Homemade hydrofoil?

[ZmOz]

I'm thinking a hydrofoil would be the perfect thing for my '74 150hp Mercury inline 6 and Glastron CV-16, but $50-100 for a peice of aluminum cut in a funny shape just seems ridiculous to me. I have heard of people making their own, and would like to do it myself. Can anyone tell me any dimensions? Is there a certain size that it needs to be, like not too small and not too big? A certain shape it has to have?

 

[catfish1]

Re: Homemade hydrofoil?

hydrofoils are not made of aluminum, they are made of plastic. if you made one out of aluminum or stainless, by the time you were done you could have bought one from ebay for about $30. and it would work better also.

 

[ZmOz]

Re: Homemade hydrofoil?

Yes some are made from aluminum...such as this. I already have a sheet of 1/8" aluminum, so it would be free.

 

[DuPont Spinner]

Re: Homemade hydrofoil?

I would suggest you re-think your idea of a home made hydrofoil. If you are really serious about improving boat performance, this is not the item to guess with. Save the few bucks that they cost and purchase one that has been designed to certain standards. However, if you truly want to attempt a hydrofoil, by all means do it. Thats whats fun about any hobby or pastime. I hope all works out well. By-the-way, how did the plastic gas tanks work out? <br /><br />DuPont

 

[catfish1]

Re: Homemade hydrofoil?

well it looks like you have your answer in the link you provided, just look at the picture and copy a guestimate size and shape. you will need to bevel the leading edge to cut down on resistance. i'm sure it will work, but how well who knows?

 

[ZmOz]

Re: Homemade hydrofoil?

Well...even if it doesn't work all it costs is the price of a jig saw blade. Anybody here make one?<br /><br />DuPont - are you talking about the ones I wanted to make? I haven't gotten around to that yet...

 

[quinnf]

Re: Homemade hydrofoil?

Mebbe the first question you should ask is, "Do they actually do anything?" I have serious doubts about that.

 

[Hopsdak]

Re: Homemade hydrofoil?

The one i have is out of stainless. And your asking if it works? Well, Put it this way.. I now adjusted my trim tabs to the full upright position and no longer use them. My boat plains at 11mph and will plane out in 1.5 boat lenths. I can load the stern with icechests and people and it will still plane. It's a must have for a tunnel boat. I can also us it as a step to get back in the boat.<br /> Nedski Side <br /> Nedski Aft

 

[quinnf]

Re: Homemade hydrofoil?

OK, I can see with the area of the plate you have installed, when getting up on plane you're going to have significant lift generated. Nice.

 

[ZmOz]

Re: Homemade hydrofoil?

Yeah, I asked about whether they work or not on a different forum and everyone said they work great.

 

[sloopy]

Re: Homemade hydrofoil?

I would not do do it, Unless you have thicker aluminum (half inch) and a way to sand it into a foil shape it would not work. A flat piece of metal will not work, water flowing over the top has to be going slower then the water flowing under it.(by the way, the water is going the same speed, but it takes longer for water to travel over the top then the bottom) This lifts the boat from the stern kinda like an airplane wing. If you build it out of aluminum and not get the math and design right you will have a piece of aluminum that has water traveling over the top at the same speed as the bottom, this will just cause more drag. OR you will have it reversed and it will suck the transom down, and if you have one side pulling down and one side pulling up it could flip the boat or make a very uneasy ride.

 

[ZmOz]

Re: Homemade hydrofoil?

What about the one linked above? Looks to me like it is just a sheet of 1/8" flat aluminum...for more than $50!

 

[Fouled Plug]

Re: Homemade hydrofoil?

ZmOz, time to bust out the tools and go for it. I like the Nedski design, and the results sound promising. If you have access to the dimensions and a sheet metal brake, build it!

 

[MajBach]

Re: Homemade hydrofoil?

Mebbe the first question you should ask is, "Do they actually do anything?" I have serious doubts about that.

You can be sure, they DO make a difference; but perhaps more signifcant on some than on others.<br /><br />Sloopy: I'm afraid you have it all wrong,<br />

water flowing over the top has to be going slower then the water flowing under it.(by the way, the water is going the same speed, but it takes longer for water to travel over the top then the bottom) This lifts the boat from the stern kinda like an airplane wing

Hydrodynamics is not the same as aerodynamics. You do not need the shape of an airplane wing to achieve the same effect. Air moves FASTER over the top of a wing (as is also the case in water) and creates a low pressure region. It does this becasue is has farther to travel to the trailing edge of the foil in order to meet the air travelling over the bottom AT THE SAME TIME. In order to fill a greater volume of air, it expands (creating a low pressure) and travels faster.<br />Water does not expand. This is why your outboard propeller is no where near the shape of an airplane propeller.

 

[Dhadley]

Re: Homemade hydrofoil?

Keep in mind that the fins are a tool that allows a higher X dimension. They were never intended to run under the surface of the water. All kinds of strange things happen when they do. <br /><br />They do work when applied correctly.

 

[quinnf]

Re: Homemade hydrofoil?

One reason for my skepticism was, first, that hydrofoils installed on the anti-ventilation plate run at or slightly above the water's surface when the boat is on plane, so I couldn't see how, unless they were submerged and met the water at some positive angle of incidence, they would generate any lift. I understand now, when a boat is struggling to climb on to plane and the anti-ventilation plate and thus the hydrofoil is submerged, it can generate lift.<br /><br />The other reason for my skepticism was that I don't see many hydrofoils used around here (Southern California salty water) anymore. Seems that several years ago every outboard had one, but I see very few now. Even the Evinrude 120 on my Mako 17 evidently had one in a previous life. All that remains are the mounting holes. Maybe the plastic ones that are so popular broke in the lumpy water and owners didn't bother to replace them, figuring they'd just break again.

 

[Dhadley]

Re: Homemade hydrofoil?

There are plenty that have been taken off because the owners didnt feel there was any benifit or worse, that the boat acted funny. Both are classic symptoms of a half done job. Once installed, the motor can/needs to be raised. Sometimes a lot. The bigger the fin, the higher you can go -- to a point. <br /><br />Tne point that is most overlooked is whats going on after we're on plane. Yes, the fins give a great holeshot but the greatest benifit is that when on plane and the fin is above the running surface of the water, it will actually "capture" water that normally passes up past the gearcase and is lost. It will actually compress that "lost" water and give the prop a better "bite" while adding stability and lift. Its not unusual to see a slight increase in water pressure too.<br /><br />When we first started fooling around with the fin idea all we were looking for was a faster holeshot for the drag boats. The added benifit of the "compressed" water was an unexpected bonus.

 

[sloopy]

Re: Homemade hydrofoil?

I still think it will not work! It needs a foil shape for a reason, HINTS THE NAME HYDROFOIL!

 

[93bronco]

Re: Homemade hydrofoil?

go for it-- there is one out there that is flat <br /> web page

 

[rickdb1boat]

Re: Homemade hydrofoil?

The way I understand the hydrofoil is that water is "Pushed" against the bottome of the foil to provide stern lift and plane the hull out faster. Then when the boat planes, the foil should?? be out of the water or at least at the surface anyway. The shape really hasn't much to do with it. You could put a square plate on there and get lift. Having it taper at the leading edge just allows the water to flow smoothly around it until it gets out of the water. Is this wrong?