Hi!

I've got a 28 foot sailboat, 7800lbs with a 10.5hp engine. It has a 3
blade prop with 10 inch diameter and 9.3 pitch. Prop is in like new
condition, so is the bottom. When I sail, I can push her up to 6 knots.

Though, when I spin the engine at 3600 rpm I only get about 3.5 knots
out of the boat. The engine easily manages more than 4000 rpm, so I
don't think it's an engine problem. I suspect that the prop has the
wrong pitch, but according to the manufacturer it's exactely the right
one.

Why don't I get more than 3.5 knots under power? Does anyone have a
similar configuration or any clues?

Thanks!

Dennis

Most sailboats are heavy displacement hulls, which work best with engine
transmissions having high gear ratios. Anotherwords, pushers with lots of
torque.
This is contrary to motor boats that plane on the water. They need high reving
engines with lots of prop speed. You may want to go to a prop with a lower
pitch, as well. It will turn slower, but have more pushing power, or torque, in

conjunction with the higher gearing Think of a bicycle where you have to
shift to a smaller front sprocket to go up a hill resulting in more turns of the
pedals
to go a given distance, but more power for climbing hills. With the boat
engine, it
should spin more times to turn the prop a given revolution pushing the boat with

more power but advancing it a shorter distance. Although you haven't stated it,

I also assume the engine has enough power to do the job. If you are seeing a
lot
of turbulence around the prop, this is an indication it is turning too fast and
not having the correct pitch and gearing to handle the weight of your boat.

Sherwin D.

Dennis wrote:

Hi!

I've got a 28 foot sailboat, 7800lbs with a 10.5hp engine. It has a 3
blade prop with 10 inch diameter and 9.3 pitch. Prop is in like new
condition, so is the bottom. When I sail, I can push her up to 6 knots.

Though, when I spin the engine at 3600 rpm I only get about 3.5 knots
out of the boat. The engine easily manages more than 4000 rpm, so I
don't think it's an engine problem. I suspect that the prop has the
wrong pitch, but according to the manufacturer it's exactely the right
one.

Why don't I get more than 3.5 knots under power? Does anyone have a
similar configuration or any clues?

Thanks!

Dennis

In article .com,
"Dennis" wrote:

I've got a 28 foot sailboat, 7800lbs with a 10.5hp engine. It has a 3
blade prop with 10 inch diameter and 9.3 pitch. Prop is in like new
condition, so is the bottom. When I sail, I can push her up to 6 knots.

Though, when I spin the engine at 3600 rpm I only get about 3.5 knots
out of the boat. The engine easily manages more than 4000 rpm, so I
don't think it's an engine problem. I suspect that the prop has the
wrong pitch, but according to the manufacturer it's exactely the right
one.

Why don't I get more than 3.5 knots under power? Does anyone have a
similar configuration or any clues?

Entirely depends upon which engine and transmission you're using, but
that seems off.

We're a nominal 6800# running a Yanmar 2GM20, and our prop (16x10x3)
allows us my target RPMs, 3400, but we normally cruise at about 5 hp
output (0.3 GPH and 22-2300 rpm), doing about 5.5 knots.

If I changed the pitch, I could pull about 3800 before the governor
kicked in, but I prefer to max out at our continuous rating.

--
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/

Well, I would suggest that before doing anything you should check your
propeller pitch.
The pitch stamped on the propeller may not be as when the propeller was new.
Plus, many propeller manufacturers are using sand casting over and over. The
pattern, the quality of the sand and the material may have changed the pitch
that was stamped on the hub.
The best way to check your pitch is to do it with a propeller die. Luckily
over here we have a Prop Shop that carry all dies. They caters mainly to
commercial fishermen. I was surprised to learn that on average the
commercial fishermen get their props check and re-pitch as much as once per
year. They get tangle up in nets and at time they hit un-identified
floating objects. Not to mention that we pleasure boat owner do the same
thing if we go on the coast often.
A Prop Shop will hesitate to correct or re-pitch a propeller for more than
(11/2) one degree and one half.
That is why that on war ships the pitch is variable and adjusted during sea
trials.

"Dennis" wrote in message
oups.com...
Hi!

I've got a 28 foot sailboat, 7800lbs with a 10.5hp engine. It has a 3
blade prop with 10 inch diameter and 9.3 pitch. Prop is in like new
condition, so is the bottom. When I sail, I can push her up to 6 knots.

Though, when I spin the engine at 3600 rpm I only get about 3.5 knots
out of the boat. The engine easily manages more than 4000 rpm, so I
don't think it's an engine problem. I suspect that the prop has the
wrong pitch, but according to the manufacturer it's exactely the right
one.

Why don't I get more than 3.5 knots under power? Does anyone have a
similar configuration or any clues?

Thanks!

Dennis

--

Roger Long



wrote in message
...
Well, I would suggest that before doing anything you should check
your propeller pitch.
The pitch stamped on the propeller may not be as when the propeller
was new.
Plus, many propeller manufacturers are using sand casting over and
over. The pattern, the quality of the sand and the material may have
changed the pitch that was stamped on the hub.
The best way to check your pitch is to do it with a propeller die.
Luckily over here we have a Prop Shop that carry all dies. They
caters mainly to commercial fishermen. I was surprised to learn
that on average the commercial fishermen get their props check and
re-pitch as much as once per year. They get tangle up in nets and
at time they hit un-identified floating objects. Not to mention
that we pleasure boat owner do the same thing if we go on the coast
often.
A Prop Shop will hesitate to correct or re-pitch a propeller for
more than (11/2) one degree and one half.
That is why that on war ships the pitch is variable and adjusted
during sea trials.

"Dennis" wrote in message
oups.com...
Hi!

I've got a 28 foot sailboat, 7800lbs with a 10.5hp engine. It has a
3
blade prop with 10 inch diameter and 9.3 pitch. Prop is in like new
condition, so is the bottom. When I sail, I can push her up to 6
knots.

Though, when I spin the engine at 3600 rpm I only get about 3.5
knots
out of the boat. The engine easily manages more than 4000 rpm, so I
don't think it's an engine problem. I suspect that the prop has the
wrong pitch, but according to the manufacturer it's exactely the
right
one.

Why don't I get more than 3.5 knots under power? Does anyone have a
similar configuration or any clues?

Thanks!

Dennis

I doubt that such small differences in pitch could account for speed
this low. He should be getting nearly twice that speed.

These numbers are so far off it makes me think that he should check
for clutch slippage. Feel the gear case, if it is getting warm or
hot, that may be the problem.

--

Roger Long



wrote in message
...
Well, I would suggest that before doing anything you should check
your propeller pitch.
The pitch stamped on the propeller may not be as when the propeller
was new.
Plus, many propeller manufacturers are using sand casting over and
over. The pattern, the quality of the sand and the material may have
changed the pitch that was stamped on the hub.
The best way to check your pitch is to do it with a propeller die.
Luckily over here we have a Prop Shop that carry all dies. They
caters mainly to commercial fishermen. I was surprised to learn
that on average the commercial fishermen get their props check and
re-pitch as much as once per year. They get tangle up in nets and
at time they hit un-identified floating objects. Not to mention
that we pleasure boat owner do the same thing if we go on the coast
often.
A Prop Shop will hesitate to correct or re-pitch a propeller for
more than (11/2) one degree and one half.
That is why that on war ships the pitch is variable and adjusted
during sea trials.

"Dennis" wrote in message
oups.com...
Hi!

I've got a 28 foot sailboat, 7800lbs with a 10.5hp engine. It has a
3
blade prop with 10 inch diameter and 9.3 pitch. Prop is in like new
condition, so is the bottom. When I sail, I can push her up to 6
knots.

Though, when I spin the engine at 3600 rpm I only get about 3.5
knots
out of the boat. The engine easily manages more than 4000 rpm, so I
don't think it's an engine problem. I suspect that the prop has the
wrong pitch, but according to the manufacturer it's exactely the
right
one.

Why don't I get more than 3.5 knots under power? Does anyone have a
similar configuration or any clues?

Thanks!

Dennis

Clutch slippage is a good place to start checking. My friend has a three
blade prop on a Tanzer 8.5 and the transmission was rebuild twice so far.
One year after going thought the reversing falls I had no forward power.
The shaft was turning free and getting out of the flange at the
transmission.
I would, also, check to see if the prop shaft is well keyed and secured at
the transmission flange.

"Roger Long" wrote in message
...
I doubt that such small differences in pitch could account for speed this
low. He should be getting nearly twice that speed.

These numbers are so far off it makes me think that he should check for
clutch slippage. Feel the gear case, if it is getting warm or hot, that
may be the problem.

--

Roger Long



wrote in message
...
Well, I would suggest that before doing anything you should check your
propeller pitch.
The pitch stamped on the propeller may not be as when the propeller was
new.
Plus, many propeller manufacturers are using sand casting over and over.
The pattern, the quality of the sand and the material may have changed
the pitch that was stamped on the hub.
The best way to check your pitch is to do it with a propeller die.
Luckily over here we have a Prop Shop that carry all dies. They caters
mainly to commercial fishermen. I was surprised to learn that on average
the commercial fishermen get their props check and re-pitch as much as
once per year. They get tangle up in nets and at time they hit
un-identified floating objects. Not to mention that we pleasure boat
owner do the same thing if we go on the coast often.
A Prop Shop will hesitate to correct or re-pitch a propeller for more
than (11/2) one degree and one half.
That is why that on war ships the pitch is variable and adjusted during
sea trials.

"Dennis" wrote in message
oups.com...
Hi!

I've got a 28 foot sailboat, 7800lbs with a 10.5hp engine. It has a 3
blade prop with 10 inch diameter and 9.3 pitch. Prop is in like new
condition, so is the bottom. When I sail, I can push her up to 6 knots.

Though, when I spin the engine at 3600 rpm I only get about 3.5 knots
out of the boat. The engine easily manages more than 4000 rpm, so I
don't think it's an engine problem. I suspect that the prop has the
wrong pitch, but according to the manufacturer it's exactely the right
one.

Why don't I get more than 3.5 knots under power? Does anyone have a
similar configuration or any clues?

Thanks!

Dennis

To add to the litany of things you should check, how much to you trust
your tach? Does the engine *sound* like it's doing 3600?

On 18 Oct 2006 20:30:38 -0700, "Dennis"
wrote:

Hi!

I've got a 28 foot sailboat, 7800lbs with a 10.5hp engine. It has a 3
blade prop with 10 inch diameter and 9.3 pitch. Prop is in like new
condition, so is the bottom. When I sail, I can push her up to 6 knots.

Though, when I spin the engine at 3600 rpm I only get about 3.5 knots
out of the boat. The engine easily manages more than 4000 rpm, so I
don't think it's an engine problem. I suspect that the prop has the
wrong pitch, but according to the manufacturer it's exactely the right
one.

Why don't I get more than 3.5 knots under power? Does anyone have a
similar configuration or any clues?

Thanks!

Dennis

-----------------------------------------------------------------------------------------------------------
Glen "Wiley" Wilson usenet1 SPAMNIX at world wide wiley dot com
To reply, lose the capitals and do the obvious.

Take a look at cpRepeater, my NMEA data integrator, repeater, and
logger at http://www.worldwidewiley.com/

Hi Roger and everyone who replied!

Thanks so much for the constructive feedback!

Couple of points to clarify:
- I forgot to mention, the gear ratio is about 1:2.06 (can't read the
label on the gearbox)
- I recently had the bottom done completely - it is as smooth as it
gets.
- I also had the propeller checked by the manufacturer and they
confirmed that the pitch is what it has been manufactured at.
- I have a brand new shaft and coupler and these are properly
connected.

So, I guess my best bet is to check the transmission. Now, how do I do
that?
- Can I check the clutch/transmission without disassembling everything?
Any ideas?
- Can I check and repair the transmission without hauling the boat out
of the water?
- I also notice that there is a very high pitch noise from the engine
after about 3700rpm until the max. rpm. Could that also indicate a
toasted transmission?

Thanks again!
Dennis

By process of elimination, it pretty much has to be something
slipping. That high pitched noise suggests a clutch. It could be as
simple as the shift cables being misadjusted so the clutch isn't fully
engaged. Unfortunately, if that is true, the transmission is probably
going to have to come out of the boat because the clutch surfaces are
glazed.

First thing to check: Cable adjustment for full travel on the lever
at the transmission. If cable adjustment fixes the problem, the
transmission is still probably on borrowed time. Don't depend on it
in a tight spot.

Next: What RPM do you get in reverse? Marine transmissions usually
have two clutches and the reverse one is unlikely to be damaged. If
maximum RPM in reverse is significantly less than when bringing it up
to full power in forward, the engine is being loaded up more. That
probably means the forward clutch is slipping. This test is hard on
the engine so just do it once and with a well warmed up engine.

You can buy or rent tachs that read a little bit of reflective foil
taped to a shaft. Check engine RPM at the flywheel to be sure the
tach is right. Then check the tach against shaft RPM.

If you verify slipping, be sure the key is still in the shaft coupling
before you pull the transmisson out of the boat. Shaftlines have been
put together before with the key missing. The set screws can wear a
groove around the shaft so it won't back out and feels tight to the
hand but the shaft will slip in the coupling. A mark or piece of tape
on the shaft will reveal this pretty quickly.

A missing key on the prop could also be overlooked since the taper
will keep the prop tight and turning until it is heavily loaded. That
could also make your high pitched noise.

--

Roger Long



"Dennis" wrote in message
ups.com...
Hi Roger and everyone who replied!

Thanks so much for the constructive feedback!

Couple of points to clarify:
- I forgot to mention, the gear ratio is about 1:2.06 (can't read
the
label on the gearbox)
- I recently had the bottom done completely - it is as smooth as it
gets.
- I also had the propeller checked by the manufacturer and they
confirmed that the pitch is what it has been manufactured at.
- I have a brand new shaft and coupler and these are properly
connected.

So, I guess my best bet is to check the transmission. Now, how do I
do
that?
- Can I check the clutch/transmission without disassembling
everything?
Any ideas?
- Can I check and repair the transmission without hauling the boat
out
of the water?
- I also notice that there is a very high pitch noise from the
engine
after about 3700rpm until the max. rpm. Could that also indicate a
toasted transmission?

Thanks again!
Dennis