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Yuloh
Does anyone have any experience building a yuloh? Specifically, I am
looking for advice as to whether to use an 8 degree or 11 degree angle on the blade. A reference to a good book on the subject would also be appreciated. Thanks Tom |
Yuloh
http://www.mindspring.com/~councill/...ng/scull3.html
"Tom Best" wrote in message om... Does anyone have any experience building a yuloh? Specifically, I am looking for advice as to whether to use an 8 degree or 11 degree angle on the blade. A reference to a good book on the subject would also be appreciated. Thanks Tom |
Yuloh
Tom Best wrote:
Does anyone have any experience building a yuloh? Not witha yuloh, but plenty sculling (single oar over the transom) and have read a good bit about them. .. Specifically, I am looking for advice as to whether to use an 8 degree or 11 degree angle on the blade. How heavy is the boat, what are the relative lever arms? A longer inboard lever and/or lighter boat would favor the steeper angle. Fair SKies- Doug King |
Yuloh
It's a Sea Pearl 21. Only about 850 lbs loaded. As this is fairly
light, I think I'll try 11 degrees. The length of the lever are is somewhat up in the air at the moment as I have two options on the pivot. One is on the transom and the other is above the rudder in place of motor mount. Since you know of such things, should the side of the yuloh that faces down be cut with an aerodynamic (sail) shape and the top side flat? Thanks Tom How heavy is the boat, what are the relative lever arms? A longer inboard lever and/or lighter boat would favor the steeper angle. Fair SKies- Doug King |
Yuloh
It's a Sea Pearl 21. Only about 850 lbs loaded. As this is fairly
light, I think I'll try 11 degrees. The length of the lever are is somewhat up in the air at the moment as I have two options on the pivot. One is on the transom and the other is above the rudder in place of motor mount. Since you know of such things, should the side of the yuloh that faces down be cut with an aerodynamic (sail) shape and the top side flat? Thanks Tom How heavy is the boat, what are the relative lever arms? A longer inboard lever and/or lighter boat would favor the steeper angle. Fair SKies- Doug King |
Yuloh
Tom Best wrote: It's a Sea Pearl 21. Aha! My wife used to have one of these. Cool boat, we should have kept it. Only about 850 lbs loaded. As this is fairly light, I think I'll try 11 degrees. The length of the lever are is somewhat up in the air at the moment as I have two options on the pivot. One is on the transom and the other is above the rudder in place of motor mount. I'd go on the transom. There will be a lot of side thrust (in fact, it will push harder sideways than forward) which will put more strain on the rudder than the motor would. Since you know of such things, should the side of the yuloh that faces down be cut with an aerodynamic (sail) shape and the top side flat? Since the leading edge alternates, you have to make it symmetrical or have a yuloh that works better on one stroke than the other. But giving it a sort of streamlided 'D' shape should help. I rowed my wifes Sea Pearl many miles, why aren't you just plain rowing the thing with good old fashioned oars? Fresh Breezes- Doug King |
Yuloh
D shape is what I was thinking. I'll give it a try. Probably right
on the transom. I was thinking the motor mount would be too wobbly. I am reliably informed that a yuloh can be used for many hours with little stress or strain. Whereas oars (fixed seat or sliding) take the starch out of me pretty quick. Thinking of doing the Watertribe's Everglades Challenge in the spring and need as many options as possible to keep moving. Thanks for the help. Tom |
Yuloh
Tom Best wrote:
I am reliably informed that a yuloh can be used for many hours with little stress or strain. If that's true, then I'd bet a lot it's because the boat is going slower with a yuloh. Whereas oars (fixed seat or sliding) take the starch out of me pretty quick. Rowing is a much more efficient way to transfer energy to the water from your muscles. Think for a minute, if that weren't true, we'd have eight man yuloh sculls. Thinking of doing the Watertribe's Everglades Challenge in the spring and need as many options as possible to keep moving. Thanks for the help. You're welcome, let us all know the results. The newsgroup rec.boats.boatbuilding might have a lot of other people interested in your results, too. Fresh Breezes- Doug King |
Yuloh
Rowing is a much more efficient way to transfer energy to the water from your muscles. Think for a minute, if that weren't true, we'd have eight man yuloh sculls. I wonder if this is true. Sculling off the stern involves primarily leaning back and forth. Very little muscle activity. Mostly just changing your center of gravity. Rowing is a much more direct expenditure of energy for movement but it also involves the recovery part of the stroke which gives you no return. On a calories expended per pound of thrust I wonder if rowing is truly more efficient. Or is it instead just more powerful and fast at the expense of true efficiency? Just a thought. Tom |
Yuloh
Rowing is a much more efficient way to transfer energy to the water from
your muscles. Think for a minute, if that weren't true, we'd have eight man yuloh sculls. Tom Best wrote: I wonder if this is true. In a while, you'll know firsthand ;) Sculling off the stern involves primarily leaning back and forth. Very little muscle activity. hmm, you must be doing it differently than I always have. .... Rowing is a much more direct expenditure of energy for movement but it also involves the recovery part of the stroke which gives you no return. True, hadn't thought of that. But it's not a very large percent of the work done overall (work in terms of FxD). The reason why I think that rowing is more efficient is that it does not involve generating lift. Thrust is generated 100% from drag, which is very easy and also instantaneous. To generate lift over a foil you have to move the foil at least one chord length so part of each stroke of the yuloh is also wasted. And you still have to fight drag, but the drag is not helping move the boat. So I look at it as this way: for each pound of work expended on the yuloh, X% is spent generating the lift for that stroke and another Y% is wasted as drag. With an oar, for each pound of work you get greater than one pound of thrust because of the leverage, minus Z% for the recovery stroke. So it appears likely IMHO that X+Y Z. Not very precise math, but so it goes. On a calories expended per pound of thrust I wonder if rowing is truly more efficient. Or is it instead just more powerful and fast at the expense of true efficiency? That's possible, the leverage is pretty good. And we all know that with a big enough lever you can move the world..... Fresh BReezes- Doug King |
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