trim tab/outboard trim

Discussion in 'Newbie Lounge - NEW' started by Gasman, Feb 7, 2017.

  1. Gasman

    Gasman Member

    May 30, 2015
    Great Lakes
    2001 29' sun dancer sold
    2000 340 sundancer
    Twin 5.0 mercruiser
    7.1 v-drives
    this is a 2 part question i have a 2001 290 dancer with twin screws... I have trim tab buttons on the dash and i have trim switches on the throttle to raise and lower the outboards... my question is when and why do i need to trim either one... i assume i would trim the outboards up if i am running in shallow water is that the only time... when would i need to use the trim tabs if ever...
  2. Lazy Daze

    Lazy Daze Well-Known Member TECHNICAL Contributor

    Apr 21, 2009
    Just as a reference on terms... You do not have "twin screws" - that typically designates inboard or v-drive engines. You also do not have "outboards", you have "outdrives" (sometimes just referred to as the "drives").

    Both your outdrives and your trim tabs can be used for better performance to adjust the boat's running attitude. Both of them can be used to adjust the boat's pitch. The tabs can also be used to adjust the boat's roll. The drives "could" be used to adjust roll, but that's usually more complicated than it's worth. By performance, I mean things such as hole shot, top speed, keeping the bow "planted" in a head sea and avoiding "stuffing" the bow in a following sea. That said, though, there's no "hard and fast" rules to using these since there are so many variables from the amount of people on board and their comfort level, to sea conditions to desired speeds, etc, etc.

    If you search for threads regarding trim tab use, you'll come up with PLENTY of informative reading material.

    Trimming drives up in shallow water (with engine running)... be careful and try to avoid trimming too high or damage can result (stay within the built-in safety limit by using "trim" only, not "tilt", unless it's an emergency).
    Last edited: Feb 7, 2017
  3. Tabman

    Tabman Member

    Jan 11, 2007
    The Tab Cave
    If you are new to using Trim Tabs you may find this helpful in learning how to use them to achieve the best results. All boats react differently to Trim Tabs and the best way to find out what works best for yours is to experiment, and remember, use short bursts of the controls and let the boat settle down between corrections. Using them will soon become second nature.

    Tom McGow
    Bennett Marine

    Getting and Staying Trimmed

    All boats assume different fore to aft attitudes at different throttle settings and vary in sensitivity to lateral weight distribution.

    A boat’s optimum running attitude is determined by the operator. While some people may define optimum running attitude as the highest possible speed for a given amount of engine RPMs, others desire the best possible fuel economy, yet others may be trimming the boat to get just the right mix of speed and wake (such as for waterskiing.)

    Optimum running attitude is when the boat is running to the operator’s satisfaction for the given operating conditions. There are as many optimum running attitudes as there are boats and boat owners

    A good way to determine a boats optimum running angle is to run the boat lightly loaded at full speed in calm water. During this test observe the boat’s bow in relation to the horizon. Most boats run at or near their optimum attitude under these conditions. This should give you a feel for the appearance of the wake and bow spray when running at an efficient attitude. Note that not all boats will achieve their optimum running attitude under these conditions. Some boats will benefit from extra lift even when running at their maximum throttle settings. If you feel the boat will benefit from added bow down trim when running at speed start with the trim tabs fully up and deflect the trim tabs in short bursts. Be alert to changes in the boats handling, as you bring the bow down. Observe any changes in RPMs and/or speed. Adjust power trim if applicable.

    Indications of Running Untrimmed
    When a boat is running untrimmed the bow spray will exit the sides of the boat far aft. The stern wave (wake) is high and curling like a breaker on the beach. The rooster tail is high and close to the stern. The engine is laboring and the ride tends to be less smooth.

    Indications of Running Trimmed
    The bow spray moves forward and is flung not as far from the boat. The wake diminishes in height, as the rooster tail flattens out and moves away from the boat. The engine is operating under less load as evidenced by the tachometer and speed as well as sounding “less strained”.

    One Step at a Time
    The key to obtaining optimal results from trim tabs is to operate them in short “bursts” and let the boat react before making another adjustment. The amount of time between corrections is influenced by the size of the trim tabs and the boat’s speed. This will help avoid overtrimming or ending up with one tab too far down when correcting lateral trim. You will quickly become acquainted with a boat’s particular traits.

    Take Off
    Properly sized trim tabs can significantly reduce the time needed to get up on plane. They also allow a boat to keep its bow down and stay on plane at lower speeds.
    As the throttle is advanced the stern of the boat begins to squat, lifting the bow. As the boat accelerates, push the bow down position of the helm control in short bursts. The boat reacts by the stern lifting, the bow coming down, speed increasing, and reduced engine laboring. If you over do it and deflect the tabs too far the boat will end up overtrimmed. When over trimmed, the steering becomes “over sensitive” and wants to pull off course to port or starboard. If this occurs, operate the control “bow up" until the desired attitude is established.

    Getting the Most from Power Trim
    Adjust the trim tabs to achieve the desired running attitude. Then use the power trim to position the propeller thrust parallel to the water flow. If necessary, re-adjust the trim tabs to fine tune the attitude. By observing the boat’s speed and engine RPMs the best combination of trim tabs and power trim will be apparent. Trim tab angle indicators and a power trim angle indicator are particularly useful in duplicating effective settings.

    Trimming to Sea Conditions
    When running into a head sea you want to trim the bow down so the sharp forward sections of the boat do their work cleaving the waves. This provides the most comfortable ride and minimizes stress on the boat (and passengers). In a following sea the tabs should be fully retracted for maximum steering response.

    Correction of a List
    The normal control setup for trim tabs operates in relation to the desired changes in trim and not the actual movement of the tabs. Therefore, do not think about what the tabs are doing, but rather on the control and what you want the boat to do. As above, make the corrections in bursts and allow the boat to settle to the new settings. You may find it easier to correct the boat’s fore and aft attitude before you correct the side to side trim.

    Correction of Porpoising
    Operate the tabs in very short bursts of about half a second. Continue until porpoising subsides. The objective is to have only a very slight amount of tab deflection, just the amount needed to cure the up and down motion of the bow.

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