|
Van Oossanen & Associates have developed a new hull form, called the "Fast Displacement Hull Form"
or FDHF (patent pending).
The development of this concept was triggered by the desire to develop hull forms which
are efficient over the entire speed range and not only at a chosen design speed. The concept is based on a number
of standard features which are not entirely new to ship or yacht design, but, when combined in a special,
well-balanced, state-of-the-art design, a surprisingly efficient hull form is obtained.
The main benefit of this hull form is the performance. At cruising speed, the performance of
the FDHF equals a very well-designed displacement hull form. At semi-displacement speeds,
the resistance values displayed by the FDHF are 15 to 20% better than those of well-designed hard
chine hull forms. Comparison of model test results for the FDHF with those of
numerous hard chine models show that only at nearly fully planing speeds a hard chine
hull is more efficient than the FDHF.
Other benefits, especially when compared to hard chine yachts are improved seakeeping
behaviour and manouevrability.
When compared to traditional hard chine motor yachts, gains are up to 40% (in resistance, fuel
consumption and range) at cruising speeds, 20% around the primary resistance hump and up to 15% at
maximum speed. Research carried out for the application of the FDHF applied to a 45 meter
all-aluminium semi-displacement yacht showed an increase of 2 knots in maximum speed, and an increase
of the range at cruising speed from 3000nm to 5500nm.
In november 2009, we signed a contract with Heesen Yachts to design their new
65m flagship, which is the first fully developed application of the FDHF concept.
Read more..
|
|
Tank Tests at the Wolfson Unit
The Wolfson Unit has conducted towing tank tests on a large number of round bilge/semi displacement motor
yacht forms and hard chine forms since 1968. A database has been compiled containing the resistance and
powering data for the majority of the tested motor yacht hull forms which calculates a comparative
performance coefficient for each resistance data point which relates the speed, length, displacement and
effective power. This then allows direct comparison with the other tested hull forms at discrete Froude
numbers.
For example, if hull efficiency at the cruising speed is the main design driver then the designer should
be looking for a hull form that is placed high up in the rankings at that particular Froude number. The
rankings are expressed as a percentage at each Volumetric Froude number increment, 0% being the least
efficient and 100% being the most efficient.
When compared to other round bilge hull forms at speeds in excess of 15 knots (cruising speed) and up to
44 knots (almost planing speed) the tested motor yacht’s ranking is typically around 100 - 140% indicating
that the design is currently ranked as the most efficient in the Wolfson Unit’s database. When compared to
hard chine forms the ranking increases to around 100 – 200%.
Dickon Buckland,
Wolfson Unit MTIA
|
|
