J/30 Class Association Forums J/30 Forum The Boat, Sails and Equipment keel fairing

who makes the best j-30 keel templates to fair to. compukeel or factory

My understanding (having made templates and discussed the results with one measurer) that keels were built thicker than the offset tables specify. I've been told most keel jobs (including the one on my boat)correct problems with chord, length, position, and trailing edge thickness; not section. The former measurements can be done with simple templates. Something to consider before spending lots of $$ on precision templates. I'd be interested in hearing contrary opinions.

I faired a keel on a Catalina 27 and it appeared that the lead mold widened at the middle due to the stress of hot lead placed in the mold. Correcting this required removing one-half inch of lead on each side of the keel in the mid portion of the chord and adding 3/4 inch to the front part of the keel. The result was amazing. The boat just begged to go upwind and pointed much higher and was easier to stay in the groove when pointing. My keel on my J-30 looks and feels smooth buti think the template can reveal what the eye cannot.

3/4 is huge. How many more crew did you have hike? I don't think you'll see more than 1/4 per side. Note there is a spec on keel weight. Truing the keel might remove enough weight to violate the low limit (not that anyone would know without weighing). But, I would be concerned with such a small, low aspect ratio keel that the loss of weight (higher metacenter, less stiff boat) offsets gains in speed (from reduction in Cd, Cl coefficients) a thinner section would provide. You can always build it back up, but not add weight (new keel). Lastly, if you thin the section, watch the stub the keel plugs into (don't cut into it). I think the stub is fat too, and would require some transition fairing to a thinner keel. A little simulation would answer the trade-off questions.

Let me ammend my comments above: I calculated some scenarios for leeway and boatspeed resulting from balance of sail and keel forces, upwind, due to a change of 1% in keel section thickness (nominal conditions, all else being equal). There is the theoretical potential, by bringing the section thickness down to spec, of a couple tenths increase in boatspeed, and about 1 degree less leeway. I used old NACA airfoil properties, which are pretty close to the J/30 keel profile. Curious thing about those curves, they show narrower sections reduce drag coefficient (Cd) by >5% per 1% change in 1/2-section thickness, whereas lift coefficient (Cl) is almost unchanged. That leads to a bigger performance benefit than I thought because as boatspeed increases to balance the lower keel drag, leeway (a.k.a. keel angle of attack) decreases to rebalance keel v. sail lift. (If Cl decreased with Cd, then leeway would have to increase and vmg improvement, if any, would not be as good.) Also, affect on heel is much smaller than I would have guessed (< 2 degrees). Numbers seem to support your experience with Catalina. Sounds like a win-win. Disclaimer - do your own math - and what you do with a power planer is your responsibility!

I re-faired my keel several years ago. It had been "done by a pro" by the previous owner. As soon as I put the templates up, I knew I had a lot of work. Luckily, about 1" had already been added to the front to make up for the short chord length, but one side needed lead ground off to make the keel thin enough. I did not thin down the fiberglass stub totally, because I was not sure of structural implications.

Ed Austin
Chinook

Ed - did you plane or grind it off? Did you notice a performance improvement? Thx.

when I did my catalina keel I added the filed off lead to the bottom of the keel -- talk about lowering the center of effort. I think that the correct shape should simulate a airplane wing not a wedge. Lift can be created with the proper shape .. I think a wide midcord is not as advantageous as shape that is wider in the forward 1/3

Hard to say whether it was a big improvement. The crew and skipper were on the steep part of the learning curve at that time (does it ever get shallower?)

We had Bebop's keel faired to start with 20 years ago, then faired keel and rudder to templates about 1990 with area added to leading edge and not much lead coming off. It was refaired a few years back when the gel coat blisters were replaced with epoxy. People tell me it is very close to the templates but I have never measured. In my estimation, there was never any noticeable performance improvement in speed or point over a basic well-faired bottom. Fresh sails, rig tune, and a clean start seem to be a much bigger factor.