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#11
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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
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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
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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
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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
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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
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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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