"Jere Lull" wrote

It seems you don't know the Chesapeake Bay well.

That's sure true. I've only sailed on it once and that was actually
motoring in a 380 foot Russian square rigged school ship. I'm working
however, for people who know it better than just about anyone.


The jets extend your baby's working area by tens of thousands of square
miles of the most environmentally "interesting" areas.

The difference in draft between the research vessel and a prop version is
actually surprisingly little. As measured, it would only be about a foot if
the prop version had partial tunnels as on the Woods Hole vessel. Not
having this expensive, delicate props and rudders right at the bottom though
means you can responsibly operate with less margin of water under the boat.
This is kind of a fuzzy figure and varies with weather and other conditions
but probably will usually let the jet boat operate in 2 - 3 feet less water
than the prop boat. Draft is still 4' - 8" at full load so a lot of the bay
is closed to her anyway. It's the region between about 6 and 9 feet that
will be more available to her than if she had props. Nobody has actually
calculated what that area is. Somewhere between hundreds and tens of
thousands I would guess


And you don't "plow" through an oyster bar, you *hit* one and stop very,
very quickly.

I didn't mean to imply that plowing through was part of the mission profile.
I expect the boat would stop. After backing or being pulled off however,
she ought to be able to continue working instead of heading for a shipyard.
She has a foot deep full length keel which is unusual for a power boat but
assists her station keeping and damps rolling. I expect that would go
pretty cleanly through a lot of stuff when they were lacking just a few
inches or a foot of draft, unlike a set of spinning props and rudders.

I forgot to answer Larry about the jets injesting stuff. The impellers in
these things are pretty industrial grade, think tree limb chipper rather
than jet ski plastic part. They will digest pretty much anything that will
fit through the intake grates and is low enough in density to either float
or be sucked up from the bottom. The impellers may get chipped and lose
efficiency but, unlike props, they don't immediately start vibrating so
badly that they have to be pulled. You can keep operating a damaged
impeller for quite a while.

--
Roger Long

"Roger Long" wrote in
:

I forgot to answer Larry about the jets injesting stuff. The
impellers in these things are pretty industrial grade, think tree limb
chipper rather than jet ski plastic part. They will digest pretty
much anything that will fit through the intake grates and is low
enough in density to either float or be sucked up from the bottom.
The impellers may get chipped and lose efficiency but, unlike props,
they don't immediately start vibrating so badly that they have to be
pulled. You can keep operating a damaged impeller for quite a while.



None of the jetski pumps use plastic impellers or stators. The
impellers are stainless steel with very close tolerances between the
impeller and wear rings around them. The stators are cast aluminum and
objects won't cause them any harm passing through the pump, either.

However, the problem with Mercury Sport Jet and jetski pumps arises
because the distance between the aft end of the whirling impeller at
high RPM and the fixed stator vanes is only about 1/4". ANYTHING over
1/4" is SURE to get WEDGED between the impeller and stator. This will
rip the gearboxes right out of them before any kind of sheer pin breaks.
Sometimes the drive shafts, both vertical and horizontal simply break
apart from the kinetic energy of the impact.

I was just wondering how much flowline clearance between the impellers
and fixed parts like a stator there is in these big pumps to prevent
such catastrophies from occuring.....

Thanks for the answer, however.... Let us know how much trouble it is
to clear the long tubular weed stalks out of the pump are WHEN, not if,
it happens....(c; I sucked up a ski rope one time and the floating
handle was the ONLY part that wouldn't fit through the intake grate. It
ate the aft end shaft seal and sleeve bearing that normally runs in
thick oil, which was ejected by the water pressure when the seal was
simply smashed away. The noise of the outer edge of the impeller
crashing into the pump housing from the lack of a rear bearing tight
enough to prevent it was DEAFENING! So wasn't the silence for about the
first hour after the emergency shutdown.

The entire pump had to be disassembled, the impeller removed while
cutting off the wound rope so tight it locked the impeller threads solid
to the horizontal drive shaft. The rope actually MELTED UNDER WATER
from the frictional heating into a solid blob of polypropylene....no fun
at all that day.

If you saw the size of the Carden shafts that connect the engines to the
jets on this boat, I don't think you would have much concern about the
impellers chopping up anything that goes through. I didn't look carefully
at the stator clearance but I think it's larger than the intake grate
spacing. Stuff like rope and weeds could be a problem but there is an clean
out port above the waterline and these units are big enough to get two hands
and elbows in to work on clearing them if necessary.

--
Roger Long

On Thu, 25 Sep 2008 00:25:01 +0000, Larry wrote:

"Roger Long" wrote in
:

I forgot to answer Larry about the jets injesting stuff. The
impellers in these things are pretty industrial grade, think tree limb
chipper rather than jet ski plastic part. They will digest pretty
much anything that will fit through the intake grates and is low
enough in density to either float or be sucked up from the bottom.
The impellers may get chipped and lose efficiency but, unlike props,
they don't immediately start vibrating so badly that they have to be
pulled. You can keep operating a damaged impeller for quite a while.



None of the jetski pumps use plastic impellers or stators. The
impellers are stainless steel with very close tolerances between the
impeller and wear rings around them. The stators are cast aluminum and
objects won't cause them any harm passing through the pump, either.

However, the problem with Mercury Sport Jet and jetski pumps arises
because the distance between the aft end of the whirling impeller at
high RPM and the fixed stator vanes is only about 1/4". ANYTHING over
1/4" is SURE to get WEDGED between the impeller and stator. This will
rip the gearboxes right out of them before any kind of sheer pin breaks.
Sometimes the drive shafts, both vertical and horizontal simply break
apart from the kinetic energy of the impact.

I was just wondering how much flowline clearance between the impellers
and fixed parts like a stator there is in these big pumps to prevent
such catastrophies from occuring.....

Thanks for the answer, however.... Let us know how much trouble it is
to clear the long tubular weed stalks out of the pump are WHEN, not if,
it happens....(c; I sucked up a ski rope one time and the floating
handle was the ONLY part that wouldn't fit through the intake grate. It
ate the aft end shaft seal and sleeve bearing that normally runs in
thick oil, which was ejected by the water pressure when the seal was
simply smashed away. The noise of the outer edge of the impeller
crashing into the pump housing from the lack of a rear bearing tight
enough to prevent it was DEAFENING! So wasn't the silence for about the
first hour after the emergency shutdown.

The entire pump had to be disassembled, the impeller removed while
cutting off the wound rope so tight it locked the impeller threads solid
to the horizontal drive shaft. The rope actually MELTED UNDER WATER
from the frictional heating into a solid blob of polypropylene....no fun
at all that day.

We once sucked up a ski rope with our Turbocraft. It was no big deal.
We simply unbolted the U-joint and turned the pump backwards with a
pipe wrench [It has a tubular auto type shaft] while pulling on the
rope. No damage, and it only took about fifteen minutes to fix the
problem. It didnt go all the way in. I wasn't there, but apparently
the operator shut off the engine before matters took their course.

Casady

"Roger Long" wrote in
:

Stuff like rope and weeds could be a problem but there is an clean
out port above the waterline and these units are big enough to get two
hands and elbows in to work on clearing them if necessary.



Oh that IS nice! I hope in a rolling sea there is enough freeboard when
the port is open to work in there in the waves without flooding the boat.

The only way to clear the external pumps of my little jetboats is to
swim....not a great idea in some gator-dense waterways around
here....Swimming can be deadly.

(Richard Casady) wrote in
:

We simply unbolted the U-joint and turned the pump backwards with a
pipe wrench

We tried turning the engine backwards, which unwound some of it, but it
wasn't successful enough times. There ought to be some kind of reverse
cranking so you can start the Sport Jet's 2-stroke engine backwards, which
it would do if you could wind the rope around the flywheel backwards, I
suppose. 2-strokes don't care. Might be able to flush the pump out
backwards if you shove the nozzle underwater with bodies on the swim
platform. I never tried that.

"Larry" wrote


Oh that IS nice! I hope in a rolling sea there is enough freeboard when
the port is open to work in there in the waves without flooding the boat.


The jets are in a separate watertight compartment. The boat would float and
most of the stuff, including the propulsion, would continue to work even if
you cut a hole in the bottom of it.

One reason for this is that the water flow through the jets is like a huge
heat exchanger so the jet compartment gets very cold and there is lots of
condensation.

--
Roger Long

On 2008-09-24 18:47:08 -0400, "Roger Long" said:

"Jere Lull" wrote

The jets extend your baby's working area by tens of thousands of square
miles of the most environmentally "interesting" areas.

Draft is still 4' - 8" at full load so a lot of the bay is closed to
her anyway. It's the region between about 6 and 9 feet that will be
more available to her than if she had props. Nobody has actually
calculated what that area is. Somewhere between hundreds and tens of
thousands I would guess

Did you say that she draws under 5 feet before anything touches?

And a foot of that is essentially a protective KEEL?? (intentional or not)

And the "wheels" can't be damaged by small stuff???

OMG! Your baby's a perfect Bay boat for all her size.

LOCK her to the DOCK before the watermen find out

I assumed without looking that her draft was over 6 with a flattish
bottom. Things like that make a WORLD of difference around here.

And my estimate of her working area INCREASED by tens of thousands of
square miles, no joke!

We draw 4.2, about what you're describing all things considered.
(Whatever cuts through the mud is not really draft ;-)

***** I invite ANY experienced Bay boater to tell me I'm lying. It's a
free shot as I won't contest your assertion unless you sound like a
sock puppet. ******

Roger, you really don't know the Bay.....

-----

If I'm guessing properly, you'll be doing her trials in the Solomons area.

When you head east across the Bay, pay close attention to the depth
around the Honga or Bloodsworth.

Hell, watch the depth display when you go south around whatever point that is.

Come to think of it, North is sorta interesting too, but those fish
traps spoil the fun, marking the shallows and all.

And there's that interesting sand spit to the west where you could
probably nudge the bow onto the shore while reading 100'+ accurately

That is, if they wait that long.... The Solomons anchorage has some
interesting features. Their entrance can be fun to the uninitiated.
(the channels essentially define a diamond, but....)

If you want to sleep comfortably, do NOT examine the charts of the area
closely unless you absolutely have to.

I am laughing so hard, I'm crying as I image the look on your face the
first time an experienced helmsman takes her out after they're
confident in her.....

Oh, I really, really wish I were there to record it.

Roger, you really, really don't know the Bay.


And you don't "plow" through an oyster bar, you *hit* one and stop
very, very quickly.

I didn't mean to imply that plowing through was part of the mission
profile. I expect the boat would stop.

Oh, I knew that. Was just pullin' yo lahg.

DO watch for the locals' sense of humor, BTW. If you do NOT react,
they'll cut it closer next time. Practice faking it.

Roger, I expect you'll really, really, really learn to love the Bay
with their help.

ENJOY friend, take lots of notes.

Please report back on the impressions of a Yankee in King Chesapeake's Court.

-----

Okay, Bay boaters.... How many of you are in pain from imagining
Roger's expression(s)?

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

Fun post Jere. However, I'm afraid I won't know the bay any better after
this is over unless I bring my boat (4' -2" draft) down there. The delivery
trip will be directly to Solomons where I will get off and head straight for
the airport. The boat will then be operated by people who have been doing
research on the bay for decades. I think the mate has worked on the bay his
whole life. Because they have been involved in research over the whole bay
and not just looking for oysters and crabs in one region of it, it would be
hard to find a boat crew on the bay that know it better.

--
Roger Long

Jere,

Have you seen this boat? It's the one the "Rachel Carson" is replacing.

http://www.umces.edu/fleet1.htm

--
Roger Long