Liar! Liar! - Pants on fire!
Clearly, one of the keys to success for our venture is the performance of grand Illusion XL - regarding speed and power requirements. Our projections, on the web page <boat design 101> were based on the performance of our 40 ft. "model" Walk on Water. You only have our word for it - as to the authenticity of this data. Seeing as the results of these projections, in regard to the performance of Grand Illusion XL, are so remarkable, some may harbor a few doubts - regarding the input data.
Let us then, use some other data for our projections - which is easily verifiable and obtained from vessels which are, in one key aspect, closer to the design of Grand Illusion XL. Let us consider 8 man rowing shells. A loaded "heavy weight" rowing shell is 55 ft long x 1.9 ft. wide and has a gross weight of approx. 1,870 lbs. Coincidentally (and importantly) the length / hull beam ratio (30 : 1) is exactly the same as that of Grand Illusion XL.
The general shape of these hulls is also virtually identical to Grand Illusion XL - with very long, perfectly straight, mid sections - as opposed to the hulls of virtually all other modern day catamarans - which are curved for their entire length. The only significant difference is that the hulls of Grand Illusion XL are V'd - while the rowing shells are round bottom.
The current world record speed for these boats, over a 2000 meter course, is a little over 12 knots. Figures given for the horsepower which a trained "heavyweight" male rower is capable of producing (over a 2000 m. course) vary between 0.2 and 0.4 hp. Let us be conservative and stipulate the higher figure. Using (2) 8 man rowing shells as our source for data we can create the following table.
Boat Waterline length Gross weight Power required Speed
(2) 8 man shells 55 ft 3,740 lbs. 6.4 hp. 12 knots
Grand illusion XL 150 ft 120,000 lbs 205 hp. 19.8 knots
If the weight of Grand Illusion was scaled up in accordance with the length, the weight would be 74, 800 lbs and the power required would have been 128 hp. If one is not happy with our extrapolation of these numbers in the above table, we can look at it another way. By using (3) 8 man rowing shells as our "input vessel" this would create the following table.
Boat Waterline length Gross weight Power required Speed
(3) 8 man shells 55ft 5610 9.6 hp. 12 knots
(3) 160 man shells 150 ft. 111,22o lbs 190.8 hp. 19.8 knots
Grand Illusion XL 150 ft. 111,220 lbs 190.8 hp. 19.8 knots
This is, in fact, a very unexpected result. It would appear that the horsepower requirement (at a weight of 120,000 lbs.) would be a little less in this case. One would have expected that, because of the increased wetted surface of 3 hulls over 2 hulls, the second table would yield significantly higher results - in terms of power requirements. Ah well, another mystery to ponder. Let us ignore these surprisingly good results, for the time being, and go back to the first table.
In reference to the first table then, one difference, which needs to be allowed for, is that the rowing shells, with their round bottoms, will have less wetted surface than the hulls of Grand Illusion XL with their V bottoms. Allowing 15 % more power, to compensate for this, provides the following, rounded up, results (no pun intended) :
Grand Illusion XL - 250 hp. - 20 knots
This result is significantly better than the results shown on the web page <boat design 101> - using "Walk on Water" as the source for our data. This does not surprise us, in the least, seeing as we have endeavored, throughout this web site, to be scrupulously honest and transparent (many would say - to a fault) and to use very conservative estimates - for all aspects of our venture.
Having made the above claim, this might be a good opportunity to make yet another. Let us assume there was a prize for the "best" pleasure boat or "Yacht" in the world - with a price tag of under say $25.000.000.00. U.S. Let us further assume that, in the judging for this prize, no points were to be awarded in the categories of "Italian styling" "Decadent luxury", "Status" and "Image".
Let us also assume that a great many points were available in the categories of "Open ocean performance" "Functionality" and "Environmental friendliness". In other words, this was to be a prize for the boat (costing less than 25 million dollars) which simply "Worked the best". We would like to think that "Grand Illusion XL" would have a very good shot at winning such a prize.
Grand Illusion XL - 55 ft. "model"
Liar! Liar! Pants on fire!
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Magic Carpet Catamarans
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