pfbanker

I just took my props into a local prop shop that uses the Prop Scan computer measuring system for speccing props. My starboard engine was running 100-150 RPM less than my port at the same throttle settings. I knew from the previous owner that the starboard prop had bent a blade when pulling the boat out one time and he had it reworked to fix the blade but the port prop had never been worked.

After the props were measured the port showed an average pitch of 25.3 and the starboard 26.1 with the previously bent blade showing up as way out of whack with the other blades. Does anyone have any clue why my props would measure so much lower in pitch than the 28p stamped on them? They part numbers for them are 48-831916 and 48-831915 as stamped on the props. Any help in understanding this would be greatly appreciated as I am totally confused.

BTW the link for the Prop Scan system is http://www.props.com.au/

Griff

Bravo props are always stamped higher than they really are. Usually they're about 1" off in pitch. They are measurered based on the highest pitched blade.

bbladesprops

Well,

This is multi facited. (spelling not good no spell check any more, bummer OSO)

First, we don't base anything on the highest pitched blade unless it is high due to impact. Then it needs to be fixed and reread.

Prop scan tools can also referred to as prop scam tools. Did I say that!? (readings need to be taken into account with the knowledge of the original castings true geometry. Not just what we read on the screen. Not used to sell services)

The user also needs to know what he is doing. Again, not suggesting any one doesn't know what he is doing.

Cup, cup, needs to be included in readings. Did they use that point of reference?

Lastly, LH 28's have some issues.

Finally, Bravo 1 castings are generally close to 1" low in pitch. Again, cupping is involved and needs to be included. This can open all kinds of various reading rules.

Bottom line, RH to LH should be the same whether it is 28 or 18 inches of pitch and no matter who's casting it is.

throttleup

The readings from various computer prop measuring systems are invaluable tools for the prop shop. What can be measured in minutes with computer measuring systems would take hours to gather the same information by the old mechanical method.

These is a setting called trailing edge exclusion. This changes what part of the blade is actually measured. If a trailing edge exclusion of .500" is used much of the cup is excluded from the measurement. Typically about an inch of pitch. If a trailing edge exclusion of 0 is used the actual pitch of the blade is shown.

Used as part of the overall reconditioning process the computer aided measurement systems are an asset to any prop company. Most manufactures use them as well, for quality control.

Bravo 1 props can vary quite a bit from the stamped pitch. Typically the taller the pitch the greater the difference is. By the time you get to a 36 Bravo 1 I have seen the pitch as low 32.5".

handfulz28

What's the average cost for scanning props? Just looking for a ballpark idea (25, 50, 100 per prop?) I just bought a used set of B-1 stamped as 26p. They need some serious cosmetic help at a minimum plus new hubs. Given their less than stellar condition I'm thinking about having them scanned before I run 'em.

bbladesprops

I agree the computerized pitch reading machines are very useful whether you own a MRI, Prop Scan or your own engineered version.

The point I was sarcastically trying to make is, knowing the personalities of propeller families, not just reading the pitch average from the print out or screen can greatly determine the ultimate adjustments needed. Just because the pitch is off 1.3 inches, you can't start to bend the prop where ever you think you should to create a equal average reading. That is the problem I have encountered with some repair sites.

These machines are very usefull. Some how we survived at Mercury Racing for 30 years with only mechanical guages.

Using these tools as tools not sales devices is what they are designed for.

throttleup

We don't charge to scan a prop. In your case I would suggest putting the prop on the proper pitch block to determine what has been done to it, if anything. While the computer diagnostics are great unless you have a scan of a Bravo 1 in your pitch and generation the scanner is not going to tell you if the prop has been modified or not.

A pitch block gives you a quick visual idea how true the prop is, it can't tell you how much the pitch or rake has been changed but will show if it has been modified.