Conference unifix::sailing

I had a Martec on the California 32 (Hull #4) I had in Hawaii and it gave
us no problems at any time.  It would always fold and would always back down
when it should.

  As usual all things are trade offs. No "special" prop, folding or feathering
is as efficient as a properly matched fixed prop.  Ultimately, you need to
decide which you need more. If you are sailing in light wind areas, the drag
induced by a fixed prop is not worth the added efficiency (personal opinion).
With a less efficient prop, however, you need to remember it isn't quite as
efficient, and allow for it when maneuvering. As stated in an earlier response,
I have had no problems with my MARTEC. However, I did have problems with a
Michigan Wheel folding prop around getting it to unfold.

Since we have a two blade fixed prop, my comments are by hearsay. 

Should one blade of a folding prop fail to open, the vibration from the
now out-of-balance prop can be severe enough (according to published
reports) to tear the shaft strut loose from the hull. Sinking tends to
result. The Marblehead PHRF handicapper gives us a 6 seconds per mile
allowance for a fixed prop. This is perhaps not enough. But on the
bright side, since we sail maybe a thousand miles a year, we only spend
about 100 minutes more sailing per summer than if we had a folding prop.

I have been told that feathering props are very prone to catching 
floating lines (like those to lobster traps) when feathered. Since 
floating lines are able to leap many feet sideways and wind around 
our prop .....

My opinion is that if you're racing, buy a folding prop. If you're not, 
don't.

Alan

One advantage of the feathering (at least Maxprop) varieties is the ability
to change the pitch.  From what I've seen most sailboats have the wrong props,
although the basic limitation is frequently the diameter.  If you are
going to change, the basic rule of thumb is to fit the largest diameter
leaving about .15 to .20 of the diameter as clearance between the blade
tip and the hull.  You can see how aperature props are real losers from 
a thrust and efficiency perspective with this rule of thumb.  The pitch
selection is complex, involving HP output of engine, hull shape, gear
reduction, etc.  The paperback "Propellers", available from most marine
booksellers is understandable if you're engineering orientated.  

A 3 blade Maxprop is going on my boat next spring, so ask me in June how
I like it!

I have been considering a non-fixed prop to improve performance in light
air (which we experience occasionally in NE). The feathering prop (like
Max Prop) has intrigued me, but I have a couple questions:

If my prop shaft is not horizontal, wont I have to ensure that I position
the prop blades vertically to take advantage of the feathering drag 
reduction ?  It seems that since these things are internally geared to maintain
equal pitch, a prop on a shaft with 15 degrees slope would feather no closer
than 15 degrees to water flow when the blades are horizontal. I guess the
same is true of folding props, except that there is only 1 apparant blade
when folded (and the Martec eliptical is about half the cost of the Max Prop).
A three blade feathering prop would have at least 2 blades dragging all the 
time.

This may seem like nit picking but what we are talking about is not just
a $1-2K prop but a shaft lock as well (at least if you dont want to waste
the prop expense).

Second question. Toward the end of the season I notice a rapid buildup of
growth around the hub of my fixed bronze prop. Does this same thing happen
to folding/feathering units ? If so, does this cause problems ?
        
Walt

With respect to the folding props, you might want to mark the reduction unit
flange to indicate the most streamlined position of the prop so that you
can manually turn the shaft while under sail and lock the shaft in position
by engaging the drive unit with the engine off.

Bruce Bretschneider

I don't recal the Maxprop requiring a shaft lock to work, so I'm not
sure why you would want a shaft lock.  Is there some other benefit?
I have received my 3 blade unit (22" dia) which I will set to 18" pitch.
It appears to be exceptionally well made, and there is no simple way
for an average season's growth to foul it.

You are correct that shaft inclination decreases the effectiveness on
three blade units, but the projected area for the typical 10-20 degree
inclination for most boats is quite small.  Two blade units should
find a vertical position and thus have only blade thickness for drag.

I'm expecting slightly more speed (eg .5 kt) but substantially better
power for head sea or wind conditions (under power).  With a 2 blade
22x18 fixed it "looks obvious" that there is mucho drag, so the hope is
for better light wind sailing speed.  The 3 blade seemed like a win-win
for the average cruiser - better light wind performance and better
power for safety.  Backing should also be better since the blades aren't
being run "backwards."

I checked with several owners, my boatyard (Burr Bros) and the boat
builder and heard no negatives except cost.  In fact, the builder and
US agent are strongly recommending Maxprops on all new boats.

I wasn't referring to Maxprops in .6.  I had heard that some of the very
fussy racing types did it with the folding props to make sure that they always
had the lowest profile with respect to drag.

BB

Re: .4, .7

I for one will be looking forward to your experience with the 3-blade Maxprop.

We just blew the '86 add-on budget, when we ordered a Trinka 10' dink.

Walt

  Wow! This note has generated some terrific discussion. There were so many
great points and questions, I can't remember which notes I'm about to comment
upon, but here goes...

  Being a fussy racing type, I have, as mentioned before, a MARTEC folding
prop. I have so far not experienced any marine growth problems on any of my
boats. In reality, I suspect there is a connection around the amount of use
the prop gets when it folds and unfolds. In our case, we generally motor to
(sometimes from) a race (usually one to two hours), and, of course, fold 'er
up for racing. As this happens anywhere from once a week to every day during
the season, it would take a hearty specimen to survive.

  About shaft locks...most transmissions these days have what passes for
shaft locks for folding or feathering props by jamming the trans into reverse
(motor off, of course) and then back into neutral. We have set up the shaft
such that the set screw is aligned to center which is how we make sure the
folding prop is in proper position.

  Yes, vibration from a half opened prop is disaster! You can bend the shaft
much more easily then you'd ever suspect, bust motor mounts, and whole lots
more! On the other hand, it's easy to detect you have a problem, and generally
easy to get the wayward prop open.

   Last but not least dept. Although we use our motor to get us to starting
lines on time, I take perverse pleasure in sailing everywhere possible,
including gas docks, yacht club docks, moorings, etc. Although our little
folder isn't the most efficient around, I've never had problems maneuvering
(usually since I'm under sail), and can drive my 35 foot hull through calm
water around 6.25 KN. at 2500rpm. Seems enough for this guy, especially
considering the advantages of speed under sail (our reason for being, right?).

Cheers!