RPM & WOT question
 

"Bryan" wrote in message
. com...

"RCE" wrote in message
...

"Dave Jones" wrote in message
...
I just re-proped my boat -- my range is supposed to be 4200-4600

is this under "best case" conditions? (flat water, no wind, light load,
trim
optimised, etc)

Or "no mater what, when you're "WOT" your engine should be between
4200-4600?

Thanks
Davie

It should be optimized for your normal loading and usage and depends a
lot on the size of your boat. That RPM range indicates a likely I/O
setup and I assume it's a single engine. You may find out, as I did
years ago, that you will have two props ... one for normal use with 2 or
3 people aboard and a second, lower pitched prop for when the whole gang
shows up for a boat ride.

RCE

www.eisboch.com


Are you telling us that you actually changed props each time your guest
list changed?


No. Not every time. Most of the time there was only one or two people on
the boat and I had a 14 pitch prop. Once in a while, if I knew we were
going to have four or five people on the boat for an outing, I'd change it
to a 12 pitch. The 12 was originally an 11 that I had re-pitched after
experimenting. This boat was an older (1982) Century 7000 Express that was
heavy and underpowered with the 260 hp GM 350 engine. It was stern heavy and
struggled to get up on plane with more than 3 people on board.

Changing the prop was a 5 minute job, even when the boat was in the slip.

RCE

www.eisboch.com

RPM & WOT question
 

"trainfan1" wrote in message
et...
Josh Assing wrote:

That's why it's a range..... 4600 lean and mean 4200 with the whole fam
damily.

But assume 4600 is max at leanest config, so if you prop it lighter,
watch
the tach and don't exceed.


So my new 21" pitch -- me alone, WOT , semi-flat water trimed right, 4300
RPM --
the prop is no good? Too much strain on the engine?

Looks good from here...

Rob


(I may have 14.5x21" prop for sale soon)



You will know after you try it with a few people on board. If you struggle
to get on plane or can't get the RPM's up over about 4000, then you are
over-proped for that load.

RCE

www.eisboch.com

RPM & WOT question
 

"Gene Kearns" wrote in message
...
On Thu, 15 Jun 2006 21:20:00 -0400, "RCE" wrote:



I think one of the outboard manufacturers (Mercury?) tried to introduce an
"automatic" variable pitch prop many years ago that had two pitch
positions.
It was costly, problem prone and it's performance wasn't any better than a
properly sized fixed pitch prop. The prop was a flop.


I think you may remember these guys...... and they are still
around.....


http://www.land-and-sea.com/marine/t...rque-shift.htm


That's likely what I remember - the tests with the Merc outboard. Time
frame is about right too - the articles date back to 1990.

It's interesting that although they sell parts for the prop on the site, but
I didn't see any offerings of the prop itself.

RCE

www.eisboch.com

RPM & WOT question
 

If it were me I would drop to a 19 or 20. The prop you have would be
good if you always went out by yourself and cruised, but I would want
something must closer to the top of the range under those conditions
so that when you have a couple people or want to get that skier ot
tuber up you can do it. If your current 21 is an aluminum, a stainless
21 might be the ticket. Just an opinion, not an expert.

Dave Hall

On Thu, 15 Jun 2006 19:09:05 -0700, Josh Assing
wrote:

That's why it's a range..... 4600 lean and mean 4200 with the whole fam
damily.

But assume 4600 is max at leanest config, so if you prop it lighter, watch
the tach and don't exceed.

So my new 21" pitch -- me alone, WOT , semi-flat water trimed right, 4300 RPM --
the prop is no good? Too much strain on the engine?

(I may have 14.5x21" prop for sale soon)


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RPM & WOT question
 

Thanks -- I can't afford a SS right now - but I do have a 19" for skiers, it
takes almost no time to swap props.

On Fri, 16 Jun 2006 10:34:05 -0400, Dave Hall wrote:

If it were me I would drop to a 19 or 20. The prop you have would be
good if you always went out by yourself and cruised, but I would want
something must closer to the top of the range under those conditions
so that when you have a couple people or want to get that skier ot
tuber up you can do it. If your current 21 is an aluminum, a stainless
21 might be the ticket. Just an opinion, not an expert.

Dave Hall

On Thu, 15 Jun 2006 19:09:05 -0700, Josh Assing
wrote:

That's why it's a range..... 4600 lean and mean 4200 with the whole fam
damily.

But assume 4600 is max at leanest config, so if you prop it lighter, watch
the tach and don't exceed.

So my new 21" pitch -- me alone, WOT , semi-flat water trimed right, 4300 RPM --
the prop is no good? Too much strain on the engine?

(I may have 14.5x21" prop for sale soon)


--- AntiSpam/harvest ---
Remove X's to send email to me.


--- AntiSpam/harvest ---
Remove X's to send email to me.

RPM & WOT question
 

"RCE" wrote in message
...

"Bryan" wrote in message
. com...

"RCE" wrote in message
...

"Dave Jones" wrote in message
...
I just re-proped my boat -- my range is supposed to be 4200-4600

is this under "best case" conditions? (flat water, no wind, light load,
trim
optimised, etc)

Or "no mater what, when you're "WOT" your engine should be between
4200-4600?

Thanks
Davie

It should be optimized for your normal loading and usage and depends a
lot on the size of your boat. That RPM range indicates a likely I/O
setup and I assume it's a single engine. You may find out, as I did
years ago, that you will have two props ... one for normal use with 2 or
3 people aboard and a second, lower pitched prop for when the whole gang
shows up for a boat ride.

RCE

www.eisboch.com


Are you telling us that you actually changed props each time your guest
list changed?


No. Not every time. Most of the time there was only one or two people on
the boat and I had a 14 pitch prop. Once in a while, if I knew we were
going to have four or five people on the boat for an outing, I'd change it
to a 12 pitch. The 12 was originally an 11 that I had re-pitched after
experimenting. This boat was an older (1982) Century 7000 Express that
was heavy and underpowered with the 260 hp GM 350 engine. It was stern
heavy and struggled to get up on plane with more than 3 people on board.

Changing the prop was a 5 minute job, even when the boat was in the slip.

RCE

www.eisboch.com

This alternating prop, so to speak, idea is intriguing. I've been wondering
how to deal with the variability of having me and 4 12-year old girls on the
boat or two families with large adults. If the prop change for my boat is a
minute job once I decide which prop to carry as my alternate ...

RPM & WOT question
 

Check your owner's manual. It should tell you the rpm that delivers maximum
horsepower. Try to match the prop with the motor so that WOT is the rpm for
max hp.

But if you don't exactly hit the number I described above, the 4200-4600
range is acceptable.


"Dave Jones" wrote in message
...
I just re-proped my boat -- my range is supposed to be 4200-4600

is this under "best case" conditions? (flat water, no wind, light load,
trim
optimised, etc)

Or "no mater what, when you're "WOT" your engine should be between
4200-4600?

Thanks
Davie