I think I have the wrong prop

[batlbot]

Let me start by quickly saying I have researched until my eyes and brain hurts! I know I am in the right place, and I hope I have all the info needed for some kind help.

I recently bought a 17' Bass Tracker Aluminum Hull with a 2000 Merc 75HP (1075412YN Model#). It has a Quicksilver SS prop 16P (OS5116?).
The problem is (and bear with me I am brand new to boating) I think it over-revs at WOT. As a matter of fact, I am sure it does, because if I run WOT for more than a minute or so the alram goes off. I am pretty sure my max RPM is supposed to be around 5000 but I am not sure, as I don't have manual (and apparently any type of info you want to get from Merc comes at a price or "from your local dealer") anyway, it revs to about 6000+ at WOT.

I am guessing that I have too little pitch or perhaps to small a diameter? I'd like to get just the right prop to keep from killing my engine. Not looking to do 50MPH in persuit of a fish, if you know what I mean. Right now, I can cruise along at 5000RPM at about 35-38MPH with 2 folks in the boat.
So to summarize:
2000 Merc 75HP
17 foot aluminum hull boat
16P Quicksilver SS prop
over revving (I think?)
Any suggestions on if this is the wrong prop (i suspect it is) and what I should do about it?

One more thing !!$400 for a new prop, please tell me this is a joke!

 

[batlbot]

Re: I think I have the wrong prop

Dang it!
forgot to add one more thing to the above post.
The previous owner mounted one of those plastic "Stabilizer/Planer" devices to the motor. I think that is what it is called. Might that have a part to play in the prop/over-revving question?

 

[WillyBWright]

Re: I think I have the wrong prop

It's a hydrofoil. Lose it. I'd think a 19p prop would do fine. You're looking for 5500. Overrevving starts misfiring once it hits the RPM limiter, it won't send an alarm. A steady tone is an overheat situation. You might want to have the water pump rebuilt.

 

[batlbot]

Re: I think I have the wrong prop

BillyB. Thanks for that.
On the alram, now I am a bit concerned... First thing I did was have a mech. replace the Pump impeller. It spews a mighty strong stream of water, so not sure why the overheat unless the over-revving and the hydrofoil are affecting it. Why do you say to lose the hydrofoil, by the way? Not questioning if you are right or wrong, I'd just like to understand your wisdom.

On the prop, so you think my 16P is not enough pitch?
Is there a suggestion or recommendation for the diameter of the prop?

Thanks again.

 

[rndn]

Re: I think I have the wrong prop

I'm not sure but there may also be a thermostat which should have been replaced with the impeller. Like I said I'm not sure your motor has one.

 

[troypolla]

Re: I think I have the wrong prop

I think his comment about losing the hydrofoil is that they are usually more hinderance than help. Trim tabs do the same thing although they cost more. Hydrofoils on the other hand can make your boat handle badly in some instances. He is also correct about that overheat alarm.

 

[steelespike]

Re: I think I have the wrong prop

BillyB. Thanks for that.
On the alram, now I am a bit concerned... First thing I did was have a mech. replace the Pump impeller. It spews a mighty strong stream of water, so not sure why the overheat unless the over-revving and the hydrofoil are affecting it. Why do you say to lose the hydrofoil, by the way? Not questioning if you are right or wrong, I'd just like to understand your wisdom.

On the prop, so you think my 16P is not enough pitch?
Is there a suggestion or recommendation for the diameter of the prop?

Thanks again.

Foils can cause more problems than they solve you need to start from scratch.Something like Smart Tabs are a uch better solution;after you are sure your setup is right.
I'm not an expert but as far as your prop pitch goes it doesn't seem to me you are to far off.I think first I would confirm your tach is accurate perhaps borrow a shop tach and test it out.
A 75 Etec on a 800lb boat similar to your tracker turns a 17in. SS prop at 5350 It would seem your motor would be within about 200 rpm of that.
Unless something else is creating problems perhaps excessive cavitation or minor ventilation or of course tach problems.