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August 28, 2014

MORE ABOUT MY STRONG RIG

Sharpii 2 is still worried about my rig. He beliefs a breaker may rip out the mast and deck fittings and leave a hole in the deck. I disagree. It is not a war zone out there. The waves are not loaded with dynamite. Let me explain:
It is the terrible capsizes and pitchpooles of big boats, like Smeetons 46 feet Tzu Hang and Erling Tambs 47 feet Sandefjord that have filled cruising people with horror. Compared to the above boats, Yrvind Ten and the old Bris are small.
Bris was capsized and pitchpooled near Cape Horn 1974. On a stormy March night 1976 the same boat capsized again, now on Georges Bank, outside Nantucket. On each occasion her 20 feet tall rig came up without a scratch. She had one pair of spreaders and the length of the unsupported column was 10 feet. Yrvind Tens unsupported column is 6 feet. Ten divided by six, squared is 2.777… That is how much stronger the geometry makes that column, according to Euler. The “shroud angle” to the supporting spar is 38 degrees. For Bris the corresponding angle is 13 degrees. The ratio of tangents for those angles is 3.38. The larger the angle, the less is the compression or buckling force. One more thing, the peripheral speed of a mast increases with its length. The length ratio between the two masts is 2.222… The hardness of water increases with the square of the hitting speed. 2.222… squared is 4.94… Now multiply these three numbers 4.94×3.38×2.777 and you get 46.36… The scale effect suggests that if the two masts are built with the same dimensions and materials Yrvind Tens 9 feet mast will be 46 times as resilient than Bris 20 feet mast.
Of course I do not have the faintest ideas of the forces, accelerations, rotational speeds, mass moment of inertia and other factors that are involved in a capsize, neither do Sharpii2, neither do Einstein or Newton. What we know is that shorter columns and larger shroud angles makes rigging stronger and that longer masts whips harder.
On the other hand, I have spent much time in small boats on stormy seas. That has educated me.
-“Is it possible that a breaker may rip out your deck fittings and leave holes”, asks the prudent navigator?
- “Definitely not,” I answer.
My small boat can never be subject to such brutish forces. She has to little mass moment and linear inertia. I know that seamen have been washed overboard from square riggers and other bigger boats. The same breakers have often hit me. That has never caused a problem. The sea is not selective. It hits everything with the same force, the rigging as well as me. If the breakers had the force to rip out my deck fittings they would have killed me long ago.
Sharpii2 says the fittings need to be strong enough to capsize the boat. Of course, that goes without saying. I am not building a toy. I am building a boat for long term, heavy duty cruising. My fittings will be strong enough to lift a boat ten times as heavy. Not only to lift it, but also to resist the dynamic forces necessary to stop a drop. Everything on my boat is solidly anchored. The deck has a sandwich core 3 cm thick. The reinforcements are spread out to a diameter of 30 cm good enough for a pull of 20 or 30 tons. So far my boats has had no problems to stand up against the elements. I see no reason why this boat should be less strong, on the contrary. I am learning all the time.
I will not worry. I will sleep deep and well even during the strongest storms because I know that if a breaker capsize her she will come up proud, happy and smiling.

With Respect and friendship, Yrvind.




August 21, 2014

FASTER HORSES

Henry Ford said: “If I had asked people what they wanted, they would have said, faster horses.”
First he built cars with people sitting outside. On rainy days that was wet and uncomfortable so he added a cabin with windows. Then came the windscreen wiper. Today windscreen washers supplement them.
Let nature be your guide. Complicate things and you will be successful. Even the simplest cell is more complicated than a boat. The KISS principle is rubbish. The trick is not to make a new construction simple but functional. My guiding principle is utility. Building a nine feet pivoting mast is no rocket science. A 75 year old pensioner can do it with simple tools.
Its complexity is in the beholders eye. Some observers get confused when they see something unconventional. To calm their minds they call it complicated. The same people outfit their boats with outboard engines, electronic steering systems, water makers and induction cookers. They are so blinded by these mass produced products they do not realize that they are much more complicated than my homemade mast.
Optimizing each subsystem independently will not lead to a good boat. Of course, non-pivoting masts would be simpler, but then the whole system, the boat, would be more complicated. I would have less trim options. With the planned rig it will be very easy to change from lee helm to weather helm. Hopefully the result is that my boat will steer herself without electronic steering systems or wind vane self-steering gear.
I do not think that I ever will convince conservative sailors of the beauty of my rig. They suffer the same mental blocks that Max Planck observed a hundred years ago. Resigned he remarked: A new scientific truth does not triumph by convincing its opponents and making them see the light, but rather because its opponents eventually die, and a new generation grows up that is familiar with it. Still, I wish my critics a long healthy life.

http://www.boatdesign.net/forums/all-things-boats-and-boating/yrvind-39341-27.html

#405
Sharpii2 have pointed out that when the masts are not vertical they are acting like a crane boom -true. I like to thank him for that comment. I welcome critics because I often make mistakes and forget details that can have dire consequences. It was a good observation.
However I do not worry and it is for two reasons. One, I do not agree, I do not think that it will put a lot of bending stress on the mast and tremendous stress on the pivoting axle and the locking pin. After all, Yrvind Tens masts are not longer than an oar. Small boats do not attract big forces because of the square cube law. Sure, things break even on small boats but that’s mostly a question of dimensioning and can easily be fixed.
The second reason is that when the wind becomes strong I am going to reduce the forces on the mast and support her.
I reef the sail. That brings the yard down to a position six feet above the fulcrum. At that point on the mast there is a fitting to which I tie it with a string. Next I slack the halyard, releasing the compression. At that moment the bowstring effect is no more. True, the wind force is still acting strongly on the reefed sail. However its leverage is now only six feet.
To break things you need leverage. Take a match, say 4 cm long and break it, no problem. Break it again, OK. Now its only 1 cm long and it starts to get hard because you do not get a grip. You have no leverage. Most catastrophic scenarios come from big boats disasters. Small boats are different. They are more resilient. Other laws apply.
Still I am a man of the belt and suspenders approach. When the wind gets stronger and the seas start to break I snug things down and beef them up. I will then support the mast with an eight feet long spar. I will attach one end to the mast at the height of the yard, six feet up. The lower end will be fastened near the root of the other mast on the axis of the fulcrums. With that geometry the mast and spar can be rotated for and aft as a unit. Thus the mast is always supported athwartships. Fore and aft support comes from ropes.
If this sounds complicated and confusing I assure you, it is less difficult than setting a spinnaker pole.

Below is a pictures of the 1/8 scale model with this arrangement. Click once or twice to enlarge.

Above mast in aft position, weather helm

Above mast in aft position, weather helm

Above mast forward position, lee helm.

laminating the centerboard slot.

Done.

To be continued…

Regards Yrvind.




August 18, 2014

LEEBOARD

Boat ideal will have leeboard. Thinking aboat leeboard has changed my mind. I have decided to have leeboard on Yrvind Ten also. Ocean going boats do not have leeboard, but traditionally ocean going boats are big structures and lika all structures subject to Gallileos square cube law. Becouse of the square cube law a small boat do not have to be simular to a big one. In fact its a big mistake to build a small boat simular to a big one. Its against the laws of nature. Bugs understand that. They to smart to try to imitate vertibrates. Each one to its own scale.

The present project will then teach me much about them. Good for the next boat. The upcoming circumnavigation will be a lot of down wind sailing. Thats were leeboards excel. Downwind a keel is really bad a centerboard better but there is still the slot causing turbulence. Then the control ropes. Traditionally there is only one rope, an uphaul. but if the boat is going to be capsize-proof you need also a down-haul to control the board in all positions. For piece of mind. I have not got these mechanism to work to my satisfaction. This is not the first time I change my mind regarding centerboards. Bris had one to beginn with Yrvind.com started with a centerboard, then a daggerboard I scarped boath of them. Centerboard worked fine for me on Bris- Amphibie, a daggerboard worked fine for me on Duga.

Leebards will also give me much more space in the saloon.

I am avare that leeboards have its own sets of problem. I will try to solve them later.

Below are some pictures. click once or twice to enlarge.

Above the 15 kilo scrapped centerboard.

Above. The centerboard case cut off above the storage.

Above the turbulence causing opening for the centerboard.

Above the turbulent causing centerboard opening starting to be plugged.

To be continued…

Regards Yrvind




August 5, 2014

SIDE BY SIDE RIG ON THE 1/8 MODEL

Here are 4 pictures of the planned side by side rig with folding masts.

The above pictures (click once or twice to enlarge) shows the rig set up for reaching in light wind.

Both sails are in clear wind. The boat has lee helm. The skipper can relax and enjoy.

The above picture shows the boat close hauled in light wind. Compared to a tandem set up the sails are much better separated thus  giving better flow and sail efficiency.

The above picture shows the boat reaching in strong winds.

When a boat with a mast in the centerline is reaching the sail and boom is off center unless its a square sail. By folding the lee mast the balanced lug sail will much like a square sail be centered avoiding excessive rudder action. The unstayed mast guaranties no chafe; a good thing on long passages.

The above picture shows the boat close hauled in strong winds. In real life the sail will be reefed to suit wind conditions. One mast is folded to reduce wind resistance and to lower the center of gravity and mass moment of inertia.

When using the lee mast there be more weather helm, desirable when you like to forereach witn little sail area up. Using the mast on the wind ward side gives less weather helm. It also reduces the tendency to dip the boom in the water. As a bonus one can also move the sails forward or aft by tilting them.

The side by side rig gives the prudent navigator many options and eliminates the need  for autopilot or selfsteering.

I also do work on Yrvind Ten. Presently it is the boooring job of filiting and taping all the pieces of plywood and composite that makes up safe stovage space.

To be continued…

Regards Yrvind.




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