Seems like 4100 rpm and 20.6 mph with the 9x6 prop is my final number, with my BackH20 26.5 EFI, for which I am most pleased. After having removed and replaced the cavitation plate several times in the process of dialing in the motor and trying out a different prop, the rubber gap seal at the top of the plate, which "seals" the gap between the plate and shaft housing is stretched, mostly from my mis-positioning it. Anybody replace this yet? Seems like I could use a piece of rubber hose and cut a slit in it and slide it over the plate edge. Any suggestions for size/brand/material for this?
I will probably do a few more runs, with both the 9x6 and 9x7, this time simulating a hunting load, and then decide which prop to use.
By the way, while the boat was in the water, I installed some EZ slide pads on the trailer bunks. Amazing how much more easily the boat loads/unloads from the trailer now! Why didn't I do this years ago??

5/16 fuel line scrap , slit with a razor knife , I change them all the time.

H Finn

Gotta make a note of that. Glades, refresh my memory. Did you pick up any speed with the 9/6 prop?


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Stu, good to hear from you! Water has crept up, got in about a 1/3 of a mile and then I was not so adventurous. I picked up nominally .5 mph. I tweaked the throttle up to 4300 rpm but I have hit a plateau at 4100 rpms @ 20.5 mph. This is with the 9x6. I will test again with the 9x7 and more weight up front and then determine what may be best.
Thank you Huck Finn! I will replace with that and once I finalize the prop to use, will Loctite the cavitation plate bolts!
I still need to move the motor up to the back hole to tip motor weight slightly forward to ease the lifting of prop.

Good speeds Glades. It probably won't drop off much with a hunt load. Lost one Cav plate last year because I didn't check the bolts. Now I use lock tight on all four and nylocks on back two bolts. Have a great weekend and Happy 4th.


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Thanks, Stu, same to you and yours!

Found a near identical hose(seal) at auto parts, Autocraft vacuum hose 7_64 " (2.8 mm) SAE J1037 part# AC3339P (Advance auto parts), flexible but stronger fits perfect between cavitation plate and shaft housing! $3.64 for 6', should last a while 5