Comparison

Propeller Calc vs iVSP

Price, ratings, monetisation and update history for both apps, side by side — with what reviewers say about each.

Head to head
About

Propeller Calc

This utility calculates propeller performance metrics like pitch, gear ratio, RPM, slip, and speed. Input any four values, and the app computes the fifth, helping users understand the relationship between propeller design and boat performance.

Highlights
  • Calculate pitch, gear ratio, RPM, slip, and speed
  • Enter any four variables to find the fifth
  • Understand propeller slip and its impact
  • Supports iPhone and iPad
  • Free to use
Features
Read full description

This calculator can determine pitch, gear ratio, RPM, propeller slip and speed parameters. Enter any four variables, and it will calculate the fifth. Use the toggle switch to choose which field to calculate. Pitch is the theoretical forward movement for one complete turn of the propeller. Every inch of the boat in contact with the water induces drag. Therefore, the distance travelled differs since the propeller is "slipping" behind the theoretical distance it should travel with each rotation. The difference between theory and reality is called slip. Depending on your application, slip typically ranges between 5% and 20%. A lower number is only sometimes what you are after. Slip of a prop changes with operating conditions and is not a direct measure of efficiency. Please consult professionals for guidance. Happy powerboating

About

iVSP

Experience ship navigation with Voith propulsion systems. Explore the mechanics and hydrodynamics of Voith Schneider Propellers (VSP) and their unique thrust capabilities on various vessel types. Learn about the innovative technology behind this propulsion system.

Highlights
  • Steer ships with Voith propulsion
  • Explore Voith Schneider Propeller mechanics
  • Understand VSP hydrodynamics
  • Simulate various vessel types
  • Learn about VSP thrust generation
Features
Read full description

The iVSP app allows users to steer ships equipped with Voith propulsion systems, in particular Voith Schneider Propeller (VSP). These are real ships of various types: Voith Water Tractors (tugs), double-ended ferries, offshore vessels, and yachts. iVSP also provides a deeper insight into the mechanics and hydrodynamics of the Voith Schneider Propeller (VSP) and its unique propeller forces. The VSP enables the fastest generation of thrust in all directions – stepless and precisely. VSPs combine propulsion, steering, and roll stabilization in a single unit, eliminating the need for rudders. Thrust and steering forces can be generated in any direction from zero to maximum. The Voith Schneider Propeller generates thrust by means of profiled blades that protrude from the ship's bottom and rotate around a vertical axis. The blades are mounted in a rotor casing that is flush with the ship's bottom. The rotational movement of the blades around the common vertical axis is superimposed by a local oscillatory movement of the individual propeller blades around their own axis. This oscillatory movement is generated by a kinematic mechanism (kinematics). The Voith Schneider Propeller is based on an idea by Austrian inventor Ernst Schneider, and its effectiveness was first successfully demonstrated in model tests in 1926. The development potential of the VSP is far from exhausted, and Voith engineers are continuously working to further improve its efficiency. In addition, the company is constantly developing new applications for various types of ships for this unique propulsion system. Suggestions for the application and further improvement of the VSP are always welcome. The relevant contact details for Voith can be found in the main menu of iVSP.

Screenshots

Propeller Calc2 screens
iVSP4 screens

Verdict

The call

The clearest difference is rating: iVSP at 5.0 against Propeller Calc's 3.0. iVSP also leads on iOS requirement (13.0 vs 17.0). On price, review sentiment, ratings volume and update cadence there is nothing between them.

Scored on Price · Rating · Positive reviews · Number of ratings · Update frequency · Ads · In-app purchases · Monetization · Best chart rank · Devices · Requires iOS

CostPrice · In-app purchases · Ads · Monetization

Both are free to download. Neither carries in-app purchases, so what you see is what you pay.

ReceptionRating · Positive reviews · Number of ratings

iVSP holds the better App Store score, 5.0 against 3.0. Both are backed by a comparable volume of ratings — 1 and 1 respectively. Written reviews split almost evenly too, at 100% and 100% positive.

UpkeepUpdate frequency

Both ship on a similar rhythm, roughly every 21 months. The most recent releases landed on September 9, 2026 and September 11, 2026 respectively.

Scorecard2 real differences · 8 level
Propeller Calc versus iVSP: the parameters behind the verdict, then further details
ParameterPropeller CalciVSP
PriceFreeFree
Rating3.0 (1 ratings)5.0 (1 ratings) — better
Positive reviews100.0% of reviews100.0% of reviews
Number of ratings11
Update frequencyEvery 21 monthsEvery 21 months
AdsNoNo
In-app purchasesNoNo
MonetizationFreeFree
DevicesiPhone, iPadiPhone, iPad, iPod — better
Requires iOS17.013.0 — better
Further details — not scored
Size3 MB384 MB
Age rating4+4+
DeveloperFrode RørvikVoith Digital Solutions Inc

Customer experience

Propeller Calc

All ratings1 ratings
Positive0.0%
Neutral100.0%
Negative0.0%
Written reviews1 reviews
Positive100.0%
Neutral0.0%
Negative0.0%

iVSP

All ratings1 ratings
Positive100.0%
Neutral0.0%
Negative0.0%
Written reviews3 reviews
Positive100.0%
Neutral0.0%
Negative0.0%

In-app purchases

None

Propeller Calc

No in-app purchases

None

iVSP

No in-app purchases

Questions

Is Propeller Calc free?
Propeller Calc is free to download, with no in-app purchases.
Is iVSP free?
iVSP is free to download, with no in-app purchases.
Which has better reviews, Propeller Calc or iVSP?
iVSP is rated higher. Propeller Calc averages 3.0 out of 5 from 1 ratings, while iVSP averages 5.0 from 1 ratings.
Do Propeller Calc or iVSP have ads?
Neither Propeller Calc nor iVSP shows ads.
Which is updated more often, Propeller Calc or iVSP?
Propeller Calc ships an update every 21 months, and iVSP every 21 months. Most recently, Propeller Calc was updated on September 9, 2026 and iVSP on September 11, 2026.

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