Sunday, June 20, 2010

Hit or Miss: the Baseball Approach to Navigation

June 20, 2010
London, ON

Learning that the Budget Committee and I crossed the entirety of Lake Ontario spending all of our time below and only checking for conflicting traffic every 15 minutes many of our friends asked if this was safe.

Some went further.  There seems to be an inexhaustible supply of people who Know-It-All-But-Have-Never-Done-Any-Of-It.  One of these mounted his high horse and saw fit to lecture us on our irresponsible navigation practices.

Poppycock and bulltwiddle. 

There is no need to scan for conflicting traffic on Lake Ontario any more often than every 15 minutes.  There is nothing on the lake that I can hit in 15 minutes.

If an object on the lake is not visible on a scan there is no way my boat can hit whatever that thing is before the next 15 minute scan.  This includes other sailboats, rocks and even lake freighters.

Here is a chart that attempts to explain this:

                             Distance  Closing  15 Min    Margin
                             Seen      Speed   Distance 

Freighter   14.5 km    38     9.5 km    5.0 km
Powerboat    7.7 km    32     8.0 km    0.0 km
Sailboat    15.0 km    24     6.0 km    9.0 km
Rock         4.5 km    12     3.0 km    1.5 km

A scan every 15 minutes ensures we have lots of warning of all threats except for powerboats.  

eg.  We can see a lake freighter when it is about 14.5 km away.  If the lake freighter was just out of sight on the first scan, ie. just more than 14.5 km away we would not see it of course.  When we performed the second scan the lake freighter would have traveled 9.5 km and when we did the second scan that freighter would still be 5 km away.  

In working the chart we made some assumptions on the height of the object: lake freighters were 15 m high, sailboats the same, powerboats were 3 m and rocks 0.  Speeds are the worst possible case, ie. the sum of Meredith's speed plus the speed of the object coming head on toward us.  If the object were not on a head on collision course its speed would be less.

For all objects save a powerboat there is ample safety margin.  If a powerboat with a horizon of 7.7 km was just over the horizon when a scan was done and it then proceeded directly towards Meredith at a speed of 10 knots then Meredith and the powerboat would actually collide just before the second scan was done.  If the powerboat were travelling faster than 20 kph then the collision would occur sooner.

This risk was one we were prepared to accept in the circumstances.  For an accident to occur the following would have to happen:

1. a powerboat would have to be in midlake, travelling at speed, and on a head on collision course with Meredith and be just barely out of sight on the first scan.
2. the powerboat would have to proceed at speed directly towards Meredith's bow with no alteration of course at all, ie. it would have to maintain its head on collision course at full speed for the entire 15 minutes.
3. the skipper of the powerboat would have to completely ignore what was coming (like we were doing on Meredith)
4. No one on Meredith would hear the engines of the powerboat.

We accepted this risk. 

The Math:

How Far Away Can You See an Object?

formula: distance in kilometres at which a person on one object can see a second object: SQRT [12.7 x (height in metres of first object + height in metres of the second object)],

How Fast Do Objects Close?

Two objects moving towards each other are moving towards each other at their combined speed.  A sailboat travelling 12 kph moving towards a freighter going 26 kph will find the distance between vessels closing at  a rate of 38 kph.

The speed of the lake freighter, 12.8 knots or 26 kph is the max speed of English River, the only freighter we have ever encountered on Lake Ontario.,

Strung Out in Oswego, NY: a Passive Aggressive Approach to Sailing

English River - Regular Visitor to Oswego  
this is not just a nice picture as you will find further along in the article

June 20, 2010
Toronto, ON

A fast run up the Erie Canal saw us make the distance from Waterford to Oswego in 3 days.  Traveling loosely with Suncast we made nightfall stops at Amsterdam and Herkimer. 

Bill on Suncast introduced us to IronOut, a much more environmentally friendly product to remove the brown mustache which identifies any boat sailed through the rivers of any state south of New Jersey.  Heretofore we had used a lovely toilet bowl cleaner whose active ingredient was 15% hydrochloric acid.  The fact it was only available for purchase in North Carolina sort of hinted at the fact the product was something to be hidden from the authorities. 

With the mast on deck we performed an inspection and were glad we did:

You inspect the rig hoping to find problem areas which you can correct before they endanger your rig.

As with so much of sailing it is a bittersweet process and there is no joy in actually finding defect.

The spreader was both deformed at the mast fitting and a small tear had begun.  The jaws on one of the stemhead toggles, shown in juxtaposition, had been badly deformed.  The storm outside Cape May had been fiercer than we thought.  We were busy enough at its passing not to have had time to look at instruments.

There was nothing for it but to repair or replace.  So much easier and less expensive with the mast already down.  A new spreader was ordered from Charleston Spars and a new stemhead fitting was ordered from Just Rigging in Boston.  These purchases knelled the end of $700.

For a few months we had been discussing whether we should replace the standing rigging on Meredith: the wires that hold the mast erect and immobile.  Existing rigging did not display signs of damage - no rust, no meathooks (broken wires that catch your flesh and slice you open), no cracks or discoloration or swelling in any swages.  However the wiring was original equipment - now 25 years old.  At some point you have to the consider the possibility that equipment will fail.  Our decision was to replace the rigging.

Our ten day pass for the Erie Canal, purchased for $37.50 allowed us to tie up at no additional cost at a beautiful park in Oswego, NY while we measured, ordered and waited for product delivery.  Every one of the 7 days allowed us under the pass was used.

Doing the work ourselves saved us a lot of money and produced better quality wire and fittings.  It does not come without cost of course: you must educate yourself thoroughly, equip yourself with proper tools, spend longer at the job and bear the cost of parts you break because of inexperience.

 Then you must actually do the work.

By the end of the process we were totally exhausted.  The mast was stepped at Oswego Marina and Bernie did his usual expert and friendly job.  Bernie was very relieved when all the newly cut and installed rigging actually fit.  Apparently this was unusual although, except for the Budget Committee measuring and remeasuring each line about 12 times we never gave it a second thought.  It is nice having a process driven with a jeweller's precision.  Sometimes.

Rising early the morning after the stepping it remained for us to get the two booms installed, the sails bent on and the rigging tuned.  We could hardly move our muscles hurt so.

The forecast was for dead calm conditions and the lake was in fact dead calm.  That decided it.  We cast off lines, set course for Cobourg ON and went below.  For the entire day we stayed below too tired and sore to do much.  Every 15 minutes the timre would sound and in rotation one of us would turtle out the companionway to scan for traffic, freighters, fisherpersons and flotsam. 

Our sailing friends are horrified that we would cross Lake Ontario without someone on constant cockpit watch.  I will address this foolishness in my next post.