I took my 28' S2 out with the new 2 bladed plastic Perfect Pitch prop
from Performance Props. My engine is the Yanmar 2gm13. At half
throttle, I got 5 kts (new bottom paint too). At full throttle, I got
6.5 kts. This seems ok. Am trying to find the log of a cruise a
couple years ago with the old three bladed bronze prop to compare
performance. I cannot yet ascertain anything about performance in
reverse although this was never an issue for me.

On 2007-12-08 20:03:16 -0500, said:

I took my 28' S2 out with the new 2 bladed plastic Perfect Pitch prop
from Performance Props. My engine is the Yanmar 2gm13. At half
throttle, I got 5 kts (new bottom paint too). At full throttle, I got
6.5 kts. This seems ok.

That does sound right. Quite possibly, you're pushing against hull
speed at full power.

Any new vibrations, particularly at mid to high power?

Am trying to find the log of a cruise a couple years ago with the old
three bladed bronze prop to compare performance.

In particular, check the difference in fuel usage at the same cruising
speeds, as I've found it's easy to set the same RPMs, benefit from
increased speeds, but suffer from decreased mileage.

--
Jere Lull
Tanzer 28 #4 out of Tolchester, MD
Xan's pages: http://web.mac.com/jerelull/iWeb/Xan/
Our BVI trips & tips: http://homepage.mac.com/jerelull/BVI/

On Sun, 09 Dec 2007 17:41:37 GMT, Jere Lull wrote:

In particular, check the difference in fuel usage at the same cruising
speeds, as I've found it's easy to set the same RPMs, benefit from
increased speeds, but suffer from decreased mileage.

Since it inevitably takes more net horsepower to increase speed,
increased fuel usage should be expected. There's no free lunch... :-)

On Dec 9, 1:14 pm, Wayne.B wrote:
On Sun, 09 Dec 2007 17:41:37 GMT, Jere Lull wrote:
In particular, check the difference in fuel usage at the same cruising
speeds, as I've found it's easy to set the same RPMs, benefit from
increased speeds, but suffer from decreased mileage.

Since it inevitably takes more net horsepower to increase speed,
increased fuel usage should be expected. There's no free lunch... :-)

Although I have not yet found the old cruising log, it is my
impression that I get a little less speed than I used to with the
three bladed prop. Going from 3/4 throttle to full throttle does not
result in any increase in speed. This might be due to the overpitch
they discuss in the manual, supposedly to give more power when it is
really needed in rough seas but I cannot evaluate this. In the past,
I never operated at full throttle even to get over 6 kts so I know it
is a little less power at near full throttle. I did not notice any
new vibrations but I did not operate it for long enough to really
notice anything.
When starting out, I did notice that it seemed like much more stirred
up water than in the past but I could not detect much increase in
power at slow speed.
I s'pose that whatever performance I gave up under power, I might get
back in sailing performance.

On 2007-12-09 13:14:12 -0500, Wayne.B said:

On Sun, 09 Dec 2007 17:41:37 GMT, Jere Lull wrote:

In particular, check the difference in fuel usage at the same cruising
speeds, as I've found it's easy to set the same RPMs, benefit from
increased speeds, but suffer from decreased mileage.

Since it inevitably takes more net horsepower to increase speed,
increased fuel usage should be expected. There's no free lunch... :-)

Well, it *feels* like a free lunch when the same fuel burn results in
higher speeds or there's less fuel burned at the same speeds due to a
more efficient prop.

When we got Xan's then-new engine, we were told to expect a 1 gph burn
because that's what the original transmissions and props gave. With our
higher gearing and larger prop, we burn only a quarter or third of that
at about the same speeds. That the difference in efficiency between a
dinky 12x8 spinning at 2500 rpms or more, and a 16x10 spinning at about
1200.

The switch from old 3-blade to modern 2-blade won't be quite as
dramatic, but I expect there will be some improvement, though it seems
he doesn't have a tach for reference.

--
Jere Lull
Tanzer 28 #4 out of Tolchester, MD
Xan's pages: http://web.mac.com/jerelull/iWeb/Xan/
Our BVI trips & tips: http://homepage.mac.com/jerelull/BVI/

On Mon, 10 Dec 2007 01:51:15 GMT, Jere Lull wrote:

That the difference in efficiency between a
dinky 12x8 spinning at 2500 rpms or more, and a 16x10 spinning at about
1200.

I understand you point. You now need less horsepower to achieve the
same boat speed because you have a more efficient prop, and are
running the engine in a more efficient power range. Was there any
impact on sailing performance?

On Sun, 09 Dec 2007 21:36:03 -0500, Wayne.B
wrote:

On Mon, 10 Dec 2007 01:51:15 GMT, Jere Lull wrote:

That the difference in efficiency between a
dinky 12x8 spinning at 2500 rpms or more, and a 16x10 spinning at about
1200.

I understand you point. You now need less horsepower to achieve the
same boat speed because you have a more efficient prop, and are
running the engine in a more efficient power range. Was there any
impact on sailing performance?


Now THERE'S a good question! :-)

Brian W

Wayne.B wrote:

On Sun, 09 Dec 2007 17:41:37 GMT, Jere Lull wrote:


In particular, check the difference in fuel usage at the same cruising
speeds, as I've found it's easy to set the same RPMs, benefit from
increased speeds, but suffer from decreased mileage.


Since it inevitably takes more net horsepower to increase speed,
increased fuel usage should be expected. There's no free lunch... :-)



Actually, there is one free lunch.

It's called efficiency.

Props are notoriously inefficient.

Any gains there could produce more speed on the same or maybe even
less power.


Richard

On 2007-12-09 21:36:03 -0500, Wayne.B said:

On Mon, 10 Dec 2007 01:51:15 GMT, Jere Lull wrote:

That the difference in efficiency between a dinky 12x8 spinning at 2500
rpms or more, and a 16x10 spinning at about 1200.

I understand you point. You now need less horsepower to achieve the
same boat speed because you have a more efficient prop, and are running
the engine in a more efficient power range. Was there any impact on
sailing performance?

I didn't sail Xan with the old engine/trans/prop, but expect there was
some "hit" with the larger 2-blade.

When we switched to a 16" feathering 3-blade, we noticed a significant
improvement under sail over the 15, mostly in low winds where we're
able to sail at 3-4 knots in conditions that we used to motor in. It
"feels" like we point a bit better under all conditions, but I can't
document that.

Also measured a slight decrease in fuel efficiency after the switch,
maybe as much as 15%, but that's only 0.26 to 0.33 gph at our normal
cruise.

--
Jere Lull
Tanzer 28 #4 out of Tolchester, MD
Xan's pages: http://web.mac.com/jerelull/iWeb/Xan/
Our BVI trips & tips: http://homepage.mac.com/jerelull/BVI/