Charles has some photos that he took and some text that I wrote and he will have it all put together shortly. I only just gave him some material. I’m running out of time in the evenings these days. I have 2 Victoria regattas this weekend and just finished a new carbon rig for the occasion. Actually, I still need to put the battens on. I weighed my Vic and I’m now a few grams under the 2041g minimum. I think I’ll run 5 AA batteries to get the needed weight. The racing bug had got me good.
I have the race details in a spreadsheet but formatting is ugly. I think I’ll post it anyway. I did find a math error from the RD’s sheet. It didn’t affect placement any but I wasn’t so close to Graham as I thought. I’ll get to it tonight.
The race report was most excellent! An event like this is both fun and educational. Since this is a developmental class in its early stages, people are still experimenting with all kinds of things, and the pictures show some of the variety.
A gathering of boats like this also presents the opportunity to see what is possible, and what really works. Was any aditional data gathered that did not show up in the race report? Were the boats weighed? There have been various reports of very light weight hulls. I suspect that Bill’s boat was probably very light, and it looks like it is carrying a lot of sail.
Bill Hagerup’s boat is interesting in a number of ways. The transparent decking (what is it?) probably saves weight. Mounting the servos on the deck is something I never considered because of wetness, but apparently it works (any comments?), and saves structural weight. It looks like he also has a very full bow.
Scott had mentioned that Bill’s boat had a mechanism to slide the mast back on a run. It can be seen in the pictures. What is the rationale for that? Does it help prevent nose-diving?
My hull is quite light, but the overall weight is still about 530 grams. It would be a bit less if I didn’t have the sliding rig.
The deck is Monocote…the stuff the airplane guys use.
The rationale behind the slider is to move the CE of the sail back to reduce the nosedive effect. It is connected to the sailwinch arm, so the rig moves forward as I sheet in and back as I sheet out, proportionally to the sheeting movement. It was inspired by the sliding rigs popular for vane sailing many years ago. I was pleased to get it working well, and it handled fine in Raleigh. It was clear that it doesn’t solve the problem, though. Big gusts still overpower the rig and the boat dives. So the jury is still out. It works, but I’m not sure that it provides enough advantage to be worth the complication. I’ll play with it some more, though, before I decide.
Bill,
Thank you for the information. More questions:
With your light weight hull, did you put extra weight in the keel bulb? Your total weight is about the same as Scott, and I believe he has 8 oz in the bulb. Also, what is your beam?
Despite its long and noble history in Marbleheads, I am rather sceptical about the sliding rig. A little playing with triangles of forces will quickly reveal that the fore-and-aft point at which the propulsive force is applied to the hull does not matter in the least. The whole structure may be assumed to be infinitely rigid and hence all the tripping forces are locked up in the rig/mast system and do not impinge on the hull/water system. This applies IF THE PROPULSIVE FORCE IS HORIZONTAL (or more exactly, parallel to the net hydrodynamic drag).
In reality, this is not the case. There will always be at least some spanwise flow (i.e. flow that is at least partially toward the top of the mast). By Newton’s third law this must give rise to additional transverse and downward components of the force on the hull - so we do indeed lift the bow to some extent. However, spanwise flow occurs mostly at fairly high angles of heel. It thus appear likely that you will lift the bow going to windward but not when you really want to - i.e. boat more or less upright, overpressed on the run.
When I were a lad learning windsurfing my instructress (thanks sarah) asked if I sailed, and; on learning that I did said I had one big thing to unlearn but that was for me to discover.
The “thing” - I swiftly discovered is that windsurfrs have a third dimension for the sail - and lean it into the wind quite sharply to get a substantial “lift” component to the force exerted. This unloads the board considerably and contributes to (especially) acceleration.
If I coud get some aerodynamic lift from the sail, (or hydrodynamic lift from the keel) then my Razor might approach the plane in some conditions (hull is right)
At Burton some idiot suggested thet the ideal sail for the conditions (in the absence of mast height restriction) would be a mylar birthday baloon floating 15 Metres above the boat.
Perhaps we should be considering the +Z dimension with as much care as the -Z that Angus writes so correctly about
mac rigs first and 2nd!
winner appears to choose mac rig over the sloop rigged boat that gets loaned out?
Bills sliding rig is interesting…in a good way.
I am sure there are other points to note as well…any comments on actual charateristics of the various designs? or is it all skipper ability based?
Having sailed vane Marbleheads exclusively with sliding rigs in my formative years I would like to add a component to the discussion that has not been mentioned.
One aspect to be noted is that vane sailing boats were quite a unique breed of sailboat. They were optimized for the upwind downwind competitions that were standard in the day, with the emphasis on upwind performance for which you won the higher score.
The hulls were designed with the sailplan well forward so there would be room for the vane to be reversed (aimed forward) for downwind sailing. This made for some challenging boat designing because no part of the rigging could extend forward of the bow. These boats were designed to be so well balanced (along with large keel fins, small rudders and skegs) that they would sail in a straight line extremely close to the wind.
For downwind we used to slide the rigs aft different amounts for different conditions, six to eight inches was the maximum before you would start to interfere with the vane. Sliding the rig aft actually unbalances the boat moving the Center of Effort of the sails in relation to the other centers. This aft movement would tend to create massive weather helm all things being equal. But the one overlooked component I mentioned is that sliding rigs were used in combination with spinnakers. Spinnakers, which were unmeasured in the Marblehead class, were often of different sizes for varying conditions but would act to rebalance the hull with the rig in an aft position. Not moving the rig aft for spinnaker use would often interfere with directional stability. Weather helm and occasional broaches from wind gusts were resisted by trimming the jib to the centerline helping to weathervane the hull and provide maximum air flow to the spinnaker. Some folks even removed the jib entirely in stronger winds.
In my opinion sliding rigs don’t really help nose-diving and were originally conceived to meet quite a different set of criteria. If Bill’s sliding rig moves the rig aft in direct relation to his winch’s swing arm position and doesn’t produce ever greater weather helm as he eases his sails out I would be surprised. I do applaud him for trying an innovative idea from the past to find a solution to a recurrent problem with these boats. Its an idea I pondered myself as a what if, but reconsidered when confronting the weight targets that have appeared in this forum.
It was a great regatta in Raleigh (and a great regatta report)! I’m sure we all came away with lots of new ideas to try.
With their sudden tacking and instant acceleration, the Footys were lots of fun to sail tactically in a big fleet.
In boat-for-boat testing (swapping skippers), with boats that are identical except for the rig, it seems that the McRig (Una rig) is always faster than the sloop rig or swing rig due to its ability to point higher. The only exception seems to be that the sloop is better in heavy chop as in Laconia. With the main twisted off, the sloop seemed to accelerate better after being slowed by waves. Of course it also could have been that Jim simply outsailed me!
It seems to me that the difference between Bill’s sliding rig and Niel’s vane Marbleheads is that I’ll bet that the weight of the sliding rig on the Footy is a higher percentage of the total weight of the Footy than the M’s is of its displacement. Also, I wouldn’t be surprised if Bill’s rig travels a larger percentage of the waterline length than the M’s did. So I think that the sliding rig’s ability to raise the bow is more a matter of weight shift than of aerodynamics. It would be interesting to try Bill’s sliding rig against a boat with a fixed rig with the weight savings that would allow.
Lots of interesting speculation regarding my sliding rig…well grounded in theory.
In actual practice, it works quite well. Considering Scott’s skillful performance and well-known tuning abilities, my boat demonstrated that it is capable of keeping pace with one of the best. I really think that with a bit more experience with my boat, I’d have beaten him one or two more times!
As I sugested, though, whether the slider contributes to performance is still unclear.
That said, it does take some fiddling to get the slider working right so that the mast is positioned to keep reasonable balance at different wind positions. It’s also a bit fiddly to get the sheet lengths right so the mast movement and sheet position are well coordinated. And it does add one ounce of additional weight. So it’s not any kind of silver bullet.
On the other hand, it did beat 8 other boats…with a chine hull.
Scott brings up another interesting point. An ounce of weight sliding fore and aft could be construed as shifting ballast. When you think of shifting ballast in most cases it means some means of defeating heeling upwind. In the case of these small boats there would be a real advantage to shifting weight aft to counteract the tendency to sail nose down or nose-dive downwind. The world is rife with unintended consequences, is it not?
Another question I think needs clarification is wether the gear above deck is part of the hull or part of the rig. The swing arm for the winch and the slider contraption might have to be below the top edge of the measurement box if they are considered to be hull parts. That would in turn shorten the keel fin reducing righting moment. Since they both are mechanically attached to the rig they might alternately be considered part of the rig and exempt from fitting below the rim of the box. Ponder away everyone!
And isn’t it interesting that there’s always a sea lawyer out there somewhere. It’s a development class people, let’s develop the breed and discover, on the water, what makes these quirky little boats go. Incidentally after Raleigh, with it’s windless holes and choppy little sea, I realise how apt Brett’s ‘Bobabout’ name is for a Footy.
I don’t think it would be appropriate for me to debate the legality of the sliding rig. If formally challenged, I’ll be glad to recuse myself and let the Technical Committe rule. I’m happy to share my thinking, but I won’t respond to additional discussion.
I anticipated the concern about shifting ballast before I built the rig. Obviously, as head of the Technical Committee, I would not have built it if I didn’t think it was legal. I don’t believe that a moving rig falls under the ERS definition of ballast. Also, there is a precedent in the USOM class which allowed a canting mast although their rule prohibits shifting ballast. Finally, taking Niel’s point to the extreme one could argue that a boom movement represents shifting ballast…an argument I hope I’ll never hear! Of course, this is all simply my opinion, and not official in any way.
I also made sure the servos, winch arm, and slider fit within the box to avoid any concerns from that end.
I don’t consider myself a sea lawyer so much as a concerned designer. I posed these thoughts as hypothetical arguments. I personally have no objection to a sliding rig but other folks might, particularly if Bill continues to do well with it. It would be a shame to have an excellent race result voided in the future for innovative thinking now.
Scott pointed out that the weight percentage is smaller for a vane Marblehead sliding rig, as a part of the whole displacement, compared Bill’s Footy rig. I would venture that in the case of a USOM canting mast the same would be true. In addition, as I pointed out before, I am not aware of shifting ballast rules that prohibit shifting weight aft, only from side to side to increase righting moment. Thats what makes this an interesting question.
