July 20, 2008


Yrvind ½ has 18 lead chambers. They are placed in three groups, six chambers in each group. They are situated to port and starboard and aft close to the transom.

The ones to port and starboard helps to control healing. In strong winds, to get more righting moment, six lead weights, each 15 kilos or 33 pounds can be shifted to windward, either all or some of them. In light wind, to dig in the chine runners deeper the weights may be kept to leeward.
The aft group is useful when running before gales with breaking waves. Weight placed so far back moves the center of resistance aft and makes the boat more course stable. Also as the mass moment of inertia increases with the square of the gyr radius the boat will much better resist pitch pooling. Naturally it will also be more easily pooped, but as the boat is strong and waterproof it is in my case a better choice.

The above picture shows the lead weights placed to windward. As can be seen, so placed they give a greater righting arm compared to, if the same wight in the form of a 200 pound man would have been placed on the rail.

This is how the starboard lead chambers look. (later I will add lockers on top of them)

Lifting the lid one can see one mock up weight with a wedge on top of it. When moving the weights from side to side they slide across the floor up on a wedge an fall down behind it. Then another wedge is jammed in filling the gap to the roof. After that a small door is closed keeping the wedge in place. Now they can not get anywhere even if the boat is capsized or pitch pooled.

The wedge which is placed on top of the weights.

A mock up of one of the 15 kilo lead weights with its stainless steel handle.

The door which keeps the wedges in place.

On its back can be seen the locking mechanism which keeps the door in its place

Its made of a piston hank. The pieces which holds the sail and attach it to the stay is cut of with a hacksaw. A piece of string is attach to the nob to easier get a grip on the piston.
I use these piston hanks to lock many lockers.

July 10, 2008


1985 designed and built Matt SWAMP THING 4m long 1.08 beam 19 cm draft with a cruising weight of 400 kilos she was the first boat to have chinerunners. Other boats based on the same concept is PARADOX and ENIGMA.
I consider it the most important innovation for small boats during the 20th century.

Here is PARADOX chinerunner.

Here is Matt with ENIGMA.

Here is a close up at ENIGMAS chinerunner.

This is how Matt did ENIGMAs chinerunner,

YRVIND ½ is a composite boat so I use a different technice.

First I attach plywood pieces insulated against epoxy with packing tape.

To them I clamp a glass fibre sheet. I fasten it to the hull with a fillet.

Now this shelf is ready to recieve several layers of glass fibre. As they are exposed I make them strong about 20 mm thick or about three quarter of an inch.

When i take the boat outside I will grind it to a nice shape.

Here is a drawing Matt made for a bigger boat.

The chinerunner concept looks simple, but dont fool yourself into thinking that they are just add ons. The idea of preventing leeway with the help of chinerunners, like most successful fluid flow devices, including the bumble bee, is a sophisticated concept. Matt is also taking help of the the lifting body concept and a large rudder.
The boat have to be relatively heavy to sink deep enough in the water, but small cruisers are not light. The ratio beam to draft has to fall within a narrow range. PARADOX beam is 1.23 m her draft is 0.23 m. YRVIND ½ has a beam of 1.3m and a draft of 0.22m
The concept gives shallow draft with no moving parts. The hull-shape gives a lot of stability as it like the catamaran quickly moves a lot of buoyancy to lee for a small angle of heel. It also gives a lot of flat floor on the inside, welcome on a small boat. It is also a hull-shape easy to build. Almost to good to be true. Strange that not more people take advantage of this windfall which has been around for quarter of a century.

July 6, 2008


Archimedes said, “Give me a long enough lever and a fixed point and I can move the earth”. Like Archimedes I like strong points. There should be attachment points on a boat not only strong enough to lift the boat, but also they should be able to withstand dynamic loads.

These points of attachment where my first job on the new hull.

To make them really strong I decided to join the outer and inner laminations. Normally there is no problem of pealing away a bit of lamination, but to my joy the combination of the NM-epoxy and the new 100 kilo Divinycell gave me a lot of problem. After cutting the inner laminate with a diamond saw I put in a chisel to bend it away, but it did not budge, so in went another chisel. No progress. I put in a third chisel hammering on the different ones alternativly to no anvil. Finally after adding two big screwdrivers did I get the piece away. It had taken a lot of work but I was happy of this strenght demonstration from my new boat.

I included apiece of stainless pipe on each side to protect the hull from chafe.

Here they can be seen from the outside.

This is my fitting 30 mm stainless steel 2 mm thick with two pieces welded on to prevent the rope from sliding up or down. To hold it in place while gluing it to the boat I temporarily attached it to a piece of plywood.

Here it is in position.

Whit the help of a bit of a plastic bottle I created a form. Now I can laminate from the inside and get a new inner laminate with a the necesary distance from the stainless pipe to give place for the rope. When that is done I cut the outside skin and inside this created cave lives my point of attachment. I made one on each side of the transom and one in the stem. Now I can turn my boat into any desired position while building her. And of course later when cruising they are invaluable.

Here they are seen with ropes attached to them. By the way, the weight of the hull came out to 150 kilos.

July 1, 2008


After getting the frames out, getting a fillet in corners, reinforcing the stem with a few layers of glassfibre and getting her nice and smouth she was ready to be sheated on the inside.

First however I could not resist the temptation to enter her and get a feeling of the size of my future home. I found her huge, here was plenty of space. I was happy I had not made her bigger.

Four people had promised to help. Unfortunatly two of them could at the last moment not come. I and the two brave ones decided to go ahead anyway. It became a very long day. We started 9 in the morning and were done 1 the following night after 16 houers of backbending work.

Here we start cowering her with NM-Epoxy.

Here the first of the two layers glass fibre comes on.
Next day I was happy to see that the work had been very succesfull.

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