The roll acceleration: What´s the best for crossing oceans?

Antonio,

Many thanks for taking the effort of posting those very useful figures. -----

Wot!! No Gunboat 62? Easy to tack, minimum pitching due to gentle, uniform rocker along hulls and with dagger boards raised, she surfs sideways and avoids tripping in a beam sea. That sounds supremely comfortable to me.

http://www.deltayachtsbrokerage.com/news/YWorld_gb62.pdf

Guillermo,

Close attention was paid to reducing vertical acceleration in the design of Destriero with a view to reducing fatigue. Three hull forms were considered and the smoothest riding was chosen.

http://www.proboat-digital.com/proboat/20071011/

The longer hulled cruising catamarans are quicker under sail than monohulls and seem to slice through waves. This suggests they have lower vertical acceleration than the monos, which have to climb the waves. I am inclined to the view that that ride quality would be another factor in favour of catamarans, as discussed elsewhere on the forum.

http://boatdesign.net/forums/showthread.php?t=4499

It will be interesting to read the conclusions in the American papers you have.

Best wishes to you both.

Perry

 

from the library i find a whole lot of info in Marchaj; seawhorthiness, the forgotten factor

 

To Guillermo. Yes it´s right the number as far as i know

To Fanie. I don´t agree with you, the seasickness
is not a mental state neither a state of mind: I rather think it's the logical cause of a serial of disturbances on the brain and in the brain. Some people don´t feel anything with 2 meter waves and, anyhow anothers get quickly a seasick. I sail "solo" and sometimes feel it, but the natural way of getting is a mix of rough seas, bad course and bad mainsail and genoa trimming. In my experience the " solo" navigation it annuls the possibility of having a mental state different from the one to be in continuous alert. But, let's pay attention,i am customary to sail in hard conditions, a person who don´t sail habitually in about of 20 minutes would have an horrible sensation of seasickness. Therefore, we should do two kinds of sailors, those who usually sail and anothers. My comment in this post it has to do with them.

To Pericles. Forgive me, i had no time to put figures, only copy and paste, but the key and the feeling of this post you have caught it, friend

Best winds

 

Antonio,
Did you work out all those MCR numbers or did you get them from anywhere else?
Anyway I'm interested in knowing the source.

Cheers.

 

Here the effects of rolling and acceleration when pitching and heaving, on crew capability, taken from Marchaj's

 

The times I have been in bad waters and where I was probably supposed to become sea sick there wasn't time to think about getting seasick, it was do or die.

Best position for a seasick passenger(s) is aft and have them look that way. Seems to work too, the water look calmer and they leave you alone to get through the mess while they sit and feel sorry for themselves

 

I agree with Antonio
If we are talking more experienced sailors for a start then motion fatigue is not a state of mind but a function of exposure. Also the best position for anyone seasick is in a prone position in the most comfortable part of the vessel.

Here's an article on predictive methods from the Australian Naval Architect (May 1999).

I also have some studies from the Australian Navy somewhere the upshot for improved habitability was nothing revolutionary but worth re-stating:

Increase Mass (as the most effective form of damping)
Increase waterline length (reduces pitching)
Avoiding flat sections fore and aft
Keep GM low (within other constraints)
Keep accommodations, workspaces etc close to midships or aft thereof.

 

Excellent paper Mike, congratulations !!! I´ve just read and it's really impressive. Although it's very technical under my point of view for most of the people. Superb explanation of brain´s reaction due to acceleration.

Guillermo, these are not by myself. Look what nice url!!!

http://www.image-ination.com/sailcalc.html and enjoy it...

Best winds

 

Nice info, Mike your comment 'Avoiding flat sections fore and aft', could you explain pls ?

Ok, doc, so if somone does become seasick, besides moving the person to the best possible location, is there a medication for this or is it something you just have to live through, incurable but you develop some resistance to it... ?

 

A deeper V gives a smoother riding hull in a seaway and also considerably reduces pounding ( a rapid deceleration).
The experienced acceleration is a function of the following; Presented waveform, Rate of change of horizontal area, Mass moment of inertia and the relative damping coefficient.

 

uh..that would be me.

The human factors associated with seasickness have been studied ad nauseum (pardon the pun) and many factors are still not understood or cross-correlated. Things like horizon view...ventilation..cabin temp..proximity to other passengers (the incidence of MSI going up sharply when several pasengers become ill, causing others to be the same around them..thus it spreads quickly amongst otherwise less-affected passengers). The influence of combined vertical and lateral accelerations is also not well-understood..the detailed studies with subjects in motion simulators were restricted to motion in one axis or the other..
...and so on.

The vast majority of studies (and resultant 'comfort level' parameters) use gross motion parameters (RMS or single-amplitude) and do not consider the frequency distribution of the motions..limiting the utility of the results to application only over a very narrow 'band' of vessel type and size..that from which they were derived in the first place..

A case in point: The early prototype wavepiercing cats appeared to be superior to conventional cats of the time in ride quality terms. It was not until the first 'big' passenger ferry wavepiercer was built that it was discovered that the motion periods were almost 'spot on' the frequency where humans are most susceptible to quickly becoming seasick. At the small scale of the prototypes, the frequency of the motions was well above that critical zone. Oops..

 

Thanks Antonio.
I already knew Carl's calculator, but hadn't visited in a long time. He has improved it a lot! Very nice source of information.

Cheers.

 

You're wellcome Guillermo. I plan to travel a few days this Christmas, till then...

Happy Christmas to all

I´ll back

 

Seasickness

From what I read on the subject, prevention is more effective than a cure. Therefore, remedies must be taken before setting sail. Medication can be obtained from pharmacies which help most people by sedating the balancing organs. http://www.seasickness.co.uk/

I haven't had it often and I don't set sail without dosing up correctly, because I want never to feel so bad again.

Here is a line from http://en.wikipedia.org/wiki/Sea-sickness

"drinking any substance that is likely to temporarily diminish their senses of sight and touch" Any ideas what that might mean? Alcohol? In which case, 2 lines down, ginger is mentioned and I like Stones or Crabbies Ginger Wine. Could this be the miracle cure?

http://captainwiki.com/index.php?title=Seasickness looks at other suggestions.

Pericles

 

The wife has a 'Home remedy book' she's been putting together for years. Ginger is well known to turn tummies the right way up, seems the ginger cookies are in, ginger wine is out.