Hi everyone. You are getting some good advice here. The Humber Jewel is a piece of nostalgia, and was never intended to be a fast boat. I've owned a couple of them, tried over powering them, and they just don't want to do much more than 40 some odd mph. Back in the day when you powered them up, they would get a power hook. That is when the back of the boat dishes inward under power and drives the nose of the boat in the water. What we used to do, was put a scissor jack under the motor well and adjust it under power. It would allow the boat to get more mph, but if over done at all, it would begin to porpoise.
The jewel has the aero dynamics of a sheet of plywood, and there are much larger boats that run with less wetted surface area and will be more stable at higher speeds.
As far as a tower of power Merc back in the day, they had no power to speak of except the 150 short shafts which when set to 23 degree timing went like hell until # 3 & 5 detonated and or the crank shaft broke. Sound like I know a bit about this??
Back to the Jewel. If you want a small go fast boat that you can actually use, some of the inflatables out there are amazing.
If you want a whole lot of fun for a reasonable amount of money and a boat that looks super cool and can handle rough water, I have 3 Four Winns U boats (17 & 19) and these things are way too much fun, cheap to operate and cost nothing to maintain. I've got to sell two of them.
Well I've got to get back to it here, but regardless of what you do, be safe, have fun, and let's all do our part to keep recreational boating the great activity that it is.
If you want photos, just ask and I'll supply them
shayward@mail.transdata.ca