Here’s some pics of what I’m talking about. Because of the curve on the transom the straight edge, or tab bracket will not lay flat unless moved way over to the left. Look at the ruler at the “10 in area”, there is about 1/8 or 1/16 inch gap. My transom has a very gradual curve to it


Fisher, that is a huge radius! Wondering when Defiance changed the mold? Anyone else with a new Arima have this same change on the transom to sponson radius? It seems a little strange as many owners that want to add tabs to their boats that they would redesign this area and reduce the available space that is already tight??
Speaking of which, just a couple of comments on tabs on Arima's. This is a much discussed topic but always good to review for new or would be owners, Like Buddy who is in the process of setting up a brand new 17' Chaser. Most agree that tabs are one of the most important improvements to their Arima. Some have mentioned already in this tread one of the benefits is the side to side trim. This is so important with the addition of kicker motors and accessories that change the balance of the boat, not to mention the live loads we add that are changing all the time, like people! But there are other important reasons for tabs on these boats.
One member named his Arima the "Fat Bottom Girl". The design of our boat makes them very stern heavy. Gas tank, 4 stroke motors, batteries, heavy transom, etc. make them sit low in the water. Trim tabs greatly assist in getting up on plane. You might not think this a big deal, but when you have extra weight in the boat, (which we all eventually do), it is so wonderful to tab down to get her up on plane versus moving weight forward! Also, the ability to "lift" the stern allows the boat to plane at lower speeds. Which comes into play in the next big benefit.
Our boats are such a stable fishing platform (which we love) because they have a wide flat bottom. There is a decent bow angle but if it doesn't come down in contact with the chop, that force hits that flat bottom and transmits immediately to your back (which we don't like so much.) :hoboy: I had a whale tail on my 90 Honda when I first bought it which never was able to lower the bow enough to cut the chop. Man, when I installed the Lencos, what a difference. Now, I'm not talking about 3' and greater "seas" but 1-2' chop and even moving slowly through a little larger stuff they help a bunch.
Finally just a word of experience to those that are setting up new boats. When I first got mine, Instruments were on the top of my to do list. And I couldn't wait to slap a transducer on the stern and immediately start filling my boat with all manner of aquatic life! Within a year I got to Trim Tabs on the list, and of course had to MOVE transducers. So, before drilling that mount for the transducer, assume that you will be installing tabs (because you will) and plan, plan, plan. In fact, thinking about Fisher's current process, if I had that much radius on my sponson/transom and limited room for a transducer I might seriously be thinking about a through hull ducer or perhaps mounting on the sponson.
Anyway, food for thought. No matter what you do, at least fiberglass is pretty easy to fill and repair! Good luck!