Re: [PCW] Convert sail cat to power part 2 - was hulls
Brian replied:
I hadn't gotten to all of my email yet, but I wanted to compliment Gary on
this submission It is a really good synopis of the subject of conversion.
There may be one other consideration in larger vessel sizes. There are some
folks (and power folks in particular) who don't want to wait for a custom
boat
build. Maybe they suddenly decided it is time to go cruising doing the coming
economic slump. They could be likely candidates for an 'upscale' sailing cat
with the rig removed (frightens some non-sailers)
------ Original Message ------
Received: Thu, 13 Mar 2008 11:34:20 AM EDT
From: gram rupert gramario@tin.it
To: Candy Chapman and Gary Bell tulgey@earthlink.net
Cc: Jacob rjacob@pvp.com.br, Roger@lists.samurai.com, Power Catamaran List
power-catamaran@lists.samurai.com
Subject: Re: [PCW] Convert sail cat to power part 2 - was hulls
On 13 Mar 2008, at 13:48, Candy Chapman and Gary Bell wrote:
Part 2:
Two other major sorts of monohull boats are seen in today's
marinas. The full displacement monohull does not have a clear
derivative in modern power catamarans, which all utilize planing to
one extent or another. The monohull sailboat contributed sailing
rig and other traditional attributes to the far more recent
development of sailing catamarans, but it's hull form was generally
abandoned (with the possible exception of daggerboards). These
sail catamarans then evolved into today's second type of power
catamarans, retaining virtually none of the monohull sailboat hull
features.
Finally, to converting sailing catamarans to power catamarans.
Why? Sailing catamarans have, by virtue of their sail rigs,
virtually unlimited range. Modern sailing catamarans are commonly
used for coastal cruising as well as routinely crossing oceans. By
virtue of their high sailing speeds, limitless range and their
unique maneuverability under power they are particularly well
suited to do so. In coastal and local cruising, sailboats of all
sorts use their engines -- and don't use their sails -- maybe 90
percent of the time. Sailing catamaran hulls are similarly as
slender as my second sort of power catamaran, or even more so, and
use the slender hull minimized bow wake approach to breaking out of
the 'hull speed wave trap.' Note please that they lack the modern
power catamaran's 'semi-displacement' planing features of flat
bottomed aft sections and powerful enough engines to achieve
significant hull lift. They operate in strictly displacement
mode. The particularly small engines needed to only approach
displacement hull speed are designed into the hull with oodles of
compromises and trade-offs which have evolved over a considerable
time to uniquely suit the hull and engine combo. Adding a larger
engine will be very challenging in terms of the strength of various
hull components, size and shape of the spaces available, etc., and
without planing capabilities in the hull shape, will not give
spectacular improvements in top speed. Interior space utilization
in sailing catamarans has evolved into very efficient and effective
designs. Significant modifications to add larger engines or much
larger fuel tankage will force some very unhappy compromises.
Primary among these are considerations of weight and balance.
Catamaran performance, both sail and power, is incredibly sensitive
to both total weight, and to the presence of significant weight far
from the center. Orders of magnitude more sensitive than the
common monohull. Adding significant weight in upgraded engines,
and far worse in increased fuel tankage to an existing evolved sail
catamaran hull will cost large penalties in sail performance and
boat motion, for small gain in top speed under power and/or greater
range under power alone. The main fuel tank in my PDQ is probably
the heaviest item aboard, and occupies the bridgedeck space where
the center of gravity of the whole boat resides. Adding a large
fuel tank to a sailing catamaran would severely compromise its
behavior if it could not be correspondingly placed. Sailing
catamarans, and my second type of power catamarans derived from
them are thought to have some difficulty in finding comfortable
marina berths. In practice, I find that my anticipations far
exceeded the reality, and I have had a little increased cost, but
no particular difficulty finding dock space, and that the catamaran
hull is particularly better suited for anchorage, by virtue of its
roll resistance and the level of comfort aboard. Anchoring out is
a particular treat in my book.
In short, if you took the considerable trouble to 'convert' a
sailing catamaran into a power only catamaran, you would compromise
off some of the finest advantages of the sail cat, while gaining
little of the advantages of the modern power cat. A modern sailing
catamaran cannot go very fast under power alone, but screams along
under sail. Sailboats of all shapes have interior spaces already
compromised for sailing, like low overheads and sail handling
cockpits. These would be difficult to reconfigure to match the
interior space utilization of a power boat. The difficulties of
sailing are that you cannot ever count on favorable winds, and
sailing catamarans are variously compromised in their upwind
performance. If you can loosen up your schedule, shed your case of
'get-there-itis' and just go with the flow, the sail performance
alone will get you wherever you would like to go, and if you are
not after the speed of a planing power boat, catamaran or
monohull. When the 'diesel wind' is used either because the wind
is wrong or the owner is lazy, he gets the performance of a full
displacement 'trawler' sort of boat, not such a bad way to go
either. The tiny diesel engines already found on these boats can
be given significantly more range by temporarily adding a modest
amount of fuel bladder or gerry can storage for a particularly long
jaunt without taking a huge penalty in handling and boat motion.
With an unmodified, or slightly modified sail catamaran one can go
anyplace today's power catamaran can go, albeit not on precisely
the same schedule. The long deep ocean passages that only the
larger power catamarans can manage are readily available to almost
any modern sail catamaran.
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