After reading
through some of the links that Brent provided to Kraken, I would guess that the quoted 6 kts. speed during
trials was on the surface dieseling (she ahs a hull optimized for surface
transit). Submerged speed on electromotive drive would be significantly
less.
R/J2
Respectfully,
Jay K. Jeffries
Andros Is., Bahamas
It is the mark of an educated mind to be able to
entertain a thought without accepting it.
- Aristotle
From: owner-personal_submersibles@psubs.org
[mailto:owner-personal_submersibles@psubs.org]
On Behalf Of Joseph Perkel
Sent: Sunday, January 28, 2007
10:30 AM
To: personal_submersibles@psubs.org
Subject: RE: [PSUBS-MAILIST]
Submerged speed calc
Jay,
Thank you
for that, I suspected as much but, needed clarification.
I took an
interest here in clues as to "sizing" the thrusters
appropriately. After having seen the output of that pair on "Dry
Diver" in New Zealand, my original thoughts on the Minn Kota's should most
likely be downsized in order to "do the job" as power efficient as
possible.
Joe
From: "Jay K. Jeffries" <bottomgun@mindspring.com>
Reply-To: personal_submersibles@psubs.org
To: <personal_submersibles@psubs.org>
Subject: RE: [PSUBS-MAILIST] Submerged speed
calc
Date: Sun, 28 Jan 2007 09:55:33 -0500
Joe &
Frank,
One of the 3
recommended design books (Chapelle, Hamlin, & Brewer are the three authors)
for the naval architecture course goes into to this issue to some extent.
The frontal area and skin area are the two major factors in determining
resistance at speed skin area dominates at low speed and frontal area dominates
at higher speeds (i.e. if I remember correctly, the transition occurs somewhere
at or just above 3 kts. for a submerged body). Six knots will take
8 times the power that 3 knots will; 4 tons will take a bit to accelerate but
God forbid if you have to stop quickly! I have seen pictures and talked
with crewmembers after the USS Ray
ran into a seamount (now named after her) at slow speed. What purpose do
you have to run at 6 kts? If it is to make headway against a swift
current, there are places a PSUB shouldn’t operate safely.
R/J2
Respectfully,
Jay K. Jeffries
Andros Is., Bahamas
It is the mark of an educated mind to be able to
entertain a thought without accepting it.
- Aristotle
From: owner-personal_submersibles@psubs.org
[mailto:owner-personal_submersibles@psubs.org]
On Behalf Of Joseph Perkel
Sent: Sunday, January 28, 2007
8:29 AM
To: personal_submersibles@psubs.org
Subject: [PSUBS-MAILIST] Submerged
speed calc
Hi Frank
"I
hope to be able to get 6 knots submerged speed out of her."
As I understand it, your typical fast attack submarine is faster
submerged then when surfaced. This because on the surface, a displacement hull
speed is calculated at 1.3 x the sq rt of the waterline length. So submerged,
the surface wave no longer factors.
So my question then...is there a rule of thumb formula that can be
applied to a submerged body? Or does one have to calculate total plate area
-vs- resistance of seawater and then account for thrust?
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