Rpm and propellers

[anytec522]

I hope that you experienced boaters can help me with my question, even though it has more to do with engines than fishing. I have a propeller on my Yamaha F 100 2008 that allows the enginge to reach 5600 RPM at WOT. According to the engine manual, WOT should give rpm between 5000 - 6000 rpm. As I understand it, this is just perfect, since I have 5600 rpm at WOT, and the engine gives it´s maximum horsepower at 5500 rpm. Now, an expert told me that I need to change prop to one that will increase rpm at WOT to at least 5800-6000. My question: Do I really have to change prop for 200-300 rpm, when I am in the correct zone already? All of you who have knowledge in these matters, pls find time to answer, since I am becoming more and more uncertain about the whole issue.

Peter

[OrygunBasser]

There needs to be more info on this question.

What type of boat, is that RPM with the engine trimmed out as far as you can and still have control of the boat? Max RPM is just that, the most you can get out of the engine with your set up!

If you want to gain a little RPM you can raise your engine up some and see how she performs. If we are talking about a pontoon boat, then you have pretty much what you have.

[anytec522]

Thank you for trying to help and inform me, OrygunBasser! The motor is as high as I can have it. It´s an alu boat (16 feet), with 21 degree bottomangle, not at all a bassboat, more of a familyboat. The reason I chose to ask this forum is that I know that bassfishers are notoriosly good in any type of question regarding boats. As I see it, the only way for me to gain rpm is to put on a smaller prop, but is it really something that needs to be done, isn´t my 5600 rpm good enough for the engine?. I am happy with the performance. I just want my engine to work in a healthy way within the recommendations, so that I will be able to enjoy the engine for years to come.

Peter

[ally260]

With what ya got and what your doing I wouldn't change a thing unless your not happy with it. Its not a hot rod. Its a family boat doing what family boats do. That LITTLE motor will probably live forever tha way it is and ya take good care of it. JMO............T

[1FASTLASER]

There's an old saying that comes to mind........the roof aint leaking so LEAVE IT ALONE..........your just fine right where u are at.

[Abbeysdad]

I'm just a novice, but it seems to me you'd spend what, $300 - $500 (or more) dollars for a new prop to go maybe 5-10mph faster at full throttle. Seems foolish to me. You don't need to get anywhere 2-5 minutes sooner! If the engine is running good, be happy.
I wouldn't waste the money cause there will be other stuff you need more.

(footnote: oh now if it were a race boat, well then yeah, we might want to raise it up so one blade was out of the water at all times and bolt on a S.S. high performance prop...or better still, yank that lil engine outta there in favor of a much bigger one!

But the best fishin isn't done on plane at full throttle, but with that thing turned right off!)

[geeforcem]

some of us enjoy getting the most performance out of our hulls.. It's a challenge!

jeff

[1FASTLASER]

Originally Posted by Abbeysdad

I'm just a novice, but it seems to me you'd spend what, $300 - $500 (or more) dollars for a new prop to go maybe 5-10mph faster at full throttle. Seems foolish to me. You don't need to get anywhere 2-5 minutes sooner! If the engine is running good, be happy.
I wouldn't waste the money cause there will be other stuff you need more.

(footnote: oh now if it were a race boat, well then yeah, we might want to raise it up so one blade was out of the water at all times and bolt on a S.S. high performance prop...or better still, yank that lil engine outta there in favor of a much bigger one!

But the best fishin isn't done on plane at full throttle, but with that thing turned right off!)

Get lots of replys like your abbeys. I wanna point out something that some folks dont think about. Optimizing performance is not always obtaining the fastest speed for a particular boat and motor combo. Its more like mating the 2 and allwoing them to work together in harmony...........speed is one of the perks but longevity of the motor is alos one as well as mpg,handling,ride,etc etc...I could go on and on but I am sure u get the picture.

[anytec522]

Thanks to you all for the input you have given me! I know now that I don´t have to worry about this issue any more, until I get as serious with boat and engine performance as all you guys! Will read the forum regurlary, and learn from the experts!! Thanks!

Peter

[Abbeysdad]

Originally Posted by 1FASTLASER

Get lots of replys like your abbeys. I wanna point out something that some folks dont think about. Optimizing performance is not always obtaining the fastest speed for a particular boat and motor combo. Its more like mating the 2 and allwoing them to work together in harmony...........speed is one of the perks but longevity of the motor is alos one as well as mpg,handling,ride,etc etc...I could go on and on but I am sure u get the picture.

I remember when I was in high school, chrome reverse wheels were the rage - amazing to see so many $200 cars with $500 wheels! lol

I hear you though regarding performance, I just question if optimizing performance starts with replacing a propeller? What about new plugs, timing, carb adjustment, slightly higher octane fuel, better/proper trim on plane...I'd consider those things before investing in a new prop or jacking the motor up higher on the transom.

I guess my "need for speed" is behind me and my focus is on smooth running and on-going reliability. Spending several hundred on a new prop so I could go just a little faster just doesn't make sense to me...and we are talkin about fishin boats here.

The other day I saw a little (Stratos?) bass boat with a 200hp outboard motor on it. Betcha that nearly flies!

[geeforcem]

i guess we assume he has already done those items.. and now is looking for more... or just looking to see if he is in the proper range.

You'd be surprise what the 'correct' propeller will do vs. the standard prop that comes with the engine. Like Laser said... performance is not just top speed...

[1FASTLASER]

Your missing my point abbeys. If that boat and motor........which is just like a car in the respect of say you dont have the correct gear ratio or the correct size tires on it.....is not turning the correct rpms at the correct time with the least amount of slip all the plugs and timing adjustments are going to be useless because the motor is NOT capable of running at its optimum. Again, just like a vehicle.....say you have a 4 wheel drive and have 4:56 gears and it NEEDS 4:11 gears to reach its maximum potential. The you can adjust and replace all you want to but to have a engine that runs PROPERLY and will have the ability to live a LONG healthy life you gotta switch gears and/or props.

[Abbeysdad]

No, I'm just thinking that 1) the engineers at Yamaha likely matched the propeller and engine correctly for overall use for the intended purpose and 2) spending $300-$500 for a new prop to get a potential 200 rpm increase at WOT probably has little return on the investment. Just because you can, doesn't mean you should. Now, if he needed a new prop anyway, then perhaps upgrading to a prop that offers higher performance makes sense (as long as the price isn't out of reach).

Footnote: I'll admit I'm old school and not a gear head. I just want a reliable boat for fishing and touring - it doesn't need to race across the lake with a 30 foot rooster tail, or jump out of the water and fly. I just want to get where I'm headed, catch some dern big fish and return safely! I can afford to go slower - we're all in to much of hurry. We even hurry up to get in line to wait!
We're not racin, we're fishin!

[geeforcem]

not necessarily true... there are so many conditions that the engineers have no control of.. boat weight, hull type, total weight of passengers plus gear, etc... even if you look at the old Quicksilver prop charts ( Mercury), they have a wide range of size depending on application.

My old saltwater boat (19' Proline) had an 200EFi merc... it will barely turn a 21" at 5600...


My Laser bass (17') with the basically the same engine (200 carb) will turn a 26" at 6500+rpms. Do you think the engineers can pick that?

That 200rpm could be critical if it is pulling too much load on the engine ( or vice-versa and over-revving). Even adding extra passenger and gear could affect the load and rpm potential of an engine.


we have about 10- 12 boats in our family.. from high performance bass boats, to saltwater rigs and even a small 13' flats skiff. We do our best to get the correct propeller for it's intended use... Yes it may be cost 2-300 bucks... but it makes up for in proper holeshot, handling, and fuel mileage!

jeff

[ally260]

99% of tha time tha DEALER does tha prop (unless factory rigged combination) thing so your left with pot luck most of tha time unless tha buyer has done his research. Some (dealers) got an idea and some don't have clue..........T

BTW, I'd gladly spend 3 ta 500 for a bolt on 5 ta 10mph in my world............

[Abbeysdad]

"Hey dad, I wanna go fast."
"Son, it's a 1962, 6 cylinder, Chevy Belair - if you wanna go fast, you need a different ride."

lol

[1FASTLASER]

I hate when good conversations end. We had a good one going here.

[Culln5]

If it were me, I would shell out the money to have my motor operate at it's fullest potential. Which, in your case, is as close to 6000 RPM's as you can get. I have set my Yammie up to run 6000 RPM's at full load and 2 people. I can, if I wanted to, push it over the rev limiter when I'm by myself.

These motors, just like the hull of your boat, are designed to operate at a specific RPM. If you were to under power your boat, you would not achieve the optimum performance out of it. Equally, if you under prop your motor you won't achieve the optimum performance out of it either.

Personally, I would re-prop it properly and use the one you have as a spare. Just my $.02.

[Abbeysdad]

Okay 1Fast, I'm a convert - I'd like to get the best possible reliable performance from my boat...if that yields more speed, I can always back off on the throttle!
Still, I'm not sure I would want to invest several hundred dollars replacing a prop just to see a small increase in WOT speed (I'm just saying).

[1FASTLASER]

Cullin5 you are SO correct.
So ya starting to see where I am coming from ey Abby. Ok here is something else to think about.......in your last post you say you dont know if you would spend say $400 for a tuned prop to see the extra 3 or maybe 5 mph.....right.........Well if your car or truck for that matter when ya bought it say had the wrong size tires on it and even though it still performed would you continue to drive it that way, knowing it was not correct and that replacing them with the correct tires would IMPROVE mileage and IMPROVE handling and topend as well. AND the biggest thing I wanna point out here is......remeber when they had the commercial about the oil......."you can pay me now or you can pay me later".....Well with correct proping you dont have to worry about "Paying later cause you will save enough on the fuel bill after a year or 2 of boating that the "400 for the tuned prop" will be an INVESTMENT!
I totally understand your statement on "spending the extra to only see a couple of mph gain" but ....the only way to know that your boat is operating at its max potential and therefore assuring you the possiblity of MAXIUM longevity of the motor and MAX mpg" is through the process of setting your boat up to be able to run at irs "MAX"

[Abbeysdad]

1Fast - I don't mean to challenge you, because I'm sure you know more about boats & boat motors than a newbie like me - you 'probably forgot more than I know'...but a couple of things jump out at me here.

1) For instance, my 90HP Mercury has a WOT rpm of about 5000. The other day, the lake was choppy, so I was running at a reduced speed (about 4000rpm). I wouldn't think this reduced speed is any different than driving my car at 50 instead of 80. (so increasing a top end speed really isn't going to improve the life of a motor - is it?).

2) Props seem like a funny thing to me. If I increase the RPM of the same prop, of course I would move more water and go faster. But if I put on a different prop, say a different pitch or even a different design, I may be able to get a higher rpm out of the motor, but that doesn't necessarily mean I'm moving more water - I may be moving less water and the reduced load increases the rpm's. So...If I get a different prop that changes the pitch a couple of inches to increase the rpm's 200-300, I'm likely moving less water (less resistance) to achieve the rpm increase, with little if any speed increase. Does this really improve engine performance or longevity?

3) Last, without speed trials to match a prop to motor and hull design, I'm not sure how you pick a single different prop off the shelf and know it's gonna ~really~ yield better performance.

...just wondering

[1FASTLASER]

Got ya thinking and in the right track buddy. Each and every prop out there has what is called a slip factor. Some of the props have more of a slip than others do. In the real world any prop that you can get MAX rpms and Max speed out of on YOUR particular hull and engine combo will have a lesser slip factor. The most knowledable prop folks out there say that 13% is about the norm..........less of a slip being a very good thing......I have heard of a few being able to get there slip coefficient down to 11% and lesser which is GREAT.
For instance.....one of my old boats comes to mind.it was a procraft 180B.....which had a XR6 on er. I had her at 2 3/4"s below pad and was running a Balanced and blueprinted Laser ll prop that had a special cut on the blades. It started life as a 25p. When I bought the prop she wouldnt even spin the wheel. Couldnt get outta the hole for nuttin. BUT.....after I did get out of the whole I had a blazing topend and so so midrange. After my prop guy got done with her the hole shot was VERY good midrange was awsome and I dint loose any topend. I had bolted other props only to find that I would loose either topend or holeshot but as you stated it was a trial and error thing. There is not hardly a hull out there that someone hasnt tried to optimize performance on so as far as picking aprop to start with you can be rest assured someone else has already done the work for ya.
On the motor longevity question I hopefully have answered your ? Just increasing rpms does not mean that you are running the motor at its max potential........max potential is a combination of getting out of the hole efficiently,having good midrange punch and being able to run max rpms with a good topend. One thing I want to say here though.........ITS VERY hard to have a break neck hole shot and blazing topend...same as a car....put in a set of 4:56 gears and smoke the tires off the rim but cant run 90...bolt in a set of 3:73's and yeah ya can turn the wheels over but you can run 120. Hopefully I have cleared up some of the prop questions fer ya. If I havent ASK AWAY.

[Abbeysdad]

Well, if nuttin else you got me thinking...I was also thinking from that other thread that just maybe my motor is a bit to deep, mounted in the lowest holes provided, looks very similar to 1600's situation. I haven't done the measurements, but can tell you that when trimmed all the way down and in low speed, I can feel the drag/excessive pull to the right. I get around this (sortof) by keeping her trimmed up about where I would at WOT.... but have to wonder if it might be better with a bit less motor down under.
But in that other example of the 4" pad to bullet measurement, we'd be raising the motor only about an inch - is that really gonna make a world of difference?

[Christopherkeene9]

While we are on the topic of motors and something that Abbeys said, why don't boat manufactures build in some right thrust on single motor boats to counter the effects of torque? Other than it may not track straight then.

We do that on planes and it works great!

[Abbeysdad]

Originally Posted by Christopherkeene9

While we are on the topic of motors and something that Abbeys said, why don't boat manufactures build in some right thrust on single motor boats to counter the effects of torque? Other than it may not track straight then. We do that on planes and it works great!

They do in the adjustable trim tab (it's a fin back by the propeller just under the cavitaion plate) - however, you adjust this such that the boat tracks and turns well on plane (at faster speeds). It's typically offset slightly to the right, acting like a rudder to help keep the motor straight. However, it's affect at slow speeds, trimmed down, seems pretty minor. That's why I mentioned trimming up at slower speeds which seems to reduce the 'torque right' effect.