On Jul 29, 2:46 pm, "Roger Long" wrote:
"Bob" wrote



I was wondering why you put the exhaust/funnels so far aft?

Look at the separate gear handling areas, one for gear that needs to go over
the side and one for gear that goes over the stern and I think you'll start
to get the idea. These boats also need windage aft to help maintain
attitude on station and the windage of those two stacks aft will help a lot.

The most critical operator view is of the wire that goes over the side
A-frame attached to perhaps a quarter million dollars worth of insturments.
That's why no uptake and stack between pilothouse and side gear handling
area.

--
Roger Long


Hi Roger, thanks for the thoughtful answer. Yeks, sounds like there is
a very sepecific purpose in that boat's future. I know little about R/
V design other than they are asked to do some really wierd things in
the name of quality data. Specialized use can make for some out of the
ordinary designs. Cool boat.

Bob

It is a jet boat because it will be operating primarily in the shallow
waters of Cheaspeak Bay and a lot of areas of interest are the thin parts.
The draft of the jet boat isn't significantly different than a prop boat
with tunnels but there is a big difference running with just a foot or two
of water under you when the first thing to strike will be spinning props
that will send you the the shipyard for haulout if they touch. The jets
will ingest a lot of oyster shells and other debris. The jet boat could
probably plow right through an oyster bar and keep right on operating
although the transducers and bottom paint would suffer.

The jets are less fuel effecient. Another way of putting this is that the
boat will burn more fuel at the same speed. We expect the cost of this fuel
to be offset by not hauling out to repair props so often and being able to
extend the working area safely into shallower waters. The jets also
contribute significantly to maneuverability since they can essentially
vector thrust in any direction.

The fins are to provide the directional stability normally contributed by
the drag of struts, props, and rudders. They also contribute to roll
damping.

--
Roger Long

"Roger Long" wrote in news:46add541$0$16582
:

The jet boat could
probably plow right through an oyster bar and keep right on operating
although the transducers and bottom paint would suffer.


That really depends a LOT on which jet pump is used. If the jet used has a
stator a few cm behind its spinning impeller, it will very soon be
destroyed by the first piece of hard flotsam that it ingests. Case in
point is any jetski jet or the Mercury SportJet pumps. The spinning
impeller is very, very close to the cast aluminum stator used to stop the
water spinning out the back and is required to produce linear thrust. If
ANYTHING gets between that stator and the prop, it eats the drivetrain,
instantly.

Not all jets are made for river bottom dragging service like those
wonderful jetboats made in Oz.....(c; You get a SportJet near the bottom,
it's going to be a very expensive cruise...very quickly.

Larry
--

On Jul 30, 2:11 am, "Roger Long" wrote:
It is a jet boat because it will be operating primarily in the shallow
waters ...
The fins are to provide the directional stability normally contributed by
the drag of struts, props, and rudders. They also contribute to roll
damping. ...

That sounds very sensible. The placement and shape of the fins is
also interesting. I was wondering if you had chosen the long, shallow
fins outboard on the chines to control the flow at the jet intakes or
increase hull lift (perhaps to make up for the absence of strakes). I
was also curious about the linkage between the jets and the engines.
On the profile it looks like you might need two CV joints because the
shaft doesn't line up. Thanks again for the education. FWIW, I
think it is a handsome design. I suspect the builders appreciate the
straight forward development of the hull, too.

-- Tom.

On 2007-07-30 08:11:00 -0400, "Roger Long" said:

It is a jet boat because it will be operating primarily in the shallow
waters of Chesapeake Bay and a lot of areas of interest are the thin
parts. The draft of the jet boat isn't significantly different than a
prop boat with tunnels but there is a big difference running with just
a foot or two of water under you when the first thing to strike will be
spinning props that will send you the the shipyard for haulout if they
touch. The jets will ingest a lot of oyster shells and other debris.
The jet boat could probably plow right through an oyster bar and keep
right on operating although the transducers and bottom paint would
suffer.

Most of the bay has a thick bottom of mostly mud, but an awful lot of
it is 6'.

Interesting set of considerations. Hope to see it operating about the Bay.

Any idea where they plan to berth it?

--
Jere Lull
Tanzer 28 #4 out of Tolchester, MD
Xan's new pages: http://web.mac.com/jerelull/iWeb/Xan/
Our BVI pages: http://homepage.mac.com/jerelull/BVI/

"Jere Lull" wrote

Any idea where they plan to berth it?

It will be based in Solomons at the UMCES Fleet Facility where the Aquarius,
the current vessel, is now moored.

--
Roger Long

The jets
will ingest a lot of oyster shells and other debris. The jet boat could
probably plow right through an oyster bar and keep right on operating

Gee, destroying the waters they're trying to research isn't exactly sound
logic. I'd also wonder how much more damage the water flow from the jets
would cause during maneuvering a boat of that size.

Not saying this as an argument for props though. More that it's dumb to
plan to go into places that will very likely cause greater harm to the
enivonment that necessary. Take a dinghy or launch instead, not some huge
vessel.

"Bill Kearney" wkearney-99@hot-mail-com wrote

(poorly thought out and semi-informed drivel)

Come on, they aren't going to intentionally go plowing through the bottom.
But, any vessel that routinely works in shallow water is bound to touch
sometime.

The bottom damaging wash of props is right down at the bottom and radiates.
The jet output is horizontal and at the surface. There is a large downward
component in reverse but at slow speeds neither this nor the suction is
going to be significantly more destructive to bottom habitat than props.

Schottle Pump Jets, another kind of water jet, were originally developed
primarily to provide propulsion over sensitive bottom areas. Only later did
they prove to be excellent bow and stern thrusters.

This is not a water sampling vessel. There are plenty of small craft to do
that job. You are not going to take the kind of gear this vessel will be
deploying in small boats.

--
Roger Long

"Roger Long" wrote in message
...
"Bill Kearney" wkearney-99@hot-mail-com wrote

(poorly thought out and semi-informed drivel)

And "**** you too".

Consider it done.

--
Roger Long