RPM & WOT question
I just re-proped my boat -- my range is supposed to be 4200-4600is 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 |
Dave
Jun 15
2006
|
| 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 <XjoshX@jAssing.com>
wrote: |
Dave
Jun 16
|
| They actually do sell the props.. on that site, but their web designer
is a real dowf. You have to really dig for the fact that they are
still available... |
Gene
Jun 16
|
| 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 <dhall987@cs.com> wrote:
|
Josh
Jun 16
|
| 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 ... |
Bryan
Jun 17
|
| 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" <nospam@spam.com> wrote in message |
NOYB
Jun 17
|
| 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 |
RCE
Jun 15
|
| 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. -W |
Clams
Jun 15
|
| Someone should invent an easily adjustable, variable-pitch prop. Maybe
I will. I just hate pulling the prop off my OMC. Jeff
Dave Jones wrote: |
Chehalis
Jun 15
|
| 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. RCE www.eisboch.com |
RCE
Jun 15
|
| Excellent advice. For my Evinrude 115(16' Glastron), I have a SS 19"
prop that is good for overall use, a SS 17" prop for heavy loads w/
watersports & gear for a day away from the dock, and a large surface
area AL 15" prop for power on demand (we sometimes pull 5 skiers with
this prop) but even with 5 skiers in tow, the engine will over-rev at
full throttle once they are up. Our old inboard is getting tired, I have 2 14", a 15", a 10" & a 9"
NiBrAl (or brass) props for it, it likes the 14" cupped Michigan the
best at 4600-4800 rpm(engine is rated 220hp at 4400) . It over revs
with the 14" Stannus, to almost 5000 rpm, this we do only for short
bursts with a good load in the boat. I/O & inboard engines(& most outboards - some Mercs are VERY sensitive
to this) really should not be run for any duration over recommended WOT max. Target the middle of the range with your usual load. Rob |
trainfan1
Jun 15
|
| I just put a 21" pitch on my boat (same range) and WHAT A DIFFERENCE! 10mph |
Josh
Jun 15
|
| 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) |
Josh
Jun 15
|
| Are you telling us that you actually changed props each time your guest list
changed? |
Bryan
Jun 16
|
| Looks good from here... Rob |
trainfan1
Jun 15
|
| 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 |
RCE
Jun 16
|
| 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 |
RCE
Jun 16
|
| I think you may remember these guys...... and they are still
around..... http://www.land-and-sea.com/marine/torque-shift/torque-shift.htm |
Gene
Jun 16
|
|
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 |
RCE
Jun 16
|
