User-defined 'Quick' Current and Wind Models
Other tactical programs enable you to simulate current and wind by entering constant values at one or more timepoints, resulting in uniform current or wind across the venue. This is often unrealistic and does not allow you to explore the tactical opportunities inherent in point to point current (or wind) variations. In contrast, Advantage provides a facility to quickly and easily define non-uniform current and wind models which can be used to explore realistic tactical scenarios (or use as a teaching tool). You begin by placing a mark and your boat token onscreen, and then select 'New Quick Model' from under Weather - Quick Model (see below).
The program creates a set of 9 model definition points that surround the venue (red boxes below), and opens the model definition form which enables you to define magnitude and direction values at each point and (if desired) modify the location of the definition points.
The model definition form (below) partially overlays the regular chart, and provides a variety of tools to define and modify your wind or current model. Note that the orientation of points on the form takes the rhumbline between boat and mark to be the vertical axis, regardless of compass orientation, so that the mark is in the vicinity of the middle point in the top row of the form.
You define magnitude and direction at each of the 9 model points, and the program then interpolates values for points in between. You can specify values for a single point by clicking the tail end of the arrow (blue box, which turns red) and editing its present values (in the magnitude and direction boxes). You can also change direction by clicking 'Rotate by,' or vary magnitude by clicking 'Scale by.'
You can edit more than one point at a time by selecting a row or column, or all of the points. To select a row or column, click on one point in the row or column and then click the appropriate 'Select' button. You can then scale or rotate all selected points simultaneously, or set them all to identical values by editing the magnitude and direction values and then clicking 'Apply' (see example below).
Most of the time, in open water, you will not need to alter the lat-lon locations of the model definition points, but you may want to do this, at least for a current model, if one or more of the original points is on land. In general, think of connecting points in any row or column by a straight line, and adjust locations if such a line would cross land at any point. There are two types of control for changing the definition points. The first, shown below, consists of expanding or contracting the entire pattern, either vertically or horizontally. Click 'Size' to bring up the 'Expand' controls, and then click one of the up or down arrows. Click 'Size' again to end this edit. Any changes made will show up on the form's representation of model points and also on the original chart (drag form aside to see those changes). The pattern of model points should be sufficiently large to span the intended sailing area, but will be more accurate if it is not excessively large.
The second way to relocate model points is to click 'Move' on the form, which opens the 'Move' controls (see below). First select an individual point, row or column (or all points), then click 'Move' and use the arrow keys to move the selected points to new locations (both on the form and on the underlaying chart). Click 'Move' again when you are done. Once you have placed the points to your satisfaction and edited magnitude and direction of each point (and edited the desired time) you can use 'Save' on the form's 'File' menu to save your model so it can be loaded for use with Advantage. If you want to specify different values for a later timepoint, click 'New Time Point', enter the later time and edit the point values to what you expect them to be at that later time (Advantage will interpolate between timepoints, just as it does with standard wind model files). Note, however, that you can only edit point locations for the first timepoint.
Once you have defined a 'Quick' model you can recall it at a later time and edit it to impose new values. If you are sailing in the same area and want to create a new model, you don't have to redefine the definition points. Just open the old model, edit to new values and use 'Save As' on the 'File' menu to save it under a different name. To use a Quick current model, use 'User Currents' under Advantage's 'Currents' menu and choose your desired model from the list. Once loaded, the Quick model will override the Local Knowledge currents, if any, that apply to the area, but will utilize the Local Knowledge shoreline data. Click 'User Currents' again to remove the Quick Model. To load or unload a Quick wind model, use 'User Winds' under Weather-Wind Model.
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