j/27 rudder replacement

[Hravn]

Hi;
I recently broke the 22 yr old rudder on my j/27 and am considering some options for replacement. When looking at the offsets, they are clearly not from the NACA 0010 or 0012 series, but have much a sharper leading edge. so two questions: 1.) how do I find out if the offsets are from a 'standard' section, and 2.) what should I be focusing on comparing if I want to consider other sections ?

The submerged foil is a 1270 x 360 x 54 mm vertical section with a slight sweep at the end. It weighs in at fifty pounds. My gut feeling is that there is probably not much to be gained in drag reduction by changing sections, especially in the 1-6.5 knot speed range, but that the most significant change will be a 10-15 lb weight reduction from using newer materials while retaining the area and section.

I tempted to experiment with a spruce of cedar cored, carbon reinforced elliptical tip planform with the same section and area. This appears to be strong enough and might come in at about 50% of the original's weight, but I'm flying blind here.

comments

thanks.

Todd.

[DaveB]

I'd suggest contacting jboats or the class association... They've got the offsets for the j35 posted so might not mind telling you about the j27...

http://www.j35.org/schematics.htm

Cheers n' good luck,

Dave

[Skippy]

You could also compare it to NACA 63015.

[Hravn]

That does look alot more like the actual offsets. thanks.

[Cliff Ruckstuhl]

You might not be able to race in class if you do this and you might take a hit from PHRF also. I replaced the rudder on our boat and took a 3 sec hit.

Cliff

[Hravn]

Indeed; I would not be class compliant, but thats not an issue around here. PHRF is another story, I've not been able to get any real answer from them, beyond, maybe a 3 sec hit.

[Cliff Ruckstuhl]

When we changed the rudder on our H 28.5 PHRF wanted to see what I was doing. I needed to give them a drawing of the rudder and it's surface area compared to the OEM rudder. I went with a rudder simular to your rudder just a straight up and down wing section. We greatly improved on the shape and ended up with a 0012.5 foil section. We were wanting the 0012 section but could not because of the rudder post needing to match the OEM size post. You will want to report this to PHRF because if you do not and you get protested it could get ugly.

Cliff

[Cliff Ruckstuhl]

Ther is another option, a Company called IdaSailor Marine sells rudders made from HDPE plastic. I have one for our 28.5 and it is real nice rudder made to 0012.5 foil section. It also comes with a life time warrenty. I would give Joel a call and see what he can do. He is making allot of rudders for Hunter's, Odays, Catalina's and so on.

Cliff

[Hravn]

thanks, I'll check that out.

[DaveB]

Hey,

These have templates:

http://www.computerkeels.com/JCOMP.HTM

Cheers,

Dave

[Hravn]

thanks, made some already from the class published offsets. Didn't cost $100 either. A local builder is laying up a new rudder to the 'official' specs and I'm strip planking myself an experimental one with a naca 0010 section and an elliptical tip. carbon over cedar. spec'd out weight at 28 lbs, just more than half the 52 lbs of the original.