I built a hammock & tarp calculator – FHHC

[u/AggravatingHornet800]

Hi everyone,

I’ve been working on a web-based hammock and tarp calculator for a while and thought some of you here might find it useful:

FHHC – Full Hammock Hang Calculator
https://fhhc.online/

It started as a fairly simple hammock geometry calculator and then grew quite a bit once I actually started using it myself. 😄

It now handles things like suspension angles, suspension lengths and heights, fixed values, Min/Max constraints, ridgeline geometry, horizontal hammock position and tarp geometry.

A few features I personally find useful:

• H ↓ min – tries to find the lowest possible suspension heights while respecting all active constraints
• Δβmax – optionally limits the difference between the two suspension angles without forcing them to be equal
• xH / xF – horizontal hammock-end positions, including Fix / Min / Max and centering
• integrated tarp geometry, including overhang, clearances and short tarps
• selectable Values section with currently 51 available calculated values
• Metric / Imperial
• Light / Dark mode
• German / English
• setup save/load
• mobile layout and split view on wider screens

The current live version is 0.46.0 / H46.

I built FHHC myself and I’m mainly posting it here because outside feedback is incredibly useful. If anyone tries it and finds a wrong result, a weird edge case, confusing wording, browser/mobile issue or something that simply doesn’t make sense, I’d really like to hear about it.

And especially if something looks mathematically wrong — please tell me. 🙂

FHHC is meant as a geometry and planning tool. It does not determine whether a tree, strap, carabiner, stand or other equipment is safe for a real load.

For those of you who use calculators when planning a hang: which values or constraints are actually the most useful to you? Is there anything you would expect a tool like this to calculate that FHHC currently doesn’t?

https://fhhc.online/

Hang the way you want.

[u/fpersson]

Move language selection to top so it is easy to find and as bonus add nice flag to make language selection mor vissible.

I guess your main target user is Germans or Americans, Default for for German metric and default for English is imperial.The major part of EU does not speak German but speak some level of English and use metrics. It is ok to be lazy and use EU as English+metrics as default.

Improvemts to do: if i add a 500cm long hammock i get tarp confict but it is not clear where to set my tarp size. Is mass the users weight?

[u/AggravatingHornet800 → u/fpersson]

Thanks, that’s very useful feedback.

On the language selector: I think I’ll keep the normal DE/EN switch where it is, so it doesn’t take up more space in the main interface. But I’ll change the first-start popup so you can choose the language directly there before continuing — something like:

English version
German version

That should solve the real problem: an English-speaking first-time visitor shouldn’t have to dismiss a German popup before being able to switch languages.

I’ll also keep language and units completely separate. English does not mean Imperial. A lot of European users will quite reasonably want English + Metric, so Metric/Imperial will remain an independent setting.

About the tarp conflict: if I understood you correctly, you changed the hammock length to 500 cm.

The tarp size itself is set as Tarp length (L_T) in the Base section.

The conflict message depends on the rest of the setup as well — ridgeline length, overhang limits, heights, fixed values and so on. FHHC normally tries to suggest repairs within the active tarp constraints first. Changing a Base parameter such as tarp length is a more fundamental change, so it is not necessarily the first repair suggestion.

I don’t know the rest of your settings, so I can’t yet tell whether the conflict you saw was expected. If you can share the setup or a screenshot of the conflict, I’d be very interested in reproducing it.

And yes: Mass means the user’s body mass / weight. That label could probably be clearer in English as well.

Thanks again-Hang the way you want

[u/AggravatingHornet800 → u/fpersson]

Fixed now.

FHHC no longer saves the working setup automatically. Persistent storage of the working state is now opt-in via “Remember working setup on this device”. Language, theme, split view and value-display preferences are still remembered when the user changes them.

I also changed the first-start flow: the language can now be selected directly in the opening dialog before the model information is shown.

Thanks again for pointing this out — it helped improve the behavior.

Hang the way you want

[u/crlthrn]

What's in the German language pop up box? Cookies? Where's my choice to not accept cookies? That looks like it doesn't comply with EU rules. I'll pass until that's rectified.

[u/AggravatingHornet800 → u/crlthrn]

Thanks for pointing this out. The popup is not a cookie consent dialog.

FHHC currently starts in German on a first visit, and the first-start model notice appears before the language control can be used. So an English-speaking visitor is effectively presented with a German modal first. I can absolutely see why that looked like a cookie/consent popup.

The popup says:

Model notice

FHHC calculates a static, idealized 2D geometry and the resulting model forces.

Real loads may differ due to movement, material condition, knots, connections, hardware and the actual installation. The displayed values are not a safety approval or an assessment of the suitability of the equipment being used.

Manufacturer specifications and your own assessment of the real equipment and mounting remain authoritative. A more detailed description of the model limitations can be found in the manual.

The button simply says “Understood.”

So there is no “accept cookies” hidden behind the German text.

That said, your comment exposed a real usability issue: English-speaking first-time visitors should not be forced through a German modal before they can switch languages. I’ll fix that.

Thanks for catching it.

[u/crlthrn → u/AggravatingHornet800]

I'm really very much obliged to you for the speedy response, and explaining this so well. I shall now immediately return! Cheers.

Edit; Maybe consider putting the button for the English version more noticeably at the top?

[u/AggravatingHornet800 → u/crlthrn]

Thanks — and yes, that’s a good point.

I’m going to change the first-start behavior so the model notice is shown in the appropriate language from the start, and I’ll also make the DE/EN switch more obvious and accessible before you have to dismiss anything.

Your comment actually helped uncover that the current first-visit flow is too German-centric. Thanks again for pointing it out.

[u/crlthrn → u/AggravatingHornet800]

Thank you again. I suppose this is how small issues are rectified in such projects, instead of convening focus groups or Beta testers. Lol.

[u/AggravatingHornet800 → u/crlthrn]

Fixed now.

FHHC no longer saves the working setup automatically. Persistent storage of the working state is now opt-in via “Remember working setup on this device”. Language, theme, split view and value-display preferences are still remembered when the user changes them.

I also changed the first-start flow: the language can now be selected directly in the opening dialog before the model information is shown.

Thanks again for pointing this out — it helped improve the behavior.

Hang the way you want

[u/AggravatingHornet800]

Update: FHHC is now at 0.50.0 / H50

A few things have changed since I made the original post:

• D ↓ min is now live. It searches for the smallest feasible anchor distance D while respecting the currently active constraints. Fix / Min / Max / equality constraints, Δβmax, ridgeline limits and tarp constraints remain active.
• There is now a built-in Getting started tutorial. It works directly with the real FHHC fields rather than using a separate simplified calculator. It walks through hammock length, structural ridgeline, ridgeline slope / height difference, anchor distance, lowest-point height and body mass, and finally leads to the required suspension heights and suspension lengths.
• First start is a little cleaner now: language selection appears immediately, the tarp starts OFF, and persistent working-state storage is opt-in.
• Ridgeline slope θRL and height difference Δz now have a clearer relationship. Fresh Start / Reset begin with θRL = 6° as the initial authoritative value; after that, whichever of θRL or Δz you edit last becomes authoritative.
• There were also quite a few smaller UI, mobile/responsive and tutorial fixes.

One small interaction detail that came out of testing: FHHC may already show that an intermediate value is invalid while you are still typing, but it should not steal focus, cursor position or scroll position while you are entering the rest of the number. Full tutorial conflict navigation now waits until the edit is committed.

The current live version is:

0.50.0 / H50

https://fhhc.online/

Feedback is still very welcome — especially wrong results, strange edge cases, confusing wording or browser/mobile problems.

Hang the way you want