Jonas
Well-Known Member
Do they have 'P' and 'S' stamped on them? Or even 'L' & 'R'?
Just realised why all the wife's knickers have 'C&A' on them...
why do (some) people hate bilge/twin keels
- Thread starter dylanwinter
- Start date
Just realised why all the wife's knickers have 'C&A' on them...
AntarcticPilot
Well-Known Member
You must have been well-respected - I thought headlines were the job of sub-editors!
A1Sailor
...
My first two yachts, a Sadler 25 and a Moody336 were both fin keel. I ended up purchasing cradles for both, which tended to determine where I'd store them each winter...
When selecting my current boat, another Sadler25, I set out to purchase either that or a twin keel Sadler26. It just seems so much more practical and flexible - you can do this, for example:
Apart from a "slapping noise" from waves on the windward keel when heeled, I haven't noticed a huge difference in performance.
When selecting my current boat, another Sadler25, I set out to purchase either that or a twin keel Sadler26. It just seems so much more practical and flexible - you can do this, for example:
Apart from a "slapping noise" from waves on the windward keel when heeled, I haven't noticed a huge difference in performance.
Searush
Well-Known Member
probably not much of a change really! 
But yes, the aerofoil curve does need to be on the inside, doesn't it!
Seajet
...
But yes, the aerofoil curve does need to be on the inside, doesn't it!
Searush,
I was going to question that, then realised you're only considering the leeward keel, which I suppose is all one can do.
One factor I've seen some designers of twin keels ( and the odd fin ) apparently ignore is frontal resistance, no point being foil shaped if it's a foot thick !
Also some people seem to be getting their knickers in a twist over twin v bilge keels;
Bilge keels were originally plates to allow a boat with a usually shallow central stub keel to dry out.
Twin keels are purpose designed without a central ballast stub.
Even some 1st generation bilge and twin keel designs had splayed keels, no reason not to as they were wooden boats.
Twin vertical keels came a touch later to make moulding early grp twin keelers possible with encapsulated keels, and be able to get them out of the mould; VicS's Sea Wych being possibly the best known example.
DownWest
Well-Known Member
But yes, the aerofoil curve does need to be on the inside, doesn't it!
Yes, I was a bit puzzled by that. I grew up next to the drawing board of my aeronautic trained father, who went on to design several boats in the 50/60s. Cox Marine asked him to design the 21, but spect twin keels. So he gave them a nice foil section and toed them in a bit. There was also a fin option, which sold a few.
The reasoning being that the angle of heel gives the leeward one a better bite to offset the windward one which is working against it. I helped a bit on that design.
There were plenty of early designs that favoured cheap moulding over performance, which may be the reason for the 'hate' talked about.
Taking the ground does allow more scope and cheaper cruising, just depends on how you go about it.
DW
Seajet
...
In honour of Down West and his Dad, I always thought she looked a good, bullet-proof sort of boat;
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DownWest
Well-Known Member
Humm,
Thick good foils stall less easily, something noticed by the high efficiency fin mob, when their thin high aspect keels get a bit off the 'curve'. Same with rudders.
Many of the popular ply boats had canted bilge keels, but often in steel plate, with no foil shape at all. Cost was important. And windward abilty less worried about as an absolute.
DownWest
Well-Known Member
Hey SJ, Thanks for that!
We had quite a few discussions on the deck layout and ergonomics of the cockpit and the plug was built by the old man at home in Norfolk.
The angular coachroof was to avoid a sliding hatch (cost)
I gather one did a Transat.
DW
Edit: Like the flowery language in the literature. Def not my father's......
We had quite a few discussions on the deck layout and ergonomics of the cockpit and the plug was built by the old man at home in Norfolk.
The angular coachroof was to avoid a sliding hatch (cost)
I gather one did a Transat.
DW
Edit: Like the flowery language in the literature. Def not my father's......
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Seajet
...
DownWest,
as you may have guessed I was the sort of brat who annoyed salesmen at boat shows going aboard everything and collecting brochures.
I saw the Cox 21 at Southampton I'm pretty sure, but my folks didn't and I had a hard time persuading them.
She was high on my list, until we saw an Anderson streak past a friends' boat, that was it !
I've only ever seen the odd one around, thought they deserved more success; maybe there are enclaves of them in different spots around the coast.
Keels look OK too !
as you may have guessed I was the sort of brat who annoyed salesmen at boat shows going aboard everything and collecting brochures.
I saw the Cox 21 at Southampton I'm pretty sure, but my folks didn't and I had a hard time persuading them.
She was high on my list, until we saw an Anderson streak past a friends' boat, that was it !
I've only ever seen the odd one around, thought they deserved more success; maybe there are enclaves of them in different spots around the coast.
Keels look OK too !
DownWest
Well-Known Member
Yes, I used to be on our stand at EC in the early days. Saw a lot like you with bulging bags of brochures (wonderwhat they did with them?) Peeps were of various types: Yours... then the ones that already had one of our boats and wanted to talk about it. The tyre kickers and.. the very few that actually were interested in buying. Father gave it up in the end. The cost never outweighed the result. Except.. if you weren't there, people assumed you had dropped off the edge. But, other advertising was more effective.
Thanks for the feedback, BUT this thread is about keels...so I will drift off.....
OGITD
Well-Known Member
I’m so glad ….. but!
I’m so glad that people haven’t forgotten the explanation and diagram from (RT) about the reduced drag, and therefore the less likelihood of being rolled in a twin-keel boat.
Also the fact that some are designed with splayed keels and incorporating an aerofoil design / casting (which mine have,) (flat inside, curved outside.)
Plus the fact that they can ‘take the ground’ and therefore offer more opportunities in small coastal harbours etc.
But! …. I can’t honestly say which way they are toed & by how much ….. so it’s out with the measure as she’s being lifted out tomorrow.
OG.
I’m so glad that people haven’t forgotten the explanation and diagram from (RT) about the reduced drag, and therefore the less likelihood of being rolled in a twin-keel boat.
Also the fact that some are designed with splayed keels and incorporating an aerofoil design / casting (which mine have,) (flat inside, curved outside.)
Plus the fact that they can ‘take the ground’ and therefore offer more opportunities in small coastal harbours etc.
But! …. I can’t honestly say which way they are toed & by how much ….. so it’s out with the measure as she’s being lifted out tomorrow.
OG.
dgadee
Well-Known Member
I never did either - looked at various deep keelers when I was looking to buy but changed mind during search and now very happy with a Seawolf 30. Sails very well indeed.
DownWest
Well-Known Member
I’m so glad that people haven’t forgotten the explanation and diagram from (RT) about the reduced drag, and therefore the less likelihood of being rolled in a twin-keel boat.
Also the fact that some are designed with splayed keels and incorporating an aerofoil design / casting (which mine have,) (flat inside, curved outside.)
Plus the fact that they can ‘take the ground’ and therefore offer more opportunities in small coastal harbours etc.
But! …. I can’t honestly say which way they are toed & by how much ….. so it’s out with the measure as she’s being lifted out tomorrow.
OG.[/QUOTE
A simple aerofoil has a flat underside and a curved topside. The highest point of the curve is around 1/3 back from the front edge. The lifting effect is caused by the differing speeds of the airflow over the two surfaces. It lifts towards the curved side, so if you are expecting the lee keel to do the lifting, the curve needs to be on the inner side.
In reality, the section would be similar on both sides, just tilted (toed in) to the centre line.
DW
OGITD
Well-Known Member
Hang on a mo!
Surely …. If the curve on the leeward keel is on the outside, then it is trying to right the boat and counter the force of the wind on the sails pushing her over, and as leeward is deeper than windward there is more pressure and therefore more force?
Surely …. If the curve on the leeward keel is on the outside, then it is trying to right the boat and counter the force of the wind on the sails pushing her over, and as leeward is deeper than windward there is more pressure and therefore more force?
mikeinkwazi
Well-Known Member
Surely …. If the curve on the leeward keel is on the outside, then it is trying to right the boat and counter the force of the wind on the sails pushing her over, and as leeward is deeper than windward there is more pressure and therefore more force?
No that is not the case. Think of a the wing on a glider, the curved bit is on the top. As the the glider moves forward and toward ground (to leaward) the wing generates lift. So in a boat the curved side of an asymetrical foil (keel) is on the inside in the case of twin keels
OGITD
Well-Known Member
I accept the curved side creates / generates lift .... but!
I'm off for a good look tomorrow! 
As I think you might be right! & it's curved on the inside!
I'm off for a good look tomorrow!
As I think you might be right! & it's curved on the inside!
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CAPTAIN FANTASTIC
Well-Known Member
Over the years, I have owned and sailed all type of keel configurations; the twin keels is a compromise which suits me and I enjoy to sail.
Most people hate them because they can not sail them. To make a twin keeler to sail well, you need to know how to trim the sails and balance the boat. In addition, the twin keelers have the advantage of going where others can not; low cost moorings; sail upright; dry out upright (very convenient in the boat yard)
Most people hate them because they can not sail them. To make a twin keeler to sail well, you need to know how to trim the sails and balance the boat. In addition, the twin keelers have the advantage of going where others can not; low cost moorings; sail upright; dry out upright (very convenient in the boat yard)
dylanwinter
Well-Known Member
I will remember that
great response
I shall remember that
you need to be a better sailor
Dylan
great response
I shall remember that
you need to be a better sailor
Dylan
Seajet
...
I think I have a fair idea how to sail and trim a boat, but it proved impossible to get decent 'feedback & feel' with a late model Centaur even when we tried various trim tabs, fences, sections and vortex generators; good luck getting any 'feel' on the helm of a MacWester !
Then again I was utterly spoilt by things like Scorpion & Osprey dinghies and the Anderson, when we came in alongside a club member once under sail at dead low speed the Macwester owner - a pro airline pilot - couldn't believe our low speed feel and control authority.