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Paddlewheels versus Propellers



 
 
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  #11  
Old November 15th 09, 08:59 PM posted to rec.aviation.piloting
Morgans[_2_]
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Default Paddlewheels versus Propellers


"a" wrote

Even more aviation: you could not maintain altitude: couldn't get up
on to planning speed.


But 5 knots? My 25 foot swing keel O'Day (think of the keel as a
vertical wing) could do that in a reasonable breeze and it
was NOT a fast boat.

s
Not surprising, to me.

Every boat has a "hull speed" than can be calculated, relating mainly to
length, that applies in a strictly displacement mode. The longer, the
faster, generally. The O'Day 25 (used to have one) had a hull speed of
about 6 1/4 knots. To go faster you would have to apply enough HP (LOTS
more HP) to get up on plane, and I suspect the one engine in the power boat
did not have enough power to get it over the hump. Also consider that a
considerable amount of one engine's HP would be consumed by rudder drag,
since the rudder would have to be nearly 45 degrees to keep the boat going
straight.. Also, the 5 knots mentioned is probably not terribly accurate,
since the accuracy of a power boat's "speedometer" is not very good at low
speeds.

It hurts my head to think about what parts of the two engines were
common, and which were different.


Not that bad, I think. Camshaft, crankshaft, oil pump, water pump, harmonic
ballancer, distributor, alternator.

_ Jim in NC


  #12  
Old November 15th 09, 11:46 PM posted to rec.aviation.piloting
a[_3_]
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Default Paddlewheels versus Propellers

On Nov 15, 2:59*pm, "Morgans" wrote:
"a" wrote

Even more aviation: you could not maintain altitude: couldn't get up
on to planning speed.
But 5 knots? My 25 foot swing keel O'Day (think of the keel as a
vertical wing) could do that in a reasonable breeze and it
was NOT a fast boat.


s
Not surprising, to me.

Every boat has a "hull speed" than can be calculated, relating mainly to
length, that applies in a strictly displacement mode. * *The longer, the
faster, generally. *The O'Day 25 (used to have one) had a hull speed of
about 6 1/4 knots. *To go faster you would have to apply enough HP (LOTS
more HP) to get up on plane, and I suspect the one engine in the power boat
did not have enough power to get it over the hump. *Also consider that a
considerable amount of one engine's HP would be consumed by rudder drag,
since the rudder would have to be nearly 45 degrees to keep the boat going
straight.. *Also, the 5 knots mentioned is probably not terribly accurate,
since the accuracy of a power boat's "speedometer" is not very good at low
speeds.

It hurts my head to think about what parts of the two engines were
common, and which were different.


Not that bad, I think. *Camshaft, crankshaft, oil pump, water pump, harmonic
ballancer, distributor, alternator.

_ Jim in NC


The notion of that O'Day hull on the plane scares me! There was no
plane as such on mine, it would have to be balanced on its centerline
somehow! Digging deep into memory I seem to remember speed increases
as power to the 1/4 power after a displacement hull is around hull
speed, trying to climb its bow wave. I think that also represents the
'kick' in power it takes a planing hull to get on its step. Hmm,
aviation link. Maybe sea planes?

There was talk a couple of decades ago about some airplanes getting on
their step, the idea might have been to getting past the desired
cruise speed then slowing down would lead to a more efficient AoA,
rather than doing what most of us do coming out of a climb -- just
accelerate to cruise, trim things up, then sit back and manage the
airplane.

I'm not sure, re common parts of an engine, that the alternator needs
to be different. I think they'd work either way, the rectifiers
wouldn't care about the phase of the AC at their input. You probably
meant to type fuel pump.
  #13  
Old November 16th 09, 12:30 AM posted to rec.aviation.piloting
Morgans[_2_]
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Posts: 3,924
Default Paddlewheels versus Propellers


"a" wrote

The notion of that O'Day hull on the plane scares me!


I did get it surfing down the face of some waves (6 to 8 footers on Lake
Erie) running before a pretty strong wind. It was... fun, I think? g
Seriously, I saw nearly 10 knots a few times, so I guess I was planning!
The steering was seriously skittish!

Digging deep into memory I seem to remember speed increases

as power to the 1/4 power after a displacement hull is around hull
speed, trying to climb its bow wave. I think that also represents the
'kick' in power it takes a planing hull to get on its step. Hmm,
aviation link. Maybe sea planes?

Yep, that sounds about right. And the step in the hull on seaplanes is to
help with the power required to get up on plane, I believe, and to make
rotation less problematic.

There was talk a couple of decades ago about some airplanes getting on

their step, the idea might have been to getting past the desired
cruise speed then slowing down would lead to a more efficient AoA,
rather than doing what most of us do coming out of a climb -- just
accelerate to cruise, trim things up, then sit back and manage the
airplane.

I have read those articles, or some of them, and the concensus was (as I
recall) that if you had not gone higher, and accellerated by diving those
few feet, the speed it settled on after a few minutes was the same in both
cases.

I'm not sure, re common parts of an engine, that the alternator needs

to be different. I think they'd work either way, the rectifiers
wouldn't care about the phase of the AC at their input. You probably
meant to type fuel pump.

I think the cooling fins need to be reversed on some alternators, from what
I recall. The fuel pump would be the same if it is a cam actuated one,
wouldn't it?
--
Jim in NC


  #14  
Old November 17th 09, 08:24 PM posted to rec.aviation.piloting
[email protected]
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Posts: 1,130
Default Paddlewheels versus Propellers

On Nov 15, 4:30 pm, "Morgans" wrote:
I'm not sure, re common parts of an engine, that the alternator needs


to be different. I think they'd work either way, the rectifiers
wouldn't care about the phase of the AC at their input. You probably
meant to type fuel pump.

I think the cooling fins need to be reversed on some alternators, from what
I recall. The fuel pump would be the same if it is a cam actuated one,
wouldn't it?
--
Jim in NC


Alternators don't care which way they turn. I had a 283 in a
small boat, and there was no room for the usual side-mounting of the
alternator. I turned it around and mounted it in front of the engine,
making it spin the other way. I went to the junkyard and found an
alternator fan that had its fins mounted radially rather than at a
tangent, so it sucked air through the alternator equally well in
either direction.

A cam-driven fuel pump isn't going to care which direction the cam
is turning, either.

Dan


  #15  
Old November 23rd 09, 08:56 PM posted to rec.aviation.piloting
Jon Woellhaf
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Posts: 221
Default Paddlewheels versus Propellers

Why would an alternator care which direction it turns?

It hurts my head to think about what parts of the two engines were
common, and which were different.


Not that bad, I think. Camshaft, crankshaft, oil pump, water pump,
harmonic ballancer, distributor, alternator.



  #16  
Old November 23rd 09, 08:58 PM posted to rec.aviation.piloting
Jon Woellhaf
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Posts: 221
Default Paddlewheels versus Propellers

Never mind ... should have read the entire thread before posting. My bad.

"Jon Woellhaf" wrote in message
...
Why would an alternator care which direction it turns?

It hurts my head to think about what parts of the two engines were
common, and which were different.


Not that bad, I think. Camshaft, crankshaft, oil pump, water pump,
harmonic ballancer, distributor, alternator.





 




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