Asking for help re the various forces at play in a triangle made up of a sailboat mast (lying horizontal, so the base of the triangle), a pole locked vertically at 90 degrees at one end of the mast (also the hinge point), and a line fastened to both making the hypotenuse. The goal is to raise the mast to vertical by pulling on the upper end of the pole (often called a Gin Pole) so that the triangle rotates around the hinge vertex and the Gin Pole becomes horizontal as the mast becomes vertical.
Intuitively (because I don't know how to calculate the forces, and really only need to grasp the basics) I think that the longer the Gin Pole the better (within bending limits).
Also, it feels right to have the hypotenuse line reach the top of the mast rather than shrink the triangle with the line attached to another point on the mast.
If anyone can point me to a source, or can share some thoughts on determining optimum pole length / forces involved based on the weight & length of the mast, etc. I will be very grateful.
#physics #structuralanalysis #fulcrum #truss #sailing #raisingasailboatmast
@Pat Thanks; I'll have a look.
@PiperPilotPaul So, I've done this before on a 29' sailboat. Rather than a gin pole, we created an A-frame, which was far easier to stabilize and provided additional strength.
I don't think photos exist, but I could sketch what we did. How large is the spar in question?
I always look back to the ancients: did you know a 19th century ship of the line could start with all her spars in a pile on deck and rig herself entirely with her own gear? Of course she also had a lot of crew :) ! #sailing
@SYPerelandra Thanks for the A frame idea. The Gin Pole solution seems to be simpler since it needs minimal construction, and uses lines and pulleys already available on the boat.
It is a Nordica 16 with a mast of about 10 m.
I've "MacGyver-ed" a prototype with bits I have available so when our weather clears I'll test it. In doing so, I've answered one of my own questions: From a strictly forces-at-play perspective the longer the Gin Pole the better since it is the lever for the system, so it's length amplifies the pulling force (I think).
(There's also something about the angles of the triangle & the re-direction of the pulling force that I'm still noodling.)
Really like your comment about the ancients. We have lost a lot over the centuries becoming "smarter" - what Quinn calls the Great Forgetting.
I imagine you are following the Viking boat building project - Skuldelev - using original methods (Viking Ship Museum).
#sailing
@PiperPilotPaul oh! I Can't believe it, I have one of those in my garage! #sailing
@SYPerelandra Hey; that's phenomenal. That could be ours except yours is much cleaner and ours is called Dandy Lion.
That's a very nice cradle rig; ours lives outside on it's trailer.
Should I assume you step the mast with an A frame?
Or does the beautiful Perelandra keep you busy?
So glad we connected! #sailing
@PiperPilotPaul This just tickles me pink - I'm glad too!
For the Nordica I just brute-strength it up - but... When I revamp my trailer the idea was something similar to what you described... possibly to a winch on the trailer tongue to simply crank it up.
Pere is definitely the "main event" at the moment. I'm going to try and rendezvous them both at anchor this summer :)
@SYPerelandra Yes; I used to lift the mast vertically from the side of the boat up to the tabernacle while balancing on the cabin roof on one leg and singing "Nearer my God to thee..."
Not any more.
Happily my prototype Gin pole works!
Got the mast up, fitted new turnbuckles on my shrouds, discovered two that need shortening (can't find turnbuckles short enough), and lowered it all again. Could even be done single handed on level ground & no wind.
@PiperPilotPaul Excellent! I do that vertical lift maneuver for my Daysailer - but there's no tabernacle on that one and the mast has to go through the deck to a step on the floor, so I do it song and all like you! Haha, that mast weighs quite a bit less, and isn't so bad. Always blows everyone's mind at the boat ramp, though!
@PiperPilotPaul
Here's an article about the forces on a sail.
https://en.wikipedia.org/wiki/Forces_on_sails