Boat length vs chop size and period

[TeddyDiver]

Originally Posted by MartinR

These are very simplified the factors affecting the movement of the boat in waves. But the shape of the bow is defining if this results in pounding or not. Flat forefoot - more pounding, deep forefoot - less pounding. The Colin Archer I had many years ago never slammed, it was always soft. Modern boats are much more prone to it, but there are still big differences. And it is often avoidable just by changing the course and i.e. the apparent wave period.

As I said a lot of other factors influence on the amount and also how that feels on board but if those two "simplified" factors don't meet there's no pounding whatsoever..

Teddy

[soares29]

From most replies sounds like the most important component is haul shape, correct? How important is haul length? Would a beneteau 55 slam more, less or much less than a 45 ? In the Mediterranean... 5 feet 5 s period...

[Suijin]

I heard in the past that the average length of a Chesapeake dead rise was found to be twice the length of the average wave in the Bay. That says volumes right there if it is true. It’s

[cyan]

Originally Posted by Pelagic

"Metacentric"

https://en.m.wikipedia.org/wiki/Metacentric_height

With so many possible funny responses, you roll in with THAT polite post??
This place is oddly civil lately. (A good thing I suppose.)

[Reefmagnet]

Hull shape, boat weight, weight distribution and boat size will affect pounding. At a certain point, the affect will be greatest for any vessel as a resonance starts to occur. The practical solution in dealing with it is to vary speed (up or down) and/or change angle of direction to the waves.

[Pelagic]

I think most of you are missing exactly what the OP was asking.
He was asking about relationship of pounding to boat LENGTH.

As I said before, the critical relationship of Boat Length to Wave Period Length is around 1 to 1 for the worst pounding

Speed, or wave height, or hull configuration, or longitudinal weight displacement (which affects longitudinal centre of gravity) (tipping point) ALL affect the severity of the pounding, but they are secondary.

It is getting near that critical wave period relationship, which initiates the worst results for all the same secondary conditions.

[Reefmagnet]

Originally Posted by Pelagic

I think most of you are missing exactly what the OP was asking.
He was asking about relationship of pounding to boat LENGTH.

As I said before, the critical relationship of Boat Length to Wave Period Length is around 1 to 1 for the worst pounding

Speed, or wave height, or hull configuration, or longitudinal weight displacement (which affects longitudinal centre of gravity) (tipping point) ALL affect the severity of the pounding, but they are secondary.

It is getting near that critical wave period relationship, which initiates the worst results for all the same secondary conditions.

Changing approach angle changes relative period.

[Pelagic]

Originally Posted by Reefmagnet

Changing approach angle changes relative period.

Exactly!
But what you are doing is artificially lengthening the wave period by transiting between two crests at an angle, rather than straight across.

[Pelagic]

Longitudinal centre of Gravity (also called longitudinal centre of floatation) is often forgotten by pleasure boat skippers when loading their boat.

Critical when you are a cargo ship but for us, it is something we should understand

http://www.splashmaritime.com.au/Mar...__Longitudinal

[Ericson38]

water depth of 50 feet with 20 mile fetch of 30 kt wind with tide against can make vertical waves. Don't know the formulas though for wavelength and period.

[Don C L]

Originally Posted by Pelagic

Exactly!
But what you are doing is artificially lengthening the wave period by transiting between two crests at an angle, rather than straight across.

Yes that AND when you come down the other side you are not falling quite so far to water again and that water below you (hopefully) has an angle to absorb the fall.
I was only going to add that ANY flat bottom boat will eventually find its favorite wave height/period/boat speed to slam in.. and then you have to adjust speed and/or angle to the waves. But with a deeper displacement hull, at least I have found, it's hard to find those conditions that will lead to slamming. But, you are going slower. To me 4 hours of not slamming beats a half hour of slamming unless you are racing or you need to get somewhere in a hurry.

[sailorboy1]

Aircraft carriers don’t care about 10’ waves.


Submarines don’t care about 50’ waves.

[EmeraldCoastSailor]

Originally Posted by Sojourner

In the mediterranean, everything will pound Short, steep little nasty waves, we call it the two-step

Reminds me of the Gulf of Mexico.

[Luckyknot]

Originally Posted by Pelagic

Longitudinal centre of Gravity (also called longitudinal centre of floatation) is often forgotten by pleasure boat skippers when loading their boat.

Critical when you are a cargo ship but for us, it is something we should understand

Longitudinal & Transverse Stability

I agree with everything you've said however LCG and LCF are not interchangeable. The LCF is always the geometric center of the water line plane. LCG may be the same number but correlates to a point (CG) that is typically some distance above or below the water line depending on the vessel.

[Pelagic]

Correct luckyknot, I was lazy in my explanation[emoji20]