SoCal Jet Boats
Tech Talk => V-Drives => Topic started by: beerjet on January 20, 2008, 10:58:42 AM
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I've been asked a few times about props and my knowlege of them is very limited . I understand what the (for example) 14 x 16 means . For the intents of learning something , could someone enlighten us on these numbers in coralation to a propeller .
The diffrences between the round ear props and the cleaver props . I'm sure there are more question but hopefully common sense will answer some others .
-beerjet-
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Simply, some props bend more than others when they hit something. Nevertheless, regardless of the prop style, it's trash after it hits something. ;D
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not true. you can fix a stainless prop ;D
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I've been asked a few times about props and my knowlege of them is very limited . I understand what the (for example) 14 x 16 means . For the intents of learning something , could someone enlighten us on these numbers in coralation to a propeller .
The diffrences between the round ear props and the cleaver props . I'm sure there are more question but hopefully common sense will answer some others .
-beerjet-
the 14 in the diameter and the 16 is the pitch. small the diameter faster it turns, also the smaller the pitch the faster you can spin it. Something like that. O0
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the 14 in the diameter and the 16 is the pitch. small the diameter faster it turns, also the smaller the pitch the faster you can spin it. Something like that. O0
I believe 14 being the diameter (like you said) 16 being the pitch (how many inches it will travel in a rotation) . The 14 x 16 prop being a little too much diameter for v-drive but more of a ski boat prop . Also when the prop bangs into a rock , it wont hang onto it and prevent you from getting back to the ramp.
-beerjet-
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oh boy ::)
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Simply, some props bend more than others when they hit something. Nevertheless, regardless of the prop style, it's trash after it hits something. ;D
Thats all I ever learned and all I ever needed to know. Oh yeah they can cut you pretty good when you are swimming around them running or not.
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The only experience I have with props has been in ski boats. Where 13x13's are common. Some are 3 blade, some are four.
Here's some info from ACME propeller relating to the skiing/wakeboarding segment. I have the new Acme 13x12 3 blade. But hey I went from a 70+MPH boat to one that maxes at 47...
"Q: Which propeller should I choose, the Acme 3-blade or the Acme 4-blade?
A: Theoretically, a 3-blade propeller should always be more efficient than a 4-blade. However, in the past, two big issues have prevented the 3-blade from taking the lead in popularity. The first was a lack of manufacturing precision, which commonly caused 3-blades to vibrate more than 4-blades. When significant dimensional variation exists in a propeller, vibration is generally more noticeable in a propeller with fewer blades. The second reason for the 3-blade disfavor was an almost certain loss of blade area in the transition from four blades to three. Consequently, even though top-end gains were achieved, performance expectations on the low-end were diminished.
Through the implementation of precision manufacturing and design improvements, Acme Propellers are giving the 3-blade the reputation it deserves. Acme is consistently holding tolerances never before achieved in propeller production. This accuracy makes the Acme 3-blade incredibly smooth. In addition, the blade area of the Acme 3-blade has been expanded to equal that of the Acme 4-blade. The translation? The Acme 3-blade has raised the performance bar. From an awesome hole-shot to an unmatched top end, and all the smoothness throughout, the Acme 3-blade leaves nothing to be desired. We believe it has an edge that everyone will appreciate. On the other hand, please do not mistake our excitement as a lack of appreciation for the Acme 4-blade, a proven winner.
It should be noted that this choice might still be mildly influenced by application, because it is possible that the most perceptive users might be able to detect slight differences that cause them to prefer one prop over the other. Even still, the overall performance of either Acme Propeller is paramount, and is that from which dreams are made. "
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They make a 2,3,4,5,and 6 blade props ;D 2 blade are for like v-drive
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ok, 3 blade prop (my boat)
(3 blade) 14.5x22 pushes it to 108mph at 10,000rpm,
(4 blade) 14.5x22 pushes it to 95mph at 9,000rpm.
(3 blade) 14.5x28 pushes it to 95mph at 8,200rpm,
(4 blade) 14.5x28 pushes it to 89mph at 7,200rpm(it will blow up)
so, it takes more power to push a bigger pitched prop.
Plus it also takes more power to push a bigger diameter prop too.
I haven't tried a 5 or 6 blade prop let ( to pricey)
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They have HUGE pitch props too. My buddy for his 22' eliminator daytona i think twin 27 degree counter rotating props. That blackhawk drive is incredibly efficient, 415 crank HP and the Son-biatch does 83! I have a video of it... The boat we were in was cruising 60, a Carrera 20.5 elite with Teague Marine 502.
You see him coming up on us, then all of a sudden takes off.
http://myspacetv.com/index.cfm?fuseaction=vids.individual&videoid=8240712
from in the boat. Water was pretty rough but not blown out.
http://myspacetv.com/index.cfm?fuseaction=vids.individual&videoid=20261788
And of course his old Pantera. The odd child in many ways... blown SBC with a Panther you can hear the blower spinning as the boat goes by. In the video I think max RPM we hit was 6200. You gas it from 6000 RPMs and the whole boat jumps out of the water with the new blower on it.
http://myspacetv.com/index.cfm?fuseaction=vids.individual&videoid=3142485
http://myspacetv.com/index.cfm?fuseaction=vids.individual&videoid=3170072
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Propeller Size
The size of a prop is described using two sets of numbers. These correspond to the diameter and pitch. The pitch always follows the diameter when describing a propeller.
Diameter
The first number listed in a propeller size. Diameter is defined as two times the distance from the center of the hub to the tip of the blade. It can also be looked at as the distance across the circle that the prop would make when working.
Pitch
The last number listed in a propeller size. Technically speaking, pitch is the theoretical distance a prop moves forward in one revolution - assuming there is no "slippage" between the prop blade and the water. In the real world, there is some slippage and therefore the distance advanced is less than the design pitch. Pitch can be visualized as the tightness or looseness of the blades as they swirl around the prop hub. If the blades appear tightly wound and angled sharply inward toward the hub, the pitch is high. If the blades appear loosely wound and angled outward from the hub (that is, they appear flatter), the pitch is low.
Cupping
Many of today's propellers incorporate a cup at the trailing edge of the propeller blade. This curved lip on the propeller allows it to get a better bite on the water. This results in reduced ventilation, slipping, and allows for a better hole shot in many cases. A cupped propeller also works very well where the motor can be trimmed so that the propeller is near the surface of the water. The cup will typically result in higher top end speed on one of these applications.
Ventilation
Air from the water surface or exhaust gases from the exhaust outlet being drawn into the prop blades causes ventilation. When this situation occurs, boat speed is lost and engine RPM climbs rapidly. This occurs most often with high transom mounting, over-trimming the engine, and sharp turns.
Cavitation
Cavitation (which is often confused with ventilation), is a phenomena of water vaporizing or "boiling" due to the extreme reduction of pressure on the back of the propeller blade. Many propellers partially cavitate during normal operation, but excessive cavitation can result in metal erosion or "cavitation burn" to the prop's blade surface. There are numerous causes of cavitation such as incorrect matching of propeller style to application, incorrect pitch, physical damage to the blade edges, etc.
Rake
Rake is the degree that the blades slant forward or backwards in relation to the hub. Rake can affect the flow of water through the propeller, and has implications with respect to boat performance. Aft rake helps to trim the bow of the boat upwards, which often results in less wetted surface area and therefore higher top end speed. Aft rake propellers also typically "bite" better on ventilating type applications. Forward, or negative rake, helps hold the bow of the boat down. This is more common in workboat type applications.
Selecting the Right Propeller For Your Boat and Engine
The best propeller size for your boat and engine combination is based on the recommended operating range at wide open throttle (w.o.t.) for your engine, which you will find in your operator's manual. This will be expressed in terms of a certain horsepower at a certain RPM (revolutions per minute).
The goal in prop selection is to determine what propeller style and size will maximize performance for your boat, while allowing your engine to operate in the recommended RPM range. The correct propeller will prevent the engine from over-revving, yet allow it to reach the minimum RPM where maximum horsepower is produced.
Run the boat/motor at w.o.t. under normal operating load to determine the maximum RPM you are able to obtain. A tachometer is necessary for this test. Adjust the motor trim angle for the optimum performance. If during this test, you begin to exceed the maximum rated RPM of the engine, reduce throttle setting to a position where maximum RPM is not exceeded.
If your test results in your being able to over-rev the engine, you need to increase the pitch of the propeller. Increasing the pitch increment by 1" will result in approximately a 200 RPM drop. If your testing shows, however, that you are only able to obtain a RPM somewhat lower than the maximum rating given by your engine manufacturer, you would need to decrease pitch. Decreasing pitch would increase your RPM.
Example:
Operating Range = 5000-5600 RPM
Top End of Operating Range = 5600 RPM
Tachometer Reading = 4800 RPM
Difference = 800 RPM
For every 1" of pitch size, the effect will be approximately 200 RPM. Knowing this, take the difference in the above example at 800 and divide it by 200. The result is 4. The prop to use will be 4" in pitch less than the prop that was used.
Switching from an uncupped to a cupped propeller will also reduce your RPM. The cupped propeller of the same pitch and diameter will typically reduce your RPM by approximately 200.
Once your wide open throttle RPM falls within the recommended range of the engine manufacturer, you have a propeller that is suited correctly for your boat with respect to RPM. If you use your boat for fishing, cruising and skiing, one prop probably won't do all three things equally well. It is best in circumstances like this to have two propellers. One to accommodate one set of circumstances and the other to perform best under the different load. It could, in fact, be that more than one propeller would be suitable for your boat and motor combination depending on your usage. It is imperative, however, that the wide open throttle RPM fall within the range specified by your engine manufacturer
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They have HUGE pitch props too. My buddy was considering a 30 pitch for his 22' eliminator daytona, he has twin 27's. That blackhawk drive is incredibly efficient, 415 crank HP and the Son-biatch does 87! I have a video of it... The boat we were in was cruising 60, a Carrera 20.5 elite with 700 HP Teague Marine 502.
You see him coming up on us, then all of a sudden takes off.
http://myspacetv.com/index.cfm?fuseaction=vids.individual&videoid=8240712
from in the boat. Water was pretty rough but not blown out.
http://myspacetv.com/index.cfm?fuseaction=vids.individual&videoid=20261788
And of course his old Pantera. The odd child in many ways... blown SBC with a Panther doing 70's+ you can hear the blower spinning as the boat goes by. Sucker would do 7000 RPMs no problem, in the video I think max RPM we hit was 6200. Standard tolerances on a panther I think were .025, this one is at .012. You gas it from 6000 RPMs and the whole boat jumps out of the water with the new engine in it.
http://myspacetv.com/index.cfm?fuseaction=vids.individual&videoid=3142485
http://myspacetv.com/index.cfm?fuseaction=vids.individual&videoid=3170072
i've got a pair of 30's cut for more rpm(for sale)or trade
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His is a single drive, counter-rotating props... Kinda like the Bravo 3 except different. Only problem is they're not really made to handle A LOT of power, Your safe/effective range is between 400-600HP.
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Choosing a prop in a v-drive is much like choosing an impeller in a jet. It all has to do with how much HP you are giving it and what it's in. The V-drive does have the gear ratio to take into account though.
My boat runs a 10 and 7/8 X 16 where as my other Cole ran an 11 and a 1/2 X 15. My Other Cole had about 300 HP less than my current boat which is why the smaller prop was needed. Both boats use 2 blade props.
You will find 3 blade props on heavier V-drives. As stated before the 3 blade gives a little bit more out of the hole but sacrifices a few MPH off the top.
Oh, and no two props are the same. Same pitch and diameter only means they are related, but can perform completely different.
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Choosing a prop in a v-drive is much like choosing an impeller in a jet. It all has to do with how much HP you are giving it and what it's in. The V-drive does have the gear ratio to take into account though.
My boat runs a 10 and 7/8 X 16 where as my other Cole ran an 11 and a 1/2 X 15. My Other Cole had about 300 HP less than my current boat which is why the smaller prop was needed. Both boats use 2 blade props.
You will find 3 blade props on heavier V-drives. As stated before the 3 blade gives a little bit more out of the hole but sacrifices a few MPH off the top.
Oh, and no two props are the same. Same pitch and diameter only means they are related, but can perform completely different.
Do diffrent props have anything to do with bow lift ?
-beerjet-
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yes ;D
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yes ;D
well....... come on now , tryin to learn something here......
-beerjet-
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The pitch is the amount (inches) that one prop shaft rotation will move the boat thru the water (theoretically) size/ diameter (od) seems to be a "science" but on average v-drive props for 17' thru 20'+ boats seem to vary by application & V-drive gears & HP in the v-drive between 10 & 3/4 to 12 inch example my 20' cruiser has a 12x 15 3 blade stainless and my Schiada runs a 2 blade steel 11& 1/8 x 15 both have 15% overdrive (prop speed is 115 %time engine rpms) BTW Yes props size can affect tail lift but so can strut angle ,prop position vs strut and transom etc etc I still go to Bracksma or Kindsvator for prop advice before I buy or apply ! Flats like different props than runners etc etc . Attached is an OLD article & some info that might help ? Also a formula that estimates speed based on a computation of V-drive boat factors you might find interesting! My Schiada turns 15% gears and a 15" prop 5800 rpm you can use the formula to factor my speed ;D (sounds like grade school math) (the attached article has a little different formula than I was taught)
engine rpms x prop pitch x gear ratio (example 115%) x .00094697 factor = T over D x .85% (slip factor variable) = MPH
(https://www.socaljetboats.com/proxy.php?request=http%3A%2F%2Fi147.photobucket.com%2Falbums%2Fr319%2Fjetboatperformance%2FTechnical%2Fwaterpump1.jpg&hash=7ff022108359ade4c65b3dbe7f104e24e0ebf3bf)
(https://www.socaljetboats.com/proxy.php?request=http%3A%2F%2Fi147.photobucket.com%2Falbums%2Fr319%2Fjetboatperformance%2FTechnical%2Fwaterpump2.jpg&hash=91c001f7d08f0fc8bc6a79f65fb9510ecfcd2e79)
(https://www.socaljetboats.com/proxy.php?request=http%3A%2F%2Fi147.photobucket.com%2Falbums%2Fr319%2Fjetboatperformance%2FTechnical%2Fwaterpump3.jpg&hash=9dbc686826a41c98cd66fe353d56f29e33b63b4c)
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Do diffrent props have anything to do with bow lift ?
-beerjet-
Prop position plays more of a role in bow lift than actual prop size. A prop that is too far forward can lift the bow. Usually a nickle or two between the output shaft of the V-drive and the prop shaft can help excessive bow lift. There ia alot more to it than that such as strut angle V-drive position etc.
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v-drive or outboard (bj) In a three blade they can make it to have bow lift O0
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v-drive or outboard (bj) In a three blade they can make it to have bow lift O0
My questions were geared more towards the v-drives but if the same applies or there is a diffrence , I'd like to know either way . I get asked alot of questions and I hate not being able to give an answer of some kind .
-beerjet-
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My questions were geared more towards the v-drives but if the same applies or there is a diffrence , I'd like to know either way . I get asked alot of questions and I hate not being able to give an answer of some kind .
-beerjet-
Although not an expert, it's been my experience that V-drives in general have bow lift (hence the reason for a down pedal). How much of it that is attributed to the prop is another question. I'm sure in V-drive applications some props may produce more lift than others but there are messures that can be taken to combat it. For instance the closer the prop is to the strut the more bow lift it will have. Spacing it back at the collar helps calm it down.
As far as outboards or 3 blades go, I have no idea since I don't bother with either.
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Is there a prop to keep the homos away if and when I buy a V-Drive ??? I just dont know if I can swing the other way . :-\
-beerjet-
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Is there a prop to keep the homos away if and when I buy a V-Drive ??? I just dont know if I can swing the other way . :-\
-beerjet-
[You crack me up bro ./quote]
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Is there a prop to keep the homos away if and when I buy a V-Drive ??? I just dont know if I can swing the other way . :-\
-beerjet-
Cut It Out, you KNOW you want one.
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Cut It Out, you KNOW you want one.
DEEP DEEP deep , down inside . Yes I do ....... :-*
-beerjet-