Seaworthiness

[longliner45]

alright ,,,I have read this thread and it seems like almost everyone is right... it depends on what you consider seaworthy,,,but shouldent all boats be built to a standard of (seaworthyness)? lets look at aircraft,,, many many standards,,,,,but when it comes to boats ,,its like no one is watching the store,,,it is all buyer beware..if I buy a daysailer it should come with a disclaimer,, but if I buy a second hand daysailer,,,Im on my own ,,,there should be some rules ,,accompanyed with titles of boats to its limitations,,lets face it many nieve buyers go and buy the 50 ft boat (day sailer)and think they can circumnavigate the globe,,,maritime law has not changed in over 200 yrs,,,,,time to shift gears,,longliner

 

[Guillermo]

I also think that comparing boats of near equal displacement is a valid idea.

May or may be not, Randy, as the gyradius can be quite different. That's why generally speaking size matters by itself for seaworthiness, not only weight. It brings weight distribution further outwards, increasing gyradius and greatly influencing inertia as it enters the formula at the power of 2. Look at the STIX formula at previous fcfc's post (#96): 'Basic STIX' (7 + 2.25Lbs) is the main factor and it depends only on length.
Cheers.

 

[Guillermo]

So the bigger the boat (Lbs), the more seaworthy.

Although we may asume this as being true generally speaking (and in spite of my previous post, which is not in contradiction with what I state here), it may be very tricky, though. Asuming STIX is a clue to a boat's seaworthiness (Which may also be tricky, as I have been highlighting at the STIX thread), the bigger the LBS the more the final STIX figure can be influenced by the rest of factors, which may increase or decrease it. Have a look at post #175 at the STIX thread. The RM 1200, although having a base length factor of 11.61 which leads to a 'basic STIX' factor (7 + 2.25Lbs) of 33.12, probably has an STIX not much bigger than this value. In fact the final figure could very well be even lower than the 'basic STIX', due to having four factors lower than 1, as we saw there.

Cheers.

P.S. (Please, remember to me your name. I think you already gave it to me, but I've forgotten. My apologies)

 

[Mikey]

I assume you're referring to a boat with a large roll gyradius being resistant to capsize by a sudden, brief gust and/or wave action. Does Marchaj address this?

For me, Marchaj's book is one that requires reading several times; Every time I read it, I get more distance to the whole subject and value its parts slightly differently. I don't see that the important message of the book has much to do with sudden events like freak waves, capzise in a huge breaking wave etc., it's more about a dynamic environment where different events lead up to an extreme situation.

Marchaj does address this; the value of displacement and size, moment of inertia, roll damping, roll gyradius, lateral plane area, the positive effects of lower aspect ratio foils and skegs, the depth of the hull vs. Pogo 40 style hulls, the effect of bow down trim on LPS when heeled, all of this in a dynamic world.

...Art claims is that Hinkley Bermuda 40s, which have a rather low LPS, nevertheless have logged an extraordinary number of sea miles with an excellent safety record.

It can have a bit lower LPS and still be very sea worthy indeed because of all the things I list down above.

This means reducing weight aloft is a mixed bag. It lowers VCG and thus increases LPS, but it also decreases roll gyradius

That would be a bad trade-off for a ocean going cruiser

Mikey

 

[marshmat]

I'd sooner have the reduced weight aloft, and put that weight in the keel to keep the roll gyradius where I want it to be.... provided, of course, that I'm not sacrificing the strength of my rig in doing so. Boat goes over, I want my mast to still be there when she comes right side up again.

If I'm taking something out in the open ocean, I want it to be able to take anything- and I mean anything- that the sea can throw at it. Big waves, gale force winds, the occasional drifting 40' isocontainer- I feel the best way to deal with an emergency is to stop it from becoming an emergency in the first place. If I lose a mast and start taking on water mid-Pacific, the Coast Guard's not going to be there right away. I would want my boat to keep me and my crew safe even in freakishly unexpected conditions.

Seaworthiness means something very different on the sheltered lakes and bays where you typically find me. Here I want a boat that can get banged around in the chop and stays comfortable, that I can take my landlubber friends out on, that handles sharp enough that I can dodge the idiots in the 28' cuddy condos. Since I'm less than 20 min from shore, I can run for shelter when things get bad, but if I were to try to wait out a storm here I'd be blown onto an island or into someone's wheat field.

Take for instance the Wolfe Islander III, a 50-odd car ferry in Kingston.... in the worst storm I've seen on this part of the St. Lawrence, she rolls about 6-10 degrees and takes maybe a few hundred litres of water over the bow as spray in the course of half an hour. She's way overbuilt for the area and is easily the most seaworthy vessel in the area given the conditions we get here. Now put her on the Sydney-Newfoundland runs. She'd probably be taking on water while still within sight of land; the big rollers out there would come right over her bow gate. Does that make her unseaworthy? No.... it just means that a boat is designed for a particular use, and seaworthiness needs to be evaluated based on the worst a boat can be expected to encounter in what it's meant to do.

 

[Mikey]

I'd sooner have the reduced weight aloft, and put that weight in the keel to keep the roll gyradius where I want it to be....

I'd argue that keeping a "normal rig" would benefit sea worthiness more than a high tech low weight rig and put the weight saving in the keel, because of the increase in roll gyradius. But it wouldn't benefit speed of course.

Mikey

 

[Guillermo]

...If I lose a mast and start taking on water mid-Pacific, the Coast Guard's not going to be there right away...

It depends on your family name. May naming oneself Bullimore be of help...?

 

[Guillermo]

Although not strictly related to this thread, this may be of interest to some of you:
http://www.nap.edu/openbook/0309065372/html/385.html
http://www.worldwideflood.com/ark/anti_broaching/wave_yaw.htm

 

[Guillermo]

Previous capsizings in the Open 60 Class, excerpted from an Steve Rizzo's info at BBC Sport's pages:

- Skipper Raphael Dinelli's yacht capsized, would not right itself, and sunk.
- Thierry Dubois' yacht capsized and would not right itself.
- Bullimore was lucky to survive when his Open 60 lost its keel
- Those three were rescued. Canadian skipper Gerry Roufs was not so fortunate. His yacht was found upside several months after he disappeared at sea.
- Isabelle Autissier's yacht, PRB, capsized in the Southern Ocean and would not right itself.
- She was rescued by fellow competitor Giovanni Soldini, whose own yacht, Fila, had rolled over a year earlier while crossing the Atlantic, washing one man overboard who was not recovered.

 

[Mikey]

Let's discuss here what we understand by 'seaworthiness', as it seems everyone has his/her personal point of view about this

The definition of sea worthiness includes the ability to take a B2 knock down and righten itself, with the rig reasonably intact.

Now the interesting question of what safety margin you reasonably would have to add to ISO 12215-9 to achieve that, any suggestions?

Mikey

 

[Alik]

But ISO12215-9 already assumes safety margin, doesn't it?

 

[Mikey]

So does the STIX numbers and we still consider them inadequate
http://www.boatdesign.net/forums/showthread.php?t=13569

Mikey

 

[Alik]

I would say they are not inadequate, but 'liberal'. Once regulations are too tight boats become not competitive.

Also, regaring to structural standards like ISO12215-5 I can say that they work only with proper production quality control. Specially in Thailand - You know

 

[longliner45]

competetive? didnt we learn from the volvo race?

 

[Alik]

Saying 'competitive' I do not mean extreme racing boats, I mean commercially successfull production boats. Overstrength means extra weight and cost. Finally customer pays his extra for safety margins introduced in rules, so they should be reasonable.