Last updated: July 12, 2026
By installing or using Snubline, you agree to these Terms of Service. If you do not agree, do not install or use the app.
Snubline is an iOS application that models dynamic rigging forces for tree work. It computes peak line tension, dynamic load factor, block force, friction-device force, and let-run distance from a closed-form spring-mass energy model, presents each result with an uncertainty band and its underlying equation and sources, and compares computed forces against the working load limits you derive from your own equipment's tag ratings and chosen design factors. It also estimates green log weight from cited species densities. All data is stored on your device. The app has no backend, no account system, and no cloud synchronization.
Snubline models negative (lowering) rigging only. It does not model climbing or life-support systems, crane picks, swing arcs, whipping, tree flex, rope heating, or cycles to failure, and it assumes a vertical drop of the center of gravity. Selecting a low-stretch (HMPE) rope triggers a hard warning because such rope provides little shock absorption. The full model, its equations, its citations, and its limitations are presented in the in-app "How Snubline calculates" page.
Snubline reports factual comparisons only, in a fixed vocabulary: Within WLL, Approaching WLL, Exceeds WLL, and Exceeds MBS. These are comparisons of a computed force against the ratings you entered at the design factor you set. They are not endorsements, approvals, or judgments about whether any operation should proceed.
The free tier includes the full shock calculator (both snubbed and let-run modes, uncertainty bands, and per-number why-sheets), the green log weight estimator, the model page, three Gear Locker items, and one job. The physics is complete and never reduced.
The Pro tier unlocks: an unlimited Gear Locker and unlimited jobs, side-by-side what-if scenario comparisons, the one-page crew-briefing PDF, custom rope profiles, home-screen widgets, and scenario share cards.
You agree to use Snubline as a planning aid only, and to enter accurate equipment ratings drawn from each item's own tag. You are responsible for the inputs you provide and for every field decision made on the job. Snubline's outputs are estimates carrying published measurement scatter; weights derived from the species estimator are flagged as estimates throughout the app and in every exported briefing.
Snubline does not provide arboricultural, engineering, or legal services. The crew-briefing PDF is a formatted summary of the inputs and computed comparisons you produced; it is not a certification, an inspection record, or a substitute for professional judgment. Any operation involving rigging must be planned and supervised by a qualified professional.
Because Snubline stores all data on your device, you are solely responsible for backing up your device. We recommend enabling iCloud Backup. The developer is not responsible for data loss resulting from device damage, device loss, operating-system errors, or user deletion.
Snubline is provided "as is" without warranty of any kind. We disclaim all warranties, express or implied, including warranties of merchantability, fitness for a particular purpose, and non-infringement. We do not warrant that the app will be uninterrupted or error-free, or that its estimates will match any particular real-world outcome.
To the maximum extent permitted by law, in no event will the developer of Snubline be liable for any indirect, incidental, special, consequential, or punitive damages, including damages for lost profits, lost data, property damage, injury, or any outcome arising from a rigging operation. In no case will total liability exceed the amount you have paid for Snubline in the twelve months preceding the event giving rise to the claim.
We may update these Terms from time to time. The revised version will be posted at the same URL. Continued use of the app after any update constitutes acceptance of the revised terms.
These Terms are governed by the laws of the jurisdiction in which the developer is resident, without regard to conflict-of-law provisions.
Questions about these terms? Email captainlongevity@gmail.com.