# Propeller Calc vs Anchor Pro

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.

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.

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.

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.

## The numbers

| Metric | Propeller Calc | Anchor Pro |
| --- | --- | --- |
| Price | Free | Free |
| Rating | [3.0 (1 ratings)](https://appshunter.io/ios/app/propeller-calc/id478119478/reviews) | **[4.8 (3.5K ratings)](https://appshunter.io/ios/app/anchor-pro/id1445476850/reviews)** |
| Number of ratings | 1 | **3.5K** |
| Positive reviews | **100.0% of reviews** | 78.9% of reviews |
| In-app purchases | **No** | Yes |
| Ads | No | No |
| Update frequency | Every 21 months | **Every 2 months** |
| Monetization | **Free** | Free with in-app purchases |
| Size | 3 MB | 23 MB |
| Requires iOS | **17.0** | 17.2 |
| Devices | iPhone, iPad | **iPhone, iPad, Apple Watch** |
| Age rating | 4+ | 4+ |
| Developer | [Frode Rørvik](https://appshunter.io/developer/478119481) | [IdeaBoys GmbH](https://appshunter.io/developer/1578331665) |

## What reviewers say

### Propeller Calc

[App page](https://appshunter.io/ios/app/propeller-calc/id478119478)

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:** macOS Compatibility

**In-app purchases:** none


### Anchor Pro

[App page](https://appshunter.io/ios/app/anchor-pro/id1445476850)

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:** Apple Watch app, Vision Pro support

**In-app purchases (1)**

| Purchase | Price | Billing |
| --- | --- | --- |
| Anchor Premium | $6.99 | per year |

**What reviewers like**

- 🚀 Reliable anchor alarm
- 👍 Easy to use interface
- 🔒 Works without cell/WiFi
- 💤 Helps user sleep soundly
- 🗺️ Detailed anchor tracking

**What reviewers complain about**

- 🐛 GPS accuracy issues
- 🔋 Drains device battery
- 🔍 Remote monitoring unreliable
- 💰 Subscription required for full features

**Reported bugs**

- App randomly shuts off
- Anchor position tracking glitches

**Requested features**

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


## Frequently asked 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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*Compared by [AppsHunter](https://appshunter.io/) from daily US App Store data. Review summaries are generated from verbatim App Store reviews.*