I like to do my best to help those who think outside the box, so to speak.
I think that area in the keel fin is less a factor than a good hydrodynamic shape. I do diagonal and angled boats and I think that there is something positive in the shorter keel depth that comes along with this type of placement in the box, less drag. I would even accept the loss of keel length to accommodate a non-dumpy bulb, so you are good there as far as I’m concerned.
There is nothing wrong with a lower rig as well, a 45 degree rig is rather radical though, but an 18 to 22 inch hoist is not too low if you can still keep the area well above 200 sq. in. for the “A” suit. Using a CF tube for the jib stay should allow a loose enough swivel to keep the rig from binding. If you haven’t already done so adding enough casting weights to the forward end of the boom will help to make the rig’s idle balance point somewhere near a beam reach, much like the jib counterbalances on the M class or IOM boats. This will make the sail more responsive so that it doesn’t just hang centered in the lulls.
The heavier bulb and the bigger rudder have improved performance, and the sail tuning has been improved. Today it handled quite well in a nice breeze. I have learned some tricks in tuning the sail, which is a littlle different with no serious backstay. It may be ready to compare to a real boat. My previous attempt at competing with other Footys, about 2 weeks ago, was not very auspicious, as the boat was obviously not ready for prime time.
As Neil has said, balancing the jib club is important. The red (B size) sail shown in the picture at the beginning of this thread actually balances perfectly without any weights, because of the weight of the carbon tube in the luff. My other sail (C size), with a longer and heavier club, required about 1/8 oz at the tack. I stupidly used a 1/8 oz sinker, which was a little too much, then clipped a paper clip to the leech, to balance it just right. Guess what? The paper clip snagged the mast, and the boat became uncontrollable. I haven’t yet built the larger A size sail, but will need it as the winds get lighter.
Progress (or lack therof)
The boat has performed very well in tests at the pond, with both an “A” sail and a “B” sail. But two attempts to race against other boats have been inconclusive. Two weeks ago, racing against our Thursday fleet, it was disabled during the first start as the sail arm bent, and poked a hole in the side. This week, we had a very strong wind, and the “B” sail (150 sq in) was too big, although it handled resonably well to windward, downwind was a problem. Everybody used their smallest sail, and I raced my other boat successfully.
I have jury-rigged a half diamond stay to see how effective it would be in stiffening the mast, and it works. However, I haven’t made it permanent, as it seems to handle OK without it so far.
The Keel-Forward hull appears to be more sensitive to broaching in a strong wind. This is probably due to the forward keel offering no resistance to the broach. A conventional keel will offer more resistance as the bow digs in and the boat tries to pivot about the bow.
A possible improvement is a more balanced rig (move the jib club pivot further aft than the present 25%, perhaps to 30%, if it can be tolerated and still allow the jib to weather-cock)
Another thought: a conventional hull with the keel slightly aft of normal will be more resistant to broaching as the nose goes under (those of you who are real naval architects probably already knew this; I found out the hard way).
As I suggested before, reducing the area of your forward fin (a more high aspect profile) and going with a larger rudder would work to balance the foils and move the center of lateral resistance aft which should make your boat more controllable. Right now I would say that the large area of your forward keel is stalling in the broach (and probably on any radical maneuver), creating a ton of drag that the boat can’t overcome to recover.
I certainly wouldn’t give up the experiment. You actually have several experiments going on simultaneously which is not the best way to analyze the variables involved and definitively say what is the cause or the causes of any one characteristic. That baby with bath water thing.
Best of luck and let us all know how you proceed.
Today we had a good wind, and were able to conduct our Thursday Old Farts Regatta. The new boat competed in 4 races. It handled well upwind, and was competitive, although it was obviously a little more tender than other boats carrying the same sail size. However, it had trouble downwind, as discussed earlier. I had built a new “A” sail to (presumably) overcome this problem, but the wind limited us to “B” and “C” sails.
I had built a new “A” rig with the jib club pivot moved aft to the 35% point. This was tested today in a suitable light wind. It doesn’t weather-cock reliably. So I moved the pivot forward to the 30% point, and it pivoted very reliably. I then put the boat in the water, and it handled reasonably well. It appears to be an improvement over the 25% position as far as downwind broaching. Now it needs to sail against other boats for comparison (perhaps on Thursday).
A little progress
Last week I played with it during lunch hour at the Connecticut race, and it handled nicely in a good breeze.
On Thursday we had a fleet of 5 boats in a very light wind. The Keel-Fwd boat was able to complete all the races without any obvious problems, and was third overall. However it obviously needs more work on the sail shape (too flat) and various trim adjustments which affected performance in the imperceptible breeze.
A little more progress
In todays races, the boat sailed very well in a light wind. It was obviously fast, and close-winded. An interesting feature is that it will always complete a tack, perhaps because of the relative locations of the CG and CLR. The sail shape problems have been solved, without resorting to a diamond stay. The wind was light enough that the tenderness issue did not matter. However the tenderness problem persists, and has 2 causes: the high weight aloft, due to 2 vertical spars (mast and luff tube), and the relatively short keel. Note that any 3-D hull will suffer from the short keel problem, and it is apparent also in the Pool Shark.
Next I will play with the rig weight and keel depth.
I have performed major surgery on the keel and mast step. The 9 ounce bulb is now shorter and fatter, which enabled it to be dropped about 1/2 inch and still remain inside the rule box. The mast diameter has been reduced to save weight aloft. It bends significantly, as can be seen in the picture. The tenderness problem has been reduced. I sailed this new configuration 2 weeks ago against the fastest Razor 3 in our fleet, and was beaten soundly. However, the hull had developed a leak, probably from the stress at the seams, and had taken on about 8 oz of water, which was apparent at the water line. So some water proofing fixes were made. The boat now weighs 15.7 oz with rig.
This Thursday it won the Old Farts Regatta against the Razor 3 and a Pool Shark. It was a light to moderate wind, and it handled very well, although still somewhat tender. At this point, I can only say that it may be competitive. It was not obviously faster than the other boats. It has some interesting characterisitics. It handles very well when severely heeled.
I had a similar idea a few years back, just in reverse. Boat had a keel on the back of the hull, angled forward 45 degrees, with the rudder in front of the keel. Unfortunately, I was never able to complete any sort of testing, as my son decided he didn’t like footies, and have since been busy building bigger hulls (2 rg65’s and 2 stars). This thread has kinda perked my interest up in it again, maybe I’ll get it back out, complete it, and we can compare notes. For reference, I’ll copy your rig, with some small changes. 1. It will have to be moved back, obviously. 2. I’m gonna make it out of thinner material, to make it more light weight. I’ll post pictures when I can.
After several weeks of competition and several improvements, I believe that this scheme has gotten about as good as it can. At thiis point, it appears to be reasonably competitive, but not a break-through. It suffers from the deficiency of any 3-D placement in the box, which is loss of keel depth and corresponding tenderness. It should have a small advantage over something like the Pool Shark, in that the sail placemet allows a lower aspect ratio, and also provides some downwind lift at the prow, but not enough to make a serious difference. It is actually slightly slower than the Pool Shark, probably because of the very rudimentaru hull shape (a tapered box). I have considered reducing the downward slope of the hull in the measurement box, perhaps reducing the WL length to 13.5", but even then there is a considerable sacrifice in keel depth. So I think maybe the best use of the keel-forward concept may be in a more conventional 2-D diagonal placement, like the Razor 3, in which there will be some downwind advantage from the forward lift. I have shown that the keel-forward concept is controllable, which was my biggest question.
A question fot Mr. Zimmerman - what is the purpose of the aft keel?
Walt, you did a great job of progressive development…really thinking it through. It was fun to see the evolution.
So what interesting idea is next?
btw…are you coming up for the Regional on the 13th? I plan to sail a prototype…round version of Ranger that Craig Huzway pulled plastic hull for like the RG65 Round Ranger that he did. It came out quite nice
Obviously I should have tested the hull before proceeding with this design, but the long icy winter prevented that. After building it, all the effort was spent in making the rig work properly. Now I know that the hull drag is excessive. So I took a look at the bow wave today, and noticed that it is quite different from my other (conventional) boat. The basic hull shapes are similar, (the chines are arcs of a circle in both top and side views) but the new boat is thinner, and has the CG moved slightly forward to allow the bulb to be a litle forward (and deeper). The prow knuckle is about 1/2" under water, but very fine (17 deg). At this point, it is unknown whether the wave difference is caused by the naked hull, or the forward keel.
Bill - I expect to be there, most likely sailing the modified Bob-About 2
I know that I’ve said this before but the size and area of the forward keel is a bit out of scale with a modern Footy to my eye. Its area probably has more effect on the bow wave than any of the factors you’ve cited above.
I still think that you are working on an interesting general concept, but with an experimental rig on an experimental boat you have way too many variables to sort through. I would like to see the same keel forward idea on a hull of known pedigree, say Bill’s Razor 2, with a conventional rig or a McRig (perhaps Scott would build one of his). For the keel fin itself go with a helicopter main blade. This type of blade would reduce skin drag but still provide the boat with lift.
I know, just one more winter project, but hey, you got yourself into this and there are a lot of curious folks peering in on your progress.
The next step is to determine whether the bow wave problem is caused by the hull shape, or the keel. Neill has suggested that the keel is the prime suspect, and I am inclined to agree. The test results also support that diagnosis, as the tow test was done without the rig, and the prow was actually out of the water, leaving the keel as the only suspect. Also, it is much easier to cut down the wood keel than to build a complete new boat.
The keel is built with a thickness of 10% of the local chord length. With the current chord of 3" at the top, the thickness is 0.3". I have seen several articles regarding keel thickness, some of which advocate thinner sections, such as 6%, on small models. I have also seen test data at very low Reynolds numbers which support the idea of very thin sections. I suspect that any effect on bow wave will come from the thickness, rather than the chord.
The chord length is important in this concept in order to allow the keel to dominate the CLR, and keep it forward, to allow the forward sail placement.
Another topic - I was surprised at the ability of this hull to sail very well when extremely heeled. I think it is because the CLR moves aft as it heels, as the hard chine becomes a larger contributor to the CLR.