Yep. I've seen the videos of it doing 24 mph on youtube, but it's on a light weight boat that's rated for a 20-25 hp engine, not your boat that's probably weights 3-5 times as much. What size engine is your boat rated for?
The height looks pretty good. Now you just need to find the right pitch prop to allow the engine to reach its wot max rpm, which I think is 4000-5000 rpm. But if that boat is rated for a 75 hp engine then you'll be lucky to even get it to plane with an 18 hp. It will surprise the heck out of me...
From previous photos it appeared that you only needed to lower the engine 2-3 inches to get the av plate even with the hull bottom, but you're saying you lowered the engine 5"? Now I have no idea of where your av plate is in relation to the hull bottom, and that is THE most important factor in...
It appears the engine is mounted as low as it can be. He doesn't need a jack plate. He just needs to raise the mounting bolts 2 or more holes to get the lower unit higher and the av plate even or slightly higher than the bottom of the hull line. When done, he will also see an increase in top...
Probably because the engine was mounted way too low on the transom. With engine in running position on trailer, I think you'll find the av plate below the bottom of the hull.
You don't want the av plate to be below the hull bottom, so I'd only notch out the minimum amount of transom to accomplish that. If that's 2", then that's all I'd remove. There's no point in removing more than needed. All that will do is weaken the transom.
Either get a long shaft engine or if you want to keep that one get a jack plate for it that will allow it to get down in the water the proper depth. Or redo the transom height. If you notch the transom down, I'd make a splash well for it to avoid taking on water.
Most/all? tachs have settings for the engine installed for. If it's not set to the proper setting, then the reading will be off. And I've seen them set wrong from the factory.
yes. if you are only talking prop rpm, disregarding gear ratio and engine rpm., or if GR is 1:1. Formulas and calc for it are here.
https://www.go-fast.com/Knowledge-base/Find-your-prop-slip/Prop-slip-calculator
Solas prop finder for 12' tiller boat weighing 250# suggest a 12 pitch amita 3 prop. If you can't get on plane now, and you have the engine at the proper height and tilt, then drop down in pitch 2" and try that.