You are 100% 0n the right track!
The special 4-blade HT props for both the 8/9.8 and the 9.9/15 are fantastic for sail applications. They have 2 major characteristics that make them the best choice: 1. Huge blade area, combined with low pitch make them "shovel" water at low speeds. Also, 2: The over-sized hub allows the exhaust to stay off the blades when in Reverse, so the motor "bites" into clean water, giving Stellar reverse control. We install a lot of them, and have had Zero complaints -- all compliments! For your boat and motor combination, I would recommend the Tohatsu/Nissan 3Z0B645143, PROPELLER (7) 4 BLADE X 10 X 7 (F15/20C), which has an MSRP of $122.58, available from any Tohatsu/Nissan dealer (including me). FWIW, I personally have one of these type props, in 5-pitch, on the 9.8 on my 7,000-pound HR-28, and it out-performs the old 15 hp OMC motor that had a 3-blade prop. You can drop me an email at the office
email@example.com, or call 716-877-8221 M-F 9-5, and we can discuss the situation.