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Scuppers and Bullets: Question

Pmarcus
01/10/11 #9890

Hey All,

From a drag factor, it seems most scuppers are right around the bottom of the pedals…..not being a marine engineer, if the scuppers are moved towards the stern by about 4 to 6 inches, could this have a negative effect on boat speed or not much change???? What says you????

Peter

Re: Scuppers and Bullets: Question
Erik Borgnes

01/10/11 #9891

Theoretically, drag should drop if you move the scuppers astern but realistically, there won't be any difference in boat speed. Remember that flow along the hull is laminar (smooth and low drag) along the first third of the hull, then somewhere about 1/3 to 1/2 the way back flow becomes more turbulent and higher drag. If you moved the scupper forwards into the laminar flow, then drag would increase. Moving it back towards the stern would have a negligent effect because the water hitting the scupper where it already is is turbulent anyway - I think.

Along the same line of thought, if you put a bungee around your hull to increase drag, you'll notice a larger difference if you wrap it around the bow as opposed to if you wrap it around the rear deck.

Erik

Re: Scuppers and Bullets: Question
Reivers Dustin

01/11/11 #9892

The physics can be fascinating, but in practice trend negligable. I believe a textured surface was applied to the local super-deluxe Epic V-10. This is an engineered surface intended to hold laminar flow further along the hull. If I remember correctly that surface is 'orange peel' type of profile. The discussion gets more fun when you factor in waves.

Any irregular surface structure triggers non-laminar flow at speed. Any 'blunt body' in liquid flow generates vortexes and thus vibration. (Ask LB for his weed guard story.) For flat surface I think the physical constant used for calculating the transition is called the 'Reynolds number'. (Add liquid density, viscosity, velocity variable, …)

The arguement about optimal boat weight has more meaning for me. I think a boat over 30 pounds is too heavy. Under 20 is too light. Maybe this is related to my own body weight or configuration.

Of course the motive power is the limiting factor in my case. So all the fine points are best considered with humor.

rd

Re: Scuppers and Bullets: Question
Larry <lbussing@…>

01/11/11 #9893

A scientist published an article awhile back that said the laminar flow only extended back a foot and a half at most. He had done several water flow experiments while in grad school. So while I lack that kind of labratory experience, I guess I have go with his results. Moving the scupper won't have any effect. Removing the scupper would. Thats why they changed the style of scupper on the V-12. For flat water, you can raise the scupper and reduce the resistance. Thats also why I think one scupper is better than two. Larry B.

Re: Scuppers and Bullets: Question
gabe newton

01/11/11 #9898

Seems like adding bullets (whether small or large) would have a much greater effect on drag reduction. I fashioned one out of acrylic for my V10L, and the boat was dry at slower speeds, but it did not drain quite as fast, so I removed it before the Wildside (destroying it in the process.) How much it reduced drag is anyone's guess, but I would guess that the drag reduction was (almost!) measurable. (I did not try doing any comparative time trials.) You've probably all seen this link on bullets and fluid dynamics, but here it is again:

(Editor: link is defunct)

Gabe

scupper_location.txt · Last modified: 2020/09/16 21:50 (external edit)