Tampilkan postingan dengan label rosin. Tampilkan semua postingan
Tampilkan postingan dengan label rosin. Tampilkan semua postingan

Senin, 14 Maret 2016

Boat Plans Aluminium Australia



I recently read an article concerning conversion of developable surfaces into flat sheet patterns.  In previous posts, I really havent discussed how to do that using a mathematical approach.  It can be done; I used this approach when I built a 20 1/2 foot sharpie design many years ago.  The only reason I havent expanded on the subject is that, once I have a hull framework constructed, it is easier to simply make a stiff rosin paper pattern by laying a roll of paper over the framework and tracing the edges.  But, for those who do not want to construct a full hull framework, being able to go directly to laying out patterns for sheathing may be worthwhile.

The method utilizes what may be best called external triangulation.  It is external because we are not calculating distances just between points within the design surface but instead are using our conic apex, located at some distance from the surface borders, as a reference point for many measurements.  Using the coordinates of the apex in conic development and the coordinates of consecutive points along the chine of the hull, we can calculate the length of radiating (ruling) lines emanating from that apex.  The chine of the hull is created using a mathematical equation; thus, by integrating this equation (the power of calculus) we can find an equation [it is a long but standard equation] to calculate the distance along the curve between any two designated points on the chine.  Those points along the chine provide the third distance in creating a series of triangles which, when plotted in sequence, will give us the shape of the developed surface.  However, part of the chine curvature may be contained within the outline of the surface itself; thus the sequential points of the chine are best first plotted along a fair batten which is then laid in place and connected to the ruling lines from the apex.  For parallel projections, instead of an apex, we would be plotting parallel ruling lines.  If you calculate the distance between two sets of coordinates in a developed surface NOT connected by a ruling (straight) line by using simply the formula square root of (x squared plus y squared plus z squared), the distance will be distorted by lack of consideration for the curvature present.

In conclusion, yes, I can create flat surface patterns for sheathing.  But is it really worth the effort when a roll of rosin paper will give me the same thing?   


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Sabtu, 12 Maret 2016

Boat Plans Catamaran


A planned trip to Pueblo Reservoir had to be cut short because of an electrical short in the power tilt/trim switch.  Diagnosis was difficult; installing a new switch was simple.  There was a crack in the rubber cover for this switch which, after a period of use, allowed moisture intrusion to complete the circuit.  This past week we went to Flaming Gorge Reservoir in Utah for some real boating.  The lake extends into Wyoming for 75-100 miles filling a deep and scenic gorge.  We explored the lake for 30-40 miles and encountered some wind and waves.  It is a light boat with little draft so, when maneuvering into the dock with a wind present, we lower the bimini top to cut windage.  Also, when cornering while planed out, the hull will skid; when cornering while accelerating onto a plane, the hull will bank well and turn sharply.  There is almost no bow rise when accelerating, and the hull rides smoothly and cuts through moderate waves with no fuss.  I switched to a 15" pitch prop for this trip.  We were operating at 6000 altitude, and the engine achieved 4700 rpm, easily exceeding the 35 mph maximum speed of the speedometer dial.  The "sweet spot" for this engine is supposed to be 5000-5200 rpm and our next outing is at Grand lake, over 9000 elevation, so I have ordered a new 13" pitch stainless steel propeller which, hopefully, will be perfect for these circumstances.  I have to think that, if we were near sea level, this boat would easily exceed 40 mph or, alternately, I could have installed a somewhat less powerful engine.

I havent yet mentioned that this new boat fits our trailer perfectly, much better than the previous boat.  We trailed it 400+ miles to the lake; other than a decrease in acceleration, you couldnt notice that we were towing.  Although I cant find anything design-wise to improve on this boat, I am always evaluating what could be made better/ more esthetically pleasing on a next boat.  This is a 12 degree deadrise hull; I wonder what a 14 degree deadrise would do to performance?  I have an idea for a more modern-looking runabout which I hope to publish here in the near future.  I already have all the offsets and need to make up some drawings.  Then perhaps construct a model.


    


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