Hull Speed

J. Austin · Post by **J. Austin** » Wed Jan 20, 2010 9:39 am

Being in Engineering, numbers kinda interest me, so this may be boring for some. Hull speed is generally equated as {the sq. root of LWL multiplied by 1.34} this supposedly can give you the hull speed of your vessel. The math on a 22 comes out to 5.84 knots? It has come to my attention that this seems drastically low. My question is this: What is the highest speed you have logged on you boat (22's and 26')?
These numbers will be given to a local math professor along with specs from our boats to help derive abetter equation for our style of boat. The more input, the more accurate this will be, so I welcome all numbers.

Thanks as Always!

CaptainScott · Post by **CaptainScott** » Wed Jan 20, 2010 9:42 am

Don't you fret over hull speed. With enough wind you can get her to plane! LOL!

I had a 28'er breaking 11kts once! Scary but FUN!

5.84 kts is indeed acurate for an LWL of 19'0"

Scott

Alanhod · Post by **Alanhod** » Wed Jan 20, 2010 10:11 am

sailbob2 · Post by **sailbob2** » Wed Jan 20, 2010 11:52 am

On my 26' "CRYSTA" I've seen 6kts.

Bhacurly · Post by **Bhacurly** » Wed Jan 20, 2010 1:08 pm

Interesting,

On our C-22 with GPS our Max speed record is 8.3 mph,, held by me

though it was a short burst,, for almost a year prior Pam held the record at 8.1mph. We've had sustained runs over 6 mph for maybe a quarter mile before the breeze would drop off...

Like Scott say's when planed out it get's interesting with lil room for error

HJakl · Post by **HJakl** » Wed Jan 20, 2010 3:02 pm

On my Sailpending 9.6 downwind wing to wing and flying asymmertical spinnaker. just on the limit...
we were quite heavy 4 crewmen and provision for 3 days camping ( lots of beer )

CaptainScott · Post by **CaptainScott** » Thu Jan 21, 2010 6:13 am

Please remember "HULL SPEED" is not the maximum speed of your sailboat! It is only the maximum speed your sailboat can go with attempting to climb up over the bow wave! Any speeds through the water above hull speed indicates you are beginning to plane. Like a power boat. You can feel the boat begin to get "wallowy" if thats a word. You know where she seems to roll to port and starboard in a slow cyclical motion.

Another fact to consider is currents. Your GPS will read "SOG" or speed over ground and not "SOW" Speed over water.Big difference in some cases. Also make sure your GPS is reading Knots and not MPH!!! That'll mess with you too!

Now LETS GO SAILING!!

Scott

Banshi · Post by **Banshi** » Thu Jan 21, 2010 8:56 am

5.84 knots = 6.7 mph

Banshi · Post by **Banshi** » Thu Jan 21, 2010 9:34 am

If you can catch a wave and gust just right cowabunga too.

You'd be surprised just how fast some flat bottom boats like a sunfish or a lightning can go, they plane really well and given the size of the spinnaker on a lightning scary is a good description but so is thrilling.

CaptainScott · Post by **CaptainScott** » Thu Jan 21, 2010 10:50 am

Banshi wrote: You'd be surprised just how fast some flat bottom boats like a sunfish or a lightning can go,

Heh heh! Not me! I grew up on sunfish and bought a Chrysler Dagger when I was 14! We took an old sunfish sail and made a jib. We hanked it onto the forstay of the dagger!!! I learned a lot about why a sloop rig has the mast stepped further aft than a cat rig! Also learned about downward forces a jib generates on a small boat!!

Picture a Dagger screaming along with two of us as far aft and windward as possible plaining along! Well, we cam upon an unusually large wave. Instead of the bow lifting nicely over the wave, it dove straight in. Next thing ya know we cartwheeled the boat and went flying! What fun!

That however was many moons ago!!! LOL!
Scott

tnc110 · Post by **tnc110** » Thu Jan 21, 2010 2:40 pm

c-22. 7.7 mph off coast of kiawah island near charleston sc. 20-30 mph winds and 6-8 foot seas. I assume the high speed came from surfing down a swell. First time on blue water, was scary at first, but turned out to be quite exciting after we got use to it.

Windwalker · Post by **Windwalker** » Fri Jan 22, 2010 8:11 pm

Windward (C26) has a hull speed of 6.4 knots, and rarely have I been above this.

However, I did do 35 - 40 knots in a Chrysler/Lone Star 16, (full run in 35 to 45 knot winds with 3 knots apparent off the stern).

Banshi · Post by **Banshi** » Sat Jan 23, 2010 2:27 am

I have a Sunfish and I can still spend all day out on the water if the winds are strong...........I just can't make that turn into shore while I'm still skipping across the top of the water at break neck speeds

Literally

Bhacurly · Post by **Bhacurly** » Sat Jan 23, 2010 12:11 pm

Windwalker!

Ok how long have you been in Spokane now & we still haven't met?!

I'm hurt....

Capt. Bondo · Post by **Capt. Bondo** » Sun Jan 24, 2010 4:02 pm

I still have my Sunfish also, nothing more fun on a warm windy day than hiking out, and making the center board sing. Sailboarders may disagree but I could never master that wind sport

bay surfer · Post by **bay surfer** » Wed Jan 27, 2010 10:16 am

Hit 8.9mph with my c-26 with 40+deg heel, one two many beers that day.
regularly hit 6.8-7.2 mph easy.

Holiday · Post by **Holiday** » Mon Feb 01, 2010 7:20 pm

http://www.youtube.com/watch?v=WKFqK0Dp ... re=related

Guillaume C. · Post by **Guillaume C.** » Mon Feb 01, 2010 8:50 pm

Hull speed is not a precise limit, it is only an approximation of the speed where wave resistance increase very quickly. Once you get past it the wave resistance decrease quickly and remain relatively stable, but frictional resistance is still growing and overall you still need more power to go faster. If you can still apply more power, and with proper hull shape, then you may get hydrodynamic lift, the frictional resistance is still growing but wave is not much of a factor at this point, that is what happen to fast powerboat.

With the Chrysler boat you are pretty much limited to theorical hull speed as an average speed, you may go slightly over it (say 7.3 instead of 6.3) but the boat is still in displacement mode and you need to apply lot of power for a very small increase in speed. Chrysler sailboat will not go over it's own wave system without being helped by gravity, that is going down the sloop of a wave. (and that is only semi-displacement mode, you can forget pure planing with a cruising sailboat)

Wish I could find a graph that show proportions of the various resistances... this one only show the general idea

http://en.wikipedia.org/wiki/File:Speed ... stance.gif