# What foil profile(s) does the MIT Decavitator (or similar vehicle) use?

I'm looking for some kind of "standard" hydrofoil profile suited for a water vehicle comparable to the MIT Decavitator (similar weight/speed/power/etc.), so I can use it as a base to get started with my own simulations/experiments. As far as I can tell, the team behind the Decavitator didn't publish details about their foils in more detail than the following:

The larger 60$$\times$$2.35-in / 1520$$\times$$60-mm (span $$\times$$ mean chord) wing is placed about 6 in / 150 mm below the pontoon bottoms, and the smaller 30$$\times$$1.4-in / 760$$\times$$35-mm wing is placed another 6 in / 150 mm lower. [...]
The wings employ a custom 14%-thick airfoil which has been tailored for the operating Reynolds-number range of 150,000 -- 400,000, using the design principles and numerical simulation methods employed for the Daedalus wing airfoils [Drela_JA88,Drela_SV89].
The structural merit of the relatively thick airfoil allows smaller wing areas and less overall drag than the 10-12%-thick airfoils more commonly employed at these low Reynolds numbers. The thick airfoil also gives the rather wide usable lift-coefficient range $$0.2 < C_L < 1.1$$ , which translates to low wing drag over a wide range of speeds.

(yes, I checked out those references, they are very general and don't have any hydrofoil example)

I have found some details on the design of foiling surf boards, but as far as I can tell they usually heavily restrict the wing span (for safety/maneuverability reasons I guess) to the detriment of efficiency so they aren't useful to me.

• What shape foils are used on the boats that hydroplane? Jul 11, 2020 at 18:52
• @SolarMike How do you mean that? In general? m-selig.ae.illinois.edu/ads/coord_database.html has a couple that mention "hydro" but the problem is that I don't know what kind of foiling boat they were designed for. For a foiling sail boat I think maybe the foil could be similar to what I'm looking for, but I think I've seen some with pretty low aspect ratio which probably has some specific sailing related reason that doesn't apply to a vehicle like Decavitator. Jul 11, 2020 at 19:10
• Start from the boats instead of a database. Jul 11, 2020 at 19:25
• @SolarMike I checked out a number of boats from humanpoweredboats.com/Photos/HydrofoilHPBs/HydrofoilHPBs.htm but couldn't find details on most. Commercial boats usually don't have schematics available, so... Jul 11, 2020 at 19:33

This is basically a list of resources gleaned from having followed the HPV boat development for the past twenty years.

Here's a good sketch of how to go about exploring the hydrofoil design space. You need human factors input very early on, a good sense of drive train layout and expected efficiency, and a realization that one pedaling person has a massive torque pulse problem that affects propeller craft totally differently from road bikes.

Human Powered Hydrofoil Design & Analytic Wing Optimization

The principal examples of HPV solo hydrofoils are Flying Fish and Decavitator. There were several incarnations of both craft. Flying Fish won in the match race, but Decavitator's air prop let it exploit a rule permitting up to five knots of wind during the record attempt. The record was set running downwind in 4 knots, giving the air prop an efficiency boost.

Tom Speer developed foils and control systems for Boeing, for land yacht record attempts, and was part of Oracle's America's Cup team. He has generously made large amounts of his research and experiences available through his web site. tspeer.com

boatdesign.net has hundreds of pages of discussions on hydofoils in several of it's subforums including Hydrodynamics, Sailing, and Powerboats. These include US navy hydrofoil engineers and control system designers, as well as Tom Speer and Mark Drela, and a host of others.

Sailing Anarchy has also, primarily in the Dingy Anarchy forum.

https://m-selig.ae.illinois.edu/ has hundreds of foil offsets.

Xfoil and AVL are freeware analytic and design programs out of MIT, largely the work of Mark Drela. AVL presumes the user has a fairly good knowledge of vehicle stability issues.

Tom Speer designed the Speer H105 foil for this application. In the past, he has provided offsets in exchange for a copy of any performance data the user obtains.

Mark Drela has indicated the Decavitator used his MRC16 foil for part of the wing. IIRC, the main foil was in three parts with different sections (middle, intermediate, and outboard). MRC16 foil discussion. MRC foil offsets

One of several outstanding discussions of hydrofoil issues on boatdesign.net foil-cavitation-at-lower-speeds-than-expected

• Thanks. lancet.mit.edu/decavitator/images/evolutionW.gif The frontmost is the high speed main wing of the Decavitator, but at this resolution it's impossible to tell how many profiles they blended, the only thing that's clear is that it tapers off somewhat. I decided I'm overthinking it (for a hobby project I'm doing to relax from my actual full time studies), I'm just going to build a proof of concept protoype using a simple H105 or MRC16 wing and see how it goes. Let's see if I can even build it, my previous composite parts had rather more generous tolerances. Jul 12, 2020 at 18:28