Exceeding Hull Speed in a 25D

[Lou Ostendorff]

Hello to All;
I was out sailing yesterday in the edges of TS Hanna with winds of 15 knots, gusting to maybe 20 or so...Karma was sailing fine with full canvas (no reefs) on her aging main and 100% Jib...I looked down at the GPS and it said 5.7 Knots...moving pretty good...then a long, gradual gust began and we picked up even more speed...the GPS said 5.9 Knots...(theoretical hull speed 5.84), then Karma started acting squirrelly and heeled way over, rounding up and slowing down...the helm was hard over trying to resist this action, but I felt I was sailing at the 'edge' of modern physics. We only had about a half hour of sailing left, so I didn't reef...but was wondering, from the old salts and sea captains...if the boat was trying to tell me she 'wanted to be reefed'...and is this normal behavior for our kind of boats, with stock rigging and some weather helm built in? TIA
Lou Ostendorff
CD25D Karma
Violating The Physical Laws of the Known Universe
Berthed in Havelock, NC



louosten@ipass.net

[Warren Kaplan]

Hello to All;
I was out sailing yesterday in the edges of TS Hanna with winds of 15 knots, gusting to maybe 20 or so...Karma was sailing fine with full canvas (no reefs) on her aging main and 100% Jib...I looked down at the GPS and it said 5.7 Knots...moving pretty good...then a long, gradual gust began and we picked up even more speed...the GPS said 5.9 Knots...(theoretical hull speed 5.84), then Karma started acting squirrelly and heeled way over, rounding up and slowing down...the helm was hard over trying to resist this action, but I felt I was sailing at the 'edge' of modern physics. We only had about a half hour of sailing left, so I didn't reef...but was wondering, from the old salts and sea captains...if the boat was trying to tell me she 'wanted to be reefed'...and is this normal behavior for our kind of boats, with stock rigging and some weather helm built in? TIA
Lou Ostendorff
CD25D Karma
Violating The Physical Laws of the Known Universe
Berthed in Havelock, NC

Lou,
Remember that GPS measures speed over the bottom (land), not thru the water. Sine Qua Non routinely exceeds hull speed via GPS if we have a good wind and we are also going in the same direction as the tide/current. The hull speed refers to speed thru the water. Not over land.
Being constantly heeled over (arbitrarily more than 25 degrees) and the resultant increase in weather helm (rounding up)if not mitigated by let's say dumping the traveler, means you should reef and possibly more than once. The fact that you even asked the question may in fact answer it for you if you believe in the old seaman's adage, "if you are even thinking about reefing you should" (or something like that).
Lot's of people know their boats sailing characteristics and will put in the first reef automatically if they get a steady 15 knots or so. Boat sails faster and more comfortably that way with better control. Each captain decides for him/herself when that reef point is.

Warren Kaplan
Sine Qua Non
CD27
Oyster Bay Harbor, NY



Setsail728@aol.com

[Neil Gordon]

First of all, as the boat heels, the waterline increases, so the theoretical hull speed increases as well.

As for winds and heeling and weather helm, I had similar conditions yesterday... full main and genoa and the wind piping up in the afternoon to more than 15 knots. I was on a beam reach with the rail closing in on the water. I was sailing fine, but was getting overpowered in the puffs, with serious weather helm and rounding up into the gust. I would have sailed more comfortably (and possibly faster) with a reef in the main.

It's all about physics. As the boat heels, the shape of the underwater part of the hull changes. It's no longer symetrical and behaves accordingly.


Regards, Neil
s/v LIQUIDITY
Cape Dory 28 #167



neil@nrgordon.com

[BobM]

Lou:

We have hit as high as ~6.5 sailing down wind under main only
with one reef in the sail. The boat was literally surfing from
one wave to the next and it must have been blowing 30+ knots.
The boat did get "squirrelly" as you described in your experience
and because we were going down wind she started oscillating back
and forth in what we call going into "death rolls". Once the
oscillation gets up it's momentum it's very hard to stop short
of letting her round up into the wind, which knocks her down.
I was also concerned about broaching the boat so made sure to
keep the stern square as possible to the fast approaching waves.
The waves were cresting but not curling so we were relatively
safe from being pooped in the cockpit. If the wind were to increase
further I would have gone under bare spars and trailed a warp
of line. Fortunately this did not happen and was glad to make
our intended port in a record time not seen since for many years.
It was exciting to say the least.

On another occasion I was in a night race serving as 2nd helmsman
on a C&C 25. It was blowing 30+ knots and the seas were curling
as we ran down wind on a 25 mile leg with spinnaker and full main
sail. The boat had a mechanical knot meter which was pegged at 8+
knots all the way down the leg. The boat is a fin keel with an out
board rudder and she surfed and skidded all over the place. It's
the first time I heard a boat groan from the rigging as the
rig was under tremendous stress from the sail we were carrying.
We also were doing "death rolls" oscillating back and forth,
which was very uncomfortable. I would have never done this without
our full crew of 5 on board. We needed all the movable ballast
and muscle we could get to keep her on her feet.

We had to gibe several times because while at the helm I could not
steer directly down wind without the boat starting to broach. So
we kind of zig-zag downwind at incredable speeds I have not sailed
since in a fin keel boat. Everytime we went down a wave I had to
get everyone of the crew to the stern of the boat to prevent her
from nosing into the next wave. We had a rooster tail behind us
and it was to this day the most exciting sail I have ever experienced
in my 40 plus years of sailing. BTW we won the race and the trophy
sits in our china cabinet as a reminder with all the other silver
trophies and glassware. As you can see I like to race as well
as cruise.

Bob
Ranger #144
CD25D 1984



ranger1442@hotmail.com

[Bob Dugan]

the GPS said 5.9 Knots...(theoretical hull speed 5.84)...

Becky and I had Cricket up to 7.1 knots for about five minutes during a squall off the Maine coast this summer. We had the main double reefed, and a No. 3 jib which was furled about half way. In addition to being on a broad reach, we probably had the current with us.

It was pretty wild!

Bob Dugan
Cricket CD25D #092
Wayland, MA



bdugan@stepzero.com

[JimL]

I found your comments interesting, as I've seen considerable difference in the accuracy of my knotmeter versus the GPS. I need to take the boat into the channel, at slack tide, and make up an "error chart" for my knotmeter. I believe it reads low because of the position of the impeller.... and it's probably the nature of the beast.

At any rate, the knotmeter is typically 1-1.5 knots slower than GPS speed. I've already tried time-to-distance on the GPS (based on constant speed under power) and it definitely tells the truth!

I sure need to take a coastal navigation course....if the GPS ever bombed, I'd have to follow all the other boats home on this "California Freeway" we call the Catalina Channel!



leinfam@earthlink.net

[Jeff Schmoyer]

It's all about physics. As the boat heels, the shape of the underwater part of the hull changes. It's no longer symetrical and behaves accordingly.

Hey Neil,

Agreed.

I'm wondering, however, about the optimal heel value.

Looking at the hull shape "by eyball" it doesn't seem like that much heel is needed to lengthen waterline by 5-10%,

Further, it appears again "by eyeball" that the hull symmetry is not that distorted with small heel angles, say 0-10 degrees.

I'm thinking physicist would seek to find the optimal heel angle of an Alberg design...a sort of sweet spot if you will...as a balance point the positive aspects of heel (lengthening of waterline) and the negative effects (increased and unevenly applied drag forces).

Now my sailing experience hints that with my CD 27 that sweet spot is around 10-15 degrees.

But I'd love to see a technical assessment...I'd imagine we'd want to conjure up some plots of the first derivatives of the above values....looking for where rates of change in parameters are equal (rather like the profit maximization problem in microeconomics).

Which brings me to my real thought...while I don't know if Alberg knew calculus or not, there's definitely a genius to his work. His designs are just right.

Jeff



jeff.schmoyer@iff.com

[Neil Gordon]

Jeff,

Exactly right... I sail best at about 10-15% of heel. After that, I'm not going any faster; it's just harder to control the boat.

BTW, the hull's symetry begins going out of whack at 1% of heel. Consider the keel and rudder as they go out of vertical. If you can lengthen the waterline by 5-10% by heeling... that's a longer waterline to leeward and a shorter waterline to windward? The more you heel the worse the ratio?

Regards, Neil
s/v LIQUIDITY
Cape Dory 28 #167



neil@nrgordon.com

[Neil Gordon]

>>I need to take the boat into the channel, at slack tide, and make up an "error chart" for my knotmeter.<<

If you can go out in a constant current, just run the course both ways and average your results.

>>I believe it reads low because of the position of the impeller...<<

Is the knotmeter adjustable? My standard horizon can be calibrated. But position is still important... and you get different results on port vs stbd tack. You also get different results depending on what size/type of critter is living in the impeller.

>>I sure need to take a coastal navigation course...<<

I remain a fan of paper charts, etc. I have a non-electronic depth meter on board, too.


Regards, Neil
s/v LIQUIDITY
Cape Dory 28 #167



neil@nrgordon.com

[Jeff Schmoyer]

Neil,

If you can lengthen the waterline by 5-10% by heeling... that's a longer waterline to leeward and a shorter waterline to windward? The more you heel the worse the ratio?

Hmmm. This is interesting topic. Hopefully more boat design gurus can weigh in, but...

I think I read somewhere that it's actually the change in the SHAPE of the waterline that matters in balance, and not so much the tilt of the keel.

I think it's true the fact that, as you heel the keel tilts and that isn't a good thing- because it lowers efficiency (more water can slip under the keel from high pressure side to low, lowering lift so you slip to leeward).

But I think I read that it's the waterline itself that hull determines balance in terms of directional stability/weather helm. At rest the waterline shape is sort of 'pointly oval', but as you heel it becomes a distorted oval(...e.g. bulging on one side more than the other). So yeah, as you say it, the leeward (more immersed) waterline would be longer.

But the key thing I'm think about: how much distortion at what angle is a function of the 3-D shape of the hull?

I guess it's how slack the bilges are, how the sides of the hull are curved. I understand it (which is probably quite imperfectly) the really GREAT hull shapes are those for which the shape doesn't change much for reasonable heel angles. It must be as if the up and down curve of the hull "absorbs" some of the distortion, thus giving you a bit of cushion.

You'd have a range of heels to play in before weather helm becomes too great.

And that- if I'm right and it's all this complex- is the best reason I can think of for having a sailboat with a hull designed by a truly gifted designer!

Jeff



jeff.schmoyer@iff.com

[Gary L.]

Lou,

Sailing is a balancing act. Although I am old, I am not salty enough, to explain it correctly, but sail trim (including reefing) has the effect of lessening the weather helm, and the strong tendencies to point into the wind. By reefing in heavy winds, you reduce the overpowering to that state of balance. As primarily a solo sailor, I tend to listen to weather forecast before I leave for a sail. If it is going to be heavy winds later on in the day, I reef as I set sail in the morning. This way I do not have to go forward to reduce sail later. A certain amount of weather helm is also necessary for me, so that I can tie off the helm (I plan on purchasing an autopilot this winter), so that I can go either forward or below for a short time.

As for speed. I have found that there are a variety of ways to check this. Foremost is checking my time over a measured distance. Usually between buoys or bridges (bridges or other fixed structures don't drift). Another way is to drop a piece of toilet paper at the bow or the boat and measure the time it takes to reach the stern. While approximate, it is usually close enough. I have and use the gps only as a backup to give my location to the Coast Guard in the event of one my most stupid antics. Fortunately for me, I have a Cape Dory, which is very forgiving of my stupid antics.

I hope this helps,

Gary Lapine
Red Witch III
CD30C, #339
Somerset, MA



dory26@attbi.com

[Larry DeMers]

Lou,

With our boats..really, any full keeled vessel, but especially the CCA designed hulls, we get a bit more hull into the water when heeled way over, which allows the LWL to increase, which then allows for a higher top end speed. Unfortunately, there is acompensating effect that also happens..increased weather helm, and decreased rudder bite! So as you heel, the boat suddenly wants to go faster due to increased hull length in the water (trying to pay attention the max hull speed rule), but it also wants to go into the wind like mad, since the boats center of effort has now changed big time due to extreme heeling. With the extreme angle the rudder is getting less and less good water to work in..and more nad more air mixed with the water. Eventually you get to the "squirrely" point, where the rudder seems tobe only partially working. You would be right in that observation, as the rudder actually has a boundary layer of air buildingup on it, from the leading edge going back. As this happens, the rudder effectively stalls out, since it is not in entirely in direct contact with water anymore. It is surrounded by bubbles of air, so it loses effectiveness. It is sort of 'cavitating'. That is why going down steep wave fronts is so risky, because as you accelerate, you will hit that speed where the rudder all of a sudden feels like it is hanging in mid air with no water around it..it is really stalled out and encapsulated in air bubbles..and is truly not effective until that layer can be removed thru speed reduction.

Similarly, keel baots being towed over their hull speed start to wander around the rudders set point, and as speed increases, the wandering increases proportionately to the speed, until the boat is out of control and breaks loose...or worse. An amateur built full sized wood replica of a Vikings Long Boat was destroyed this way a few years back, up in New Foundland, as they were being towed out of the ice fields. The ship could not stand the stresses of the high speed tow and buckled and sank. I am friends with their Navigator, who was on the towing vessel that day. It was as ad loss, as the builder was then diagnosed with cancer, and never got a chance to rebuild the ship again (as we had hoped he would try to do).

In your case, you had too much sail up, plain and simple, and were way outside the sailing envelope for that boat. Reduce the sail to a third reef and you would find that she handles like normal almost, except for higher windage effects. The noise is a lot higher of course. But it can be sailed if the right sail combo is present.


Larry DeMers
s/v DeLaMer
Cape Dory 30 Lake Superior

Hello to All;
I was out sailing yesterday in the edges of TS Hanna with winds of 15 knots, gusting to maybe 20 or so...Karma was sailing fine with full canvas (no reefs) on her aging main and 100% Jib...I looked down at the GPS and it said 5.7 Knots...moving pretty good...then a long, gradual gust began and we picked up even more speed...the GPS said 5.9 Knots...(theoretical hull speed 5.84), then Karma started acting squirrelly and heeled way over, rounding up and slowing down...the helm was hard over trying to resist this action, but I felt I was sailing at the 'edge' of modern physics. We only had about a half hour of sailing left, so I didn't reef...but was wondering, from the old salts and sea captains...if the boat was trying to tell me she 'wanted to be reefed'...and is this normal behavior for our kind of boats, with stock rigging and some weather helm built in? TIA
Lou Ostendorff
CD25D Karma
Violating The Physical Laws of the Known Universe
Berthed in Havelock, NC

demers@sgi.com

[Al Levesque]

I found your comments interesting, as I've seen considerable difference in the accuracy of my knotmeter versus the GPS....

Since using a GPS I have uncovered more currents that I never realized existed but recall my father telling me about years ago. For example, we have tidal currents some distance offshore that run parallel to the coast. Inshore, the currents are all over the place. Now that I watch for them, I can see them at the lobster pots and navigational aids.

This realization that there are currents in many places has helped me to understand some memorable navigation errors when I had used speed through the water with assumption of no currents. I never use the speed through the water for navigating anymore. There just isn't enough current data to make it usable. When the data is available, the work to calculate over several hours of changes becomes tiresome and error prone.

Al



albertlevesque@cove.com

[Larry DeMers]

Generally speaking, the optimum angle for sailing a CD is 20 degress heel, not more. Any more than this spills too much wind out of the sails. Any less, and there is still more LWL to immerse. Practically, 15-20 deg. is about right.

Larry DeMers
s/v DeLaMer
Cape Dory 30

It's all about physics. As the boat heels, the shape of the underwater part of the hull changes. It's no longer symetrical and behaves accordingly.

Hey Neil,

Agreed.

I'm wondering, however, about the optimal heel value.

Looking at the hull shape "by eyball" it doesn't seem like that much heel is needed to lengthen waterline by 5-10%,

Further, it appears again "by eyeball" that the hull symmetry is not that distorted with small heel angles, say 0-10 degrees.

I'm thinking physicist would seek to find the optimal heel angle of an Alberg design...a sort of sweet spot if you will...as a balance point the positive aspects of heel (lengthening of waterline) and the negative effects (increased and unevenly applied drag forces).

Now my sailing experience hints that with my CD 27 that sweet spot is around 10-15 degrees.

But I'd love to see a technical assessment...I'd imagine we'd want to conjure up some plots of the first derivatives of the above values....looking for where rates of change in parameters are equal (rather like the profit maximization problem in microeconomics).

Which brings me to my real thought...while I don't know if Alberg knew calculus or not, there's definitely a genius to his work. His designs are just right.

Jeff

demers@sgi.com

[Dana]

Lou,

Doesn't surprise me about your speed having sailed the CD25D myself and noting it is very similar to my CD26. My guess is you were sailing off the wind with a following sea. Not unusual, especially if your hull speed was close to matching the wave speed for your direction of sail. You can get those long surge effects coupled with a decrease in the amount of bow wave in front of the boat to "sail over" so the hull speed formula rule is bent a bit. As a following wave passes it wants to pick up the back of the boat and move it forward..ahead of the bow..sort of twisting if you are not directly going downwind as your boat starts to sail down the wave. In some boats this action is severe and can lead to broaching. Unless you are sailing directly downwind when the passing wave goes by, you have the natural tendency to correct the boat directional stability by turning the boat in the direction with the passing wave until it passes. This is because your stern is trying to "walk around" your bow. I have heard (maybe incorrectly) that canoe sterns may handle the directional stability better...

Dana

_____________________________________________

Hello to All;
I was out sailing yesterday in the edges of TS Hanna with winds of 15 knots, gusting to maybe 20 or so...Karma was sailing fine with full canvas (no reefs) on her aging main and 100% Jib...I looked down at the GPS and it said 5.7 Knots...moving pretty good...then a long, gradual gust began and we picked up even more speed...the GPS said 5.9 Knots...(theoretical hull speed 5.84), then Karma started acting squirrelly and heeled way over, rounding up and slowing down...the helm was hard over trying to resist this action, but I felt I was sailing at the 'edge' of modern physics. We only had about a half hour of sailing left, so I didn't reef...but was wondering, from the old salts and sea captains...if the boat was trying to tell me she 'wanted to be reefed'...and is this normal behavior for our kind of boats, with stock rigging and some weather helm built in? TIA
Lou Ostendorff
CD25D Karma
Violating The Physical Laws of the Known Universe
Berthed in Havelock, NC

darenius@aol.com