On Wed, 15 Dec 2004 19:00:24 -0500, "Eisboch"
wrote:


"Short Wave Sportfishing" wrote in message
.. .

I've hit things at speed with my outboards and, well to put it
plainly, F'd 'em up pretty bad, but I've never ripped a lower unit off
at speed. Broke a casting once, lost a skeg once and seriously
mangled a prop shaft and prop once.

Then again, neither of my boats weigh 15,000 lbs either.

When a youngster with a Sears 12' aluminum boat and 7 hp outboard, I seem to
remember leaving the motor unlocked, so if I hit something the motor would
just flip up. (It was embarrassing when you forgot and revved it up in
reverse).

Hell, I still do that. :)

Anyway, it just seems to me that a heavy boat at speed isn't
going to stop in time=zero if it hits a rock higher up than the nosecone and
the energy of the impact has to go somewhere. Maybe the leg will stay
together, but the transom will get ripped off.

The only incident I can compare to was off of Fisher's Island when I
hit a telephone pole type log going 30 or so in my Ranger. It was
just below the surface so I didn't see it until I was right on top of
it. The log hit the motor dead on between the middle section and the
lower unit. Totally cracked the mid section, broke the lower unit
open and mangled the prop shaft and prop.

Fortunately, nobody was hurt, but Sea//Tow had a long tow back to the
launch. :)

Later,

Tom

Eisboch wrote:
"Short Wave Sportfishing" wrote in message
...

On Wed, 15 Dec 2004 17:02:27 -0500, "Eisboch"
wrote:


So, what happens when you hit a rock or log at 25 knots with an Alpha or
Bravo drive?

I don't think it falls off as this one is designed to do.

Later,

Tom


I don't know. I've never had the experience, but assume a 15,000 lb boat
doing 25 knots and it hits an unmovable obstruction like a rock ... lemmie
see, energy = mass x velocity squared ... seems to my intuitive analysis,
something's going to give.

Eisboch


They get damaged the leg/gearcase part mostly badly damaged, but the
leg raises up & usually doesn't rip the transom out of the boat.

The hydraulic rams are designed to allow the stern drive to come up if
there's enough "sudden" force applied. The rams have twin walls &
compound pistons so they can sorta suck a momentary vacuum allowing the
drive to come up. The Volvo ones are similar & older ones had a
mechanical release.


K

In article ,
jetcap wrote:


Karl Denninger wrote:
Azipod units also aren't usually set up as "pullers".

Azipod is a trade name registered to the ABB corporation. Azipods are
podded azimuthing electric drives, and their design is based on placing
the propeller forward in undisturbed wake for highest efficiency.

You may be thinking of what are called "Z-drives" that are mounted on
tugboats and other small vessels. "Z-drives" are not Azipods but they
are azimuthing thrusters and may or may not incorporate a nozzle.

Rick


Yep....

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"K. Smith" wrote in message
...
Eisboch wrote:
"Short Wave Sportfishing" wrote in message
...

On Wed, 15 Dec 2004 17:02:27 -0500, "Eisboch"
wrote:


So, what happens when you hit a rock or log at 25 knots with an Alpha
or
Bravo drive?

I don't think it falls off as this one is designed to do.

Later,

Tom


I don't know. I've never had the experience, but assume a 15,000 lb
boat
doing 25 knots and it hits an unmovable obstruction like a rock ...
lemmie
see, energy = mass x velocity squared ... seems to my intuitive
analysis,
something's going to give.

Eisboch


They get damaged the leg/gearcase part mostly badly damaged, but the
leg raises up & usually doesn't rip the transom out of the boat.

The hydraulic rams are designed to allow the stern drive to come up if
there's enough "sudden" force applied. The rams have twin walls &
compound pistons so they can sorta suck a momentary vacuum allowing the
drive to come up. The Volvo ones are similar & older ones had a
mechanical release.


K

Makes sense. Nice to know they are designed to "give". I can visualize
the leg kicking back which would allow it to provide lift up and over the
object as an inclined plane, so to speak.

Eisboch

Karl Denninger wrote:



The Volvo system does not azimuth 360 degrees. Its more like an outdrive in
its range of motion, among other differences.

Azipod units also aren't usually set up as "pullers".

--

Yup, I mis-read and assumed azimuthing.
Azipods are set up as pullers.

At any rate, although I can see some increased risk for damage to props
and rapping up lines, If the breakaway feature is well designed, it
might be better than driving a set of skegs, props and rudders back up
through the hull .... time will tell.

otn

otnmbrd wrote:
Yup, I mis-read and assumed azimuthing.

You assumed correctly. They are azimuthing thrusters.

Rick

On Wed, 15 Dec 2004 17:02:27 -0500, "Eisboch"
wrote:


"S. N. Ot" wrote in message
news

"WaIIy" wrote in message
...

http://www.ybw.com/auto/newsdesk/200...42mbynews.html

Tiara is going to use it.

This is going to be a nightmare. Look at the schematic and
read what will happen to the drive under impact.

Yeah - I really want the drive unit to break off and sit
on the bottom.

Are you sure it's not April 1st over in Sweden?



So, what happens when you hit a rock or log at 25 knots with an Alpha or
Bravo drive?


The drive and trim rams are designed to "give" backward to absorb much
of the shock. At slower speeds, you might get away with only prop and
skeg damage. Higher speeds have been known to punch a hole into the
nose cone. I also had a friend who had an unfortunate encounter with a
rock at high speed and it pretty much sheared the drive off at the
gimbal mount. In this particular case, water started to seep in
through what used to be the shaft bellows, but it was not enough that
the bilge pump couldn't keep up until we towed him in

But without that built-in "give", something WILL break.

Dave

On Thu, 16 Dec 2004 07:00:46 -0500, Dave Hall
wrote:

On Wed, 15 Dec 2004 17:02:27 -0500, "Eisboch"
wrote:


"S. N. Ot" wrote in message
news

"WaIIy" wrote in message
...

http://www.ybw.com/auto/newsdesk/200...42mbynews.html

Tiara is going to use it.

This is going to be a nightmare. Look at the schematic and
read what will happen to the drive under impact.

Yeah - I really want the drive unit to break off and sit
on the bottom.

Are you sure it's not April 1st over in Sweden?



So, what happens when you hit a rock or log at 25 knots with an Alpha or
Bravo drive?

The drive and trim rams are designed to "give" backward to absorb much
of the shock. At slower speeds, you might get away with only prop and
skeg damage. Higher speeds have been known to punch a hole into the
nose cone. I also had a friend who had an unfortunate encounter with a
rock at high speed and it pretty much sheared the drive off at the
gimbal mount. In this particular case, water started to seep in
through what used to be the shaft bellows, but it was not enough that
the bilge pump couldn't keep up until we towed him in

But without that built-in "give", something WILL break.

Even with the give, something will break.

Later,

Tom

Does this remind anyone of an OMC(?) item called Saildrive??? I hope it
works and works well. Volvo seems to be an outfit that takes engineering
seriously. Not too many Volvo orphans out there such as the Yamaha stern
drive.

Butch
"WaIIy" wrote in message
...
On Tue, 14 Dec 2004 20:42:49 GMT, (Karl Denninger)
wrote:


In article , WaIIy To
wrote:

http://www.ybw.com/auto/newsdesk/200...42mbynews.html


Tiara is going to use it.

Forward facing propellors with no protection eh?

That ought to be interesting the first time you hit something solid at 40
knots.

Oh yeah, I read the part about the leg shearing off and not puncturing the
hull. Uh huh. And if that seal fails? Exactly how big is that mounting
hole? Bet 'ya can't jam a wooden plug in THAT slot.

--

Well, I'd guess Volvo and Tiara know a bit about boats.

jetcap wrote:
otnmbrd wrote:

Yup, I mis-read and assumed azimuthing.


You assumed correctly. They are azimuthing thrusters.

Rick

LOL Then I'm back to square one on this system. Like all systems, it
will have advantages and drawbacks which will require more or less care
when operating.
One big disadvantage will probably involve maintenance and repair cost.

otn