RE: [PSUBS-MAILIST] Thrusters behind vs thrusters at sides?

[Alec Smyth <Asmyth@changepoint.com>]

Side control is just like a V-tail plane... the rudders. I didn't see a
point in a side thruster since I will always be going forward except at
dockside. But being able to reverse either motor should allow for
maneuvering on or off a trailer.

- Alec

-----Original Message-----
From: MerlinSub@t-online.de [mailto:MerlinSub@t-online.de]
Sent: Monday, July 30, 2001 2:58 PM
To: personal_submersibles@psubs.org
Subject: Re: [PSUBS-MAILIST] Thrusters behind vs thrusters at sides?


> Alec Smyth schrieb:
> 
> Now the pictures are on in the PSUBS picture gallery, may I put out a
> general question for discussion?
> 
> If you look at the concept drawing, I have two thrusters plugged in at
> the stern, a la Deep Flight. This has a couple of advantages:
> 
> - I can carry a SCUBA tank (or two) easily on the thruster chassis.
> Because this is external, the tanks can also be easily replaced.
> 
> - Carrying the tank outside means it does not add any weight to the
> hull.
> 
> - Less chance of entanglement, and better protected at dockside.
> 
> - I have not yet found a set of counter-rotating props for trolling
> motors, so this should minimize the torque due to both props turning
> in the same direction.
> 
> - If one motor dies, I think its more likely the survivor can be used
> for getting home (as opposed to going in circles) if its close to the
> centerline.

No point - you can build in the MD-80 configuration both thruster 
with a 2-3 degree outside angle from the middle axis. Depents on  
speed the boat will drive strait forward with one engine running. 

> 

Best point : 
In this configuration both motors are well protected and will not 
catch a rope or net (like in the MD-80 config.) From a prone position 
sub you can no look to the stern..
.. so you never will find out which dammed force catch your sub and
force 
you on the bottom - maybe for ever.  

Also in this configuration the thruster can use some of 
the frictional wake of the hull - this can be save on a submarine
up to 10-20 % of thrust power consumption (Depents on the speed and hull
configuration.) 

> 
> 
> But on the other hand, if I mounted the thrusters in fixed positions
> one on each side, near the stern but on the side of the hull (like an
> MD-80 airliner):
> 
> - There's no fairing to build or break.
> 
> - I would have greater maneuverability at dockside.
> 
> - The boat gets several feet shorter, which would make it easier to
> trailer, and perhaps more maneuverable in flight.

The boat get shorter - thats a good point. 

> 
> The big unknown to me, since I do not know much about aerodynamics
> (ok, hydrodynamics), is which of the two configurations might be the
> more efficient in terms of drag. And this is probably the most
> important consideration of all. Any feedback would be very welcome!
> 
> thanks,
> 

In which way you have side control ? 
Carsten

> - Alec