Boat Handling Under Engine, Part 1: The Getaway…
As it’s often easier to understand the how if we have first grasped at least some of the why, let us start with a little bit of theory:
It’s a net of forces…
In any berthing manoeuvre there are a number of forces acting on the boat. Some of these (the propeller, rudder and warps) we can control. Others are in Mother Nature’s remit and can be used if they happen to be working in our favour, or must be conquered if not. A key point to understand is that our craft will always be acted on by all of these forces at once, with each playing their part in the delivery of cheering or jeering from the crowd mustered ashore.
Tide can be our best friend, our worst enemy or a completely disinterested bystander when it comes to parking. What is for sure is that only a brave skipper or a fool will ignore it if it’s running. Typically in UK waters our harbour-masters and marina designers will have done their best to ensure that the worst effects are mitigated, however there are still plenty of “cross-tide” pontoons out there to catch out the unwary. Time taken to understand what the tide is actually doing at the exact spot that you are manoeuvring will never be time wasted.
With a knot or two of tide running, even being “blown on” is no problem. Here simply putting the rudder over is providing enough impetus to bring the nose of the boat away from the pontoon.
Operating above the waterline where we can see and feel the effect; the wind is more obvious than the tide and often attracts the undivided attention of the in-experienced skipper. When there is no tidal flow this may well be justified. However, a gentle Force 3 blowing us on or off a pontoon will have a negligible effect if 2 knots of tide is sweeping along it. Essentially if the tide is fast enough to give us steerage with no forward motion then the chances are that the wind will play a secondary part in the manoeuvre.
Whilst we might not be able to do anything about the wind direction and strength, we can choose to increase its effect on the boat by hoisting sails. With a breeze on the beam, sails forward of the boats pivot point will tend to push the bow away whilst those set aft (e.g. a mizzen sail or hoisting just the peak of a gaff main) will give the stern some sideways impetus. Even with the wind forward, a backed staysail can perform miracles when we’re requiring the boat to turn away.
Putting aside for now the horrors of offset propellers, the modern affectation of sail-drives and those boats with dual engines, the vast majority of us are dealing with a single propeller sitting on the centre-line in a cut-out section of the rudder. In forward gear this fires a stream of water backwards, which Newton tells us provides an equal force propelling us forward. In reverse however the prop has a tendency to fire more water to port or starboard of the hull, an effect known as “Paddle-wheeling”. Until the keel and rudder have enough water flowing across them to negate it, this effect causes the stern of the boat to move crab-wise in the opposite direction in an effect known as “Prop kick”.
Prop Kick / Prop Walk
Without water flowing across it the rudder is as useful as a chocolate teapot. However when sufficient flow is established, say by moving the boat through the water, it becomes the directional control of choice. For most traditional craft a knot or two of water flow will give us steerage. The key thing to realise here is that the rudder cares not a jot about whether the boat is actually moving or not, as long as the water is.
The required flow over the rudder can be provided by tide or even by the propeller if it is mounted directly forward of the rudder blade. In turn this gives us the ability to deflect the propeller’s water flow to port or starboard, forcing the stern to move in the opposite direction. This is known as “Prop wash” and can be very useful indeed. Unfortunately due to the geometry of the prop and the cut-out in the rudder we can lose some of this effect (and at extreme rudder angles can lose it all) but on a boat where it exists it’s a key tool.
Leaving the boat securely tied to the pontoon with breast lines and fore and aft springs will severely restrict our ability to manoeuvre. Once one or more warps are removed or slackened off however, all sorts of possibilities unfold. A warp secured at one end to the boat and at the other end to a pontoon allows us to create a lever via which a force (the wind or flow of water from the propeller) can be used to alter the position of the boat before we commit to anything rash. This is known as “springing-off”.
It is worth getting a little more specific about this effect before we continue. Having listened to Archimedes, folks sometimes attempt to make these spring lines as long as possible in order to “lengthen the lever”. Whilst that’s a correct reading of the theory, it’s a misunderstanding of where the lever and pivot exist in this case. The lever here lies between the thing providing the force (the propeller) and the point around which the boat is pivoting. Initially this lies between the bollard on shore and the connection point on the boat however as soon as the front or back of the boat makes contact with the pontoon it becomes that point instead.
The key is to ensure that spring warp runs from the aft-most corner forward (if we plan to reverse onto a stern spring in order to get the bow out) or the foremost point heading aft (if we are driving forward to get the stern clear). Assuming that the breast lines have been led directly ashore or even slightly inward it’s often the case that they’ll work perfectly well as a bow or stern spring.
Using a stern spring and the engine in reverse to bring the bow out. Note the relatively small length of lever – more revs will be needed here to promote the effect.
Using a bow spring with the engine in forward gear to get the stern clear. Note the relative size of the lever created when the rudder is used to redirect the prop wash.
Enough with the theory – on with the practical
Let’s assume that we’re preparing to leave a berth with a yacht or two ahead and more behind with all of their owners looking on nervously at our (relatively) big heavy boat about to leave. On the Amelie Rose we’ll run through the following 4 point checklist if the solution is anything apart from blindingly obvious.
1) Assess the situation & form a getaway plan
2) Prepare the boat and crew
3) Test the plan
4) Execute the getaway
Step one: Assess the situation & form a getaway plan
Our first thought is always to look out for the tide. The best route to a controlled departure will be to head into any tidal stream that’s available. If it’s running from fore to aft then the exit may be as simple as putting the helm down, engaging the engine, letting the lines go and ferry-gliding gently away. With tide up the chuff things get more complicated due to the potential effects of prop walk and any bow-end accoutrements that will now be sweeping across the pontoon. Being pushed off by the tide is generally a boon, whilst a being pushed on may require help from Houdini or at least a harbour master with a powerful launch.
Next our attention falls to what the wind is playing at. If we’re being blown away from the pontoon and the tide isn’t playing silly buggers then simply letting go of lines should again work out well. If we’d like the bow out first then we might consider holding on to the stern line for a while or holding on to the bow line to get the stern out first. Popping up a little staysail or jib or peaking up a little of the main/hoisting some mizzen can also help to make use of an off-pontoon breeze.
Wind fore or aft with a negligible or agreeable tide further inclines us to head in that direction but with wind working against tide the maths gets trickier as it now depends on which force is stronger. When the wind is full onshore is when we’re almost certainly going to find ourselves resorting to springs to lever the boat outwards.
With a rough plan in mind based on Mother Nature’s offerings we can now think about how to arrange the forces that we do control in order to affect a clean getaway. It’s at this stage we think about which way the prop kick will take us if we need to reverse, whether sails could be useful, the potential to use springs and if we might use prop wash to any useful purpose. Having mashed all of this together into our best prediction it’s now time to get prepared.
Step two: Prepare the boat and crew
The best laid plan is almost bound to fail if the boat and crew are badly prepared. For the crew this means having a reasonable grasp of the whole plan and a detailed understanding of their part in it. For the folks controlling dock-lines it’s imperative that they are also briefed to do nothing until requested and then to communicate clearly when their task is complete or if anything goes awry.
From the boat’s perspective it means having everything that might be needed to execute the plan ready for instant use. On board Amelie Rose we will typically set up bow and stern lines and any springs we intend to use as “slips” (one end made off on board, the other going round the cleat ashore then back into the hands of a crew member via a turn around a strong point aboard). We do this as we prefer to have all of our crew aboard as we prepare to leave but it does mean that extra care must be taken to ensure that the slips don’t get snarled up.
It’s also worth remembering at this point that no berthing manoeuvre was ever ruined by the liberal use of fenders. We always include one “roving fender” to jam into any unforeseen contacts and at least one or two big fellas stuffed in at the stern or bow if we’re intending to spring off. Lastly, if we’re planning anything that might see the bowsprit heading ashore we have a jolly good think about whether it might be safer just to run it in.
Step 3: Test the plan
Especially when the elements are competing or our plan calls for the use of springs or something even more esoteric then having a trial run without letting go of anything is a great way to subtract the guesswork. If the bow and stern lines are set up to slip and are long enough then the crew can ease away to check the scheme without committing to it. If using a spring bear in mind that adding more force (i.e. revs) to the lever will increase the effect and (for a bow spring) using prop wash to redirect the force can also add an extra couple of feet of clearance.
If the plan doesn’t work (e.g. the bow refuses to clear an obstacle ahead) then the boat can be brought back alongside and a new plan formed. It pays to make sure that everyone understands that this is only a test – letting slip a line at this point could be costly. Conversely, if all works well, then a properly briefed crew can now be asked to let go of the lines and we’ll be away.
Step 4: Execute the getaway
With a proven plan we can now go ahead and direct our getaway. A common issue at this point is failure to control the deck. Being specific about each action as and when we want it to happen will mean that we are in control of what happens next. It’s also worth one last look around before we give the order to let go and find ourselves blundering into another vessel.
So now we’re away – but there’s still the entrance to reach and we’ll have to get back ashore again later. Next time we’ll have a look at some close quarters boat handling and mooring techniques that will get us out to sea without drama…
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