viva
New member
Dear learned salts, I want to have constructed an A frame to assist in the lowering of my tabanacle mounted wooden mast. My question is how tall does it need to be as a percentage of mast height ?
many thanks
many thanks
A Frame - For Mast Lowering
- Thread starter viva
- Start date
Wooden Boat Fittings
New member
I think it just depends on how much work you want to do. The more nearly your A-frame approaches the mast's height, the more easily you can lower the mast. Clearly this can be taken to extremes. With the right tackle, either from the stemhead or (less probably) from the bowsprit end, a frame 1/3 to 1/2 the mast's height should be fine in my opinion.
If you can arrange the situation such that the chainplate fastenings and the tabernacle hinge-point are in a horizontal line the whole thing can become quite simple, as shroud tension doesn't need any adjustment as you go. (If they're not already in alignment, you can add purpose-built 'chainplate extensioners' to arrange for that to be the case.)
I believe that some vessels use a combination of hinged bowsprit and bowsprit shrouds as their 'A-frame', but I haven't seen this in the flesh.
Mike
If you can arrange the situation such that the chainplate fastenings and the tabernacle hinge-point are in a horizontal line the whole thing can become quite simple, as shroud tension doesn't need any adjustment as you go. (If they're not already in alignment, you can add purpose-built 'chainplate extensioners' to arrange for that to be the case.)
I believe that some vessels use a combination of hinged bowsprit and bowsprit shrouds as their 'A-frame', but I haven't seen this in the flesh.
Mike
ProDave
Well-known member
If you are lowering the mast using the bow roller as your front pulley, then the ideal length for the A frame is exactly the length from the mast foot to the bow roller.
jpay
New member
On the Norfolk Broads the boats used this arrangement, leaving the A frame on deck matching the lines of the bow meant that it was useable within minutes.
BarryLeat
Member
You do not state the mast length. However, I made my own A Frame to lower the mast on my Albin Vega. The length of the 'A' frame was such that when in place the apex was about 15ins above the spreaders. It was made from 3 by 2 timber, 2 pieces for each leg simply bolted together with coach bolts. At the apex I attached a simple steel plate, 1ins wide by 1/4ins thick with a bolt hole each end, one hole for the fulcrum bolt. This is held between the 2 pieces of timber. To the lower end I attached with a shackle my mainsheet block. From the mainsheet block I attached a simple lifting sling (a/v from SCREWFIX), which is placed around and below the Spreaders. The feet of both legs are firmly attached to the toe rail or main shroud fixings at deck level. Simple lines are attached near the apex (say about 18 ins below) and secured at both sides to the aft mooring cleats and to the forward deck cleats. This prevents the 'A' frame moving when erected in place. Your colleague who is helping you takes up a slight tension on the mainsheet. Loosen and remove the forward and aft shrouds from the deck. Loosen the main shroud bottlescrews. Note the mast is not going to fall down as it is supported by the 'A'Frame. Loosen the tabernacle bolt and remove completely. The mast is now able to swing forward or aft. The choice is yours. Lift slightly on mainsheet to clear tabernacle and then swing mast. Your colleague does all this with the mainsheet. Just ensure you have sufficient rope in the tackle to lower to the deck. Lower carefully till down. It takes about 30 mins to erect and lower. Repeat for raising. If you have foil attached to the forestay someone needs to guide this away from the boat to prevent bending. Don't forget to remove the main shrouds from the deck fittings.
TSB240
Well-known member
If you have a good tabernacle with plenty of support dont bother with an A frame us a Gin pole.
https://www.dropbox.com/sc/0w5rrza9l15fqte/zI8x0ytw8J
This shows our gin pole set up.
It is more complicated as we dont have a good tabernacle to support the base of the mast and have to add temporary stays to give the support that a good tabernacle provides. They stop the mast swaying sideways in a cross wind or swell.
Length as per other poster but it could be longer than distance from front of mast to bow roller if you want to reduce the lifting effort required. I find the load using our standard mainsheet tackle is quite high on initial lift but rapidly reduces as you lift the mast to the vertical.
Our ginpole can be used as a genoa pole for more comfortable downwind sailing. Its made from an old CF windsurfer mast. It takes up next to no space so you can keep it on board at all times.
Fantasie 19
Well-known member
Lakesailor
New member
Are you meaning an a-frame to lift the mast or a gin pole to allow you to lower the mast using the tabernacle, which would be the most sensible.
ProDave
Well-known member
There does seem to be some confusion.
I think of an A frame as a 2 legged Gin pole, that always remains at 90 degrees to the mast, and rises up as the mast lowers. Such an A frame has sideways stability unlike a gin pole.
the "A frame" in your first picture above I think of as a Derek, that remains stationary as the mast is lowered, and is by far the more clumsy way to do it imho.
I think of an A frame as a 2 legged Gin pole, that always remains at 90 degrees to the mast, and rises up as the mast lowers. Such an A frame has sideways stability unlike a gin pole.
the "A frame" in your first picture above I think of as a Derek, that remains stationary as the mast is lowered, and is by far the more clumsy way to do it imho.
Lakesailor
New member
Quite, The OP seems to be suggesting the lifting frame. If it was a gin pole the obvious solution it to make it the length from the mast base to the forestay. On mine I had a tab on the pole to attach the bottom of the furling gear (or forestay) to.
On a small boat with a mast less than 25/30 feet the sideways consideration is not important. You can steady the mast by hand.
On a small boat with a mast less than 25/30 feet the sideways consideration is not important. You can steady the mast by hand.
William_H
Well-known member
So it is all a question of terms. An A frame as Lakey used in his first picture must be higher than the centre of gravity of the mast. Even higher if it is a keel stepped mast where this method can be used to lift the mast up out of the deck. Just like you would use a crane.
A gin pole as used in Lakey's second picture allows the mast to be pivotted down on a hinge type mast base or tabernacle. To confuse the names many of us use 2 poles pivotted near the gunwhale and abeam the mast as a gin pole (or 2 gin poles) which might be called an A frame.
The length of the gin pole or poles should be as close to the distance mast to forestay attachent if you are going to lower using the forestay. If you use a halyard rather than forestay often easier because of furling drums etc then the gin pole or poles can be shorter but I think anything much shorter than the full distance mast to forestay would lose much of its "purchase" power in raising the mast. So where is vica to explain his question? olewill
A gin pole as used in Lakey's second picture allows the mast to be pivotted down on a hinge type mast base or tabernacle. To confuse the names many of us use 2 poles pivotted near the gunwhale and abeam the mast as a gin pole (or 2 gin poles) which might be called an A frame.
The length of the gin pole or poles should be as close to the distance mast to forestay attachent if you are going to lower using the forestay. If you use a halyard rather than forestay often easier because of furling drums etc then the gin pole or poles can be shorter but I think anything much shorter than the full distance mast to forestay would lose much of its "purchase" power in raising the mast. So where is vica to explain his question? olewill
viva
New member
Yes 2 gin poles to form an A Frame
Y
Many thanks to all who have responded. There are some very wise heads out there. Yes above is exactly what I mean i.e. 2 x gin poles fixed to gunwhales to form an A Frame. The mast is heavy and I want to avoid sideways movement. See photo - My thoughts were to put a large round wooden fence post across the foredeck and in front of the coachroof extending over the gunwhales. Call this the base pole (It will be padded). To the ends of this base pole I intend to attach the two gin poles and lash them at the top to form a triangle. To the apex of this I will attach a block and use a halyard to lower via a second block attached to the end of the bowsprit. The base pole will be free to revolve as the mast is lowered. See photo. Boat is a Norfolk Smuggler . Your thoughts on this approach much appreciated. My original question stands. Will the gin pole be long enough if they extend to the end of the bowsprit. The bowsprit is fixed. It will be a first for me !
Y
Many thanks to all who have responded. There are some very wise heads out there. Yes above is exactly what I mean i.e. 2 x gin poles fixed to gunwhales to form an A Frame. The mast is heavy and I want to avoid sideways movement. See photo - My thoughts were to put a large round wooden fence post across the foredeck and in front of the coachroof extending over the gunwhales. Call this the base pole (It will be padded). To the ends of this base pole I intend to attach the two gin poles and lash them at the top to form a triangle. To the apex of this I will attach a block and use a halyard to lower via a second block attached to the end of the bowsprit. The base pole will be free to revolve as the mast is lowered. See photo. Boat is a Norfolk Smuggler . Your thoughts on this approach much appreciated. My original question stands. Will the gin pole be long enough if they extend to the end of the bowsprit. The bowsprit is fixed. It will be a first for me !
Lakesailor
New member
Right. With you now. I would say that extending as far as the stemhead will be all you need. That lever will be 7/8ft long and will provide plenty of control of your mast as it's being lowered.
Don't forget that if you have two poles going to the end of the bowsprit that could be 12/13ft so when the mast is lowered you then have a 13ft high construction consisting of two poles to manhandle down. Almost like doing the mast all over again. Even with the shorter pole it is still standing quite high when the mast is down. Plenty of mechanical advantage
I would suggest better than lashing, to make brackets bolted to the poles with pivot bolts and also a bracket at the apex of your frame. You don't want to end up with a half down mast that has lashing which move/undo/develop looseness as the angles change.
Are you doing it on the berth in the picture?
I would use a single gin pole to the stemhead which I would transfer the furling drum to. A line under the bow roller. if there is one, and haul two lines up on the main halyard. Two people, one to each side if the boat with these lines, possibly on the finger pontoons, or further apart, could stabilise the mast as it comes down. The forces are not major and humans are better at adjusting the force as required.
You can control the lowering line using a winch drum.
In the picture of the yellow boat I used a mast-mounted winch to control the lowering and this allowed me to control the sideways movement of the mast as well. To take the picture I cleated the line and got down to take the picture.
It was a smaller mast, but still weighed as much as I could just comfortably lift on the ground.
It is a gaff rigged boat so the mast won't be that tall. Neil Thompson boats suggest that
In fact, having found a picture of it, the tabernacle lends a lot of support to the mast against sideways movement until the weight of the mast is acting in a downward direction. It must achieve almost 45° before the foot of the mast leaves the sideplates of the tabernacle. I can't see any issues with lateral displacement.
Don't forget that if you have two poles going to the end of the bowsprit that could be 12/13ft so when the mast is lowered you then have a 13ft high construction consisting of two poles to manhandle down. Almost like doing the mast all over again. Even with the shorter pole it is still standing quite high when the mast is down. Plenty of mechanical advantage
I would suggest better than lashing, to make brackets bolted to the poles with pivot bolts and also a bracket at the apex of your frame. You don't want to end up with a half down mast that has lashing which move/undo/develop looseness as the angles change.
Are you doing it on the berth in the picture?
I would use a single gin pole to the stemhead which I would transfer the furling drum to. A line under the bow roller. if there is one, and haul two lines up on the main halyard. Two people, one to each side if the boat with these lines, possibly on the finger pontoons, or further apart, could stabilise the mast as it comes down. The forces are not major and humans are better at adjusting the force as required.
You can control the lowering line using a winch drum.
In the picture of the yellow boat I used a mast-mounted winch to control the lowering and this allowed me to control the sideways movement of the mast as well. To take the picture I cleated the line and got down to take the picture.
It was a smaller mast, but still weighed as much as I could just comfortably lift on the ground.
It is a gaff rigged boat so the mast won't be that tall. Neil Thompson boats suggest that
I'm just guessing that all he is suggesting is that you rely on the tabernacle for stability.
In fact, having found a picture of it, the tabernacle lends a lot of support to the mast against sideways movement until the weight of the mast is acting in a downward direction. It must achieve almost 45° before the foot of the mast leaves the sideplates of the tabernacle. I can't see any issues with lateral displacement.
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CreakyDecks
New member
Most important word of advice. Do not let any helpful volunteer stand in the cockpit. If it all collapses he will try and catch it and probably kill himself!
PS. I'm not clear what your "base pole" is for.
PS. I'm not clear what your "base pole" is for.
afterpegassus
Active member
![IMG_78937660705571[1].jpg](https://ybw-data.community.forum/attachments/3/3756-4f36b7fcafd5c7e5245a7d680a49c7b1.jpg)
Lakesailor
New member
Neil Thompson Boats...
Jaguar 25
Member
Here's how it is done on a Catalina 25 (similar to Jaguar 25)
Don't know how to do a proper link but the following can be pasted in!
http://www.youtube.com/watch?v=r33VCObNroY
It's pretty impressive and does use an A frame.
Don't know how to do a proper link but the following can be pasted in!
http://www.youtube.com/watch?v=r33VCObNroY
It's pretty impressive and does use an A frame.
William_H
Well-known member
Hello viva. Just to clarify 2 poles will not stabilise the mast from sideways movement. The 2 poles stabise them selves compared to one pole which must be stayed sideways.
Stabilising the mast sideways can be done by hand by a person on the cabin top provided water is very flat and you are careful. Other wise the mast is stabi;lised by keeping the cap shrouds tight in the traverese down. This can be done by extended chain plates so shroud pivots ina line with the mast pivot. Or it can be done by attaching ropes to the shroud about 700 mm above the chain plate (use a clamp on the wire) then running this rope froward to a block smae on each side to tension the cap shroud as mast goes down.
Coincidentally I am off shortly to start a race for our club. 20 boats from 22ft to 34 ft will be starting in the ocean. This means all 20 boats will have to lower their masts to get under bridges (while under way) this morning then again on return home tomorrow. So it is not a new science.
Iuse dedicateed rings on the side decks for the spin pole attachment. But I lower it often. My best advice is get a quite tall A (2 metre) frame crutch at the transom to catch the mast. goood luck olewill
Attachments
viva
New member
Mast lowering equipment
Yes, thanks I had been in touch with Neil Thompson but he wanted a staggering £1200 for the mast lowering equipment. It is a permanent fixture that replaces the pulpit. Hence my attempts at DIY.
Yes, thanks I had been in touch with Neil Thompson but he wanted a staggering £1200 for the mast lowering equipment. It is a permanent fixture that replaces the pulpit. Hence my attempts at DIY.
Spyro
Well-known member
Not so much about height but strength and what pulleys you use. Mine was about 9ft for a 30ft mast on my trapper300
I made a tripod fixed to the toe rails and mast base.
