From: jfh@cs.brown.edu (John F. Hughes)
Subject: Re: Tricky docking
Organization: Brown University Department of Computer Science
Date: Wed, 7 Oct 1992 21:14:28 GMT

In article <1992Oct7.194635.15889@mprgate.mpr.ca> kell@mprgate.mpr.ca (Dave Kell) writes:

>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 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       AAA
>       DDDDDD
>       DDDDDD
>       DDDDDD       .
>       DDDDDD BBB     .
>       DDDDDD BBB      .              /|\
>       DDDDDD BBB      .               |  Wind
>

(Picture above abbreviated)

>The problem was to dock in the open spot on the dock, which was only
>a bit longer than Covivant (maybe 6 feet extra).  

A tricky situation. Let me suggest a different approach to the whole thing:
get yourself in the location marked "AAA" in the diagram, and toss two
lines ashore to people who can make them fast to cleats on the dock. Don't
make them fast aboard until you see them attached to cleats on the dock,
lest someone on the dock decide to "help" by pulling hard or something...
   Now holding yourself in position AAA with your engine (and having the
jib ready to roll out at a moment's notice!), and steering slightly to
stbd, begin warping yourself in towards the pier. Dangers: (1) the engine 
dies, and you need to let go fast---this is why you should warp in by hand
against lines fixed to the dock, so that those aboard can let go when they
need to. (2) The wind increases, and overpowers the current's effect => you
let go and try a different strategy. Others?

   You could also, perhaps, set out fenders and secure yourself to the
upcurrent boat, and then warp yourself back into the slot.

>[Decided, rightly to approach from down-current]
>[stern pulls to port in reverse.]
>
>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.  [...]

>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.
>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?

This is really the tough question: what do you do to get out of the hole
you're in? I think that the secret may be your engine's peculiarity: I
would consider slamming into reverse *hard*, using the port pull of the
stern to swing your bow a little out into the current, and then shift back
to forward with almost straight rudder, until the stern is next to the
slot; turn hard to stbd; your stern swings in, bow swings out, and you go
off to rethink things...

Of course, all this depends on how close you are to that boat, etc. 

You might also (if you have a *very* cool head) roll out your
roller-furling jib partway, which will tend to pull your bow out into the 
stream, while reversing to keep from ramming the boat ahead of you. Can't
say I *like* this plan, but it *might* work... It'd be far better if the
wind were coming a little offshore, though.

Nice problem. As you point out, the solution may be to apply Clint
Eastwood's philosophy: "A man's gotta know his limits..." (which is a good
rule in Calculus class, too). 

-John