Tim,
I made the oar. I scarfed two pieces of ash together and covered the scarf with two layers of carbon fiber. It's actually 14'10' long. Here is the link to the build.
http://www.farreachvoyages.com/projects ... yoars.html
There are a couple of important consideration to making the sculling oar work. It's not just the oar but the entire system of oar, oar lock, oriental lanyard, etc.
(1) Oar length. I determined the length by deciding the best place to scull from would be on top of the seat lockers--specifically on the top of the LP gas locker directly behind the tiller. It gave me good visibility and reduced the length of the oar. If I stood on the cockpit floor the oar would have been huge. For the kind of oar I use, I wanted the oar to be about 40 degrees to the horizontal surface of the water. I determined the rough length by using a simple PVC pipe mock up. I then built the oar a little longer at 16' long then cut it back to 14'10" though trial and error.
(2) The oar lock. The oar lock has to be bullet proof. I read a few blogs where people tried to lash together a cheap oar lock and the system failed. There is a lot of power being applied to the oar lock. So, regardless the design, it has to be tough enough to handle the loads and it has to have as little friction as possible. The oar leather and how it is lubricated is important. Friction is your enemy. You want minimal friction.
(3) Oriental lanyard. The OL is a line (about 1/4") that runs from an attachment point on the loom about halfway between the oar lock and the handle on the oar directly down to a pad eye on the deck. The OL makes the oar controllable By tensioning the OL correctly the loom remains at the correct height/angle and imparts the correct twist to the loom. You don't need an OL sculling your dinghy but you sure as hell do when sculling a large heave displacement hull. The forces at play are just to great.
There has been a fair amount written about sculling oars and I think most evidence agrees the Chinese yuloh and Japanese Ro are more efficient than the western style oar for sculling. But a yuloh would have been longer, heavier, and harder to store on my boat. Also, I felt like I was mixing designs in a way that was not pleasing to my eye . . . I didn't think the yuloh would look right. Also, I talked about the asymmetric blade design issue, that is a point of discussion on the internet, with Larry Pardey, and the oar they used for forty years on both boats was a standard western style symmetrical design. I figured he has more experience than just about anyone in the world sculling a heavy displacement sailboat. So, I followed his recommendation.
The sculling oar works. It's not a perfect solution. I am not an expert but I have sculled my boat a reasonable amount of time to feel like I have an experienced opinion. I'd say I can scull in about 6 knots of wind but I would not want to. In a calm, it is easy and I think I can get the boat going about 1 1/2 knots. It will turn on a dime. I have read you can back a boat up by reversing the feathering motion but I have not had a chance to try it out . . . yet. It's a lot of work but like anything, I think in the beginning one relies on a lot of muscle and brute force but as the technique is learned the muscle is less important--it's almost all technique and finesse. I think it would be all I need if we were on a mooring ball. But in a marina, with wind and current, it not very practical . . . at least with an 18,000 lb boat. I like it. I am glad I have it. It's part of my simple system. But it has limitations--just like that little 9.8hp outboard we use.
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