Saturday, February 27, 2010

The Art of Climbing down Gracefully - The Long, Dedicated Declined to Dignified Decrepitude

Notes: much of what follows, including the title, have been paraphrased or borrowed from an article by Tom Patey, previously published in Mountain Number 16, and republished in the book Games Climbers Play, edited by Ken Wilson. Tom Patey, a famous Scottish ice climber, was tenacious in his sport, consistently humorous in his writing, and penetrating in his understanding of climbers and what makes them tick. His article contains 16 'ploys' for not completing or even beginning to climb; I've only quoted the few that seem to fit best; However, his article is a riot and the book Game's Climbers Play is an excellent introduction to the climber's mind. Get a copy.

It's not hard to find obstacles to an adventurous path, to see defeat coming, and to invent clever and rational explanations for yourself and others as to why you should retreat. A few weeks ago I found myself certain I could make significant passages across oceans, to Bermuda and beyond; now faced with a parade of small stumbling blocks, I find myself 'climbing down', retreating to the convenience of coastal cruising that I know so well. Clearly, Tom Patey knew the heart of sailors as well.  

The Art of Climbing Down Gracefully is a catalog of traditional mountaineering ploys that experienced climbers rely upon when age, situation, infirmity, lack of practice, or loss of nerve prevents them from making the grade a the local crag. I will paraphrase a few:

3. The 'Chossy Climb' Ploy. "'Poxy', 'chossy', 'spastic' and 'rubbish' are all terms characteristically used by English and Welsh climbers to denigrate Scottish routes which they've either failed to climb or failed to find (without searching too minutely)." When sailing, I think this applies to shallow waters and small harbors that are dismissed as being of no interest to the cruising sailor.  Maybe they're tricky to find or challenging to negotiate. But just maybe the there is more food for the soul in these places that at dock-side eateries. Sounds like the Delmarva Coast challenge. No, I don't use this one much.

7. The 'Responsible Family Man' ploy. "Don't seem to get away much nowadays, they mutter prominently.  Can't take the same risks - unfair to the kids. This is very effective because of it contains an element of pathos, and brings a lump to the throat of the most hardened of the hardmen. Some aging climbers, no longer able to make the grade on the crags, have been known to contemplate matrimony is the only honorable way out."  Actually, my wife is extremely supportive. She never interfered with my rock and ice climbing habit either. 

12.  The 'Fohn Wind' and other Bad Weather Ploys. The standard British climbing mantra of the golden age was that it took more courage to retreat than to advance. Perhaps the best loved variation was to "give the mountain best." Hurricane season, to sailor, seems the most obvious, but it isn't because that one is real. Better examples are spring storms, and fall storms, and of course winter storms.  With the ploy in full swing, planning any passage becomes impossible.  

By comparison, I can easily use these ploys to stay in the Chesapeake Bay:

1. Insurance is a killer. I just don't cruise off-shore enough to dilute the cost. There are college expenses, 401(k), the boat payments, and the rights of my family.

2. My daughter is in school. Although there are some that take their children out of school, I disagree.  I'm sure there's very much to be learned about the nature of the world and the nature of people, by cruising the oceans and experiencing something other than the rat race.  But in my mind, there's far more for a teenager on land and there is at sea, and I don't just mean school. Let's be practical; we're land born creatures and not fish, and we live our lives in this community.

3. I would never ditch it all to go cruising. It wouldn't be my vision of paradise.  There are too many things to like on dry land: rock climbing, ice climbing, bicycling, snow skiing, ice skating, rollerblading, hiking, and traveling to meet all of the people on dry land. This isn't a criticism of those who choose to go or a rationalization of my own fear; I like dry land and doubt that I would ever wish to cruise for more than a season.

4. Health. Both a reason to go, and a reason to stay nearer to home. Well past 50, a vigorous life has accelerated the accumulation of aches.  I can't see a good reason to postpone cruising until it's more difficult.  And yet, as I go sailing now I find myself less tired than I did when I was 30.  I'm smarter about it and use my energy much less wastefully.  I hear cruisers complain of bruises and bumps; I sustain far much less wear and tear that I used to. There is also my wife to consider; she is a brittle diabetic and to go far offshore, beyond the reach of paramedics, wouldn't be responsible. I can't remember how many times we've had an ambulance come to the house after she has lost consciousness from low blood sugar.  It's not because of poor attention on her part - sometimes I've helped her monitor her medication, diet and activity as they apply to maintaining consistent blood sugar - because often the deviations positively defy simple explanation. Stress and variable sleeping schedules makes maintaining consistent blood sugar even more challenging.

Note: I don't climb rock as much as I used to either, but I don't use complicated ploys to avoid it. I explain that I'm old and lame. If my daughter is with me, she's quick to support the veracity of these claims. Ice on the other hand, still holds mysteries for me and my skills continue to improve. The damn thing is Virginia is short on ice.  Whoops, there I go, using the 'Fohn Wind' ploy.

Wednesday, February 3, 2010

How Strong is She, Really?

rev. 2-19-2010

From time to time every sailor wonders how strong a given part of their boat is. Magazines and books suggest that everything should be reinforced, because there are under-built boats out there to which bad things have happened. The PDQ 32 is among the more carefully built and conservative designs; little upgrading for strength is needed. What follows is a collection of rough calculations I have gone through; I will add to this post over time as I collect more. So far I have found that the PDQ engineers seem to have checked their details.

Note: I am a chemical engineer, not a structural engineer, so I have made only rough calculations and kept my assumptions to myself. There are always guesses regarding lay up details. But I have applied practical expereince gained on this and other more fragile boats - I have been sailing long enough to have broken and repaired many things - and I think I am reasonably close. It would have been nice to have some of this information in the manual, but then I would have nothing to puzzle through during the winter (20 inches of snow are predicted to fall tomorrow).

The davits are a simple design; two 1 1/2-inch stainless pipes cantilevered out through the transom and bolted to an inner bulkhead. I used a simple pipe cantilever beam formula from Mark's Handbook of Mechanical Engineering. Because they have a twist bent into the design and because pipe is subject to buckling failure and not simple fiber over-stress, the calculation is complex. However, assuming a 4:1 safety factor (conservative, to allow for buckling), ignoring the slight inward curvature, I came up with a safe working load (SWL) of 188 pounds. The heavy end of the tender, with motor and accessories, is about 80 pounds. If we allow for 50 pounds for water and a 140% dynamic load factor, we get a load of 182 pounds. Very close. If a sailor leans hard on the davit while entering a boat in the water, perhaps a 190-pound force is applied. I have leaned hard while digging out an incredibly heavy snow load and it felt very solid, though it certainly flexed. So, it seems PDQ engineers designed for all common use scenarios and used a conservative design factor.

What if we add a wind generator? The generator plus mounting pole add ~ 30 pounds. The downward thrust generated by the wind (as transferred through the braces) might be about 40 pounds, but this depends on the exact arraignment. Now we have a maximum load on the davit of 264 pounds. We are beyond the design limits; it will probably be fine, but it is going to flex significantly and possibly crack some day. Taking the outboard off would solve the dilemma, but I like the convenience of leaving it mounted. Choices. Adding solar panels present similar stresses - more weight but less wind load.

What if we add seats, such as those on the Gemini 105Mc? That would be about 480 pounds (people plus structure), plus a 140% dynamic load factor but supported a bit closer in, so it's equivalent to a 220-pound load addition to each end. Added to the dingy load, we get about 484 pounds, not counting falling into the seat or crowding one end, which could easily push the load right to the breaking point. Additional support is defiantly needed. Better, or at least simpler, would be to fabricate a replacement davit from 2-inch stainless tube. Strength goes up roughly with the cube of diameter, and so the SWL should be about 450 pounds. If you have a big family, perhaps 2 1/2-inch tubing is in order. Beefing up the glass in the area with a few more layers might be a good call, too, and going with a slightly larger flange.

The deck in the area of the cleats is 5/16" solid glass (I drilled a hole near the bow cleat while mounting a chain lock). They are mounted with two 3/8" bolts and large fender washers. If we assume a shear strength of 30,000 psi (conservative - 45,000 psi would be more typical of a vacuum bagged laminate), assume that a 2-inches length of laminate would need to fail to pull a cleat (generally a failed cleat pulls a large hole in the deck because of the fender washer on the nut), assume the stress is horizontal and athwartships, and that the leverage is applied 2 rope diameters from the deck, we get a failure strength of about 17,000 pounds. In fact, we may see crushing under the cleat before that, but I would be surprised if the strength was less than 10,000 pounds. There is no mooring or sea anchor load on a bridle that is going to come close. Typically a 1/2-inch line is recommended for each bridle leg, which has ~ 8,000 pound failure strength and a working load of about 1,800 pounds. For comparison, a single 5/16-inch rock climbing anchor bolt is known to hold 5,500 pounds in shear.

Winch Base
After I pulled a winch out while sailing hard on the wind in a sustained 20-knot breeze with a 130% genoa, I considered adding backing plates to all of them. After confirming that the failed winch was incorrectly owner installed in a cored deck section, I realized the factory winch installations in solid glass were fine.

The winch that pulled out had been mounted to a cored deck without the benefit of fender washers or any core replacement. The failure was shearing of the skin and crushing of the core around and under three 5/16-inch nuts. There was no water damage to the core, although there were some signs of minor leakage (perhaps the leakage all occurred during the 2 weeks we sailed with a floppy winch sealed with duct tape). The mounting failed at full load (just less than 1,000-pound line pull, based upon the gear ratio, handle length, and assumed level of one-hand effort). If we give no value to the core resistance, figure the laminate to be 1/32-inch thick (not counting gelcoat), and count 2 bolts, failure would have been expected at 2000 pounds of line pull, but given some unequal loading between bolts and fatigue, a failure at 1000 pounds after11 years of service seems very reasonable. With either an oversized solid glass backing plate, or if installed in solid glass (1/4-inch in this area), the pull-out strain will be similar to a deck cleat (more leverage, but more laminate area) or at least 10,000 pounds and 2,500 pounds SWL, which is more than enough to provide a long no-flex and no-crack service. Failure would likely be where the solid glass tapers to cored construction.

Note regarding bedding of winches. The existing bedding was silicone, it was not stiff, and probably had not failed. The winch pealed up very easily - actually, a 1000-pound line pull removed it, so I'm guessing. Still, I like butyl rubber better for mounting things that may move a bit under extreme load, I know I will remove some day, and are well secured with bolts. Examples are stanchions bases, cam-cleats, traveler and genoa tracks, windlasses, and fresh air vents.
  • Butyl bonds to the deck and never gaps. Even so, it is easily removed with mineral spirits.
  • Installation is neat. Simply trim the excess with a dullish knife a few minutes after you tighten the bolts. A bit more will squeeze out over the next hour, but I generally leave that as an extra gasket. It could be trimmed. No cleaning excess with big messy wads of paper towel, or pre-taping to limit the spread.
  • Butyl doesn't go bad in storage. Keep a roll on the boat.
  • No drying time.
  • Silicon is very difficult to re-seal. Even silicone won't stick to it.
Use the gray material, available from RV parts stores. The black material, more often used for windows, can stain porous gel coat and clothing. Do not use it below the waterline. Do not use near heater vents or where gasoiline or oil exposure are probable; it will turn into goo.

I use 3M 4200 or or even 3M 5200 for things that I won't be moving or that are mounted with screws and could use some extra bonding. But I warn you; 3M 5200 is about as easy to remove as epoxy and getting the hardware off can be ugly. They do sell a de-bonding product, which helps good deal. Trichlor works too.

Windlass Mounting
The deck several feet back from the bow is cored, and there was no evidence on my boat that core had been replaced with solid material. The line pull on the windlass and the winch are similar - 1,000 pounds. However, the windlass came with an integral flange which distributes the load over the full circumference. Additionally,  the horizontal pull on the windlass is much closer to the deck than it is on the winches. This combination of factors gives a much stronger mounting, with failure expected at nearly 10,000 pounds and with a SWL of 2,500 pounds. The winch will stall well before damage is done. What a difference a change in angle and a simple backing plate make, when compared to a sheet winch.

Attaching a Drogue
The Jordan Series Drogue advise is to attach the bridle to the transom with dedicated plates; sound general advise when the construction of a specific boat is not known, for mono-hulls where the cleat spacing is often too narrow to cause a sufficient turning moment (catamarans are wider - this is not a PDQ issue), and to provide for low chafe. Sound practice for serious storm application. Can you attach a drogue line to the winches? I would not. Although there is little chance that even a Jordon Series Drogue could pull them out of a PDQ deck, I wouldn't be surprised if the winch mechanism was damaged, and the strain would be too great to adjust the bridle under load. A tugboat hitch would take the stain of the palls, but the beam is still less.

Will the stern cleats do? Certainly. Attach the drogue to the stern cleats (a single round turn to insure load sharing), backed-up by the mid-ship cleats, allowing substantial extra line in the bridle so that it can be eased in case of chafe. By backing-up the bridle with the mid-ship cleats, the tension on the mid-ship cleat hitch will remain moderate and can be released under load; this is a common construction riggers procedure. It is also simple enough to slack one leg and transfer it to a winch for recovery.

Chafe protection should be provided through the use of anti-chafe gear where the rope moves against the deck under the stern railing. Watch out for sharp spots on the stanchion bases and deck bolts. Examine every connection point for sharp edges, loose thimbles (the above webbing can sometimes make a very serviceable thimble if threaded onto the rope before splicing and it is not prone to working loose), and movement when under load; although I haven't enjoyed a major storm off-shore, I have seen plenty of chafe failures in industrial applications. Just as it is easier to cat a line with a knife when it is under load, chafe accelerates under high load factors.