The z-score deployed to create the Bluewater Value allows comparing and combining values for several criteria and is thus more reliable.

In contrast, using Capsize Screening Formula (CSF) and or Comfort Ratio (CR) alone means that a tiny 2 feet long radio controlled toy boat can get the same score as a 60 feet long, deep keeled vessel, displacing many tons.

If there is a reason for not including draft, Bluewater Surf Value (BWSV) should be deployed instead of Bluewater Value, as the former does not include draft. See Bluewater Surf Value (BWSV).

No value assessing seaworthiness is perfect or complete. Deciding what criteria to deploy demands careful consideration regarding validity (that the resulting measure actually reflects seaworthiness) and reliability (including that each criteria deployed is reliable).

Below follows the reasoning behind what is included in Bluewater Value:



Capsize Screening Formula (CSF) and Comfort Ratio (CR)

Both Capsize Screening Formula and Comfort Ratio have been widely discussed and criticized. They both have some merit, but more so in combination with the other variables included in Bluewater value (BWV).



Length in Waterline

Research from Southampton University has highlighted a significant risk to sailboats, showing how a breaking wave equal to 55% of a vessel’s length can cause a capsize. Moreover, a longer waterline means being able to go faster, i.e. potentially escaping approaching problems and finding safety faster.

With everything else equal, and within the boundaries of the characteristics of the distribution deployed for calculating the z-values, the longer the boat is in the waterline, the more seaworthy it is.



Displacement

A heavier boat has a greater moment of inertia, which is its resistance to changes in its rotational motion. This means it takes more energy to get a heavy boat to roll or capsize compared to a lighter one.

With everything else equal, and within the boundaries of the characteristics of the distribution deployed for calculating the z-values, the heavier the boat, the more seaworthy it is.

In other words, please note how this assumption applies to the existing population of boats, the more than 8000 designs that the Bluewater value draws on when it is calculated. These boats do not have most of their mass at the top of their mast (which is often used as an example of why displacement is not a useful variable). That said, no single value is perfect, but mass is relevant enough to take into account when comparing boats.



Draft

A deep draft provides superior stability, counteracting the heeling forces of wind on the sails. It allows the boat to cut through waves with less effort, and it can allow a sailboat to sail closer to the wind

Thus again, with everything else equal, and within the boundaries of the characteristics of the distribution deployed for calculating the z-values, the deeper the draft, the more seaworthy the boat is.

Of course, this is not to say that there are no drawbacks with a deep keel. Obviously a deep draft can limit the numbers of available safe harbors that a boat can enter. This is a valid argument. But it tends to be situation specific.

To create any form of measure of seaworthiness, situation specific conditions must always be disregarded to some extent, as a strength can always be a weakness under very specific situational conditions. That said, the Bluewater Surf Value (BWSV) does not include daft in the calculation. Bluewater Surf Value may also be relevant when boats come with more than one keel option as the version with the deepest draft was sought for each boat model when the Bluewater value was calculated.



Situational Specific Conditions etc.

The number and variants of situational conditions regarding the seaworthiness of a vessel are endless. An older boat may be built with a thicker hull, or not; it may come with an older (unreliable) engine, or not; previous owner(s) may have tampered with installations, or not. Water tanks, water makers etc. can be added or removed. Such variables and the general condition of the boat is impractical to assess and include (due to low validity and reliability) in any generic value such as the Bluewater Value.

Common hull materials include fiberglass, wood, aluminum, and steel, with each offering unique benefits in terms of strength, weight, cost, and durability for different boat types and uses.

If you intend to hit a floating container (or face playful orcas) the most seaworthy hull for that is most likely made of steel or aluminum. However, material thickness, exotic composites, bulkheads and chain lockers serving as collision bulkheads complicate the matter. Thus, evaluating different materials, their thickness, and next, ascribing the differences degrees of significance in relation to the other criterion included in the Bluewater value, would be rather arbitrary (low validity and reliability). Importantly, hull material is easily identifiable and taken into account when choosing a vessel. Consequently, hull material is not taken into account in the Bluewater Value.

Another variable to potentially take into account in the Bluewater Value is the height of the mast(s). However, the relationship between mast length and mast weight is complex. Making the mast heavier can increase a sailboat’s resistance to capsize (dismasted boats are often rolled repeatedly in breaking waves), while reducing the boat’s ability to recover from a knockdown or capsize. Hence the validity is weak. Moreover, masts can be changed, and the calculations would have to take into account designs with more than one mast. Consequently, mast height is not taken into account in the Bluewater Value.

An intrinsic value like the Bluewater value is useful and valuable. However, how the boat is handled, including avoiding rough weather when possible, is often more important.