Flemming Torp wrote:
"Roger Long" skrev i en meddelelse
...

OK, here is the answer you are looking for.

Unless you have a highly unusual powertrain set up and
strangely pitched prop, determine the position in which
the most blade area is shadowed by keel and hull. Mark
the shaft inside. Stop the shaft in that position. Sail
the boat. It's very unlikely you'll go faster doing
anything else.

Now we are getting close to 'basics' Roger ... but, but ...
as I wrote in the introduction, it has so far been very
difficult to get hard evidence from the log when trying to
let the propeller run and have it locked, as the speed of
the boat is a function of so many things, and I'm convinced
that there is not a big difference - so may be my question
is of a more theoretical type, as reliable data are hard to
get in the real world ... In a bassin, it might be easier
... I have seen som reports, where different kinds of
propellers - folding with two blades, folding with three
blades, fixed with three baldes etc. were compared ... and
the result indicated differences in 'thrust' and in speed
up to between ½ - 1 in worst case ... But I have not seen
any reports on the comparison between a locked and a free
wheeling propeller ... but I have certainly got a lot of
input ... also from the aviation world, that I know nothing
about ... thank you.

But your final proposal is very logical, operational and
easy to implement ... when the water gets warmer, we might
do what you have recommended ... or do as Larry - use the
energy coming from the rotating propeller - og invest in a
folding propeller ... time will show, and thank you so much
for your keen interest in learning me some physics ...



Roger's advice is correct, but it does sidestep your original
question. Locking a prop in the "shadow of the hull" is generally a
winner. Even with a 3-blade prop you should have one blade lined up
with the hull. With a two blade prop the gain can easily be enough to
win a race, or come in before dark on long passage.

I've heard of two studies that addressed this. One, a publicized MIT
study showed that free-wheeling had less drag. However, this did not
directly model yacht props so it really doesn't apply. (In fact,
their prop wasn't actually free, it was powered at a speed that
minimized turbulence.) Other study, which I've heard of third hand,
"proved" that locked was less drag for yacht props. Dave Gerr, in his
"propeller Handbook," says rotating is less drag (unless you can lock
it behind the keel) but he doesn't give a reason or cite a reference.

Consider two cases: first take a hypothetical "flat prop" with zero
pitch. Obvious, it won't spin and it will have a lot of turbulence,
indicating a lot of drag. Now give it a bit a pitch. It will start
to spin, but the small pitch will mean that it has to spin very fast
fast to match the boat speed. Since it can't, there will still be a
huge amount of turbulence. Will it be less than the flat blade? Hard
to say, because there are a variety of factors - the shape of the
turbulence is different and the rotation means that a larger volume of
water is disturbed. This approximates the yacht prop where the free
rotation is very unlikely to match the boat speed and the turbulence
will be high and quite complex.

Now consider a feathering prop, where the blades are lined up with the
flow and cause no turbulence. Give them a some pitch - as long as the
flow is smooth there will be little drag. Increase the pitch
(actually a smaller number since feathering the pitch is infinite) to
the fastest spin with low turbulence. The drag will still be low at
this point. Now lock it - the turbulence (and the drag) will jump
up. Here's a case where the free rotating prop will have less drag
than the locked one, but it probably does not resemble a typical yacht
prop. It does come close to large ship props, so its not surprising
that there are some studies and anecdotal evidence from other forms of
props, that say free wheeling is less drag.

My point is (as I mentioned in my first post) that its impossible to
determine intuitively the drag for the case of a yacht prop, where the
turbulence is high whether locked or not, and analogies from other
type of props simply don't apply. The issue of the heat buildup in
the transmission is a "red herring." It is a significant side issue,
since yacht transmissions do have a lot of friction, and thus heat
problems, when free wheeling, but the dominant factor is the
turbulence. This approach tries to measure the energy extracted from
the water by the work done by the shaft, but this is only valid if the
turbulence is low and the prop is working in a relatively efficient
mode. When the turbulence is high, most of the energy goes into
heating the water, and this is rather difficult to measure.

In article , "Flemming Torp" fletopkanelbolle2rp.danmark wrote:


I'm not sure I get your conclusion ... ;-) Sorry, but do
you recommend me to let the propeller turn og should I stop
it from turning, if I'm only concerned with the speed of the
sailboat - when only using the sails?


I guess I'm too long winded.

It is my guess that a freely turning propellor would produce
less drag than a locked propellor. This is assuming that
there is no load on thepropellor other than the friction of
the bearings that support the propellor shaft.

Why 65 replies on a simple question. Amazing. ;-)

Now tackle this one...how many sailors does it take to screw in a light
bulb?

In "*JimH*" writes:

Why 65 replies on a simple question. Amazing. ;-)

Because it is not as simple as you and the majority of posters seem to
think. By the way this discussion is repeated about once in three years
and same unfounded arguments and simplifications are represented over
and over again.

Now tackle this one...how many sailors does it take to screw in a light
bulb?

There are not enough wise men to enlighten the ones that prefers to stay
ignorant. Looks like no lightbulbs are needed.

- Lauri Tarkkonen

In HarryKrause writes:

Lauri Tarkkonen wrote:
In "*JimH*" writes:


Why 65 replies on a simple question. Amazing. ;-)


Because it is not as simple as you and the majority of posters seem to
think. By the way this discussion is repeated about once in three years
and same unfounded arguments and simplifications are represented over
and over again.

Jim Hertvik (JimH) doesn't actually have a boat, and, when he claimed he
last had one, he said he spent most of his time aboard it while it was
tied to a marina's dock in southern Lake Erie. Thus, a discussion about
feathering or engaging a sailboat prop would not be something to which
he could contribute, at least not from a point of knowledge.

Perhaps his point of discussion is arrogance.

- Lauri Tarkkonen

"Lauri Tarkkonen" wrote in message
...
In HarryKrause
writes:

Lauri Tarkkonen wrote:
In "*JimH*" writes:


Why 65 replies on a simple question. Amazing. ;-)


Because it is not as simple as you and the majority of posters seem to
think. By the way this discussion is repeated about once in three years
and same unfounded arguments and simplifications are represented over
and over again.

Jim Hert (JimH) doesn't actually have a boat, and, when he claimed he
last had one, he said he spent most of his time aboard it while it was
tied to a marina's dock in southern Lake Erie. Thus, a discussion about
feathering or engaging a sailboat prop would not be something to which
he could contribute, at least not from a point of knowledge.

Perhaps his point of discussion is arrogance.

- Lauri Tarkkonen


Not at all Lauri.

First of all, if my original post offended you or anyone in this NG I
apologize. It was certainly a brain fart on my part as I certainly respect
the nautical and operational knowledge I have personally observed from most
of the sailors I have had the opportunity of meeting or observed in action.

As to my boating experience that Harry Krause questions: We have owned
boats for over 25 years. We had to sell our 32 footer at the end of the
2003 season due to my wife's medical condition, a condition that caused her
to take a medical retirement from her teaching career. Krause knows that
yet for some reason shows little consideration for that fact. That alone
should speak loudly of his moral character.

Yes, we are currently boatless but hope to purchase a smaller more
manageable (for me) boat in 4 years when we retire riverside (Huron River
off Lake Erie).

We live in Northern Ohio and would normally log 55-80 hours on the boat
annually....not many hours according to hard core fishermen or year round
boaters, but we did indeed spend every weekend on the boat as well as 2 full
vacation weeks during our summer vacation. We would use our boats mainly
for cruising to swimming spots or (as in the case of our 27 and 32 footers)
cruise to various ports in Canada and Michigan. Overnight trips on the hook
in protected areas were magnificent. And to the surprise of Harry Krause,
we would actually spend weekends on our boat (along with our 2 children)
even when the weather/Lake conditions were bad, spending time at the marina.
Our fishing would be limited to early season (me and my buddies) walleye
fishing and late season perch fishing.

Our children fondly recall our time on the boats (they are now 17 and 20
years old respectively) and I would not give up our experience on our boats
as a family (even though they do not meet Harry Krause's requirements).
Our children were with us on the boat since the age of 6 months.

Do not pay attention to Harry Krause. He is a bitter old man who for some
reason has to spend his time posting personal attacks on folks who disagree
with him politically. I actually feel sorry for the guy.

"*JimH*" wrote in message
...

"Lauri Tarkkonen" wrote in message
...
In HarryKrause
writes:

Lauri Tarkkonen wrote:
In "*JimH*"
writes:


Why 65 replies on a simple question. Amazing. ;-)


Because it is not as simple as you and the majority of posters seem to
think. By the way this discussion is repeated about once in three years
and same unfounded arguments and simplifications are represented over
and over again.

Jim Hertvik (JimH) doesn't actually have a boat, and, when he claimed he
last had one, he said he spent most of his time aboard it while it was
tied to a marina's dock in southern Lake Erie. Thus, a discussion about
feathering or engaging a sailboat prop would not be something to which
he could contribute, at least not from a point of knowledge.

Perhaps his point of discussion is arrogance.

- Lauri Tarkkonen


Not at all Lauri.

First of all, if my original post offended you or anyone in this NG I
apologize. It was certainly a brain fart on my part as I certainly
respect the nautical and operational knowledge I have personally observed
from most of the sailors I have had the opportunity of meeting or observed
in action.

As to my boating experience that Harry Krause questions: We have owned
boats for over 25 years. We had to sell our 32 footer at the end of the
2003 season due to my wife's medical condition, a condition that caused
her to take a medical retirement from her teaching career. Krause knows
that yet for some reason shows little consideration for that fact. That
alone should speak loudly of his moral character.

Yes, we are currently boatless but hope to purchase a smaller more
manageable (for me) boat in 4 years when we retire riverside (Huron River
off Lake Erie).

We live in Northern Ohio and would normally log 55-80 hours on the boat
annually....not many hours according to hard core fishermen or year round
boaters, but we did indeed spend every weekend on the boat as well as 2
full vacation weeks during our summer vacation. We would use our boats
mainly for cruising to swimming spots or (as in the case of our 27 and 32
footers) cruise to various ports in Canada and Michigan. Overnight trips
on the hook in protected areas were magnificent. And to the surprise of
Harry Krause, we would actually spend weekends on our boat (along with our
2 children) even when the weather/Lake conditions were bad, spending time
at the marina. Our fishing would be limited to early season (me and my
buddies) walleye fishing and late season perch fishing.

Our children fondly recall our time on the boats (they are now 17 and 20
years old respectively) and I would not give up our experience on our
boats as a family (even though they do not meet Harry Krause's
requirements). Our children were with us on the boat since the age of 6
months.

Do not pay attention to Harry Krause. He is a bitter old man who for some
reason has to spend his time posting personal attacks on folks who
disagree with him politically. I actually feel sorry for the guy.




BTW: For your information about this person posting as Harry Krause:

1. He has stalked me and my family on the internet because my political
views did not agree with is.

2. He subsequently posted my real name (I had posted under an alias for
obvious reasons), address and wife's name to rec.boats.

3. He obtained a picture or our house via the internet.

4. He made personal threats to me and my wife.

As a result we have tracked Harry Krause's posts and continued threats to us
and forwarded them to our attorney.

He has admitted to all these things in rec.boats.

There are many active member of rec.boats.cruising who can attest to this
type of behavior by Harry Krause as similar things happened to them.

He is a sick man and I suggest you treat him with caution.

On Tue, 07 Jun 2005 15:43:23 -0400, HarryKrause wrote:

Lauri Tarkkonen wrote:
In "*JimH*" writes:


Why 65 replies on a simple question. Amazing. ;-)


Because it is not as simple as you and the majority of posters seem to
think. By the way this discussion is repeated about once in three years
and same unfounded arguments and simplifications are represented over
and over again.

- Lauri Tarkkonen


Jim Hertvik (JimH) doesn't actually have a boat, and, when he claimed he
last had one, he said he spent most of his time aboard it while it was
tied to a marina's dock in southern Lake Erie. Thus, a discussion about
feathering or engaging a sailboat prop would not be something to which
he could contribute, at least not from a point of knowledge.

Are you not able to make enough personal attacks in rec.boats?
--
John H

"All decisions are the result of binary thinking."

"John H" wrote in message
...
On Tue, 07 Jun 2005 15:43:23 -0400, HarryKrause
wrote:

Lauri Tarkkonen wrote:
In "*JimH*" writes:


Why 65 replies on a simple question. Amazing. ;-)


Because it is not as simple as you and the majority of posters seem to
think. By the way this discussion is repeated about once in three years
and same unfounded arguments and simplifications are represented over
and over again.

- Lauri Tarkkonen


Jim Hertvik (JimH) doesn't actually have a boat, and, when he claimed he
last had one, he said he spent most of his time aboard it while it was
tied to a marina's dock in southern Lake Erie. Thus, a discussion about
feathering or engaging a sailboat prop would not be something to which
he could contribute, at least not from a point of knowledge.

Are you not able to make enough personal attacks in rec.boats?
--
John H



The simple answer is..........................................NO.

Quite sad.

I dare anyone to show a NG where Harry Karuse is both respected and shown as
credible and believable.

Not much to ask.

I dare you.

(Lauri Tarkkonen) wrote in
:

Do
you know that some boat trhansmissions get very hot if you let the
propeller to free wheel? Some energy is needed to heat it up.


Yes. The newer transmission that came with the replacement Perkins 4-108
was said to be one that would heat up. So, we kept the much larger
"hydraulic" transmission that was on the old engine. It doesn't even get
warm and I can spin the unloaded shaft by hand.