placement of seats and oarlocks in a new boatgreenspun.com : LUSENET : Open-water rowing : One Thread
I want to fit a boat for fixed-seat rowing that hasn't been rowed before, so I'm concerned about the proper placement of seat and oarloacks. The gunwales are 51" wide at maximum beam and about 15" above the water. I can place the seat and oarlocks wherever they work best. According to formula, 8 ft. oars should be about right; is this correct? The questions are: Is there a benefit to canting the oarlocks outward? What is the proper position for the seat thwart,i.e. how far below and forward of the oarlock? How wide is ideal for a thwart? What else should I consider? I have a Swampscott dory that I regard as OK that I can use as a pattern, but for all I know, it's not ideal, and I just am used to it.
-- Kim Apel (firstname.lastname@example.org), March 01, 2000
There is no formula that can determine precisely what set-up will work best for you. Anything that you read anywhere, including here, should be viewed simply as a rough guide. The 8' oars should be a pretty good match for your boat. From my experience, when using ordinary oarlocks, canting, or not canting, makes no appreciable difference where performance and comfort are concerned. If your boat's hull has flare there will be a tendency for your locks to tilt outward. If it has vertical sides they will want to be upright. Don't fight it. Only if your hull has extreme flare or a significant amount of tumlehome should you make an effort to adjust the tilt of the sockets. More important than the tilt of the oarlocks are the relative positions of the thwart (seat), the oarlocks and the footbrace. I have designed many boats of similar depth to yours and I've found that it's a safe bet to place the top of the rowing thwart a least 7" below the gunwales or sockets and the the sockets about 11- 12" aft of the trailing edge of the rowing thwart. The footbrace should be about 6" or 7" or so below the top of rowing thwart and as far aft as is comfortable. How you make the footbrace is not important, but having a solid one is. Use your Swampscott dory as a guide, comparing its spatial arrangement to my recommendations. Where you see there need to be changes, make them. I hope you find info helpful.
-- Andre de Bardelaben (email@example.com), March 01, 2000.
Upon rereading your query I realize that I may have misjudged the depth of your boat and also that I failed to provide an answer to one of your questions. I'll try again to address these matters. You said that the gunwales are 15" above the water. I assumed that you meant that your boat is 15" deep, which may or may not be the case. I've designed many boats that are 14-15" deep, which in use puts the socket tops 9-12" above the water, depending on the boat and the load. The spatial recommendations I made are still valid. As for the width of the thwarts, I've found that a seat measuring 9-10" wide, fore and aft, allows enough room for most people to find a comfortable position if the footrest is in approximately the right place. Just as important for comfort, the top edges of the thwart must be smoothly rounded over. If you follow these recommendations you should find that your boat, assuming it is well designed overall, will be both comfortable and efficient.
-- Andre de Bardelaben (firstname.lastname@example.org), March 01, 2000.
Thanks Andre, for your advice. The dimensions you specified are consistent with my dory, so it's good to know that my current boat is also set up correctly. When I cited gunwales 15" above the water, I was taking draft into account; the center depth of the hull is about 18". As a designer and builder, you may be interested to know that the hull I intend to retrofit is a Chestnut "freighter" canoe, 19'L x 51"W, with a wineglass transom. It is certainly big enough to have two rowing stations, though I understand the aft station would have a smaller spread on the oarlocks. It sounds big and unwieldy, but the hull weight is only about 180 lbs. and the bottom shape looks sweet and efficient to me. And you have the option of loading it with (no joke) over a thousand pounds of gear/supplies. You know...LONG trips. What do you think?
-- Kim Apel (email@example.com), March 01, 2000.
You may not be aware that my designing/building career began with canoes. I started designing professionally in the mid-1970's, during the early days of modern canoe design. Designers of that era were just beginning to make some headway selling the virtues of low profile, assymetrical, keel-less hulls. Solo canoes were my specialty. They taught me to get the most out of a small, simple hull. I still make them and will always have a special fondness for them.
While Chestnut canoes did not represent cutting edge design they were solid trustworthy craft. For decades Chestnut canoes were the workhorses of the Hudson's Bay Company. That knowledge should be comforting to anyone contemplating an adventure in your boat.
For recreational purposes, your boat will almost certainly function better as a rowing craft than it would as a canoe. It will retain some reasonable paddling capabilities which might come in handy in certain situations. Your boat sounds more practical for cruising than most rowing shells and most of those back-breaking coastal workboats. Your "freighter" would probably be better for double rowing than single, but it should reasonably manageable by a single oarsman. I wouldn't be concerned that there isn't sufficient beam anywhere in the middle two thirds of your Chestnut for a pair of sockets. The widest rowing craft in my line has a molded beam of 46". We don't use outriggers on any fixed seat craft wider than 38". Your boat has a lot of possibilties. I think you'll be happy with it. May the winds always be in your favor.
-- Andre de Bardelaben (firstname.lastname@example.org), March 03, 2000.
KIM: You asked about canting oarlocks outboard. If you are using round oarlocks and oars that are round in section, there is no significant impact. However if you are using oars that have a flat bearing surface against a flat oarlock face then there is an impact on oar blade pitch. Pitch is the angle of the face of the oar blade relative to vertical when the blade is being pulled through the water. When your blade digs too deep or washes out, that's pitch. With a round oar in a round lock, the adjustmest for pitch is made by feel. With a flat oarlock face and a flat bearing surface on the oar, pitch is built in. Positive pitch means that the blade angle is set so that the oar tends to dive. Negative pitch means that the oar tends to wash out. Pitch can be built into the oar such that the oar is made so that the face of the blade is turned a few degrees off of the bearing surface of the oar. However, pitch is usually achieved by tilting the oarlock bearing surface. In sliding seat commpetitive rowing, the oar is normally built with zero pitch and the desired pitch is achieved by adjusting the fore and aft tilt of the oarlock. Normally in sliding seat rowing, pitch is set at 5-6 degrees negative pitch (washout)to keep the blades just below the surface of the water and to facilitate a quick exit at the end of the stroke (release). On the other hand, many fixed-seat, open-water rowers use positive (dig) pitch to keep the blades deep in the water so as not to be disrupted by waves and chop at the surface. Now, finally, to get to your question about outboard tilt of the oarlock. If the oarlock is tilted outboard at the top, this has the effect of changing the pitch of the blade during the stroke. For example: If you are rowing with a zero pitch oar against an oarlock that has no fore and aft tilt but does have 4 degrees outboard tilt and your stroke swings through a 90 degree horizontal angle from catch (entry) to release (exit) then you would have approximately 2 degrees of negative pitch (washout) at the catch and 2 degrees positive pitch (dig) at the release. Competitive sliding seats types usually rig with 2-4 degrees of outboard pitch to help keep the oar from diving at the catch and washing out at the release. The flat-water, sliding-seat competitive types are really into rigging dimensions and adjustments, of which pitch is just one of many. Books have been written on rigging. The fixed seat folks seem to be much more relaxed about it all--which is one of the reasons I have come to fixed-seat, open-water rowing after many years of sliding-seat competition and coaching. If your email address stands for University of California at San Diego, you might go down to the boathouse at Mission Bay and talk to a rigger working on an eight and you will be very glad you are about to head out in your big canoe. Keep pullin' John Mullen
-- John Mullen (email@example.com), March 26, 2000.
Regarding pitch. The easiest way to measure and adjust pitch is to buy or borrow a pitch guage. They are not particularly expensive and make the task relatively easy. Instructions come with them.
Regarding stretcher position. Make sure that the stretcher is adjustable and that the distance from seat to stretcher can be adjusted so that the legs are slightly bent at the beginning of the stroke. That way you will be able to use the power in your legs and lower back more effectively.
-- Richard Gooderick (firstname.lastname@example.org), April 10, 2000.