[C320-list] Hull speed

Sat Apr 22 14:38:04 PDT 2006

They are surf boards with keels.

Regarding 1.34 times the square root of waterline length:  that formula
was developed for wave theory not for boats.  Basically a displacement
boat creates a wave in front of it, and that wave can only go that 1.34
etc.  If the displacement boat goes faster than that it submarines.  I
have only had that happen once, not on my boat, and it was scarier then
heck to see the bow pointed down and water lapping up to the mast while
the boat kept sailing down.

The bottom line:  you can't change the laws of physics Jim.

-----Original Message-----
From: C320-List-bounces at catalina320.com
[mailto:C320-List-bounces at catalina320.com] On Behalf Of Jeffrey Hare
Sent: Thursday, April 20, 2006 9:31 AM
To: ola7442000 at DELETEgmail.com; 'C320-List'
Subject: Re: [C320-list] Hull speed

Those modern racing boats like the Open series aren't true displacement
hulls are they?

-Jeff

-----Original Message-----
From: Stan [mailto:ola7442000 at gmail.com] 
Sent: Thursday, April 20, 2006 12:02 PM
To: C320-List
Subject: Re: [C320-list] Hull speed

Hi Everyone.

The formula for hull speed [SQ RT of WL*1.34] is very basic and was
developed a long time before the modern sloops such as the 320 were even
imagined.  This formula will get you close but a number of other hull
factors, especially the wide beam carried aft will result in a higher
hull speed.  Extreme examples of this are the open 50s and 60s.  You can
completely throw the formula out on those boats.

That said, the actual hull speed for a 320 based on observation of the
bow wave in pretty flat water with 12-14 Kts., is somewhere around 7.2 -
7.5. It was hard to nail down the actual hull speed because of the GPS
time lag. As the bow wave went beyond the stern the boat speed would
plumment but the GPS would lag making an exact reading impossible.  One
of those perfect days on a beam reach.

The fastest I have sailed my 320 was in the middle of Lake Michigan on
the South end.  I was sailing in the high 8s to low 9s and peaking at
10.3 Kts.
(GPS) with the Asym. up and 2-4 footers.  The bow wave was noticably
beyond the stern of the boat, indicating surfing. I was singlehandling
at the time, making it was a bit hair raising.  But what a ride.

Stan
"Our Little Amusement" #744

On 4/20/06, Steve Magennis <magenns at yahoo.com> wrote:
>
> Hull speed on our C-320 is 7.09 knots.  All that means is that it 
> takes a whole lot of energy (or surfing) to get our boats going much 
> faster than that (has to do with wave mechanics).  I know one other 
> owner who has had his up to 14 knots, surfing with the spinnaker up in

> the Chicago -Mackinac race.  Said he was on the edge of disaster.
>
> Under power with a clean bottom and flat water, I have had the 
> Alchemist up to 8 knots (GPS and speedo), but I burned up a whole lot 
> of dinosaurs doing it.
>
> Be happy with the speed you achieved.  It's entirely believable and a 
> whole lot of fun.
>
> Steve
> Alchemist C#909
>
> --- "Lachance, Michael B (ISD, IT)" <MLaChance at thehartford.com> wrote:
>
> > 1st sail of year in good wind with new Gori 2 blade folding prop. 
> > Slack water, blowing 20-30kt, 1-2 ft seas, full main, 110 jib on 
> > close reach, speedo consistently reading high 7's with peak at 8.2kt

> > confirmed with GPS. I thought hull speed was 6.3kt. What gives? Btw 
> > I'm loving the new prop Mike Lachance
> > Seychelle, 141
> > Noank, Ct
> >
> >
> >
> >
> >
> >
> >
> >
> >
> >
> >
> >
> >
> >
> >
> >
> >
> >
> >
> > --------------------------
> > Sent from my BlackBerry Wireless Handheld (www.BlackBerry.net)
> >
> >
> > -----Original Message-----
> > From: C320-List-bounces at catalina320.com
> > To: C-320 Catalina
> > Sent: Wed Apr 19 19:27:57 2006
> > Subject: [C320-list] GFO report
> >
> > I replaced the packing with GFO and am very pleased, no drips and no

> > heat in the shaft.  Pretty cool having a dripless packing gland for 
> > only $15.00. Herb Creech
> > Cloud Chaser #606
> >
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--
Stan
C320 "Our Little Amusement" #744
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