[C38] performance

[Les]

On Sat, 2007-10-27 at 16:24 -0700, Kenneth M. Sutto wrote:
>   I recently bought a '83 Catalina. I am in the process of getting to
> know the boat and how it handles. It has the standard Universal 21hp
> engine and two blade prop. My big problem is every time I try to back
> out of my slip the stern wants to got to the port no matter which
> way I turn the wheel.  I have a tight slip length and width wise.
> Is there some way I can get more control performance wise other than
> getting a bigger engine? Would a three blade prop help? What is the
> best way to turn the wheel once I get water flowing past the rutter?
> Ken  Catalina #251

Hi, Ken,
	That is called prop walk.  It is endemic to all single screw vessels.
Fortunately we have very large rudders.  Either hand the boat out to get
about a 1/2 knot and use the rudder, or do as I do and burst the engine
speed, then slip it into neutral, burst and neutral until you get the
speed you need.  Nancy and I are in our 60's so strong handing it is not
a good option for us.  Otherwise, if possible choose your dock to get a
good path to port astern and go for it ;-)  

	Other techniques utilize dock lines as springs to control the boat's
motion, but you will occasionally (in my case every time) scrape the
boat a bit when levering against the spring when the fender pops out
(mine always do).  There are some books and notes on line about
dockmanship (as opposed to seamanship) which describe some of the neat
tricks used by sailors to overcome the sort of issues as propwalk, or
give techniques to use the problem to advantage.  For instance, to turn
your boat in its own length, (practice this in a good open space with no
other boats or "hard stuff" in the vicinity) from slow ahead, stop the
boat using reverse.  If you keep reversing all the time until you stop,
the boat will begin to fishtail to port from the propwalk.  So, to get a
straight line stop, reverse until the speed drops way down, then put the
transmission in neutral and swing the wheel back and foth (to get a
gentle fishtail motion of the boat) this will cause eddying around the
rudder and kill the remaining speed.  When the boat is stopped, put it
into reverse, and the boat will prop walk to port.  Just as the boat
begins to go back, put the engine in neutral, then spin the wheel to
starboard.  Put the engine in forward and rev it a bit.  The boat will
quit moving back and continue to spin on its keel.  Again to neutral,
spin the wheel to port, put the engine in reverse and burst it again and
the spin will continue some more (don't get too much spin going, it can
be hard to stop).  and repeat until you have spun the boat 360 degrees
without moving.  This is a nice to know trick when you get to that new
dock that has someone's dinghy stuffed in it or another boat in it.
Practice this as it will give you a good method to use.  

	Next from a stopped position, practice putting the engine in reverse,
reving it up then down and then neutral.  as the boat begins to move use
the rudder to control the direction, and once you get about 1/2 know,
put the engine in reverse and give it just enough to gently keep moving,
and you will see that you now have control and the prop walk is
minimal.  

	When you are doing these things visualize where the boat is pivoting.
It will be about 1/3 back on the keel.  This will be about 1/3 the
length of a sail boat from its bow  The reason for this deals with how
the boat has to balance its sail power against the lateral resistance of
the keel.  

	On a power boat with little or no real keel stub, it will be about 25%
back from the bow.  

	Practice backing down (stopping the boat) so you can do it with no
major propwalk effects.  

	Once you have the pivot, the backing up and the backing down in hand,
you can begin to think about windage.  Our 38's have high bows, which
means a beam wind will push us off course to leward.  In 20 knots of
wind, this can aggravate or completely cancel the propwalk, depending on
the direction of the wind.  Current catches our keel, and pushes it down
current, so by clever use of the balance of propwalk, windage, and
current, you gain more mastery over your vessel.  It is both fun and
challenging to learn the techniques to manage these things when you can
choose when and where.  It is stressful, and occasionally dangerous to
learn them "on the fly".  Do take some time to learn how your boat (or
what ever boat you are helming) reacts to wind, current, prop and power.
It will really pay off.

Regards,
Les H