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foils_on_surfskis [2023/06/04 16:11] preavley |
foils_on_surfskis [2025/03/23 19:49] (current) |
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| ===== Foils on Surfskis? ===== | ===== Foils on Surfskis? ===== | ||
| - | (and flatwater boredom) | + | [[:surfski_foils|Main Surfski Foil Page]] |
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| + | (and flatwater boredom) [[https://www.facebook.com/groups/395803743862021/permalink/5961160853992921/|facebook link to this thread]] | ||
| **Mike Kane** \\ | **Mike Kane** \\ | ||
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| **Comments** | **Comments** | ||
| - | **Per Ason** \\ | + | * **Per Ason** Wouldn't it just seesaw the whole thing and dip the fore deeper? |
| - | Wouldn't it just seesaw the whole thing and dip the fore deeper? | + | * **Reply** |
| - | + | * **Shaun Hulley** Per Ason this is what I thought too… lift needs to be evenly distributed otherwise it will just upset things, and in this case lift too far rearward could cause the bow to be buried… now, if OP decided to put a foil below the cockpit, that could be interesting… | |
| - | * **Reply** | + | * **Gary Cziko** Per I don’t think so. A normal hull displaces a volume of water whose mass is equal to the mass of the boat plus paddler. But with part of the mass supported by the foil, there should be less water displaced and less wetted area, both of which will reduce drag. With your boat floating without you, lift the the stern. Does the bow sink farther into the water when you do? Makes no sense to me that it would, although of course the boat will be inclined more forward which in itself might be disruptive. But overall drag should be less. |
| - | * **Shaun Hulley** Per Ason this is what I thought too… lift needs to be evenly distributed otherwise it will just upset things, and in this case lift too far rearward could cause the bow to be buried… now, if OP decided to put a foil below the cockpit, that could be interesting… | + | * **Reply** * **Per Ason** Gary Cziko I understand your reasoning but intuitively, I'd say that my bow would sink farther into the water if I lift it at the stern. Of course, science doesn't care about what's intuitive to me, so I probably have to try it next time 😅 Imagine you are at the beach and floating in the water, flat on your back. If I would suddenly lift your feet, wouldn't your head dip down under the surface? |
| - | * **Gary Cziko** Per I don’t think so. A normal hull displaces a volume of water whose mass is equal to the mass of the boat plus paddler. But with part of the mass supported by the foil, there should be less water displaced and less wetted area, both of which will reduce drag. With your boat floating without you, lift the the stern. Does the bow sink farther into the water when you do? Makes no sense to me that it would, although of course the boat will be inclined more forward which in itself might be disruptive. But overall drag should be less. | + | * **Reply** |
| - | * **Reply** * **Per Ason** Gary Cziko I understand your reasoning but intuitively, I'd say that my bow would sink farther into the water if I lift it at the stern. Of course, science doesn't care about what's intuitive to me, so I probably have to try it next time 😅 Imagine you are at the beach and floating in the water, flat on your back. If I would suddenly lift your feet, wouldn't your head dip down under the surface? | + | * **Gary**** Cziko** Per Ason A floating human body is more complicated than a floating hull as the legs are typically more dense than water (they tend to sink) and the upper body (with inflated lungs) is less dense than water (it tends to float). So let’s stick with the boat hull that is buoyant from stern to bow. If you lift the stern of your surfski just out of the water while it is floating in the water, I doubt very much that you will see the bow sinking further into the water. I am travelling now in Spain so I can’t try it myself. But anyone else could and let us know what they find. |
| - | * **Reply** | + | * **Reply ** |
| - | * **Gary**** Cziko** Per Ason A floating human body is more complicated than a floating hull as the legs are typically more dense than water (they tend to sink) and the upper body (with inflated lungs) is less dense than water (it tends to float). So let’s stick with the boat hull that is buoyant from stern to bow. If you lift the stern of your surfski just out of the water while it is floating in the water, I doubt very much that you will see the bow sinking further into the water. I am travelling now in Spain so I can’t try it myself. But anyone else could and let us know what they find. | + | * **Per Ason** Gary Cziko I would say that that argument works against you. I agree that the upper body is more buoyant, and I am convinced that it would dip down anyway. Doesn't a surfski typically have more volume and therefore buoyancy at the bow? I see a similarity to a human body there… What would happen if you'd over exaggerate and lift the stern like 30 degrees, would the bow still not dip? Or does some other factors come into play then? For the record, I'm not saying you are wrong, I'm just discussing. |
| - | * **Reply ** | + | |
| - | * **Per Ason** Gary Cziko I would say that that argument works against you. I agree that the upper body is more buoyant, and I am convinced that it would dip down anyway. Doesn't a surfski typically have more volume and therefore buoyancy at the bow? I see a similarity to a human body there… What would happen if you'd over exaggerate and lift the stern like 30 degrees, would the bow still not dip? Or does some other factors come into play then? For the record, I'm not saying you are wrong, I'm just discussing. | + | |
| * **Reply** | * **Reply** | ||
| * **Keith Wieland** I like the way this guy thinks. Lateral stability would be challenging for foils with surf skis. | * **Keith Wieland** I like the way this guy thinks. Lateral stability would be challenging for foils with surf skis. | ||
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| * **Reply** | * **Reply** | ||
| * **Michael Jose **Hydrofoil Kayak (Foilkayak) | * **Michael Jose **Hydrofoil Kayak (Foilkayak) | ||
| - | * ... | + | * … |
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| * **Reply** | * **Reply** | ||
| * **Paraka Mitchell **Been around for ages😎 \\ K1 vs. K4 flyak- kajak 27km/h HQ | * **Paraka Mitchell **Been around for ages😎 \\ K1 vs. K4 flyak- kajak 27km/h HQ | ||
| - | * **...** | + | * … |
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| - | * ... | + | * … |
| * **Reply** | * **Reply** | ||
| - | * **Tony Brown** Paraka Mitchell I wonder if it'll take off? | + | * **Tony Brown** Paraka Mitchell I wonder if it'll take off? |
| * **Reply** | * **Reply** | ||
| - | * **Paraka Mitchell** Tony Brown ahh no. Paddle length is longer due to elevation of boat and cadence is a lot higher to keep it up on the foils | + | * **Paraka Mitchell** Tony Brown ahh no. Paddle length is longer due to elevation of boat and cadence is a lot higher to keep it up on the foils |
| * **Reply** | * **Reply** | ||
| - | * **Oliver Barnicoat** It’s been done | + | * **Oliver Barnicoat** It’s been done |
| - | * ... | + | * … |
| ---- | ---- | ||
| - | **Flyak hydrofoil kayak “he’s flying!”** {{ youtube>hHVKJzWXS1I }} | + | **Flyak hydrofoil kayak “he’s flying!”** |
| + | |||
| + | {{ youtube>hHVKJzWXS1I }} | ||
| ---- | ---- | ||
| * **Reply** | * **Reply** | ||
| - | * **Shawn Burke** Reducing the wetted area reduces friction drag. But drag comprises three components, and at all but the lowest speed is dominated by wave-making drag and form drag. You'll still have those no matter what – see my article at the link – it's like death and taxes. Since you only want _some_ lift, and not a hydrofoil that lifts the entire hull out of the water (as other commenters have noted and linked), the supporting supporting strut / rudder will add a lot of drag itself. Monohull America's Cup sailboats did some nifty things with winged keels back in the 80s but I think the hydrodynamics are different than for us (running under sail, running heeled, very different Reynolds Number). [[https://thescienceofpaddling.net/part-36-total-drag|https://thescienceofpaddling.net/part-36-total-drag]] Part 36: Total Drag THESCIENCEOFPADDLING.NET | + | * **Shawn Burke** Reducing the wetted area reduces friction drag. But drag comprises three components, and at all but the lowest speed is dominated by wave-making drag and form drag. You'll still have those no matter what – see my article at the link – it's like death and taxes. Since you only want _some_ lift, and not a hydrofoil that lifts the entire hull out of the water (as other commenters have noted and linked), the supporting supporting strut / rudder will add a lot of drag itself. Monohull America's Cup sailboats did some nifty things with winged keels back in the 80s but I think the hydrodynamics are different than for us (running under sail, running heeled, very different Reynolds Number). [[https://thescienceofpaddling.net/part-36-total-drag|https://thescienceofpaddling.net/part-36-total-drag]] Part 36: Total Drag THESCIENCEOFPADDLING.NET |
| * **Reply** | * **Reply** | ||
| - | * **William Glamore** Shawn Burke this is very impressive. I’m a hydraulics professor and love this explanation. Thanks. | + | * **William Glamore** Shawn Burke this is very impressive. I’m a hydraulics professor and love this explanation. Thanks. |
| * **Reply** | * **Reply** | ||
| - | * **Shawn Burke** Thanks, William, that article was fun to write! (If you enjoyed that my book, The Science of Paddling, went on sale today. 😉 ) | + | * **Shawn Burke** Thanks, William, that article was fun to write! (If you enjoyed that my book, The Science of Paddling, went on sale today. 😉 ) |
| * **Reply** | * **Reply** | ||
| - | * **Russel Breyer** But what point? | + | * **Russel Breyer** But what point? |
| - | * **Dave Faulkner** Hmm, interesting? | + | * **Dave Faulkner** Hmm, interesting? |
| - | * **Rick Giannini** I was told there would be no math | + | * **Rick Giannini** I was told there would be no math |
| - | * **Mike Kane** Author Think trim tabs | + | * **Mike Kane** Author Think trim tabs |
| + | * … | ||
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| * **Reply** | * **Reply** | ||
| - | * **Mike Kane** Author, Here’s the experiment: enter a flat, slow, moving river that has a surface flow rate at 7 mph. Tie the nose of the surfski to a force gauge that measures drag on the boat. sit in the boat in the paddling position. compare the force gauge value for different weight paddlers, boat length as well as the benefit or lack of benefit of a lifting foil attached to the rudder location. | + | * **Mike Kane** Author, Here’s the experiment: enter a flat, slow, moving river that has a surface flow rate at 7 mph. Tie the nose of the surfski to a force gauge that measures drag on the boat. sit in the boat in the paddling position. compare the force gauge value for different weight paddlers, boat length as well as the benefit or lack of benefit of a lifting foil attached to the rudder location. |
| - | * **Mark Sundin** Easy fix mate, get out on the ocean and you'll stop thinking about things like this…!🤣 | + | * **Mark Sundin** Easy fix mate, get out on the ocean and you'll stop thinking about things like this…!🤣 |
| * **Reply** | * **Reply** | ||
| - | * **Mike Kane** Author, Mark Sundin Sadly, I’m landlocked. 😩 | + | * **Mike Kane** Author, Mark Sundin Sadly, I’m landlocked. 😩 |
| * **Reply** | * **Reply** | ||
| - | * **Adam KingtonClay** Lift at the rear would mean nose diving, greater surface area at the bow isn’t ideal, nor is an increased chance of pearling | + | * **Adam KingtonClay** Lift at the rear would mean nose diving, greater surface area at the bow isn’t ideal, nor is an increased chance of pearling |
| * **Kristin Kronsnoble** i listen to music | * **Kristin Kronsnoble** i listen to music | ||
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