From: gerard@progress.COM (Gerard Bras)
Subject: Re: Tricky docking
Organization: Progress Software Corp.
Date: Wed, 7 Oct 1992 21:55:35 GMT

kell@mprgate.mpr.ca (Dave Kell) writes:

...lead in deleted

>I was attempting to dock on a club float which is usually affected by 
>tidal currents.  The current is in line with the dock, and this time the
>wind was against the current, at about 15 kts.  The current runs from
>0 to about 1 knot here, always the same direction.

>Here goes the ASCII art:


>       DDDDDD  B
>       DDDDDD BBB       |
>       DDDDDD BBB       |  Current
>       DDDDDD BBB       |
>       DDDDDD BBB       V              The DDD is the dock
>       DDDDDD BBB                      The groups of BBB are other boats
>       DDDDDD                          The ... are my route in to the dock
>       DDDDDD
>       DDDDDD
>       DDDDDD
>       DDDDDD
>       DDDDDD
>       DDDDDD       .
>       DDDDDD BBB    .
>       DDDDDD BBB    .
>       DDDDDD BBB     .
>       DDDDDD BBB     .
>       DDDDDD BBB      .              /|\
>       DDDDDD BBB      .               |  Wind
>       DDDDDD  B        .              |
>       DDDDDD           .              |


This is a tricky situation and ut really depends on what you boat
will do in the exact circumstances.  No two situations are exactly 
alike.

There are a couple of ways you might approach this.  None are guaranteed.
In your position I'd of just picked up a mooring unless I was really sure
of all the factors and ahd a good crew plus maybe help on the dock.

Tricky maneuver #1

	Pull up next to the up-current boat and back in.  If you
pull to port enuf in reverse it should go.  It would be advisable to 
verify first whether the bow would get pushed to port by the wind or
to starboard by the current.  Once the stern is almost touching the
boat behind you ( the upwind one) put it forward and give it a hard
sqirt to port.  Don't gun it enuf to gather headway.  Make sure somebody
is ready with lines.  Once in the space you should be able to hold
position pretty well, with maybe the stern bearing on the dock a little.
A fender could take care of that.  The advantage you have with this 
approach is that you alway can get out moving forward so your risks are 
lower.

Tricky maneuver #2

	Bring the boat across the wind/current.  See what it does.
What you want to find out is which way it will drift.  Then put the
bow in the "up-drift" end of the space and fasten a line to the dock.
Nature should do the rest.  If things are neutral you can  bring
the bow to the straboard end of the space, fasten it and put the mill
in reverse.  If you have substantial port pull it should walk you right
in.


Traditional maneuver #1 (aka the graceful way)

Add up all the forces actin on the boat.  Calculate how long it will take
to move the boat the required distance sideways.  Calculate how far
the boat will move forward, relative to the dock, at the proposed speed 
through the water, during this interval.  This is distance, more or less, 
that you need to be from the further boat (off your bow) when you make your turn.

The problem is that this is not an exact process.  It just not possible
to be mathematical about this in the allotted time.  This is where 
experience and "feel" come in.  It is also not cut and dried.  You
have to be ready to jigger the helm and throttle all the while.

>The problem was to dock in the open spot on the dock, which was only
>a bit longer than Covivant (maybe 6 feet extra).  People on the dock
>assured us there was room for our boat.

>Before making our approach, we put the engine in neutral to see whether
>the wind or the current had more control of us.  To my surprise, we
>drifted with the current, into the wind.  I concluded from this that
>we'd be better off approaching from down-current, since it's really
>hard to stop the boat against the dock with a tail current.  Also, our
>stern pulls to port in reverse.

>I made the approach quite slowly, running nearly parallel to the dock,
>but with over a knot of boat speed through the water.  I checked a few
>times on approach, and was convinced that the wind was parallel to
>the dock.

See what's happening here is that although you are moving smartly 
through the water, you are only barely moving with respect to to the dock.
So your turns are going to look very exagerated compared to your
motion over the ground.  Now the sideways component of you motion,
that was moving at normal speed.  Think vectors.

>Nonetheless, once I had the bow in the hole between the boats, it became
>apparent that the boat was moving towards the dock faster than the stern
>was passing the windward boat.  I couldn't turn out to abort the approach
>because the stern would swing into the windward boat.  If I turned to port,
>perhaps the people on the dock could have walked the bow up-current, but
>I think the stern would have swung into the windward boat also, plus the 
>possibility of hitting the dock hard.

>In the end, our lifelines in the cockpit got caught on the windward boat's
>trolling gear (no he wasn't fishing), the people on the dock took our bow,
>and we pushed clear of the other boat.  After having done it, our conclusion
>was that we shouldn't have attempted the approach at all, but anchored out.

Nah, just practice.  Someday you'll do this and really impress the crowds.
Practice when nobody else is at the dock though.  A rainy weekday perhaps.

>However, my question is, was there something I could have done to minimize
>the error, once I found out I was drifting in too fast?

Once you were in that predicament it was probably hopeless.  The only thing
that might have helped is more speed.  To quote the professor:

	"More rockets, Flash!"

Whether you had enough time to apply more speed depends on good your
acceleration is.

>Two points of note: 

>a. Two weeks before, under pretty similar conditions, I watched someone 
>   else do exactly the same thing on this dock, and he got caught in the
>   anchor of the upwind boat.

Yeah, but that wasn't very instructive, except maybe for the other guy.

>b. After thinking about it, I realized that slowing down the boat speed
>   changed the amount of effect the current had on the boat.  If I had
>   approached at a constant speed, I wouldn't have been caught.

More than this, it had a disproportionate effect on your speed with repsect
to the stationary dock.  Assume one knot though the water against a one
knot current.  Adds up to zero.  You'll never get anywhere at that rate.

Cheer up though.  This stuff is not obvious until you've been publicly
humiliated by a few failed attempts.  Current is much trickier than
wind when it comes to close quarter maneuvering.

cheers,
gerard