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Replies to PropExpert
Survey Comments
Monday, 02-APR-2007 by Donald
MacPherson - Technical Director
Periodically, we ask our software customers for
feedback by way of a "user survey". We recently conducted such
a survey for our PropExpert users, and the responses are now coming back
to us. The respondents from this round of surveys offered up some
particularly interesting comments, critiques, and suggestions, so we
felt it would be valuable for me to provide an on-going discussion of
these as a blog article. And here we go...
(As a sidebar, we donate $10 to the Juvenile
Diabetes Research Foundation for every completed survey. If you are a
PropExpert user and have not completed the survey, please consider
helping us and the JDRF by taking a few minutes to do so. Look for the
email from us that lists the web page link. Thanks.)
To view my replies, just click the arrow icon [ ]
to open or close a dropdown paragraph.
What features would you
like to see added?
Weight calculation of
the propeller
-
A number of simple formula have been
developed over the years to estimate the weight of a propeller
from the basic parameters (e.g., diameter, blades, BAR, material
type), but the error range of these formula is typically pretty
big. However, quite coincidentally we are preparing a new
technical paper for presentation in June about estimating the
properties of propellers for vibration analysis, and one of the
topics is weight estimation. So, once we have our paper completed,
I would expect that we could provide a weight estimation as a
group on PropExpert's Utility page. [Propeller builder]
Material sheer strength
for 316 stainless
Need better sort options
in the propeller data. If I know I want a 4 blade propeller, I should
be able to display just 4-blade propellers. If the customer wants a
Michigan wheel, I should be able to just display Michigan wheels or
just 4-blade Michigan wheels that are available in the selected
diameter or diameter range.
-
This is a fair criticism. Right now, we have sorting
options for the propeller library (as well as all of the other
libraries), but no filtering options - which is what I
think you are really seeking. You can sort by Manufacturer or
Blades, but not both simultaneously. You can also change column
headings, so you can set up the columns as Manufacturer, Model,
Blades, and BAR, for example. As most of our users are propeller
companies (builders, distributors, dealers), this has been
sufficient as they already know what product model they want to
use. As an engine builder, I can see how better filtering could be
very useful. Adding filtering code is not trivial, but we will add
this to our development plan for PropExpert and try to get some
type of filtering option added. [Engine builder]
A before & after,
side by side ability to print analysis.
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I am not sure if this fully satisfies your
objectives, but you do have a before-and-after comparative
analysis when using the Prior trial option. This gives you
three columns of data and results in the Sizing Analysis - top
speed, cruise speed, and the prior trial condition.
However, if you are referring to the ability to compare one
project against another, then you are correct, this feature is not
currently in PropExpert. [Propeller dealer]
A complete engine
selection guide, along with more propeller data. Data of most common
gear boxes.
-
Since we introduced PropExpert back in the
mid-90's, we have struggled with the topic of how to best
integrate third-party data for engines and propellers (and more
recently for reduction gears). At one time, we worked with a
magazine publisher for the licensing and resale of engine data in
database form. However, the supplier was not able to keep the data
fresh, and we became concerned about providing data that was
obsolete. It is probably useful for me to share one of our core
philosophies as it pertains to our software development, which is:
"we would rather give you no answer than the wrong
answer". So, we no longer provide any collection of engine
data, and do not plan on providing reduction gear data. We do,
however, plan on adding a reduction gear library feature to
PropExpert so that users can maintain their own library of data.
(Product model data for propellers is much more stable, so we do
supply a library of commercial propeller data which we update as
frequently as possible.) Given the accessibility of engine and
reduction gear data on the web from the manufacturers' various web
sites, we feel that the relative inconvenience of asking users to
seek out their own engine and gear data is outweighed by the
resulting accuracy of getting this information directly from the
manufacturers. This leads me to the following... [Propeller
distributor, Propeller dealer]
You could maintain
Engine and Propeller databases on your web site so that the user could
just pull them down when needed instead of manually loading the data.
This could be a cooperative effort with engine and prop manufacturers
so that they maintain and update their data on your web site.
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This is great in theory, but requires a
serious commitment and cooperation from the manufacturers. This
has been discussed with virtually every major engine builder, and
the reasons that are given to us why they cannot support this
request are many - they are too busy, they don't want to maintain
multiple variants of their data, they don't want to make it too
easy for people to consider competitive products (this one I just
don't get), and "for legal reasons" they don't want to
provide the impression that they "endorse" a particular
piece of software (which I can understand to a certain extent,
except that they all provide CAD drawings in AutoCAD DWG or DXF
format). If we cannot absolutely rely on support from the
manufacturers, then we are back to our original philosophical
position - we would rather give you no answer than the wrong
answer. One thought that we have kicked around is to somehow help
develop a truly independent PropExpert user data page, perhaps on
some forum, where interested users and helpful manufacturers can
post whatever data they wish. We will not be responsible for the
data, but we could provide some general oversight to get things
started. Any ideas out there? Here's your chance to help fulfill
your own request. [Engine builder]
Better bollard and
towing calculations. Calculate free running speed with a prop sized
for bollard or towing conditions.
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I'm not sure quite what you mean by
"better" calculations, but I think that this may be just
a case of getting a deeper understanding of the calculations that
are taking place. PropExpert does calculate Top speed when you
select a Towing analysis. The lower Tow speed analysis is
an equilibrium torque technique whereby the analysis (i.e.,
thrust, power, efficiency, cavitation) for that speed is based on
finding the RPM that gives the maximum thrust for the available
power (corresponding to the engine's power curve). On the other
hand, a bollard analysis, which is shown in PropExpert as Bollard
(rated RPM), simply takes your two speeds and runs the
analysis using the rated RPM. The Towing analysis predicts
what you would expect to see "on-the-hawser" during
towing operations (such as dragging a fishing net) or during a
real physical bollard pull test. The Bollard (rated RPM)
analysis is a traditional, albeit somewhat fictional, calculation.
I would refer you to additional information in the PropExpert help
pages, starting with 5.04 - Propulsion Analysis. [Engine
builder]
Better project database
management
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Just as background, I have been told that
this propeller dealer has over 3000 PropExpert project files on
his computer. I would suspect that his project management
requirements are a bit different than most. Having said that, I
fully understand his desire to simplify how PropExpert presents
data to the user. We will add this to our upcoming development
schedule. One idea that we have tossed around is to allow the user
to select a subfolder from a drop-down list. (This might also help
with the filtering request discussed above.) For example, there
might be Active, Inactive and Obsolete sub-folders, from which you
could select which group to see. Under each of these folders, you
might break up your data into manufacturers (for propeller and
engine data) or year (for project data). You would have control
over your own arrangement and naming of sub-folders and PropExpert
would limit the display of data to that folder or to all folders.
Comments? [Propeller dealer]
Today's props have
variable pitch and camber. The model does not allow for this. Could we
input pitch distribution and aspect ratios for camber?
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We're ahead of you on this. First, last
summer we added a Blade Scan Analysis utility that allows
you to take pitch and chord length at various radii (from any
propeller scanning device) and calculate the effective
hydrodynamic pitch. (It also estimates BAR.) This accounts for the
effect of variable pitch distribution and gives you a pitch to use
for the propeller calculation. Look for this under the new Tools
menu item. How this will relate to the propeller library data is
something that is still under review. With respect to camber
(actually "face" camber, also called progressive pitch),
this is something that we are already actively developing. In
fact, we are using a prototype calculation model for our own
internal consulting work and it looks pretty good. Developing new
analytical features (like our work on cupping, cavitation
breakdown, shaft angle effects, and now camber) takes analysis of
available propeller performance data, followed by development of a
calculation model, and finally testing and validation. It will not
be put into PropExpert until I'm completely satisfied that it is
ready to go. The trick with this new feature will be to make the
definition of camber both simple enough to be universal but with
enough detail to reliably predict the effect of face camber. What
do you mean when you refer to the "aspect ratio for
camber"? [Propeller dealer]
What features do you
dislike?
Cruise speed seems to
jump around unpredictably when prop size changes.
-
There had been this behavior with heavily
cavitating propellers. This resetting of the cruise speed was
necessary to allow the solution of propeller sizing to continue.
However, new propeller sizing solution code was developed for
recent versions of PropExpert that greatly improved this behavior.
[Engine builder]
Updating to new versions
never seems to go smoothly.
-
I'm not sure how to reply to this, but say
that unfortunately there is always a learning curve when
introducing a new version of any piece of software to your
existing process. In fact, it is probably harder for a user of a
prior version to learn a major upgrade (such as when the new
interface and data management was introduced in PropExpert 2004),
than for a new customer. You'll have to take this on faith, but we
do not make major changes to our software just to create a new
product to sell. We have enough to do with the development of
useful and valuable new technical features. Every major change was
carefully considered and deemed of greater benefit that the
potential (and expected) inconvenience of working through a new
version. In spite of this, let me end this reply with "I do
feel your pain". [Propeller builder]
Conversion from 4 to 5
blades doesn't seem to have much effect on the sizing
-
I'm not sure how to reply to this, but say
that unfortunately there is always a learning curve when
introducing a new version of any piece of software to your
existing process. In fact, it is probably harder for a user of a
prior version to learn a major upgrade (such as when the new
interface and data management was introduced in PropExpert 2004),
than for a new customer. You'll have to take this on faith, but we
do not make major changes to our software just to create a new
product to sell. We have enough to do with the development of
useful and valuable new technical features. Every major change was
carefully considered and deemed of greater benefit that the
potential (and expected) inconvenience of working through a new
version. In spite of this, let me end this reply with "I do
feel your pain". [Propeller dealer]
Pitch & Diameter
range are in the Prop data but don't seem to be consistently applied
to the output.
-
You are correct. (I think that you are
referring only to diameter, however.) There is a Min and Max
diameter field in the propeller library records. These were
entered solely for descriptive purposes when considering what
propeller model to use. They are not used in any way in the
calculations. [Engine builder]
Some errors actually
lock our licenses and require a reboot of the NetSentinel on the
server.
-
The NetSentinel is the earlier network
license management service that was used for all of our software.
Depending on the version that you were running, and the
configuration of your network, some types of errors could lock up
the program and require resetting the service as you described. We
have taken a number of steps to improve this. First, quite simply
we have developed new code to reduce the number of errors that
PropExpert throws (such as previously with very heavily cavitating
propellers). Second, we trap more errors to allow PropExpert to
exit gracefully if it should encounter something "really out
there" that it cannot handle. Finally, we now support a new
network licensing option (SuperProNet) that is proving to be more
well-behaved. Give us a call and we can discuss how to convert you
to the new network security option. [Propeller builder]
The program can be
closed without saving the current work. The current project should
always be saved [with a unique name] and can be recalled the next time
the program is opened.
-
Are you sure about this? I don't want to
dispute your comment, but I just re-checked closing the current
version of PropExpert after entering some data, and it pops up a
message box asking if you want to "Save project before
closing". It is certainly possible that the code accidentally
overlooks some entered data item, so we will review the code to
insure that the user always is accurately prompted to save the
data before closing. [Engine builder]
Fuel consumption and
duty cycle should be expanded, possibly to use the ISO 8178 E3 &
E5 cycles to calculate fuel consumption or at least allow more than
two operating conditions. In many applications, idle time is
significant and that greatly reduces total fuel consumption.
-
We'll do some research into this. Please
understand, however, that development resources must be allocated
so that they provide the greatest benefit to the greatest number
of customers. I'm not suggesting that we cannot add your
suggestion, just that at face value it may not have universal
interest and until we review it, I cannot make any guarantees. We
work very hard to appropriately focus our resources to keep costs
as low as possible for our PropExpert customers - both for new
purchases, as well as for updates through our Maintenance, Support
and Update (MSU) subscription programs. [Engine builder]
PropExpert is excellent
as long as you will feed the accurate data. The speed prediction is
often below the actual speed, but we like to play safe though.
-
This has always been one of the criticisms of
PropExpert - that the speed prediction is too conservative. Of
course, we all want as accurate an answer as possible, but your
final sentence says it all, "we like to play it safe".
Having said that, we did not intentionally make it conservative,
it is just that the algorithms we use do not quite represent the
performance of most contemporary hulls. So what is the solution?
On one hand, you might suggest that we improve the algorithms. On
the other hand, most people have developed an understanding of how
the speed prediction works and make their own accommodation for
it, so changing a prediction formula takes away their accuracy.
Our first response to this some years ago was to add the Average
hull formula Multiplier field. This allows you to shift
the power prediction as you see fit. If you want the original
formula, you would use a value of 1.00, while a value of 0.90
might be used to reduce the predicted power and allow the boat to
go faster. (Of course, none of this is an issue if you use the Prior
trial feature, where the multiplier is based on the actual
existing performance of the boat.) We are currently working on an
idea where PropExpert might have more than one Average hull
formula, and instead of changing the formula as we have an
opportunity to improve it, we will add the update as a
"new" formula option. Finally, let me refer you to
Knowledge Library Report 130 - Tips for Predicting Speed with
PropExpert. [Propeller builder]
Additional comments
I have tried to address the various suggestions and
critiques that were given in the surveys. In conclusion, I would like to
list some of their compliments to us without any comment on my part.
Easy to use.
[Engine builder]
I was at the seminar last METS and that was
very interesting.
[Propeller dealer]
With a sea trial you can fix almost any
propeller problem
[Propeller dealer]
Easy working, complete system
[Propeller dealer]
Keep up the great work!
[Propeller dealer]
Thank you for your care and service. I am very
glad to use PropExpert.
[Propeller builder]
And finally, the response of which we are most
proud is that when asked
Would you recommend
HydroComp products and services to others in your industry?
Every one of these PropExpert users
replied Yes.
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