Pivot Point

[charliehows]

Originally Posted by LIboater

On my 34 ft SR there are metal tabs along the gunwhale indicating where the slings should be placed for a haul out. I must assume that the point that marks the center point between these 2 tabs is the CoM or very close because you want the boat as perfectly balanced as possible when you haul it out. However, the center point between these sling tab markers is nowhere near the observed pivot point of the boat. Granted drag might affect that, but it is hard to think it makes that great a difference.

Whoa! might be being pedantic but the assumption that markings for the slings are a guide to CoM is way off. Placement of slings is dictated by the architecture of the hull - balance is a minor consideration at best, as long as each slings is somewhere in the vicinity of each end of the boat they will work. Its much more important to avoid placing them at the extremities of fins, keels, skegs, props, rudders, steep slopes, sensors or other protrusions etc., etc.

[StuM]

Originally Posted by Lodesman

I can't believe this is still being discussed. You got your answer in post 14. The pivot point is not fixed - at rest it's near (and usually just forward of) the longitudinal centre of the boat, and moves forward or aft from that point as the boat increases speed going forward or astern respectively. It varies with the hull shape.

No, it was not answered in post 14.

The question was "Ignoring drag of any sort on hull, wind, current or other external factors". Post 14 and your response above provide practical information in the real world, not the theoretical, perfect world of the OP where the pivot point WOULD BE fixed.

[Lodesman]

Originally Posted by StuM

No, it was not answered in post 14.

The question was "Ignoring drag of any sort on hull, wind, current or other external factors". Post 14 and your response above provide practical information in the real world, not the theoretical, perfect world of the OP where the pivot point WOULD BE fixed.

I assumed we were still talking about a boat in water and pivoting or yawing around a vertical axis. If the boat is floating in space, then the props have no effect and any pivot point will necessarily be a factor of where an external force is applied - it would only be CoM if the force was applied at the very end of the boat.