natural ferequency

[saeedeh]

hi guys
how can I calculate ang get some info. about natural ferequency of planning boat?
is it important item in design?after that I want to compare it with frequency of porpoising? is there any similar study?
thanks before

[Fanie]

As far as I know if your boat porpoises the motor trim angle is incorrect

[Frosty]

Trim will sometimes correct it bit is not neccesarily the reason for it.

[powerabout]

saeedeh


The 2 are not related, it a force-drag-lift issue ( and hence speed related)and as the guys say trim can fix it more often on slow boats less often on faster boats say 50kts and over being fast.

A boat that performs best in a slight chop may well porpoise in dead flat conditions.( drag goes up)

Quite often a longitudinal weight transfer can also stop it. ( angle of attack change)

Different styles of propellors can also stop or create porpoising, due to their bow or transom lifting properties.

If your talking a shaft driven boat you lose the ability to alter drive trim but weight and prop are still avaliable.

Cheers
Powerabout
(newbie)

[Guest625101138]

Originally Posted by saeedeh

hi guys
how can I calculate ang get some info. about natural ferequency of planning boat?
is it important item in design?after that I want to compare it with frequency of porpoising? is there any similar study?
thanks before

This planing hull calculator will indicate if the boat has a tendency to porpoise:
http://illustrations.marin.ntnu.no/h...ing/index.html
It is a function of many factors. Speed and longitudinal location of CoG are important factors. Moving weight forward does indeed reduce the tendency.

Rick W.