Howard, Gary, and others:
Let me throw some numbers at you for your comment.
First, assume there is no friction or other losses. :{)
Assume the blade of that 15 ft. oar is 3 ft long. The distance
from the handle end to the center of the blade is then 13 and 1/2 ft.
Assume the distance from the handle to the oarlock is 3 ft.
The distance from the oarlock to the center of the blade is then 10
and 1/2 ft.
If you apply 10 pounds of pressure to the oar handle, you only
transfer 2.9 pounds of force to the water. That is, 10 pounds
multiplied by the ratio of 3 over 10 and 1/2.
If you could locate the oarlock at the midpoint of the 13 and ½ ft.
distance, then 10 pounds of force would be transferred to the water
for every 10 pounds you pull. So an arm would have to extend
roughly 4 ft. from each side to support the oarlock. By doing
this, you have multiplied your rowing effort by a factor of 3.5.
If you could row for 1 mile before, now you can row for 3.5 miles
with the same effort.
There is an additional benefit as well by reducing the arc. By my
quick calculations, if you swing an oar through a 90 degre arc,
only 63% of your effort goes into propelling the boat forward. The
reminder goes to pushing water away from the boat at the beginning
of the stroke, and pushing water toward the boat at the end of the
stroke. If you could reduce the arc to 60 degrees, your propulsion
fraction increases to 70%. For 40 degrees of arc it is 80%. I
think with oarlocks on the coaming you would have roughly a 90
degree arc if you do “full extension” rowing. By moving the
oarlock to the mid point it is closer to 30 degrees.
By combining both factors, you would go from rowing one mile to
about 4.5 miles with the same effort.
I have run these numbers by non-sailors and they agree with this
analysis. What do you guys think?
steve
Steve R.
M-15 #119
Lexington, KY
*************************************************************
I thought the way Bob put those oarlocks on was pretty neat. Have
wondered how well it worked to row the boat. I've also heard of guys
fitting oar locks into the top of sheet winches, which are about the
right location, but that leaves the oar height somewhat high.
On the Japanese sculling oar, I've built one of those too. First
attempt
was a crude one to see how well it worked. Initial attempt on the
Spindrift was disappointing as it didn't want to rotate in the
oarlock,
so I went back and modified it some. Didn't have a chance to try it
again and it's gotten pretty cold now for boating. I think it might
work, but so would the other one.
http://i112.photobucket.com/albums/n165/haudsley/Picture260.jpg
http://i112.photobucket.com/albums/n165/haudsley/Picture262.jpg
http://i112.photobucket.com/albums/n165/haudsley/Picture263.jpg
The Spindrift gets rowed or sailed. The oars on it do pretty well and
1.5 to 2 knots is pretty easy to get. You can cover a lot of ground
doing 2 knots. This was just playing around on it. I view the rowing
option on the Montgomery as a third, emergency form of propulsion.
Something I know will work when there is no wind and the motor won't
start.
*****************************************************
Rowing the M17: Check out the Strawanza photos at the following link.
Bob Eeg mounted oarlocks on the toe rail track and used 12-foot
break-
down oars.
http://www.MSOGPhotoSite.com/mpage.htm
I'm playing around with the idea of a Japanese sculling oar design,
called a "Ro", ironically. It places the blade vertically at rest
rather than horizontally and may be more efficient.
The following web site discusses that design with video.
http://www.amateurboatbuilding.com/articles/howto/sculling_oar/
--Gary Hyde
2005 M17 sailboat #637 'Hydeaway 2'
We can't change the wind, but we can trim our sails.
On Dec 2, 2007, at 8:41 AM, Steve R. wrote:
Hi Harry,
Welcome to the group.
You raise some interesting points for an off season discussion.
I have been pondering a post I read here (I think) recently about
the difficulty of using a single oar as an Oriental yuloh. I
believe the geometry is wrong for efficient use of oars with our
small boats. Our boats have a narrow beam, short cockpit and high
freeboard. If you place an oarlock on the top of the coaming or
transom, you have poor leverage for seated rowing or use of a yuloh
(yulohing?). Some people stand up, which increases the angle of
the blade in the water, and improves the leverage situation by
allowing use of a shorter oar. I would be comfortable standing in
calm water, but not in extreme conditions.
So…if I HAD to use an oar I would think about installing oar
ports. The ports would be located about waist high along the sides
if I wanted to row or in the transom for a yuloh. Bolger has used
oar ports as did the Dovekie. In extreme weather the ports could
also function as cockpit scuppers or be closed off if necessary.
Ports would also have the advantage of allowing the use of shorter
oars.
Or..I would consider using some sort of an arm that would locate
the oar lock several feet outboard. The leverage situation would
be improved, although longer oars would be needed. Modern racing
shells often have oar locks mounted outboard.
And..I would give a lot of thought to a sliding seat with a
pivoting brace for the feet.
steve
Steve R.
M-15 #119
Lexington, KY
************************************************
Greetings from N. shore of L. Superior: -15F,snow& wind last
couple of
nights but at least my M15 is safely tucked away in its dome
shelter!
Bob Eeg's tale of the specially equipped M17 that he constructed
for the
Austrian man was fascinating and raised a couple of questions about
the
M15: (1) Has anyone tried rowing one, and if so how was it? and (2)
What
were the worst conditions a M15 has survived intact (wind, waves)
with
all sails down and only motor power? Pardon me if these questions
have
been asked before- I joined just last year. If they have please
point me
in the right direction and I'll check it out. Thanks and safe
sailing to
the lucky souls in the south. Harry Elmslie
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