Is it possible to bend blades on alum prop?

[4.3sunbird]

since I put my hustler 23p prop <br /><br />first day out at wot I got 61mph on my speedo at 5200 rpm <br /><br />its now getting slower each time I go out <br /><br />today my speed would only go 59.5 and was turning 5250 <br /><br />nothing has changed on the boat since the first day except I actually have less weight in the boat<br /><br />when it did the 61 by my speedo I had a passenger .. today I was alone and had less fuel in the tank<br /><br />heres the main thing ..I gps'd it at 5250 rpm gps was showing 56.5 mph<br /><br />with 0 slip that would be 66.87 mph at 5250 rpm<br />so it only doing 84.5% now <br />which shows 15.5% slip <br /><br />isnt that a little much slip for a cupped prop ?<br /><br />ignore the trim gauge its stuck up there <br />and the part of a compass the top of it is in the bildge <br /><br />

 

[4.3sunbird]

Re: Is it possible to bend blades on alum prop?

btw should I get a turbo prop now

 

[jaybirdtx]

Re: Is it possible to bend blades on alum prop?

61 out of a 19' with a 4.3 is OUTSTANDING. It doesn't get any better than that and your very lucky to get what you did out of her. Center-of-gravity (CG) has a lot to do with prop performance and speed. If the differences were this small I wouldn't worry too much. It's normal to not get the exact readings on a continuous basis. Your getting more than spec. output for this set up....don't change a thing!!!!

 

[4.3sunbird]

Re: Is it possible to bend blades on alum prop?

I just went thru all the other dash shots I took at different cruize speeds and all of them are showing 17-18% slip that is in the 30 to 50 mph range <br /><br />I just think that is alot of slippage for an aftermarket cupped prop <br /><br />Is that really normal for alum <br />what is a normal slip percent for a turbo 1 prop?<br /><br />I did hit 61 on my speedo the other day but from the looks of it my speedo is about 3mph higher than gps so 58 mph <br /><br />its not really a mph thing now what Im looking for is less prop slip <br /><br />with the factory omc alum 21p speedo said 58 at 5400 rpm ..<br /><br />take away 3mph to agree with gps and I show that the omc prop was only 11-12% slip ..I'd expect a aftermarket high performance prop would be at least as good as a foctory alum <br /><br />

 

[stevens]

Re: Is it possible to bend blades on alum prop?

Ask Walleyehed about what he thinks you could gain by going from a 23P Hustler to a 23P Turbo.<br /><br />My guess is you might go from a 14% slip to, say, 10-12% slip, which would then at best maybe give a speed gain of 2 mph, from 58 to 60 mph (according to http://www.go-fast.com/Prop_Slip_Calculator.htm ). I wouldn't bother.<br /><br />Walleyehed - what do you think?

 

[umblecumbuz]

Re: Is it possible to bend blades on alum prop?

Do you keep the boat in the water?<br /><br />If so, what is the state of the hull? A small build-up of algae can cause a huge efficiency loss. You can still hit the revs, but the boat is slower.<br /><br />Many owners who pull their boats and clean them through the winter find that they're faster at the beginning of the season.

 

[willamettejeff]

Re: Is it possible to bend blades on alum prop?

Are you sure your tach is reading correctly since it also figures into the slip calculation? Also, suggest you try again with a passenger. I'll bet you'll see the same numbers as you did the first time.

 

[4.3sunbird]

Re: Is it possible to bend blades on alum prop?

I trailer the boat and atleast rinse it off even on the bottom if not actually wash it <br /><br />I live not far from the boat ramp so Im known like earlier tonight to go drop in the river for an hour or so then come back and Im planning to be on the water later today so no way can I wash it each time <br /><br />heres the latest <br /><br />I went out ealier and was working on tuning the carb alittle better since Im showing a little too lean for my likings on the plugs<br /><br />well thats another story <br /><br />the latest on the prop is Im now showing cavitation burn on the back of the prop blades <br /><br />Its peeling the coating right off my new prop <br /><br />Im thinking I may never get this problem solved with this outdrive because I cant get any bigger diameter prop for it <br /><br />Im going to get a turbo1 23 pitch ordered up this week and If that dont help all I can do from there is get the right outdrive on it so I can run bigger diameter props<br /><br />does it sound to any of you guys that Im fighting a diameter problem ? I say that after doing a google search on cavitation burn and in the list of causes I found prop diameter too small for the engine <br /><br />I dont know ..If any of you do feel free to tell me .. or call me a idiot ... wont hurt my feelings any <br /><br />and before I get hollered at for tuning a boat on dark water .. its not the case .. where I play at night like that is between a well lit bridge and a 5 mile long very lit up newport news shipbuilding so I got a good lit up place to play <br /><br />oh and Im not possitive the tach is dead on but its got to be close ..I'll hook up one of my autometer ones later today when I go out to compare <br />

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[walleyehed]

Re: Is it possible to bend blades on alum prop?

Where the "coating is peeled off" is the wrong side of the blade for cavitation...<br />The pitting on the outer portion of blade is sand/gravel pits from trailoring.

 

[4.3sunbird]

Re: Is it possible to bend blades on alum prop?

Cavitation –<br /><br /> In the case of propellers this is the action of water boiling or vaporising in the extremely low pressures generated on the back of a propeller blade, if water is unable to fill the void created by the push of the blade through the water. Can be caused by poor blade design, damaged blades, excessive rpm’s or simply too much power for too small a propeller. In severe and prolonged cases this can erode the metal from the propeller blade.<br /><br /><br />Cavitation Burn – <br /><br />Erosion or marking on a propeller caused by prolonged cavitation.

 

[4.3sunbird]

Re: Is it possible to bend blades on alum prop?

from iboats site<br /><br />Cavitation<br />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 physical damage to the propeller's blade surface due to the collapse of microscopic bubbles on the blade.<br /><br />There may be numerous causes of cavitation such as incorrect matching of propeller style to application, incorrect pitch, physical damage to the blade edges, etc...<br /><br />Be advised disturbances in the water flow forward of the 4 propeller can result in blade damage which appears to be blade cavitation, but is actually due to non-favorable water flow into the propeller.

 

[4.3sunbird]

Re: Is it possible to bend blades on alum prop?

from propellerworld<br /><br />What is cavitation? <br />Cavitation can give the feeling of slip whilst the propeller is in use. It is actually bubbles in a partial vacuum caused by use of a damaged propeller, excessive propeller speed, loading or an incorrectly sized propeller being used. When a propeller moves through the water, the water is forced against the suction side of the propeller. The faster the blades cut through the water the more vacuum bubbles implode against the propeller. This implosion can happen with such force that the bubbles actually suck the metal right off the surface causing erosion or a "cavitation burn". Although it is not possible to repair cavitation burns it is possible to reduce cavitation and therefore reduce the possibility of further damage. This is done either by cupping the trailing edge of the propeller or ensuring that the propeller has the appropriate exhaust ring fitted if applicable, we can provide both of these services for you. You may also have the propeller blades thinned down as this reduces the high pressure build up on the blades

 

[walleyehed]

Re: Is it possible to bend blades on alum prop?

Still on the wrong side of the prop blade to be cavitation.<br />Suction side is the aft side...the side you view from the rear.

 

[4.3sunbird]

Re: Is it possible to bend blades on alum prop?

that is the back side of the blades (toward the boat)<br /><br />the push sides look brand new still <br />not a nick anywhere except where these pits are forming on the pull sides of the blades

 

[walleyehed]

Re: Is it possible to bend blades on alum prop?

The side of the blades torward the boat, is refered to as the front of the blades...the Push side (rear) is where the low pressure boiling takes place.<br />As you say, That is the "back" side of the blades,actually it is the front, but torwards the boat....this is not the side cavitation burns show up on.<br />I don't think your are spinning the prop fast enough to be causing this, as some outboards when set up for high RPM, are spinning the prop the same if not faster.<br />If you want performance for real, you're going to need to use the Hustler as a paperweight...simply put, it doesn't have the goods to transfer the power your engine has, to the water.