Decided to throw something together about rake length with some numbers. It seems that whenever rake length is brought up, all the builders question wether or not its good. So I decided to put some numbers on paper for a "just see" purpose. That and its f'n raining and I'm bored.
So, what we are looking at when we look at rake is the amount of surface area that is in contact with the water surface, thus friction. Now there are several factors to consider when doing this, wave friction, air, wind resistance. But all things considered, Boat A & Boat B will have to travel in the same conditions, so wave and air resistance are eliminated.
The basic formula for friction resistance is similiar, but manely R=Cf x S x V2.
R = Resistance in lbs
Cf = coefficient of friction using Reynolds Number
S = surface area in ft2
V = speed
The Reynolds Number for:
15' hull = .01093 (lots of factors went into this)
20' hull = .01052 (lots of factors went into this)
So if we have 2 boats A & B
Boat A is 18'48" with a 7.5' rake
Boat B is 18'48" with a 6' rake
R = Cf x S x V2
Cf on 18' hull is .01069
S on 7.5' rake = 18' - 7.5' = 10.5' of actual "wetted" surface area
S on 6' rake = 18' - 6' = 12' of actual "wetted" surface area
This is to say, how much hull is in direct contact with the surface, not up the sides, but surface. So to eliminate another factor, lets put the hull on dry land on a level surface. How much of the hull is in direct contact with the ground, the "wetted surface".
So since were not moving, we will use V as 1 so V2 = 1.
Boat A 7.5' rake
R = Cf x S x V2
R = .01069 x (10.5' x 4') x (1)2
R = .01069 x 42 x 1
R = .44898
Boat B 6' rake
R = Cf x S x V2
R = .01069 x (12' x 4') x (1)2
R = .01069 x 48 x 1
R = .51312
Doesn't seem like much but there is a difference. Now figure in wave resistance, "riding in a chop". The longer rake has more of a gradual slope that the shorter rake. Thus the shorter rake has more of a blunt surface and is much more prone to "plow rather than skim. Everytime a wave hits the short rake, the hulls slows down. And take into consideration that I negated speed. The faster your hulls moves, the more of a difference. Remember the speed is V2
Boat A
1 mph R = .44898
20 mph R = .44898 x (20)2 = 179.592
30 mph R = .44898 x (30)2 = 404.082
Boat B
1 mph R = .51312
20 mph R = .51312 x (20)2 = 205.248
30 mph R = .51312 x (30)2 = 461.808
The faster you go, the less drag and the more the gap get between the two.
Now most on here will argue that it really doesn't make that big a deal, but a little friction goes a long way. Why the hell is Frog selling that fantastic product, it reduces friction. So now when you hit a grass patch or lillies, your hull won't slam on the brakes, it will skim through that shit. Thus Gatorglide has lowered the coeffecient of friction between your hull and the water surface.
Again, this was just to throw some numbers out there for discussion or clarification.
