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Catalina 25 Specific Forum

Hull speed

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JanS48
Navigator

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USA
141 Posts

Initially Posted - 08/03/2015 : 22:21:10

Greeting all,
I had my boat out Sunday [8/2] and was heading into the Atlantic with both sails up when it got somewhat windy. We then decided to head back into Newport harbor and just enjoy the stiff breeze without the swells (and chop). There was plenty of wind. When I checked the speed using a RayMarine GPS with just the jib up [a 135] it was measuring up to 6.2 k's on occasion. My question is: it that a good speed? What is the max hull speed to expect with both sails up [SR FK] with a 135 jib?

Not related to speed - is a C25 considered an easy boat to capsize? I would hope not but... Is it possible for a strong gust of wind to actually blow one over (mast hitting the water)? Will it come back up?

Thanks
Jan

82 C25 SR FK
Sailing out of Newport Harbor.

hewebb
Admiral

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USA
761 Posts

Response Posted - 08/04/2015 : 03:01:34

On a broad reach I got to 7.2 knots one day. Haven�t done it since. Six to 6.5 comes often in a breeze. My hull needs cleaning to get speed up again.

I was knocked down once. I don�t think the mast got in the water, just the boom, several inches of water in the cockpit. The boat came back up easily. A friend with a fin keel saw his spreader hit the water and boat came back up.

1988 WK/SR w/inboard diesel Joe Pool Lake
Hobie 18 Lake Worth

Life is not a dress rehearsal. You will not get another chance.

Davy J
Master Marine Consultant

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USA
1511 Posts

Response Posted - 08/04/2015 : 04:33:49

quote:
Is it possible for a strong gust of wind to actually blow one over (mast hitting the water)?

Two techniques can be employed to prevent getting "knocked down". One is to watch for gusts on the water and head up, or turn slightly into the gust, you may slow slightly but won't heel as much. As the gust passes turn back to the original course.

The other is to keep the mainsheet in your hand, when you get to the point of being over-powered, loosen the mainsheet and spill some of the wind from the main.

I never had it happen, but supposedly at some point, the rudder will leave the water, the boat should round up and then stand back up...

Davy J

2005 Gemini 105Mc
PO 1987 C25 #5509 SR/SK
Tampa Bay

NautiC25
Admiral

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USA
957 Posts

Response Posted - 08/04/2015 : 05:15:35

I've never had a "knock down", which I assume the wind and/or waves hit you so fast that the boat can't react naturally and round up. When gusts hit mine, the boat always rounds up and this happens because the rudder comes out of the water.

1989 C-25 TR/WK #5894
Miss Behavin'
Sittin' in LCYC on Canyon Lake, Texas

Steve Milby
Past Commodore

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USA
5851 Posts

Response Posted - 08/04/2015 : 06:01:38

A C25 can be knocked down. In fact any boat ever built can be knocked down. A C25 is fairly well behaved when it happens. If it happens suddenly, it will take a dollop of water into the cockpit, over the gunwale. If it happens more gradually, it will simply lay on it's side until the rudder comes out of the water, and stay there until you ease the sheets or until the wind eases. When it happens gradually, it probably won't take any water into the cockpit. It's very rare that the spreaders will dip into the water during a knockdown.

After a lifetime of racing and sailing, I have experienced many knockdowns, and nobody on any boat I have been on has been injured, and no significant damage has happened as a result of a knockdown. It can certainly happen, but it's rare. I only know of one person who was ever tossed off the boat during a knockdown. That was on a Venture 22 that got hit suddenly by a microburst, and she was uninjured. My point is that, if you sail long enough, you'll probably experience a knockdown, and, while it will get your attention, it will not likely result in damage or injury.

Coincidentally, my 13,000 lb C&C 35 was knocked down last Saturday by a microburst from a little black cloud that didn't really look like it was big enough to produce such a wind. I was sailing on starboard tack after having rounded a race mark. Suddenly, the wind reversed 180 degrees, the jib was backwinded hard against the rig, and the boat's rail went down into the water. As soon as I released the jibsheet, the boat stood up again. The microburst probably produced winds in the vicinity of 45-50 kts, but it only lasted 20-30 seconds, after which the wind eased to about 18-20 kts.

Before you sail on any given day, you can check the weather, and the predictions will often vary widely. Some will predict strong winds and others will predict moderate winds, but the reality is that you have to be prepared to cope with whatever conditions the weather produces.

When it happens, release the sheets, and the boat will stand up. Re-adjust the sails for the new wind direction and get the boat sailing again, because, as soon as you do, you will be in control of the boat. Once you're back in control, you can decide whether you should continue sailing, or take down the sails and start the motor.

Steve Milby J/24 "Captiva Wind"
previously C&C 35, Cal 25, C25 TR/FK, C22
Past Commodore

Edited by - Steve Milby on 08/04/2015 06:05:48

Kim Luckner
1st Mate

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USA
96 Posts

Response Posted - 08/04/2015 : 06:35:29

If you look at the owners manual on this site, left column, it shows the LWL (Length at Water Line) as 22.167 feet. That's the only number you need for a full displacement boat. The below web site explains the physics pretty well and has a calculator that returns 6.36 knots as the hull speed. (slightly greater than the hand written note on page 7 of the Pre '88 manual)

http://www.cncphotoalbum.com/technical/hullspeed/hullspeed.htm

Hope this helps.

And yes you can "surf" down a wave front for short bursts of speed greater than "hull speed". Sail size has more to do with acceleration than speed. There are other calculators out there to show various "stability factors" associated with our boats.

Seeadler
'79 C25 SR/FK #1432
Mentor Lagoons

Stinkpotter
Master Marine Consultant

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Djibouti
9013 Posts

Response Posted - 08/04/2015 : 07:10:31

Essentially, the "theoretical hull speed" (THS) is that speed at which, to go any faster, the boat has to climb over its own bow wave. The length of the waterline determines the length of the "trough" between the bow and stern "peaks" the boat sits in at hull-speed. Longer wavelengths travel faster through the water, so the longer boat can go faster while sitting in that trough. To exceed the THS, the boat has to start to plane--something the narrow C-25 hull is not really designed to do. But you know when it's happening--spray coming off the hull from aft of the bow. Great fun! I've done it on a broad reach, helped by surfing the back-sides of some waves on our C-25, but didn't get a speed reading at the time. (A Sunfish or Laser can do it in a snap!)

EDIT: I just looked at Kim's link--guess I didn't need to try to explain THS--especially without the graphics.

The calculated "capsize ratio" for the C-25, as I recall, is something like 1.95, where anything under 2 is considered safe for coastal use--the boat will come back up from a knockdown in "reasonable" sea conditions. To get it past the point of coming back up, you would need a large broadside wave that pushes it past 90 degrees--at some point the keel can lose its leverage and you could end up turtled. (A keel pointing straight up has zero righting moment.) True "blue water" cruisers with more ballast and deeper keels can recover from almost any angle--thus can be rolled completely over and come back up (assuming all hatches are battened down!) As others have found, in the environment for which the C-25 was built, she's very safe. Just don't sail over the horizon into an ocean storm you can't get away from.

Dave Bristle
Association "Port Captain" for Mystic/Stonington CT
PO of 1985 C-25 SR/FK #5032 Passage, USCG "sixpack" (expired),
Now on Eastern 27 $+!nkp*+ Sarge

Edited by - Stinkpotter on 08/04/2015 07:22:08

Steve Milby
Past Commodore

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5851 Posts

Response Posted - 08/04/2015 : 07:49:10

The hull speed limitation is purely theoretical. It isn't an absolute limit. It can be exceeded. Hull speed is most commonly exceeded by a "cruising" hull by surfing briefly down the backside of a wave, as Dave described. When the boat gets to the bottom of the wave, the boat usually slows down enough so that the wave moves forward of the boat, and the boat has to climb up over it again to resume surfing.

I have had two occasions when the boat has been able to climb up over it's own bow wave, and surf down the face of it's own bow wave continuously for hours. Because the bow wave moves continuously at the same speed as the boat, the boat continues to surf down the face of it's own bow wave for as long as it can stay ahead of the wave.

The first time was when racing a 45 year old 30' Coronado in the Governor's Cup. We raced her with twin headsails, nearly dead downwind in 18-25 kt winds, and she sailed at between 8-9 kts continuously all night.

The second time was when sailing my C&C 35 south from Annapolis in small craft warnings. The wind was out of the west at about 25 kts. I kept her near the western shore, so that she was in relatively smooth waters. She maintained a steady speed between 8-9 kts for hours, and, when I looked over her gunwale, I saw that her bow wave had moved aft to the winches. That told me she had climbed over her bow wave and was surfing on it's face.

I have never done that on a C25, but see no reason why it couldn't happen, if given similar ideal conditions.

Steve Milby J/24 "Captiva Wind"
previously C&C 35, Cal 25, C25 TR/FK, C22
Past Commodore

JanS48
Navigator

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USA
141 Posts

Response Posted - 08/04/2015 : 19:50:38

Great info guys - thanks to much.

Jan

82 C25 SR FK
Sailing out of Newport Harbor.

Derek Crawford
Master Marine Consultant

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USA
3312 Posts

Response Posted - 08/05/2015 : 13:03:43

I once stuck the bow of a 24' Wavelength directly behind the stern pulpit of a C30 - we crossed the lake going to weather at just over 9 knots. What a ride! I guess that you can "draft" in a boat much like in Nascar...

Derek Crawford
Chief Measurer C25-250 2008
Previous owner of "This Side UP"
1981 C-25 TR/FK #2262 Used to have an '89 C22 #9483, "Downsized"
San Antonio, Texas

Dave5041
Former Mainsheet Editor

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USA
3754 Posts

Response Posted - 08/08/2015 : 20:57:42

Keep in mind that calculated hull speed is an "average" hull. A long, narrow hull, say a scull, can exceed that number without planing by penetrating the bow wave without riding over it and producing a trailing wave, while a barge requires excessive power to even reach it since it must ride up a bit to even keep the wave at the bow. Where precise location of the C-25 is in that range is undetermined, not that the max or min is likely to vary too much from the median.

Dave B. aboard Pearl
1982 TR/SK/Trad. #3399
Lake Erie/Florida Panhandle

Stinkpotter
Master Marine Consultant

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Djibouti
9013 Posts

Response Posted - 08/09/2015 : 09:43:50

My recollection on a beat in our SR/FK is that a little over 6 is all we could attain. That's the point of sail where planing is least likely or virtually impossible for a cruising monohull. So the theory is probably about right for that fairly normal hull.

On a broad reach, with a little help from quartering seas, we have gotten up on plane and exceeded 7 a few times--bow up and spray coming off at about mid-ship.

Sailboats with long overhangs fore and aft, when beating, tend to heel in such a way that the LWL increases substantially, thus increasing the THS beyond what the boat's standard measurement would suggest. That was the strategy behind the old Herreshoff designs like the New York 30--a 44' hull with a 30' LWL. Most measurement rules now are based on overall or deck length, so bows are plumb and in some cases transoms raked to achieve the longest waterline for the boat's measurements under a particular rule. They're always scheming!

Dave Bristle
Association "Port Captain" for Mystic/Stonington CT
PO of 1985 C-25 SR/FK #5032 Passage, USCG "sixpack" (expired),
Now on Eastern 27 $+!nkp*+ Sarge

Edited by - Stinkpotter on 08/09/2015 09:45:48

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