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Design of the rudder


esmikell

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I am new to the group, hello everyone.

I am pondering the different designs I have seen in rudders. Most go straight down from the transom; however, a few design have the rudder go out aft of the boat so that the rudder does not go below the draft of the hull. Is there a benefit to this design other than the shallow draft?

Second, can some people suggest a good 12-14ft sailboat that is good in light airs. I plan to build it and enter a river race in May.

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Not sure about the rudder issue, but we do have some design folks here who should chime in.

The B&B Spindrift (see this link for more) has won several races, although I think that was with the designer Graham Byrnes at the helm.  Graham keeps winning races with his designs and I suspect he's a pretty good sailor!  The Spindrift comes in a 12' version, but not larger, as far as I know. There are several people who own them in the B&B Yachts Forum here.

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Rudder plan form (profile) can take on many different configurations, often a difficult set compromises between; shoalness, effective steering, participation in lateral area, complication and drag inducing resistance.

The most efficient rudder plan forms have a relatively tall aspect ratio (depth verses width), but these suffer from bottom strikes. A "kick-up" or other retracting feature can be employed to address this concern at the expense of complication, more drag and efficiency lose.

The "barn door" style of rudders, which seem to extend aft rather then down are naturally shoal, but limited in efficiency and effectiveness in some conditions. Well heeled over, these types of rudders can loose their "bite" with resulting lose of steering control. This can also be true in rolling conditions or steep seas, where the slightly immersed rudder is repeatedly plunged and exposed, as the boat makes way.

In the end, the designer will make a choice which set of difficulties they can live with most (a common theme in yacht design decisions). With clever engineering both styles can be effective, within the performance envelope they were intended to operate.

There are a lot of performance 12' to 14' sailors available. I have two, a single man and a two man, both 14'. If you'd like to contact me by email, I'll send you some study plans.

Graham has a number in this size range, as well as several other designers, some of which have links on this very site.

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In my opinionated opinion, in the size you speak about, the kickup seems to have the edge since that size boat is more of a semi protected water use. I am not sure that the more broad and shallow rudder is as pretty either for small hulls. SO I am not sure if comparing barndoor styles should enter into the discussion.

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He's a Florida boy Ken so I'll wager St Johns River and the Mug race!  8)  Your best bet is to go with the rudder configuration specified by the designer.  He or she has already optimized the rudder parameters for the hull in most cases. Some designs have room for improvement but normally the gain in efficiency is not worth expendature of time, materials, and effort.

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You may want to find a design with a Spinnaker.  If the winds are southeast it will be a nice ride down river.  A MX Ray kind of boat.  Also a Hobie 17 would work also.  In a long distance race a longer waterline would be nice.  I would like to do the Mug Race also.  But my Peep Hen would be to slow...LOL  Maybe see if i can get a ride on a Farrier Tri would be the best for me.  Nothing like doing teens on one of those babies.

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LOL- I've done  three Mugs. Once in 1973 in  a San Juan 21- 2nd in class, once as a ride along ( not racing) and once in 1981 in my Cross 35 trimaran-  Boat was totally empty- didn't even have water tanks. We weren't officially entered- started after EVERYONE else had, then cranked it on-we blew off over 300 boats that day ;D ;D

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