54 THE DETERMINATION OF THE RESISTANCE OF SHIPS. 



It has been with considerable regret that I have avoided extending this paper 

 to cover, in a similar manner, the literature of the screw propeller. It would have 

 been impossible to adequately cover both of these branches of the subject in the time 

 at my disposal, and I would suggest that a corresponding paper on the propeller 

 side of the question be prepared for next year, if the council consider it worth 

 while. 



A few paragraphs follow in which matters of current interest in ship propul- 

 sion are touched on, together with a list of references which contain practically all 

 that has been published of late years on this subject. 



EFFECT OF INCREASED BEAM. 



It has long been known, and acted upon, that large beam, generally speaking, 

 involved high resistance; we realize nowadays that too high a price can be paid 

 for small beam and resistance. Increase of beam, accompanied by increase of sta- 

 bility and decrease of fullness, by no means necessarily spells increase of power; 

 for the same or less power a healthier type of vessel can generally be obtained, at, 

 however, a somewhat increased first cost of hull material in most cases, due to in- 

 creased wetted surface and wider decks. 



We have arrived at a point where increased safety is demanded in passenger 

 carrying vessels ; it is no use putting in bulkheads to enable a ship to keep afloat 

 after damage if the other danger — loss due to lack of stability in the damaged con- 

 dition — is not also provided for. Loss of buoyancy and loss of stability must both 

 be kept in mind when settling on dimensions in a given case. 



The effect of this on speed and power will by no means be proportional to the 

 increased beam, as might appear at first sight. 



A far worse enemy to good driving is full waterlines in the forebody. In two 

 recent cases of relatively fine and fast ships that have come directly under my 

 notice, the forward waterlines were forced out by considerations of stability to the 

 point of a marked decrease in speed when compared with similar ships of the same 

 principal dimensions and power. This feature, also, has its limitations, for in full 

 and slow cargo boats the exact opposite is true below a certain speed. This con- 

 dition is brought out by Professor Sadler in his 1909 T. S. N. A. paper and was 

 verified in a recent case by direct experiment for a vessel about to be laid down. 

 While this is true for smooth water there remains the question of loss of speed in 

 head sea. This question has recently received considerable attention and is re- 

 ferred to elsewhere in this paper. 



It is safe to say that passenger ships generally will show a tendency to in- 

 creased beam in the future, extra life-saving equipment, the natural desire of pas- 

 sengers for deck cabins and extra stability for damaged condition all tending the 

 same way. This will not necessarily entail more power, because we know more 

 about good forms and because ships are tending to be somewhat finer to give better 

 sea performances. The cruiser stern is another way out of this difficulty. 



