I agree that the crutch is a little low to do a straight pull. In engineering circles it's known that at around 18 to 20 degrees on a line, you are more pulling an object forward than upwards........
Just wondering whose pictures are you guys looking at? I haven't seen any pictures of his setup yet, just ours. Did I miss them somewhere?
This is our boat...
.... and we don't have a problem.
The mast is low, but the pull angle is not to the mast, but from the foredeck up to the top of the gin pole. The length of the gin pole determines the lever arm that you are using to try and lift the mast and as you mentioned the angle of pull on that lever arm will come into play as to the total effort that is required. Above you can see that the angle from the deck up to the top of the gin pole isn't too bad of an angle considering what we are trying to do. If the gin pole was longer the lever arm would be longer, better deal, but the pull angle would get worst.
The weight you are trying to lift is determined by the weight of the mast and where the line from the gin pole to the mast is attached to the mast. If that line was attached to the very top of the mast and it was horizontal you would be lifting 1/2 the weight of the mast since one end would be resting on the deck and the other end would be held up by your gin pole/block and tackle. Just as if you and someone else were carrying the mast and each of you was at the end of the mast.
The problem is if you use the jib halyard and it is not at the top of the mast then you are lifting more that 1/2 of the weight at first. Imagine one person lifting the mast at the end and the other lifting the other end say 10 feet in from the end. The second person would now have more than 1/2 of the weight.
The gin pole is attached to the mast with the jib halyard which in our case is attached down the mast some. So at the beginning of the lift you are lifting all of the mast's weight from the halyard attach point to the top of the mast and and also 1/2 the weight between where the jib halyard attaches to the mast down to the mast base. You are lifting a lot of weight at that point, more than 1/2 of the masts total weight.
As the mast goes up, more and more of the mast's weight is now down at the foot of the mast until at vertical all of the weight is down on the deck. Also as the gin pole is pulled down towards the deck the pull angle gets better there so it gets a lot easier to pull the mast the last part with the good angle and less and less weight that you are trying to lift.
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