Trimaran lifting foil alternative

Discussion in 'Multihulls' started by kiwi_bob, Aug 27, 2011.

  1. kiwi_bob
    Joined: Aug 2011
    Posts: 18
    Likes: 0, Points: 0, Legacy Rep: 10
    Location: New Zealand

    kiwi_bob Junior Member

    There seems a lot of designers going for the banana style lifting foils in the floats. Orma 60's, USA 17, Farrier getting in on the act etc. They seem difficult and expensive to make (along with the cases), heavy and tricky to get right and only apply over certain wind strengths or boat speeds (the Orma 60 in NZ only use thiers in over 15 knots). You have pull them up and down when tacking/gybing etc.

    Other people are going for mega big floats but I don't think that is the right path as you have extra weight and windage in the light.

    As an alternative; Say you've got a tri with small-ish foats that you are worried about burying when pushing hard, you'd like more righting movement up forward in the heavy conditions. Why wouldn't you just install a fixed horizontal lifing foil on the side of the float (inside or better, outside or even both) high enough so that it doesn't get wet in the light conditions and dips and creates more lift for the leeward float in the heavy conditions. Sure, you are not going to fly all three hulls like you may possibly do with the banana boards but we are talking about racer cruisers here and I think 2 hulls flying is about it for me anyway. I guess I am thinking about a poor mans banana foil - I'd think it is far easier to attach what I have described rather than replacing the floats or buying the cases and installing foils???

    Has anyone tried this, how did it go? Please critique idea.
     
  2. Doug Lord
    Joined: May 2009
    Posts: 16,577
    Likes: 297, Points: 93, Legacy Rep: 1362
    Location: Cocoa, Florida

    Doug Lord Flight Ready

  3. rapscallion
    Joined: Oct 2006
    Posts: 504
    Likes: 15, Points: 18, Legacy Rep: 132
    Location: Wisconsin

    rapscallion Senior Member

    catry trimarans have lifting foils on small volume floats. I have sailed on a catry 27; it's an awesome ride! 17 knots in 8 foot waves, and i could set my soda on the deck and not worry about spilling it.... it's an awesome boat.
     
  4. thudpucker
    Joined: Jul 2007
    Posts: 885
    Likes: 31, Points: 0, Legacy Rep: 453
    Location: Al.

    thudpucker Senior Member

    The NAVY tried Multi-hull's with only TWO lifting foiles per each craft. In all the Hulls they tried out (told us about) they had some pretty wide craft.
    Always the two in front are seperate.
    But the two aft were joined down at the Skeg by a 'flying' wing.

    They say the four (above) will take a heavy 100+ Foot craft, up to 60 Mph in Bad water and can turn in a very tight Radius even under those conditions.
     
  5. cavalier mk2
    Joined: Mar 2010
    Posts: 2,085
    Likes: 40, Points: 48, Legacy Rep: 214
    Location: Pacific NW North America

    cavalier mk2 Senior Member

    I've pondered those but like a horizontal pivoting trunk for skinny bows so you an get them out of the way when you don't want them. In practice we haven't come lose to needing them in the strong stuff. To windward our floats stay even and when we ease off a few degrees the bows come out like a cork. As pointed out in the America's cup thread it is worth pondering whether you want them lower down for less wave impact or to work with piercing bows. Boats like Colas' old tri Manureva had the bows modified with chins for lift and I've seen a few Crowther's with angled "spoon " plates on the bows.
     
  6. kiwi_bob
    Joined: Aug 2011
    Posts: 18
    Likes: 0, Points: 0, Legacy Rep: 10
    Location: New Zealand

    kiwi_bob Junior Member

    Thanks for the replies guys.

    I suspect what I'm pondering would be closest to the "spoon plates" idea but, correct me if I'm wrong they were more of a last resort to attempt to lift the bows when you are about to "go down the mine" and were quite high out of the water normally? Did they actually work?

    What I'm pondering would be further back and would use a lifting foil shape rather than angle of attack to achieve lift. Compared to a curved lifting foil (or a straight one) the difference is that it would not immediately be in deep water and in transition would be in and out of waves etc and god knows what the effect would be, I suspect that may be the reason why nobody does this...

    Related topic: is there some software which takes Nacra foils in water and tells you how much lift they generate a what speed etc.
     
  7. Doug Lord
    Joined: May 2009
    Posts: 16,577
    Likes: 297, Points: 93, Legacy Rep: 1362
    Location: Cocoa, Florida

    Doug Lord Flight Ready

    The DSS concept ,as far as I know, hasn't been applied to multies and would probably only have value(if any) on trimarans. It is very close to what you suggest. The disadvantages would be in adjusting the angle of incidence and, maybe, keeping the foil deep enough without getting the ama too deep. There is science that suggests that a foil approaching the surface(say, under 2.5 chords from the surface) has very increased drag. And that a foil such as the one below operating just on its bottom-sort of planing-is also very draggy.
    However, the guys actually doing DSS say that does not appear to be the case: see the Quant 28 thread under "sailboats" for more on this type of foil and a spectacular video. http://www.boatdesign.net/forums/sailboats/quant-28-foil-assist-keelboat-dss-38421.html
    --
    The more research I've done the more curved foils look like the best solution because of their adjustability and ability to lift 60-70% of the boats weight (or more). Also, they can be designed to operate with a main hull daggerboard or without one. Operational range of the foil(any foil) is strictly a design choice though with a curved foil you can adjust the amount of vertical lift without interfereing with any lateral resistance developed by the foil.
    -------
    UPDATE: If the DSS system can be used effectively on amas then it has a big advantage over curved or straight angled foils in that the lift can be centered in line with the ama CB or even outboard to leeward increasing RM over curved, "J" or straight angled foils -all of which decrease RM when deployed. The DSS has the same 100% retractability of the others....

    Picture from Ocean Navigator:
    click on image---
     

    Attached Files:

  8. Ilan Voyager
    Joined: May 2004
    Posts: 1,186
    Likes: 100, Points: 63, Legacy Rep: 758
    Location: Cancun Mexico

    Ilan Voyager Senior Member

    Kiwi Bob Look at the thread http://www.boatdesign.net/forums/multihulls/alternative-marvelous-buccaneer-24-a-32382-4.html.
    It's the kind of tris you're looking for.

    The post #58 with 2 pics of Marc Lombard's foilers designed in the 80ies. KER CADELAC (not Ker Cadillac) was a very well mannered winner.

    Simple straight foils. Not use a symmetric NACA that won't work, and it's dangerous as it works as well UP lifting and DOWN lifting...Imagine the situation with a foil going down... Curved foils plus the boxes are a pain to make. Straight one can be made with laminated wood, a planner, some E glass UD and satin plus a touch of carbon. Cheap for a cruising boat. But that worked on Ker Cadelac without problem...

    Asymetric foils are better for this job. The very "primitive" Eppler 193 is a good start for a 12-15 knots boat. Neutral angle +7 degrees, works until 15-20 degrees, hard to stall. Flat underside on more than 80% of the chord, easy to make. Very tolerant. CG at 35%. Good in low Reynolds and not bad in higher.
    Ok it's a profile for model planes, used also for propellers, not the best for a foiler but it works rather well in the water. With 10.22% of thickness is strong enough and doesn't drag too much.
    You'll find plenty of info in Internet.
    After you have better profiles but it's another matter.
     
  9. Doug Lord
    Joined: May 2009
    Posts: 16,577
    Likes: 297, Points: 93, Legacy Rep: 1362
    Location: Cocoa, Florida

    Doug Lord Flight Ready

    The biggest problems I see with straight foils compared to curved foils:
    1) With the curved foil you can adjust vertical lift separately from lateral resistance. With a straight foil any adjustment of the foil angle of incidence affects both vertical lift and lateral resistance,
    2) No matter how much you retract a straight angled foil you always have the same percentage of vertical lift and lateral resistance where as when you retract curved foil you can eliminate most of the vertical lift while still developing lateral resistance-at least you have that option at the design stage.
    3) a retracted straight angled foil will stick out considerably past the max beam of the boat.
    4) I agree that an asymetric section is probably best for a "normal" setup.
    ------
    If you spend much time with foils you'll find that adjustability is your friend and that's where a curved foil is clearly superior to almost any other foil configuration.
    I don't see why a curved foil is much more of a "pain" than is a straight foil to build. I've built dozens of straight foils with matching trunks and the work is very similar. I haven't built curved foils yet but I am about to and have done tooling of one sort or another for years and I just don't see the problem...
    Here is the plan I am about to use for building the curved foils and trunks for my test model. The work is identical to the way I'll do it on the full size 18 footer:
    http://www.boatdesign.net/forums/hy...fting-foils-monohulls-multihulls-37508-2.html post 25

    Rough sketches: 1) comparison of almost equivalent straight angled foil to curved foil( for the Tantra II dinghy but roughly comparable to a tri installation)-
    2) illustration of the reduction of vertical lift as the curved foil is retracted-note that lateral resistance is virtually unchanged. Allows "tuning" for the conditions. Impossible with a straight angled foil since as it is retracted the proportion of vertical lift and lateral resistance remains the same.
    click on image--
     

    Attached Files:

  10. cavalier mk2
    Joined: Mar 2010
    Posts: 2,085
    Likes: 40, Points: 48, Legacy Rep: 214
    Location: Pacific NW North America

    cavalier mk2 Senior Member

    The whittling is the same except for being bent....The curved foils should take longer to make because they must be shaped in a 3rd plane and the other shaping can't be done as a straight line process. If the curve is symmetrical around a center jigs could be made for rotation for "straight line" shaping but the easy way is using molds which is takes time for a one off. Either the part has to move or the tool has to move or the foil is molded.
     
  11. Gary Baigent
    Joined: Jul 2005
    Posts: 2,959
    Likes: 102, Points: 63, Legacy Rep: 509
    Location: auckland nz

    Gary Baigent Senior Member

    Doug, look at the lateral resistance area on a curved foil; it is a small percentage of the foil's shape; mostly a curved foil provides lift vertically or near vertical and does NOT provide much lateral resistance ... to gain that you require a conventional daggerboard in the main hull ... and that is what all the ORMA's and MOD's have, long floats, curved foils and DEEP daggers. The sketches you provide have highly curved foil shapes, the NACRA 20 has much shallower curved foils ... and with such a setup, you're getting considerably more anti-derive, plus near vertical lift as well, a compromise.
    I'd say, after building my J foils for Sid, that building highly curved foils would require many, many hours of work ... and then you've got the cases. Not saying it is impossible, just a long process. J's on the other hand have simple straight cases, simple straight upper sections, tightly curved areas lower down (in deep water) plus large areas of vertical lift as well ... so you're getting high lateral resistance plus high lift in one foil. Lifted, J foils have the curved to horizontal lift area close to the float; I can live with that.
     

    Attached Files:

  12. Gary Baigent
    Joined: Jul 2005
    Posts: 2,959
    Likes: 102, Points: 63, Legacy Rep: 509
    Location: auckland nz

    Gary Baigent Senior Member

    Last sentence correction: "Lifted, J foils have the curved to VERTICAL lift areas close to the float ..."
     
  13. Doug Lord
    Joined: May 2009
    Posts: 16,577
    Likes: 297, Points: 93, Legacy Rep: 1362
    Location: Cocoa, Florida

    Doug Lord Flight Ready

    ==================
    Gary, one of the beauties of curved foils is that they can be designed precisely to the lift/lateral resistance requirements of a particular boat-they are not all the same. And the lift from any curved foil is infinitely variable("tunable")-while maintaining nearly 100% of its designed for lateral resistance. And that is unlike any other foil configuration as best I can tell. All that and 100% retractable....
    For instance, look at the NACRA foils(plenty of lateral resistance) and then compare them to the Farrier foils( optimised for vertical lift since they work-one at a time with a main hull daggerboard:
     

    Attached Files:

  14. Gary Baigent
    Joined: Jul 2005
    Posts: 2,959
    Likes: 102, Points: 63, Legacy Rep: 509
    Location: auckland nz

    Gary Baigent Senior Member

    Agreed, the NACRA's are only slightly curved, in fact they could even be straight ... except then the exit positions, top and bottom, would be compromised (itswatIz in slightly differing words) .. and the Farrier has tight curve foils PLUS dagger.
     

  15. Doug Lord
    Joined: May 2009
    Posts: 16,577
    Likes: 297, Points: 93, Legacy Rep: 1362
    Location: Cocoa, Florida

    Doug Lord Flight Ready

    =================
    Exactly......
     
Loading...
Forum posts represent the experience, opinion, and view of individual users. Boat Design Net does not necessarily endorse nor share the view of each individual post.
When making potentially dangerous or financial decisions, always employ and consult appropriate professionals. Your circumstances or experience may be different.