Newly installed used paravanes failed.

[ofer]

I bought a set of paravanes from a commercial fisherman next to my boat. It was a good buy and I am glad I did.

I installed and tasted them on the water for three days and they exceeded my expectations. On the fourth day otw to kodiak one bent 90 degrees. Not fun until I was able to get some coverage at the baren islands.

I have made two new polls using 2.5 inches schedule 80 alum. Old ones were schedule 40 and had signs of rubbing in areas etc.

All in all I am very happy with the results and am glad I got that one off my list.

[Max1]

Congrats.
I know the admiral would like something like that on our boat.

[denverd0n]

Obviously you over-stressed that pole beyond its limit. I have to wonder if you were going too fast at the time. If I recall my physics correctly (which is no sure thing) then the force on the pole should go up with the square of the velocity. That is, double your speed and you quadruple the force exerted on the pole.


Meaning, when you deploy the fish you should probably slow down at least a little bit.

[hollywood8118]

Originally Posted by denverd0n

Obviously you over-stressed that pole beyond its limit. I have to wonder if you were going too fast at the time. If I recall my physics correctly (which is no sure thing) then the force on the pole should go up with the square of the velocity. That is, double your speed and you quadruple the force exerted on the pole.


Meaning, when you deploy the fish you should probably slow down at least a little bit.

You may be correct but it looks like the load at the end of the pole was distributed partially to the center lift point vs totally at the end. The load path needs to be carried totally by the end of the pole ( with exception of some compression which goes up it the pole is taking load at the center) The load path needs to go to the fixed stay that connects to the top of the mast and the pull from the foreguy. It's all about angles.
Hollywood

[DavidM]

Most structural elements on boats have a significant design safety factor, meaning it shouldn’t fail until the load gets to several times its design load. So you exceeded that poles design load by several times.

Changing to schedule 80 pipe probably increased the design load by a couple of times but that means you are probably still exceeding that higher design load.

You need to increase the pipe diameter and/or intstall gussets along the pipe in the direction of the load to increase the design load further.

Slowing down as noted above will reduce actual loads, generally by the square of the change.

Also have you considered the loads you are putting on the mast, compressive and bending. If the two fins are running perfectly, the bending loads are cancelled but rolling and sea state will allow one side to apply significant bending forces while the other side may apply none.

I think your entire system needs a review by a naval architect.

David

[KnotYet]

On this design I would avoid using the center-ish pole lines. They serve no function.
The poles can be raised and positioned from the masthead lines. Any preload from
other directions can initiate a flex that might result in permanently deforming them.
Going to schedule 80 is a step in the right direction to determine the best size poles.

[Bmarler]

It looks like you caught something with that stabilizer. We snapped wooden poles and bent aluminum ones on the trollers when we inadvertently caught a log or something. No way to prevent something like that from happening, just gotta repair and move on.