Keels and Keels Again!

Terry
Sailing boats like this are mostly shell. The structure is not like a normal frame in a timber boat. There are strategically placed stiffeners that stop the shell from flexing too much. The shell provides the strength and there are full and partial bulkheads to stop the shell from collapsing. They are not like a timber boat with framing and a skin to keep the water out.

Rick W

 

I'm with you Rick
99% of the yachts I see, the bolts go through the skin and not the transverse beams as they are usually not solid as you say.
They are also usually the floor level so there is no room for the studs and nuts.
Many are also molded liners that are just gunked to the skin.

How about a photo competition to see who can post the first production boat that bolts through the beams???

 

I didn't say they must to be through the beams.. It was you Rick questioning "if they were used to through-bolt" coud it be done. So the answer is yes they can, but the beams must be solid in that part..
Bolting to skin is a common practice, but then the skin must be strong enough and the back plates to be large enough. Neither was done in CF38..

 

There was a photo showing the stiffeners. I was referring to these when I said they would not be suitable for through bolting. I was not saying you could not through-bolt beams but they need to have adequate compressive strength to avoid compression failure with the hugh bolt pre-load needed to avoid the keel flogging. A joint like this relies on the bolt tension being high enough so the keel stays in contact with the shin and does not cause a guillotine along the top edge of the keel that slices the skin.

Rick W

 

@teddy

rick just pointed out, that those beams from your fotos are hollow and would not take the stress from the keel but crushing instead and leaving the keel loosely connected until they are completely compressed to the skin - then you can tighten the bolts again...
if you follow your own link - you see that very clear:
http://www.eliboat.com/?p=65

 

I think all the keel should be bolted through a structure ( suitably designed for that) rather then the surface skin as it then makes the laminate ( the none homogonous material)critical and the failure catastrophic rather than just a leak.

I dont know what the yacht industry thinks about slamming fatigue but in race powerboats due to the fact that there have been some spectaculalar failures, old boats are never raced.
Just sailing a yacht with the normal keel load on anything but a dead flat day for me would be the same as a race boat at race speed as that is what they are both designed to do.
J boats comment about keels will fall off old boats seems not to had that much publicity in the yacht world but seems normal to me with my powerboat experience.
I would also say the slamming load on the yacht on a rough day is just the same has crashing waves when it goes wrong in a powerboat at high speed.
I dont hear of a yacht owner saying, I cant sail it any more as its done too many miles but all the guys with restored old race powerboats drive them slowly and on calm days as they know...

 

Not neurotic.....overly sensitive maybe.

In some ways I agree with you, but the issue doesn't seem to be as simple as other people being wrong in the boats that they enjoy. Not all fans of ultralights are simple-minded and easily influenced, and the part of the post I objected to was the stereotyping.

Yes, I can certainly tell the difference in the helm and feel when a boat is 5% faster than another. After all, that's about the same difference in pace as a 34 footer compared to a 30 footer. It's similar to the difference between a top yacht of 1968 (a Scampi 30 or the original Ragamuffin) and a boat of the mid '70s, like an early Farr. It's the difference between a Laser and a Tasar. I don't know a good sailor who couldn't tell the difference, just like a good musician can tell the difference between their best and second-best viola, or a keen cyclist can tell the difference between a road bike and a time trial bike.

In a competitive sport, 5% is a massive speed difference. I happen to have chosen the 5% slower boat, because I personally prefer it.
Like you, I tend to think it's preferable overall, but IMHO it does lose something of the joy you get in a racier craft. On the other hand, there are many people who love sailing even slower craft, and good on them.

But for you and I to have our own personal choice, because it suits our own tastes, is one thing. To claim that such a matter of personal taste is "a reality" that is only created by popular culture is another thing entirely.

And yes, there is a culture that anything but an ultralight is a pig. But in just the same way as you take issue with that culture, surely others can take issue with the culture that anyone who chooses to sail a light boat does so merely because they don't know better.

 

Rick .. sorry! Understood your comment being more general than it was. Vimes.. the Bavaria keel was the excample of poor structure.

Hollow beams are quite easy to fill with high density filler afterwards if needed

 

i have seen a lot of keels mounted in that poor bavaria-like way on some charteryachts and i always wondered:
"why is that keel not just dropping off out of sheer embarrasement?"

some other things i always asked myself...
why isn't there some sort of wider counterplate/frame fitted tightly to the transversal and longitudinal stiffeners with the keelbolts driven through and mounted to that frame...
ist it a weight consideration?
or is there just not enough space?

 

It seems to be common practice to bolt the keel to the skin between stiffening ribs, although I still find it hard to believe. The narrow areas of skin between the ribs and keel bolt spreader plates transfer considerable forces on the keel and are severely flexed in the process. It seems like thoroughly bad engineering practice from a durability standpoint, as well as a performance standpoint since the energy absorbed by the skin could be driving the boat faster.

A far better scheme would be to have inter-costal battens between the ribs and bonded to them as well as to the skin. In effect this would constitute a keelson. This would create a continuous longitudinal surface that would transfer the keel forces to the hull structure without local stress concentration. It could be provided with crush resistance by simply surfacing it with a strip of G10. This would add a tiny fraction to the durability of the boat and increase its racing and sailing life immeasurably, as well as its safety. It would likely improve performance by a small amount, much as a stiff chassis is better for a car.

This is essentially the same point as the previous post, didn't see it before. There is no reason why there should be weight penalty; the skin in the keel locality is no longer reacting the keel forces so there is no reason why it should be reinforced to the same degree.

 

sure it would be much better to drive the bolts through proper dimensioned stiffeners than through the skin alone... yet there is the problem that the material is not suited for taking high concentration of loads in a very small area...

GRP: strong and stiff but only as long as the fibres are not breached...
wood: strong with a good flex but soft...

surely the drillholes would be reinforced with resin building a ring and helping distributing the pinpoint loads from the bolts to a little wider area...
but resin cracks easily... it has no flex whatsoever...

the best material for taking high loads which stress the construction in a very small area via the bolts is metal - steel preferably... so why not covering the keelson with a frame holding the bolts...
the rest of the material will get the loads from the keel distributed via the frame over a wide area and this pinpoint stresses are taken from the steelframe...
a thin 3-5 mm sheet or such should suffice...

 

Swan did that on many boats in the past, not sure now
Making a hard point is very simple even inside a hollow beam ( before you install it.)
There are many custom made compounds like chock fast let alone the correct FRP mix which the designer could calculate for the crosssection of the beam and then spec the make up.

 

G10 is an industrial glass reinforced resin material which is formed under pressure.

It has a high glass to resin ratio and is significantly harder than either regular molded-on-the-spot fiberglass or wood. Its strength characteristics are well-defined and are midway between the metal used for spreader plates and the hull material of a fiberglass boat. This should be helpful for engineering a proper solution to the vexing problem of keel loss. that would distribute the concentrated forces from the keel into the hull without less tendency for local failure.

It is available in a variety of shapes and sizes, sheets, tubes, rods etc. For the amount of material needed to reinforce a keel attachment location it would not be very expensive. I am sure boat builders (and designers) are aware of this material.

 

Interesting reading this thread.

Back in 1991 I was on a Cole 31 heading up a narrow channel with a very strong incoming tide that was doing around 6 knotts and we were hard under motor as well so we would have been doing a good 10 - 12 knotts of ground speed when we hit a rock.

The rock chose not to move and we simply stopped dead. I landed on top of the other crew who were all smashed into the cabin, some with good injuries. The next day we raced without inspecting the hull and won the race. We sailed back down the coast to Sydney without inspecting the hull. In fact, we raced the old girl for 6 weeks offshore with great success. The diver was asked to clean the hull and returned to the surface suggesting we take it immediately to the nearest shipwright with a sling.

Turned out the following had happened:

She has 10 keel bolts
the first 4 had sheered
a few more were bent
the ones at the rear were fine
There was a section of solid led the thickness of the keel and 8 inches high / 6 inches back that was basically torn out
The hull had basically delaminated from the stringers, especially where the back of the keel had transferred the load onto the rear bolts that were secured through the stringer

It was a big repair but the guys at RSYS did a fantastic job of fixing it.

I came accross the same yacht 3 months ago for sale. The current owner had let it go so it was generally in a bad way. But...on inspection...the repairs to the keel and hull were still perfect. Not one crack and stress mark.

You could still see the line on the keel where it was repaired but only just.

I can say that Cole designed one very strong yacht and whoever built did a great job. any lessor yacht would have lost her keel with that impact. Damage was significant, but the yacht still held together despite racing it in some very oridinary conditions after the impact.

Some of the newer yachts are very ordinary in their keel structure. Nothing wrong with modern keel designs but for the sake of aesthetics, they dont bring them through the floor. I am looking at a yacht at the moment to buy that has a 9 foot keel but it extends nearly 4 feet up into the old centerboard case which is structural. It is supported by a heap of epoxy and bolted in three places. It is not going anywhere....unless it sheers off

Craig

 

You were very irresponsible and lucky, indeed!

Cheers.