Snubline
Shock Loads, WLL & Job Plans
Only for iPhone
Free · In‑App Purchases
iPhone
The physics is free forever: both shock modes, uncertainty bands, and every equation shown. Pay once for the crew workflow - jobs, what-if compare, and briefing PDFs.
Do the math before the cut.
Snubline turns "how hard will that piece hit the rigging?" into numbers before the saw starts. When a cut section free-falls before the rope catches it, peak force can run several times the static weight - enough to fail a sling or pull the rigging point out of the tree. Snubline computes that force from a documented spring-mass energy model and checks it against the ratings printed on your own gear's tags.
THE SHOCK MODEL (free, full physics - never reduced)
- Snubbed mode (worst case, the default): closed-form peak line tension from the fall factor.
- Let-run mode: set your brake's slip tension and Snubline returns the run distance needed to absorb the rest of the energy - the first tool that puts numbers on the groundworker's art of letting it run.
- Outputs: peak line tension with an uncertainty band, dynamic load factor, stretch, force at the block, and force at the friction device.
- Every number is tappable - open the equation, the inputs, and the sources behind it.
VERDICTS AGAINST YOUR GEAR, NOT OUR GUESSES
Enter each block, sling, rope, and friction device with the MBS from its tag and your own design factor. Snubline compares the computed force at each system point and reports a factual verdict - Within WLL, Approaching WLL, Exceeds WLL, or Exceeds MBS - with the margin shown. The verdict reads only the gear you entered.
GREEN LOG WEIGHT ESTIMATOR (free)
Trunk, frustum, and limb modes using cited green densities for about 50 species. Every estimate is flagged, and that flag follows the weight through the model, the verdicts, and the briefing sheet.
JOB PLANS + CREW BRIEFING PDF
Build scenarios per job, compare them side by side (snub vs run, block higher vs lower, fatter rope vs skinnier), and produce a one-page tailgate briefing sheet for the morning meeting.
IT SHOWS ITS WORK
The "How Snubline calculates" page lays out the full model: the equations, the citations (Kane / ISA; Donzelli & Lilly; HSE rigging research; published rope-elongation classes; species-density references), the uncertainty band, and an explicit list of what the model does not cover.
A PLANNING AID, HONEST ABOUT ITS LIMITS
Snubline is a planning aid for professional arborists. It is not a substitute for on-site assessment by a qualified arborist, and it makes no judgment about whether any operation should proceed. It models lowering rigging only - not climbing or life-support systems.
YOUR DATA, YOUR DEVICE
Everything you enter lives on your iPhone. No account, no sign-in, offline on any landing zone. Snubline runs no analytics and connects to no network.
FREE
- The full shock calculator, both modes, with uncertainty bands and why-sheets
- The green log estimator and the model page
- Three Gear Locker items and one job
PRO (one-time or subscription)
- Unlimited Gear Locker and unlimited jobs
- What-if scenario comparisons
- Crew-briefing PDFs and scenario share cards
- Custom rope profiles
- Home-screen widgets
The physics is free forever. Pay once for the workflow.
Pro is available as a one-time Lifetime purchase, an annual plan with a 7-day free trial, or a monthly plan. Subscriptions are charged to your Apple ID and renew unless auto-renew is turned off at least 24 hours before the period ends; you can manage them in your Apple ID settings.
Privacy Policy: https://app-legal-pages.vercel.app/snubline/privacy
Terms of Service: https://app-legal-pages.vercel.app/snubline/terms
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The developer, 慧慧 高, indicated that the app’s privacy practices may include handling of data as described below. For more information, see the developer’s privacy policy .
Data Not Collected
The developer does not collect any data from this app.
Accessibility
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Information
- Seller
- 慧慧 高
- Size
- 3.8 MB
- Category
- Productivity
- Compatibility
Requires iOS 17.0 or later.
- iPhone
Requires iOS 17.0 or later.
- iPhone
- Languages
- English
- Age Rating
4+
- 4+
- In-App Purchases
Yes
- Monthly $2.99
- Annual $11.99
- Lifetime $29.99
- Copyright
- © 2026 Huihui Gao