Csail
N/A
Why don't yachts have them on the keel to increase stability?
Ailerons
- Thread starter Csail
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AngusMcDoon
Well-Known Member
Too much of a faff to antifoul.
snooks
Well-Known Member
At a guess, an aircraft is traveling through a liquid (air) and a yacht is traveling on a liquid water, and is subjected to all manner of different movements from the water surface
Proly why you see horizontal fins on subs and not on yachts
I can't see that two fins either side of the keel blade would be in the right place either. Surely they would have to extend horizontally from the line a yacht pivots on it's fore/aft axis?
Proly why you see horizontal fins on subs and not on yachts
I can't see that two fins either side of the keel blade would be in the right place either. Surely they would have to extend horizontally from the line a yacht pivots on it's fore/aft axis?
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prv
Well-Known Member
I think a handful of racing yachts might do. Sure I've seen adjustable flaps on the aft edge of the keel (that aren't the rudder!)
Pete
Pete
snooks
Well-Known Member
Those are trim tabs and act like the flaps on an aircraft wing to add shape (increasing the effective draft of the aerofoil section) and therefore lift to the keel, they're not for stability.
Poignard
Well-Known Member
Something like the stabilisers fitted to passenger ships?
They are fine as long as they don't go wrong! A ship I was engineeer on developed an unforeseen electronic fault with the system and, instead of stabilising the ship, it did its best to capsize it.
EBoat126
Well-Known Member
Americas Cup yachts had trim tabs on the rear edge of the keel, a couple also dabbled with a fore rudder towards the bow.
Foiling dinghies (Moths) have horizontal trip tabs on main and rudder foils to control 'altitude' of flight. Main one controlled automatically by a 'wand' at the bow and the rudder tab controlled by a twisting tiller.
Foiling dinghies (Moths) have horizontal trip tabs on main and rudder foils to control 'altitude' of flight. Main one controlled automatically by a 'wand' at the bow and the rudder tab controlled by a twisting tiller.
Signed Out
Well-Known Member
Could the answer be anything to do weight, by any chance? Not something that aircraft wings make use of.
I have though, seen designs in the past where there was a small trimmable appendage below the bulb on a deep racing keel, as well as trim tabs on trailing edges.
I even think somewhere I once saw a design of a keel, or at least foil, with a certain level of controllable rotational flex- the end could twist. Can't recall where though, or if it was in a dream/flight of fancy.
Also recollect adjustable wings on a keel, which could've been an AC boat (12m I suspect).
I have though, seen designs in the past where there was a small trimmable appendage below the bulb on a deep racing keel, as well as trim tabs on trailing edges.
I even think somewhere I once saw a design of a keel, or at least foil, with a certain level of controllable rotational flex- the end could twist. Can't recall where though, or if it was in a dream/flight of fancy.
Also recollect adjustable wings on a keel, which could've been an AC boat (12m I suspect).
Twister_Ken
Well-Known Member
One or two of the development dinghy classes played with 'tackable' dagger boards which could be rotated a degree or three to windward on the beat, to try and improve pointing. Dunno what happened and whether they're still out there - lost interest in racing dinghies a long while back.
Skysail
Well-Known Member
It's a long time since studying aerodynamics, but IIRC ailerons are control surfaces. They do not increase stability - that's provided by wing shape, dihedral, the fin, etc
Ubergeekian
Well-Known Member
I presume he means reducing roll of the boat, rather than dynamic stability. In theory you could put an aileron on the trailing edge of the keel to vary the lift produced, but it would also produce a turning moment which would require rudder correction. Lots of extra drag!
Resolution
Well-Known Member
Lots of the bigger motorboats have them and I am told they can be extremely effective in reducing roll.
jimbaerselman
Well-Known Member
I'm unsure what purpose the OP has in mind for ailerons. Roll damping? Extra keel lift? Less leeway?
A way to reduce the amount of rolling on a sail boat is to use a gyro activated fin to oppose the rolling moment caused by waves (or rudder use!). The optimum position is radially as far from the centre of gravity of the boat as possible. The keel, or a twisting piece added to the end of the keel, would do nicely.
To prevent a turning moment being created, the position of this "rolleron" fore and aft would have to be aligned with the C of G.
I don't think I'd like one of these on my boat. Too vulnerable. I spend too much time aground. Not always intentionally, either.
A way to reduce the amount of rolling on a sail boat is to use a gyro activated fin to oppose the rolling moment caused by waves (or rudder use!). The optimum position is radially as far from the centre of gravity of the boat as possible. The keel, or a twisting piece added to the end of the keel, would do nicely.
To prevent a turning moment being created, the position of this "rolleron" fore and aft would have to be aligned with the C of G.
I don't think I'd like one of these on my boat. Too vulnerable. I spend too much time aground. Not always intentionally, either.
Ceirwan
Well-Known Member
At a guess, an aircraft is traveling through a liquid (air) and a yacht is traveling on a liquid water, and is subjected to all manner of different movements from the water surface
Proly why you see horizontal fins on subs and not on yachts
I can't see that two fins either side of the keel blade would be in the right place either. Surely they would have to extend horizontally from the line a yacht pivots on it's fore/aft axis?
Don't mean to be anal, but air is a gas not a liquid
(well a lot of different gasses) I'd have though that any aileron on the back of the keel would produce a turning moment on the boat that would need to be counteracted by the rudder, hence more drag?
noelex
Well-Known Member
Good idea
I presume you would mount them on a short wing a right angles to the keel. The ailerons could then "bank" the yacht helping to counteract the heel.
I think the trouble would be that with a short lever arm you would have to generate a lot of force. Lots of force equals lots of drag.
I presume you would mount them on a short wing a right angles to the keel. The ailerons could then "bank" the yacht helping to counteract the heel.
I think the trouble would be that with a short lever arm you would have to generate a lot of force. Lots of force equals lots of drag.
tinkicker0
Well-Known Member
Yup drag. Any force exerted on a fluid in order to gain an equal and opposite reaction will result in induced drag.
Form drag will also be a great factor, specially if you have barnacles or weeds growing on your underwater fins.
Form drag will also be a great factor, specially if you have barnacles or weeds growing on your underwater fins.
gardenshed
Well-Known Member
Trim tabs were fitted most of the "modern" 12meters i.e. from around the time of "Intrepid" in 1967.
If you look at photos of these 12's you'll see a second wheel inside the main wheel and this adjusted the trim tab. Too much and the drag outweighted the benefit of increasing the lift generated from the keel to reduce leeway. Reducing leeway was the aim, not increasing stiffness, i.e. generating more righting moment.
Very early IOR boats experimented with trim tabs but this was outlawed by the rating rule so as a result, mainstream cruiser racers didn't develop them and most rating rules have a moveable appendages clause that only allows one moveable appendage under the hull. Canting keels are a different concept and typically, a canting keel boat has swings ballast (the bulb) up to windward to increase rigting moment (stiffness) and then uses dagger boards to reduce leeway (VOR 70's, Open 60's etc)
Some of the last 12's used canards (forward rudders) but this has never caught on in other boats/classes mainly due to the complexity of the linkage/mechanism and the weight in the bow of the boat that can contribute to pitching moment.
Other "wings" etc fitted to bulbs (americas cup last generation monohulls) didn't move and are fitted to control/reduce tip vortices in a concept to the wingtips at the end of an airbus, 747 400 or other modern aircraft wing.
If you look at photos of these 12's you'll see a second wheel inside the main wheel and this adjusted the trim tab. Too much and the drag outweighted the benefit of increasing the lift generated from the keel to reduce leeway. Reducing leeway was the aim, not increasing stiffness, i.e. generating more righting moment.
Very early IOR boats experimented with trim tabs but this was outlawed by the rating rule so as a result, mainstream cruiser racers didn't develop them and most rating rules have a moveable appendages clause that only allows one moveable appendage under the hull. Canting keels are a different concept and typically, a canting keel boat has swings ballast (the bulb) up to windward to increase rigting moment (stiffness) and then uses dagger boards to reduce leeway (VOR 70's, Open 60's etc)
Some of the last 12's used canards (forward rudders) but this has never caught on in other boats/classes mainly due to the complexity of the linkage/mechanism and the weight in the bow of the boat that can contribute to pitching moment.
Other "wings" etc fitted to bulbs (americas cup last generation monohulls) didn't move and are fitted to control/reduce tip vortices in a concept to the wingtips at the end of an airbus, 747 400 or other modern aircraft wing.
noelex
Well-Known Member
Trim tabs would analogous to flaps on an aircraft. Ailerons are quite different.
boguing
Well-Known Member
Snooks' use of the term 'liquid' when he actually meant 'fluid' is pretty good for a layman. Leave the boy alone!
Having read his account of his Northern cruise, I'm more interested in the liquids consumed. Did he visit Tallisker? Which was his favourite? Did his brief stop on Arran allow a trip to the Araan distillery. (Very fine).
snooks
Well-Known Member
Liquid/fluid I knew what I meant.
Distillery wise we did Lagavuin which was the best tour we did, we also visited Laphroig and Ben Nevis but didn't do a tour. But we did do tours of , Highland Park, Oban and Arran. Old Pultney was closed, and we went to Lossiemouth to visit Speyside, but had to leaven a weather window so we didn't make it. But for my final project I did a photographic essay on the production of whisky in Speyside. 12 distilleries in 8 days!
