Naval Architecture by Vripack

DESIGN BRIEF
The design brief is critical to defining both the performance and functionality of a boat. It’s therefore vital that, from the outset, a yacht’s exterior and interior design development runs in parallel with the hull development to truly deliver on the Owner’s wishes and avoid assumptions.

WEIGHT
Weight target estimations and detailed calculations sit at the heart of classic naval architecture. To reach an optimum weight calculation, the naval architect and designer need to work in unison, aligning their skill sets and knowledge; the designer makes creative amends to meet necessary weight allowances, while the naval architect understands how much weight needs to be allocated, and where.

These plans, calculations and weight distributions are crucial to guiding the shipbuilder on careful weight monitoring during the build. It all contributes towards proactive weight monitoring management.

Central to this topic is understanding how to operate within required margins. In every weight calculation there is an allowance made for future weight growth, as typically a yacht’s displacement increases over time. This ensures performance and safety remain optimum throughout a yacht’s entire lifespan.

HULL LINES
A yacht’s concept, layout and related weight distribution is what drives volume distribution and dictates the hull lines. Any set of hull lines requires a fine balance between hull efficiency, space efficiency and comfort. By working in close collaboration with the designers, the naval architect can optimise the amount of space found on board by fine-tuning the hull volume.

HUMAN COMFORT INDEX
The impact of various movements on human comfort when at sea is defined by the so-called Effective Gravity Angle (EGA); the total forces experienced by the body between vertical and side moving forces. Typically, the maximum EGA for Owners and guests is 3 degrees and 9 degrees for crew.

A polar diagram illustrates how a yacht’s movement correlates with the maximum EGA values. Ultimately, this allows us to determine comfort differentiators in various areas on board. The polar diagram shows the EGA values in differing locations on board in various defined headings.

UNDERSTANDING YACHT’S ACCELERATIONS
By applying what we know regarding EGAs in various sea states and various speeds, we can also determine the areas onboard that have a greater or lesser impact on vertical accelerations. Typically, vertical accelerations play a pivotal role in onboard comfort.

The graph illustrates the vertical acceleration at various speeds where the effects of a potential elongation has been quantified.

COMFORT AREA DETERMINATION
As vertical accelerations tend to play a dominant role in the level of comfort experienced on board, we can apply what we know regarding EGAs and calculated vertical accelerations to determine which areas on board have a greater or lesser impact on vertical accelerations.

The image shows the difference in guest comfort when occupying what are arguably the two worst areas on board a boat; headsea and bow quartering.

STABILISER OPTIMISATION
Choosing the stabilising system that is most effective and suitable for a particular yacht.
As roll is typically considered to be the most uncomfortable ship movement that humans experience, we can zoom in on this movement to try to mitigate it. To control and minimise roll, we first need to select the most suitable and efficient stabilising system, or combination of systems. Through extensive calculations, we can determine the most efficient stabiliser system suitable for a combination of speeds and headings to deliver the most effective setup for all relevant conditions.

The table illustrates the difference in roll responses at a defined speed at various headings when a stabiliser system is switched on and off. It helps us to understand the effectiveness of active stabilisers at each heading when running at a particular speed.

Particularly with high(-er) speed yachts, the angle of heel in a turn is also relevant. Stabilisers can not only reduce such a heel, but their overall contribution, as well as that of the interceptor, can be optimised using calculations.

The table shows the difference in heel angles between interceptors when on and off at various speeds.

EXTERIOR WINDAGE OPTIMISATION
In any yacht, there is great value in having the exterior seating areas in the right location regarding draft and lee. Whether at anchor or while sailing, guests always appreciate it when the dining table is positioned in a wind protected area, the sun bathing areas receive the right amount of breeze and the views from the observation deck forward are fully protected from the elements. With often remarkable results our in-house tooling we can simulate the airflow and optimise wind protection by modifying shapes and adding the right well-chosen deflectors where needed.

CFD HULL AND APPENDAGES OPTIMISATION
The benefits of an enhanced hull can vanish if not all the appendages are CFD optimised. Often, a lot of efficiency can be gained by establishing an undisturbed waterflow around the many hull appendages that sit in and around the underwater body. Aside from efficiency gains, proper alignment also reduces noise and vibration.

TRANSPORT EFFICIENCY
One of the most valuable parameters used to quantify hull efficiency is calculating the so-called transport efficiency index. Offsetting transport efficiency to speed will allow for a direct apple to apple comparison between various designs/yachts.

HEAVY WEATHER PERFORMANCE
In addition to comfort calculations and related indexes in heavy sea and/or high sea states, our use of in-house tooling means we can calculate the added resistance of water/waves and windage related to sailing in heavy weather. This means we can calculate any additional power required to maintain a certain speed e.g., to pre-empt and prevent a drop in speed due to adverse weather conditions.

The graph shows the difference between sea state 2 (2bft and 0.3m waves) Vs sea state 5 (7bft and 3.3m waves), illustrating the impact that certain weather has on speed.