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Author Topic:   Lifting Foils

jimh posted 09-28-2013 10:54 AM ET (US)
Please take a look at this image:
http:/ / proxy. storytellerhq. com/ cache/ 37/ 9d6b5e53bc79d6dccd5de8094 7243b7498cce8ec?url=http%3A%2F%2Fwww. oracleteamusamedia. com%2Fdata_fol io%2Fapi_img%2F791%2FGG13-SFOMAY-00097%2A%2AzYUMpfnW6ylg1367868607. jpg
You will see a very large, 15,000-lbs boat being raised out of the water by the lift created from an underwater foil. The general size and shape of the foil can be seen by comparing it with the one on the raised port hull. The foil is generating what seems to be incredible lift.
The development of these foils suggests to me that perhaps outboard engines could benefit from having a foil appendage below the propeller, that is, attached to the bottom of the skeg. A small foil appendage there might be able to generate significant lifting force, which could help lift the hull of the boat out of the water, reducing wetted surface, and reducing drag.
After seeing how a foil can lift a giant boat like an AC 72, one would think a smaller version might help lift a classic Boston Whaler 22-footer.
frontier posted 09-28-2013 03:53 PM ET (US)
Curses, foiled again.
Jerry Townsend posted 09-28-2013 04:33 PM ET (US)
JimH - a foil below the skeg would provide some stern lift - but the foil on the Oracle boat has to be fairly large, somewhat centered under the hull and the surface attitude cannot be contolled.
Money is of no concern regarding the Oracle boat. And, a lot has been spent in the design, performance, testing, et al. of the Oracle boat - and other similar boats.
Years ago, Boeing, with perhaps others, built one or two boats using foils conducted tests on Puget Sound. They were powered, as I recall, by gas turbines. Fairly large - 30 - 40 feet. They were fast and the hull was raised clear of the water surface as I recall. I don't recall seeing any information for a long,long time. Tom will certainly have more recollection. --- Jerry/Idaho
frontier posted 09-28-2013 04:59 PM ET (US)
The Boeing hydrofoil Jerry is talking about, I think, is the "Plainview".
It somehow ended up beached years ago on the banks of the Columbia River, between Longview and Ilwaco, Washington.
It was still there as of a few years ago when I drove by, on the Washington side of the Columbia, near the Astoria Interstate Bridge.
Quite a sight.
jharrell posted 09-28-2013 05:33 PM ET (US)
I always preferred the hydrofoil supported catamaran designs or "Hysucat" to gets the benefits of a hydro foil avoiding protrusions from the hull: http://fastcc.hysucraft.com/Default.asp?Page=Principles
For a hydrofoil to work properly and not cause the boat to become unstable it must be properly balanced at the center of gravity.
I know my friend had a foil appended attached to his stern drive cruiser a while back. Since with a stern drive the A/V plate was submerged even at planing speed the foil cause it to become unstable because it generated so much stern lift. The rear end wanted to break lose at any provocation while the bow was firmly planted.
Then of course there is always the Navy: http://en.wikipedia.org/wiki/File:PHM-4.jpg
jimh posted 09-29-2013 12:33 AM ET (US)
A monohull with lifting foils on the hull does not look like a boat that can be trailered--well, at least trailered and launched off the trailer on a ramp. That is a significant drawback.
I was thinking of a small foil on the bottom of a skeg as a way to generate what we would otherwise call stern lift.
frontier posted 09-29-2013 01:10 AM ET (US)
Remember the "Air Chair" and "Sky Ski" hydrofoil water ski's?
Still sold and used.
They do look like fun.
Tom W Clark posted 09-29-2013 11:47 AM ET (US)
Years ago I used to see a trailered hydrofoil runabout in Seattle quite a bit. It was a Russian built VOLGA from the 1960s or 1970s. It was usually parked on the street over in Wallingford near the launch ramp there. I saw it running in Puget Sound off of Shilshole once. It definitely got your attention. That may have been its greatest asset.
The VOLGA has its own discussion forum:
http://www.volga-hydrofoil.net/phpBB3/index.php
Boeing has built many hydrofoils over the years, most for the military. The 90' LOA Boeing 929 Jetfoil was the only passenger hydrofoil they built but dozens were made and most are still in service today.
I rode a Boeing Jetfoil from Maui to Oahu in 1976. It was a very smooth and comfortable ride.
http://www.boeing.com/boeing/history/boeing/hydro.page
dfmcintyre posted 09-29-2013 01:57 PM ET (US)
It's all about the balance and trim.
Second view of your noted image shows how the daggerboard (I think that's what we called them in racing 18 Hobies....) is retracted up tight to the upwind hull. She's actually running on the downwind 'board and the two rudders, each having a foil.
It does not look like the board has the ability to pivot, though the rudder might.
Interesting.
Don
jimh posted 09-29-2013 02:25 PM ET (US)
The AC 72 boats' rudders may have small end plate foils. The windward rudder is often clear of the water when the AC 72 is really going. Yes, there must be some marvelous method of maintaining balance when the whole boat is ridding mainly on the leeward hull's foil. I think that is part of the secret stuff each team developed. And, yes, the windward hull foil was typically immediately retracted as soon as the boat speed increased and the catamaran began to naturally lift the windward hull. But I am not so much interested in the AC 72 sailing techniques as I am in application of lifting foils to outboard boats.
It seems that foils are quite adaptable to twin-hull boats. This is quite appropriate for the Boston Whaler boat, which, if you recall, began as a variation of the Hickman Sea Sled, a boat with a hull form of two V-hulls. A Hickman Sea Sled with a lifting foil would be an interesting hull form.
jimh posted 09-30-2013 12:27 PM ET (US)
The animation shown in
http://www.youtube.com/watch?v=8bweBQHF3UY
appears to demonstrate a concept for a lifting foil for an outboard-powered mono-hull boat.
The recording seen in
http://www.youtube.com/watch?v=w54-OEWulDE&feature=youtube_gdata_player
shows a lifting foil applied to a 24-foot cabin cruiser, apparently with some success.
In occurs to me that any sort of lifting foil attachment to a hull will require a very strong and reinforced point of attachment. In conventional hull construction it might be possible to retro-fit a foil to an existing hull (like we see in the recording above) by through-bolting and reinforcement with backing plates. I think it would be very difficult to adapt a Boston Whaler Unibond hull to attachment of a foil, as it would be difficult to spread the loading forces to the hull unless the hull already was constructed with suitable reinforcement at that point and sufficient strength to bear the high load of forces that would result.
jimh posted 09-30-2013 12:29 PM ET (US)
The linked recording (above) of the cabin cruiser also seems to demonstrate an electronic control system for the foils. The notion that the foils are able to be steered or rotated or controlled in some way is quite interesting. The result is an active system for stabilization.
dfmcintyre posted 09-30-2013 02:56 PM ET (US)
The "surface follower" device reminded me of the same type of device used by some custom sailing catamaran rigs designed for the speed record.
Don
kwik_wurk posted 09-30-2013 07:22 PM ET (US)
I don't think objects that add draft to a vessel will help much as far as mass adoption, especially if a propeller has to stay in the water. I could see modified trim tabs that are more like hollow squares, providing lift or keeping the vessel up and out of the waves.
And foils can have a static shape such that attitude, lift, etc can be compensated to keep the vessel foiling while undergoing these mentioned motions. For example, when the foil lifts the vessel to much, parts of the foil are exposed and the foils loose some lift (not very special), same happens with heal, or pitching.
The requirement for two foils will always exist (fore and aft or mid and aft as typically seen). There are very few airplanes without two foils for example.
With Moth class sailboats, the lowest and smallest end of foiling sailboats, there is a wand that drags the water to compensate for height. Mainly because this is cost effective, when compared to a customized foil. However the nice boats have nicer foils and control lines, which makes things generally easier to control. These things are a blast but wipe outs are equally precarious.
Jerry Townsend posted 09-30-2013 09:55 PM ET (US)
The first link of JimH's is purely someone's figment of imagination.
The second link of the Bayliner cabin cruiser is interesting. It looks to be supported at just three points - the bow and at each aft corner. But, the Bayliner is relatively heavy, so the foil surface area at those three points has to be fairly large.
And as Jim mentions, the attachment to the hull requires addressing those high loads
The "surface follower" on the bow seems to be flexing/moving - but I did not have the impression that it was following the water surface. Further, to move that fast and with the forces required on the bow foil, that control motor would have to really put out some power. So, is the device controlled, or flexing, for example, via some relatively heavy spring?
But, the video is interesting - and the fellow who designed it and put it together, knew what he was doing.
Tom's insight and hopefully some direct knowledge of the boat would be interesting. ---- Jerry/Idaho
kwik_wurk posted 10-01-2013 05:34 PM ET (US)
The surface follower simply trims the the lead foil for more bow up, bow down lift. They do no need to be very robust, as trimming the foil as very incremental, and not loaded. I looking at the design on the bayliner, it is a little robust and seems to be designed with response to wind waves versus overall vertical clearance.
You can see here on moth boats, the follow is nothing more than a stick that uses the friction of the water to trim the foil. (There is also a trim adjustment on the tiller handle (you twist the tiller), for the rudder foil.)
https://www.google.com/search?q=moth+sailboat&client=firefox-a&hs=rz8& rls=org.mozilla:en-US:official&tbm=isch&tbo=u&source=univ&sa=X& ei=wj1LUvu0DoebygGt5oDoAQ&ved=0CDEQsAQ&biw=1169&bih=618&dpr=1
Binkster posted 10-01-2013 07:14 PM ET (US)
Hydrofoils are nothing new. They were a big novelty in the early mid '50's. I remember seeing one running around in the bay when I was about 14. No one thought anything about it becuase the boating industry was coming out with new oddball stuff all the time. They were usually mounted on 14-16 foot trailerable runabouts. They folded up for trailering. I sure would like to find one. I could mount it on my 14 ft. Sea Fury with its 75 Evinrude and maybe reach 55 mph. It would be a hit at the AOMCI meets. Here's a link to the hydrofoils I remember.
http://www.foils.org/upright.htm
rich
Jerry Townsend posted 10-01-2013 10:01 PM ET (US)
Just one more comment/question - The purpose of a "surface follower" seems to be neglible - as the foils are below the surface - and the performance of the foils couldn't care less about the surface conditions. --- Jerry/Idaho
Tom W Clark posted 10-01-2013 10:05 PM ET (US)

quote:
...the performance of the foils couldn't care less about the surface conditions.
Audit Oceanography 101 at your local community college. You will learn how wrong that statement is.
Jerry Townsend posted 10-02-2013 12:37 PM ET (US)
Gee Tom, I, and others were discussing the lifting foils whereas your suggestion regarding Oceanography 101 as:
"Course Description
This course will introduce you to the fundamental principles of oceanography by focusing on the waters that surround us – the Washington coast and Puget Sound. Topics including the geologic history of the Pacific Northwest, the physics and chemistry of coastal waters, marine foodwebs and ecology, and environmental concerns will be introduced using relevant and timely case studies. ...."
addresses basic oceanography.
Now, to be clear - any control of a foil has to be based on speed - which will be indicated/measured via pressure (which varies as the velocity squared). This pressure measurement would be made underwater near the foil. As such, the depth and surface conditions will have an effect, albeit neglible, on that pressure relative to the speed. ---- Jerry/Idaho
Binkster posted 10-02-2013 12:41 PM ET (US)

...the performance of the foils couldn't care less about the surface conditions.
Probably has something to do with the size of the boat. If you read the entire link on my post you will find that rough water brings on many problems, as do hitting a floating beer can or a plastic bag.
rich
Tom W Clark posted 10-02-2013 12:47 PM ET (US)
Also taught in Oceanography 101 is how waves move.
Waves do not merely affect the surface of the water, they also move the column of water underneath it as well. This will have a very great effect on foils traveling through them just as the animation illustrates.
Tom W Clark posted 10-02-2013 01:01 PM ET (US)

quote:
The first link of JimH's is purely someone's figment of imagination.
No, here it is:
http://www.youtube.com/watch?v=x8H0h0j9PNs
cooper1958nc posted 10-05-2013 01:49 PM ET (US)
No, waves do not affect the way a foil interacts with the "water column" under the wave. The pressure shows local increases, but density does not vary with pressure.
Foils reduce drag compared to most planing hulls. Here are some back of the envelope calculations.
1. Drag force on a typical hull.
To make the math easy, lets assume we are going 37 mph (55 fps) and using 12 gph. That is a pretty low fuel flow even for a small (18-20) foot boat that weighs in the 3500 pound range. Specific fuel consumption at cruise is usually around 1 gph/hp, so we are developing 120 hp. Efficiency at the prop is typically 80%, so we have 100 hp thrust horsepower. One hp is 550 ft-lb/sec, so our thrust and our drag is 1000 pounds. (100*550)/55 (ft-lb/sec) / (ft/sec). The lift to drag ratio (overall) is 3.6 to 1 (3600 pounds of lift, 1000 pounds of drag). Not very impressive.
2. Now lets look at a hydrofoil. Hydrofoils have a big advantage in that the hull itself does not contribute to hydro drag (only aero drag, which we are ignoring for good reason). Decent airfoils have lift to drag ratios of 7 or 8 to one, which would mean the foil or foils could support 3600 pounds with maybe 400 pounds of drag. Add some strut drag, but still, its way under the hull drag above.

To see how big the foil has to be, we know a light aircraft in the 3600 lb range typically have wing areas of 180 or so square feet, yielding wing loadings of about 20 lbs per square feet. These wings will support the 3600 pound airplane at about 60 mph. Lift is proportional to density and to speed squared. The density of water is about 700 times the density of sea level air. So to see a foil operating at 20 mph in water, to support a 3600 pound boat, you need 180 * (60/20)^2 * (1/700) = 2.3 square feet. That's all it takes.
There are big problems with maintaining proper angle of attack with foils. When the boat hits a wave, the angle of attack tends to increase, causing further pitch up. This instability must be controlled with mechanical or electric control of angle of attack. Perhaps this is what the author above was seeing when he made his remark about the "water column."
jimh posted 10-05-2013 06:00 PM ET (US)
'coop: thanks for the math to go with the foils. It is very interesting stuff. I like mathematical expressions of relationships.
Jamesgt727 posted 10-11-2013 06:57 PM ET (US)
In 1997 i rode on this actual boat from Sorrento, Italy to the Isle of Capri:
http://youtu.be/4yn6J8zMQzo
The only comment that I can make is that if the columns of water you mention are not felt, we were in 2 meter seas, running 35-45 knots?, and it felt like glass. On the way back we were on a conventional hulled "fast ferry" at half the speed and we couldn't wait to get off of it it was so rough.
GSH posted 10-18-2013 08:12 AM ET (US)
[Not sure why, but the author addressed this comment only to me, but it seems like a comment of general interest to readers of this thread--jimh] Take at look at Swedish "Foiltwister"; please head over to www.foiltwister.se for more information (also in English).
jimh posted 10-18-2013 10:31 AM ET (US)
I have already visited that website, but thanks for posting. (It was mentioned in the animation video I linked to above.)
jimh posted 10-18-2013 11:08 PM ET (US)
It seems like foils are often used in applications like ferry boats. I was just watching an older movie, RUSSIA HOUSE, and in several of the scenes in Russia there is a large hydrofoil ferry boat seen in the background.
In my initial article where I proposed application of a lifting foil to a boat like a classic Boston Whaler 22-footer, I was not thinking of a foil that would be large enough to lift the entire hull out of the water, but rather of a smaller lifting foil that might raise the hull a bit more. This would reduce the running surface on plane, and improved the performance.
The general basis for success for a foil is that is has to create enough lift to reduce drag by getting the hull out of the water. The foil also creates its own drag. To be effective the added drag of the foil has to be much less than the amount of drag reduction gained by the lift.

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Author	Topic: Lifting Foils
jimh	posted 09-28-2013 10:54 AM ET (US) Please take a look at this image: http:/ / proxy. storytellerhq. com/ cache/ 37/ 9d6b5e53bc79d6dccd5de8094 7243b7498cce8ec?url=http%3A%2F%2Fwww. oracleteamusamedia. com%2Fdata_fol io%2Fapi_img%2F791%2FGG13-SFOMAY-00097%2A%2AzYUMpfnW6ylg1367868607. jpg You will see a very large, 15,000-lbs boat being raised out of the water by the lift created from an underwater foil. The general size and shape of the foil can be seen by comparing it with the one on the raised port hull. The foil is generating what seems to be incredible lift. The development of these foils suggests to me that perhaps outboard engines could benefit from having a foil appendage below the propeller, that is, attached to the bottom of the skeg. A small foil appendage there might be able to generate significant lifting force, which could help lift the hull of the boat out of the water, reducing wetted surface, and reducing drag. After seeing how a foil can lift a giant boat like an AC 72, one would think a smaller version might help lift a classic Boston Whaler 22-footer.
frontier	posted 09-28-2013 03:53 PM ET (US) Curses, foiled again.
Jerry Townsend	posted 09-28-2013 04:33 PM ET (US) JimH - a foil below the skeg would provide some stern lift - but the foil on the Oracle boat has to be fairly large, somewhat centered under the hull and the surface attitude cannot be contolled. Money is of no concern regarding the Oracle boat. And, a lot has been spent in the design, performance, testing, et al. of the Oracle boat - and other similar boats. Years ago, Boeing, with perhaps others, built one or two boats using foils conducted tests on Puget Sound. They were powered, as I recall, by gas turbines. Fairly large - 30 - 40 feet. They were fast and the hull was raised clear of the water surface as I recall. I don't recall seeing any information for a long,long time. Tom will certainly have more recollection. --- Jerry/Idaho
frontier	posted 09-28-2013 04:59 PM ET (US) The Boeing hydrofoil Jerry is talking about, I think, is the "Plainview". It somehow ended up beached years ago on the banks of the Columbia River, between Longview and Ilwaco, Washington. It was still there as of a few years ago when I drove by, on the Washington side of the Columbia, near the Astoria Interstate Bridge. Quite a sight.
jharrell	posted 09-28-2013 05:33 PM ET (US) I always preferred the hydrofoil supported catamaran designs or "Hysucat" to gets the benefits of a hydro foil avoiding protrusions from the hull: http://fastcc.hysucraft.com/Default.asp?Page=Principles For a hydrofoil to work properly and not cause the boat to become unstable it must be properly balanced at the center of gravity. I know my friend had a foil appended attached to his stern drive cruiser a while back. Since with a stern drive the A/V plate was submerged even at planing speed the foil cause it to become unstable because it generated so much stern lift. The rear end wanted to break lose at any provocation while the bow was firmly planted. Then of course there is always the Navy: http://en.wikipedia.org/wiki/File:PHM-4.jpg
jimh	posted 09-29-2013 12:33 AM ET (US) A monohull with lifting foils on the hull does not look like a boat that can be trailered--well, at least trailered and launched off the trailer on a ramp. That is a significant drawback. I was thinking of a small foil on the bottom of a skeg as a way to generate what we would otherwise call stern lift.
frontier	posted 09-29-2013 01:10 AM ET (US) Remember the "Air Chair" and "Sky Ski" hydrofoil water ski's? Still sold and used. They do look like fun.
Tom W Clark	posted 09-29-2013 11:47 AM ET (US) Years ago I used to see a trailered hydrofoil runabout in Seattle quite a bit. It was a Russian built VOLGA from the 1960s or 1970s. It was usually parked on the street over in Wallingford near the launch ramp there. I saw it running in Puget Sound off of Shilshole once. It definitely got your attention. That may have been its greatest asset. The VOLGA has its own discussion forum: http://www.volga-hydrofoil.net/phpBB3/index.php Boeing has built many hydrofoils over the years, most for the military. The 90' LOA Boeing 929 Jetfoil was the only passenger hydrofoil they built but dozens were made and most are still in service today. I rode a Boeing Jetfoil from Maui to Oahu in 1976. It was a very smooth and comfortable ride. http://www.boeing.com/boeing/history/boeing/hydro.page
dfmcintyre	posted 09-29-2013 01:57 PM ET (US) It's all about the balance and trim. Second view of your noted image shows how the daggerboard (I think that's what we called them in racing 18 Hobies....) is retracted up tight to the upwind hull. She's actually running on the downwind 'board and the two rudders, each having a foil. It does not look like the board has the ability to pivot, though the rudder might. Interesting. Don
jimh	posted 09-29-2013 02:25 PM ET (US) The AC 72 boats' rudders may have small end plate foils. The windward rudder is often clear of the water when the AC 72 is really going. Yes, there must be some marvelous method of maintaining balance when the whole boat is ridding mainly on the leeward hull's foil. I think that is part of the secret stuff each team developed. And, yes, the windward hull foil was typically immediately retracted as soon as the boat speed increased and the catamaran began to naturally lift the windward hull. But I am not so much interested in the AC 72 sailing techniques as I am in application of lifting foils to outboard boats. It seems that foils are quite adaptable to twin-hull boats. This is quite appropriate for the Boston Whaler boat, which, if you recall, began as a variation of the Hickman Sea Sled, a boat with a hull form of two V-hulls. A Hickman Sea Sled with a lifting foil would be an interesting hull form.
jimh	posted 09-30-2013 12:27 PM ET (US) The animation shown in http://www.youtube.com/watch?v=8bweBQHF3UY appears to demonstrate a concept for a lifting foil for an outboard-powered mono-hull boat. The recording seen in http://www.youtube.com/watch?v=w54-OEWulDE&feature=youtube_gdata_player shows a lifting foil applied to a 24-foot cabin cruiser, apparently with some success. In occurs to me that any sort of lifting foil attachment to a hull will require a very strong and reinforced point of attachment. In conventional hull construction it might be possible to retro-fit a foil to an existing hull (like we see in the recording above) by through-bolting and reinforcement with backing plates. I think it would be very difficult to adapt a Boston Whaler Unibond hull to attachment of a foil, as it would be difficult to spread the loading forces to the hull unless the hull already was constructed with suitable reinforcement at that point and sufficient strength to bear the high load of forces that would result.
jimh	posted 09-30-2013 12:29 PM ET (US) The linked recording (above) of the cabin cruiser also seems to demonstrate an electronic control system for the foils. The notion that the foils are able to be steered or rotated or controlled in some way is quite interesting. The result is an active system for stabilization.
dfmcintyre	posted 09-30-2013 02:56 PM ET (US) The "surface follower" device reminded me of the same type of device used by some custom sailing catamaran rigs designed for the speed record. Don
kwik_wurk	posted 09-30-2013 07:22 PM ET (US) I don't think objects that add draft to a vessel will help much as far as mass adoption, especially if a propeller has to stay in the water. I could see modified trim tabs that are more like hollow squares, providing lift or keeping the vessel up and out of the waves. And foils can have a static shape such that attitude, lift, etc can be compensated to keep the vessel foiling while undergoing these mentioned motions. For example, when the foil lifts the vessel to much, parts of the foil are exposed and the foils loose some lift (not very special), same happens with heal, or pitching. The requirement for two foils will always exist (fore and aft or mid and aft as typically seen). There are very few airplanes without two foils for example. With Moth class sailboats, the lowest and smallest end of foiling sailboats, there is a wand that drags the water to compensate for height. Mainly because this is cost effective, when compared to a customized foil. However the nice boats have nicer foils and control lines, which makes things generally easier to control. These things are a blast but wipe outs are equally precarious.
Jerry Townsend	posted 09-30-2013 09:55 PM ET (US) The first link of JimH's is purely someone's figment of imagination. The second link of the Bayliner cabin cruiser is interesting. It looks to be supported at just three points - the bow and at each aft corner. But, the Bayliner is relatively heavy, so the foil surface area at those three points has to be fairly large. And as Jim mentions, the attachment to the hull requires addressing those high loads The "surface follower" on the bow seems to be flexing/moving - but I did not have the impression that it was following the water surface. Further, to move that fast and with the forces required on the bow foil, that control motor would have to really put out some power. So, is the device controlled, or flexing, for example, via some relatively heavy spring? But, the video is interesting - and the fellow who designed it and put it together, knew what he was doing. Tom's insight and hopefully some direct knowledge of the boat would be interesting. ---- Jerry/Idaho
kwik_wurk	posted 10-01-2013 05:34 PM ET (US) The surface follower simply trims the the lead foil for more bow up, bow down lift. They do no need to be very robust, as trimming the foil as very incremental, and not loaded. I looking at the design on the bayliner, it is a little robust and seems to be designed with response to wind waves versus overall vertical clearance. You can see here on moth boats, the follow is nothing more than a stick that uses the friction of the water to trim the foil. (There is also a trim adjustment on the tiller handle (you twist the tiller), for the rudder foil.) https://www.google.com/search?q=moth+sailboat&client=firefox-a&hs=rz8& rls=org.mozilla:en-US:official&tbm=isch&tbo=u&source=univ&sa=X& ei=wj1LUvu0DoebygGt5oDoAQ&ved=0CDEQsAQ&biw=1169&bih=618&dpr=1
Binkster	posted 10-01-2013 07:14 PM ET (US) Hydrofoils are nothing new. They were a big novelty in the early mid '50's. I remember seeing one running around in the bay when I was about 14. No one thought anything about it becuase the boating industry was coming out with new oddball stuff all the time. They were usually mounted on 14-16 foot trailerable runabouts. They folded up for trailering. I sure would like to find one. I could mount it on my 14 ft. Sea Fury with its 75 Evinrude and maybe reach 55 mph. It would be a hit at the AOMCI meets. Here's a link to the hydrofoils I remember. http://www.foils.org/upright.htm rich
Jerry Townsend	posted 10-01-2013 10:01 PM ET (US) Just one more comment/question - The purpose of a "surface follower" seems to be neglible - as the foils are below the surface - and the performance of the foils couldn't care less about the surface conditions. --- Jerry/Idaho
Tom W Clark	posted 10-01-2013 10:05 PM ET (US) quote: ...the performance of the foils couldn't care less about the surface conditions. Audit Oceanography 101 at your local community college. You will learn how wrong that statement is.
Jerry Townsend	posted 10-02-2013 12:37 PM ET (US) Gee Tom, I, and others were discussing the lifting foils whereas your suggestion regarding Oceanography 101 as: "Course Description This course will introduce you to the fundamental principles of oceanography by focusing on the waters that surround us – the Washington coast and Puget Sound. Topics including the geologic history of the Pacific Northwest, the physics and chemistry of coastal waters, marine foodwebs and ecology, and environmental concerns will be introduced using relevant and timely case studies. ...." addresses basic oceanography. Now, to be clear - any control of a foil has to be based on speed - which will be indicated/measured via pressure (which varies as the velocity squared). This pressure measurement would be made underwater near the foil. As such, the depth and surface conditions will have an effect, albeit neglible, on that pressure relative to the speed. ---- Jerry/Idaho
Binkster	posted 10-02-2013 12:41 PM ET (US) ...the performance of the foils couldn't care less about the surface conditions. Probably has something to do with the size of the boat. If you read the entire link on my post you will find that rough water brings on many problems, as do hitting a floating beer can or a plastic bag. rich
Tom W Clark	posted 10-02-2013 12:47 PM ET (US) Also taught in Oceanography 101 is how waves move. Waves do not merely affect the surface of the water, they also move the column of water underneath it as well. This will have a very great effect on foils traveling through them just as the animation illustrates.
Tom W Clark	posted 10-02-2013 01:01 PM ET (US) quote: The first link of JimH's is purely someone's figment of imagination. No, here it is: http://www.youtube.com/watch?v=x8H0h0j9PNs
cooper1958nc	posted 10-05-2013 01:49 PM ET (US) No, waves do not affect the way a foil interacts with the "water column" under the wave. The pressure shows local increases, but density does not vary with pressure. Foils reduce drag compared to most planing hulls. Here are some back of the envelope calculations. 1. Drag force on a typical hull. To make the math easy, lets assume we are going 37 mph (55 fps) and using 12 gph. That is a pretty low fuel flow even for a small (18-20) foot boat that weighs in the 3500 pound range. Specific fuel consumption at cruise is usually around 1 gph/hp, so we are developing 120 hp. Efficiency at the prop is typically 80%, so we have 100 hp thrust horsepower. One hp is 550 ft-lb/sec, so our thrust and our drag is 1000 pounds. (100550)/55 (ft-lb/sec) / (ft/sec). The lift to drag ratio (overall) is 3.6 to 1 (3600 pounds of lift, 1000 pounds of drag). Not very impressive. 2. Now lets look at a hydrofoil. Hydrofoils have a big advantage in that the hull itself does not contribute to hydro drag (only aero drag, which we are ignoring for good reason). Decent airfoils have lift to drag ratios of 7 or 8 to one, which would mean the foil or foils could support 3600 pounds with maybe 400 pounds of drag. Add some strut drag, but still, its way under the hull drag above. To see how big the foil has to be, we know a light aircraft in the 3600 lb range typically have wing areas of 180 or so square feet, yielding wing loadings of about 20 lbs per square feet. These wings will support the 3600 pound airplane at about 60 mph. Lift is proportional to density and to speed squared. The density of water is about 700 times the density of sea level air. So to see a foil operating at 20 mph in water, to support a 3600 pound boat, you need 180 (60/20)^2 * (1/700) = 2.3 square feet. That's all it takes. There are big problems with maintaining proper angle of attack with foils. When the boat hits a wave, the angle of attack tends to increase, causing further pitch up. This instability must be controlled with mechanical or electric control of angle of attack. Perhaps this is what the author above was seeing when he made his remark about the "water column."
jimh	posted 10-05-2013 06:00 PM ET (US) 'coop: thanks for the math to go with the foils. It is very interesting stuff. I like mathematical expressions of relationships.
Jamesgt727	posted 10-11-2013 06:57 PM ET (US) In 1997 i rode on this actual boat from Sorrento, Italy to the Isle of Capri: http://youtu.be/4yn6J8zMQzo The only comment that I can make is that if the columns of water you mention are not felt, we were in 2 meter seas, running 35-45 knots?, and it felt like glass. On the way back we were on a conventional hulled "fast ferry" at half the speed and we couldn't wait to get off of it it was so rough.
GSH	posted 10-18-2013 08:12 AM ET (US) [Not sure why, but the author addressed this comment only to me, but it seems like a comment of general interest to readers of this thread--jimh] Take at look at Swedish "Foiltwister"; please head over to www.foiltwister.se for more information (also in English).
jimh	posted 10-18-2013 10:31 AM ET (US) I have already visited that website, but thanks for posting. (It was mentioned in the animation video I linked to above.)
jimh	posted 10-18-2013 11:08 PM ET (US) It seems like foils are often used in applications like ferry boats. I was just watching an older movie, RUSSIA HOUSE, and in several of the scenes in Russia there is a large hydrofoil ferry boat seen in the background. In my initial article where I proposed application of a lifting foil to a boat like a classic Boston Whaler 22-footer, I was not thinking of a foil that would be large enough to lift the entire hull out of the water, but rather of a smaller lifting foil that might raise the hull a bit more. This would reduce the running surface on plane, and improved the performance. The general basis for success for a foil is that is has to create enough lift to reduce drag by getting the hull out of the water. The foil also creates its own drag. To be effective the added drag of the foil has to be much less than the amount of drag reduction gained by the lift.