Flat stern bottom extention on displacement power boat?

[Jeff in Boston]

Hi folks!

Looking at various displacement power boat hulls I see flat stern bottom extensions on many of them. I assume these are designed to be near the waterline? Just under?

Example:



I understand that immersed transom area increases displacement speed drag. When these are at the waterline they wouldn't have much immersed transom area. These flat areas at the stern add surface drag I would expect. But not that much?

Won't this cause slapping when the boat rolls if it is near the waterline?

Am I thinking about this correctly?

Thanks!

 

[Mr Efficiency]

I'd say the idea there is to get some extra speed beyond the displacement "hull speed", that flat section would act to reduce squat.

 

[messabout]

Roll velocity is small enough that the addition of "squat boards" is not likely to cause excessive noise or splashing.

 

[Mr Efficiency]

When the boat is powered up, it certainly would not be a problem, in some circumstances it might slap at rest

 

[Jeff in Boston]

Thanks folks!