Prop damage, new prop, performance gone!!!

[rushcreek]

Hey guys, here is my problem. I have an F & F 20/72 Mod-V aluminum hull boat with a 2006 Tohatsu 115 TLDI. I bought new last year.

After testing a few props, my best performance came with a Ballistic 13.5 * 17 three blade. My motor would push out 5800 rpms and run 46-48 mph.

In October I was idleing (and I mean idleing) on Reelfoot Lake at low water and eased onto a stump stopping the boat. I just eased the boat forward until it came off of the stump slowly. The stump was in the very center of the boat and when the back of the boat dropped as the stump came off with the motor tilted up, it broke a small piece (approx 1.5 * 3.5) from the front left side of the cavitation plate. Later in the year I bent two of the blades of my prop on a stump.

I ordered a 19 pitch ballistic thinking that it would really boost my speed. It did not, it bogged it down bad. So I returned the 19 pitch prop and got an identical 17 pitch to my old one that had worked great prior to dinging.

When it came, it performed just like the 19 that I returned. It would only turn at 5200 rpm and would run 36mph. The bow would not trim and lift. This really killed me as we love to ski and ride KY lake in the summer.

Last week I tried some other props (4 blade 15 and 19) both ran 36 mph at very different rpms, and both would trim the boat out right.

Question: Is is common for there to be that much difference in performance in props that are supposed to be identical?? The bent 17 will now cause the engine to overrev and neither will lift the bow.

Any suggestions, I really don't need to go 46 mph, but it could before and it really bugs me that it doesn't now.
rushcreekoutdoor

 

[steelespike]

Re: Prop damage, new prop, performance gone!!!

I think you should take a close look at the bottom of the boat.Look for any depressions in the bottom may be back near the stern.Wouldn't take much
could create drag and keep the bow from coming up.

 

[TBarCYa]

Re: Prop damage, new prop, performance gone!!!

Are the two 21" pitch props the same brand? I had two props one Mercury and the other Quicksilver which is OEMd from Mercury and the Quicksilver prop is almost 10mph slower than the Mercury. It actually performs more like the 19" pitch that I have as a spare.

 

[Randybeall]

Re: Prop damage, new prop, performance gone!!!

Check your hull for damage, alumnium can bend when you run over a stump. Good news is it usually can be bent back! Check your lower unit, make sure the prop shaft is not bent. I would take the prop off and put a dial indicator on it and turn it though a full turn. If the shaft is bent at all it will make the prop very inefficent. Since several props give about the same performance I have to suspect something besides the prop is limiting your get up and go.