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Thrust vectoring
wayne, please read what you wrote and you will find you are saying exactly what
I am saying that you are disagreeing with so strongly. the boat MUST be **moving** for the rudder to have an effect in reverse. please read what you wrote again. When the sternway becomes sufficient, the rudder exerts Absolutely right. give it a burst of power in reverse ... get it moving sternward at a knot or two, let the boat coast backward on momentum while maneuvering with the rudder. Once the boat is moving the keel and rudder take over |
Thrust vectoring
Once the boat is moving the keel and
rudder take over, forward or reverse. in forward, you can use the prop blast to move the rudder. in reverse, you can't. but, yes, once the boat is moving in reverse the rudder can be used to turn the boat. |
Thrust vectoring
Subject: Thrust vectoring
From: Brian Whatcott Date: 03/28/2004 19:26 Pacific Standard Time Message-id: On 28 Mar 2004 19:11:58 GMT, (Shen44) wrote: G Never hoid of this Feynman character, before this thread.... Shen He won a Nobel prize. He was an accomplished bongo player too, and had a taste for women. But I think you can take it that his bongo-playing talent and Nobel class research endeavours are pretty well independent from boat-handling skills. No Nobellist has ever won a major boat race, as far as I know. G haven't heard of too many that are pilots, either. Shen |
Thrust vectoring
Subject: Thrust vectoring
From: "JimB" j Shen44 wrote in message OK, think I see what you're saying. First off, I used to run a 65 foot boat with a similar configuration and remember a beautiful old 45' ketch with the same thing ... both had large degrees of "propwalk". Interesting. Some of the older boats had engines added later, of course, and sensibly had prop shafts installed with an offset so you could remove the shaft without taking the rudder off. That changed the prop wallk picture a bit! True There are many varying degrees of propwalk, for varying reasons (offsets, kort nozzles, rope guards, to name a few). I normally board a boat and find out type and rotation of prop to determine expected direction of walk, then as soon as possible, if it's new to me I'll try to create a situatuion to test it out. I've learned to expect a certain direction and amount of walk for some boats, but always keep in mind that sometimes, especially on some boats they may walk opposite to the expected (normally this will be a wind, current, or existing turn situation, but not always.). .... at any rate, expect it, test it, and then be ready for the unexpected. Secondly, I think we may have different views of what is the major cause of prop walk (I attribute it to the pitch of the blades pulling to a greater degree on the "down stroke" side of the revolution, than the "upstroke side"). OK. The only certainty about prop walk is that it must be caused by the prop in reverse squirting more water to one side of the boat than the other. We could discuss the mechanism for ages - but there wouldn't be much practical use to that unless we were designers! Again true, although there is still prop walk when going fwd, it's just not normally as noticeable. BG Why would I want to design "propwalk" out? "Propwalk" is my friend! Especially pulling the stern in as you come alongside.... bit of a sod when it's the wrong side though. G Can also be used when docking the other side too, to stop the stern coming alongside as you stop. There is no doubt, that at times, prop walk is a pita, because it is contrary to what you want and need to do, but in a high percentage of cases, it can be made to work for you. Shen |
Thrust vectoring
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Thrust vectoring
Something that I've noticed, though I'm not sure if it's universal or
even really true: When I punch it, the prop walk seems to be minor. When I want maximum prop walk, idle speed is the way to go. It could be just that the duration is so much shorter, or that the higher thrust straightens things out. -- Jere Lull Xan-a-Deux ('73 Tanzer 28 #4 out of Tolchester, MD) Xan's Pages: http://members.dca.net/jerelull/X-Main.html Our BVI FAQs (290+ pics) http://homepage.mac.com/jerelull/BVI/ Could it be due to a short duration of a "punch" in reverse, or due to the factor that sternway (and therefore rudder effectiveness) increased enough at the higher RPM ? :-) |
Thrust vectoring
Subject: Thrust vectoring
From: Jere Lull I don't doubt that this is true for your boat (since you've observed it) but, I'd bet it's not universal and would depend on the boat, set-up, and conditions. Why it occurs, would take someone familiar with boat props, and I would wonder if it had anything to do with the fact that the prop might be working more efficiently when starting at slower RPM's than at higher, especially if the boat is DIW. Another observation along the same lines .... I'm more apt to see the effects of prop walk when going ahead, if boat speed is low. Shen Something that I've noticed, though I'm not sure if it's universal or even really true: When I punch it, the prop walk seems to be minor. When I want maximum prop walk, idle speed is the way to go. It could be just that the duration is so much shorter, or that the higher thrust straightens things out. |
Thrust vectoring
Not another one of your "what I did on shore leave" Navy stories, JAX.
can't be. I was never in the Navy. R. |
Thrust vectoring
In article ,
(Gould 0738) wrote: Something that I've noticed, though I'm not sure if it's universal or even really true: When I punch it, the prop walk seems to be minor. When I want maximum prop walk, idle speed is the way to go. It could be just that the duration is so much shorter, or that the higher thrust straightens things out. -- Jere Lull Xan-a-Deux ('73 Tanzer 28 #4 out of Tolchester, MD) Xan's Pages: http://members.dca.net/jerelull/X-Main.html Our BVI FAQs (290+ pics) http://homepage.mac.com/jerelull/BVI/ Could it be due to a short duration of a "punch" in reverse, or due to the factor that sternway (and therefore rudder effectiveness) increased enough at the higher RPM ? :-) I've been tending toward that explanation except that a few seconds of near-idle reverse can slide the transom over a foot without moving very far; punching it for a few seconds (2000 rpm out of 3600), we don't seem to pivot at all. When I shift to neutral, we don't have authoritative steerage way yet. Our prop (16x10x3 AutoProp) is pretty close to the rudder... Could we be getting enough flow across it to counteract the walk? What got me thinking about it and taking closer notes was watching a new 36 or 38' Catalina on charter try to back into a slip at idle last September. Actually rotated more than it backed. The rudder never got a chance. I'd never seen a sailboat do that badly, though I've seen a few powerboats humble some mighty fine helmsmen. -- Jere Lull Xan-a-Deux ('73 Tanzer 28 #4 out of Tolchester, MD) Xan's Pages: http://members.dca.net/jerelull/X-Main.html Our BVI FAQs (290+ pics) http://homepage.mac.com/jerelull/BVI/ |
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