{"id":15701,"date":"2011-03-13T20:00:51","date_gmt":"2011-03-14T01:00:51","guid":{"rendered":"https:\/\/setsail.com\/?p=15701"},"modified":"2011-07-17T03:18:13","modified_gmt":"2011-07-17T08:18:13","slug":"fpb-112-design-cycle-working-through-the-tradeoffs","status":"publish","type":"post","link":"https:\/\/setsail.com\/fpb-112-design-cycle-working-through-the-tradeoffs\/","title":{"rendered":"FPB 115 Design Cycle – Working Through The Tradeoffs"},"content":{"rendered":"

\"MG<\/p>\n

Ed Firth, one of Circa’s engineers, has been with us in Arizona the past week, refining the preliminary FPB 112 design. We thought a few comments on the process might be of interest.<\/p>\n

<\/p>\n

\"Wb<\/p>\n

As we have discussed before, capsize resistance and recovery are critical components of yachts intended for offshore work. This is a function of the center of the gravity and bouyancy as the hull rolls through various heel angles. So our first step with Ed is to complete a detailed<\/em> weight analysis to confirm displacement and VCG. There are inumerable items to look at in terms of weight and position. The spread sheet, a small sample of which is above, has thousands of cells \u00a0of data. The earlier work was done with educated guesses, but at this point in the cycle we need confirmation of the numbers.<\/p>\n

With displacement and CG in hand, we do roll over simulations in different load conditions, varying liquids, and looking at lead ballast options (including no ballast). The image below shows the boat at three quarter load, heeled 45 degrees.<\/p>\n

\"114<\/p>\n

Note how she floats with the deck edge barely awash. Even at this heel angle Dorade vents, hatches, and doors are still above the static waterline. As we have detailed before, the FPBs are designed to skid easily, which helps to absorb wave impact minimizing extreme heel risks in the first place. There is little to impede sideways motion in in this attitude.<\/p>\n

\"114<\/p>\n

At 90 degrees the Dorade vents on the coamings are wet, but of course they have closure plates to secure them, which are operable from inside the boat.<\/p>\n

\"114<\/p>\n

And 120 degrees. Note that most of the deck is still dry. These images and their accompanying stability curve help us fine tune the heeled volumes, and define what is and is not practical within the design envelope.<\/p>\n

With the basics now defined the hull design cycle is restarted to see what can be done to improve sea keeping and efficiency. SInce the vertical center of gravity is a bit lower than originally estimated – a bonus we are happy to take – \u00a0freeboard can be increased if desired. Adding to the topsides means more weight up high, so amendments are made to the spreadsheet, and new models with higher freeboard\/VCG are tested for ultimate stability.<\/p>\n

\"114<\/p>\n

The stability curve above is a worst case scenario, half tanks and no lead ballast. The data on the left has been omitted – there is a limit to what we will share. Data across the bottom represents heel angle in degrees. Note there is no stability indicated below the horizontal line. This indicates that the FPB 112 in this trim has positive stability through 180 degrees of heel. <\/span><\/p>\n

\"FPB<\/p>\n

Here is an updated (to June 20 2011) look at the direction we are heading. Freeboard (topside height) has been raised 12 inches\/300mm. The coamings and window mullions are up a slightly smaller amount. From which we derive the following benefits:<\/p>\n