The U.S. Coast Guard has issued a Technical Note regarding Rigid Inflatable boats for passenger vessel service. As anyone knows who has tried to get them certified in the past, they don't quite fit the mold for some of the regulations -- freeboard, downflooding, drainage and stability testing to name a few of the issues.
The Hawaii MSO had their own guidance, given their experience with these vessels, but it was not "legal" or accepted in other jurisdictions. The new note, MTN 01-08, is intended to provide consistent guidance recognizing the unique features of these vessels. The pdf can be downloaded from the MSC website, or directly here: MTN01-08
Inclining test for RHIB's???
Looking over the MTN for RHIB's I see they have completely ignored the possibility of a simplified stability test for RHIB's, but instead are requiring an inclining test and full intact stability calculations with Subchapter S.
They note that in order to keep the tubes out of the water, which would significantly change the waterplane area, the test may need to be done for smaller angles than the specified 3 to 4 degree range. And they point out that longer pendulums may be needed to obtain the required 6-inch spread of pendulum deflections. They don't mention it, but the requirement is to use 3 pendulums too.
To require an inclining test for these boats is ridiculous -- they are too small to effectively perform the test. Just imagine trying to do an inclining test on a 21' RIB with 3 pendulums that will need to be on the order of 25-30 feet high! That may still not be enough as the collar may actually be touching the water at rest. Then what?? There is no way to incline the boat without a substantial change in waterplane area.
I applaud the Coast Guard for recognizing that a separate standard is needed for these vessels, but it looks like this standard was not thought completely through. Is stability a really big issue for RHIB's? A simplified standard, with maybe a freeboard measurement and wind-heel in the case of RHIB's with cabins would be in order, but not a full inclining test and full IMO intact stability evaluation.