transom edge sharp or not

Does the transom edge need to be sharp on my boat?

I calculate a Froude number of about 0.9, based on a 9m/s velocity and a 10 meter long hull. If the calculation is bad, forgive me, I can redo it.

Someone told me the boat would go 2-3 mph faster with a sharp edge.

 

This is almost full planing speed, so the transom must be as sharp as possible.
JS

 

"Sharp" needs to be defined, but losing 2-3 mph would require some kind of crazy radius.

 

How's this? Sorry bout the rotation.

 

Nothing to worry about, I'd say.

 

Mr E. is right.

That radius will not cost you 2 to 3 MPH. If you make it into a sharp edge the corner will become vulnerable to chipping and breaking which may cost more speed that you might have gained

 

The sharp edge helps the boat to develop lift faster, to plane faster, and to avoid the transom running deeper in the water
at high speeds (avoiding increased drag). A rounded trailing edge goes against all that. Race boats never have a rounded
trailing edge unless someone got sloppy. The correct Froude nr. is the depth F-nr. at the transom.

 

To all. I did in fact run a bead of cabosil and milled glass there. Both will be finished sharp, but paintable sharp.

Thanks.

 

True, but some chipping is better than a rounded edge for performance. All five of my classic runabouts have sharp trailing edges.

 

Hi everyone, I have a similar question for a different situation: wing and surf foil boards. Early foils were slower and lower aspect, so boards were designed with sort of displacement tails with cutaways to allow for the rider to pitch the board up and out of the water. Now foils are faster, higher aspect, and less tolerant of higher AOA, so full planning speed at takeoff. But many boards still have rounded tails, and when you touch down I think that makes them stick more than them need to. This is important because in many situations, like light wind winging and downwind SUP foiling, there is so little energy that a little friction fora moment can take you down. So my question is: how much of a difference would sharper release edges make in that situation? I’ll try to post some examples.

 

Appletree Skipper Downwind SUP | The Foil Board Shop https://foilboardshop.co.uk/product/skipper-downwind-sup/

 

As sandhammer notes, sharp is always best.
How much, ... simple trial and error will tell you the absolute amount - ie test with radius and after made sharp.... as too many variables to state categorically.

 

In a hydrodynamic sense, a general definition would take the radius in relation to the actual boundary layer thickness.