+1 on the 23 Penn Yan!!!
Great maneuverability on that boat. At least as compared to other single screw inboards.
However, searching for the right prop took talking with the owner of PY, at least 6 prop shop experts, 7 props and 8 or 9 adjustments. It was quite the science project. Costly, but also a lot of fun.
The advantages of the tunnel were primarily low draft, and a shallow shaft angle that put the engine very low and centered in the small boat, ideal for the center of gravity.
I eventually got fairly decent performance on a new higher hp engine, but it took a LOT of experimentation. The tunnel was very finicky on how it responded. Since the prop diameter was essentially fixed, you had to play with blade number, rake, cup to get the tunnel to flow more water. Off even by a little and efficiency would tank.
My buddy had a twin tunnel screw 33 but he only drafted a couple inches more than I did. We traversed some shallow rocky water together at speed! I once went clean over a hiding tree with no damage to the prop at all.
I’m left with mixed feelings. It was really fun on a small boat for someone who loved to tinker, but could become prohibitively expensive on a vessel with larger, expensive props. Lots of guys in the PY community ran around with some pretty horrible perf, large rooster tails, slow speed and just lived with it as normal. I hear some pretty bad reputations on larger boats with pockets and can’t help but to wonder whether the problem is really just non ideal props and too expensive to troubleshoot coupled with few people who know how to make it work.
First question/principle if I went with prop tunnels would be to get very clear on what my goals were and in what order. To get something, you will need to give something else.
