C FOILS FOR TRIMARANS - a question of priorities

The case for and against

There’s a strong consensus among professional sailors that C foils in trimaran floats are an advantage for trans ocean racing, especially if those races include a lot of reaching in fresh conditions. Maybe not so much as a speed boost, but to help maintain stability and keep the bow from burying in steep seas.


For smaller boats that are mostly racing inshore or doing relatively short offshore passages - say 24 hours or less - the advantages of C foils are not quite so clear cut. The fact is that a trimaran float with a beam to length ration of around 1/16 or so is fairly slick piece of equipment and if you’re going to add some devices to it you need to be sure they’re making a positive contribution in a given set of conditions. 


 The C foils will contribute to your drag when they’re not operating in a speed range where they can contribute significant lift. They will add cost to your project. If they are going to be efficient and reliable they need to well engineered, have the right profile, and be carefully built to meet the required specifications.

There are five boats that have been actively racing under OMR with C Foils in recent years; Bare Essentials, Carbon Credit, Crosshair, Wilparina and Sweet Charriot.


Wilparina actually has straight boards at a 45˚ angle - so they are not strictly “C” foils but they are designed to serve the same function. Wilparina’s original owner Rob Remilton says; 

“we found them great for ocean sailing as they kept the boat going with an easier motion, and reduced nose diving.”

None of these boats has demonstrated convincingly and consistently that they are race winning material under OMR.

Given that lifting devices are not penalised under the OMR you would expect these boats to be taking advantage of this and piling up a nice little trophy collection.


Of course this is not clear cut evidence that C Foils don’t work. Overall performance is a complex mix of factors and there could be other forces at play. However we can say with confidence that the C Foils are not a guaranteed free lunch to racing success for smaller trimarans mostly racing inshore.

Bare Essentialshas been a very strong performer on the Australian racing circuit over an extended period of time. How much the lifting foils have contributed to her successes is not clear but until now she has not claimed a significant title like the Australian Multihull Championships in spite of her foils not being rated under OMR.


I have to say though she is a very fast boat and seems to fly the main hull more easily that the other boats mentioned here. Is it the foils, the floats, or a combination of the two?

Seacart 26 Sweet Charriot with C foils. Owner Henry Kaye previously owned a Seacart 30 which he raced very successfully without C foils. After Sweet Charriot he has now moved back to a Seacart 30, once again without C foils.

So to answer the question that is popping up in my inbox on a regular basis these days; “Should I have C foils?” I answer it this way; Put it in the right place in your list of priorities. Here is my personal list of priories:


1. A stiff but light platform. The engineering needs to be thorough. You have to have the right materials and the right build process. You can change the rig and sails anytime. Not so easy the platform.


2. Rig and Sails. Think of them as one. Each comes from people with very different skills and working methods - but the bottom line is they are working to the same goal - to provide you with a reliable and easily controlled driving force that is efficient through a wide range of conditions. Be clear on the philosophy behind the rig and sails. Design is critical and good communication between all parties involved is important.  Yes, the designer will give you a rig and sail plan - but that’s just the starting point. Get your sail maker and your preferred rigging company on board as early as possible in the project.


3. Look at other details that you can deploy to further boost your performance. In this category I put rotating wing mast (this might surprise you - more on this in a later article), C foils (or angled boards), and canting mast. For this kind of equipment you have to consider the cost, additional weight, additional engineering and build time, and the increased number of on board controls you have to contend with when you might prefer to be attending to navigation, sail shape or looking for shifts in the breeze. 

Having more of this kind of equipment requires more skills and more attention to how your boat is set up and trimmed. Franck Cammas makes all this stuff work wonders. Not everyone can pull strings the way Franck Cammas pulls strings, and not everyone wants to.


Clearly the decision to fit or not fit C foils is a personal one and it needs to be considered in the context of your level of skill and how you like to sail. If you’re considering C foils then seek out evidence that they will be of benefit to the type of sailing you want to do and consider whether you have adequately covered points one and two above as a first priority.

Wilparina, a strong performer and by all accounts the angled boards were a significant advantage downwind in offshore conditions. Previous owner Robert Remilton now owns a Diam 24