[PCW] Displacement

[natale ramondetti]

Good morning from Brussels

As student of yacht design I would appreciate to receive your article of 
March 2004 in Professional Boat Builders about "Power catamarans and the 
LCG"

Many thanks for your cooperation and best regards

Natale Ramondetti
----- Original Message ----- 
From: "Malcolm Tennant" <malcolm at tennantdesign.co.nz>
To: "Power Catamaran List" <power-catamaran at lists.samurai.com>
Sent: Thursday, April 17, 2008 4:22 AM
Subject: Re: [PCW] Displacement


> As a practising designer I would just like to endorse Gary Bells piece on 
> the
> importance of the longitudinal moments of inertia in the area of boat 
> design.
> Two of the most important variables in naval architecture are [1] full 
> load
> displacement and [2] the concept of moments. When we  are calculating the 
> mass
> and the position of the various centroids we end up with many  thousands 
> of
> items and somewhere between 40 and 60 pages of spread sheet calculations. 
> But
> the result of this is that we can expect our boats to float within 3 to 
> 4mm of
> where they are supposed to and that we can predict with certainty what 
> will
> happen to the trim of the vessel as the tanks are filled, or emptied ,of 
> the
> many thousands of litres of fluids required for long distance travel.
>
> When calculating all the various centroids LCG, VCG, TCG, CB and CF it is
> important to keep in mind that they are all sums of moments. ie: mass X
> distances, volumes X distances, areas X distances. What this means in 
> practice
> is that moving a large mass a short distance has exactly the same effect 
> on
> trim as does moving a small mass a big distance and goes a long way toward
> explaining why designers are so fussed about keeping weight out of the 
> ends of
> the boat.
>
> I have been told by clients that I am obsessed with weight/mass.Probably 
> true.
> Certainly in March 2004 I wrote an article about my concerns for 
> Professional
> Boat Builder called "Power Catamarans and the LCG [a cautionary tale]" 
> this
> was accompanied by a case study for a 19.6m power catamaran that 
> illustrated
> what can go wrong when you start "improving" the original design and 
> moving
> mass around.
>
> If any of the members of the list would like a copy of this article send 
> me
> your e-mail address and I will e-mail you a copy.
>
> Regards,
>
> Malcolm Tennant.
>
> MALCOLM TENNANT MULTIHULL DESIGN LTD
> PO Box 60513, Titirangi.
> Waitakere 0642
> NEW ZEALAND
> Ph: +64 9 817 1988
> e-mail: malcolm at tennantdesign.co.nz
> www.tennantdesign.co.nz
> www.catdesigners.com
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