Prop basics??

[traveler]

I'll admit to being totally dumb about props...my only experience to date is with -25 hp motors, so basically none. Now I've made the leap into the bigs and would apprecate an overview from someone in the know. I have a 150 V-max, the prop it came with (used) seems to do the job, just like the one that came on my 25:) So why would I change, and to what? If anyone feels like taking the time to explain how, when, and why a certain style/pitch/brand of prop is useful I'd appreciate it.

[PerchJerker]

The strength of stainless steel allows props to be made in many unique shapes and configurations that cannot be made with aluminum. You need a high horsepower motor to really realize these benefits, my opinion is at least a 90 or 115 HP.

Basic theory is that fewer blades (like 3) are faster, vibrate more, and are slower out of the hole. More blades (like 4 or 5) are not as fast at WOT but are quicker out of the hole and are smoother and better handling and will vibrate less.

Higher pitch props give more speed (more distance traveled per revolution) but are harder to spin so they bring down your rpms - lower pitch props spin easier and bring your rpms up but will not be as fast at WOT.

Other characteristics like the rake (angle) in the prop blades, and the shape of the blades, can be used to do things like raise the bow or raise the stern, but those are small tweaks vs. big adjustments.

If your boat handles good now and the rpms are right then you probably shouldn't change props. One reason to change would be if you need to adjust the rpms your motor is turning. Another reason to change would be if you want more holeshot, or more top speed, or better handling, etc. That is where prop experimentation comes into play, you can get good recommendations but until you try them on your boat you won't know what's right and what's right and what's not quite right.

Hope this helps, good luck.

[delmuts]

nice explanation!

[deepportage01]

I was a prop retard until now , good job

[traveler]

Thanks Perchjerker! I appreciate the help. A couple follow up questions (of course:) How do I know what RPM's I want to be running? Is there a "safe" range for extended cruising? How about gas mileage? Any advantage to one prop or another there? I guess I don't really have anything to compare this boat/motors performance to, I just haven't run enough bigger boats. It seems good, but maybe it could be better? Do prop shops let people try different props before they buy? Seems like it could be an expensive thing to figure out...Thanks again!

[PerchJerker]

Your motor has a recommended range that your rpms should be in at wide open throttle, my guess is maybe something like 5200 to 5700, but look in your owners manual or talk to your dealer or post the question in the forums and someone will know for sure.

Your motor is made to run WOT, you won't hurt it running WOT or a few hundred rpms below WOT. Your most fuel efficient speed will be whatever is just enough to easily keep you on plane. With my boat I burn around 6 gallons per hour at 3000 to 3500 rpms and run about 30 mph, at WOT I run 5500 rpms and low-mid 50s mph and burn 17 gallons per hour.

I'd guess a 5 blade prop would be the most fuel efficient because that's probably the best prop for cruising -- probably the easiest to run at the slowest planing speed. But you're splitting hairs here and if you run faster than your slowest planing speed you probably wouldn't notice any difference in fuel consumption. Best way to conserve fuel is to get on plane quick and then run at the slowest speed that will keep you on plane.

There are some dealerships and prop shops around that let you try props, you pay a fee of about $25 to borrow the prop and give them a credit card deposit on the prop in case you wreck it. There are also some places on the internet where you can find used props for about half-price. I would try before you buy if at all possible.

Different styles, sizes, and weights of boats will perform better with different props - for example, a lot of walleye style boats run the Mercury Tempest prop. Lots of I/Os run the Mercury Vengance prop. Mercury's web page has a prop selector program that will give you several recommendations, but until you try them on your specific boat you can't know for sure.

If your boat runs and handles good now - if it gets out of the hole, runs fast enough, turns the right rpms, doesn't blow out or cavitate, and if you don't have any complaints, you probably don't need to do any prop testing.

[Whoaru99]

Quote:

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The strength of stainless steel allows props to be made in many unique shapes and configurations that cannot be made with aluminum. You need a high horsepower motor to really realize these benefits, my opinion is at least a 90 or 115 HP.

Basic theory is that fewer blades (like 3) are faster, vibrate more, and are slower out of the hole. More blades (like 4 or 5) are not as fast at WOT but are quicker out of the hole and are smoother and better handling and will vibrate less.

Higher pitch props give more speed (more distance traveled per revolution) but are harder to spin so they bring down your rpms - lower pitch props spin easier and bring your rpms up but will not be as fast at WOT.

Other characteristics like the rake (angle) in the prop blades, and the shape of the blades, can be used to do things like raise the bow or raise the stern, but those are small tweaks vs. big adjustments.

If your boat handles good now and the rpms are right then you probably shouldn't change props. One reason to change would be if you need to adjust the rpms your motor is turning. Another reason to change would be if you want more holeshot, or more top speed, or better handling, etc. That is where prop experimentation comes into play, you can get good recommendations but until you try them on your boat you won't know what's right and what's right and what's not quite right.

Hope this helps, good luck.

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Good explaination.

The only thing I might add is that stainless props do have some benefits, but also additional risk, IMO. The risk is higher possibility of prop shaft/lower unit damage if you catch a rock with the prop.

[wayne123]

Great information -- I always wondered why stainless steel was used.

[marine_man]

Good explanation Perch Jerker!

marine_man

[PerchJerker]

Quote:

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The risk is higher possibility of prop shaft/lower unit damage if you catch a rock with the prop.

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Very true. The hub assembly (plastic) should break loose before the lower unit is damaged but I hope I never find out first-hand. If I used my boat a lot in areas where I was worried about rocks I would not use a stainless prop.

[Hydra Sport]

You might want to look at a composite prop. They are comparable to stainless for performance but don't have the risk of shaft damage if you hit something. As a matter of fact they are designed to snap off to prevent damage. I have had comprops and Pirhana composite props. The comprop needs to be replaced if damaged but the pirhana has seperate blades that can be replaced individually if damaged. it takes about ten minutes and the blades cost about 20 bucks each. My son snapped one off my merc 115 and I replaced it last week no muss no fuss. If you run where there are rocks and stumps etc its a good idea to keep some spares in the boat. At the cost of an aluminum you get the performance of stainless. If you want you can also have a set of another pitch to put on if you want to pull skiers or modify the boats performance. I went to a 4 blade from the 3 blade and had a noticeable increase in performance. It was a cheap way to find out if the performance was worth plunking down stainless money without paying stainless money. Check the pirhana out you won't regret it.

[traveler]

Well, that answers my thinking about stainless...although I don't expect I'll be fishing this boat in quite the same areas I usually fish, I still expect there to be a few rocks around. I think aluminum should be fine for me.

[AQUAJOE]

Man great explanation! thanks

I'll give you a situation and lets see what your opinions would be.

I have a Crestlner 1750SC FishHawk with a 90HP Evinrude FICHT. I have a Factory 3 blade prop that has a stamp of 13 3/4 X 15 on it.(Please explain what is what)

The boat tops out at 42mph so I have real good top end for the boat and motor. And the mileage is really good.

But I do get blow outs and cavitate quite a bit. And blow outs are common in heavy turning with lots of power or pulling skier or tube.

I don't mind losing top end to minimize the blow out or cavitation and better handling.

What do you think and which way do I go with prop and why?

Thanks in advance.

[Ralph Wiggum]

Quote:

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I have a Factory 3 blade prop that has a stamp of 13 3/4 X 15 on it.(Please explain what is what)

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13 3/4 inch diameter X 15 inch pitch. The pitch means that "theoretically" for every revolution of the prop, your boat will move 15 inches. But you lose some of that because of "prop slip".

I would guess that a 4 blade will help with blowouts, but there are some more knowledgable folks on here that will chime in with a better idea of what to go with.

[PerchJerker]

Most of what I know is from working on my own boats, I am not the best one to give recommendations on other boats. I have a few guesses but the best thing to do would be to talk to a dealer or prop shop. Another thing you can do is find someone else that runs the same boat and motor and find out what prop they're running and how high their motor is mounted.

One thought is it could be the aluminum prop causing your problems - aluminum will flex under heavy loads whereas stainless steel won't. It could be as simple as going to steel to stop the problems.

Another thought is that you motor may be mounted too high on the boat. Look where your motor bolts onto your transom, there should be some extra holes above and/or below the bolts. If there are empty holes above the bolts your motor could be lowered and bolt through those holes. Lowering the motor is a great way to get rid of cavitation and blowout problems.

A higher pitch prop or a larger diameter prop won't spin as easily and could stop the blowout, and like the other poster said a 4 blade prop should give you better bite and might stop the blowout. It might not be that simple though, because changing props might change your rpms so you may have to do a lot of experimenting to find the best compromise.

Your prop doesn't have any exhaust vents, ports, or holes in it, does it? I doubt if it does, and even if it does it shouldn't cause the problems at high speeds, but it's possible.

I have a buddy with the same boat as you with a Yamaha F115. I know he replaced his aluminum prop with a stainless prop, I'll try to find out what he has on his boat.

[Whoaru99]

I have four props, the factory aluminum, a stainless, and two of the ComProps.

The ComProps are the ones that are on the boat most of the time (one is 17P and one is 19P), and the factory aluminum is the one that is most seldom used.

The aluminum and stainless are also both 19P. The stainless is good for a few MPH more than either the 19P ComProp or the 19P aluminum.

My boat really porpoises easily with the factory aluminum, and much less sensitive to porpoising with either the ComProps or the stainless.

The ComProps have less steering torque when you are not perfectly trimmed and run real smooth. The boat seems to handle better with the 4-blade ComProps too.

[Whoaru99]

Some of your blowout / ventilation could also be due to being trimmed out too far. Do you usually have a front heavy load when this happens and are using the trim to try to keep the front end up?

[AQUAJOE]

Quote:

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My boat really porpoises easily with the factory aluminum, and much less sensitive to porpoising with either the ComProps or the stainless.

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Front Heavy Load. For the Blow out. I wonder if that aluminum is flexing to much with the load?

My boat is very sensitive to the Porpoising.

[marine_man]

Aqua Joe - one other thing you're missing is what are you turning for RPM at Wide Open Throttle (WOT)? That'll affect what pitch / size of prop you should be considering.

marine_man

[AQUAJOE]

Quote:

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Man great explanation! thanks

I have a Crestlner 1750SC FishHawk with a 90HP Evinrude FICHT. I have a Factory 3 blade prop that has a stamp of 13 3/4 X 15 on it.

The boat tops out at 42mph so I have real good top end for the boat and motor. And the mileage is really good.

But I do get blow outs and cavitate quite a bit. And blow outs are common in heavy turning with lots of power or pulling skier or tube.

I don't mind losing top end to minimize the blow out or cavitation and better handling.

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So I upgraded my PROP to a 4 blade aluminum.

Went from a 13 3/4 X 15 factory. TO

Solas Amita 4 Blade Aluminum 13" dia. X 15" pitch SR

I tried to keep it as close to the pitch and rake of the original prop.

I have a great hole shot now. Tops at 44mph. Way better handling and it does not blow out or cavitate under load now.

The boat does not porpoise at high trim now so I think thats where the extra 2 mph came from.

My top end RPM is 5800 so I am right in where it needs to be.

The prop was $107 bucks. It was well worth the money.

Thanks for the info guys. The 4 blade aluminum was the most bang for the buck I think.

[stmichael]

I have a 13 3/4 x 19 on my motor and it is a 1982 75 h.p. Evinrude. Do you think that a four blade would help me? My RPM's at WOT are 4900-5000, I tried a 14 x 17 it ran 5100-5200. or would I be better off staying with the 3 blade and, dropping the pitch to 15 or lower? I have a crappie hole shot and top speed is 32 mph.

Boat is a 16ft 1982 Sylvan

Thank you,

Mike

[marine_man]

I'd drop to a 15 pitch prop... that'll dramatically help your hole shot and get you closer to the upper limit on you rpm's (reccomended between 5000 - 6000)

marine_man

[stmichael]

Thanks Marine Man,

What do you think about going with the 4 blade prop? should I stay with 3?

[marine_man]

4 Blade props are very beneficial in certain applications. If it were me, with your lower HP setup, I'd probably stick with the 3 blade.. but that's me. I think you'll see a big improvement in performace with a lower pitch and shouldn't need a 4 blade to get there.

marine_man

[stmichael]

SWEET!!!