[PCW] Convert sail cat to power part 2 - was hulls

[brian eiland]

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 at tin.it>
To: Candy Chapman and Gary Bell <tulgey at earthlink.net>
Cc: Jacob <rjacob at pvp.com.br>, Roger at lists.samurai.com, Power Catamaran List
<power-catamaran at 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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