Trim Tabs vs. Outdrive Tilt & Trim

[bhollis]

Many of us have boats with outdrives with tilt & trim, but also have trim tabs. Here's the question: What's the best way to use trim tabs and the outdrive's tilt & trim together to achieve the best performance/mpg?

There seem to be two competing views. One says to use the outdrive's tilt and trim as much as possible, and the trim tabs only to the extent that the outdrive's tilt & trim needs some help to get the job done. The theory behind this approach is that the trim tabs cause a lot of drag and are best used as little as possible.

The other approach says to use the trim tabs to control the boat's attitude in the water, and the tilt & trim to maximize thrust.

How do you do it?

[sweepint]

I use the trim tab to level the boat out P versis S or vis versa. The out boards tilt & trim are to raise or lower the bow.

Yes i do agree that the trim tabs will put more drag on the boat by lifting the sturn and lowering the bow.

My 26' has both and i am still figuring and tuning the best mix and loving every bit of time i spead on her

Regards T

[Myers]

Once I get it up to speed and holding steady, I hit the tab one click one way or the other every so often to correct for a wave or ripple. My boat has a "sweet spot speed" that seems to be consistant for many wave conditions, -obviously small craft advisory stuff not included. In ideal conditions when I'm really clippin' along my tabs will be almost completely up, except I may click one down more to maintain the side to side level. In a good three foot chop I may have them down even more. When I am setting all the adjustments, throttle, tilt, tabs, I am staring at the GPS speedo making sure I am getting the most knots for my adjustments.

[skydiver]

For my sterndrive, I get up on step with trim tabs down and outdrive in. Then tabs all the way up and then adjust the outdrive for best fuel mileage. Then if boat needs leveling I use the tabs for that.

[jrogers]

My understanding is that you can use the motor to change the attitude of the boat, but if you do this you are really directing some of your thrust up or down, which is less efficient. Because of this you should use your trim tabs to level and adjust the attitude of the boat where you want it, and then use the motor trim for highest RPM or highest boat speed, which is it's most efficient setting. Something else I was told recently that I did not know is that when you are running into quartering seas it is best to trim the side of the boat high that is taking the seas for the most comfortable ride. This way the seas are not striking your hull as a flat surface, but you are pointing the V of the boat at the seas which makes for a softer ride.

Jim

[bhollis]

jrogers,

Your approach sounds consistent with the second approach I mentioned in my post above. It's also the approach I've tended to use.

But I've been doing some reading on the web lately, and there's a fair body of opinion out there that any loss in thrust efficiency from using the outdrives tilt and trim to control the boat's attitude is more than made up for by the reduced drag from not using the trim tabs (or using them less).

Don't really know what the truth is, but I plan to do some experimenting this summer.

[BrianW]

While it's true trimming the outboard, or outdrive, raises or lowers the bow, it's my opinion the real reason for trimming and outboard/outdrive is to insure the prop is running parallel thru the water.

It's an advantage over straight drive boats, which always have some degree of angle thru the water.

When I had a boat with an outdrive, I tried to keep any angle (in relation to the boat, not the water) at a minimum in order to reduce stress on the gimbal u-joint(s). That's where outboards come in handy, you can trim them and there's no addition wear on parts.

[Vek]

Most of your experimentation should be done in still water with GPS on, so that you can monitor relative speed changes as you fiddle with the controls. With that said, here's how I run a welded aluminum, outboard powered boat with trim tabs:

For cruising at normal cruising speed, trim tabs used only to adjust port/starboard trim to compensate for loading or wind direction (boat will always dip toward the wind when taking wind from the side). This means only one tab in the water, if any. Motor trimmed out to maximize speed at a given throttle setting. Note, I said speed, not RPM. If you have a trim gauge, make a mental note of the motor trim setting.

For cruising at a reduced speed to compensate for a bigger chop, I'll still trim my motor out to where it is when cruising at normal speed, but will back off the throttle and adjust boat attitude with the trim tabs. This means both tabs in the water, boat leveled, and nose attitude down a bit to take the chop with the vee. My experience is that the motor still operates pretty efficiently when trimmed out, even with some trim tab in the water.

For slogging through big seas, engine trim and trim tabs positioned to maintain operation on plane at speeds down to 14-15mph. You'll burn some fuel this way, and boat handling might be a bit sluggish.