I have a Pacific Seacraft Flicka 20 weighing around 5500-6000 pounds that I've repowered with a Nissan NSF6B4 - and yes I know it is a compromise but even with the standard prop, I'm pretty pleased with the performance I've seen so far. I recognized prior to purchasing that I needed a high thrust prop but have been looking for info on the best prop to get.
TohatsuGuru, do you have any comment as to how the Tohatsu 399B645121M compares with the Mercury 48-812951A1? The Merc part looks like it runs about $70-$80, a significant savings over the Tohatsu price. Is there a significant fit or performance difference to warrant choosing the Tohatsu over the Merc part? Apparently the Merc part fits. There is another Flicka sailor on the Flicka list who has installed it but I haven't heard back from him as to what difference it made in performance.
My Flicka gets to about 4.4 knots at about 1/2 to 3/4 throttle with the 6HP using the standard prop. Past that it doesn't go any faster.
My old motor is the Yamaha 9.9 HT. It pushed the boat at about 5 knots around 3/4 throttle and around 5.2 to 5.6 wide open. Hull speed for my Flicka is also around 5.2-5.6 or so. I'm keeping it and plan to rebuild it as it was getting unreliable but it was also considerably heavier than I liked, canting my boat towards the left side (left stern mount) because of the weight. The tiller is external and center on the transom so the outboard has to go either left or right. As mentioned in other posts, the Yamaha 9.9 is incredibly quiet when it is running but it is a heavy beast to be hanging off the back of a sailboat...