[PSUBS-MAILIST] Propane subs

[CWall@swri.edu]

I'll reply to more than one poster here, just to keep the traffic down.

Ron, I don't mind posting and I invite criticism, but I was really just putting
 out a concept for comment, in hopes of identifying a "showstopper".   Because
it's just a paper design at this point, and because I already have a pretty
full plate of projects, it would be disingenuous to make it sound like this was
 at the hardware stage.  (However, if I don't find a big objection and I happen
 to come across a the right piece of steel, I could potentially start cutting
metal this coming summer. )

On to the other things:

1) I have tentatively chosen the Honda Long Life engine, which is nominally
aircooled- but that is not set in stone.  However, since I would be severely
derating it in cruise mode, I believe I could get away with air cooling in a
vented compartment. I'm talking about a half-horsepower here, and that 200 mile
 range would be at 2 kts- and yes, that's 100 hours.  That would turn most
people off, but I happen to be a little more "process" oriented than your
average solo voyager. The extra horsepower would be put to use if I needed to
buck a current.  Liquid cooling an engine like this can be accomplished with
either a different cylinder head or with cooling tubes inserted between the
cooling fins.  Either way, I am NOT going after a lot of horsepower, and the
engine will be derated more than a little. And it may not be the Honda; I'd go
for an outboard motor power head, except you need a 4-stroke-   trying to mix
oil with propane vapor isn't very practical, and I don't like oil injection.

2) The engine compartment is still labile designwise- I would anticipate a
separate compartment with a hatch communicating with the crew compartment, but
this depends on number of factors.   Snorkels would be short- not much above
the "conning tower".

3) I used the term "syntactic" foam, but I have access to appropriate materials
 where I work, and I don't require the expensive stuff that you are thinking
of. And in fact, I could make my own formulation.   Yes, the ballast system I
proposed is overkill, and I have seriously considered deleting the side ballast
 tanks.   But I am also thinking about extra freeboard and rough water
stability that might be very nice at times, and you don't have to blow it if
you don't need it.   I do have a notion that being able to surface with the
crew compartment flooded is a nice capability, and the design as it now stands
could actually be taken to that point, but that makes the ballast volume eat
way into the crew volume, and right now I'm designing for normal operation with
 the side ballast omitted and internal ballast able to do everything, so that
the side ballast, if I added it, would be much less critical.... and I could
concentrate on surface performance shaping rather than trying to get a lot of
side ballast volume. Besides....I like redundancy.  I anticipate operating with
 no support at all.   Self-rescue capability is something I put a lot of value
on.

4) The reason I seem to be hedging on some of particulars is that the design as
 it stands is actually a spectrum of features, mainly because I want to be able
 to use expedient materials- which is to say....I don't know what dimension
tube I will acquire.  I have described options for a sub from 14 to 24 ft in
length, and things like the engine compartment details will change depending on
 how big the damned thing is.   I prefer smaller, but if I got a really good
deal on a few items I might go for the bigger option.

5) The other thing to remember is that the vehicle will go through a couple of
incarnations if I build it- the first season is likely to be in "towed" mode,
with no propulsion installed, just proving out the ballasting systems.  
Obviously, more flexabiltiy is available with a larger hull, and the options
I've mentioned would not be invoked until the primary systems were
well-understood.    

Try to pin me down and I'll just weasel, simply because I'm hold a lot of
options open at this point.   But I'm actually encouraged that I haven't heard
any objections that are insurmountable. Most of what I see as potential
problems can be addressed with procedure.

To wind this up, there is one thing that strikes me as problematic, and that is
 refueling. I can get propane nearly anywhere, but the ideal setup would be to
simply change out bottles. This brings up the question of hatches into the
ballast tanks, something I'd rather not have to deal with. If anyone has a
suggestion for a decent "soft patch" or the equivalent, I'm all ears.  (The
driver for this is that handling discrete bottles makes quantifying the propane
 easier- you can do it by weight. Otherwise you have to weigh the mass you
deliver to onboard tankage, and you can't see corrosion on fuel tanks buried in
 place, etc...)

Craig Wall