A series of conversations between Randy and Dan Ketterman... From: Randy Devol Received: by waltz.rahul.net To: cliff.sojourner@cisco.com Subject: Here it is. ------------------------------------ Subject: Re: Blade Runnings Volume 7 Date: 10/10/96 To: randyd@rahul.net In a message dated 96-10-04 14:14:46 EDT, you write: Here is another way Trifoilers are very different from most boats. I think I understand how Trifoilers behave when overpowered. (Dan, correct me if I am wrong!) >The leeward foil must provide upward lift to keep the boat upright. At the same time, the windward foil must pull down to keep the boat from tripping over the leeward foil. However, the amount of lift needed from the two foils is very different. Since drag is a linear function of lift, there is much more drag from the leeward foil than the windward foil, which tries to turn the boat downwind. At speeds lower than 25 mph, the rudder can easily keep the boat on track, but at higher speeds, the rudder rides higher, and rudder aeration (air getting sucked down the trailing edge of the foil) both work to disable the rudder, which makes it unable to keep the boat sailing in a straight line. Hi Randy, I am glad you had a great day of sailing and have some friends in the area to go play with. To answer your question about your theory, which is a good one, but; I don't believe so. You are very close. Greg and I have noticed that when the rudder suddenly requires a major amount of helm to maintain a straight course, it is caused by one of two problems. 1) 90% of the time it is caused by ventilation on either main foil or even sometimes the rudder. The way to tell if this is happening, is look at the wake in the water. If there is a lot of white foam or a huge white rooster trailing off behind a foil, then there is your problem. I can always hear the extra noise of water falling. So I know which way to look. Now, how to correct for it. Sometimes just letting the fences do their job works. If the problem is really severe, you may have to let out the sails or round way up or down to reduce the side loads to get the water reattached. Then you are good to go. This has been a factor of concern for us because as you can tell there is a loss of steering control. 2) Debris. If seaweed or a clear plastic bag gets wrapped around only one of the mail foils. This causes the boat to suddenly decelerate and requires helm adjustment. This is usually not as bad as ventilation unless the debris is really big. Even ventilation causes the boat to slow down, so if the boat feels like it is going side ways, and no signs of white water, pull over to a complete stop upwind and backup for a few yards to clear the debris. Hope this helps next time you notice it. Feel free to pass this along you others on your mailing list. Hobie Trifoiler factory boys. Dan Subject: Re: Blade Runnings Volume 7 Date: 10/11/96 To: randyd@rahul.net In a message dated 96-10-11 13:00:57 EDT, you write: >Two observations: I have noticed that when I lose steering control, I *always* have to turn the boat into the wind to go straight. The boat always (so far) tries to turn downwind. Also, easing the sheet always allows me to steer normally. If I am getting rudder ventilation, why would easing the sheets correct the steering problem? (Easing the sheet helped dramatically both times this happened.) >More likely, there is a combination of factors: X% ventilation + Y% overpowered = steering problems. Hi Randy, Here is a common scenario. The fastest point of sail on the Trifoiler is about 110 degrees off the true wind. You may notice at this angle that the wind over the deck is relatively low and things get a little bit quieter. Somewhere within this range the loads of water and wind get much more in balance. At this time the main foils are just coasting except for the sensors are feeding a lot of input through the ama to foils. This is because the waves are going in the same direction so the frequency is slower and the amplitude feels higher. This is just food for thought. Now here comes the beef. With the apparent wind much less but still coming from in front, the drive vector of the sails is with the true wind and the masts are leaning forward more than usual, this raises the back of the boat and the rudder is less buried, therefore as the troughs go by, the fences can't do their job. Subject: Re: Blade Runnings Volume 7 Date: 10/15/96 To: randyd@rahul.net In a message dated 96-10-14 01:06:21 EDT, you write: >Thanks for that tid bit. I was wondering. Do you or Greg have anything like a polar diagram for the Trifoiler? Hi Randy, I'm glad to hear that you had a reasonably good day of foiling around. When ever you go blasting by another fellow Hobie catter, you should yell at them "Hobie's Rule" :-) Give them a big thumbs up with a cheesy smile. :-} >I had Blade Runner out yesterday and saw (and heard) the rooster tail you were talking about, but only on the forward foils. I never noticed it coming from the rudder. The wind was not as high as it was two weeks ago and the rudder remained responsive, even when one of the forward foils was aerating/cavitating. Aerating is OK to describe the ventilations, but very rarely can you say cavitating. Which you never can see on the surface of the water. Cavitation is caused by extreme negative pressure causing water to vaporize which starts to cause major drag to lift problems. >Cliff (a new Trifoiler owner here) told me that I needed to rake the rudder forward; I was tail dragging (this week). All that agrees with what you mention above. Maybe I was rooster-tailing my rudder last week. If you were dragging in the stern, this would help explain the sensor rising. If the rudder is too far back, the stern will be low which rakes the mast back and basically shortens the adjustments on the shock absorbers. Buying new shocks will not help the sensor rising problems. Having an extra person of considerable mass will cause sensor rising also! Sometimes there isn't enough forward adjustment in the rudder in connection when for example: If trying to get from displacement to foil borne while pointing high sheeted in close hauled. This puts alot of heeling movement on the rigs causing the leeward foil to pitch ahead of the pivot point, causing the sensor to climb skyward. This is why there are springs inside the shocks. To push the foil backwards. After the boat reaches speed and levels out, the springs are slack! Now the center of lift is barely in front of the pivot point and the drag of the water over the foil helps to keep the sensor down. The faster you go, the more drag, the harder the sensor gets smashed into the water and the sensor arm gets bent upward, this is when the race boats (and the production model) could use a system of the shock pulling the ama bow upward instead of usually downward. Also, I had such trouble keeping my port sensor down than I lengthened the port shock too much and it broke. It might be a good idea to make the shocks with "don't unscrew it past here." We experimented with some waterproof stickers that were plastered all over the boat that said things like: check drain plugs, check port boom before lowering mast, check owners manual and this and that. We have a general caution label about safety and one about your Trifoiler. Rule Number One: Have Fun! >The screw was only in the threads about 1/4 inch. I am not surprised it broke. It was quite spectacular. The port ama pointed up at the sky and the sensor was about 6 feet off the water. This episode reminds me of the early years of experimenting with the race boats. You should see what happens to the one piece beamed boats when the shear pin breaks in the rudder. We have video of the whole boat out of the water by about 4 feet. WOW. >At the same time, I angled the port foil back some (I don't know the measurement to the knuckle) and that helped the sensor rising problem *some* but seemed to make it hard to get the port ama out of the water on a starboard tack. Sounds like you angled the foil back too much. Here are the dimensions that we use at the factory. Port = 58 3/8 inches. Star. = 58 5/8 inches. The way to measure: Put the foil on the ama and locked on. Hook the tape measure on the trailing edge of the foil (about 9 inches from the tip) and measure forward to the bottom of the ama bow where the sensor arm socket ends. This is good for about 90% of the time. Fine tuning may be necessary. >Cliff said that he had a sensor rising problem until he got new shocks two weeks ago. Did he know how to adjust shocks? Could have been something else that changed. Because the shocks have not been made any different. The adjustment may have been longer from the factory. I just got two shocks from Wind Toys that I don't see why they wouldn't work. Maybe a little leakage? >The port shock definitely has a different feel than the starboard shock. Perhaps getting a replacement will solve the sensor rising problem also. I will contact Wind Toys for a replacement. Could you be more specific? What difference? Spring distance, damping rate? Thanks for the feedback. Dan Ketterman Subject: Blade Runner Date: 10/17/96 To: randyd@rahul.net Hi Blade Runner, I started to read your last e-mail, but got distracted and didn't finish. So then I started deleting all the other mail on the list and accidentally washed your copy out also. I'm sorry and would like to know if you can re-send it. :-( I'm also sorry that I forgot to address your first question about polar diagrams for the Trifoiler. The answer is unfortunately No. We gave it a lot of thought during the race days. The instrumentation and sensors were not as available back in those days. GPS's and radars etc. This information would be extremely useful when going to speed events halfway around the world. You may be able to imagine that the boat is very poor in low wind conditions at any angle. But it would go off the chart in 12-15 when reaching then tapering off until about 150 degrees, and then it would drop to wind speed at about 180 degrees. If the wind was 15-20 degrees at 180 degrees, the boat maintains a more linear chart. Does this make sense? I know there are a lot of gaps. As far as your forestays go, they could be shortened a little bit by using a shackle direct to the bow plate. This will only slightly rake the mast forward because the stay angle is minimal compared to the backstays. About all this will do is tighten the whole rig. It puts alot more tension in the King post wire. Another Key to adjusting the rake is how high the sail link is above the deck. Sail link height is about 4 inches above. I believe your boat is around the generation when we were trying to get rid of the chain plate adjuster in front. What you and I need to figure out is how much rig tension exists. Compare yours to Cliff's boat. More rig tension could also mean that your amas are depressed into the water more. Considering measuring the beam defection from end to end when rigged. If you are happy with the way the rigs and sail link is, and just trying to make the spring rate higher in the shocks, consider making the adjusting slug inside the bottom of the shock closer to the ends. Drilling the two rivets and redrilling a half an inch lower and putting a screw through with lock nut. This makes effectively a longer shock with a coarse adjustment. This is all I can remember reading about. I know there was more. I would be more than happy to reply. Please resend, hopefully your system doesn't auto delete files. Dan Ketterman Subject: Blade Runner Tid Bits Date: 10/18/96 To: randyd@rahul.net Hi Blade Runner, In a message dated 96-10-18 13:34:45 EDT, randyd@rahul.net (Randy Devol) writes: >Instead of 10 knots being the full scale boat speed, 40 knots should do it. Perhaps a logarithmic boat speed scale would be useful? :-) >I want to see a polar diagram because I still have little or no intuitive feel for how the boat sails, especially in the marginal conditions: 8-12 knots of true wind. Getting up on the foils is so critical, and seems so difficult. And yes, I still have the fairings I can add to the amas. But that won't help my understanding of the dynamics which is what I really want. I will try to make a polar diagram from the top of my head, of course for you it will have to be two. 1) one person in the boat, 2) two people in the boat. Not tonight. >A shackle to the bow plate might shorten the forestay by an inch. Right? Can you recall my particular boat? Not exactly, I have some notes at work, in the archive boat descriptions. >Should I borrow a shroud tension measuring device or is it sufficient to know whether I have "more tension than Cliff or less tension than Cliff?" I don't think so. The wires on these boats are not highly strung, except the king post wire. The way to check tension is by trial and error. When sailing along in a good blow, watch to see if the windward forestay goes slack and how much. I have seen this happen many times. Pretty scary. Tighten if necessary. A little bit once in a while is OK. Use Cliff's as a comparison. >OK. How do I measure deflection? Height above the pavement before and after the masts are up? That might work. We have never done it that way. We use a small size cord and pull it tight across the top of the beam with the rigs tight. Stretch it from mast to mast so that the center is tangent to the center of the beam. Now mark from the ends of each outer beam on the masts where the ends of the cord touch the masts and measure up from the top of the beam to the mark on both of the masts and add the two dimensions together and divide by two to get the average. I believe that something like 8-10 inches is the ballpark. >That's news to me, but I understand your explanation. It makes sense. >It would be really nice to have a parts list for the Trifoiler, just like there is a parts list for the Hobie 16. I can help here. Our parts department uses one when other customers place orders. Your local dealer should have a copy. Ask him if he can make you a copy. >I have sailed (for quite a distance) with one of the forward foils out of the water, but not both. Did you fly a weather foil on purpose or was it accidental? Was the reentry smooth or did you crash down hard in a panic. This could break something! >There was a 1/2 to 3/4 inch of travel where the oil was not damping the motion. That is now how my port shock works. My starboard shock has no travel without damping. The difference is quite noticeable. I don't quite see how this would cause sensor rising, though. Here is some inside info. Your shocks are probably of a generation of when I used to fill the tubes completely full of ATF. Auto. Trans. Fluid. If the shocks were left in the sun to bake, reaching temps well over 160 degrees F., the internal pressure would go up to about 1500 PSI. This causes the seals to stretch and/or blow. The fix has been to deliberately top off the ATF and then remove a inch worth to create an air void for heat expansion. So a portion of the stroke doesn't have any damping. That would be the very top of the stroke which is a good thing because when the ama gets lifted quickly out of the water by say a gust, the sensor can drop much faster. So don't worry about the differences between your shocks. The starboard is OK and the port is better. :-) Conclusion: What I am hearing is that you have two problems: 1) Have hard time in getting foil borne. 2) Have sensor rising. The second problem must be filed. However, keep this in mind, the shocks push the amas down which angles the foil back, reducing AOA. Even though you pull up on the sensor retraction line to get the sensor off the water, (in marginal conditions), the foil may not come up the same amount of rotation due to the raking the mast forward or making the shocks longer. Therefore making it even harder to get foil borne. Maybe more practice and technique is prudent. Rudder rake? Extra equipment and supplies onboard? Overtighten the outhaul? Maybe excessive growth of barnacles and mussels have accumulated on the bottom? I don't know. Next time you're out with Cliff, swap boats and see what the difference is in feeling. I will try to remember to build a polar diagram. Good luck! Dan Ketterman Subject: Re: Blade Runner tid bits Date: 10/21/96 To: randyd@rahul.net Hi Randy, In a message dated 96-10-21 15:39:33 EDT, you write: >Thanks for the inside info, but I have a hard time believing that my port shock, which now behaves like Cliff's just before they were replaced, is better than my starboard shock, which is just like the *new* shocks that Cliff just received. Maybe there is a problem with bubble formation; just after sailing, the damping is sloppy because of bubbles but after the air collects at the top of the shocks, is back to *normal.* It is quite possible that the oil is foaming while sailing. So I ask you this question. Do you notice a significant difference between the port and starboard side when flying along at say 25 mph? What I want to know is if the port side is going through alot more gyrations. If so, then there is a damping problem. If no noticeable difference is seen or felt in the amas shaking or the sensor bouncing up and down in the waves, the shock is OK. The shock has two functions: 1) controls sensor rising. 2) smooths out the ride height of each foil. The fact that you have not mentioned the problem above, leads me to think that oil level and feel of the shocks compared to each other means that the shock is OK. BUT!! Put the two shocks together side by side and push down on them lightly until the springs start to compress. Check the height difference. They should be pretty close together. If not, check to see where the difference is. The adjustment at the bottom will obviously cause a major change. If only about a 1/4 inch is detected, (the port being shorter), this could be a problem. If the adjustments are at the same place and there is a height difference, the internal components have been damaged. Check how still each shock is toward the bottom of the stroke. Should take all your weight. >Let's focus on these two frustrations: >1) I have a hard time getting foil borne on a starboard tack compared to the port tack. 2) The port ama has some serious sensor rising compared to the starboard. Is the above frustration related? When it is hard to get foiling, is it because the sensor is rising or because it feels like there is enough wind but the boat just struggles? I just had another idea! We have played with small changes of foil camber and toe. It is hard to check these differences because conditions change. Until two boats get together and race for speed, I need a test tank. Check how vertical the main foil is, think of the vertical section as part of the horizontal portion, if the vertical part was more under the boat, you have effectively increased the lifting area. The bow wire tension can very slightly effect the toe which can also increase AOA. A coarse adjustment to the camber and toe is to add washers between the foil and foil plate casting. The toe is set at the factory by the position of the beam saddle. (Casting which the outer end of the bow wire is attached). This casting is riveted on the beam squared to the foil plate and outer beam before the foil is mounted. I need your address to send this polar diagram via snail mail. I will have to figure out how to resend prior Blade Runner volumes. This is all for now. Dan Ketterman. Subject: Re: Blade Runner tid bits Date: 10/25/96 To: randyd@rahul.net Hi again Randy, In a message dated 96-10-23 00:34:09 EDT, you write: >You can put all your weight on the shock without hitting bottom? It depends on how much lunch you had, with my wieght, no. I am about 145 pounds. I come to about a half an inch from bottoming out the shock. >First, I fly across the bay with a 100 lb friend in the back seat. On a port tack, it's a piece of cake. Then I jibe on the foils and start back. This is where I get sensor rising problems, even though I had none on the port tack. This sounds like the shock has to be longer. For what reason that it has to be much longer than the starboard side, I don't know. >Now if the jibe puts me back in the displacement mode on a starboard tack, I have a really hard time getting back up. There seems like enough wind, because the port ama is sending water everywhere! I am wasting tons of energy by spraying water. And there was very little of this when starting out on the port tack. This sounds like there is water inside the port ama? Or, some combination of some of the problems that I have discussed in previous letters.. I know that the Trifoiler has a ton of apparent wind, sometimes when we sail across the channel we don't realize how deep from the true wind we are sailing, After jibing we try to steer back to the beach where we launched which is a much higher course to the true wind, If this is the case; the conditions are for your above problem are going to be more pronouced. Sailing a beat to weather puts more leeward pressure on the foil, which causes sensor rising. What I am thinking is that you are not possibly reaching back and forth exactly 90 degrees to the wind. Ignore what the wind waves say. The next time you notice the leeward sensor starting to rise slowly off the water, bear away to accelerate, this will help lessen the loads and at the same time increase the water drag which pushes the foil backwards. Once the sensor gets back where it's suppose to be, head up to where you want to go. When beating upwind, watch the speedo, keep it at no less than 17 mph. >Thanks again. You know, if you and/or Greg are going to be hosting another Trifoiler get-together sometime this fall or winter, I would like to come down again and let you look at the boat in person. I don't want to adjust the foil toe or the forestay length without the "factory's" blessing. All this is information is getting a little overwhelming, especially since I have not had a chance to take the boat out and sail-adjust-sail-adjust it. I will try to let you know in as much advance as possible. How about tomorrow? Just kidding. Polar Diagram is in the mail. Pretty crude though. Dan Ketterman P.S. I am moving this weekend, so I may not be able to reply for a while.