I own a Newport 33 which has a waterline length of 27 ft. According to
the formula, the theoretical speed for the boat is 6.96 knots.
I have a 16 HP diesel with a 2 bladed impeller, and a maximum engine
RPM of 3300 RPM. Running the engine at 2700 RPM I can readily reach 6.5
knots.
In a good wind I can go to 7 knots. The maximum speed I have ever done
was 11 knots on the GPS surfing down a wave with full sails up on a
very broad reach in about 30 knot wind. Many other boats of the same
design ( relatively light displacemnt, fin keel and spade rudder)
report he same thing.
Racing boats in the around-the world alone race routinely exceeded hull
speed for long periods surfing down waves. The hull speed for a 60 ft
boat is 10.4 knots andthey were achieving more than 20 knots I seem to
remember. So that is the way to go faster than hull speed, find a wave
and then surf down.
Catamarans also go faster than hull speed all the time. So if you put
enough power into the boat in relation to the displacement and wetted
surface, you can exceed the Hull speed.

I think that traditional full keel boat with a high displacement would
have a lot of trouble getting close to Hull speed.
Rolf


Jeff wrote:
However, there are games played with multihulls so that the waves
from
one hull cancel the wave from the other. For one thing, this must be

considered to understand how the chop will slap on the underside.

However, advanced work has been done on more complex configurations
of
three or four hulls with an eye towards high speed and efficiency. I

don't think this has led to any recreational sailboat designs.


Roger Long wrote:
The float would have a hull speed limitation based on it's length.
If
it was shorter than the main hull, it would be a big drag.

Rolf wrote:

I own a Newport 33 which has a waterline length of 27 ft. According to
the formula, the theoretical speed for the boat is 6.96 knots.
I have a 16 HP diesel with a 2 bladed impeller, and a maximum engine
RPM of 3300 RPM. Running the engine at 2700 RPM I can readily reach 6.5
knots.
In a good wind I can go to 7 knots. The maximum speed I have ever done
was 11 knots on the GPS surfing down a wave with full sails up on a
very broad reach in about 30 knot wind. Many other boats of the same
design ( relatively light displacemnt, fin keel and spade rudder)
report he same thing.
Racing boats in the around-the world alone race routinely exceeded hull
speed for long periods surfing down waves. The hull speed for a 60 ft
boat is 10.4 knots andthey were achieving more than 20 knots I seem to
remember. So that is the way to go faster than hull speed, find a wave
and then surf down.
Catamarans also go faster than hull speed all the time. So if you put
enough power into the boat in relation to the displacement and wetted
surface, you can exceed the Hull speed.

I think that traditional full keel boat with a high displacement would
have a lot of trouble getting close to Hull speed.
Rolf

Hull speed is the absolute maximum that boat can travel through water.
All your examples have the water moving forward also so the boat is not
exceeding hull speed through the water.

Stephen

Actually, the water does not move forward in a wave but you are right
that the surfing examples are irrelevant examples since the waves are
pushing the boat forward in other ways.

The speed length ratio of the Newport 33 at 7 knots would be 1.35,
just a hair above the generally accepted displacement hull maximum of
1.33. If the hull has an easy run, the counter becomes part of the
waterline length as the stern waves rise up under it. Adding a foot
brings the ratio down to 1.32, exactly what you would expect for an
easy hull like that one.

--

Roger Long



"Stephen Trapani" wrote in message
...
Rolf wrote:

I own a Newport 33 which has a waterline length of 27 ft.
According to
the formula, the theoretical speed for the boat is 6.96 knots.
I have a 16 HP diesel with a 2 bladed impeller, and a maximum
engine
RPM of 3300 RPM. Running the engine at 2700 RPM I can readily reach
6.5
knots.
In a good wind I can go to 7 knots. The maximum speed I have ever
done
was 11 knots on the GPS surfing down a wave with full sails up on a
very broad reach in about 30 knot wind. Many other boats of the
same
design ( relatively light displacemnt, fin keel and spade rudder)
report he same thing.
Racing boats in the around-the world alone race routinely exceeded
hull
speed for long periods surfing down waves. The hull speed for a 60
ft
boat is 10.4 knots andthey were achieving more than 20 knots I seem
to
remember. So that is the way to go faster than hull speed, find a
wave
and then surf down.
Catamarans also go faster than hull speed all the time. So if you
put
enough power into the boat in relation to the displacement and
wetted
surface, you can exceed the Hull speed.

I think that traditional full keel boat with a high displacement
would
have a lot of trouble getting close to Hull speed.
Rolf

Hull speed is the absolute maximum that boat can travel through
water. All your examples have the water moving forward also so the
boat is not exceeding hull speed through the water.

Stephen

In article ,
Stephen Trapani wrote:

Hull speed is the absolute maximum that boat can travel through water.
All your examples have the water moving forward also so the boat is not
exceeding hull speed through the water.

I thought I mentioned this before. Hope I'm not repeating myself.

Hull speed is a suggestion for our boat, not the law. Though our
theoretical hull speed is 6.65 knots, we regularly exceed that with
aplomb, close hauled, close reach, broad reach, whatever point of sail.
Spent a wonderful afternoon with 6 other sailors last season. As long as
I was on the tiller, pushing her to where she likes to be, we were well
above the theoretical hull speed. As we pinched to get back into the
harbor, she insisted on doing over 7 knots directly into the wind (okay,
about 15 degrees off). That last was our lovely lady showing off, of
course, as what we did was clearly impossible.

1.34 was derived from observing boats about a century ago. Depending on
the hull, that constant can be quite a bit different. As I recall, some
multi-hull boats' K is in the 2 or 3 range. Xan's fat ass and sharp
transom keeps her driving towards a 1.7 or so constant.

--
Jere Lull
Xan-a-Deux ('73 Tanzer 28 #4 out of Tolchester, MD)
Xan's Pages: http://members.dca.net/jerelull/X-Main.html
Our BVI FAQs (290+ pics) http://homepage.mac.com/jerelull/BVI/

On Sat, 16 Apr 2005 22:22:00 GMT, Jere Lull wrote:

In article ,
Stephen Trapani wrote:

Hull speed is the absolute maximum that boat can travel through water.
All your examples have the water moving forward also so the boat is not
exceeding hull speed through the water.

I thought I mentioned this before. Hope I'm not repeating myself.

Hull speed is a suggestion for our boat, not the law. Though our
theoretical hull speed is 6.65 knots, we regularly exceed that with
aplomb, close hauled, close reach, broad reach, whatever point of sail.
Spent a wonderful afternoon with 6 other sailors last season. As long as
I was on the tiller, pushing her to where she likes to be, we were well
above the theoretical hull speed. As we pinched to get back into the
harbor, she insisted on doing over 7 knots directly into the wind (okay,
about 15 degrees off). That last was our lovely lady showing off, of
course, as what we did was clearly impossible.

1.34 was derived from observing boats about a century ago. Depending on
the hull, that constant can be quite a bit different. As I recall, some
multi-hull boats' K is in the 2 or 3 range. Xan's fat ass and sharp
transom keeps her driving towards a 1.7 or so constant.

Jere,

It sounds like your speed-length parameter is higher than 1.34 - a
testimonial to your hull designer.

The 1.34 comes from the fact that speed-squared of a wave = g/2*pi
times wavelength.

If your hull's stern really places the stern wave a distance back from
the bow wave equal to your design waterline length, then 1.34 is
pretty accurate as the point where the curve of additional HP to yield
additional speed for a displacement hull becomes almost vertical.

However, with sweet butock lines, stern reflexes and other
sophistications of hull design, the stern wave can actually be moved a
bit aft of your transom. The wavelength thus becomes greater than your
DWL.

Since speed-squared is proportional to wavelength, and since your boat
speed and the wave speed must match, you get a speed-length parameter
that's higher than 1.34 as the effective multiplier times the square
root of your DWL (since DWL is now less than the wavelength).

At least that's my simplified understanding of a very complex subject.

Al
s/v Persephone
Newburyport, MA

In article ,
Albert P. Belle Isle wrote:

On Sat, 16 Apr 2005 22:22:00 GMT, Jere Lull wrote:

In article ,
Stephen Trapani wrote:

Hull speed is the absolute maximum that boat can travel through water.
All your examples have the water moving forward also so the boat is not
exceeding hull speed through the water.

Hull speed is a suggestion for our boat, not the law. Though our
theoretical hull speed is 6.65 knots, we regularly exceed that with
aplomb, close hauled, close reach, broad reach, whatever point of sail.
Spent a wonderful afternoon with 6 other sailors last season. As long as
I was on the tiller, pushing her to where she likes to be, we were well
above the theoretical hull speed. As we pinched to get back into the
harbor, she insisted on doing over 7 knots directly into the wind (okay,
about 15 degrees off). That last was our lovely lady showing off, of
course, as what we did was clearly impossible.

1.34 was derived from observing boats about a century ago. Depending on
the hull, that constant can be quite a bit different. As I recall, some
multi-hull boats' K is in the 2 or 3 range. Xan's fat ass and sharp
transom keeps her driving towards a 1.7 or so constant.

Jere,

It sounds like your speed-length parameter is higher than 1.34 - a
testimonial to your hull designer.

Full agreement.

The 1.34 comes from the fact that speed-squared of a wave = g/2*pi
times wavelength.

Yes, I agree with the derivation of the formula -- as long as we include
that wavelengths can differ. Swells have wavelengths 100s of feet and
periods many seconds from crest to crest, while wind-driven waves have
quite a bit shorter wavelengths and periods. And wind-driven waves have
different periods and wavelengths.

If your hull's stern really places the stern wave a distance back from
the bow wave equal to your design waterline length, then 1.34 is
pretty accurate as the point where the curve of additional HP to yield
additional speed for a displacement hull becomes almost vertical.

However, with sweet butock lines, stern reflexes and other
sophistications of hull design, the stern wave can actually be moved a
bit aft of your transom. The wavelength thus becomes greater than your
DWL.

Our resting WL is 24'. To maintain a 1.34 constant and get the speeds
we've verified while definitely not surfing, our effective waterline
would have to be greater than 35'. That's a LONG way behind our transom!

Since speed-squared is proportional to wavelength, and since your boat
speed and the wave speed must match, you get a speed-length parameter
that's higher than 1.34 as the effective multiplier times the square
root of your DWL (since DWL is now less than the wavelength).

It feels like you left a bit out and mixed a couple of things here.
Again, I agree that it probably has something to do with the wave speed,
which has a certain value when the constant is 1.34. Change the wave's
speed and you change the constant, and wave length.

At least that's my simplified understanding of a very complex subject.

Al
s/v Persephone

After having chased several NA's explanations for a few years, I finally
gave up trying to explain and simply accept that it's more complex than
1.34, since other hull shapes have much higher observed constants.

--
Jere Lull
Xan-a-Deux ('73 Tanzer 28 #4 out of Tolchester, MD)
Xan's Pages: http://members.dca.net/jerelull/X-Main.html
Our BVI FAQs (290+ pics) http://homepage.mac.com/jerelull/BVI/

On Mon, 25 Apr 2005 04:06:45 GMT, Jere Lull wrote:

In article ,
Albert P. Belle Isle wrote:

On Sat, 16 Apr 2005 22:22:00 GMT, Jere Lull wrote:

In article ,
Stephen Trapani wrote:

Hull speed is the absolute maximum that boat can travel through water.
All your examples have the water moving forward also so the boat is not
exceeding hull speed through the water.

Hull speed is a suggestion for our boat, not the law. Though our
theoretical hull speed is 6.65 knots, we regularly exceed that with
aplomb, close hauled, close reach, broad reach, whatever point of sail.
Spent a wonderful afternoon with 6 other sailors last season. As long as
I was on the tiller, pushing her to where she likes to be, we were well
above the theoretical hull speed. As we pinched to get back into the
harbor, she insisted on doing over 7 knots directly into the wind (okay,
about 15 degrees off). That last was our lovely lady showing off, of
course, as what we did was clearly impossible.

1.34 was derived from observing boats about a century ago. Depending on
the hull, that constant can be quite a bit different. As I recall, some
multi-hull boats' K is in the 2 or 3 range. Xan's fat ass and sharp
transom keeps her driving towards a 1.7 or so constant.

Jere,

It sounds like your speed-length parameter is higher than 1.34 - a
testimonial to your hull designer.

Full agreement.

The 1.34 comes from the fact that speed-squared of a wave = g/2*pi
times wavelength.

Yes, I agree with the derivation of the formula -- as long as we include
that wavelengths can differ. Swells have wavelengths 100s of feet and
periods many seconds from crest to crest, while wind-driven waves have
quite a bit shorter wavelengths and periods. And wind-driven waves have
different periods and wavelengths.

If your hull's stern really places the stern wave a distance back from
the bow wave equal to your design waterline length, then 1.34 is
pretty accurate as the point where the curve of additional HP to yield
additional speed for a displacement hull becomes almost vertical.

However, with sweet butock lines, stern reflexes and other
sophistications of hull design, the stern wave can actually be moved a
bit aft of your transom. The wavelength thus becomes greater than your
DWL.

Our resting WL is 24'. To maintain a 1.34 constant and get the speeds
we've verified while definitely not surfing, our effective waterline
would have to be greater than 35'. That's a LONG way behind our transom!

Since speed-squared is proportional to wavelength, and since your boat
speed and the wave speed must match, you get a speed-length parameter
that's higher than 1.34 as the effective multiplier times the square
root of your DWL (since DWL is now less than the wavelength).

It feels like you left a bit out and mixed a couple of things here.
Again, I agree that it probably has something to do with the wave speed,
which has a certain value when the constant is 1.34. Change the wave's
speed and you change the constant, and wave length.

At least that's my simplified understanding of a very complex subject.

Al
s/v Persephone

After having chased several NA's explanations for a few years, I finally
gave up trying to explain and simply accept that it's more complex than
1.34, since other hull shapes have much higher observed constants.

The physics says that extra-long-wavelength swells just propagate more
slowly. The c-squared = lambda*g/2pi is pretty fundamental for surface
waves (as opposed to deep pressure waves, like tsunamis).

There's a passage in John Craven's "The Silent War" where he gleefully
chants the formula from the sail of a nuclear submarine as he watches
her bow and stern waves demonstrate the validity of something he had
drilled into his head in grad school. Maybe you have to be a geek to
appreciate it g.

However, the oversimplified nature of my "push-the-stern-wave-aft"
explanation is, of course, quite true. IANA.

If you haven't already read it, Jere, van Dorn's "Oceanography and
Seamanship" has a pretty good discussion of the speed-power curves for
planing, semiplaning and displacement hulls - as well as, among other
things, a nifty nomograph for predicting sea-state from duration or
fetch of sustained winds.

Good sailing.

Al
s/v Persephone

On Mon, 25 Apr 2005 20:16:09 GMT, Albert P. Belle Isle
wrote:


Our resting WL is 24'. To maintain a 1.34 constant and get the speeds
we've verified while definitely not surfing, our effective waterline
would have to be greater than 35'. That's a LONG way behind our transom!


Jere -

As a quick calculation, 24ft DWL would yield a hull speed of about
6.6kt with a speed-length coefficient of 1.34. To get to 7kt, the
effective DWL at 1.34 would be a little over 27ft - not 35ft.

My previous boat had a DWL of 28ft, for which a speed-length
coefficient of 1.34 would predict 7.1kt.

I easily got 7.4kt on beam reaches, which would say my real
coefficient was almost 1.4 (or that my effective DWL at 1.34 was a
little over 30ft - a two foot "push-back" of the sten wave, which was
roughly how the peak of the stern wave looked from my cockpit.

Regards,
Al

On Mon, 25 Apr 2005 04:06:45 GMT, Jere Lull wrote:

In article ,
Albert P. Belle Isle wrote:

On Sat, 16 Apr 2005 22:22:00 GMT, Jere Lull wrote:

In article ,
Stephen Trapani wrote:

Hull speed is the absolute maximum that boat can travel through water.
All your examples have the water moving forward also so the boat is not
exceeding hull speed through the water.

Hull speed is a suggestion for our boat, not the law. Though our
theoretical hull speed is 6.65 knots, we regularly exceed that with
aplomb, close hauled, close reach, broad reach, whatever point of sail.
Spent a wonderful afternoon with 6 other sailors last season. As long as
I was on the tiller, pushing her to where she likes to be, we were well
above the theoretical hull speed. As we pinched to get back into the
harbor, she insisted on doing over 7 knots directly into the wind (okay,
about 15 degrees off). That last was our lovely lady showing off, of
course, as what we did was clearly impossible.

1.34 was derived from observing boats about a century ago. Depending on
the hull, that constant can be quite a bit different. As I recall, some
multi-hull boats' K is in the 2 or 3 range. Xan's fat ass and sharp
transom keeps her driving towards a 1.7 or so constant.

Jere,

It sounds like your speed-length parameter is higher than 1.34 - a
testimonial to your hull designer.

Full agreement.

The 1.34 comes from the fact that speed-squared of a wave = g/2*pi
times wavelength.

Yes, I agree with the derivation of the formula -- as long as we include
that wavelengths can differ. Swells have wavelengths 100s of feet and
periods many seconds from crest to crest, while wind-driven waves have
quite a bit shorter wavelengths and periods. And wind-driven waves have
different periods and wavelengths.

If your hull's stern really places the stern wave a distance back from
the bow wave equal to your design waterline length, then 1.34 is
pretty accurate as the point where the curve of additional HP to yield
additional speed for a displacement hull becomes almost vertical.

However, with sweet butock lines, stern reflexes and other
sophistications of hull design, the stern wave can actually be moved a
bit aft of your transom. The wavelength thus becomes greater than your
DWL.

Our resting WL is 24'. To maintain a 1.34 constant and get the speeds
we've verified while definitely not surfing, our effective waterline
would have to be greater than 35'. That's a LONG way behind our transom!

Since speed-squared is proportional to wavelength, and since your boat
speed and the wave speed must match, you get a speed-length parameter
that's higher than 1.34 as the effective multiplier times the square
root of your DWL (since DWL is now less than the wavelength).

It feels like you left a bit out and mixed a couple of things here.
Again, I agree that it probably has something to do with the wave speed,
which has a certain value when the constant is 1.34. Change the wave's
speed and you change the constant, and wave length.

At least that's my simplified understanding of a very complex subject.

Al
s/v Persephone

After having chased several NA's explanations for a few years, I finally
gave up trying to explain and simply accept that it's more complex than
1.34, since other hull shapes have much higher observed constants.


It isn't a different constant. It is just that many boats nowadays are
light enough so they aren't limited to the length of the wave they
make.

If you observe a tug traveling without a tow, you will see very easily
what wave we are talking about.



Rodney Myrvaagnes NYC J36 Gjo/a


"Curse thee, thou quadrant. No longer will I guide my earthly way by thee." Capt. Ahab

Stephen Trapani wrote:
Hull speed is the absolute maximum that boat can travel through water.

Not really. "Hull Speed" is sort of a convenient shorthand for
indicating where the graph of a vessel's speed vs power begins to get
inconveniently steep.


All your examples have the water moving forward also so the boat is not
exceeding hull speed through the water.

Even catamarans? How about planing types?

DSK