AC 36 Foiling Monohulls

Discussion in 'Sailboats' started by OzFred, Sep 13, 2017.

  1. OzFred
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    OzFred Senior Member

    It's good to go over some of this stuff from time to time. Sailrocket is a unique boat designed to meet a very specific design goal within a very narrow performance range. The design has been significantly modified over the years and is a very different boat to the original Sailrocket, though the basic proa layout has survived.

    Canting the rig greatly reduces heeling moment, but it also reduces power from the rig. That doesn't bother Sailrocket as there are no class rules limiting the size of the rig: they can just make it bigger to get whatever their designed power requirement is. The goal is to have the boat in perfect balance at +50kn.

    So you can't just take a particular feature in isolation and think "Sailrocket has this feature, therefore that feature will make any boat faster". Every time you think that, remember that Sailrocket is fundamentally a planing boat, not a foiler. ;)
     
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  2. Doug Lord
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    Doug Lord Flight Ready

    From a control standpoint SailRocket is a foiler: the key to Sailrocket is the mainfoil that lifts vertically for takeoff(above the radius) and then pulls down at an angle to balance the sail force(below the radius) .According to Paul Larsen the foil is "self-regulating".

    After much looking I found a version of what I was looking for:
    from www.sailrocket.com/node/497 (comments-"reply armchair")

    Yes, the foil is blunt above the transition (radius). The foil above the radius is affected by both the leeway angles of the boat and the pitch settings of the foil. Seeing as the upper foil is at 30 degrees to the HORIZONTAL, the horizontal pitch settings affect this section of the foil more than the more vertical lower section. The upper section of the foil is more responsible for generating vertical lift. If it generates too much then the back of the boat rises until we reach the transition (radius) of the foil where the vertical component lessens. If we go too far then only the bottom section is left in and that is angled so it is pulling down more than the rig is lifting i.e. we will have net negative lift and be pulled back down to the transition. The boat should seek balance around this transition. If we are riding too low we can increase the pitch of the foil to generate more lift on the top section or decrease the whole inclination/roll of the foil. Getting the right settings is key to making the foil perform. We are still playing with it.
    Cheers, Paul.

    sailrocket_works from  yting wrld.jpg
     
  3. AlexanderSahlin
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    AlexanderSahlin Junior Member

    Some 15 years ago we were at least 3 independent projects that canceled the heeling moment from the sail by canting the rig to windward and having the forces from sail and lateral-plane aligned. Beside Sailrocket there were the Monofoil, that had a working model and also started the construction of a full-scale version. And our Paravane-speedsailer, where we had a paravane connected to the sail by thin lines. The craft was designed for 60+ knots, but I think we reached about the same speed as Sailrocket did before they went to Namibia. What we learnt was that periods of wind above 18 knots usually are too short to reach speed above 40 knots in the Stockholm area. For the paravane we used a base-ventilated section with attached flow on both suction-side and pressure-side. Capable of safe sailing without any cavitation or torsional divergence up to at least 62 knots.
     
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  4. Doug Lord
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    Doug Lord Flight Ready

    Alexander, great information--thank you and thanks for the video!
     
  5. AlexanderSahlin
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    AlexanderSahlin Junior Member

    On boats, where the foil's distance to leeward of the CG is of the same order as the height of the sail's CE, canting the rig by adjusting the shrouds can be a way to trim the sail's heeling moment arm around the leeward foil. Ice-boats do this by having quite loose shrouds, so the rig cant to leeward, and their rigs get a shorter heeling moment arm around the leeward runner. And hence, they can have more power in the sail. If you on the other hand cant the rig to windward, you can increase the heeling moment arm on a foiler like Macif above, so you can make the main hull fly in less wind. This could probably also apply on the new AC-75. On a development of the alternative foiler, I suggested in my post #285 earlier in this thread, I could get twice as long heeling-moment arm around the leeward foil with the rig canted 30° to windward instead of 30° to leeward.
     
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  6. DCockey
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    DCockey Senior Member

    A contrarian view from JB Turner of Front Street Shipyard from an interview in Trade Only, March 2019 issue: https://www.tradeonlytoday.com/marinas-and-boatyards/jb-turner

    (Interviewer) As a lifelong sailor, you must be excited about the America’s Cup coming up. Do you think that event might breathe life into the sailing market?

    (JB Turner) Technologically, I think they’re too far out there with foiled monohulls. And for recreational sailors, the foils are dangerous. You come off the foil, and you go from 40 knots to 10. That’s why they have to wear helmets.​
     
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  7. Doug Lord
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    Contrarian alright, uninformed and unfortunate. Boats are dangerous for recreational sailors that don't know what they're doing. It's smart to wear a helmet on any small performance boat-foiler or not-mono or cat! And "recreational" sailors sailing a foiler at 40 knots is nonsense.
    Interesting to see stuff like that-wonder where it comes from?
    ---
    The Quant 23 is the first monohull keelboat to foil(top speed around 26 knots) and from what I hear from people that have sailed it is one of the safest and easiest to sail foilers around. And takes off in lighter wind than does the 11' Moth! The direction some new foiler designs are taking- both mono and multi- is to develop easier to sail, much more comfortable foilers that takeoff in light air even if that reduces top end speed.
    ============================
    Response to JB Turner On "Trade Only":
    ===========================================
    I respect JB's accomplishments but I disagree emphatically with his characterization of recreational sailors foiling at 40 knots! That's just not true and a big time exaggeration as well as being uninformed. There are new foilers available to the recreational market that are capable of foiling safely and comfortably in a 5 knot breeze with top speed around 26 knots(Quant 23-the first foiling keelboat). There are very few professional sailors that have ever done 40 knots on foils and there are very few ,if any, boats capable of that kind of speed available to "recreational sailors". Many of the new foilers are designed to be safe and easy to sail.
    The new AC boats are not reflective of the type of foiler available to recreational sailors but few AC boats ever are.
    The foiling revolution is producing exciting new ways to sail and design and development of new foilers is focusing more and more on being able to fly in the lightest wind and on comfort for the crew. There's a lot more to modern foiling for "recreational sailors" than topend speed!
    -----
    PS- I'd like to invite JB to take a look at the discussion going on on boatdesign.net-- https://www.boatdesign.net/...
    and join in -maybe we could discuss this further?
    ===========================================

    Quant 23 foiling in very light air. Note crew positions:
    Quant 23 production boat.jpg
     
    Last edited: Apr 14, 2019
  8. CT 249
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    CT 249 Senior Member

    While on the subject of the Quants, I saw that this modern 23 footer got hammered in a significant series by the old Thompson-designed T780 conventional sportsboat, as did the Quant 30s. I wonder whether the all-round real-world performance of the AC75s will be similar?

    With reference to the piece DCockey quoted; Doug, can I ask how many times you've been foiling at high speed on a monohull? You are such a fanatic that you must be really experienced with modern foiling monos and foiling beach cats by now. So, how many times have you crashed a monofoiler or fast cat, and what happened?

    After all, you post time and time and time and time again about how much fun foiling is, and how addictive it is. Anyone who shows so much passion MUST have spent heaps of time sailing Moths, modern foiling cats and the other boats that write so much about, surely?

    Also, how many times have you sailed a really high-performance course-racing boat, with or without a helmet?
     
    Last edited: Apr 11, 2019
  9. AlexanderSahlin
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    AlexanderSahlin Junior Member

    I thought this was a forum about boat-design and not about the issue wether Doug is wearing a helmet. And I also thought it was open for everybody independently of experience. But now I am not sure if I am qualified. I must admit I have very little experience of sailing more extreme course-racing boats than the International Canoe. My hydrofoiling experience is mostly from the human-powered and engine-powered craft I have designed. I started wearing helmet on the Paravene-Speedsailer after we passed 30 knots. I humbly wish this is OK.
     
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  10. Doug Lord
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    Doug Lord Flight Ready

  11. OzFred
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    OzFred Senior Member

    You call someone who has spent about 35 years in the marine industry, build up a large and successful ship building firm and sailing a variety of boats over decades is "uniformed"? You might disagree with his opinion, but calling him uniformed is plain offensive.

    I think your detachment from reality is demonstrated by presenting a Quant 23 as evidence that the AC75s will not be dangerous or difficult to sail.
     
  12. OzFred
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    OzFred Senior Member

    Thank you for the link. I don't think his statement that "The main foil is designed so that it carries the weight of the boat…" is entirely accurate. The front bulb has the rudder, if it lifts up the boat loses steering so there must be a positive loading on the front bulb that keeps it in contact with the water. From the on–board footage, it's an extremely rough ride which also points to the boat being in contact with the surface, not fully foiling above it. It's impossible to tell from the videos I've seen how much the rear bulb flies or skims, it would be interesting to know how much time it spends flying.
     
  13. Doug Lord
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    Doug Lord Flight Ready

    ====================
    Turner stated that recreational sailors sail at 40 knots which is completely FALSE and that needed to be pointed out. He was ,without a doubt, uninformed to make a statement like that.
    The Quant 23 was not presented "as evidence that the AC75's will not be dangerous or difficult to sail" -far from that it was presented to show the kind of boat some recreational sailors sail and to show the top speed of 26 knots as compared to the quote of recreational sailors at 40 knots. JB Turner is obviously "detached from reality" when making such an absurd statement about recreational sailors coming off the foils at 40 knots! Showing the Quant 23 foiling in light air with the crew obviously relaxing illustrates a design direction now being followed by more and more foilers-the idea being to foil throughout the wind range especially in very light air even at the expense of top-end speed.
     
    Last edited: Apr 12, 2019
  14. OzFred
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    OzFred Senior Member

    Your experimental boats are very interesting, but a paravane is a very different proposition. I don't think canting to leeward is ever helpful for sailing boats, it's just a fact of life for most boats as they can't keep the rig upright.

    The AC75s have very little roll resistance in the hull, they're a balancing act of lowered and raised foils plus sail trim. That also means they'll be able to control the windward/leeward heel of the rig pretty easily using sail and foil controls without canting the rig. And since all the boats will have virtually identical rigs, I think they will want to keep them upright to maximise power. They might heel them to windward slightly to promote foiling in the way a Moth does (which is to ease the sheet to cause the boat to fall to windward, then bear away and sheet on to catch it and use the power to accelerate and get foiling). But I just can't see them sailing the boat consistently heeled to windward.

    But of course I may be completely wrong about that. :)
     

  15. OzFred
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    OzFred Senior Member

    He did not. The article says:

    "Technologically, I think they’re too far out there with foiled monohulls. And for recreational sailors, the foils are dangerous. You come off the foil, and you go from 40 knots to 10. That’s why they have to wear helmets."

    He is talking about the consequences of coming off foils in a large foiler like those used for AC racing, not about recreational sailors in general.

    Thank you for agreeing that the Quant 23 is irrelevant to this discussion.
     
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