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What do You know about Rudders?

Nov 26, 2012
1,529
Hunter 34 Berkeley
I am considering building a better, faster, more high performance rudder for my Hunter 34. This thought just creeped into my brain in the last couple days so it is in its infancy. The reasoning is that the boat is squirrelly in big wind and not particularly well balanced. The stock rudder is the same for both the deep keel and the shoal draft boat and since I have the deep keel I have a little room to extend it deeper. (No, I do not have the undersized rudder that came with the early models).
I am learning a little about aspect ratios for performance and structural considerations. Any thoughts on how or if this might (or might not) affect the boat's performance are appreciated as well as advice on how to go about such a project.

Cheers
 
Jan 19, 2010
10,002
Hunter 26 Charleston
Well I have built one rudder (out of wood) for a smaller boat and did my best to give it the correct foil shape. I used an electric planner. It was okay but not noticeably better. On the other hand, I put a new rudder on a Balboa 26 made by rudder craft. It was a dream. The added lift allowed me to make much smaller adjustments to the rudder for the effect I needed. My suggestion would be to contact rudder craft and ask them if they have a rudder blade you could adapt to your needs.
 
Sep 24, 2021
39
Beneteau 35s5 Telegraph hrbr Thetis Island
Tricky business, I think. The balance area is pretty critical, a designers' input would be advisable.

Years ago my brother had a Ranger 28 with an unbalanced rudder on a small skeg. The boat was a beast to drive and a real broach machine in heavy air. I saw a slightly newer version (same profile) but had the skeg area now as part of the rudder (adding a balancing tab). During a winter haulout we made that modification, but in hindsight made the balance area too large. Now the boat was a dream to drive under sail but the propwash on the tab made the tiller difficult (and tiring) to hold under power.... Not the worst trade-off but not ideal either.

Maybe try to modify the existing rudder as a trial of your proportions before diving into a total build??
 
May 17, 2004
3,474
Beneteau Oceanis 37 LE Havre de Grace
Before redesigning the rudder I would check a couple other things to deal with the steering issues. First, what’s the condition of your sails? As sails age and get blown out they definitely add to weather helm which will unbalance the boat. Also, if you have a fixed prop consider switching to a folding or feathering model. We had problems with our OEM fixed prop causing turbulence over the rudder and stalling it. After switching to a folding prop the margin for error for imperfect sail trim or reefing went up about 5 knots of wind speed.
 
Jan 11, 2014
7,839
Sabre 362 113 Fair Haven, NY
The reasoning is that the boat is squirrelly in big wind and not particularly well balanced.
I'm assuming the squirrelly problem is down wind sailing and the "well balanced" part is up wind or on a reach.

Late 1970s and early 1980s designs were often built around then current IOR rules. One consequence of the IOR rules were boats were given very skinny aft sections. When running downwind the boats would squirrelly because their butts were too skinny. Current designs have broader aft quarter which make the boat more stable going down wind. A larger rudder probably won't help much, at least not enough to justify the time and expense of building a rudder of new unproven design.

The balance issue can be addressed by rig tuning, sail trim, and having good sails. Typical of boats of that era, the main is high aspect, i.e, tall and skinny, and the gennoa is huge. In stronger winds the genoa will over power the main. Reducing genoa size yield better results than a new rudder.

A new better designed rudder may help with going to weather. This is where the rudder provides lift and help with pointing. If the rudder isn't balanced a new balanced rudder will make helming easier and reduce weather helm. The Tanzer 22 class went this route. Moving from a scimitar shaped rudder to a balanced rudder similar to that on a J24 made a huge difference in the boats steering.

Mads on SailLife rebuilt his rudder. He started by making a mold of the original rudder and then built a new one. The video below is the first of many this project.

 
Nov 26, 2012
1,529
Hunter 34 Berkeley
I'm assuming the squirrelly problem is down wind sailing and the "well balanced" part is up wind or on a reach.

Late 1970s and early 1980s designs were often built around then current IOR rules. One consequence of the IOR rules were boats were given very skinny aft sections. When running downwind the boats would squirrelly because their butts were too skinny. Current designs have broader aft quarter which make the boat more stable going down wind. A larger rudder probably won't help much, at least not enough to justify the time and expense of building a rudder of new unproven design.

The balance issue can be addressed by rig tuning, sail trim, and having good sails. Typical of boats of that era, the main is high aspect, i.e, tall and skinny, and the gennoa is huge. In stronger winds the genoa will over power the main. Reducing genoa size yield better results than a new rudder.

A new better designed rudder may help with going to weather. This is where the rudder provides lift and help with pointing. If the rudder isn't balanced a new balanced rudder will make helming easier and reduce weather helm. The Tanzer 22 class went this route. Moving from a scimitar shaped rudder to a balanced rudder similar to that on a J24 made a huge difference in the boats steering.

Mads on SailLife rebuilt his rudder. He started by making a mold of the original rudder and then built a new one. The video below is the first of many this project.

Thanks, dlochner. Good stuff. She is, Indeed a product of that era. 1984. The improved rudder is part of an overall effort to improve performance that includes the things you mention here. I sail SF Bay where 20 knots is typical from April though September. My plan is to try to make several small improvements and see what I can come up with.
 
Jan 4, 2010
983
Farr 30 San Francisco
Phils foils might have one already made up in Ottawa, but I think they changed their name. Longer and thinner, some area ahead of the shaft to give it balance
 
Jan 13, 2009
362
J Boat 92 78 Sandusky
Hunter had a deeper redesigned rudder in the later years of the 34. It was around 1-1/2 feet deeper. The boat had a wide non IOR transom. A couple of friends had H34s. Big interior. Forward hull would oil can upwind in a seaway. Leaks under mast caused damage and trapped water in ladder frame compartments. All fixable but at a cost. Ida Rudder and CCI composites are good sources for an improved rudder
 
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DArcy

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Feb 11, 2017
1,250
Islander Freeport 36 Ottawa
Mar 20, 2011
592
Hunter 31_83-87 New Orleans
Foss Foam Florida (ask for Al @ 352-529-1104) Built the mid eighties rudders For the 31s and 34s. I’ve read in the past the later year H34 did install a larger rudder. Perhaps discussing with Al and he can provide some history on the earlier/later rudder versions And what can meet your needs.
 
Apr 26, 2015
642
S2 26 Mid On Trailer
If you haven't already, check out Boat Design Net. I've been thinking about a transom hung rudder on my S2 shoal draft to replace the unbalanced barn door (2.5' x 2.5') spade rudder that I have now.