What's the fascination with long keels?

[RobbieW]

Stability

On a more serious note, one of the aspects of yacht design that this thread seems to highlight is that of stability. I strongly suspect that yachts which rely more on 'ballast' stability than on 'form' stability are the ones which are going to give a more comfortable ride in a seaway. Those are generally exemplified by the sorts of boat that have been described - Malos, Westerlies, Swans, Nics, Vancouvers etc.

One downside I find is that such boats often heel quickly in not a lot of wind but then stay at 15-20 degrees for the rest of the day. When you've been selling the stability of the boat to a novice, the sudden heeling can be a little shocking. Mostly they get used to it though

 

[Robin]

Who would really want to spend days on end heeled at 20 degrees? How about multihulls? Rolling down the tradewinds in a pendulum holder wouldn't appeal to me at all, let alone going upwind, or what passes for upwind in some boats, whilst needing one leg 2ft longer than the other. Nothing wrong with form stability, the idea that heavy and deep gives stability was disproved after the 1979 Fastnet when tank tests proved that boats are rolled by waves and not wind pressure and that any boat will roll if the wave is 'right'.

 

[Conachair]

Who would really want to spend days on end heeled at 20 degrees? How about multihulls? Rolling down the tradewinds in a pendulum holder wouldn't appeal to me at all, let alone going upwind, or what passes for upwind in some boats, whilst needing one leg 2ft longer than the other. Nothing wrong with form stability, the idea that heavy and deep gives stability was disproved after the 1979 Fastnet when tank tests proved that boats are rolled by waves and not wind pressure and that any boat will roll if the wave is 'right'.

A bit more fuel

http://www.landlpardey.com/monohull...ly-opinionated-round-up-of-pros-and-cons.html



If you're thinking upwind then sack the route planner. Though agree with rolling. A quick look at the log always confirms that the memory of rolling is often much less than the reality. But even with that, a close to perfect bluewater boat would be a tough as nails monohull which magically sprouted an extra hull just as the anchor dug in

 

[Blueboatman]

Pot still boiling...
Dear ol Shane Acton in his tiny bilgekeel Caprice was one of the first who I read to state on paper that wee shallow draft bilgekeelers are the LEAST likely type to be rolled( along with catamarans) because they simply slide sideways with the breaking crests.
And I can confirm from personal experience that a wee bilgekeeler running in the trades rolls as nothing compared to a long or fin keeler.
And, in mine own case I had junk rig which by dint of all it's weight aloft, can be raised or lowered by one 'reef' to noticeably affect the roll moment...
I trust that has muddied the waters a bit.
Btw I used to clock up 100miles a day on a 'teenager' sized waterline

 

[Babylon]

Long fin keel, deep bilges, Spade rudder with 3" SS Shaft, Narrow and deep with low windage and encapsulated keel. All bunks are on water level.

Fin keels can be very sensible. Most high production ones are built to be cheap and good in light conditions, when most people do most of their sailing.

What is it?

 

[Wansworth]

Excalibure 36 Van de stat built by Sothern Ocean Shipyards .....Poole?

 

[RobbieW]

What is it?

The file name, excalibur_36_drawing.jpg, might be a clue

 

[RobbieW]

Nothing wrong with form stability, the idea that heavy and deep gives stability was disproved after the 1979 Fastnet when tank tests proved that boats are rolled by waves and not wind pressure and that any boat will roll if the wave is 'right'.

I wasnt conciously trying to argue that ballast stability was inherently more stable than form - however I think in a roll-over situation a boat with high ballast stability will right more easily than one with high form stability.

 

[Kukri]

Who would really want to spend days on end heeled at 20 degrees? How about multihulls? Rolling down the tradewinds in a pendulum holder wouldn't appeal to me at all, let alone going upwind, or what passes for upwind in some boats, whilst needing one leg 2ft longer than the other. Nothing wrong with form stability, the idea that heavy and deep gives stability was disproved after the 1979 Fastnet when tank tests proved that boats are rolled by waves and not wind pressure and that any boat will roll if the wave is 'right'.

That is not quite what Tony Marchaj says in "Seaworthiness". At least, not in my copy. Yes any boat can be rolled but that's only a small part of the story. Another part concerns recovery to the upright position after the boat is rolled...which is very much more likely with a "lead mine".

Marchaj also points out the considerable damping effect of a long keel...

 

[john_morris_uk]

Excalibure 36 Van de stat built by Sothern Ocean Shipyards .....Poole?

I was trying to remember the make as another example to the ones I had already given. Bit embarrassing as a very good friend owns and sails one and we have sailed on company with him and his family over several years. His has already been round the atlantic twice. There are issues; his daughter really doesn't like sailing it as the cockpit is so low and the waves appear as if they are going to swamp the boat. They aren't but she really prefers our boat with its higher centre cockpit...

 

[Robin]

I wasnt conciously trying to argue that ballast stability was inherently more stable than form - however I think in a roll-over situation a boat with high ballast stability will right more easily than one with high form stability.

Yes and no. The determining factor I think is the upside down shape and buoyancy, wide and flat flush deck is very stable upside down, wide with a raised coachroof and so on is not. The important thing is not to get upside down in the first place!

 

[Robin]

That is not quite what Tony Marchaj says in "Seaworthiness". At least, not in my copy. Yes any boat can be rolled but that's only a small part of the story. Another part concerns recovery to the upright position after the boat is rolled...which is very much more likely with a "lead mine".

Marchaj also points out the considerable damping effect of a long keel...

See previous reply. I think that the topsides shape which forms the underwater shape if inverted determines the ability to self right quickly, it needs to be unbalanced enough to get the keel to an angle where it then levers things over, if that makes sense. The lead mine bit I think too is a bit misleading, because modern fins are deeper and often have bulbous bottoms so that the effective righting moment is just as great as it is on a shallower but heavier long keel.

 

[Sybarite]

Who would really want to spend days on end heeled at 20 degrees? How about multihulls? Rolling down the tradewinds in a pendulum holder wouldn't appeal to me at all, let alone going upwind, or what passes for upwind in some boats, whilst needing one leg 2ft longer than the other. Nothing wrong with form stability, the idea that heavy and deep gives stability was disproved after the 1979 Fastnet when tank tests proved that boats are rolled by waves and not wind pressure and that any boat will roll if the wave is 'right'.

What about a monohull with the horizontal foil which stops heeling?

http://www.mysailing.com.au/news/dynamic-stability-systems-go-fast-gear

 

[Babylon]

What about a monohull with the horizontal foil which stops heeling?

http://www.mysailing.com.au/news/dynamic-stability-systems-go-fast-gear

My first thought was "that looks like a weapon!"... then reading the article the guy says "cool and menacing."

Its weakness is that its a mechanical system, so it could fail the robustness test. If the foil jams for any reason or gets bent by striking a submerged object offshore, you're condemned to a single tack until you eventually hit land. If the yacht is conceived for speed and built around this concept, then it isn't going to have a lot of stability without it. Heaving-to? Running before a big sea?

 

[doug748]

..... Nothing wrong with form stability, the idea that heavy and deep gives stability was disproved after the 1979 Fastn....

I am sure that is not what you meant to say, is it?

 

[oldbilbo]

I am sure that is not what you meant to say, is it?

Is that a very gentle way of saying 'doesn't know arris from elbow'...?

 

[LouisBrowne]

I would have misgivings about horizontal foils for crossing oceans. A boat's tendency to heel is nature's way of relieving stress. If a yacht is too stable the loads will get too high and things will start to break.

It is good to have a boat that gives you warning when things are getting too much and the systems or rig should ensure that it is easy to reduce sail.

 

[flaming]

I would have misgivings about horizontal foils for crossing oceans. A boat's tendency to heel is nature's way of relieving stress. If a yacht is too stable the loads will get too high and things will start to break.

It is good to have a boat that gives you warning when things are getting too much and the systems or rig should ensure that it is easy to reduce sail.

That is of course assuming that the boat wasn't designed with that level of stability in mind and fitted with apropriate equipment. Which of course it would be.

It's an interesting concept, but not one that I would expect to become mainstream on cruising boats though. I think the appearance of "Open" type boats on the cruising scene is far more interesting.

 

[Robin]

I am sure that is not what you meant to say, is it?

That rather depends on how you understood it, I thought I knew what I meant to say.

What I meant is that a deep narrow wineglass shaped hull with a long (but shallower) heavy keel is no less likely to be rolled over than a flatter hull shape with a deeper narrower keel that maybe weighs a bit less. Boats in the 1979 Fastnet (in weather about as extreme as it can get around here) that rolled over were rolled over by the seastate not by the wind pressure. Subsequent tank testing at Southampton University proved that any boat regardless of design will roll if it meets the 'wrong' wave. The narrower deeper keel might well right quicker if rolled than a wide flat one (as were quite a few Fastnet boats), simply because of being less stable upside down, but wide boats with some volume in the area above deck such as with coachroofs will also be unstable enough to initiate the righting process.

All of which is relevant only to those who expect to be rolled over, but some people have this idea that long keeled boats are immune to such things which they are not.

 

[doug748]

Is that a very gentle way of saying 'doesn't know arris from elbow'...?

Well er, would not like to comment further.