When viewed from astern a clockwise rotating propellor (right handed prop) not only moves the boat forwards and backwards - it also pushes the stern to starboard when moving forward and to port when in reverse. The effect is more marked at low speed where the rudder effect is proportionally much less. Furthermore the effect in reverse will be much more pronounced when the engine is reversed to stop forward movement as opposed to reversing from a stationary position. This is caused by the rudder losing effectiveness as the boat slows and, at the point where forward motion stops, the rudder will have no effect for a while - and not until significant rearward movement takes place.
In practice this means that for a right-handed prop the boat's turning circle will be smaller to starboard when going forward. In reverse the same craft will turn tighter with the stern going port.
For a boat with a left handed prop all these affects are reversed. If the prop can be seen the direction of rotation can easily be determined from the blade shape. Fortunately where the prop can't be seen there is a way to establish its rotation direction. With the boat on a mooring engage reverse and look at the water on both sides of the boat just aft of the prop. One side will have more water action than the other and it is away from that side that the stern will swing. So if most water action is on the starboard side when in reverse the swing will be to port - as for a right handed prop.
Techniques for leaving a jetty or coming alongside need to take into account not just wind and current but also propellor effects - particularly for the boat with an inboard engine and a single prop. In craft with outboard drives the propellor effects described will usually not be apparent - because of the direct side thrust available.
The effect of transverse propellor thrust is most evident on a vessel with a flat bottom and an inboard engine where rudder alone is the primary steering means. On a vessel powered with an outboard or on one with a deep keel this effect will usually not be noticeable..
There are four basics methods of handling a
sailing vessel in big seas when survival is the only concern. Each option
has its variations and no single option will be the best for all boats in
all conditions. The following considerations might be of use in making a decision
which would be best for a particular craft. The options are :
1. Running
under control - with / without storm sail, drogue(s) and positive steering,
2. Running
free,
3. Heaving
To, and
4. Heaving
To with Sea Anchor deployed.
Considerations - Running under Control
The greatest danger in a fully developed sea
is from a breaking wave strike in which the mass of water in the wave crest
is moving at wave speed - which can be 20K or more. The vessel itself can
become part of the wave top and be accelerated to wave speed and thrown into
the trough or rolled. Given that a skipper at sea can do little about the
inertia characteristics of the vessel there only remains the ability to present
the boat at the best angle to the waves and at the optimum speed for the conditions.
For most craft the best angle will be in the
order of 0-15 degrees of the stern. Certainly the boat may be knocked down
but a full pitchpole is more likely to be avoided. This usually means that
the vessel will need to be positively steered. The main dangers are broaching
and going too fast down a wave leading to burying the bow and a possible pitchpole.
It will be better to go across the wave face and square off at the crest.
Too slow may also create problems - speeds of about 6K seem to be best for
the average boat.
To slow a vessel down one or more drogues will
need to be deployed. These can be bought or made - a simple yet very effective
drogue can be made from car tyre(s) or rolled-up hose wrapped in netting with
a suitable attached weight such as an anchor or a length of chain. Such a
drogue is then deployed from a strong hard point with sufficient strong line
to ensure the drogue and weight stay well below the surface - at least 120M.
To better resist broaching a small foresail sheeted to the centreline could
be useful.
Properly set-up the boat will sit at an average of about 60 degrees off the wind and the crew should go below - except for periodic checks on deck.
When the water at the bar is flat with little swell or wave action the main consideration will be the depth of water - in which case there are no major factors except timing. However the combined effects of wind, swell and current will often demand deeper consideration and planning together with patience and a keen awareness of the dangers present.
When a bar crossing will be a bit scary the boat should be properly secured first. This involves at least a thorough check on deck and below to secure loose items - taking below those item not essential for the crossing. Hatches and vents should be closed. There will be times when life jackets should also be put on and the wash boards put in place. All crew should be on deck - tied on if thought prudent.
For the actual crossing navigation marks and leads must be positively identified - and not just by the helmsman who should be the most experienced of those on board. The sea in the vicinity of the bar should be watched carefully and for some time to establish whatever wave patterns there might be. Commit the vessel as the lowest wave patterns approach and use most of the available speed.
Procedures should be set up to prevent or reduce
the risk of crew falling overboard. If it happens then recovering the person
who has gone overboard will be a severe test of skill in all but the most
benign conditions. There will always be two stages for a full recovery
1. Getting
the MOB reattached to the vessel &
2. Getting
the MOB back on board.
Factors affecting the recovery operations include at least the following :
1.
Recovery gear available,.
2. The
state of the MOB (conscious? hurt? incapacitated?),
3. The
sea and wind conditions,
4. The
number of able bodied crew left on board and their skill levels.
Recovery Gear
Assuming the MOB is capable of
some self help an early priority will be to get a suitable line overboard
- and not just any line. If the MOB can reach a thrown line there are
likely to be considerable forces especially in rough seas. Therefore the
recovery line should be designed to give the MOB the best chance - and
such a line ought to be prepared beforehand and be located in an easily
accessible place. The design shown could be permanently rigged and stowed
in the pushpit area while at sea
the tail can help with the haul out. The last loop
needs to be bigger than the others to allow the MOB to get their arms
and shoulders through to create a sling - about 1.5M around would suit
all but the biggest frames. Finally a small float just in front of the
last loop will help to keep the line on the surface. Naturally a full
life vest incorporating a strong harness would be a good substitute or
addition at the tail loop. Prudent skippers will often deploy such a line
anyway when the conditions deteriorate - in which case a life vest at
the tail would probably not last very long. The recovery line should be
attached on the same side as any side-mounted boarding ladder
Physical State of the MOB
If
the MOB is unable to grab the recovery line
or otherwise help themselves the rescue becomes very difficult and will probably
require another crew member to go into the water with appropriate safety gear
on a separate line attached to the boat. Such action may not be at all wise
in extreme sea states - the risk of losing another crew will be too high.
Where there is only one person left on board a grappling attempt is about
the only viable option - and this is only likely to succeed in fairly low
sea and wind states. The ability of one crew keeping the MOB in sight and
handling the boat alone will make a recovery a matter of luck. For these reasons
all crew should appreciate just how important it is to be secured to the boat
by a strong safety line when conditions become difficult.
Sea & Wind Conditions
The worse the
sea and wind states the more important it becomes to keep the MOB in sight
- a difficult task even in moderate conditions by day. At night with little
moonlight it will probably be impossible and the crew will need to rely on
knowing the exact MOB location, sound, lights on the boat, good crew co-ordination
and luck - at least until daylight. Where possible one crew member should
be given the sole responsibility of keeping the MOB in sight or when that
fails to know continually the precise location of the MOB incident. (including
the geographical co-ordinates and the position relative to the boat) In this
regard a log should be kept if possible of the wind speed and direction since
the incident. For these reasons crew should appreciate how important it is
to wear a life vest with suitable safety gear (ie Whistle, Torch and even
a Flare) when conditions become difficult - including at night all the time.
Number of Crew
Where the MOB
was the only one on deck and the act of going over was not witnessed the are
no immediate vital actions to be done. The time and position of noticing should
be logged and normally a reciprocal course would be taken up. The first person
to notice a crew actually go overboard should immediately raise the alarm.
From this point the number of available crew
now on board determines the subsequent courses of action. The skipper would
normally assume control as soon as practicable - restrictions being imposed
where the skipper or other crew have been aroused from sleep. Immediate actions
include
A Life Ring and Dan Buoy should be thrown towards the
MOB ASAP,.
Turn
to keep close to the MOB or to at least try and keep the MOB in sight - using
engine assist,
One
crew designated to keep the MOB in sight,
Recording
the incident position - from GPS if so equipped. This position will be
the start point for a search
pattern if the crew lose visual contact with the MOB.
The
best person for the helm should assume control of the boat bearing in mind
what each member has been
doing in the 30 minutes leading up to the MOB incident,
Deploy
a recovery line.,.
Deploy
a series of floating markers to help in returning to the scene.
Naturally several or indeed all of these tasks might fall on the shoulders
of one crew member so it pays to have thought of this eventuality beforehand
and even practised some of the actions and techniques now required.
Collecting the MOB
Good crew co-ordination will now be required
to bring the vessel back to a position where the MOB can reach the recovery
line, at which point the boat will need to be almost stationary. It can involve
reducing and/or lowering sail(s), jibing and tacking - normally with the engine
assisting. The diagram shows one method suitable for when
Hauling an MOB on Deck
Where the MOB can be hauled alongside the boat equipped with a boarding ladder the final haul out is relatively easy - the main precaution being to have anyone over the side stay attached to the vessel by safety line and to avoid fouling the prop. In heavy seas this will usually involve one crew member being dedicated to clearing any lines in the water. For this task a well equipped boat will have a rope ladder already available. Note that a rope ladder can easily be made from thick rope with the better types having plastic or wooden spreaders bound to the rope sections acting as the footholds.
Where there is no ladder available or the MOB cannot climb on board some kind of hoist will need to be used. For this purpose an arrangement of boom(s), halyards, spinnaker pole, pulleys, ropes, netting and winches can usually be found to make a recovery derrick of some kind. How it is constructed depends on the configuration of the vessel - the most important thing being that such an apparatus should be constructed and trialled in controlled conditions to ensure as much as possible that it will work when needed in anger. Note that, if a boom is to be used, the regular topping lift will most probably not be able to do the job and spare halyards will be needed to help support the weight which is to be lifted.
Unconscious MOB
When the MOB is unconscious they will likely have drowned unless wearing a life jacket of the type that holds the head out of the water. Even with such a lifejacket the chances of recovering an unconscious MOB are very low in rough seas and / or at night. There are only two courses of action available - set up a grappling attempt or a volunteer goes into the water on a safety line. Grappling will be a matter of luck especially if the life jacket has no grappling loops - and most off-the-shelf ones don't. An extra man over is a matter of high risk and conditions could be so bad that the skipper may have to veto in the interests of the safety of the remaining crew.
Moral
From a perusal of the above it should be obvious that all the retrieval gear in the world together with a well drilled and practised crew may still not be good enough to retrieve a MOB. The driving strategy must be to ensure that no one falls overboard in the first place. To help reinforce this approach inexperienced crew need to be made aware of the problems in retrieving a MOB - especially at night and when conditions are rough.
