Sorry, but another Trim Tab question

[DougDoty]

My tabs on my 39 sedan seem like they are just running out of power at higher speeds. As an example I was out for a boat ride with a friend a couple of weeks ago and with just the two of us on board, one in each pilot seat we had a list to starboard as I was a little lite on port tank fuel and real low on water with it's tank on port side also and if you must know the cooler was located to starboard as well. The perfect trim storm... Here is the question, I could correct that list with trim tabs but if he got up to move about the boat and moved to center while checking on said cooler, that list would come back and be too much for me to trim tab out. I ask because I want to install the Bennett auto tab control system I bought for the boat a couple of years ago but have always questioned if things were working right and that it needed sorted out before adding another layer of confusion. These boats get so trim finicky on top of the water, I am just not sure if I am expecting too much from the tabs or what. The problem does show up more at higher speeds and it is progressive with increasing speed. We were running at about 28-29 mph as that is a favorite get there speed without the four barrels talking. At WOT which I have trouble not playing with all to often it more noticeable yet. I know balancing the boat is #1 on the list of fixes but when I take several people out I refuse to constantly direct the fat people on where to sit as I resemble that remark so I want and need more tab authority.

#1) Am I asking too much of the stock system or is there even a problem -vs- normal. What is you experience.

#2) If this is even somewhat normal, what is the favored solutions for gaining more authority on the tabs.
A: Dual or triple actuators
B: Longer tabs, kind of like K planes

[jralbert]

Doug.. I am not qualified to dig down deep into your excellent question but do have an observation: boat trim gets trickier at higher speeds and you were moving at what I'd call a higher speed. Otherwise, maybe your fuel and water weight imbalance was greater than suspected. Maybe the tabs aren't big enough for that size boat. Finally, while I respect the crowd sourced expertise you get here, I like to call on the experts at the mfr's tech department for (usually) solid advice.

[Fastjeff]

Had that same problem with my 32 footer with myheavy dink boat on the back. The 70 hp motor's weight produced an incorrectable port list underway. I added a 1/2 inch block of aluminum under the ram (attached to the tab). Since that corrected it the problem was NOT a lack of power in the hydraulic unit.

In your case--assuming it's a lack of tab travel--you'll need one block per side. Easy fix.

Jeff

[DougDoty]

Jeff, That is an excellent consideration. Since I drive from below at all times for obvious reasons, I tend to use the tabs to drop the bow down about 50% of what the tabs are capable of doing for best visibility and I have verified with GPS that this has no effect on speed until I go to 75% to almost full tabs. As an addendum question it seems reasonable to assume that since I see no reduction in speed at 50% of the tabs stroke at cruise I am also not loosing any appreciable economy ?? Your thoughts ?? It seems that the tabs would have to add drag but could this be being offset by propellor efficiency running at a flatter attack angle or something else ?? Once again, Your thoughts ??

I do think I will call Bennett as well. They just seem to be billed as such good people with phone tech support.

You can see the catty wampass water trailing off the back in this picture on the first WOT test run of this season.

[Fastjeff]

Being (anal) and a former test engineer, I played with the trim constantly as I roared down the river; and I can assure you speed and gas milage CAN be improved a bit by shoving the bow down. That sounds wrong--the tabs are obviously 'dragging'--but it works. It takes patience (and a smooth, uninterrupted 'test range' ) to determine the setting, however. You have to make tiny adjustments, then wait half a minute for the changes to 'settle out.' I eyeball my FloScan at the same time, and there the real improvements can be made.

Have fun!

Jeff