Posts: 3508
Location: Elk River, Minnesota | O.k everyone, we now have two different things going on here dealing with this: wetted surface and coefficient of friction when in contact.
So...clarification here: Running in a light chop will increase speed due to less wetted surface in the water. This happens because the friction coefficient of air is much less than that of water. Waxing a hull will reduce the ability for water to adhere to the hull, thus a slower hull.
I've been thinking a bit about the air as a fluid thing which is correct, but you are talking about two very different fluids. On a surface such as your car, you are looking to reduce adhesion of many things...not just water. Waxing a car will reduce the amount of "stuff" (dirt, debris, etc) that can adhere to it, which increases it's aerodynamic efficiency. Air is much more "fluid" than water, thus is much more easily disrupted in it's flow as compared to water....the more disruption, the more turbid the air becomes, which will slow your speed. With a waxed automobile, you still will get air molecules adhering to the surface, which also reduces the amount of friction acting upon the vehicle.
In a wetted surface, you want a sheeting action between two surfaces, and a sheet of water is slipperier upon itself than is just the hull on water. Wax repels water by design, so the sheeting action cannot happen anywhere near as efficiently, thus slowing your hull.
The sanding mentioned by fin69 will not introduce air to the hull since it is a submerged area...it would create a larger surface area for water to contact and adhere to. What you are referring to would be something on the lines of a "stepped" hull. A stepped hull will by design create pockets of air on the underside of the hull due to the size of the step, reducing the wetted surface.
As for gaining 4 mph on an aluminum hull such as mentioned...I'm curious...what pitch prop, what RPMs were you running, what is the max rpm for the motor and what is the gear ratio of the lower unit? Oh...and what were the RPM's before you waxed the hull? I'd also be interested in the numbers for the 6 mph gain too..
Steve
Edited by VMS 4/16/2010 5:26 PM
|
