Re: [PSUBS-MAILIST] Boucher, RPM - sub info.

[Erik Muller <emuller@naic.edu>]

Thanks Ian et al.,
I don't think I agree that the accuracy needs to be THAT good. We can 
use statistics to pull out good, average emprical values....

At the extreme risk of condescending everyone (which is absolutely not 
my intent), can I break this question down and chase it along on email 
here? (I KNOW this looks patronising, but it more helps clarify what is 
in my jumbled up head) - also remember that I don't actually have a 
machine, so I am talking from a relatively uninformed aspect.

What is the issue here?
We are asking for some data regarding performance of working submarines. 
The problem is that the data accuracy (and precision) will certainly 
vary from owner to owner.

What do we want the information for?
Well, we can either:
a) improve, design or build a submarine based entirely on these 
empirical numbers - therfore, we need very good data - of a high and 
known accuracy.
b) do some little STAISTICAL analyses as necessary/interesting and 
obtain a better overall understanding of the general trends. (i.e, in a 
hand-wavey way, how does velocity). The key here is that not all data 
points are going to be exactly on the same line, but that is ok!  - we 
can do a trend analysis, reject outliers etc. In this case, we can get 
away with low-quality (read 'low accuracy and precision') data.

What are the problems associated with these alternatives?
a) It is unreasonable and excessive to demand high quality data from the 
owners/builders.
b) We need a big-ish number of owners to contribute their data.

So:
The problems associated with option b are much more surmountable that 
those for a, and the outcomes are just as useful although in a slightly 
different way. It is not appropriate to design and build a submarine 
based entirely and exactly on somone elses empirical figures anyhow, 
therefore, there is no need to demand this high-accuracy data. However, 
all we can do with the low quality data is make neat little plots and 
flesh out trends to optimise the next generation of subs.

Of course it is important to get the data as GOOD as possible - within 
reason. Data with errors which are more than 10% are probably not 
useful, though I think that is an easily-achieveable upper limit. Im 
sure it is possible to measure the length of a 2m sub to within 20cm or 
so!  I really think it is uncessary (and impudent) to impose measurement 
techniques,  as if to suggest that the owner - who has built a SUB from 
the ground up, is incapable of achieving this kind of accuracy through 
their own ingenuity. By NOT dictating measurement techniques, we can get 
more data, and faster, since people dont have make special trips to 
measure them - unless they choose to (and for some owner/builders it 
will be a point of interest and pride anyhow).

Im pretty confident that, say, Carsten can measure the length and speed 
of his behemoth sub without me telling him how to do it. I am even more 
confident that he already has most of these numbers in his head and does 
not need to make a special trip to find them out (the speed at this 
point is pretty easy I suppose ~ 0 kts?!!).

Furthermore, the person who has entered their data will presumably be 
contactable later on for futher discussion on their measurements.

Apologies for the lengthy email!
EM.

P.s. Ian, to answer your questions: For reasons of simplicity of coding, 
previous data is not editable. To modify the data you need to contact 
Wyatt. This is straightforward though, Wyatt is very communicable.
Having said that, I am not adverse at all to moving the site to 
somewhere more visible, I am sure Wyatt would not mind either - this 
was  a bit of a prototype (which unfortunatly didn't draw the crowds 
that we had hoped..).

P.P.S - the caribbean water is cool today..





************************************************************************
************************************************************************
************************************************************************
The personal submersibles mailing list complies with the US Federal
CAN-SPAM Act of 2003.  Your email address appears in our database
because either you, or someone you know, requested you receive messages
from our organization.

If you want to be removed from this mailing list simply click on the
link below or send a blank email message to:
	removeme-personal_submersibles@psubs.org

Removal of your email address from this mailing list occurs by an
automated process and should be complete within five minutes of receipt
of your request.

mailto:removeme-personal_submersibles@psubs.org

PSUBS.ORG
PO Box 311
Weare, NH  03281
603-529-1100
************************************************************************
************************************************************************
************************************************************************