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More Brick - literally

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  • graeme19121984
    Water Beetle-10 ... #680... @ USD125. Written up in MAIB (June 09, p42). Is the - a typo, or does -10 imply a range of NanoCruiser lengths? (Yes, yes, I
    Message 1 of 1 , Mar 17, 2010
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      "Water Beetle-10"... #680... @ USD125. Written up in MAIB (June 09, p42).

      Is the "-" a typo, or does "-10" imply a range of NanoCruiser lengths? (Yes, yes, I know about that of Super size!)

      You've heard of the PDR boating phenomenon? PDR is based on Brick, and various well regarded boat designers have taken a turn at getting aboard. In common they seem to say it didn't strike them as much of a boat design at first glance, however on consideration they came about. The PDR is a restricted development racing class. It's good sport, it's growing, and good on it. The bottom shape and size of the hull to a height of 10" is the restricted part, and that's a bottom claimed to sail better and faster than that of Brick. I don't know about that. Let's see.

      PDR has significantly less rocker depth, it is said, and maximum rocker depth is placed further aft than that of Brick, it is said. Well, it's 3" less rocker depth than Brick as measured down from the bottom of the bow transom. That's 6" as to 9" or 33% less. However, draft is different as is shape, meaning either boat may have more or less draft when loaded and heeled, and ballast will work better at that low point in Brick, and flat spots can make for turbulence, and. There's a 1ft flat inserted aft of midships in PDR. The gentler PDR rocker grants a longer waterline for higher theoretical hull speed it is said. This rocker, with the flat spot, and maximum rocker further aft are said to see the PDR able to sail better and faster than the Brick. It is said. Is the claim that PDR rocker is further aft valid?

      Which point on the bow do you compare a PDR and Brick from, aren't there two? Yes, there literally are, and the bow transom sides are not what I meant! As there's usually an inclined bow transom on a PDR, as there is on the Brick, is longitudinal comparison made from the upper or lower edge of the bow transom as a reference point? Most PDRs sides are 16" - 18" high, yet if the sides are no higher than the class legal height of 10" then the bow is vertically snubbed, and LOA is 7' 9". Boats of higher sides could be of this shorter length too, but most have the inclined bow transom and are about the length of a plywood sheet at 8ft long like Brick. It's 8ft LOA boat hulls to be compared first then, followed by hulls as measured back from the bottom of the bow transom.

      Measuring from the upper bow the PDR maximum rocker depth occurs at the 1ft flat spot which has its centre only 56.25% aft at 4.5ft. (The aft end of the flat spot is 62.5% aft of the upper bow at 5ft back.) The Brick maximum rocker depth is 56.25% aft of the upper bow at 4.5ft. Busted, 'cause Brick has max rocker depth centred similarly to a PDR.

      Measuring back horizontally from the lower bow (the foremost edge of the bottom) the PDR maximum rocker depth at the the 1ft flat spot centre occurs 4ft back along an overall span of 7' 6" = 53% aft. (The aft end of the flat spot is at 4.5ft = 59%.) The Brick maximum rocker depth is 4' 2" back along an overall span of 7' 8" (4.2ft in 7.6ft) = 55.2%.

      Is the simple claim that PDR rocker is further aft valid? No, that's busted, cause it's just not a big enough deal! Then there's the actual load waterline length according to how much the hull and all aboard it weigh. Then there's heeled waterline stretch. Then there's trim attitude, and ballast effect. Then there's the heeled lob-sided vesica (outline of the waterline plane shape) probably providing more lift to Brick. There needs to be a long series of controlled match races to decide on the fastest hull.

      Last week on another Yahoo boating group one of those well regarded small boat designers had this to say about their latest PDR design contribution towards helping to get people out sailing: "As I drew it I worked up stability and resistance curves, load carrying ability and so on, and found that Bolger must have had his head working well the day that he designed the "Brick" which inspired Shorty Pen who started the PD Racer movement."

      There's now the 12 ft PDR dayboat "Goose". How about a 12 ft Brick? If there's anything to that gentle rocker stuff then a simple stretch might see another Brick eating poultry. It might be that perhaps the rocker proportions should stay as they are for best speed as implied by the well regarded boat designer? Add a Water Beetle winged box keel from a NanoCruiser under and leave the poulty in a flap?

      Graeme
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