Trim Tab Size Increase

jrybak

Dock Holiday
Feb 11, 2019
163
Lake Ozark, MO
Boat Info
92' Sundancer 370
Engines
7.4L Mercruisers
1D72BFEA-1C7E-4175-AC57-4EEA245536C0.jpeg I have a 92’ 370DA that I am looking to upgrade the tabs to 12”x36” w/ dual 3” drop fins from the OEM 8”x30” tabs no drop fins, Has anyone increased tab size on their boat?
 
I'm wondering why you need to do this as I have the same boat and find the tabs very effective and more than enough in any conditions? Now I have had other boats and other Sea Rays that I have extended the tabs and it made a big difference. A friends 2002 340 ran full tabs all of the time and he definitely could have used more.
 
I'm wondering why you need to do this as I have the same boat and find the tabs very effective and more than enough in any conditions? Now I have had other boats and other Sea Rays that I have extended the tabs and it made a big difference. A friends 2002 340 ran full tabs all of the time and he definitely could have used more.

Anytime I am looking to replace a component I try to research and maksure I am aware of any potential upgrades or increase in performance that I could have prior to replacing the component, I also didn’t understand why I had tabs and how they help, so I started research on why they are there and what they do.

I found the trim tab guide from Bennett Marine the OEM supplier for our boats and this was my first area that I would point to as needing to potentially upsize the tabs.

The guideline says for a standard 9” cord you try to achieve 1” of span for ever foot of a boat on boats that travel less than 40mph, they further explain that if you have twin motors or limited stern space due to conflicts 12” cord may be bennifical.

I have a 37’ boat and would think a 36” span in place of a 30” span would be in-line with their guide. I also added a 3’ swim platform that just from looking at how it mounts up was a little worriesome, looked like maybe it would be exposed to water pressure from the bottom side while the boat is getting on plane so I figured extending the tabs to 12” tabs would help ensure that would be minimized. I also reviewed posts on this forum that people that increased their trim tabs were then able to hold plane at lower RPMs which means less fuel and perhaps a more plesent ride experience for my passengers on a very active lake.

I also assume Bennett Marine’s Eng Dept has dialed these calculations in better now being that our boats were designed when hand held cell phones were state of the art and the guy that designed this hull / tab configuration didn’t have the ability to click a few buttons to see the best possible setup and configuration.

Additionally, since Tom “Tabman” has passed away Bennett’s new tech resource I spoke with agreed that this boat would benefit from more tab.
 
tiara in the snow 01.JPG
We had a 1993 370 Express. Trim tabs were not even remotely undersized. They were perfectly sized for the hull and provided very responsive trim adjustments. Save you money unless a prior owner has screwed some up with what the factory installed.
 
can trim tabs be oversized? what is the negative of oversized trim tabs?
 
C65EBF67-F6A7-49B7-8E22-BAC566DB6C06.jpeg 5A806EF6-394D-4B69-BE42-108AD798E73A.jpeg

After some further investigation and PMs with folks on this site I went ahead and pulled the trigger on the FULL MONTY!!

New 36”x12” w/3” Dropfins, Autotrim Pro, Pro Sensor Kit. Thanks to BOE Marine, great service, price and reward bucks for the next order.
 
how much did all of that cost including install? and can you post a pic of the tabs on the boat from behind when extended? thank you
 
$885 material from BOE, and I have about $20 worth of reward bucks from that purchase.

Install I am guessing a couple of hours so maybe another $200.

When I get them I will post images. They may not make it in time for this removal from water, however I am planning another latter this year. The lift my boat is on is a hot item this time of year and I don’t to screw the marina.
 
Dear LORD, did my wife call you? o_O the wife hasn't even seen the boat in person yet.

I have had her out twice, both days the wind was gusting 20mph+ and light rain.:p

Pre-1st Season Improvements could be over the top to some, but I know myself well enough to know that I will end up doing it all anyway, why wait. I have done it with my home theater, outdoor kitchen, basement, (2) older Porsches, old corvette etc.... I may have a problem but if I ignore it is it really my problem, LOL!!!

SEE TAG LINE BELOW!!! My wife says that a lot.
 
I increased my tabs on a 400DA. Also added the drop down fins. Over all slight decrease in deck angle. She did tend to get out of the hole a bit quicker.
 
I tried monitoring it pretty closely. Best fuel burn was 0.8 gal to a mile. That was just up on plane not really hauling butt. I did it more for the deck angle. It did help lower that. At higher speeds I had to retract them a bit where before they were pretty much fully deployed. So more control over all.

I'm in the process of getting a new boat, would like doing the fins again. Bennett techs said those improved effectiveness of the standard tab by 15-20%. Not so sure about that, but it has to improve the trim tab performance some what. Defiantly worth the effort if the boat is out of the water anyway. I tried locating those stainless drop down fins but Bennett folks are not all that responsive. Use to have to order them through West Marine.

One thing they did do was put up one heck of a spry on both out board tabs. Spray came up through those drink holes between the deck and swimm platform. Had all kind of fabrication schemes to lock this inconvenient byproduct of my personally contrived modification. In the end I just made a few lops with 1 inch rope and sicured the ends in place. Pretty solved that problem.

Ron
 
Just be 100% sure that the new tabs mount the actuators exactly the same distance from the transom. I saw a tab upgrade where the attachment for the actuator was slightly closer to the transom than stock, made the tabs angle down about 5deg.. the effects on handling were horrendous.
 
While I was doing this deal of making my trim tabs 30 % bigger there was some guy that just simply added a new pump and tabs. Think he located them some were over the tunnel of his 400DA. I'm not a big fan of drilling holes below the water line. I tried locating the photos and notes of my posted; no luck
 

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