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These propeller shops upgraded their measurement practices by installing TrueProp Software into their existing (or shop-made) measurement devices.
Wondering how they did it? Contact us!
and why it's important to take a close look...
Propellers are a critical piece of boating equipment. Many boat-owners know the cringing sound of a propeller strike - whether it’s a log, rope, or running aground, that impact resonates across the deck, through your shoes, and right to your wallet. To get back on the water, you might choose to have the prop repaired at a reputable propeller shop. (P.S. The National Marine Propeller Association, NMPA.org, can help you find a certified shop in your area!) These shops utilize computer-assisted measuring equipment to inspect and repair damaged propellers to better-than-new condition.
It’s often said that propeller repair is a blend of both art and science. This is absolutely true, and experienced repair professionals can save heavily damaged propellers. Many shops, proud of their work, provide inspection reports to customers to document the before and after conditions of the propeller. These reports contain a wealth of information, but many boat-owners have questions when reviewing them. In this article, we will go over the format of a standard propeller scan report, as well as discuss a few tips on how to interpret it. Let’s start with the first part of the report you read, the heading.
The Report Heading
The heading gives information about the repair shop, the customer, and equipment used, as well as the date and whether the report is for the initial condition or the final condition.
When a shop inspects your propeller, most times they are checking the position and size of each blade in multiple locations. The positions and sizes should match from blade to blade, within some acceptable margin. This margin is known as a tolerance. For inspecting propellers, the tolerances for the geometric accuracy are based on the International Standard Organization's rules for propeller manufacturing. The standard is ISO-484 and it has 4 levels of increasingly tighter tolerance “classes”.
The pressure face of the propeller is measured at several pre-defined locations. These locations are described as a percentage of the blade’s length (or more accurately, the blade’s radius). You may see data reported for these positions; for example, “70R” indicates the measurements are taken at 70% of the blade’s length. The higher the class accuracy, the more measurement positions are required.
The ISO criteria require inspection of many different parameters of the blades. Propeller performance is greatly influenced by the propeller’s pitch, or the angle of the blade. There is an average pitch for the entire propeller, as well as a pitch for each blade. There is also pitch reported for each blade’s measurement locations (i.e. 50R, 70R, 90R). The reports tend to use Bar graphs to report the Pitch of each blade at the measurement locations (ex. “70R” will have a pitch value and bar graph for each blade). Overlaid on the bar graph results is the tolerance window, which gives us the minimum and maximum acceptable pitch for the desired Class. Measurements of pitch that exceed the tolerance window must be adjusted and repaired to meet the desired Class. The measurement locations (i.e. 70R) can also be broken up into smaller segments to ensure the pitch is consistent from the leading edge (forward edge) of the blade to the trailing edge of the propeller (aft-most edge). This is known as local pitch and is required for the higher repair classes.
While pitch is an important parameter, ISO-484 includes other checks on the blade shape and position. The length of the blade at each measurement location is known as the chord length. Chord length is reviewed because it is important to maintain the same surface area for each blade. The spacing between blades as well as the position of the leading edge of each blade is checked for consistency. Blade spacing is important for smooth and quiet propeller performance. Lastly, the axial position of each blade is checked. This ensures that each blade is raked (or swept backward) the same amount. (This is sometimes referred to as propeller track.)
There is typically a statement of compliance (or non-compliance) near the top of the report that gives the overall pass/fail status of the propeller with respect to the desired Class accuracy.
In addition to the overall compliance, sometimes the compliance of an individual criterion (pitch, chord, blade spacing, track, etc.) is detailed. This provides a nice overview of the work required for damaged propellers or the work performed on repaired propellers.
Some software, such as TrueProp, includes a wheel view that displays the shape of the propeller as seen from above. This view is great for finding the damaged regions on the propeller, which are usually marked with a different color or large dot. The wheel view often includes the spacing between blades, as well as reporting pitch values for each blade and the average of the propeller as a whole.
In a full report (not usually provided to the customer), the dimensional values for the blade parameters are listed. The repair technician can compare these values to the expected values in order to determine how to repair the propeller. While this data is extensive and hard for a boat-owner to understand, it is essentially a tabular version of the bar graphs and wheel plot data. If you are interested in learning more about this propeller data, we encourage you to talk with your repair professional or contact TrueProp Software.
They say: “knowledge is more valuable than money,” and
So next time you damage your propeller, remember that often the propeller can be repaired to better-than-new condition by a professional propeller repair shop. The inspection information provided by repair shops can be intimidating and non-intuitive for boat-owners, but a little knowledge about the inspection process and standards can help you interpret your own scan report and ensure your propeller has been repaired to as-good or better-than-new condition.
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Cool Breeze Marine - The Prop Specialists, has been operating for twenty-six years in Osage Beach, Missouri, and is the only certified propeller repair shop in the Lake of the Ozarks. They serve all the United States and several other countries. What does all this attention mean for owners George and Dorothy Peter, on a day-to-day basis?
“Chaos from the second we open our eyes,” says George. “Things get thrown at us constantly.”
Upon finishing college, George became a marine mechanic. After working in this field for a while, he noticed his affinity for propellers. George would visit propeller shops and realized he was better equipped to answer repair questions than the supposed experts. There was a local demand for propeller repair knowledge, since many of the lake’s mechanics and marinas were not tooled or equipped to work on propellers. When a propeller business went up for sale in 1992, George jumped at the opportunity.
Since the 1992 acquisition, George and Dorothy have been very successful. In fact, this year, George had to stop working on boats altogether due to the demand for propeller repair for Cool Breeze - The Prop Specialists. Recently, Cool Breeze acquired a new propeller scanning device and the PropPress 360, a Digital Data Scanner and a hydraulic propeller bending machine from Linden Propellers (Dubuque, Iowa), which together with the new TrueProp Software (Durham, NH) led them to achieve more precise measurements. The Peters are fervent supporters of the combined technology.
“TrueProp, partnered with the Linden DDS and the PropPress 360, is the most accurate system on the market,” says George.
TrueProp is the only independent and widely compatible software available for propeller inspection and repair and makes it easier for people like Dorothy and George to do their jobs. Before Cool Breeze incorporated TrueProp Software, they used manual methods to assess and repair their propellers.
“We cleaned the prop a bit, assessed whether it was repairable with manual gauges, and beat the propeller with rawhide or brass hammers to get it to lay on a pitch block,” says Dorothy.
“Then we beat it to the block with heat if necessary. We would weld the missing parts and grind it back to the appropriate thickness and shape, finish them, check and recheck, balance and ship. But we would never really know if it was 100% correct, how could we?”
George adds that heating and hammering the propeller would leave dents and marks and ruined its temper. “Anyway,” he says. “We’re all getting old. Our days of swinging around the sledgehammer are limited, the hydraulics save us from that. No heat is used to bend our propellers. The only heat the propeller sees is from the TIG welder.”
Now Cool Breeze can offer accurate repair to the highest standards available in the industry. “We can show our customers what was wrong with their prop, and then show them how it has been corrected. We are now having larger propellers shipped to us from all over the United States to repair.”
The arrival of the new technology at the lake has changed everything. “We have the ability to prove that the work was done right,” says Dorothy. “Customers have complete confidence in us. Big props that used to go to Florida now come to us.
"You can’t lie to TrueProp, and TrueProp doesn’t lie to you.”
Since the acquisition of the new PropPress 360 and Linden DDS system with TrueProp Software, the everyday business routine at Cool Breeze may still be chaos, but it is easier to manage. It is catalogued chaos, held together in part by numbers and reports, technology and precision. There is no more need for guesswork, since TrueProp always gives them the best, the truest, results.
Download the article, here.
2018 was an incredibly productive year for TrueProp! We would like to first and foremost thank you all for your support. Our first year was full of exciting developments, expanding features, and solutions to everyday propeller inspection. So much has happened we wanted to share our major milestones...
Propeller Inspection Enhanced
Joint Industry Project Announced
Open Compatibility Established
Social Media Up and Running
Yet to come...
TrueProp Software at work with the Linden DDS and the Prop Press 360.
TrueProp Software LLC of Durham, NH USA is excited to announce the launch of the new Improved Propeller Inspection and Metrology Joint Industry Project (JIP). This novel six-member JIP will address the development of methods and software code for improvements in propeller inspection, geometric modeling, and compliance standards.
A group of six companies – led by TrueProp Software LLC, and including HydroComp, Inc., Linden Propeller, Padgett-Swann Machinery, Wildcat Propellers, and Argonaut Enterprises – kicked off this project on February 23rd, 2018. The propeller specialists at HydroComp will be the lead investigators.
Geometric inspection of a propeller’s blade shape is a critical step in the quality assurance for new propeller manufacture and propeller repair. This JIP aims to resolve a number of identified deficiencies in metrology, compliance criteria, and inspection practices to achieve the following objectives: improved workflow productivity, cost savings, better product outcomes, and connectivity for new and legacy inspection devices. Members will participate in development, application, and testing of new modules in the TruePropTM propeller inspection software.
The story was shared on The Motorship, The Maritime Journal, VPO (Vessel Performance Optimization), and, the May/June issue of International Tug & OSV!
Available for download, here.