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 Post subject: Foiling Bravo
PostPosted: Fri Mar 02, 2018 9:25 am 
Site Rank - Deck Hand

Joined: Tue Mar 08, 2016 10:10 am
Posts: 16
Hey everyone. I've been toying with a crazy idea; I want to add a foil to a Bravo. What can I say, I love speed. Anyway, my idea is pretty simple; build the foil on a board with bolts going up through the drain holes. I can place boards on in the bed and tighten the pieces together.

Has anyone tried something of the sort? I would luuuuuuuuuurve to see the results.

 Post subject: Re: Foiling Bravo
PostPosted: Thu Mar 15, 2018 5:24 am 
Site Rank - Captain

Joined: Wed Aug 08, 2007 10:20 pm
Posts: 104
Location: South Boardman, Mi
I have some bad news. Making a boat that foils isn't easy. You need stable, efficient foils mounted to a light platform, with sails to match. If you really want a foiling Bravo, you will likely need to work your way up to it. Start with something that foils well, and learn how to sail a foiling boat. Then taking what you have learned from sailing a tried and true foiling boat, consider starting to make modifications to your boat.

For Reference a foiling moth weighs ~30kg with a 8.25m^2 sail. A stock Hobie Bravo weighs over 80kg and has a 7.99m^2 sail. The moth sail shape is much better suited for high speed sailing.

Lastly, foils carry a ton of load. They must carry the boat, the crew, and resolve almost all of the force imbalance from the sail loads. Add to this any maneuvering loads (Force=Mass*Accel) and you will find that they handle a s**t ton of forces. All of these loads must be transferred through your connection point. It is unlikely that the transom alone could handle these loads.

This book is a decent starting point for the non engineers out there:

For engineers/dedicated learners, look for a college textbook on marine engineering of high speed vessels.

 Post subject: Re: Foiling Bravo
PostPosted: Thu Mar 15, 2018 6:42 am 
Site Rank - Old Salt

Joined: Sun Apr 20, 2008 6:18 am
Posts: 2837
Location: Sarasota,Key West FL
The bravo has pretty much the same sail as the TI, which just doesn’t have the neccessary power to be able to foil. Plus the furling unstayed sail design and floppy mast makes it really really hard to add the additional sail area you would need to get up on the foils.
You would be much further ahead starting off with an F18 type boat with a giant square top sail. You would of course need to widen it quite a bit, which brings up another problem, making it un-trailerable, ( too wide for roadways).
Weight will be a problem so you would likely need exotic materials for new hulls, ( uber expensive).
If you look at existing foiling boats like the Rave you can see all the re-enforcement needed to make the boat strong enough.
The moth boats are a pretty mature technology, you might be able to pick up a used one and play around.
Making the foils themselves is the easy part, designing and making everything else is a huge undertaking, starting with something that is already very fast and powerful helps make the task a little easier.

We had foils on our TI for a while, everything worked, (we could get up on the foils), but we had to have 260 sq ft of sail area to do it, ( the boat was heavily modified). Definately not worth the effort, and really dangerous.
If your really interested you might be further ahead starting with an older Moth, Rave, or Trifoiler, then re-engineer the sail systems to wing sail technology, ( that’s what I would do).
Hope this helps

If it was me and I could afford it, (not likely) I would pick up an old Trifoiler and modify the sails to a Hybrid jointed wing design similar to what Randy Smyth did on his boat Synergy, (see video below).
Basically you build a stub wing off the mast, then attach the existing sail to the back of the wing, (of course you would need two of everything with a trifoiler). You would have one additional control rod across the center, to control pitch of the joint. The wing on the Trifoiler would be much less deep, I'm guessing around 2-3 ft max, and slightly less tapered than shown on video. Doing this would give you a much wider performance window, and should increase the top speed by quite a bit, maybe even break the current record.
No need to re-invent the wheel on the hull design and all the foiling functions, those work really well on the trifoiler.
You could likely do the same conversion on an old RAVE, (might be slightly easier).
Plus it would be very fun to do, (only for your own personal use of course).

Video courtesy of Tom Ray. (from watertribe EC-2018)

If you google trifoiler you will see lots of videos, and can visualize the conversion task, (pretty daunting). Here is a nice video showing some of the structural design of the sail assembly. This was taken where I typically launch, Dean is very knowledgeable about these boats, (he owns trifoiler #41).

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