I pulled the trim tabs off the boat in order to barrier coat behind them, and also to clean and check them over before re-installing. I did some rough calculations on the size of the tabs while they were off the boat, and started to get that uncomfortable feeling I get every time I look at the design compromises the factory has to make when building a production boat. A bit of searching on some Internet forums confirmed my fears - the tabs on the 340s of this vintage are undersized. The tabs on the diesel version of this boat are 6 inches wider - 12" x 24" instead of the 12" x 18". But if you look at the hull, 24" wide tabs really don't fit that well, since the flat section of the hull, between the lifting strake and the prop tunnel, isn't 24" wide. Don't get me wrong; 24" tabs can be installed, but they won't allow for a smooth flow of water at the edges, and that is NOT how I intend to maximize speed and economy. With the price of gas the way it is these days, every little bit counts.
So, what to do? If you consider that the tabs main purpose is to provide lift, it is clear that a longer tab is more effective than a wider tab. A longer tab applies the lift farther from the center of rotation of the hull, and therefore has more leverage. It follows that, for a certain amount of lift, a longer tab can do the job with reduced drag. Take a look at Mercury Racing's K-planes - they are long, stiff, and not very wide. Since a longer tab is more efficient, and my hull won't support a wider tab, I decided to modify the existing tabs to maximize performance. (I just can't leave well enough alone, it seems).
Here is how the tabs looked when I pulled them off the boat:
This coming weekend, I am lifting one of the engines in - it's time. The other will follow soon after.