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Author Topic:   Trim Tabs
Thurmanator posted 01-10-2004 05:01 PM ET (US)   Profile for Thurmanator   Send Email to Thurmanator  
Im new to these and need to know the best way to adjust the list of the boat? is sit best to adjust before up on plane or after? Also wondering if ther is any matienance other than checking the fluid. ( Benette Trim Tabs )
gimcrack225 posted 01-10-2004 06:01 PM ET (US)     Profile for gimcrack225    
Do a search for trim tabs. There are hundreds of threads.
Eddie Mucciolo posted 01-11-2004 12:26 PM ET (US)     Profile for Eddie Mucciolo  Send Email to Eddie Mucciolo     
Tabs up. Bring your boat on plane to your cruise speed and make adjustments slowly. Give the boat time to catch up to the changes you make. Remember each rocker switch adjusts the opposite side tab. Good luck.
Thurmanator posted 01-11-2004 12:35 PM ET (US)     Profile for Thurmanator  Send Email to Thurmanator     
Thanks Eddie, Thats what i thought but wasnt sure. The only list is from the extra weight of the trolling motor being on the same side as the pilot, i guess this is normal.
Tabman posted 01-11-2004 05:01 PM ET (US)     Profile for Tabman  Send Email to Tabman     


Below, you will find a little “Trim Tabs 101” I wrote for an artical a while back.

You can downlowd a maunal from our home page for your Trim Tabs that covers system specifications and maintanance. It is a handy refrence to have.

I hope this is helpful,

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 (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

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.

Holy Cow posted 01-12-2004 09:48 AM ET (US)     Profile for Holy Cow  Send Email to Holy Cow     
Good Day!
I just wrote to Bennett this morning! I have reseached back to 2002 and found some info on the For/or Against to adding Trim Tabs to a 170 Montauk! What I am looking for is if they will actually let two to three riders in 2-3 foot seas actually stay on plan with out banging between sets of waves??? I have the 90 Four stroke with a 5 horse 68 pound kicker on the port side! Please let me know! Or do I have to buy an 18 Foot Outrage to chine walk! Is it just that the 170 will only be able to chine walk on 1-2 foot waves and that is what the 1440 pounds will do for you! How bout those Eagles!
erik selis posted 01-12-2004 10:11 AM ET (US)     Profile for erik selis  Send Email to erik selis     
Holy Cow,
What is your definition of Chine Walking? It sounds like you want to chine walk. From what I have heard and read about chine walking, this seems to be something that boaters want to avoid. Maybe I don't understand what you mean by chine walking.
Holy Cow posted 01-12-2004 10:50 AM ET (US)     Profile for Holy Cow  Send Email to Holy Cow     
Chine Walking to me is walking the dog on top of the waves! The Bow breaks down the waves and the rear chines sit on top of those choppy 1 to 2 to 3 footers and your standing at the helm not getting beat up by bow pounding! HC
erik selis posted 01-12-2004 11:11 AM ET (US)     Profile for erik selis  Send Email to erik selis     
Ok, thanks HC. I think I understand what you're talking about now. I think you mean surfing on top of the wave. No?
Actually Chine Walking is something completely different.
As I understand it your 170 Montauk doesn't walk the dog as well as an 18-foot Outrage. Could you describe what happens in a bit more detail? Thanks,
Holy Cow posted 01-12-2004 03:22 PM ET (US)     Profile for Holy Cow  Send Email to Holy Cow     
Erik... The 170 as far as I can see it will not scoot across the 2-3 foot chop as it does on plane at 4000 and up RPMs on 1-2.5 foot chop... I have read and heard and seen the 18 foot early and late Outrages can scoot across the 2-3 foot chop! I tried to cut through that 2-3 foot chop and the 170 has to go with bow up into the 2-3 foot chop at about 3500 rpms and slam. Just my two cents. Nothing wrong with the 170, just that that is the limitation of the 170. What it comes down to is I do not want to get beat up when the winds pick up and I am far off shore! HC
erik selis posted 01-12-2004 03:54 PM ET (US)     Profile for erik selis  Send Email to erik selis     
HC, I had a simular experience this summer while following an 18-foot outrage with my 170 MT. There was a 2 to 3-foot chop with a fairly strong sidewind. I was riding in the wake of the Outrage approx. 50 feet behind her at about 4000rpm. It felt very strange because the bow tended to come up and the boat seemed to want to slow down. I decided to get out of the wake and ride beside the Outrage. The boat then handled much better. Eventhough the chop was not broken by the Outrage. Trimming the motor down a bit and then finding just the right rpm's gave us a super ride.
I think alot has to do with correctly trimming the motor as well as finding just the right speed. Maybe trim tabs could make things on the MT 170 even easier. Just my 2 cents.
Thanks for sharing your info HC,
erik selis posted 01-12-2004 04:01 PM ET (US)     Profile for erik selis  Send Email to erik selis     
One more thing I would like to add. I have a 90hp 2-stroke and don't have the 27gal. pate tank. In the situation as described above there were 2 adults seated on the cooler in the front and my wife and I behind the console at the wheel.
I don't know if you have the larger fuel tank but it seems you have alot of weight at the back with the 4-stroke and the kicker motor there. It makes a difference. I think trim tabs would help you out alot.
Holy Cow posted 01-12-2004 05:48 PM ET (US)     Profile for Holy Cow  Send Email to Holy Cow     
This is a letter I sent to Bennett: I was wondering how will a pair of trim tabs would work on a new 2003 170 Montauk Whaler? The motor is the 90 4 stroke. I would like to know if the tabs would offer any extra planing ability for a 1440 dry weigh Montauk in 2.5 to 3 foot seas. It seems I am banging the haul too much because I can not get up on plane in a 20 mph in your face wind and a 2-3 foot chop. Any info would be appreciated! I have a 90hp 4-stroke. (408 lbs) I have the 27 gallon Pate tank. (182 lbs) There are 2 adults behind the console. (375 lbs) I have a 5 HP kicker motor (68 lbs). What will trim tabs do for me and my heavier 170 Montauk Whaler? Dan


Trim tabs will allow you to plane quicker and stay on plane at reduced speeds to handle these situations, since they lift the stern and allow the forefoot of the hull the cut the wave as it was designed to do. As it is, the four stroke is heavier than a two stroke, so you are already at a disadvantage with this added weight in stern. Of course, everyone uses their tilt/trim to help get on and stay on plane, but you are using your engines thrust to lift the stern which would be better used to propel the vessel (the intended design of a prop). The trim tabs will take this burden off of the engine and allow to you trim the prop for its best performance, which is parallel to the water flow (equal pressure all around the prop). They will also allow you to trim out any listing you may have from passengers moving around or uneven weight placement from gear and you can use them to raise either side bow (port or stbd) to cut down on some the spray coming over the bow from the wind. Many clients love this ability quite a bit, since it will keep them dryer! The M80’s will most likely be your best choice for your installation, but you may need to have our External Line Upper Hinge Conversion kit (see attached photo) to run the hydraulic lines over the transom vs. through. Of course, you know the lay out of your transom & vessel better than I, but if you need them place let me by providing me with your mailing address and I will send it to you at No Charge!


M.J. Thomas

Client Services

Bennett Marine Inc.

JohnJ80 posted 01-12-2004 10:25 PM ET (US)     Profile for JohnJ80  Send Email to JohnJ80     
I would think your boat would definitely benefit from tabs in 2-3' waves (mines does - Dauntless 15'). If you can get the nose down a bit you will be able to split the waves instead of slamming into them with the aft flat portion of the hull.

This was exactly the reason I got tabs for my boat and they have met the expectation I had for the improved ride. You rean really keep a planing attitude and also reduce your speed at the same time. I have also noticed my motor seems to run freer now - less straining. It is also easy to tell when the trim is correct on the motor since the steering becomes very easy at the right amount of engine trim and proper trim tab setting.


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