Everything it takes to carry more than six passengers on a RHIB: the Coast Guard COI process from design standards to the stability letter, and the stability checks themselves. Upload a 3D model and a profile drawing. You get a deadweight-survey worksheet, the wind-heel check under 46 CFR 170.170 as applied by MTN 01-08, and the collar-puncture cases — all computed from your own hull, on pages you can work through with a reviewer.
Submit a vessel for testing See the exampleEvery check on this site is a direct application of the regulations and MSC guidance that govern stability testing and Certificate of Inspection for inflatable-collar passenger vessels. No proprietary criteria, no shortcuts: the criterion, the number, and the margin, in the order a reviewer reads them.
This is an actively maintained reference. When MSC issues a revised technical note or a policy letter changes how a criterion is applied, the method here is updated and the change is noted. It is a new way to prepare a stability submission, not a new standard.
A complete worked case you can click through: freeboard stations and the fitted waterline, the wind-heel margin with hardtop length and ballast you can change, and each collar chamber deflated in turn in 3D.
Paste the vessel link or ID from your confirmation email. Password-protected vessels ask for the password on the next page.
Stations on your profile, predicted freeboards for the light ship, and the fitted waterline from your measured port and starboard readings — the numbers a reviewer compares against the model.
Projected lateral area and heeling arm for protected, partially protected and exposed routes, applied as MTN 01-08 §5.5. Slide the hardtop length and ballast and watch the pass/fail margin move.
Each chamber deflated in turn: equilibrium heel, range, righting energy and GZ-max against the criteria, drawn in 3D so the governing chamber is obvious.
Place seats on the plan view and choose who sits where for the minimum, half and full-load conditions of PRG H1-01 §8.1.2. The analysis re-runs with those positions.
Protect a vessel with a password when you submit it, and only people you give the password to can open its pages. Public vessels are listed here by choice.
Pages are laid out the way the calculation is read: criterion, number, margin. Add drawings and models to a vessel any time from its results page.
Every load condition, seat position, weight and dimension on these pages is an assumed condition derived from the drawings and model the owner supplies. The results are only as good as those drawings. Submitting a vessel includes a statement that the drawings and model are accurate and current, and the deadweight survey on the real boat, witnessed by the Coast Guard, is what confirms the lightship the model predicts. This is an engineering aid for the owner and whoever prepares the submission — it is not a Coast Guard approval. The Marine Safety Center reviews the submission and issues the stability letter.
A shade top is the single biggest change you can make to a RHIB's stability: it adds windage high above the water, and the wind-heel check (46 CFR 170.170) is usually what sets the limit on an inflatable-collar boat. The same goes for a longer bracket, a heavier engine, a new console or a bench moved aft.
Submit your boat as it is today, then open its windage page and slide the hardtop length, its height above the deck, and any fixed ballast or batteries. The page shows the margin against the criterion for your route — protected, partially protected or exposed — so you can see how big a top you can carry and where ballast would have to go to keep the route and conditions already on your Certificate of Inspection.
An alteration still has to go to the Coast Guard before it is made (46 CFR 176.700), and a change that affects stability means an updated submission to the Marine Safety Center. What this gives you is the answer before you spend the money — and the worked case to send with the request.
Every inch of top adds projected area and raises its centre; the page recomputes the heeling moment and required GM as you slide.
Fixed weight low in the boat buys back margin. Slide the amount, how far forward, and how high above the keel to see what it takes — and what it does to trim.
Switch between protected, partially protected and exposed to see whether the change costs you a route — or what it would take to add one.
Everything on this site starts from an accurate 3D model and drawings of your boat as it is built. Many owners have neither — a builder's brochure drawing is not enough, and the collar manufacturer's tube drawing is only one piece.
We produce them with you: measurements taken on the boat, a hull and collar model, the profile and plan drawings, the seating arrangement, the hardtop and fixed-weight details. Naval architecture services are available to prepare the stability calculations and the submission to the Marine Safety Center, which reviews it and issues the stability letter.
Tell us what you have — photos, a builder's drawing, a collar drawing, nothing at all — and we will tell you what it takes to get to a submission.
Photos from the side, above and astern; any builder or collar drawings; hull length, beam and collar size; engine and passenger count.
A measured hull and collar 3D model, side-profile and plan drawings, hardtop and seating arrangement — the files the checks run from, and the files a reviewer asks for.
The vessel goes through the same pages as the example: deadweight survey, wind heel, collar puncture, seating — and, if you want it, we prepare the stability package and submit it to the Marine Safety Center. MSC reviews it and issues the stability letter to the owner.