# Propeller Calc vs BoatAlarm

The clearest difference is in-app purchases: Propeller Calc at none against BoatAlarm's 4. BoatAlarm's advantage is update cadence (every 6 weeks vs every 21 months) and iOS requirement (15.0 vs 17.0). On price, ads and device support there is nothing between them.

Both are free to download. BoatAlarm sells 4 in-app purchases, starting at $2.99 per month. Propeller Calc asks for nothing beyond the download.

Propeller Calc ships an update every 21 months, BoatAlarm every 6 weeks. The most recent releases landed on September 26, 2026 and October 6, 2026 respectively.

## The numbers

| Metric | Propeller Calc | BoatAlarm |
| --- | --- | --- |
| Price | Free | Free |
| Rating | **[3.0 (1 ratings)](https://appshunter.io/ios/app/propeller-calc/id478119478/reviews)** | — |
| Number of ratings | **1** | — |
| Positive reviews | 100.0% of reviews | — |
| In-app purchases | **No** | Yes |
| Ads | No | No |
| Update frequency | Every 21 months | **Every 6 weeks** |
| Monetization | Free | — |
| Size | 3 MB | 40 MB |
| Requires iOS | 17.0 | **15.0** |
| Devices | iPhone, iPad | iPhone, iPod |
| Age rating | 4+ | 4+ |
| Developer | [Frode Rørvik](https://appshunter.io/developer/478119481) | [Lobuwin Solutions UG (haftungsbeschränkt)](https://appshunter.io/developer/956649107) |

## 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


### BoatAlarm

[App page](https://appshunter.io/ios/app/boatalarm/id1450867758)

**Features:** macOS Compatibility

**In-app purchases (4)**

| Purchase | Price | Billing |
| --- | --- | --- |
| BoatAlarm Premium 1 Monat | $2.99 | per month |
| BoatAlarm Premium Monthly | $3.99 | per month |
| BoatAlarm Premium 1 Jahr | $9.99 | per year |
| BoatAlarm Premium Annual | $11.99 | per year |


## Frequently asked questions

### Is Propeller Calc free?

Propeller Calc is free to download, with no in-app purchases.

### Is BoatAlarm free?

BoatAlarm is free to download, with in-app purchases available.

### Do Propeller Calc or BoatAlarm have ads?

Neither Propeller Calc nor BoatAlarm shows ads.

### Which is updated more often, Propeller Calc or BoatAlarm?

Propeller Calc ships an update every 21 months, and BoatAlarm every 6 weeks. Most recently, Propeller Calc was updated on September 26, 2026 and BoatAlarm on October 6, 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.*