There are alot of misconceptions associated with boat weight, some falsehoods even.





First of all, the same water that is pushed out of the water pushes back against the hull on the rear part of the hull and thus negates a very large portion of the "push-away" drag on the front part. The form drag is actually ONLY the net difference between the "push-away" and "push-back" phenomenon and in a frictionless fluid this net difference would be zero, resulting in zero drag. In real life fluids like water are not frictionless and the amount of internal friction forces for a given fluid determines the amount of form drag. That is why the same hull in water has less form drag then say in oil.

Therefor the popular representation ;"each extra lb. of weight in the boat/crew is another lb. of water that water that has to be moved out of the way for each boat length travelled" is misleading as it omits the part where the same additional lbs pushed back later and gives back some of the energy lost on the front part of the hull.

Secondly for some factor to be very important for the overall performance of a sailcraft it needs to constitude a significant part over the overall drag. If a given component only makes up 10% of the total drag then a 25% reduction of that factor only amounts to 2.5% drag reduction of the total with an even less performance gain (= for floating objects typically (1-1.5%)

The team for the C-class catamara Miss Nylex publized some of their research data and I give some of their conclusions regarding drag factors.


Hull drag (subtotal = 35%)

-1- wave/form drag = 15%
-2- skin friction drag = 20%

Sail drag (subtotal = 25%)

-1- form drag = 9%
-2- induced drag= 16 %

Centreboards = 20%

parasitic drag (group of 7 subcomponents like rigging and crew each less the 4%) = 20%


Note that even form and skin drag combined only make up for 35% of the total drag on a C-class catamaran with a highly efficient wingsail. On our catamarans the rig is less efficient and the sail associated drags will increase reducing the relative magnitudes of the hull form and skin drag factors.

35% may sound like a large portion but we still haven't completed the analysis yet. 1% additional weight doesn't increase the hull related drag by 1% of 35% = 0.35%, it is less. This is because of the non-linear dependence of volume (weight) and surface area upon size. We all know this to be true as a bottle that is twice as large will have 4 times the surface area and 8 time the enclosed volume (weight).

Assuming the hull can be optimized for a given boatweight and crewweight then for each 1% of additional weight you only have to entlarge the hull by 0.33% resulting in similar fractions (0.66%) of increased hull area and crossectional area. Also the fractions became smaller within increased additional weights, again due to the non-linear behaviour.

Basically (a simple example) an additional kg on a 100 kg boat + 75 kg crew (0.57% weight increase) results in a hull drag reduction from 35.00% to 34.86%. Which on the total drag of a sailcraft like Miss Nylex results in a less then 0.140% reduction => ... => on average 0.1% performance increase for a waterborne craft (= about 3 second per hour racing). Of course this is for lightweight boat with a singlehanding crew with everything else like sailcut and windconditions being perfectly equal. When looking at doublehanded crews on heavy boats the difference becomes MUCH smaller as 1 kg difference here will be a much smaller fraction of the total. In effect the solo sailor on a lightweight singlehander is the worst case scenario. However, allowing different sailcuts (formula classes instead of One-design) is so potent that it is able to complete ofset this weight dependancy, as proven over and over again in the A-cat class where 85kg skippers are competitive with 65 kg skippers on a world championship level. That is how small the dependence of weight in the larger picture can be and why OD garanteed equality in performance is such a myth. In several cases the OD character of a class makes the differences in performance worse !

We should now do the analyis on 1% difference in sailarea and see the difference between that and the dependency on weight. That tells an interesting story as well and why water or sand ballast can be an advantage on sailboats and landyachts.

Wouter