Am I over propped??

[merc150]

I have a 2003 merc 150 carb motor motor originally came with a 17 pitch prop and mercury recommends 5500-5600 rpm at WOT. With the 17 pitch prop my boat plows (even with the motor tilled up as far as it will let me) and has a hard time getting on plain (1994 19ft Hydra sports flats) but I can get to 5600 rpm @ WOT. I put a 21 pitch prop on it and the boat runs like a bat out of hell (no plowing and gets right up out of the hole) but I only turn 4800-4900 rpm WOT (i usually run it at 4500 rpms or so) Is 4800-4900 rpms not enough? I fish alot of tournaments so the boat gets alot of use. THANKS

 

[Chris1956]

Re: Am I over propped??

The performance seems dramatically different between the two props. That is not usual for "families" of props. What kinds of props are both of them? One have more rake than the other?

It sounds like a 19" pitch of the same kind of prop as the 21" pitch, would be the "bomb". How did you get a merc on a Hydra sport anyway?

 

[merc150]

Re: Am I over propped??

The performance seems dramatically different between the two props. That is not usual for "families" of props. What kinds of props are both of them? One have more rake than the other?

It sounds like a 19" pitch of the same kind of prop as the 21" pitch, would be the "bomb". How did you get a merc on a Hydra sport anyway?

bought the boat used without a motor and dropped a merc on and ran the wiring. stock prop is a mirage and the 21 pitch cant remember the name (had a big pink sticker with black writing) both props 3 blade stainless

 

[Silvertip]

Re: Am I over propped??

Don't understand why the boat has an issue with a 17P but performs much better with a 21. That is counter to logic. 17 is a like a lower gear in your car. Should come out of the hole like a shot but would easily overrev but you gave no WOT rpm information. 21 is like a higher gear in your car. Lower engine rpms but good speed. But the 21 in comparison should be a slug out of the hole compared to the 17. So something is wrong with your description, your observation, or the prop itself is not really a 17P. The 21P is 700 rpm under the manufacturers WOT rpm. To get to 5600 you would need to drop pitch by about 3-4 inches so that says the 17P is correct. Sorry, but numbers don't lie. Only observations, data, and instrument accuracy tell the truth. You should start by verifying the accuracy of your tach. It may be that the 17P is "blowing out" (not getting bite) so that might account for the plowing. But to answer your question, yes -- you are overpropped IF (note the IF) the tach is accurate.

 

[dan02gt]

Re: Am I over propped??

Sounds like the 21 pitch has the correct blade geometry for your hull type but is to much pitch and the 17 pitch is giving you no bow lift.

A 19p Mercury Tempest Plus would run great on your hull. Another (cheaper) option would be a Laser II. Both of these have the Mercury PVS system to help you tune your hole shot and you would want to use the large plugs.

 

[smokeonthewater]

Re: Am I over propped??

I see a HUGE red flag in your first post "plows even with the motor tilted up as far as it will let me"

you need to tilt the motor all the way DOWN to start with and then trim up gradually after getting on plane

 

[Fastatv]

Re: Am I over propped??

I see a HUGE red flag in your first post "plows even with the motor tilted up as far as it will let me"

you need to tilt the motor all the way DOWN to start with and then trim up gradually after getting on plane

What he said. Always start with motor trimmed all the way down. Prop grabs more water, and bow rise is greatly reduced. Strange about the props. One would think that the 17 pitch would have an incredible hole shot as compared to the 21, unless the 17 is damaged or a grossly incorrect diameter and rake. Good luck.

 

[merc150]

Re: Am I over propped??

I see a HUGE red flag in your first post "plows even with the motor tilted up as far as it will let me"

you need to tilt the motor all the way DOWN to start with and then trim up gradually after getting on plane

It is a 17 Pitch mercury prop. I checked the part number and it even says 17P on it. Like i was saying the main reason for changing the prop was because of severe plowing at WOT. The bow would catch the waves bc it was plowing so bad (out of control). I took my uncle (mercury mechanic for 31 years) for a ride in it and he suggested the 21 pitch just to see how the boat would react. Ive tried tilting the motor down and up at WOT and off idle with the 17p and the overall performance sucked compared to the 21p. Keep in mind its a beefy heavy flats boats. Thanks

 

[merc150]

Re: Am I over propped??

The 17 pitch came with the motor from the factory

 

[merc150]

Re: Am I over propped??

Seems like theres a lot of drag with the 17p and no bow lift at WOT. The boat is desent at take off and mid throttle. Also the 17p prop is in perfect condition. Im thinking maybe a 19p might be better

 

[merc150]

Re: Am I over propped??

We also tried raising the motor up and down one hole on the transom with the 17 p and still wasnt good. Ive been boating for 20 years and have had four boats so I have experience boating

 

[limitout]

Re: Am I over propped??

let me ask this, are you 100% certain the tach is hooked up correctly and that it is giving the correct rpm readings? bad connections and selector switches on some tachs can throw your readings off.

you say it runs so good at (wot) that's nearly 1000 rpms below the suggested rpm I have to wonder if its reading right

 

[merc150]

Re: Am I over propped??

let me ask this, are you 100% certain the tach is hooked up correctly and that it is giving the correct rpm readings? bad connections and selector switches on some tachs can throw your readings off.

you say it runs so good at (wot) that's nearly 1000 rpms below the suggested rpm I have to wonder if its reading right

The tach is a brand new teleflex along along with all my other gauges. 17p gives me 5500-5600 and 21p 4800-4900 tested both props last weekend.

 

[merc150]

Re: Am I over propped??

What im saying is the 21p prop is WAY better all the way around. It is a little bit slower with the 21p at WOT but not much.

 

[merc150]

Re: Am I over propped??

What im saying is the 21p prop is WAY better all the way around. It is a little bit slower with the 21p at WOT but not much.

is there maybe a 17p prop that is a different style or more aggressive that I could use? 3 blade or 4 blade? Like is said the main problem is plowing at WOT. Also noticed a bit of prop blow out when slightly turning with the 17. THANKS FOR ALL THE HELP

 

[smokeonthewater]

Re: Am I over propped??

let's work on narrowing down the issue..... judging by the rpm's I think you need to stay with a 17" pitch

when you say plowing, which I would take as meaning the bow is sky high and it doesn't want to plane, do you actually mean the bow is staying low to the water instead if rising?

on the motor height, is the antivent plate even with or slightly above the bottom of the boat"

 

[merc150]

Re: Am I over propped??

Im mean plow as the nose of the boat is real low in the water or nose diving at WOT. The cav plate on the motor is one inch above the bottom of the hull (which is where its the best with the 21P) and with the 17P there really was much difference in the height of the motor

 

[merc150]

Re: Am I over propped??

my 21p prop is a stilla prop (think thats the name) is supposed to be a bow rising prop and it works great its the WOT RPMS i was worried about. Thanks

 

[merc150]

Re: Am I over propped??

my 21p prop is a stilla prop (think thats the name) is supposed to be a bow rising prop and it works great its the WOT RPMS i was worried about. Thanks

 

[smokeonthewater]

Re: Am I over propped??

pretty simple then you need a 17" pitch with a bow lifting design

done deal

BTW do not continue to run the 21.. you are lugging the engine at all throttle settings with it