Subject: Re: : Re: : Re: : Re: : Re: : Re: : Re: [harryproa] Re:: Diesel Electric Drive
From: "Rick Willoughby rickwill@bigpond.net.au [harryproa]" <harryproa@yahoogroups.com.au>
Date: 3/21/2015, 9:39 AM
To: harryproa@yahoogroups.com.au
Reply-to:
harryproa@yahoogroups.com.au

 


On 21/03/2015, at 11:48 PM, "taladorwood@yahoo.com.au [harryproa]" <harryproa@yahoogroups.com.au> wrote:

Funny I see a submerged bulbous bow, swath type hull that is explicitly trying to mimic a submarines hull.  No wonder you are confused.


This is a displacement hull that does 44kts.  You would have considerable difficulty convincing the designer, builder and operator that they are mimicking a submarine.  In fact they are regarded as shallow draft vessels so they can operate in undeveloped coastal waters.  This type of vessel is commonly referred to as a stabilized monohull .  They operate in displacement or semi-displacement mode but not planing and definitely not submarine.   Their waterplane area is as large as any area of the submerged hull so definitely not Small Waterplane Twin Hull  (SWATH) vessel.  In fact they have three hulls.  The long slender central hull typically has slenderness ratio close to those of the harryproa although the higher speed variants have a transom stern rather than a reversible bow of a proa.

There was an experimental boat that aims to reduce the wave drag through use of submerged buoyancy.  It is termed HYSWAS:
https://www.youtube.com/watch?v=kRuUtOmMGR0
It is primarily a submerged displacement hull relying mainly on hydostatic lift with hydrofoils for some dynamic lift and dynamic stability control.  Low waterplane vessels such as HYSWAS and SWATH have vastly different hull forms to surface hulls like the LCS Independence. This is closer to a submarine hull and has lower wetted surface for displacement than SWATH craft or any displacement craft of reasonable form.

None of these vessels are amenable to using Crouch's formula to determine their power requirement.  For the same reasons the formula is not applicable to determining drag on a harryproa - They are all primarily displacement hulls relying on hydrostatic buoyancy to support their weight rather than hydrodynamic forces to support their weight.  Crouch's formula is only applicable to planing hulls where hydrodynamic lift is the prime means of supporting the vessel weight.  If you cannot understand this yet then you are not trying.


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Posted by: Rick Willoughby <rickwill@bigpond.net.au>
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