Saturday, May 31, 2014

RO Water--What Are We Missing

 (This is a work in progress. I'll be back)

There's been a lot of talk on the web about distilled water and RO water being bad for you, leaching minerals from the body, cause heart disease and all that. Although we filter out most of what we read in the tabloid press and web, perhaps there is a kernel of truth, hear and there, accidentally, it seems. As I begin researching drinking water filtration for a serice of up-coming articles, I find there is substance to to concern over the lack of substance in pure water. While I'm not a health researcher, there is enough scholarly work out there by respected organizations to take seriously. I like reading things from the World Health Organization (WHO).

WHO Symposium on Low-mineral water.
WHO paper.

Please read these at length. Google strings with "drinking water," magnesium," and "calcium." Try to read between the fluff and ignore all sites that are selling something.

There are many concerns; the three that seem best supported by science are:
  • Heart Disease. A shortage of magnesium is well correlated with certain forms. Also stroke.
  • Kidney Stones. It seems that dietary supplements increase risk, while calcium in the water decreases the risk. Different absorption mechanism.
  • Heavy Metal Absorption. If there is enough calcium in the system it out-competes many toxic materials. In fact, precipitation with lime is the basic industrial treatment for most heavy metals.
It seems all of that traditional stuff about healthful mineral waters had substance. Funny how that happens. Funny how your parents get smarter over the years.

What does this mean to the sailor?
 

Even though single-stage RO water (typical sailboat water maker) is not ultra low in Ca or Mg, it is considerably lower than most surface waters and lower than the general guidance available to us. I'm not sure what this means at a practical level. If you swim enough swallow a few mouthfuls of seawater, that's actually a good thing (a few percent seawater will solve the problem). Bottled water helps. Supplements may, but a dash of seawater in the cooking is simpler!

For coastal sailors I think the message is clear; using dock water with some on-board treatment (I'm researching that) is a better bet than running a water maker.


Monday, May 26, 2014

Jacklines, Tethers, and Why Monohulls and Catamarans are Different

Often I post just to help order my thoughts. Some comments are posted and some come by e-mail and are not posted. They all help.

I've posted on tethers many times, always with caveat that my views were catamaran-specific. Now I have begun with actual drop testing, with an eye towards a published article, and solutions must be more universal. Or at least we need solutions for all boats and all uses.

A few of my notes. Scary if you can read them.


The crux is figuring out where sailors actually fall.

The bow, catamaran. On a cat the bow is wide and you should be on the windward jackline, even if it is long. If very rough and I need to lean out to add something to a clew, I've been known to clip both the leeward jackline with the short tether and something else with the windward line (the windward line will not allow me to lean out). If you do happen to go over, there is no bow wave trying to suck you under and drown you; the hulls are too fine for that. Upwind, waves can come over and wash you around, but a tight line to the weather jackline manages that, and falling on a tramp doesn't hurt. Getting thrown forward is the greater risk, as the boat stuffs a wave and slows suddenly; the cure is to terminate the jacklines some distance aft of the bow, just as they terminate forward of the transom. A clipping point in the center of the tramp is often handy, as many cats lack a forward lifeline, and on many boats the lacings are strong enough and serve very well. Lacking that, adding several strong sewn points 3-5 feet aft of the forestay can be logical and simple. Because the tethers are long, stretch is needed to reduce impacts, but only when clipped to a hard point; jacklines provide cushion. Falling off the weather side is managed by running the jacklines well inboard--we've got wide decks.

Getting lifted off the deck is also a problem. Catamarans commonly experience negative Gs up front, and the best answer is to have a jackline you can pull up against, keeping the feet on the deck. Again, the jackline should be well inboard, since the lift can throw you to windward or leeward. Again, a hard point on the tramp near the forestay is handy; when kneeling near the forestay it is common to float upwards.  For the longer tether leg, shock absorption is nice; I've been thrown 12 feet before, airborne from the cabin roof, landing on the tramp. Between the give of the tramp, tether, and jacklines, not a bruise.

Catamaran, aft. The risk here is simply falling off the back, and stumbling cause by a cat's quick motion. Since the tether is clipped to a hard point, there is no shock absorption, and the tethers are long. Getting swept by away by a wave is a minor risk on most cats; forward, yes, but not in the cockpit, not ever. The boats move over and away from waves. However, tethers are needed when working outside and aft.

Monohull, bow. The scary fall is to leeward, under the bow wave. Folks have drown there. And thus, a quick release is required, something of much less interest to a cat sailor. The answer there is a short working tether to a fixed point to weather, and a secure grip. It gets skinny up there, something cat sailors don't face.

Monohull, aft. All documented tether failures have been in the cockpit. The helmsman was stuck by a wave, thrown the width of the cockpit, and lacking any shock absorption (clipped to hard point by a static tether), overloaded the system. Broken ribs and other injuries due to tether impact forces were involved. There are 2 answers to this problem: clip short and use a dynamic tether.

Climber's bolt hangers provide solid, simple, inexpensive hard points.
Short, working tethers are important, particularly for boats racing in extreme conditions. Very few falls are documented while people are moving; they are holding on. It is when they get to the work station, take their hands off the rails and focus on the task, that they get thrown. Thus, there should be a good anchor for every station, located such that the sailor cannot get thrown. On boats prone to stuffing the bow--some cats and some sport boats--a tether from behind may be prudent.The new AC cup boats have a tether requirement, specifically directed at stuffing a bow when bearing off. Keeping sailors on-station can prevent a capsize, since they can still do their job. The personal tether must have a short leg, or a fixed tether can be provided at each station.

Dynamic tethers are another part of the answer. ISO standards now required a drop test that should create nearly unbreakable tethers, but they may break the sailor in the process (unlike climbing drop tests, they did not specify a maximum impact force). I'm still using 8mm dynamic rope tethers, which are considerable lower in impact and tougher (can absorb more impact) than ISO  tethers, but they have one drawback; the rope can roll under foot. I would love to find a webbing with required stretch properties, but I'm not certain it exists; the weave may prevent that.

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There are other issues.
  • The best quick release.
  • The quick releases must be accessible when the PFD is inflated (most are not).
  • Harness design. The ergonomics are terrible, but there is no practical test method, and short of a full body harness, no good way to transfer the load to a body without damage.
  • Where you you park the spare tether leg clip when not in use? Don't clip it to your harness, or you will have no release. But most tethers provide no alternative. My advice is to add something.
  • Folks don't like tethers, particularly if there is crew on board.  But is the crew skilled enough to get the chute down and get back to you? Hmmm.

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So what are your MOB concerns? Where can you take a hard fall on your boat? What have you witnessed or read of? We need data to design solutions. 

Monday, May 19, 2014

Speed Polar, PDQ 32/34

Several years ago, after I adapted to sailing my new-to-me PDQ 32 fairly well, I set about developing a speed polar diagram, to help me better understand how she could be sailed to best advantage. I'm a cruiser, not a race, but I like to get where I'm headed. As an engineer, I can't relax on a boat that is not well-trimmed. No, I'm not a trim and grind racer--I'll set things and let the autopilot keep her steady. But I like things set properly.

A speed polar will never be right and never be finished. Most properly, there would be a family of graphs, one for every combination of load, sea state, and bottom condition. This is just sort of average for me, with a little growth on the bottom, a tender on the davits, family, a mix of new and old sails, and fullish tanks. If you're a little slower, perhaps there is a sail adjustment that will perk things up. If you're a little faster, good! If you here of a speed several knots faster than what is here... I doubt it.

And if all of this is confusion and frustration, turn the page and don't bloody worry about it. There are days when I can't hit these numbers--perhaps a foul tide or sloppy wave conditions--and it just ain't worth stressing over.

Speed and course over ground vs. true wind speed. Where the curve ends the heeling force is too great for my comfort; sails will stretch, sheets must be out of the self-tailers, and someone experienced stationed on the winch.



Apparent wind speed at true wind direction vs course. This is the partner to the above graph. I generally reef when the apparent wind is over 21 knots up-wind, and 10-15 knots off the wind, depending on the sails and waves. I'll reef earlier if I simply don't feel like working so hard, am single handed, or if the weather seems changeable.



What is the Portsmouth Yardstick rating? While the US Sailing figure is based on limited information, it is rated at 72.5, which is about the same as the Stiletto and common beach cats. How could it be so close? The rating does not count reaching speeds, only windward/leeward, and the PDQ is pretty solid going to weather. How much have I shaved? I suspect the revised Yardstick is now  under 70, based upon side-by-side trials and the polar. Who'd of thunk?

And for those of you with PDQ 36s, I pulled this from a 1991 Multihulls test. I can't vouch for the circumstances, but I'm pretty sure she was factory prepped, fresh paint, empty tanks and no junk in the lockers, no dingy and hard top. Cheating, in other words. A little more weatherly (the jib is in closer), a little faster in heavy winds, and probably just about identical everywhere else when carrying a load.I also clipped the PDQ 32/34 curves where I think cruisers will reef. They did not. For the non-racer, pressing canvass that hard is just asking for stretch.


For comparison, the speed polar of a typical 41-foot cruising monohull (NTP 41). A different shape curve, weatherly in lighter winds, but slow in comparison in a breeze. An 8-9 knot speed limit; that just when it starts getting pleasant!

And just for those of you that care about measurements and PHRF ratings:

I - 40.33
J - 12.75
P - 35
E - 13.75

"P" is the luff length of the mainsail, measured along the aft face of the mast from the top of the boom to the highest point that the mainsail can be hoisted or black band.
"E" is the foot length of the mainsail, measured along the boom from the aft face of the mast to the outermost point on the boom to which the main can be pulled or to the black band.
"I" is measured along the front of mast from the genoa halyard to the main deck. The main deck is where the deck would be if there were no deckhouse.
"J" is the base of the foretriangle measured along the deck from the headstay pin to the front of the mast.
"JSP" is the length of the spinnaker pole or the distance from the forward end of the bowsprit (fully extended) to the front face of the mast.
"ISP" is measured from the highest spinnaker halyard to the deck.
"PY" and "EY" are, respectively the luff length and foot length of the mizzen of a yawl or ketch measured in the same way as for the mainsail.
"IY" is the measurement from the staysail halyard to the deck.
"JY" is the measurement from the staysail stay to the front face of the mast.
"LP" is the shortest distance between the clew and the luff of the genoa.