Comparison

Propeller Calc vs Anchor Pro

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

Anchor Pro

This app helps boaters set and monitor their anchor position in real-time. It allows for defining safe zones, tracking boat movement, and receiving alerts for critical changes. Remote notifications and Apple Watch integration enhance its utility for secure anchoring.

Highlights
  • Set anchor location in real-time or manually
  • Define custom safe swing zones
  • Monitor boat movement and track history
  • Receive real-time alerts for position, GPS, and battery
  • Remote notifications via Telegram or email
  • Apple Watch companion app for key metrics
Features
Read full description

SET THE ANCHOR Set your anchor location in real time as you drop it, or specify it later by entering distance and bearing. Advanced users can also input exact coordinates. DEFINE THE SAFE ZONE Define the allowed swing area as a simple circle around the anchor, or create a more precise zone by setting two different radii at specific angles. MONITOR MOVEMENT Stay on top of every movement with comprehensive real-time data. Review key metrics on the main screen or switch to the map view to see your boat's track — ideal for analyzing whether your anchor is holding or dragging. GET ALERTED WHEN IT MATTERS Monitor position, GPS signal strength, and battery level — and receive alerts the moment any of these fall outside your set thresholds. REMOTE ALERTS Leave your phone on board and stay informed from shore. Receive alarm notifications via Telegram or email. With Telegram, you can also request a live status update at any time. APPLE WATCH Keep distance, bearing, and battery level on your wrist with the Apple Watch companion app — all updated in real time. TRY ANCHOR PRO FOR FREE Core features are always free. Want to explore everything? All premium features are available during a free trial period — no commitment required. Anchor Pro is ad-supported. Purchasing an Anchor Premium subscription removes ads and unlocks extra features. Payment is charged to your iTunes Account at confirmation. Subscriptions renew automatically at the same price unless auto-renewal is turned off at least 24 hours before the current period ends. You can manage auto-renewal anytime in your Account Settings. Anchor Premium is $6.99 USD/year (pricing may vary by country). Any unused portion of a free trial is forfeited upon purchasing a subscription, where applicable. Terms of use: https://links.ideaboys.net/anchor-ios-terms.html GOOD TO KNOW Anchor Pro uses background audio and location services to keep alerts active when the app is not in the foreground. Please note that continuous GPS use will drain your battery faster than usual.

Screenshots

Propeller Calc2 screens
Anchor Pro4 screens

Verdict

The call

The clearest difference is rating: Anchor Pro at 4.8 against Propeller Calc's 3.0. Anchor Pro also leads on update cadence (every 2 months vs every 21 months) and ratings volume (3.5K vs 1). Propeller Calc's advantage is in-app purchases (none vs 1) and review sentiment (100% vs 79%). On price, ads, device support and iOS requirement 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. Anchor Pro sells 1 in-app purchase, starting at $6.99 per year. Propeller Calc asks for nothing beyond the download.

ReceptionRating · Positive reviews · Number of ratings

Anchor Pro holds the better App Store score, 4.8 against 3.0. That said, the two scores are not equally well evidenced: Anchor Pro has 3.5K ratings behind it against 1, so its average is the more settled of the two. Written reviews complicate that: 100% of Propeller Calc's written reviews are positive against 79% of Anchor Pro's, so the app with the better star average is not the one people write more warmly about.

UpkeepUpdate frequency

Propeller Calc ships an update every 21 months, Anchor Pro every 2 months. The most recent releases landed on September 26, 2026 and October 17, 2026 respectively.

Scorecard6 real differences · 4 level
Propeller Calc versus Anchor Pro: the parameters behind the verdict, then further details
ParameterPropeller CalcAnchor Pro
PriceFreeFree
Rating3.0 (1 ratings)4.8 (3.5K ratings) — better
Positive reviews100.0% of reviews — better78.9% of reviews
Number of ratings13.5K — better
Update frequencyEvery 21 monthsEvery 2 months — better
AdsNoNo
In-app purchasesNo — betterYes
MonetizationFree — betterFree with in-app purchases
DevicesiPhone, iPadiPhone, iPad, Apple Watch — better
Requires iOS17.0 — better17.2
Further details — not scored
Size3 MB23 MB
Age rating4+4+
DeveloperFrode RørvikIdeaBoys GmbH

Customer experience

Propeller Calc

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

Anchor Pro

All ratings3,496 ratings
Positive96.5%
Neutral1.7%
Negative1.7%
Written reviews180 reviews
Positive78.9%
Neutral3.3%
Negative17.8%

Bugs and requests

Propeller Calc

Not enough reviews yet to summarise bugs or requests.

Anchor Pro

Reported bugs

2 issues
  • App randomly shuts off
  • Anchor position tracking glitches

Requested features

3 requests
  • Customizable anchor icon/color
  • Integration with marine GPS/chartplotter
  • Ability to adjust alarm parameters remotely

In-app purchases

None

Propeller Calc

No in-app purchases

1 purchases

Anchor Pro

Subscriptions1
  • Anchor Premium7 Days trial$6.991 Year

Questions

Is Propeller Calc free?
Propeller Calc is free to download, with no in-app purchases.
Is Anchor Pro free?
Anchor Pro is free to download, with in-app purchases available.
Which has better reviews, Propeller Calc or Anchor Pro?
Anchor Pro is rated higher. Propeller Calc averages 3.0 out of 5 from 1 ratings, while Anchor Pro averages 4.8 from 3.5K ratings.
Do Propeller Calc or Anchor Pro have ads?
Neither Propeller Calc nor Anchor Pro shows ads.
Which is updated more often, Propeller Calc or Anchor Pro?
Propeller Calc ships an update every 21 months, and Anchor Pro every 2 months. Most recently, Propeller Calc was updated on September 26, 2026 and Anchor Pro on October 17, 2026.

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