CA1263926A - Keel structures for sailing vessels - Google Patents

Abstract

ABSTRACT

KEEL STRUCTURES FOR SAILING: VESSELS

A tandem keel structure (12) for a sailing vessel such as a yacht (10) comprises a main keel (14). A bridge (16) extends forwardly from the foot of the main keel (14) and a forward foil (18) is attached between the forward end of the bridge (16) and the hull of the yacht. The forward foil (18) is separated from the main keel or foil (14) by a slot (20).

Description

~:6 KEEL STRUCTURES FOR SAILING VESSELS

This inven-tion rela-tes to keel structures for sailing vessels, for example, sailing yachts.
According to one aspect of the present invention there is provided a keel structure for a sailing vessel, said keel structure comprising a fixed main keel having a foot and a bridye extending forward:Ly from sai~ foot, said bridge having a forward end9 and a forwar~l foil adapted to be mounted between the underside of the vessel and said forward end of said bridge, said main keel and said forward foil when in use of said keel structure having a high pressure side and a low pressure side, said forward foil being disposed forwardly of and in tandem with said main keel to define with said main keel slot means which during use of said keel structure causes water to be accelerated through said slot means from the high pressure side of said forward foil to the low pressure side of said main keel, said forward foil being smaller than said main keel.
According to a further aspect of the present invention there is proviaed a sailing vessel having a keel structure in accordance with said one aspect of the invention.
~ A keel structure in accordance with the present invention, in which a forward foil is disposed forwardly of the main keelj provides weed deflection, which in turn allows increased flexibility as regards the shape of the main keel, which can enable improvement in the hydro-dynamic efficiency and/or righting moment of the main keel.
; 30 ~ The invention will now be further descri~ed, by way of illustrative and non-limiting example, with reference to the accompanying drawings, in which like references indicate like items throughout and in which shaded areas indicate trimmable sections or;surfaces which can be adjusted while sa11ing. In the drawings:

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la Figure 1 is a side view of a sailing yacht fitted with a tandem keel structure embodying the invention;
Figure 2 is a diagrammatic view from above illustrating a slot effect that can take place between forward and main foils or keels of the keel structure, whereby the flow between the foils is accelerated;
Figure 3 is an enlarged side view of a tandem keel structure embodying the invention in which the main foil does not possess sufficient sweepback at the 1.eadinq edge to deflect weed effectively, such deflection being supplied in part by the orward foil;
Figure 4 is an enlarged sidè view of a tandem keel structure embodying the invention in which a strong degree of forward sweep is incorpora-ted in the leading edge of the main foil, weed deflection being provided by the forward foil;

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Figure 5 is an enlarged side view of a tandem keel struc-ture embodying the invention in which the forward foil i5 articulated at upper and lower joints thereof to provide a trimmable surface capable of varying the flow over the main foil;
Figure 6 is an enlarged side view of a tandem keel structure embodying the invention having a trimmable forward foil which is sufficiently powerful to act as a rudder, obviating the need for a separate stem rudder;
Figure 7 is an enlarged side view of a tandem keel structure embodying the invention in which a trim tab has been incorporated in the aft section of the main foil;
Figure 8 is an enlarged side view of a tandem keel structure embodying the invention in which a trimmable section on the rear foil is sufficiently powerful to act as a rudder, obviating the need for a separate stem rudder;
Figure 9 is an enlarged side view of a tandem keel structure embodying the invention in which both the ~forward foil and the aftermost section of the rear foil are trimmable;
Figure 10 i5 an enlarged side view of a tandem keel structure embodying the invention in which both a trimmable forward foil and an aftermost rear foil section can be used, independently or in conjunction, to steer the boat, obviating the need for a separate stem rudder;
Figure 11 is a diagrammatic view from above of a tandem keel as illustrated in Figure 10, with control surfaces shown deflected to steer the boat to port; and Figure 12 is an enlarged side view of a tandem keel structure embodying the invention in which a rear trim tab or rudder is joined at the base to, but separated by a slot from, the main foil.

~3~6 2a Figure 1 shows a sailing yacht 10 fitted with a tandem keel structure 12 comprising a non~movable main or rear keel or hydrodynamic foil 14 having a bridge 16 extending forwardly from its foot, and a se~_ond keel or hydrodynamic foil 18 which is fitted between the underneath of the hull of the yacht 13 and the forward end of the bridge 16 so as to be disposed forwardly of and in tandem with the main foil 14 with a slot 20 being defined between the foils.
Preferably, but not essentially~ the second or forward foil 18 is smaller than the non-movable main foil 14, such forward foil 18 preferably having chord length which is less than half the average chord length of the non-movable section of the main foil 14 as illustrated in the drawings. In r lation to each of the forward foil 18 and the main foil 14 the chord is, of course, the straight line between the leading and trailing edges of the foil. Also, the slot 20 is generally V-shape, such slot having a longer chord length at the root (top) than at the tip (bottom), such longer chord length as well as the average ~hord length of the slot 20 being less than the average chord length of the non-movable section of the main foil 14 as shown.

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~2i~ 6 When the ~andem k~el otru~turc l? Is tmder lo~d ~or ~xample, whlle the yacht 10 ~alls to windw~rd), ~ bl~ne~icla5 ~iot effect dev~iops In the ~lot 2D betwe~n the folls 14, 18 wch that ~ l~low nf w~ter 1~ ee~elerate~ thraugh the ~lot 20 ~nd over the windward ~ide ~f the reEIr foll 14, Irnproving the 'lift' of the reer foll 14, I.e. c foree tending to move the foll 14 to windward.
More speclfic~lly, as shown in Flgure 2, In whlEh an arr~w W Indieates the wind direction, Q w~ter ~low denot~d by ~n ~rrow A i8 sub~e~ted to ~oce1eration through ehe slot 20 ~ the water passes from the high pressure side ~f the forward foil 18 tD the low pressure side o~ the re~r foU 14, ~- 10 tller2by ~cceler~ting flow over the windward side c~f the rear ~oil (main keel) l4 and thus Jn turn increasing the lift (repre3ented by en arrow L) generated ~y the keel 14 to windwerd, thereby oounteractirlg leeway and providing a reductisn in the overa~l drag caused by the hull in motion.
The Illu~trated ~orward foi3 ~ ~nd r.ear or .main- foi l. _conflgur~tion is highly resistant to stall, in a manner which ~t is believed may be somewhat analogous to the Ytall resistance exhibited by closely coupled canard/main wing configurations to be found in severe~l types o~ modern combat aircrsft.
At or near stall, the forward foil lB ensures flow over the low-pressure side of the main or re~r foil 14. The resulting st~ resistanoe is important during tacking manoeuvres, in particular immediately sfter the tack, when way has fallen nff, the leeway ~ngle is increased, and the lFlow may thuls becnme partially or wholly detached from the foil. The improved resist~nce to stal~
of such a tandem configuration thu~ tends to improve aco~leration after the tack, which is an import~nt p~tential advantags in comp~titive racing.
The forward foil 18, which has ~ swept back leading ~dge ~nd projects forwardly of the forward end of the bridge 16, permits considerable variation in shape of the rear foil 14, while the tandem keel structure 12 85 a wh~le maintains useful weed-deflecting properties. Structurslly, a wide variation in the sweep ~ngle of the leading edge olF the re~r foil 14 becomes possible, ~s does a greater degrce olF inverse taper for eny given sweep-back angle o~ the ~ai~ing edge o~ the rear foil 14. (Recent research on 12-metre kee~s has indicated the possible benefits of invers~ tap~r in shifting the centre of effort of the keel away from the free air^water ~ur~ace, and in permitting ~Iso a lower centre of gravity for ~ given weight o~ keel).
The main or reer fo}l 14 may incorporste wch various fe~tures as redueed b~cksweep on the leading edge, ~ near vertic~l or v~rties31 leading 4 ~

edge, a forward swept or strongly forward swept leadlng edge, and may be so shaped as to incorporate reduced taper, no taper, inverse taper, or substantial inverse taper. This freedom to select the required shape of the main keel or foil 14 can enable improvement in its hydrodynamic efficiency and/or righting moment. For example, the righting moment may be increased by so shaping the keel 14 that its centre of gravity is lowered.
The forward foil 18 may also be of a variety of shapes.
Figure 3 shows, by way of example, a tandem keel structure in which the leading edge of the rear or main foil or keel 14 is near vertical and therefore does not possess sufficient sweepback at the leading edge to deflect weed effectively. However, such a configuration can be used since weed deflection is provided b~ the forward foil or keel 18. Further, Figure 4 sh.ows a structure in which the leading edge of the main foil or keel 14 is strongly swept forward. In a conventional keel structure, a strong degree of sweepforward at the leading edge (say more than 15) is undesirable, because the keel tends to gather weed, detritus lobster pots and so forth, which can reduce performance, and can even be dangerous in the event, for example, of fouling a mooring rope or chain. The deflection action of the forward foil 18, whose leading edge is swept back, enables the use of a swept forward main foil 14 ~which can be advantageous as regards improved hydrodynamic efficiency and stall-resistance) with relative safety.
Figure 5 shows a keel structure 12 in which the forward foil 18 is movable or trimmable about an axis 22 extending between the underside of the vessel and the briage ky means of joints at its upper and lower connection -points to the hull and bridge 16, respectively, which permits varying control both of the 'slot effect' between the forward and rear foils 14, 18 and flow over the rear foil 14. If sufficiently powerful, by virtue of size or placement or both, e.g. if positioned forward of the centre of effort, such a forward foil 18 also has 4A ~2 ~3~2 6 potential steering properties which may in turn obviate the need for the yacht 10 to have a rear or s-tern rudder:
see Figure 6.
~he improved attachment of flow to -the low-pressure side of -the rear or main foil 14 also enhances flow at-tachment to surfaces of a trimmable or movable member 24 (trim tab or rudder) which may be incorporated in the rear section oE the main foil 14 so as to be rnovable about an articula-tion join-t defining an axis 26 at the forward end of the movable member 24 extending generally perpendicular to the underside of the vessel: see Figure 7.
Improved flow attachmen-t on such surfaces upgrades -their efficiency with respect to windward lift or boat ~3~

directlon eontr~l for ~ g~Yen dra~ p~nalty. If the rrember 2418 8ullt'1cl2ntly powerful (see Flgure 8), by virtue ~ ~iz~ or plaof~ment or both, It m~y be used Ir) place of a reE~r ar ~tem rudder.
~FIgure 9 ~h~iWs e tnndem keel structure incorporating both a trimmahie forwsrd foll 18 (~s In Flgure~ ~ end 6~ ~nd ~ trlmm~ble m~mber 24 et the r~r of the m~in foil 14 ~as In F~gure~ 7 ~nd 8~o Ths intera~tlon between the ~orward trimm~ble foil 1~ ~nâ the reaF trlmmabl~ ~eotion ~t, the main fviI 14 ~s complex, but must be b~ed in l~rg~ p~rt on tIle observation that, ~s the defIect~on ~1~ the re~r trim t~b or ~eetion 24 increas~s, ao the upwa~h generat~d by the rn~in foi~ iners~s 143 ~nci thus in turn the angle of aLt~ck of the forwsrd f~il 18 (whioh Inhabits the orea of upwash caused by the main foil) is increased. ~rimming of the ~orward ~oil 18 ~nder such circumstances would consi~t of experim~nting with trim angles for ~iven settings of the rear trim tab 24 in order to discover optimum lift-drag ratios.
The overall adv~ntage of ~uch configurations is that by trimming the movable sections l:o form a lilFting shape which is more efficient than 8 non-mvvable keel9 the size ~nd weteed ~ea of the kee~ 23s ~ whole ~an be reduced9 in tum reducing the overall drag relative to ~ iFixed kee3.
Forwsrd and rear control surf~es constituted by the trirnmable forward fnil 18 and the rnember 24 can be used in conjunction tD ~eer the boat: ses Figure 10. Figure 11 is a view from above of the keel ~truoture of Figure 10 which shows how the boat may be steered by trimming the ~orward foil 18 and the rear section 24 of the main foil 14 to produ~e a rotating moment sbout a centre of effort E located in the fixed s0ction 14.
Force produced by the forward ~oil 18 is denoted by ~n arrow F, ~nd force pruduoed by the rear section 24 of the main ~il 14 i~ dænoked ~y an arrow R. Figure 11 3ilOWS the two oontrol surfaoes de~le~ted to tum the boat to port. To tum to starboard, the respective de~leotions ~ræ rever~ed.
Figu~e 12 ~hows ~other form of the tandem k~2) struct~e 12 in which ~n ~dditlon~l ~epsration or slot 28 i8 formed b~t~veen a ~ar trimmable ~oil 24 and the rnain flxed foil 14.
The invention can of course be imp3emene~d In oth~r wsys th~n tho~e described above by way of ex~mple. For in~tance~ ~ny t3~ndem ke~l ~tructur~
~s di~clo~ed ab~ve~ which incolporate~ In the Ibase o~ one or both ~oils a b~slb, endplate or hydrodyn~mic winglets, w131, bec~use of the tand~m ~oil ~mflguration of 1~ vert3cal ~urf~es~ ~ail wlthln the II~ICDp~ ol~ the,~ olalrn~-~3~2 Fur~hermore, ~ny k2el whl~h~ In ~ddltlon to the tend~m 1~ol3 configur~lon e~ outlin~d ~bov~, In~orpor~t~s ~ furth~r foll or foll3 In such a msnner ~ th~t all ~olla~ whether ~Ix~d or rnovable, ere )oln~ t Ithe b~ by e bridge, ~ 8D will tl9ll withln th~ ~cope of th~ clE~im~.

Claims (18)

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. A keel structure for a sailing vessel, said keel structure comprising a fixed main keel including a non-movable section having a foot and a bridge extending forwardly from said foot, said bridge having a forward end, and a forward foil adapted to be mounted between the underside of the vessel and said forward end of said bridge, said main keel and said forward foil when in use of said keel structure having a high pressure side and a low pressure side, said non-movable section of said main keel having an average chord length, said forward foil being disposed forwardly of and in tandem with said main keel an average distance less than the average chord length of said non-movable section of said main keel to provide a relatively close coupling of said forward foil to said main keel to define with said main keel slot means which during use of said keel structure causes water to be accelerated through said slot means from the high pressure side of said forward foil to the low pressure side of said main keel to increase the lift acting on said main keel, said forward foil being smaller than said non-movable section of said main keel.

2. The keel structure of claim 1 wherein said forward foil has a leading edge that is swept rearward, and said main keel has a leading edge which is closest to said forward foil that is swept forward.

3. A keel structure for a sailing vessel, said keel structure comprising a fixed main keel including a non-movable section having a foot and a bridge extending forwardly from said foot, said bridge having a forward end, and a forward foil adapted to be mounted between the underside of the vessel and said forward end of said bridge, said main keel and said forward foil when in use of said keel structure having a high pressure side and a low pressure side, said forward foil being disposed forward of and in tandem with said main keel to define with said main keel slot means which during use of said keel structure causes water to be accelerated through said slot means from the high pressure side of said forward foil to the low pressure side of said main keel to increase the lift acting on said main keel, said forward foil being smaller than said non-movable section of said main keel, and means for mounting said forward foil between the underside of the vessel and said bridge for movement of said forward foil in its entirety about an axis generally perpendicular to the underside of the vessel.

4. The keel structure of claim 3 wherein said forward foil acts as a forward rudder, obviating any need for the vessel to have a separate stern rudder.

5. The keel structure of claim 1 wherein said main keel has a rear section that is movable relative to said non-movable section by means of an articulation joint between said rear section and said non-movable section.

6. The keel structure of claim 5 wherein said articulation joint has an axis generally perpendicular to the underside of the vessel.

7. The keel structure of claim 5 wherein said rear section of said main keel acts as a rudder, obviating any need for the vessel to have a separate stern rudder.

8. A keel structure for a sailing vessel, said keel structure comprising a fixed main keel including a non-movable section having a foot and a bridge extending forwardly from said foot, said bridge having a forward end, and a forward foil adapted to be mounted between the underside of the vessel and said forward end of said bridge, said main keel and said forward foil when in use of said keel structure having a high pressure side and a low pressure side, said forward foil being disposed forwardly of and in tandem with said main keel to define with said main keel slot means which during use of said keel structure causes water to be accelerated through said slot means from the high pressure side of said forward foil to the low pressure side of said main keel to increase the lift acting on said main keel, said forward foil being smaller than said non movable section of said main keel, said main keel having a rear section that is movable relative to said non-movable section by means of an articulation joint between said rear section and said non-movable section, said forward being movable in its entirety by means of an articulation joint between said forward foil and said bridge and the underside of the vessel.

9. The keel structure of claim 8 in which said forward foil and said rear section of said main keel are sufficiently powerful to be used to steer the vessel, thus obviating any need for the vessel to have a separate stern rudder.

10. The keel structure of claim 1 wherein said forward foil has an average chord length which is substantially less than the average chord length of said non-movable section of said main keel.

11. The keel structure of claim 10 wherein the average chord length of said forward foil is less than half of the average chord length of said non-movable section of said main keel.

12. The keel structure of claim 1 wherein said slot means is generally V-shape having a longer chord length at the top than at the bottom, said longer chord length of said slot means being less than the average chord length of said non-movable section of said main keel.

13. The keel structure of claim 1 further comprising at least one further foil joined to the base of said main keel.

14. The keel structure of claim 13 wherein said further foil is fixed.

15. The keel structure of claim 13 wherein said further foil is movable.

16. A sailing vessel having a keel structure as claimed in claim 1.

17. The keel structure of claim 1 wherein said non-movable section of said fixed main keel comprises a single member.

18. The keel structure of claim 1 wherein said non-movable section of said fixed main keel is imperforate.