there was a used one for sale a few weeks ago at “marine consignment
of wickford” in wickford RI. my dimensions are for a 3gm30f, i
installed a pyi flex coupling as well to protect the prop. distance
from aft end of cutlass housing to fwd end of hub 2-1/8", aft edge of
aperture to hub 4-1/4". this gives 3/4" tip clearance when feathered
and allows a low clearance donut zinc collar to be installed with 3/4"
space for water flow to the cutlass. if i need to remove a broken
flexi coupling, i can remove the zinc and slide the shaft forward. i
can also reinstall the old 3 blade fixed prop if need be. i initially
pitched it incorrectly (it’s pretty easy to do it right) with 12.2"
pitch and later careened to back it down to 11". this is what my old
prop was and what pyi recommended. i forget the angle. i get about
3400 rpm. the previous owner had repitched the fixed prop from 11
down to 10, then back up. i was getting some soot at full throttle at
12", now only minimal. i figured the next step down (to less than 10"
i think) would be too little prop.
i am very happy with it. i think i give up only a very little in
forward speed and power due to the non-helical blades and the
difference in reverse is dramatic. she backs strait and powerful.
with a bit of way on, i can actually steer some. i have a hard time
estimating the difference under sail. the thing feathers very
easily (e.g. back down on the anchor rode and it feathers from the
recoil or current while at anchor). very few moving parts and they
only move in the feathering process so i do not think wear would ever
be a problem. quality of machining is excellent. other than cost, i
cannot think of any reason not to get one. keep the zincs on it and
that capital cost should be spread over many years.
john churchill
John,
What is the diameter of your Max-Prop?
Steve Osborne
----- Original Message -----
From: <jchurchill@erols.com >
To: <bcc@yahoogroups.com >
Sent: Wednesday, September 12, 2001 7:49 AM
Subject: [bcc] maxprop
there was a used one for sale a few weeks ago at “marine consignment
of wickford” in wickford RI. my dimensions are for a 3gm30f, i
installed a pyi flex coupling as well to protect the prop. distance
from aft end of cutlass housing to fwd end of hub 2-1/8", aft edge of
aperture to hub 4-1/4". this gives 3/4" tip clearance when feathered
and allows a low clearance donut zinc collar to be installed with 3/4"
space for water flow to the cutlass. if i need to remove a broken
flexi coupling, i can remove the zinc and slide the shaft forward. i
can also reinstall the old 3 blade fixed prop if need be. i initially
pitched it incorrectly (it’s pretty easy to do it right) with 12.2"
pitch and later careened to back it down to 11". this is what my old
prop was and what pyi recommended. i forget the angle. i get about
3400 rpm. the previous owner had repitched the fixed prop from 11
down to 10, then back up. i was getting some soot at full throttle at
12", now only minimal. i figured the next step down (to less than 10"
i think) would be too little prop.
i am very happy with it. i think i give up only a very little in
forward speed and power due to the non-helical blades and the
difference in reverse is dramatic. she backs strait and powerful.
with a bit of way on, i can actually steer some. i have a hard time
estimating the difference under sail. the thing feathers very
easily (e.g. back down on the anchor rode and it feathers from the
recoil or current while at anchor). very few moving parts and they
only move in the feathering process so i do not think wear would ever
be a problem. quality of machining is excellent. other than cost, i
cannot think of any reason not to get one. keep the zincs on it and
that capital cost should be spread over many years.
john churchillBRISTOL CHANNEL CUTTER OWNERS ASSOCIATION
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i put a max on about a year ago and am very happy with it. you
order it by diameter and shaft size, pitch and rotation are selected
during installation. i have a 3gm30f and bought the boat with a fixed
3 blade prop, 16x11. the previous owner had had it repitched to a 10,
then back up to 11. it seems neither was quite perfect as she would
not get to max throttle with a 10 nor to full rpm with the 11. when i
put the maxprop on, i picked 11 pitch again. i actually goofed in
installing it and set it at 12 despite the fact that it is pretty
simple to set correctly. had to reset it to 11. she still does not
reach full throttle (3400 rpm with a clean prop) and i may try going
down to 10 at some point. PYI will tell you 11 is correct. it can
only be set in increments of about an inch, so you cannot pick 10.7
for instance.
i did some additional things while i had her all apart. i wanted to
install a flexible coupling to protect the prop in case i hit
something. a fringe benefit is reduced vibration. the
original coupling was a beast to get off as the set screws just bore
down on the shaft raising a dimple that prevented the coupling from
sliding. i drilled a little recess for them to go into and so now
removal is easy. i wanted to be able to reinstall the fixed prop if
needed. when the max goes on, any excess at the threaded tip is cut
off. therefore i could not put 2 nuts on with the old prop. i had a
machine shop drill a new cotter pin hole ($20 seemed like a bargain to
get it in the right place, square and true) to lock a single
castellated nut in place. i wanted to retain a shaft zinc in addition
to the zinc on the maxprop itself. by using a low clearance donut
type zinc, i was able to preserve space for water flow to the cutlass
bearing. by removing the shaft zinc, i can slide the shaft forward
in case i need to remove the flexible coupling (like if it broke).
this all required a bit of figuring so here are the dimensions i used:
4 1/4" from the aft edge of the aperture to the forward face of the
maxprop hub, 2 1/8" from the aft face of the cutlass housing to the
hub (your housing may be different than on my hull #65). this gives
at least 3/4" clearance from the tip of the blades to the rudder.
that is all i can think of. i am really happy with it. it
feathers amazingly easily (like during the recoil from setting the
anchor) and works great in reverse. she backs up strait and i am
able to steer a little when she has way on. power in forward is not
quite the same due to the lack of helix in the blades, but is not a
significant issue. if they weren’t so costly, everyone would have
one.
john churchill
Hello Group:
From time to time there are queries on the forum regarding
feathering props. I recently installed a PYI MaxProp (3-blade
Classic) on our BCC and thought I’d share the process/results to date.
After considerable hand wringing and research I finally opted
to install the 15" version of the prop a couple of months ago. It
almost fit in the aperture w/o cutting the shaft but when the blades
were feathered there was the possibility of the rudder coming in
contact with the folded blades when the rudder was hard over; plus it
sat too far back anyway. (See MaxProp Initial Fit.jpg) I had the
shaft cut/re-keyed so that the prop fits just about in the center of
the aperture. With a shaft donut zinc installed there is one inch of
clearance from the cutlass bearing housing to the donut zinc. (See
MaxProp Final Fit.jpg) I set the prop with 20 degrees of blade angle
(10.3" pitch) (X=K and Y=E).
As others have noted, the most dramatic difference is in
reverse (which was really dramatic in our case as we originally had a
fixed two blade). A lot more power and one can actually spin it up
in reverse quickly, get sternway, then throttle down and actually get
the boat to turn the way one wants. (Had a hard time doing that with
the two blade). Going from ahead to reverse, or vice versa, is
seamless, i.e., there is no discernable lag from one direction to the
other.
Going ahead improved significantly as well since we went from two to
three blades. I was able to get some reasonably accurate data on
speed using GPS (w/ WAAS/Differential functioning) during a run
through the ICW canal east of Choctawachee Bay w/ no wind and no
discernable current over a period of 10-15 minutes. Bottom of the
boat was clean and fair. Results were (engine is the ubiquitous
Yanmar 3GM30F):
2250 rpm: 6.0 - 6.1 knots
2500 RPM: 6.6 Knots
Since I was in brown water at the time I couldn’t bring
myself to run the engine up to 3400 RPM (visions of silt impacting my
impeller more furiously) to see what would happen. After a hundred
plus hours of motoring in varied conditions (just completed a trip
from the Gulf of Mexico to Jacksonville FL) I suspect the prop is
somewhat underpitched. The engine will easily go all the way to 3600
RPM (in fact I have to be careful not to over rev it) with little
change in boat speed from around 2800. Apparently the prop could use
more “bite” to take better advantage of the engine’s power at higher
RPM’s but I confess to not having any kind of appreciation for fluid
dynamics of propellers.
As far as the effects of the feathering feature, Quis scit?
During the recent sail across the Gulf I was on a very deep reach in
light air for a number of hours and was making 4.5 - 5.0 knots which
seemed reasonable so I guess the prop helped… but I couldn’t prove it.
On a separate note; we also installed a Free Hand Wind Vane
during the last haulout. Neat gadget.
Pete
S/V TwoLoose
p.s. I could not figure out how to attach pictures to this email so
I ended up putting pics on the photos section of this forum in
the “TwoLoose” folder