Righting Moment Part 1 keel boat, dinghy, Hobie 16, 49er skiff, windsurfer, kite surfer

[@Cptnbond]

Thank you, Mark, for the excellent presentation. I appreciated your highlights of the differences between these designs. Did you simplify the cross-sectional area for the CB, or did you use a CAD program to get a more accurate estimate of the underwater body? I'm not a marine architect, but the subject, as a DIY amateur, of boat design is fascinating. Please keep doing more of this kind of theoretical episode. Cheers.😀

[@markpalmquist]

@@Cptnbond yes it is simplified. But the horizontal distances are fairly accurate and so are the weights.

[@bobthevirus]

Kite strings are 3 or 4 mm diameter, its not zero drag bug its pretty low. On ice people have achieved even higher speeds. The big difference between kites and everything else is being able to lower your centre of effort almost all the way to the water line via a seat harness. Almost no leverage there means the limiting factor becomes leg strength and being able to hold the edge,

[@markpalmquist]

@@bobthevirus that makes sense. I did not go into the sails, sail angles and vertical distance of the CE. I’ll probably put that in part 2. If the kite strings have round cross sections they can be improved quite a bit with a fairing.

[@ChristianNally]

@@markpalmquist I saw a research paper and experiment on this once. I think the kite 'string' ended up vibrating a lot.

[@sebcam9498]

Kite lines actually are somewhat thinner, maximum 2mm diameter, race ones more like 1mm diameter (yes, dyneema is strong). Although maximum kitesurf speed records occur in strong wind, at low wind speed, it is possible to at least double the wind speed, even 3x with hydrofoil. And yes, having the possibility to use all the body weight, to leverage the kite pull, is of great advantage.

[@markpalmquist]

@@sebcam9498 according to NASA's website the drag coefficient of a circular cross section changes quite a bit with speed ranging from .07 to .5, but it did not go into what speed range this covers. I bet they would be helpful to push the top speed higher.

[@OleSeaHound]

Very well represented Mark. Some things should be mentioned. The captains SKILLS and payload weights also impact the overall speed performance. Also how long (time frame) the crew is capable of holding the vessel in peak conditions on the limits can be questionable. A weak crew or captain with not so much experience will run into the high risks, turtle the boat. Just saying. Many thanks 👍🙏 for sharing. Very interesting.

[@markpalmquist]

Thanks. I agree. That is what makes a trimaran easy for long races. Less running around and more stability in big waves. I ran out of time for including the trimaran. I could do a few different versions, low ama volume and high ama volume.

[@Richard-y2r]

this is pure gold! thanks for going thru these exercises. I'm coming from sailing hobie 16's and tigers, and currently designing a small trimaran. There are many similarities with your calculations on what I am up to. Thanks for sharing! I am just wondering about the hull shape on the wingmaran... I know you mentioned the version in this video is an old design, and don't know if this is viable, but have you thought of widening the hull, then extending the chamfers on the hull toward a subtle v to match the heel angle needed for optimal planing on the wing? Could that provide a better planing surface on the mail hull when heeled, potentially reducing drag? Im not sure if the v would produce too much friction at low speeds that building enough velocity to plane would only be possible with a dangerously overpowered rig or very high wind conditions. My design case has brought me to the same issue... in relation to the heel angle when an ama alters the righting moment, and whether a wider sublte v shaped hull when heeled would produce a better surface for planing, on less wetted area. I've been thinking a flat bow with a thin flat central section (just to make the centreboard build simpler), then wide chamfers for planing up to raked in hull walls. I think the main compromise would be requiring a wider hull and angling in the hull walls to get at least one vertical plane when heeled?

[@markpalmquist]

@@Richard-y2r the next wingmaran I make will have 15 degree chamfers on the bottom of the main hull to improve planing there.

[@Richard-y2r]

@@markpalmquist interesting! I am aiming for 15º as well. Will you chamfer to the center-line?

[@markpalmquist]

@@Richard-y2rno, only 1/3

[@Aheitchoo]

Love the comparison between the 16 and the 49er. As is common wisdom these days, the hobie nosedives if you go too fast. This isnt demonstrated be the cross sectional analysis you are doing here but it IS tied to displacement vs planing lift. The planing lift center of lift location is a function of speed, whereas the displacement lift center of lift position is static. The center of lift is just too far aft on the hobie, with insufficient reserve boyanct forward. The 49er has reserve planing lift forward to reaist more forward force on the sails and turn it into speed baby! This is also why Hobie 16's tend not to carry big downwind sails...

[@markpalmquist]

@@Aheitchoo that makes sense. Glad you like the video. I agree there is more to it than the 2D presentation and I agree the 49 has a downwind advantage. The wings extending slightly behind the transom also help.

[@Aheitchoo]

@@markpalmquist Maybe my Hobie needs forward planing lift generators...

[@markpalmquist]

@ I designed the skimming lift amas to be insertable into the hulls of a catamaran but I can’t recommend that until I try it first. You have to know where the waterline is, know the pitch angle, and mount them 5-6 degrees positive to that at about 30 degrees in front of the CE, which is about 1 foot behind the mast, going forward diagonally from there till it hits the hull. If you follow that procedure it would work.

[@Aheitchoo]

@@markpalmquist I am partially joking, though 'anti pitch pole' devices are sold for the hobi boats. That is helpful information. I do believe it would expand the performance envelope of the boat.

[@astrayalien]

Another thought, what if you made the wings neutral bouyancy. It would move the cm outwards and allow for righting if it goes over.

[@astrayalien]

I forgot about the wing on the other side, doh. The cm wouldn't change.

[@christophejournoud2773]

Hi, Very interesting. Perhaps you should take the sail area in square meters instead of square feet because of the righting moment using meters. It would change SA/RM in absolute

[@markpalmquist]

@@christophejournoud2773 yes that would have made more sense. I should convert SF to SM, agreed.

[@astrayalien]

Excellent. You've given me something to think about. Also, and it's a minor point, your maths for the wingmaran was wrong, 80 + 80 is 160.

[@markpalmquist]

@@astrayalien thanks and thanks for pointing that out, I will look into that. I made these pages a few years ago but did some editing yesterday. It lowers the sail size to around 120 SF, which means a Hobie 14 rig would be ideal.

[@ChristianNally]

Sounds like there’s a part 2 coming for the fancy proas? If so I’d love it if you add this kite boat, where the kite itself is mounted to an arm which swings. That induces a righting moment in the opposite direction to where the total righting moment necessary might go to zero! Also the kite will pull up a bit, which reduces required buoyancy and other lift required of the hull even more. (That’s been the driver for my R2AK thinking.) kzbin.info/www/bejne/jJKUdn2Kra-CidEsi=hpBp0PPMET8O_o3n

[@ChristianNally]

SP80 is doing the same thing

[@ChristianNally]

Oh… and the kiteboarder kite line goes to a harness and the attachment is near their body’s CoM, not their arms. If it were arms, they’d get way too tired. These diagrams are great BTW! Very instructional. I’d be interested to hear your comments on the kiteboat, where the need for a righting moment might go away almost entirely. Of course you still want one to keep from flipping, but it’s the waves and aerodynamics that would cause that, not propulsion!

[@markpalmquist]

@@ChristianNally yes, the SR2 has direct alignment between forces. I did not get into that but I will cover that in part 2.

[@markpalmquist]

@@ChristianNally yes, I agree. Placing the weight between the sail and angled anchor foil is the next logical evolution and it should break the record if they can reduce the drag on the kite and kite string.

[@TinyHouseHomestead]

Hey, start holding that pencil properly! 😱😁🤪😝🤣👍👍🇺🇸

[@markpalmquist]

I also don’t hold my fork and spoon properly 😀

[@TinyHouseHomestead]

​@@markpalmquist 🤪😝🤣👍👍🇺🇸

[@sebcam9498]

Who cares?

[@Aheitchoo]

I have a hard time believing the surfers can only go wind speed, though I dont have experience with them, cant they broad reach 2-3x windspeed?

[@markpalmquist]

@@Aheitchoo if you put a T foil on a windsurfer it improves your low end speed and your ability to point but not your top end speed. Without longer arms the amount of sail area you can carry is limited. So windsurfers have low weight, low drag but also low distance. If you improved the distance you could carry more sail and go faster than wind speed.

[@Aheitchoo]

@@markpalmquist Interesting point. I think my lack of understanding here is that there are many factors that limit top speed, Boat Speed as a function of wind speed is not just determined by the stability, but also my the effeciency of the sail, the for aft lift balance, the change in lift balance with speed, the hull drag charachteristics ... so my mind reaches. Still a great highlight of stability though.

[@Aheitchoo]

@@markpalmquist I love talking about this stuff though! So I think hull drag, sail efficiency and possibly lift balance as a function of speed warrant a breakdown as you have done here.

[@markpalmquist]

@ thanks! I agree you can go deeper. I know reducing drag is the key for high speeds and distance to weight ratio is just as important.

[@markpalmquist]

@@Aheitchoo I agree

[@RulgertGhostalker]

"center of buoyancy" would be the phrase you're looking for in some cases. of course at semi-displacement, and planning speeds, you adding some lift to that: but it generally doesn't change the position much at all.

[@RulgertGhostalker]

for the sake of getting the point across, 50%. but people have to remember to subtract the ballast displacement in water from the effective RM .... so there is a % you have to leave alone, but that goes down also with a smaller ballast.

[@NICOLAS25478]

Dear sir, you are telling a lot of stupid things in your videos. But now I had enough of it. Just a few examples i need to address here. You say your vessel can go faster than a 49er? You say your vessel can go over 25 knots? Realy?? Please watch the videos I send here below, then you will have a feel of what it takes to go that fast in real boats and then review your 'science'. If you vessel is so fast, maybe try to beat a Sunfish as a proof of concept to start with, which i strongly doubt because your planing surface will hold you back instead of helping you. The only way to go, is to have a real wide planing hull (to get your planing effect) or to put a fully submerged foils (Imoca style). Or you can put an extra hull to leward but then you have a Proa or a Trimaran, which is going back to the basics. kzbin.info/www/bejne/laLFl2irit-lpJY kzbin.info/www/bejne/fmqqoIqQidCLopI

[@markpalmquist]

@@NICOLAS25478 let’s look at the facts. My father took a G-cat catamaran, removed a hull and added a hydroplaning wing and improved its top speed from 19 knots to 21. I took a sunfish sail and put it on my prototype 1 wingmaran (same length as a sunfish) and reached a speed of 12 knots. A sunfish can only reach 10 knots. In both cases, the top speed was increased by 15-20%. I have raced a Hobie Holder 12 and smoked it. Those are the facts. My prototype can handle a much bigger sail so I am not even close to reaching max speed yet. And no, the planing surface(wing or skimmer) does not hold you back, it is more efficient than the main hull of a 49er but it is located in front of the CE. My next prototype, if I make it the same length as a 49er and put a 49er rig on it would attain speeds over 25 knots. And I have watched your videos and I have sailed with my father on a hobie 16 off the beach in Fort Lauderdale, Florida in 25 knots of wind and know what it’s like to go over 20 knots. I also have windsurfed about 25 knots. The wing of a Wingmaran is more efficient than a windsurfing board because of its orientation and position relative to the sail. You would love sailing one.