William_H
Well-known member
Re: Mast \"A\" frame construction ....
Nigel I am unclear on the term "blade" for the mast step.
My boat has what might be described as a blade which the mast base straddles. It has a pivot bolt at the front through lugs on the mast and through the blade on a raised point. This is actually an excellent form of pivotting mast step becuase it can accomodate huge amounts of mast swing sideways when near down without real damage.
Many local boats have a commercial cast aluminium base with 2 lugs set about 12cms apart and this distance is not enough to stop the mast swinging but is enough to snap the lugs off very easily.
Mast swing occurs if it is not sufficiently stayed sideways when half down and you encounter a wash when motoring. As in under bridges.
I reckon the secret to mast lowering (or raising) is to have very long (high) A frame or mast support at the transom. It should be so high that you can only just lift the mast into it while standing at the back.
You lift the mast into the support then slide it forward to the engage the base. This means the mast is closer to balance (ie less top heavy) and so it is easier to get the base engaged. But more importantly much of the early raising (angle) has been done by physically lifting at an easy lifting point. (Provided it is not too heavy.)
So you might get the first 20degrees from Horozontal done before you start hauling on your tackle. This means less compression loads on your A frame and less load on the tackle.
Your main sheet will almost certainly not be long enough. You need to be able to take it back to a halyard winch or sheet winch for the first (lowest ) part where the real load is. You then revert to pulling by hand as it gets near vertical. So 4 part purchase is prefered.
It is all very doable as we see on Swan river 75fters with 100ft of mast lowering the mast this way while under way under bridges. Yes that is a bit scary but many smaller boats, but still larger than yours, do it regularly. One acquaintence does it on a 40 fter single handed as a matter of habit (without stopping)
I think that the poles you have in mind will be a little light and susceptible to failure in column compression (buckling). Needs larger diameter. You could use a single spin pole but it is likely too log and really tedious in staying it sideways compared to 2 poles.
To "graham" re. staying the mast. On a mast head rig you extend the chain plates in rigid steel tube or rod to a popint in line with the mast pivot. This forces the stays to remain tight even with the mast at 45 degrrees. On a fractional rig the chain plates usually are well aft of the mast so they go slack when mast goes down. I use a small tackle attached to the shroud about a metre above deck and can tighten the shrouds as it goes down. However a system is growing popular here where a slider is fitted in the main sail track, two poles are attached pivotted on the gunwhale towards the transom. As the mast goes down the slider and poles move toward the mast top supporting it sideways all the way. It can even be used as a support when the mast is down but if angles are too acute they won't have as much vertical support. Some even advocate actually raising the mast by hauling the slider down the track although I feel the loads would be too great.
good luck to you all be carefull and have helpers until you get it all running smoothly. olewill
Nigel I am unclear on the term "blade" for the mast step.
My boat has what might be described as a blade which the mast base straddles. It has a pivot bolt at the front through lugs on the mast and through the blade on a raised point. This is actually an excellent form of pivotting mast step becuase it can accomodate huge amounts of mast swing sideways when near down without real damage.
Many local boats have a commercial cast aluminium base with 2 lugs set about 12cms apart and this distance is not enough to stop the mast swinging but is enough to snap the lugs off very easily.
Mast swing occurs if it is not sufficiently stayed sideways when half down and you encounter a wash when motoring. As in under bridges.
I reckon the secret to mast lowering (or raising) is to have very long (high) A frame or mast support at the transom. It should be so high that you can only just lift the mast into it while standing at the back.
You lift the mast into the support then slide it forward to the engage the base. This means the mast is closer to balance (ie less top heavy) and so it is easier to get the base engaged. But more importantly much of the early raising (angle) has been done by physically lifting at an easy lifting point. (Provided it is not too heavy.)
So you might get the first 20degrees from Horozontal done before you start hauling on your tackle. This means less compression loads on your A frame and less load on the tackle.
Your main sheet will almost certainly not be long enough. You need to be able to take it back to a halyard winch or sheet winch for the first (lowest ) part where the real load is. You then revert to pulling by hand as it gets near vertical. So 4 part purchase is prefered.
It is all very doable as we see on Swan river 75fters with 100ft of mast lowering the mast this way while under way under bridges. Yes that is a bit scary but many smaller boats, but still larger than yours, do it regularly. One acquaintence does it on a 40 fter single handed as a matter of habit (without stopping)
I think that the poles you have in mind will be a little light and susceptible to failure in column compression (buckling). Needs larger diameter. You could use a single spin pole but it is likely too log and really tedious in staying it sideways compared to 2 poles.
To "graham" re. staying the mast. On a mast head rig you extend the chain plates in rigid steel tube or rod to a popint in line with the mast pivot. This forces the stays to remain tight even with the mast at 45 degrrees. On a fractional rig the chain plates usually are well aft of the mast so they go slack when mast goes down. I use a small tackle attached to the shroud about a metre above deck and can tighten the shrouds as it goes down. However a system is growing popular here where a slider is fitted in the main sail track, two poles are attached pivotted on the gunwhale towards the transom. As the mast goes down the slider and poles move toward the mast top supporting it sideways all the way. It can even be used as a support when the mast is down but if angles are too acute they won't have as much vertical support. Some even advocate actually raising the mast by hauling the slider down the track although I feel the loads would be too great.
good luck to you all be carefull and have helpers until you get it all running smoothly. olewill
