Rate my current rpm/mph and help suggest new prop or tell me to leave it.

[dirttrax]

I have a 1993 pro 17 bass tracker with the factory 40hp evinrude. Fresh rebuild bored .30 all new parts. Motor runs like a champ but is turning a little much for me. It has a 3 blade 11-3/4 x 17 prop. I have no idea if its stock or even close to what it should be. The anti cavatation or ventilation plate(not sure which is correct term) is about level with bottom of boat.

Here is what it does

WOT 6100-6200
MPH 29-30

Now this is with the motor trimmed all the way down, it planes out quick but when I trim the motor up I see now difference till the prop starts to cavatate/ventalate/slip out of water? Then rpm's go up and boat slows down. But doesnt seem to matter what I trim it at.

Over 6000 is to high for me so i back it down to 5500 and it runs about 24-25 motor seems happier. But when I go from 5500 to 6200 the boat accelerates very fast and just feels smoother on the water. Its like the boat is happy over 30 and the motor is happy at 5500 or less.
So can I get 30mph and about 5200-5300 with 5500 max rpm with a prop? Or am i asking to much and should just run it the way it is? Thanks for any help or advice in advance.
And im not deadset on the 30 and 5200 if you know of another route i should be shooting for im open to any suggestions.

 

[craze1cars]

Re: Rate my current rpm/mph and help suggest new prop or tell me to leave it.

You're going thru exactly what I did recently...with a similar boat...trying to make a prop decision with bad data...and I am 100% convinced you have bad data. My recent saga where I wasted a bunch of time with bad data: http://forums.iboats.com/prop-quest...on-2-stroke-17-aluminum-bass-boat-619141.html

Assuming you have a 2.42 gear ratio (can you please confirm...I believe this to be correct) Prop slip calculator shows at 6150 rpm, 29.5 mph, and 17 pitch prop, you have 28% slip.

This is not mathematically possible on a small planing boat.

Therefore, either you have inaccurate speed, inaccurate RPM, or as in my case, BOTH my speed and RPM were inaccurate and I had to do GPS speed and a tach repair before I could make any accurate propping decisions...

You are in a similar boat. Pun intended. Something ain't right with your current numbers. What is the exact source of your figures, and have they been verified with a 2nd source?

I also found that A/V plate level with bottom of boat was WAAY too low. The only way to verify is to peer over the back of the boat and look at the A/V plate while at top speed. If you can't see the plate, it's dragging thru water and too low. In the end I had to raise my motor 3 full holes above level, bringing the A/V plate to about 2" above the bottom of the boat, to get it skimming just above the top of the water while near top speed. Every hull will be different so you have to experiment and try. Mine is not an actual Bass Tracker but a Landau Bass 170...similar but different.

 

[jestor68]

Re: Rate my current rpm/mph and help suggest new prop or tell me to leave it.

I would suggest verifying the accuracy of your tachometer before doing anything.

If you are in fact turning 6000+ rpm with that 17 pitch prop, it indicates excessive slippage; probably due to the prop being a older lousy design.

If your rpm's are accurate, I'd try a Solas or Turning Point 17 pitch prop(both under $100). Either of these props will bite and hold better and serve to pull the rpm down a bit.

I wouldn't mess with the motor height if it's about even or slightly above the bottom. If you're experiencing slippage now, raising it will only make it worse.

I do not recommend to ever hang out the back of a boat trying to look at the AV plate. That IS NOT how we determine motor height.

 

[craze1cars]

Re: Rate my current rpm/mph and help suggest new prop or tell me to leave it.

I wouldn't mess with the motor height if it's about even or slightly above the bottom. If you're experiencing slippage now, raising it will only make it worse.

I do not recommend to ever hang out the back of a boat trying to look at the AV plate. That IS NOT how we determine motor height.

I made the same assumptionyou did until I tried it....raising motor made no sense to me since I already had easy blow-out with little trim and excessive slippage with motor on the lowest setting. Yet with each hole I raised, my slippage was reduced and it now handles better than ever after raising 3 full holes. How does that work? I dunno...but it did.

If A/V plate skimming over the top of the water is not how you determine motor height...then what is the correct height and how do you find it? When mine was about even with the bottom of the boat, the A/V plate was dragging hard under the water. So even with bottom or even slightly above did not work for my boat, I needed about 2" above.

Obviously you want to be safe with another driver and on calm water when looking over the back at speed.

Here's a nice video showing incorrect, better, and followed by correct motor heights with some annotations and explanations within: http://www.youtube.com/watch?v=_Pb5cGHikwc
and here is a nice website with good explanation of the same concept:
http://www.veradoclub.com/smf/index.php?topic=137.0

Just sharing my results with a similar boat to OP...so I stand firm by my recommendations. Not trying to start any arguments but not real crazy about someone telling me I'm wrong without even offering any explanation of what is right...

Dirttrax, I also forgot to mention I found some improvements each time I got more weight out of the bow and into the stern. So weight distribution may also be something you want to play with, particularly batteries, anchors, and other heavy items you may have in storage.

 

[BigDfromTN]

Re: Rate my current rpm/mph and help suggest new prop or tell me to leave it.

I made the same assumptionyou did until I tried it....raising motor made no sense to me since I already had easy blow-out with little trim and excessive slippage with motor on the lowest setting. Yet with each hole I raised, my slippage was reduced and it now handles better than ever after raising 3 full holes. How does that work? I dunno...but it did.

If A/V plate skimming over the top of the water is not how you determine motor height...then what is the correct height and how do you find it? When mine was about even with the bottom of the boat, the A/V plate was dragging hard under the water. So even with bottom or even slightly above did not work for my boat, I needed about 2" above.

Obviously you want to be safe with another driver and on calm water when looking over the back at speed.

Here's a nice video showing incorrect, better, and followed by correct motor heights with some annotations and explanations within: Proper outboard height - YouTube
and here is a nice website with good explanation of the same concept:
Propping correctly & how to test props.....

Just sharing my results with a similar boat to OP...so I stand firm by my recommendations. Not trying to start any arguments but not real crazy about someone telling me I'm wrong without even offering any explanation of what is right...

Dirttrax, I also forgot to mention I found some improvements each time I got more weight out of the bow and into the stern. So weight distribution may also be something you want to play with, particularly batteries, anchors, and other heavy items you may have in storage.

Dont take this too personal. What I read from other poster was not to peer over rear of boat when under power. WHICH I would believe to generally be very good advice. I have looked over the rear of my while running but mine is a pontoon with a fishing seat right at the rear of the deck and it provides safe clear sight of the prop and A/V plate.

 

[dirttrax]

Re: Rate my current rpm/mph and help suggest new prop or tell me to leave it.

Thanks for the advice/help guys. Craze1cars the gear box is correct and my MPH was verified by way of gps unit. My tach however has not been verified. I will work on getting something to check this with this week. As far as the a/v plate the motor is mounted in the lowest position so it probably is dragging. I will try to find a bud to help me check it on the water this weekend and report back results. Not sure if the prop is original or not . It appears that it could possibly be a 93 model prop not terrible shape but im sure worn if measured. Which leads me to another question its a 11-3/4 prop how do i measure that?

 

[dirttrax]

Re: Rate my current rpm/mph and help suggest new prop or tell me to leave it.

BigDfromtn im also from TN I live in lexington, bout midways between memphis and nashville.

 

[craze1cars]

Re: Rate my current rpm/mph and help suggest new prop or tell me to leave it.

Which leads me to another question its a 11-3/4 prop how do i measure that?

I think you will likely find that your tach is reading too high.

11 3/4" refers to the diameter of the prop. Measure from center to tip of a blade, times 2...

But props don't "wear" and get smaller with time if I'm understanding what you are asking...unless it has hit a bunch of stuff over and over again, and someone has been doing a lot of filing over the years...

Only a prop shop can verify/measure pitch to make sure the blades have not been bent.

 

[dirttrax]

Re: Rate my current rpm/mph and help suggest new prop or tell me to leave it.

I think you will likely find that your tach is reading too high.

11 3/4" refers to the diameter of the prop. Measure from center to tip of a blade, times 2...

But props don't "wear" and get smaller with time if I'm understanding what you are asking...unless it has hit a bunch of stuff over and over again, and someone has been doing a lot of filing over the years...

Only a prop shop can verify/measure pitch to make sure the blades have not been bent.

Ok thanks. I misunderstood then I thought I had read the aluminum would wear down and get smaller in overall size. First chance i get im going to try to verify the tach with my snap-on timing light. It has a 2cy selection and reads rpm's so im gonna use it.

 

[BigDfromTN]

Re: Rate my current rpm/mph and help suggest new prop or tell me to leave it.

BigDfromtn im also from TN I live in lexington, bout midways between memphis and nashville.

I know where Lexington is.
Have some family that lives there. We also used to camp at Beech Lake on a regular basis. We now rent a lot on TN river at Bath Springs.

As for Props... I used Finley Prop service in Enville, TN. They let me trade props 3 times until I went to a 4 blade and Im happy now. He also said he would add cup later If I needed him to.

 

[steelespike]

Re: Rate my current rpm/mph and help suggest new prop or tell me to leave it.

Aluminum prop will wear especially in heavily silted water , heavy weed conditions sandy,muddy shallows.
Not likely in a few years but with excessive use and over time.

 

[steelespike]

Re: Rate my current rpm/mph and help suggest new prop or tell me to leave it.

Aluminum prop will wear especially in heavily silted water , heavy weed conditions sandy,muddy shallows.
Not likely in a few years but with excessive use and over time.A 20 year old prop could show wear.
Using 30 mph and 12% slip I get about 5125 rpm

 

[jestor68]

Re: Rate my current rpm/mph and help suggest new prop or tell me to leave it.

If A/V plate skimming over the top of the water is not how you determine motor height...then what is the correct height and how do you find it?.

Simple really. You raise the motor until you experience too much prop ventilation; then lower it back to that hole where you did not experience too much ventilation; that is the optimum height.

It might be 1 inch above; it might be 3 inches above the keel; or it might end up even with the keel. Every hull is different and you cannot point to a picture of some guys set up and say they all need to look this wa

Bear in mind that these guys are running expensive SS props. Do you really think that you'd see that picture running the standard aluminum prop?

There is no need to go back and look at the AV plate; but that is entertaining.

 

[dirttrax]

Re: Rate my current rpm/mph and help suggest new prop or tell me to leave it.

I know where Lexington is.
Have some family that lives there. We also used to camp at Beech Lake on a regular basis. We now rent a lot on TN river at Bath Springs.

As for Props... I used Finley Prop service in Enville, TN. They let me trade props 3 times until I went to a 4 blade and Im happy now. He also said he would add cup later If I needed him to.

I live 15-20 from beech over on natchess trace. Chances are we have past eachother on the road or river then. I growed up at martins landing in bath springs and hang out there, saltillo, riverheights etc.

 

[dirttrax]

Re: Rate my current rpm/mph and help suggest new prop or tell me to leave it.

Aluminum prop will wear especially in heavily silted water , heavy weed conditions sandy,muddy shallows.
Not likely in a few years but with excessive use and over time.A 20 year old prop could show wear.
Using 30 mph and 12% slip I get about 5125 rpm

Going to test it tommorow i hope your right and its about a grand off. Just seems if it was it would be way off ayt idle though.

 

[dirttrax]

Re: Rate my current rpm/mph and help suggest new prop or tell me to leave it.

Got a buddy going to ride along tommorow eve and check the A/v plate. I will post results from that and the tach readings.

 

[BigDfromTN]

Re: Rate my current rpm/mph and help suggest new prop or tell me to leave it.

I live 15-20 from beech over on natchess trace. Chances are we have past eachother on the road or river then. I growed up at martins landing in bath springs and hang out there, saltillo, riverheights etc.

We may well have pasted each other.

We launch our pontoon at Martins Landing and beach it just down stream about 1/2 mile. The lot we rent is just down stream between the first and second house past Martins Landing development. If your on the river this weekend and see our Fisher with a green top give me a shout out... Hey Big D!

Im curious about your tach. I suspect it is off by a percentage like a speedometer does. The higher it gets the more its off. Does that tach have multiple settings on the back. Maybe it is set on 3 cylinder vs 2 cyl????

 

[dirttrax]

Re: Rate my current rpm/mph and help suggest new prop or tell me to leave it.

Happy to report you guys were right and I was wrong which inturn saves me money! The tach was wrong after verifying it with my snapon light. Not sure how bad but around a 1000 as you all guessed. It was 100rpm off at idle and 600rpm off at 4000 rpm. That was the highest I could get everything in order by myself. So figure by the time it hit 6100-6200 it would be at least a grand off. Also this eve my bud came over and we ran it and checked the a/v plate and its perfect just skims the top of the water.

I really wanted to give you guys thanks for all the advice and help that kept me from buying a prop I didnt need.

 

[dirttrax]

Re: Rate my current rpm/mph and help suggest new prop or tell me to leave it.

We may well have pasted each other.

We launch our pontoon at Martins Landing and beach it just down stream about 1/2 mile. The lot we rent is just down stream between the first and second house past Martins Landing development. If your on the river this weekend and see our Fisher with a green top give me a shout out... Hey Big D!

Im curious about your tach. I suspect it is off by a percentage like a speedometer does. The higher it gets the more its off. Does that tach have multiple settings on the back. Maybe it is set on 3 cylinder vs 2 cyl????

Wont be out this weekend got to work. Back years ago before all the houses at martins landing my dad kept a camper at the boat ramp and one just up the road before the curve by the old bridge. I spent every weekend and summer there growing up. My dad would roll over in his grave if he saw all the houses and stuff down there now. He was a true river rat. We would get up of the mornings take the boat over to the island get a bar of soap and bath on the sand bar! lol It was good times though.

 

[oldandintheway]

Re: Rate my current rpm/mph and help suggest new prop or tell me to leave it.

Dont take this too personal. What I read from other poster was not to peer over rear of boat when under power. WHICH I would believe to generally be very good advice. I have looked over the rear of my while running but mine is a pontoon with a fishing seat right at the rear of the deck and it provides safe clear sight of the prop and A/V plate.

I agree about not looking over the stern while running at WOT.
Ed