Lifting Strakes vs Spray Rails

[crustysailor321]

I'm no naval architect or marine engineer and my understanding of hull shape and design is limited to the basics (i.e. difference between displacement, semi-displacement and planing hulls, deep v hulls with substantial deadrise for better seakeeping, stepped hull increase lift etc). Beyond that, those complicated calculations I see the architect and engineers work on is all Greek to me. Still, I am curious to know one thing. Those spray rails I see on the bottom of the boat, how do the naval architects know where exactly to place them and what angle to place them to maximize its effectiveness? Besides, I use "spray rails" and "lifting strakes" interchangeably, but I'm told they are not the same. What is the difference between them? The strakes also increase dynamic lift for the boat in addition to getting rid of sprays, while getting rid of sprays is only what spray rails do, correct? Although are they only effective at planing speeds? At displacement speeds they would increase the wetted area and therefore increase drag? Thanks.

 

[benjenbav]

I'm no naval architect or marine engineer and my understanding of hull shape and design is limited to the basics (i.e. difference between displacement, semi-displacement and planing hulls, deep v hulls with substantial deadrise for better seakeeping, stepped hull increase lift etc). Beyond that, those complicated calculations I see the architect and engineers work on is all Greek to me. Still, I am curious to know one thing. Those spray rails I see on the bottom of the boat, how do the naval architects know where exactly to place them and what angle to place them to maximize its effectiveness? Besides, I use "spray rails" and "lifting strakes" interchangeably, but I'm told they are not the same. What is the difference between them? The strakes also increase dynamic lift for the boat in addition to getting rid of sprays, while getting rid of sprays is only what spray rails do, correct? Although are they only effective at planing speeds? At displacement speeds they would increase the wetted area and therefore increase drag? Thanks.

They could be designed via sophisticated 3D computer modelling or, given that these are boats, they could be designed by salty old-seadogs nailing on a couple of lengths of 4x2 and then lopping bits off with an adze until it was about right.

Who can say?

 

[zapcat]

The purpose of the rails is fairly well covered in Sonny Levi's book Dhows to Deltas if thats any help - but not the easiest or cheapest book if you are just curious, but is an excellent book to have on the shelf.