Fin Keels

[andygc]

Have not heard of too many wings coming off. Maybe they have cracked (!) the problem

So you are fairly ignorant of some well-documented glider accidents - like this one: http://www.bbc.co.uk/news/uk-england-13369919. I'd describe that as "too many wings coming off" - two too many, actually.

 

[FWB]

So you are fairly ignorant of some well-documented glider accidents - like this one: http://www.bbc.co.uk/news/uk-england-13369919. I'd describe that as "too many wings coming off" - two too many, actually.

Actually it's the fuselage that comes off, but I don't see what this has to do with boats.

 

[vyv_cox]

Is it not the case that if the wind forces against the mast and sails and the balancing forces against the keel are equal and the mast is stayed off with shrouds and fore & aft stays then is it not inevitable that the keel will eventually give way if it is only attached to the glass fibre hull with a few keel bolts ?
It seems that no matter how clever the designers are historically this problem keeps recurring.

I cannot imagine why you think it 'inevitable' that bolted joints will fail. Bolted joints have been around for more than 1000 years and some of the original ones are still holding together. Throughout every field of engineering there are far more complex bolted joints than the keel of a yacht, every one that has been designed and manufactured correctly performing exactly as intended.

 

[JumbleDuck]

So you are fairly ignorant of some well-documented glider accidents - like this one: http://www.bbc.co.uk/news/uk-england-13369919. I'd describe that as "too many wings coming off" - two too many, actually.

It's been a few years since I was an active glider pilot, but I an remember very, very few accidents in which wings and fuselage parted company. In fact, I can only remember one - the Astir which was partially rigged at Portmoak for a potential buyer and then flown later that day, after conditions improved, withoutthe main pinds in place. Even then it flew OK and the wings didn't fall off till after it landed.

I suppose the Oly which got a touch of anhedral at Sutton Bank might count, but that was a glue failure in the main spar rather than an attachment failure.

 

[Resolution]

In all this discussion of keel types I am surprised that no-one has compared the effects of hitting rocks ( or whales, containers or any underwater obstruction). All this focus on keel bolts, but nothing on a) the angle of attack of the keel , or b) the material of which it is made. I have twice hit rocks at full speed, luckily each time with keels made of lead. On lifting out each keel showed lots of deformation, but this had been impact absorbing and no real damage up at the hull keel joint.

 

[andygc]

It's been a few years since I was an active glider pilot, but I an remember very, very few accidents in which wings and fuselage parted company. In fact, I can only remember one - the Astir which was partially rigged at Portmoak for a potential buyer and then flown later that day, after conditions improved, withoutthe main pinds in place. Even then it flew OK and the wings didn't fall off till after it landed.

I suppose the Oly which got a touch of anhedral at Sutton Bank might count, but that was a glue failure in the main spar rather than an attachment failure.

There have been others. I can't find the details, but several years ago there was an experienced glider pilot (serving in the RAF, if I remember correctly he was a gliding instructor at Bicester) flying an aerobatic display during which the wings came off. Like the August 2010 accident it was a rigging error. By "came off" I don't actually mean separated completely, but the difference is insignificant - a folded wing doesn't generate a lot of lift.

Mind you, accidents where boats and keels part company are also pretty uncommon.

 

[doug748]

As others have said, there are at least two key problems with encapsulated keels. Firstly it is not presently possible to mould a slim fin of great depth, with ballast at the extremity, to serve as a racing keel. Secondly they are more expensive than bolt on types.

In their turn cast metal keels are problematic. If their section is constant much of their weight is inefficiently placed; if they carry some form of bulb, and slim section/deep draught, then hull attachment is very difficult. There are few terminal failures but partial ones are well known and regular maintenance is required.

I think few would deny that drilling holes in a perfect monocoque and bolting on ballast is step backwards in engineering terms. A handy solution but an interim one.

Personally, a metal keel would give me nothing I particularly wanted so have always sought out plastic designs. I have, on the whole, been happy to pay the surcharge and have one less maintenance headache.

 

[geem]

Encapsulated keels came about in that transition period when "wood shaped" boats were built of GRP and it made sense just to create a GRP envelope the same shape as a wood boat then fill the bottom with ballast. Many of the designs also had tumblehome in the topsides so were moulded in two halves, joined together along the keel and filled with ballast.

Very quickly though designers discovered ways of making keels into foils once they were free of the structural requirements from wood that necessitated a full length keel. You can see the evolution from looking at say the S&S designs of the late 1960's when keels became separate entities from the hull and it was no longer possible to build using the encapsulated method. Variations included moulded stubs and bolt on ballast which was very popular from late 1970's to around 2000. However the benefits of flatter bottom hulls, lower ballast ratios and separate foils for keel and rudders has led to the almost universal use of bolt on foil shaped ballast keels - most of which in production boats stay very firmly attached to the hull and the internal framework they are bolted to.

As has been noted many times, encapsulated keels are not problem free. Firstly they restrict keel shape and limit performance as well as being mostly used on hulls with narrow beam and restricted interior space. Many are very badly built, either through the use of steel punchings and concrete for ballast or by poor quality GRP moulding, particularly in deep narrow keels. Some builders even built GRP tanks integral with ballast keel and you can imagine the problems that creates if there is any leakage. The best builders usually did a good job, but there are some real horrors around, even in boats that have an otherwise good reputation. The defects are usually hidden and only come to light for example after a grounding or even after blasting the hull in preparation for refinishing.

I cannot agree with your view. You are generalising to suit your argument.
My yacht was built in 1980 to Lloyd's 100A1. She is lead encapsulated. The hull is fin and skeg and has no tumblehome.
There are good boats and there are bad boats. Don't assume the one you don't have is the bad boat. My tanks are integral. I have read numerous post on this forum of leaking s/s tanks. Mine don't leak!
You can build any boat badly. Poor construction is not exclusive to any particular design. In the end it comes down to quality. I will be crossing The Ocean again this year. I didn't choose the design by accident.

 

[Tranona]

I cannot agree with your view. You are generalising to suit your argument.
My yacht was built in 1980 to Lloyd's 100A1. She is lead encapsulated. The hull is fin and skeg and has no tumblehome.
There are good boats and there are bad boats. Don't assume the one you don't have is the bad boat. My tanks are integral. I have read numerous post on this forum of leaking s/s tanks. Mine don't leak!
You can build any boat badly. Poor construction is not exclusive to any particular design. In the end it comes down to quality. I will be crossing The Ocean again this year. I didn't choose the design by accident.

Oh dear! Why do you have to take things so literally? I was just explaining why encapsulated keels were popular for a while - not saying every boat in the period was built in a particular way. There never was any clear point where one method of construction was suddenly superseded by another - always a process of evolution and different designers and builders used different methods or combinations. So, for example, many Holman and Pye boats had both tumblehome and bolt on fin keels because that was a their solution to achieving the ratings they were aiming for. Equally some builders (HR for example) built in GRP tanks on top of encapsulated ballast giving many owners grief 40 years down the line. However, it is true to say that encapsulated keels were only common for a very short period before hull and foil shapes changed and they no longer held any advantage - indeed became a disadvantage. This is not to say that no boats were built subsequently using that method, just that mainstream designs moved on to different solutions.

So yes I am generalising - but not to suit my argument as I don't have any axe to grind but just to try and explain why particular features of design and construction fall in and out of use. That does not mean that every boat using a feature is either good or bad. There are some real horrors lurking within some so called "quality" boats, in just the same way that there are some "cheap" boats which have proved well built and durable.

Incidentally I have owned for over 35 years a long keeled hard chine ply built boat built in 1963, which conventional wisdom suggests should be on the scrap heap by now - but it was built by people who knew what they were doing (just like I assume your boat was) and it is still sound. So I hope nobody dismisses my boat just because it is built in a material that is out of fashion. Hopefully they accept it for what it is rather than what they think it should be.

 

[William_H]

Performance isn't everything though. I always fancied one of the Bruce Roberts Spray designs if I ever get enough cash together for long term cruising.

Racing boats are usually exciting because they are uncomfortable and have an element of danger.

That description of racing boats seems to come from one who has never experienced (skippered) a performance boat. It is not the nature of the boat but rather how they are sailed. Sure if you sail a performance boat on the very edge of overpower then it goes well but requires work to do so. Most performance boats however when depowered with sensible sail area can be really lovely to sail especially to windward. My litttle trailer sailer performs quite well. As an example I have acheived about 25 outings this last summer and not used the engine once. A good performing sail boat with a good performance keel can make that possible. olewill

 

[Daydream believer]

I have studied these pics very carefully & come to the inevitable conclusion that your yacht has fallen off
I hope you got into the car in time, did you phone home re re this, When was the car last seen leaving the yard?
When were the tyres last checked for pressure. Were the crew wearing keys
re the yacht I suggest someone calls the fire brigade to check all the bonfires to see if there is any trace

 

[DownWest]

I was mulling the analogy to aircraft: I got a phone call from the CAA to ground a Zlin we had after Neil Williams suffered a structural failure at Hullavington. The bottom tie bar between the wing mountings broke, allowing one wing to fold upwards. Incredibly, he managed to get it back in place by inverting the plane and landed it out of a roll. Our Zlin was NDT tested with a magnetic system and found to be OK. ( Most inspections are initiated by notices in varing colours up to red, if urgent. A phone call indicated they were really worried)
In France, the CAP 22 is a common aerobatic club aircraft. They found cracking in the main spars was affecting several aircraft. Why? Because the pilots were routinely exceeding the design limits. They have G meters fitted and these record the max loads. One might equate this to bumping a keel and not looking to see if there was damage. Not saying that this applies to the case, but certainly it did to the previous one in the Scillies.

 

[vyv_cox]

Incredibly, he managed to get it back in place by inverting the plane and landed it out of a roll.

Special mention in YM for anyone who can do this in a boat! :encouragement:

 

[AndrewB]

Performance isn't everything though. I always fancied one of the Bruce Roberts Spray designs if I ever get enough cash together for long term cruising.

Be a little wary of BR Spray designs. The two I've been aboard both suffered from a bugbear of steel yachts - poor stability. Probably not a fault in the design, but more likely because the amateur builder decided to raise the headroom or add a coach-roof.

I'm a great fan of steel boats for long-distance sailing precisely because of the strength of their keels. I once ran into a reef at 7kts with mine which was no more than an annoying mishap, but might well have sunk a fin-keeled production GRP boat. However, under 42ft, to achieve good stability they do seem small and cramped compared with GRP boats.

 

[jwilson]

That description of racing boats seems to come from one who has never experienced (skippered) a performance boat. It is not the nature of the boat but rather how they are sailed. Sure if you sail a performance boat on the very edge of overpower then it goes well but requires work to do so. Most performance boats however when depowered with sensible sail area can be really lovely to sail especially to windward. My litttle trailer sailer performs quite well. As an example I have acheived about 25 outings this last summer and not used the engine once. A good performing sail boat with a good performance keel can make that possible. olewill

+1
With the exception of some very, very extreme designs, such as foilers, you can always slow a fast boat down, and usually they are very nice indeed to sail when you do - well "within the envelope" and no rounding up in a gust or fighting the helm. You just can't speed up a slow boat, and many have little "feel".

Personally I don't buy into the 'Spray' mystique, and cannot understand why anyone would want to build a sort of replica. I say sort of because although the original's hull lines were taken and are known, few modern versions are anything like her, and in any case I have always suspected that the original had a centreboard. And it's not as though she was designed and built for her task of ocean cruising - she was built for inshore oyster dredging in shallow water - she's just the boat Slocum happened to have when his luck as a big square-rigger captain ran out.

I'm not against traditional boats: one of my dream boats is a true modern replica of one of the bigger (and faster) Bristol Channel pilot cutters (with all maintenance done by Mashfords or similar yard). Another though is a Dashew-style ultralight.

 

[TimBennet]

Be a little wary of BR Spray designs. The two I've been aboard both suffered from a bugbear of steel yachts - poor stability.

Finally some good advice in this thread!

 

[Twister_Ken]

There is another way of attaching a fin keel to a modern hull shape. Arcona and (I think) X-Yachts do it. Maybe other builders do to?

It involves putting a metal backbone in the yacht, and bolting through the hull on to that. As here: http://www.arconayachts.com/index.asp?p=About

In Arcona's case, it's done because it's a brand with Baltic heritage, and in the Baltic rock-bashing is - if not obligatory or even recommended - almost inevitable.

 

[Tranona]

There is another way of attaching a fin keel to a modern hull shape. Arcona and (I think) X-Yachts do it. Maybe other builders do to?

It involves putting a metal backbone in the yacht, and bolting through the hull on to that. As here: http://www.arconayachts.com/index.asp?p=About

In Arcona's case, it's done because it's a brand with Baltic heritage, and in the Baltic rock-bashing is - if not obligatory or even recommended - almost inevitable.

The principle is exactly the same as most modern boats except that others (the majority!) use a framework constructed of GRP or other composites rather than galvanised steel (or stainless). You can construct arguments to support both types of material. Using steel is an easy "sell" with its connotations of strength, but often it is used in conjunction with lighter hull mouldings as the hull does not have to take such heavy stresses from rigs and keels. You can find the same principles applied in high performance boats from the past where many designers used steel frameworks within wooden hulls to take the loads.

 

[Sailfree]

There is another way of attaching a fin keel to a modern hull shape. Arcona and (I think) X-Yachts do it. Maybe other builders do to?

It involves putting a metal backbone in the yacht, and bolting through the hull on to that. As here: http://www.arconayachts.com/index.asp?p=About

In Arcona's case, it's done because it's a brand with Baltic heritage, and in the Baltic rock-bashing is - if not obligatory or even recommended - almost inevitable.

As you know I am a fan of Aconas but the 46 that I know hit an object (the owner insisted it was a slow speed) and the amount of damage surprised everyone.

These arguments though have a similarity to 911 eg what redundant strength should a structure have to withstand the impact (and fire) from an aircraft strike. If designed now to be OK then what about 30yrs time with inevitable larger heavier aircraft?

I have an AWB that I consider adequate for my purposes. If I was to go long term cruising its not a bolted v encapsulated keel that I would worry about but whether GRP was with the right boat material compared to aluminium or steel. Whatever we design there will always be circumstance that the design would be inadequate.

The majority of posts have avoided costs - cost is a factor - the final decision on an economical design is fit for pupose and that is not fit for extreme circumstances. Lets face it 100's are killed on the roads in vehicles that fail to protect the occupances from the impact forces the vehicle is frequently subjected to (far more frequent than the consequences of a keel failure) yet I don't see many posting that cars should be limited to 10mph or built like a tank!!

 

[Twister_Ken]

As you know I am a fan of Aconas but the 46 that I know hit an object (the owner insisted it was a slow speed) and the amount of damage surprised everyone.

I think I know the incident to which you refer. The owner may have insisted it was at slow speed, but I'm told his chart plotter disagreed with him. The object was very substantial, both above and below water.