Seakeeping Standards

I agree MII would possibly be better. But one would need to use the GLFE rather than the LFE which does not account for heave.

Or...you can wade through the endless new silly EU rules :

 

Would this buried assumption also invalidate its use for vessels under sail, where roll is much, much slower and more damped than pitch?

What is your book?

 

No..the MII is not vessel dependent.

The MII is basically the number of cycles and probability of an event, the event being the GLFE..or generalised lateral force estimator, rather than the LFE. The GLFE takes into account the accelerations due to sway + roll induced acceleration + effects of heave. What is known about MII/GLFE is that motions which are 'slow' will result in a lower value of MII...so may be a slow yacht may not produce ideal results.

 

That may be why we've only used that standard for mono hull craft, Chris.

 

Misc:

Bill: Oh yes, and so do I! And in your case I know that you have access to even more sophisticated models. No criticism implied.

David: Interesting question I had not previously thought about. Yes, I suspect that the STANAG criteria will be unduly restrictive for the case of vessels under sail. This would be an interesting area of research. Does anybody know what Marchaj has to say in terms of motion criteria?

And regarding my book, I have a small textbook on the design of Advanced Marine Vehicles (SWATHs, SES, Multihulls) that I use in my teaching. It is for sale on Amazon - search for my name as author.

All the best,

Chris McKesson

 

I would definitely agree with that, especially if your focus is on the human factors and habitability elements of sea keeping.

We've been "hanging" our habitability assessments on the ISO 2631 criteria for MSI and FDP for many years now (although those criteria were not always incorporated in 2631 and before it was the underlying research was referenced instead..or the old MIL-STD-1472, etc.

 

If it is about small craft (L<24m), there are currently no common seakeeping standards and those for big ships (such as STANAG) are hardly usable. The same refers to ISO2631 that is appropriate for public transport but would force to ban any high speed small craft operation.

As a PRACTICAL guideline of acceleration levels, values presented in Savitsky-Koelbel paper are useful.

BUT seakeeping it is not just accelerations, but also, say, wetness. Always the forgotten factor with all those Axe-bows and similar shapes.

 

There are multiple things to be considered. It's about accelerations that a human can stand as well as a craft. Then there are design pressures affecting to hull including global load like in HSLC DNV code, but some of new ISO standards give some more appropiate approach (LH<24m) like for multihulls (part 7). Estimating accelerations for a boat which might get airborned is one tricky thing, as if it would be easy to estimate real accelerations and construction affecting frequensies thats are most remarkable. Then consideration about water on deck situations especially when there are cockpits there. And of cource stabitily (statik and dynamic). A boat which can jump from wave to next, is one completely different to lead sleds like fast over 24 m vessels which ever get airborned but is rumbling thourgh waves.

 

Also, somebody asked about PASCAT. What in particular would you like to know? There are several members who know a lot about the subject...[/QUOTE]

First question

What is the difference between an HCAC and SES and PASCAT. They are all semi air cushioned twin hull vessels as I know ??