Concept Discussion - Hydrofoil on a pontoon boat (not the motor)

[HotTommy]

I found myself surfing some videos about hydrofoils like those on the America's Cup sailboats. I eventually found my way to a website about a hydrofoil that could be mounted between the twin hulls of a powered catamaran style boat. It looks like an inverted T that attaches to the bottom of the boat and to each hull. It got me thinking about whether such a device might work wonders on a two log pontoon boat. .... So has anyone ever heard of such a device being tried on a pontoon boat? (I don't need to hear about the WaterGlide.) ... If one were to build such a device, how would you know where to mount it (fore and aft)? Acutal knowledge and wild speculation are both welcome. But please indicate which you are offering.

 

[GA_Boater]

How will you launch?

 

[bruceb58]

If you have enough HP to make that work, just have some lifting strakes welded on.

 

[HotTommy]

I take that to mean "I don't know."

 

[bruceb58]

I take that to mean "I don't know."

Since you don't give any info on what you are working with..length of pontoon, width of tubes...horse power...Yes, I don't know based on a bunch of info you haven't supplied.

 

[HotTommy]

I guess you guys have seen so many people come here asking how to do either ridiculously hard or economically unfeasible things to their boats that you're spring loaded to the "that's not a good idea and here's why" position. I'm not planning to build anything, I just wanted a discussion about the concept. I don't think additional detalis are needed to answer these two questions:

• Have you ever heard of or seen a hydrofoil on a pontoon boat? I haven't.
• Would the best place to locate a hydrofoil be forward, aft or at the center of gravity of the boat? My wild guess is slightly forward of the COG. On further reflection, perhaps two foils, one forward and one aft, would be even better

 

[ahicks]

Agree Tommy. This "I don't know unless you give me all the specifics" or "I'm not going to try to answer your question unless you can provide me with all the data I request" often doesn't cut it on a lot of questions - especially when it comes to your original question which states specifically you're just playing with ideas.

To me, they're just trying to make it more difficult to get an answer - in this case, one that's not likely available no matter how much data you provide. Pretty much counter productive in a forum format like this one, that depends on newbies getting up the courage to ask a question.

And for what's it's worth, I would say you would need 2 or possibly even 3 or 4 hydrofoils. 2 to just make it possible to get the boat on top, as balancing a boat like this on one sounds impossible, and 3 or 4 to make it stable. I don't know for sure, but it would seem that enough power to "get on top" would not be that difficult. From a practical standpoint they would almost have to be retractable - another fairly challenging factor for sure!

Last thought, we're considering lifting the boat up out of the water on hydrofoils. Part of that concept would include how you plan to keep the prop in the water when you do that....

 

[HotTommy]

Yep. Getting the prop right on a boat that rises on a hydrofoil seems to be a common challenge in most boats equipped with them. I know there are expensive, technologically complicated solutions like hydraulically movable transoms, but on a pontoon boat you might be able to get by with a long shaft outboard that sits a bit deeper in the water than usual. I wouldn't expect a pontoon boat to rise more than 12" or so. .... One feature that has been used on some hydrofoil boats is a movable foil that is controlled by a system of arms and bell cranks connected to a float in the water. When the boat is low in the water, the float rises causing the foil to move to a position that pushes up on the boat. As the boat rises, the float goes down (relative to the boat), moving the foil to a more neutral angle of attack. When adjusted properly, it allows the boat to rise up quickly under power and then automatically settle at whatever height the designer wants. ... All I was imagining was a pontoon boat that skimmed across the water with just the bottom 2" of the logs (and the foils) in the water.

 

[ahicks]

The foils really don't work right (or maybe aren't fully effective) until the boat is up out of the water and clear of the waves. Minus that resistance, they can go like hell.

With 2" still in the water, strakes are likely the better plan. A lot more practical for starters.... to my way of thinking anyway.

 

[GA_Boater]

Changed the title of the thread to show that this is not a serious effort to actually try to build a Hydro-Toon, just bar talk.

My first question earlier was how can it be launched. This would be highly impractical;



Retractable foils seem to be the only way at this point in researching. Ran across this site with some interesting concepts. Something on the order of these drawings could be adaptable to fit a pontoon;




Getting power to move one of these is problematic. Wind, jet engine and aircraft propellers are the easiest, but not practical on a toon. Outboards power these early prototypes;



The stern isn't completely lifted, so a long or extra long shaft OB could work. The other ways are electrically powered props on the foils or a long shafted inboard propulsion system. The link has examples.

In the meantime, I'm going out on my totally conventional tin boat.

 

[garbageguy]

Great pics and info GA. Interesting concept and fun to discuss. Like most of these ideas, they've been thought about, a lot, before - but have not gone into common use. Although sometimes the ideas, or parts of them do.

In this case; I have not seen them on a toon, I think one forward and one aft on each log would be the placement.

Practicality often gets these concepts - and I think the desire for a certain owner/user to put in the additional/different effort to utilize the concept play a part in its applicability. Concepts that go on to widespread use have often been modified to be "acceptable" to the masses.

 

[HotTommy]

This is the picture of a hydrofoil between the twin hulls of a catamaran that inspired me to start this thread. As you see, it doesn't lift the boat entirely out of the water. Rather, it lifts the boat mostly out of the water using the hydrofoil more than the planing effect of the hulls.

Plainly, engineering such a device for a pontoon boat would be no simple matter, but it could be done. For example, I can envision the foil and the vertical support as a single, rigid piece that attaches to the two logs and underside of the deck/crossmember with some sort of quick release mechanism at each point. Most of the force applied to the hydrofoil would be pushing up and aft, so perhaps it could slide into brackets from front to back and then be held with pins or bolts. If it were easy enough to install/uninstall, it would be feasible for someone who launched and recovered their boat only once each season. It could also work for someone who kept their boat on a lift at their boathouse.

If one didn't want to use the logs for supporting the foils, then two retractable foils through the deck (as in the yellow and blue boat pictured earlier) might work. But that would require the deck to be strong and rigid enough to both support the entire weight of the lifted boat and resist the fore/aft and side/side loads on the foil arms. My intuition tells me that would be a huge challenge.

 

[Cat nip]

You could use some sea legs for the base of the foils so they can be retracted and still be able to get it on A trailer and have a jack plate made or modified to travel the distance required. This would have been a great episode of monster garage!

 

[HotTommy]

There's a million dollar idea: "Pontoon Boat Monster Garage." Are you listening Velocity Channel?

P.S. Here's the show I'd like to see. Two competing teams each get a 20 year old two log 24' pontoon boat, a new 115 HP outboard motor and controls, and $8,000 cash to build the fastest and coolest boat.

 

[Cat nip]

Sign me up!