Bennet Electronic Trim Tabs Sizing questions for re-fit.

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biggarfish

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I'll be swapping out the hydraulic Bennet Trim Tab system on my 1988 Grady Gulfstream for a new Electronic Bennet system over the winter. My question is: Based on the fact I have a customized pod that mounts the twin 150's and 15 hp Pro Kicker out a little farther than a stock configuration (has a flotation chamber midship on the pod) should I gravitate toward the larger 24" x 12" trim tabs or will the 24" x 9" do the trick just as well?
 

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What size are the existing tabs? If you were satisfied with their performance, I guess that size is appropriate, What size does Bennet recommend?
The 24 by 12 sounds big to me for a 23 foot hull but on the other hand, many feel that bigger is better.
 
seasick said:
What size are the existing tabs? If you were satisfied with their performance, I guess that size is appropriate, What size does Bennet recommend?
The 24 by 12 sounds big to me for a 23 foot hull but on the other hand, many feel that bigger is better.
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Actually they're 12" x 8 1/4". So... yeah 24" is probably overkill. 18" wide will suffice and now curious if anyone has any feedback on the depth from the transom. Choices are either 9" or 12".
 
Deeper tabs are usually better especially since the 232 is a heavy boat.
 
Generally speaking, span is more important than the chord measurement. So going wider has more impact on performance than depth. If you have room for 24" go for it. The three extra inches in chord will help - but to a much lesser extent.
 
DennisG01 said:
Generally speaking, span is more important than the chord measurement. So going wider has more impact on performance than depth. If you have room for 24" go for it. The three extra inches in chord will help - but to a much lesser extent.
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Have you seen issues where a long span lifts out of the water stream on hard turns?
 
seasick said:
Have you seen issues where a long span lifts out of the water stream on hard turns?
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In my experience, no. I have either 18" or 24" span (I forget, right now) on my Offshore - which is only an 8' wide boat. They have a 9" chord.

But I think the only way that would happen is if the actual hull ALSO came out of the water... and for that to happen, there would be more things to worry about :eek:

I can't think of any downside (functionally) to having tabs with the largest span feasibly possible.
 
DennisG01 said:
In my experience, no. I have either 18" or 24" span (I forget, right now) on my Offshore - which is only an 8' wide boat. They have a 9" chord.

But I think the only way that would happen is if the actual hull ALSO came out of the water... and for that to happen, there would be more things to worry about :eek:

I can't think of any downside (functionally) to having tabs with the largest span feasibly possible.
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I have to think about the dynamics of tabs with the same total area but with different dimensions.
For example, would there be a difference in performance (or lack of) for two identical hulls, one with 9 x 12 tabs and the other with 12 by 9. I don't think I know enough fluid dynamics to figure that out.
 
I would definitely go with the larger tabs. I went from 9x12 (way too small) to 12x18 on my 228 and it made a huge difference. With the smaller tabs, I had to get off the throttle towards the top of each swell or I'd launch and pound. With the new tabs, in most conditions, I can just throttle up and let the boat go, it rolls over swells that it used to launch it.
 
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