Theretics of my new prop

[steelespike]

Re: Theretics of my new prop

Not to imply that topglock isn't right but don't you think the etec tests I reported on are closer to what you need at 15".
If a 17 turns out to be too much the motor will be lugging throughout its rpm range at anything over no wake speed.
If you go to the 15 and its too light you can still use it while being sure not to over rev.
The 15 will should give better hole shot,better water sports performance and likely stay on plane better at reduced throttle.

 

[Philster]

Re: Theretics of my new prop

olivialyn11: Take any production car and add HP and you will probably get a faster top speed.

Why you ask?

Because, if you think every car out there is redlining in top gear, you are lalalalalalalala dreaming. The top speed attained in most cars is happening either in a gear other than the top gear or, while in top gear, the engine fails to redline. What happens exactly depends on the driver and/or transmission and who/what selects the gear.

On a boat, HP can make a boat 'hook up' better -- well, launch better. In a car, even though a given engine can overpower a clutch or tire grip, having the flexibility of extra HP allows one to modulate power better, and when she does bite, the engine can launch from that point on. Slip might be more dynamic on a boat, but at the end of the day, the prop is playing the role of final drive gear and traction. At some point, it will bite. You might not drop full throttle to launch on a boat or car. The key is that HP can only help, because you have more power to modulate power and punch it when slip is overcome (on a boat, it's not zero).

 

[topglock]

Re: Theretics of my new prop

Not to imply that topglock isn't right but don't you think the etec tests I reported on are closer to what you need at 15".
If a 17 turns out to be too much the motor will be lugging throughout its rpm range at anything over no wake speed.
If you go to the 15 and its too light you can still use it while being sure not to over rev.
The 15 will should give better hole shot,better water sports performance and likely stay on plane better at reduced throttle.

...and I most certainly defer to SS's opinion...

 

[olivialyn11]

Re: Theretics of my new prop

olivialyn11: Take any production car and add HP and you will probably get a faster top speed.

Why you ask?

Because, if you think every car out there is redlining in top gear, you are lalalalalalalala dreaming. The top speed attained in most cars is happening either in a gear other than the top gear or, while in top gear, the engine fails to redline. What happens exactly depends on the driver and/or transmission and who/what selects the gear.

On a boat, HP can make a boat 'hook up' better -- well, launch better. In a car, even though a given engine can overpower a clutch or tire grip, having the flexibility of extra HP allows one to modulate power better, and when she does bite, the engine can launch from that point on. Slip might be more dynamic on a boat, but at the end of the day, the prop is playing the role of final drive gear and traction. At some point, it will bite. You might not drop full throttle to launch on a boat or car. The key is that HP can only help, because you have more power to modulate power and punch it when slip is overcome (on a boat, it's not zero).

Added hp does not increase your top speed if your already bouncing off your red line, i dont know what fatasy world your living in if you think that... you would have to allow the car motor to rev faster wich would mean doing a blueprint and balance on the bottem end of the motor. now if you wanted to drop a turbo and up your hp, then change gears in the trany or the rear then it would be possible but simply adding hp does not give you a higher top speed once your bouncing off the red line.

Not to imply that topglock isn't right but don't you think the etec tests I reported on are closer to what you need at 15".
If a 17 turns out to be too much the motor will be lugging throughout its rpm range at anything over no wake speed.
If you go to the 15 and its too light you can still use it while being sure not to over rev.
The 15 will should give better hole shot,better water sports performance and likely stay on plane better at reduced throttle.

im not saying your wrong, but my origional post i also asked for a spiffic prop, then was told that my cousins boat does not proform the way i satated, you have no idea what my motor is capable of, for all purposes the 85hp motor currently has 120 raw hp at the crank... i was asking for aid in locating something im having a hard time locating as well as some other advise, i dont need to be told im wrong when ive seen other thing in action

 

[steelespike]

Re: Theretics of my new prop

go to it and good luck

 

[dazk14]

Re: Theretics of my new prop

We have set up that EXACT rig numerous times, and 85's hundreds of times as we were an Evinrude dealership and there was also a Galaxy dealer ~70 miles away.

The OP is clueless, which is why this forum exists with countless VERY GENEROUS and experienced members donating their time and incredible knowledge.

The OP is also behaving like an insulting @ss with his comments to Frank A. that has over 7,000 posts and the OP's apology was a joke.

I won't shed a tear when he grenades that motor and learns the hard way the term, "A Debt of Gratitude".

I'll pass on this one.

 

[Philster]

Re: Theretics of my new prop

Olivian11, I don't know who you think you are, but if you are going to argue, read what you are arguing with first. Your response to me, in which you quoted me, clearly reflects you didn't read my post.

First, more HP adds more speed to most boats even if the prop ain't changed because rare is the day that a given setup runs spot on to redline. On your little wagon, the prop isn't tuned to hit the exact redline of the engine. Props are compromises. Chances are, it's falling short. Add HP and she'll run closer to redline and bingo: More speed.

Second: A 4-blade prop has more surface are to hook up and getting out of the hole is better/faster, but it comes at the expense of top speed.

There is so much wrong with your understanding of speed and RPM, the only way you have a chance is to come back humble. While you're mulling over cars versus boats, just realize that props are like the rear gearing in a car. If you want more speed, you need to run a taller final drive ratio. To do so, be it in a boat or car, you have to come back with more power.

To spin a 25p prop and run 75-80, you'd have to get things a spinnin', and you'll be needing more power.... just to magnify the 'just spin it faster' thing rattlin' 'round inside your head.

If only it were that easy. Physics doesn't play nice. Sorry. It's not linear.

 

[Silvertip]

Re: Theretics of my new prop

Im fully aware what horse power is but the same reason my ford ranger can out pull full size pickups when im running 340hp vs their 410hp because of my gearing, or the same reason a civic with 200hp can out run a car with 320hp, they are geared to do so, raw hp at the crank is not the same as hp at the wheels, the same way with a boat, after the ratio takes place in the unit that effects how fast it spins.
hp in a car is bennificial when your talking about accelleration, more torque is a benifit when your towing more... HP is not everything. The same reason a mac truck can pull 80,000lbs wether it has 650hp vs 800hp because the trany is geared for the diofference to compensate with torque.

As a performance car enthusiast (aka racer) those vehicles have several advantages that a boat power plant does not. Your "racer" has a multi-speed transmission whereas a boat does not. It has one gear so in effect the boat is starting out in high gear all the time. it must launch you, cruise at a reasonable rpm and the engine must be able to reach the manufacturers recommended WOT rpm. If it can't, you have too much prop. If it over revs, you have too little pitch. That prop, whether it is a two, three, four or five, blace, steel or aluminum will provide whatever speed that prop and engine combination is capable of. Increasing pitch beyond that WOT rpm is of no benefit because the engine simply can't twist it. While "race" engines can turn very high rpm, in a boat they will be dead before you pull away from the dock due to water injestion due to valve overlap. Radical cams cannot be used in a recreational boat for that reason. Put your 15,000 rpm powered bike in high gear and try to move off the spot. That sir, is comparing a car/bike to a boat. And the crack about a diesel being the best boat engine -- it is. they can turn monster props at relatively low rpm. They do it in ships all the time. About 450 - 600 rpm wide open, pushing a gazillion tons of scrap metal and 5000 people. at 30 MPH.

 

[Philster]

Re: Theretics of my new prop

The OP is negligent in forgetting about power-to-weight ratios; further, when they want to make a case about gear reduction and the wonders of it, they neglect to mention that top speed plummets with gear reduction.

With boats, the top speed is often flirted with; on cars it rarely matters. Hopping up a car can be just dropping to a short gear (higher numerically) or adding HP or both, because cars are all about acceleration. Sure, give me 50HP and let me switch out to a shorter gear.

A 35 MPH boat will run at 30-35 A LOT. If you jack up a boat to get a screamin' hole shot and she runs at 25-27 instead, that's a bigazz difference. And cruising RPMs? Jeesh.

(Cars/trucks can have gear reduction beyond stock, but boats are already running at max gear reduction or darn close to it. We can talk about custom labbed props, which is like gear reduction down to increments not available 'off the shelf'. Sort of like having 4.11's and actually getting the whole rear rebuilt to magical 4.13's. Imagine that! On a boat, with the prop, you can do that with a prop shop).

 

[sublauxation]

Re: Theretics of my new prop

im not saying your wrong, but my origional post i also asked for a spiffic prop, then was told that my cousins boat does not proform the way i satated, you have no idea what my motor is capable of, for all purposes the 85hp motor currently has 120 raw hp at the crank... i was asking for aid in locating something im having a hard time locating as well as some other advise, i dont need to be told im wrong when ive seen other thing in action

This is kinda fun Actually, and you guys can correct me if I'm wrong, older outboards were rated at the powerhead whereas newer motors are rated at the prop. That would imply that your 85 (or your cousins) is actually less than 85 at the prop shaft, or less than, for instance, the 90 ETECs mentioned several times for comparison. Now if your motor is really a 120 then let us know as that will surely change the advice given to you. I think SS is right with the 15P recommendation. This is not a urinating contest, turning a bigger prop does not a bigger man make There is no shame in a 15 pitch prop though admittedly the big gnarly ones with high rake look cool, especially in stainless.

On that note I highly recommend having a custom prop shaft made so you can put a big prop on that thing. Please report back to us your results so we can pass them along.

Seriously, These people know what they are talking about. They are trying to help. It would be good to listen to them.

 

[Philster]

Re: Theretics of my new prop

Let the OP keep mulling over this and I think it'll 'click':

Prop too small = better hole shot and lower top speed with chance engine can run way past redline
Prop too big = terrible hole shot and top speed probably falls short because engine is lugged and cannot reach redline

Prop too small is actually a better condition for the engine provided the engine has a manual rev limiter called an informed operator, or an automatic electronic rev limiter.

Prop too big is bad all around. The engine is being lugged, placing internal stresses on it that -- depending on a variety of factors, such as engine design -- might result in serious internal engine damage or advanced wear/stress.

Keep thinking of the prop as the rear gearing or final gearing that affects final drive ratio. On a boat, unlike a car hot-rodded to provide acceleration, well, a boat will run at/near its top speed so often that you generally don't want to play with the final gearing so much so that you knock off too much top speed.

Drop to shorter gears on a car and you bask in the wonders of gear reduction, and you get better accel numbers, which is what is desired in most cases that I can cite. Drop to shorter gear on a boat (smaller prop) and you can get better acceleration (potential is there) but...but...but -----> read this next part alert ----->but.... a boat will typically operate up near its top speed a lot... and sometimes will run at its top speed most of the time, especially the little 2-strokers. Most people are not interested in taking a 35 MPH boat and turning it into a 30 MPH boat that will blow redline, nor should they want a 35 MPH boat that is overpropped and lugging, fails to reach redline and is experiencing loads (via lugging) that it might not be able to handle.

To turn taller gears (bigger props), you need more power.

 

[aerobat]

Re: Theretics of my new prop

what a fantastic thread !

1: If the speed in wich the prop turns and the pitch determins the speed in wich the boat travels, why do people boast a higher HP motor when they are just adding weight?

correct !!! because of that i plan to scrap my heavy 150hp V6 evinrude and put the much lighter 5hp kicker yamaha on the transom and plug in the 14.5 x 20p stainless from the rude. as a further benefit the yamaha revs higher than the evinrude and since speed is just prop pitch x revolutions because the prop spins "free" in the water i should go ballistic ! :facepalm:

cheers !

 

[Philster]

Re: Theretics of my new prop

Just gear it so it spins a whole bunch and you'll leave them 300 HP stroker* motors in your wake!



*Even the stroker motors that are actually oversquare, but billed as being strokers.

 

[olivialyn11]

Re: Theretics of my new prop

got the motor dynoed, i have 123HP
found this prop that aperently they have no reason to produse,
http://www.savvyboater.com/rubex-hr4-stainless-prop-9453-130-21-rbx106.aspx

is their still any objections or better advice then my motor is worthless?

 

[steelespike]

Re: Theretics of my new prop

What rpm is the 123hp developed at? I believe the 85 uses a 2.29 ratio, and 115-130 and more use a 2.00.

 

[olivialyn11]

Re: Theretics of my new prop

What rpm is the 123hp developed at? I believe the 85 uses a 2.29 ratio, and 115-130 and more use a 2.00.

5K. Motor is rated 4500 to 5500. As we went closer to 5500 saw numbers closer to 130

 

[smitty477]

Re: Theretics of my new prop

Interesting post - we are on the second page and I think this is where we are at:
- No baseline data avaiable on props or rpm's
- No comparable weight on this combination
- An unknown lower unit ratio
- An 85 hp outboard that is perhaps actually 123hp (45% up)

And the questions are revolving around picking the correct prop for this application.

 

[1080tommy1]

Re: Theretics of my new prop

For someone that just got into outboards this is an interesting discussion. Threads like this while on the surface could seem negative actually have great explanations of how to prop a certain setup and the reasons why. I think that the first post the OP is stating that he would like to keep speed but adding a four blade prop will reduce top end speed and give a better hole shot. I also in all of my reading understand that a motor which is smaller such as an 85 hp would be more appropriate for a three blade prop because of hull design and horse power. I am not trying to add negativity to this post and create a pissing contest but rather attempting to understand prop selection because I am still trying to dial mine in. Just seems like all I have read also states that if you are going to add a four blad prop, pitch should be decreased and I am assuming this is to account for the drag and pitch of the extra blade reducing rpms. Seems to me 15 to 17 pitch would be right in the ball park at least for starting out and attaining a baseline from which to really dial in the right prop.

I have to say you may want to listen to these guys because everything I have been advised has worked out pretty well from this site and I was starting much the way you are because my motor was severely underpropped and the prop was dinged up pretty bad so it really was of no use in development of what prop I would finally wind up with.

I hope you do find the right prop and get her going well but I have to say reading all that I have in the past month or so on props, a 23 four blade would probably have your motor lugging pretty good and I think being underpropped is better than overpropped becuase if you are underpropped, at least you can use that particular prop. Overpropping is a no go because anything over no wake will result in stress on the motor.

 

[Captain Shikaboo]

Re: Theretics of my new prop

 

[olivialyn11]

Re: Theretics of my new prop

I i would like to jump on this, i dont care how many posts you have, it just shows that you spend time in front of a computer instead of a boat, Also i Like that you have data and speffic memory of a boat and motor that today are 40+ years old. And the motors not stock, if i tear it apart, will throw new sleaves or a power head on it and destroy it again.

We have set up that EXACT rig numerous times, and 85's hundreds of times as we were an Evinrude dealership and there was also a Galaxy dealer ~70 miles away.

The OP is also behaving like an insulting @ss with his comments to Frank A. that has over 7,000 posts and the OP's apology was a joke.

I won't shed a tear when he grenades that motor and learns the hard way the term, "A Debt of Gratitude".

I'll pass on this one.

This is quite funny

Interesting post - we are on the second page and I think this is where we are at:
- No baseline data avaiable on props or rpm's
- No comparable weight on this combination
- An unknown lower unit ratio
- An 85 hp outboard that is perhaps actually 123hp (45% up)

And the questions are revolving around picking the correct prop for this application.

I origionaly stated that it was a 85 motor, never stated it was a stock unit, when i tried to relay any data i had which was my cousins boat, i was told that i was wrong, and aperently me having a boat is just like owning a car, i can throw some biggger tires on and make my car go super fast.

We are working or motors to get the most out of a powerhead, weve modofied intakes, heads and are going to start on lower units soon, I also previosuly stated on page 1 that the unit had 120 hp, if i was going to spend 2k buying every different prop for my boat i would have never asked for advice the nearest place for me to get parts for my boat is 45minuts in one direction and the lake is and hour in the other. so borrowing every prop is not an option. and aperently props im looking for shouldnt exist because they would have no use but ive found them after all my uncle-in-laws who spend just about every day on the water cant be wrong either, he had a 19' with a real 85hp with a 17" pitch and it ran 35mph at 5200rpm, if i had the same stock motor i would have just boght a 17" blade and ran it circles.... but this is not a stock motor,

The lower unit is off of a 1977 150hp
Uper unit is a heavly modified 1975 85hp prodicing around 120-130hp