screw displacement hulls.What it does on smaller light weight boats is make them "lean".On our 8m glass boat ,single screw shaft driven,we fitted a large ply wedge to the port side and adjusted it to suit until we reached a happy attitude when underway.It was then glassed over and became part of the hull.Alot cheaper than fitting tabs.But i wouldn't recommend you do this to a trailer boat.Jim