Minimum size for ride comfort?

Discussion in 'Boat Design' started by SamM1234, Nov 26, 2007.

  1. masalai
    Joined: Oct 2007
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    Location: cruising, Australia

    masalai masalai

    Long, Long ago, in the days before steam, a cruising sailor suggested

    Your boat should be as small as will meet your needs, yet as big as your maintenance budget will allow.
     
  2. Fanie
    Joined: Oct 2007
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    Location: Colonial "Sick Africa"

    Fanie Fanie

    O-hor, you must choose the chicks better so they won't get sea-sick on the one you have :rolleyes:

    Why hasn't someone come up with a sea simulator you can practice in so you won't get seasick after a while ?

    Did you take your sea sickness pills ?
    No, I was on the simulator this time... :D
     
  3. SamM1234
    Joined: Nov 2007
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    SamM1234 Junior Member

    Yes, I'd be interested in hearing more cons of catamarans as far as the ride is concerned. Efficiency wise, I know they are about the same as mono hulls at slow speeds. The builder is suggesting a cat saying it is better at anchor and more comfortable. But, I could obviously save some money if I go with a mono hull (or build a bigger one). I've also never been on a wave piercing cat. Does that really help anything or is just a fad?

    No way, I'm not cruising solo any more. I need to get a girlfriend!
     
  4. masalai
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    masalai masalai

    Sam, I was not suggesting to cruise solo, but in cruising, attract a sea-kindly partner.

    Might I suggest several bare-boat charters of different cats to get the feel. That is the best way to sort out any differences in form & function.

    I may be biased (I am but), from my observations, American designs seem to have a narrower beam overall (to fit in marina berths?) than cruising forms in Europe, South Africa and Australian regions.

    Your ocean playground looks as though it will be the Pacific. Compare the seas in your area, I guess at a long swell as opposed to the short chop (comparatively) in the Caribbean? - showing my lack of local knowledge - having never sailed that side.

    If that is the case, look at NZ and designs built/popular in Qld Gold Coast, NSW in Australia, or South Africa. Not to discount others, but to narrow the initial range/choices arbitrarily.
     
  5. longliner45
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    longliner45 Senior Member

    the old addage comes to mind,,,you cant please all the people all the time ,,if they get sea sick ,,its not your fault,,,you can try to accomodate them all ,but that is futile, they must help themselfs,,if they cant do that ,,after you have gone through some lengths and exspence,,,,,,get new friends ,its cheaper and easier,,espesially if you have a boat,,,longliner
     
  6. masalai
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    masalai masalai

    Yo longliner, Great minds think alike. My play area as power-linesman was 33k & 11K volts of private powerlines from Dampier thru Tom Price to Parabudoo iron ore mines. It powered after transformers, the switch gear & railway controls. Good fun when major work was at hand otherwise dead boooooring.
     
  7. ted655
    Joined: May 2003
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    ted655 Senior Member

    Seats should be...... 17" high, 34" wide & 14" deep. That was THE question, right?
     
  8. rwatson
    Joined: Aug 2007
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    rwatson Senior Member

    Ted655

    You missed the real minimum dimension - lay back seats - people dont get sea sick when they are asleep, and closing ones eyes cures sea sickness.

    Just dont pack the layback seats close together - the snoring keeps everyone awake!!
     
  9. Fanie
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    Location: Colonial "Sick Africa"

    Fanie Fanie

    I have a better idea. You dump the scuba gear when no one looks. Then get a piece of cedar (I've heard the Kiri may even be better :rolleyes:) and use it as the plank. Then get a friend who likes to go diving walk the plank and disappear after falling off, reason is he got sea sick last time, sorry standard practice of getting rid of sea sickness in these parts. No one will sleep and no one dares to get sea sick ;) No snoring either.

    Eh, there's a shark ! Who's sea sick ? Come on people we need entertainment around here.
     
  10. SamM1234
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    SamM1234 Junior Member

    This will work, but you can't seal the deal if she's ill, if you know what I mean!

    I think we need to come up with some objective standard for ride comfort measuring. In my previous life, I was a pilot. In aviation, they have a way to report in flight turbulence, which is different from how the sea states are recorded. Sea states are classified based on something that can easily be measured such as wave height. In the air, no one can see the air flows, so they apply the "coffee cup" scale. E.g. a mild turbulence is the one that creates some ripples on the coffee, but none is spilled, moderate is when some amount is spilled, and so forth. Severe is when the cup is thrown violently around the cockpit. Now, it is a well known fact that the turbulence experienced inside an aircraft is inversely proportional of its size (and the wing load ratio). What a Cessna reporting as heavy might feel only as mild in a 747.

    Maybe, we can apply something similar to boats. I know in my boat in 3' swell, objects will shift and often fall of the shelves, if I do not secure them (I haven't attempted the coffee cup). Obviously, as the boat gets bigger relatively to the waves, there should be less motion inside. But the question remains, given the constant wave height (say up to 6'), is the motion inside a linear function of the size? Or, does it drop fairly quickly at small sizes and then the slope becomes shallower as it approaches 0 at big sizes? I think it has to be the latter, as the motion cannot be less than 0. Sorry if I sound technical, but what I mean is if the motion feels mild in a 100 footer, it will still be mild in a 200 footer, so there’s no need to spend the money on a 200 footer, if a 100 footer will do (for sickness purposes). So, I'm looking for that critical boat size, beyond which the "slope is shallow," and the motion is only felt as mild. Any thoughts, anyone?
     
  11. PAR
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    PAR Yacht Designer/Builder

    MCR = Disp / (2/3*((7/10 * LWL)+(1/3 *LOA))*Beam4/3 )

    Above is a commonly employed formula, which has marginal results. Below is taken from Ted Brewer's web site describing this "Motion Comfort Ratio" formula.

    "This is a ratio that I dreamed up, tongue-in-cheek, as a measure of motion comfort but it has been widely accepted and, indeed, does provide a reasonable comparison between yachts of similar type. It is based on the fact that the faster the motion the more upsetting it is to the average person. Given a wave of X height, the speed of the upward motion depends on the displacement of the yacht and the amount of waterline area that is acted upon. Greater displacement, or lesser WL area, gives a slower motion and more comfort for any given sea state.

    Beam does enter into it as wider beam increases stability, increases WL area, and generates a faster reaction. The formula takes into account the displacement, the WL area, and adds a beam factor. The intention is to provide a means to compare the motion comfort of vessels of similar type and size, not to compare that of a Lightning class sloop with that of a husky 50 foot ketch.

    The CR is : Displacement in pounds/ (.65 x (.7 LWL + .3 LOA) x B1.333). Ratios will vary from 5.0 for a light daysailer to the high 60s for a super heavy vessel, such as a Colin Archer ketch. Moderate and successful ocean cruisers, such as the Valiant 40 and Whitby 42, will fall into the low-middle 30s range.

    Do consider, though, that a sailing yacht heeled by a good breeze will have a much steadier motion than one bobbing up and down in light airs on left over swells from yesterday's blow; also that the typical summertime coastal cruiser will rarely encounter the wind and seas that an ocean going yacht will meet. Nor will one human stomach keep down what another stomach will handle with relish, or with mustard and pickles for that matter! It is all relative."​

    http://www.tedbrewer.com/yachtdesign.html

    Like many of the formulas used in yacht design, it isn't perfect by any means, but can serve as a base for comparative study, across several yachts.
     
  12. SamM1234
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    SamM1234 Junior Member

    This does seem like a good estimate based on a boat reaction to a single wave. It should work well for comparing boats of similar size. But, I think as the boat size goes up relatively to the length of the waves, it no longer fits entirely in a trough and sits on multiple crests. So, multiple waves are acting on the hull at the same time; some are causing it to raise, some to descent. In this situation, many wave forces cancel each other out. If the boat size is really large relatively to the waves, they would not be felt at all. So, the larger length should actually increase comfort in this scenario.
     
  13. longliner45
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    longliner45 Senior Member

    I also dont think it matters that of the size of the boat; people get sick on super yachts and dingys ,,I recomend ginger root ,,gingerale and dramamean patches ,,and a view of the horizon is good too,,some times people who are alreaddy a little bit sick on land ,,like a cold or light flu,,have the symptoms amplaphide on a boat because your body never really gets to relax.you are constantly holding or pushing or gripping,,even when you sleep ,I have always felt sorry for people who get sea sick,,longliner
     
  14. Frosty

    Frosty Previous Member

    Admiral Lord Nelson was sea sick for the first 3 days of a voyage.

    Every body can get sea sick or at least nausea. Fear of sea sickness can make you sick.

    There is no reason to be sick ,--it is all in the head.

    However it can cause loss of conciousness in a serious case.

    Throwing a violently sick person over the side with a rope tied round them may seem cruel but it will revive them. It cuts out the third motion ---just you and the sea instead of you, the boat and the sea.

    It also cleans them up a bit.
     

  15. Willallison
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    Willallison Senior Member

    Aha - at last! Frosty, you have made a sensible suggestion;)

    The problem is - as others have already said - is that different things will make different people sick. Catamarans, as a result of their increased beam and subsequent initial stability, tend to have a short, fast, jerky motion. Vessels with less initial stability and a slower roll period have a correspondingly slower more gentle motion. Some will tend to be upset by the 1st set of circumstances, others the latter. Then there are those who get motion sickness on an escalator.

    The wave-piercers tend to be very good in a surface chop. The sort of slop that would make many other vessels uncomfortable. But the instant they are exposed to larger waves (like swell), then they are definitely one of the quickest means of recycling carrots...
     
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