What I've Learned About Props
 

Lloyd Sumpter wrote:

On Sat, 25 Oct 2003 18:07:58 +0000, Jere Lull wrote:


Overall cost savings don't much enter into this sort of purchase.
Cheapest by far would be a fixed prop. It would take us a very long time
to consume $1500 worth of fuel, much less save that much on fuel. (In
1067 hours, we consumed 341 gallons.)

Agreed!
I can see some non-monetary reasons for going to a feathering or folding
prop, but can't see the advantage of the auto-prop.


The AutoProp's an unusual beast. After some discussions this past
season, I might consider an AutoProp for a trawler or other
mostly-powered boat: the blades keep a constant *relative* pitch, giving
better thrust and keeping the engine better loaded at reduced RPMs.

I'm now torn between the 3-blade fixed Campbell Sailor and the AutostreaM.
I like the AutostreaM's stainless-steel:

I like the *idea* of SS as well, but our SS shaft gets considerably more
growth than the bronze blade, even at the hub. And bronze seems more
suited to hard knocks. I've been thinking of switching back to a bronze
shaft....

I'd also like the feathering advantage, although I was jokingly adding up
all the "fasters" I could get: feathering gets me 1-2 knots faster, the
Sail Guy said a new headsail would get me at least a knot, clean bottom
would give me an extra 1/2 to 1 knot...and I was going 6 knots in an 8
knot breeze. So add that all up, and I'd be going about 9-10 knots! :)


They apply at different speeds. Once the wind's up and you're pressing
against hull speed, you're wasting power intentionally. I honestly have
noticed the speed bump up a half to full knot when I locked the blades
at 4-5 knots. The bottom makes the most difference at lower speeds, as
can the sail. Adding all of the effects together can make the difference
between 2-3 knots and not being able to move at all. THAT can surprise
neighboring boats.

--
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/

What I've Learned About Props
 

You seem to have it nailed, Lloyd. One comment: I know three guys who
went AutoProp in the last three years, and none of them liked the
price one bit, and all of them are ecstatic with the result and babble
on endlessly on how great they are.

I must admit, my friend with the original 1979 Volvo 35 hp on a
full-keel Wallstrom steel ketch of about 16 tons says that buying the
AutoProp meant a whole second lease on life for his engine, although
he suspects greater wear due to torque on his coupling and
transmission. He now goes hull speed (couldn't before), gets better
fuel economy, and docks like he's parallel parking a minivan. It's
quite impressive to see him "braking" to a full stop....this prop has
phenomenal bite.

They cost a lot because they are custom casting. You have to take
extensive geometry off the arse of the boat. Also, he cut away part of
his rudder (it's skeg-mounted) to take full advantage of the prop
swing.

Not everyone can or wants to do that, but not everyone has $15-20K for
a new diesel in the 50-75 HP range.

R.

On Thu, 23 Oct 2003 15:18:22 -0700, "Lloyd Sumpter"
wrote:

Hi,
After the "What prop should I use", I've done some research and thougth
I'd post what I've learned about various props.

Fixed-blade prop:
This is the simplest and least expensive option. The blades are fixed
at a certain pitch. They also give the most drag under sail. To reduce
this, most sailing props are thinner, "high-aspect-ratio", and usually
have more advanced foil designs like "cupping" to increase drive in
forward. The downside of THIS is that in reverse, the advanced foil is
going through the water backwards, reducing effectiveness.

Examples: Michigan Wheel "Sailor" series and Campbell Sailor props.
Cost: around $500 CDN

Folding Prop:
This is the ultimate sailing-compromise prop. Under sail, the blades fold
down to become hardly more than a giant "teardrop" on the end of the
shaft, giving virtually no drag. Under power, the rotation pushes the
blades out, and the backward force pushes the blades out
completely. The downside of this is that in reverse, the force is
trying to FOLD the blades, and centrifugal force is all that's keeping
them out. This means VERY poor performance under power in reverse.

Examples...?
Cost: ??

Feathering Prop:

Instead of the entire blade folding down under sail, they rotate,
("feathering") so that the leading edge is all that is presented. This
is not QUITE as low-drag as a folding prop, but far lower than a fixed
prop. When under power, the blade rotates to a fixed pitch angle. The
side benefit is that it rotates the opposite way to reverse, so the
leading edge is leading in both forward and reverse, meaning any
cupping or advanced foil design is used in both directions. Another
side benefit is that most props allow you to adjust the "fixed" pitch,
some easily enough that it can be done underwater, eliminating the
need to haulout to get that "perfect" pitch.

Examples: Maxprop and AutostreaM
Cost: About $2000 CDN

Auto-prop:

This is the same as a feathering prop, but instead of a fixed pitch,
the pitch varies with speed, torque, etc. similar to the "torque
convertor" on a ski-doo. This allows max power at all settings, best
fuel economy, fastest cruising and WOT speed, etc. The downside of
course is the cost.

Example: AutoProp (don't know of any others)
Cost: $3000 CDN

Lloyd Sumpter
"Far Cove" Catalina 36

What I've Learned About Props
 

First, MaxProp is made in Italy, the home of Ferrari and Fiat, so I'm
not sure how the place of origin cuts as against Australia.

Second, perhaps I have the old fogey's prejudice against using
stainless underwater. Shafts are one thing -- they're simple, one
piece, no moving parts (as it were). A feathering propeller is much
more complex. I'd worry about crevice corrosion and galling.
(Galling is the micro-welding of one metal part against another.
Stainless is very prone to it, as you've probably learned if you've
run a lot of stainless nuts onto stainless machine screws dry,
particularly if there's any fiberglass dust around).

Galvanic corrosion is also an issue. Bronze is more noble than most
other metals used on a boat, so a bronze propeller is automatically
safe. A stainless prop would possibly be subject to problems from the
shaft (probably not the same alloy) and other pieces.

Finally, bronze is much easier to repair. A propeller shop can do
wonders with bronze, adding material, reshaping dents and bends...
Stainless is much harder to work.

As I say, maybe this is just old predjudice. One of the troubles and
joys of our sport is that many aspects of it are difficult to analyze
completely, so we tend to do things the way they've always been done.
As I've said many times, I'm no Luddite, far from it, but I don't see
a convincing reason to use a stainless prop.

All of this is less of an issue with a fixed prop on a powerboat.
And, I'm not sure I care what most powerboaters think. There are
certainly powerboaters (including, perhaps, me) who are well informed
and whose opinion I solicit, but the vast majority don't know top of
the line from junk.

Jim Woodward
www.mvFintry.com

"Lloyd Sumpter" wrote in message .. .
On Tue, 28 Oct 2003 07:31:12 +0000, Jim Woodward wrote:



Finally, FYI:
Martec AutoStream 6000 series $3,000
MaxProp 70322, $3,035
(Both three blade, bronze, 22" for 1.375" shaft)
Other sizes may differ. Martec's stainless series are cheaper, but
I'm not sure I'd want a stainless prop.

http://www.martec-props.com/prices-feathering.htm
http://www.pyiinc.com/?section=brows...sku=70322&sn=5



First, I wonder if the popularity of the MaxProp is because it is US made,
whereas the AutostreaM is made in Australia. Check out:
http://www.seahawk.com.au/ (the REAL website for AutostreaM)

Second, why not a SS prop? Most powerboaters regard a SS prop as "top of
the line" (of course they're usually comparing to aluminum...). The SS
prop has no "give" so it can utilize advanced foil designs like cupping
better (again, mainly compared to aluminum, but I'd probably add composite
to this). Also, my SS shaft seems to be less susceptable to electrolysis,
corrosion, and marine growth than my Campbell Sailor bronze.

Not saying you're wrong, just wondering why you wouldn't want a SS prop.

Lloyd Sumpter
"Far Cove" Catalina 36

What I've Learned About Props
 

Jim Woodward wrote:

First, MaxProp is made in Italy, the home of Ferrari and Fiat, so I'm
not sure how the place of origin cuts as against Australia.

Having once been the owner of a 1985 Farrari 328 GTB I can state with
some authority that Austrailia is at a distinct advantage here. Martec
could ship parts via Thor Higerdal and they would get here faster than
they would from Modena.

--
Glenn Ashmore

I'm building a 45' cutter in strip/composite. Watch my progress (or lack
there of) at: http://www.rutuonline.com
Shameless Commercial Division: http://www.spade-anchor-us.com

What I've Learned About Props
 

One area where stainless, or even monel if you can get it that way is far
superior than bronze and that's if you are around Mississippi River/Delta or
similar very much. The silt in the water will chew up blades and for that
matter impellers et. al. faster than you can change them. Bronze for clean
water application but if there's any chance of "Big Muddy itis" the extra
cost of stainless is a better choice. Not a concern for most I trust.
Which brings up a follow on question. Are anhy of these props made in
Monel?

Michael

What I've Learned About Props
 

A slight divergence from the original topic:

Our company is starting to work with urethane resins to produce custom
enclosures for our electronics products. In the documentation from the resin
manufacturer, they show a propeller being cast from one of their specialty
resins. I've never heard of a plastic prop of any substantial size, but the
characteristics of some of the higher-end resins seem quite advantageous for
such an application. Nearly as strong as metal, but no corrosion and much
lighter. Presumably quite inexpensive to manufacture, even for one-off
applications.

I'm wondering if this is something that might become more commonplace as resin
technology advances, or if there is some reason why metal is superior. At the
very least, it could be a cheap way to make an inexpensive emergency replacement
prop. We have no interest in developing props ourselves, I'm just curious.

--
Chuck Cox
SynchroSystems Motorsport Computers
Hopped/Up Racing Team

http://www.synchro.com

What I've Learned About Props
 

I have seen some on outboards and high powered inboard ski boats but not
on cruisers. Piranha makes a replaceable blade composite outboard prop
that they claim is stronger than aluminum and I understand that
composite props up to 9' diameter are being produced in the UK.

The thing is, when they hit something the blades don't get bent. They
totally disintegrate.

Charles Cox wrote:
A slight divergence from the original topic:

Our company is starting to work with urethane resins to produce custom
enclosures for our electronics products. In the documentation from the resin
manufacturer, they show a propeller being cast from one of their specialty
resins. I've never heard of a plastic prop of any substantial size, but the
characteristics of some of the higher-end resins seem quite advantageous for
such an application. Nearly as strong as metal, but no corrosion and much
lighter. Presumably quite inexpensive to manufacture, even for one-off
applications.

I'm wondering if this is something that might become more commonplace as resin
technology advances, or if there is some reason why metal is superior. At the
very least, it could be a cheap way to make an inexpensive emergency replacement
prop. We have no interest in developing props ourselves, I'm just curious.

--
Chuck Cox
SynchroSystems Motorsport Computers
Hopped/Up Racing Team

http://www.synchro.com

--
Glenn Ashmore

I'm building a 45' cutter in strip/composite. Watch my progress (or lack
there of) at: http://www.rutuonline.com
Shameless Commercial Division: http://www.spade-anchor-us.com

What I've Learned About Props
 

Sometimes having the prop disintegrate is one of the
better options. I've got both a power boat and a sailboat, and my power
boat has a stainless steel prop on it. I really liked the idea
of having that tough prop on the boat until a friend of mine--a long
time boat dealer and mechanic--pointed out that when a stainless prop hits
the rock, the prop shaft is usually bent, and the lower unit seal destroyed
in addition to the prop being damaged. With aluminum props, its usually
just the prop.

The problem is somewhat more complicated for the sail boat, since the
prop is usually protected from grounding by the keel. This just leaves
relatively "soft" objects such as fishing lines to worry about. In the
event of hitting something hard such as a coral head with a prop, its
probably better to have the prop give instead of your shaft or transmission.

One more thing to think about.

Don W.



Glenn Ashmore wrote:

I have seen some on outboards and high powered inboard ski boats but not
on cruisers. Piranha makes a replaceable blade composite outboard prop
that they claim is stronger than aluminum and I understand that
composite props up to 9' diameter are being produced in the UK.

The thing is, when they hit something the blades don't get bent. They
totally disintegrate.

What I've Learned About Props
 

On Wed, 29 Oct 2003 15:41:20 +0000, Charles Cox wrote:

A slight divergence from the original topic:

I'm wondering if this is something that might become more commonplace as resin
technology advances, or if there is some reason why metal is superior. At the
very least, it could be a cheap way to make an inexpensive emergency replacement
prop. We have no interest in developing props ourselves, I'm just curious.


Check out Kiwi props:

http://snoopy.falkor.gen.nz/kiwiprop/home.html

or Pirhana props

I'm sticking with what i know (metal props) even though they cost more.

Lloyd

What I've Learned About Props
 

Charles Cox wrote:

A slight divergence from the original topic:

Our company is starting to work with urethane resins to produce custom
enclosures for our electronics products. In the documentation from the resin
manufacturer, they show a propeller being cast from one of their specialty
resins. I've never heard of a plastic prop of any substantial size, but the
characteristics of some of the higher-end resins seem quite advantageous for
such an application. Nearly as strong as metal, but no corrosion and much
lighter. Presumably quite inexpensive to manufacture, even for one-off
applications.

I'm wondering if this is something that might become more commonplace as resin
technology advances, or if there is some reason why metal is superior. At the
very least, it could be a cheap way to make an inexpensive emergency replacement
prop. We have no interest in developing props ourselves, I'm just curious.


CDI might be the company. They have/had a line of props that looked VERY
sweet and were guaranteed to be more efficient, but they seem to have
stopped developing new ones. Just checked: they have a few on their
page: http://www.sailcdi.com/

--
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/