Keels small and big and the effect of scale

Here is the text:
KEELS ON BIG BOATS ARE BRITTLE

Look up Swedish boat Sailing Aurora on YT and the playlist Grounding repair if you want some professional tips.
The above is a comment by Sgt-Bond on my video on twin keels. He is suggesting that I would learn something to use from the professionals.

I am glad I looked because this is what I saw:
A 40ft Hanse had hit a rock in good weather and the damage was enormous. It took a year or so before they were back in the water.
It was not the first time I had heard about big boats hitting rocks. 2020 in Porto Santo I met a Swedish Hallberg Rassy 42 feet long or so. They had left Las Palmas a year before, but the first day out they had hit a rock. Also their boat had to be lifted out and have extensive repairs done. Each of the two boats lost a year or so. Before I had not realized just how much damage a grounding did. The Sailing Aurora videos was very educational. I am glad that I looked at those well made videos.

It turned out that there is whole industry doing nothing else but fixing production boats that had run aground. In my childhood before there were production boats, running up on a rock was no big deal unless it happened in bad weather.

Three things make production boats brittle. Their size typically 40 feet long and ten tons displacement. Sizes that big make boats weak. Reason is the square cube law that says that strength increases only with the square of the scale while the deforming forces increase with the cube of the scale.
Double the scale and strength increases four times but the deforming forces increases eight times.

An other thin is that the kinetic energy increases with mass times speed squared.

I estimate that Exlex, my present cruising canoe, with one ton of displacement will have an average speed of abut three knots. That gives her a kinetic energy of 3 squared times 1 = 9

A 40 feet production boat with a mass of ten tons may sail at a speed of six knots. That gives her a kinetic energy of 6 squared times 10 = 360. That is 40 times as much living energy as my boat that will be stopped by hard objects.

Then there is the keel geometry. Exlex leading edge slopes 45 degrees while the leading edge of a production boat is nearly perpendicular. Exlex is those likely to slip over an obstacle that will stop a production boat.

Structurally the two keels are also different. The depth of a production keel is about the same as her base, 1:1.
The depth of Exlex keel is 0.25 meter but her base is 1.55 meter a ratio of 6:1.

People pay much for production boats. The boat owners like to believe what the salesman tells them. For example Auroras owner said:
”This boat is category ”A Ocean” therefore it is made for weather stronger than force 8”.
This is actually completely wrong. The recreational directive do not say that. It says that category is good for winds up to and including force 8 but not for stronger winds. There is no way an, economically produced, big boat can be to cope with storms and the boating industry knows that very well.

”Category A is designed to be able to make longer passages during witch the the wind can exceed force 8. Storms, severe storm and big waves are excluded”.
To me this is absolutely crazy but I am not in the boating business I am a boat building amateur. The word amateur comes from the French language the meaning of it is to love. I build boats because I love it not to make money.

Exlex is designed to be able to make long ocean passages in any weather condition including severe storms. She will have positive stability up to 180 degrees of heel. She is designed to be able to capsize and pitchpole with no harm done to her.

More about that in my Manifesto that you can find on my site Yrvind.com

There you can also support my project with donations via Pay pal or Swish 0706 200 550