[Rhodes22-list] How fast does your R22 go?

[Ronald Lipton]

Some gratuitous physics (mostly from the "Symmetry of Sail").

Hull speed occurs when the speed of the wave front generated by the
bow wave has the same wavelength as the boat.  At that point the
boat has to "climb it's own wave".  Wavelength and velocity for a
a water wave are related by V = sqrt(gL/2pi).
Most of you know that, but there is an exception:

 In water which is shallow compared to the
wavelengh wave propagation is dominated by the depth - and for the
longer wavelengths  V = sqrt(gD) (D is the Depth) or
V(knots) = 6.2*sqrt(D(meters).  This means that the effective "depth
speed" in shallow water is much larger than that at larger depth for a 
small boat.
This also means that all waves, of whatever wavelength,  generated below
"depth speed" move ahead of the boat, decreasing wave friction.  However
the bow wave at "depth speed" would be enormous.

Wave drag is one component of the drag forces on a boat. The other
major forces are skin frictional resistance and vortex drag.  Skin 
friction appears
to dominate until about 2/3 of hull speed.  Wave drag goes "through the 
roof" with
respect to the other drag forces as the nominal hull speed is exceeded.

Ron


Eric Nelson wrote:
> Imagine my suprise to see this. GPS was reading between 8.5 and 9 MPH. Was 
> lots of fun since the slightest tug on the Main Sheet would send the boat 
> heeling, and my wife and daughter screaming. Only lasted about 5 minutes, 
> but long enough to snap this photo.
> ----- Original Message ----- 
> From: "TN Rhodey" <tnrhodey at gmail.com>
> To: "The Rhodes 22 Email List" <rhodes22-list at rhodes22.org>
> Sent: Sunday, January 25, 2009 5:20 AM
> Subject: Re: [Rhodes22-list] How fast does your R22 go?
>
>
>   
>> Sailing on lake/river I can motor 6 knots with my 6 hp motor wide open. 
>> This
>> may seem hard to believe but I have toppped 7 knots a couple of times 
>> under
>> sail. This speed was sustained for periods of around 5 minutes or so and 
>> was
>> on a run that turned into a reach that turned into a broach.
>>
>> The first time happened in a race under very windy conditions (20+). I
>> posted this story 6 or so years ago. It was in January with temps in the 
>> 30s
>> and snow on the ground/. The conditions were such that we only had 7 boats
>> in the race. Two pulled out right after the start. A Catalina 30 shredded
>> their main. A husband/wife crew didn'tt think their marriage would survive
>> the race. We were now down to 5 boats.
>>
>> I was sailing my R22 single handed with with 60% furled main and a 125 
>> jib.
>> The RC didn't want to mess with buoys because it was so cold. The race
>> course was around Half Moon Island and back through the starting gate. It
>> was upwind towards the island. The wind was really blowing, the sky was
>> gray, and then it started snowing. I was over powered several times and 
>> had
>> a hard time keeping flat. By staying in the shallow side in the lee of the
>> island I was able to shorten the course and find some calmer weather. I
>> decided to unfurl the main to take advantage of the lull.
>>
>> Once crossing the island I jibed to turn back towards the finish line. I 
>> was
>> no longer in the lee and the boat took off like a rocket. My GPS was 
>> showing
>> a steady 7 plus knots for minutes at a time with occasional bursts going
>> over 9. It was not a smooth ride as the boat kept wanting to head up.
>> Finally the boat was over powered and broached. Rudder control was useless
>> at this point and I rounded up heeling hard.. I furled the main back in 
>> and
>> ran the rest of the way to the line chugging along at 6 - 7 knots steady.
>> Note this is measured speed over ground. I do not have knot meter. I can't
>> remember the results but i remember I finished 4 out of 5. I beat a 
>> Newport
>> 28 before they corrected the time! I think I corrected to 2 or 3.
>>
>> Remember hull speed is only theoretical. The RC measured wind speed that 
>> day
>> at 18-23 with gusts measured over 30.
>>
>> Fair Winds,
>>
>> Wally
>>
>> On Sun, Jan 25, 2009 at 7:36 AM, Metaphor <mwager at bluecrab.org> wrote:
>>
>>     
>>> I had it up to about 70 on the way to the put-in ramp, but I got kind of
>>> scared when it started heeling too much around the turns, so I backed it
>>> down to the 50 mph speed limit...
>>>
>>> --
>>> View this message in context:
>>> http://www.nabble.com/How-fast-does-your-R22-go--tp21641761p21651283.html
>>>  Sent from the Rhodes 22 mailing list archive at Nabble.com.
>>>
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