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Author Topic:   To trim tab or not to tab
crawl posted 07-14-2005 01:33 AM ET (US)   Profile for crawl   Send Email to crawl  
05 nantuckett with 135 optio I plan on using this mostly in the ocean would trim tabs help stabalize or not?
highanddry posted 07-14-2005 03:44 AM ET (US)     Profile for highanddry  Send Email to highanddry     
Yes, it is on my get list.
bluewaterpirate posted 07-14-2005 08:58 AM ET (US)     Profile for bluewaterpirate  Send Email to bluewaterpirate     
Don't leave home without them. Here's a terrific overview of what tabs can do for your boat.

"This written by Tom McGow of Bennett Marine, 954 427 1400, Deerfield Beach, Fl.

Trim Tabs and motor trim are best used together to get the maximum performance:

It is a common misconception that if a boat has power trim on the outboard or outdrive it does not need trim tabs. Power trim can be used to adjust the boat's attitude, but it is highly inefficient. A propeller is designed to force the boat forward. When trimming the boat with the prop, the prop must not only push the boat forward but raise the stern as well. In this situation, prop slippage is greatly increased thereby wasting R.P.M.'s. Power trim cannot correct listing, and is ineffective at slower speeds. Trim Tabs, in combination with power trim, enable both the hull and prop to be trimmed independently. The trim tabs trim the hull, while the power trim adjusts the prop. The result is optimum performance and efficiency not attainable by the use of power trim alone.

To acheive maximum performance, first adjust the trim tabs to achieve the desired running attitude. Next, 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.

The key to getting the best out of Trim Tabs is experimenting with them since all boats are different. Use them in short bursts and let the boat settle down between corrections. Below you will find a little Trim Tabs 101 that should help you get started.

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 (see side bar Optimum Running Attitude) 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

As previously mentioned 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 athwartship 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."


jimh posted 07-14-2005 09:47 AM ET (US)     Profile for jimh  Send Email to jimh     
Trim tabs have almost no effect on stability. The hull form and weight distribution are the principal influences on stability.
diveorfish posted 07-14-2005 12:30 PM ET (US)     Profile for diveorfish  Send Email to diveorfish     
I would imagine that a Nantucket is a large enough to benefit from trim tabs. Just by going from half a tank of fuel to a full tank and putting a couple of average sized fishing buddies in the stern seats would add around 600lbs of extra weight making you stern heavy and probably cause you run too bow high in most conditions except flat out on smooth water. The tabs would allow you to overcome the added weight and make you run at a proper attitude at slower speeds which is necessary when the conditions get rough. Tabs will also help you run straight and level just in case one of those fishing buddies in your stern seat is substantially heavier than the other one.

I couldn’t even run my boat without without tabs. Two passengers, the extra weight of a full vs. half a tank of gas, and the extra weight of a twin engine is around 1300 lbs.

Sal A posted 07-14-2005 12:36 PM ET (US)     Profile for Sal A  Send Email to Sal A     
That's a great excerpt Tom. Thanks for that.
mikeyairtime posted 07-14-2005 12:42 PM ET (US)     Profile for mikeyairtime    
Properly used trim tabs are a very valuable tool for offshore work.
mikeyairtime posted 07-14-2005 12:46 PM ET (US)     Profile for mikeyairtime    
BTW Jim, trim tabs can have an effect on the stability of a properly designed boat by compensating for an uneven load while underway.
highanddry posted 07-14-2005 01:48 PM ET (US)     Profile for highanddry  Send Email to highanddry     
I would like to have tabs to compensate for load variations and to help trim the bow down at very low speeds.

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