More about Kolika, and bipod mast engineering
As it happens, I am proceeding with purchase of Kolika, having gone through her with the surveyor and have done some more research. Globaldude (if you are still around) - your visit to the boat and discovery of some of the problems turned out to set the stage - they lowered the price some more.
It's not a done deal yet but well along the way.
According to the builder Mr. Klimmek, the bipod mast weighs only 400 lbs. It is hollow wood with fiberglass skin. As he wrote, it weighs about 2/3 what a single mast would weigh. (You can read more at the web site for the boat, http://www.sail-works.com/KOLIKA/
This makes sense to me, as the masts do not have to deal with any significant bending moment - all forces are either tension or compression, and the rigid spreaders (with crossed tension wire) allow the two to act together as a single trust. I think that a single mast has to deal with much higher bending forces.
Also according to the builder, aerodynamically, the masts do not cost as much as might be expected. They are airfoil-shaped, so their windage is lowered. If I recall correctly a round object has the same drag as an airfoil ten times the width.
Perhaps most importantly, a single mast 'dirties' the air flowing across a sail significantly causing loss of lift, especially at high angles of attack. On the Kolika the sail's leading edge is almost completely clean, with only the roller furling to impede the flow.
I finally learned about the unusual prop and rudder design. The rudder has two sections behind the prop that are angled about 10 degrees from straight, in opposite directions. It turns out this has the effect of straightening out the propwash, eliminating prop walk. The circular foil around the prop is called a 'Kort nozzle'. This increases the efficiency of a prop - there is an article in Wikipedia. Overall though I think this arrangement has more drag when sailing than a more typical setup.
The trim tab apparently did not work as expected, and Mr. Klimmek locked it in place at some point.
[edit: One more interesting tidbit. The surveyor discovered that the original painted waterline was incorrect, and a new one applied. The boat evidently rides about six inches lower in the water than planned, which means the boat is heavier than planned. With 320 gallons of water and 180 gallons of diesel, plus 80 additional gallons hot water storage, that amounts to roughly two additional tons to haul around.]
As it happens, I am proceeding with purchase of Kolika, having gone through her with the surveyor and have done some more research. Globaldude (if you are still around) - your visit to the boat and discovery of some of the problems turned out to set the stage - they lowered the price some more.
It's not a done deal yet but well along the way.According to the builder Mr. Klimmek, the bipod mast weighs only 400 lbs. It is hollow wood with fiberglass skin. As he wrote, it weighs about 2/3 what a single mast would weigh. (You can read more at the web site for the boat, http://www.sail-works.com/KOLIKA/
This makes sense to me, as the masts do not have to deal with any significant bending moment - all forces are either tension or compression, and the rigid spreaders (with crossed tension wire) allow the two to act together as a single trust. I think that a single mast has to deal with much higher bending forces.
Also according to the builder, aerodynamically, the masts do not cost as much as might be expected. They are airfoil-shaped, so their windage is lowered. If I recall correctly a round object has the same drag as an airfoil ten times the width.
Perhaps most importantly, a single mast 'dirties' the air flowing across a sail significantly causing loss of lift, especially at high angles of attack. On the Kolika the sail's leading edge is almost completely clean, with only the roller furling to impede the flow.
I finally learned about the unusual prop and rudder design. The rudder has two sections behind the prop that are angled about 10 degrees from straight, in opposite directions. It turns out this has the effect of straightening out the propwash, eliminating prop walk. The circular foil around the prop is called a 'Kort nozzle'. This increases the efficiency of a prop - there is an article in Wikipedia. Overall though I think this arrangement has more drag when sailing than a more typical setup.
The trim tab apparently did not work as expected, and Mr. Klimmek locked it in place at some point.
[edit: One more interesting tidbit. The surveyor discovered that the original painted waterline was incorrect, and a new one applied. The boat evidently rides about six inches lower in the water than planned, which means the boat is heavier than planned. With 320 gallons of water and 180 gallons of diesel, plus 80 additional gallons hot water storage, that amounts to roughly two additional tons to haul around.]
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