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

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

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

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

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

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

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

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

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

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