Help with mast raising system please.

[davidpbo]

I have a Jeaneau Tonic. 23ft trailer sailor, the mast is fairly heavy duty for the size of the boat, it is an aluminium mast Z spars Z230 section (web page) deck stepped on the mast foot shown (1101) on link in front of the cabin roof. The mast is approx 10 metres long, I would estimate the total weight to be about 35KGS. It can only be lowered so far because of the cabin behind it, its height is about 2.5m at the transom.

It drops onto a home made post (50mm aluminium scaff tube) with a roller on the top. The pin is then removed from the mast foot, the foot of the mast lifted and moved forward to the pulpit rail where it rests on a block of wood. I can then just about lift the mast off the roller.

To bring the mast from the vertical to the point where it is resting on the rail I rig a pole (50mm ally scaff again) out of the front of the base of the mast to above the Samson post to this is attached a block and tackle with three sheaves at each end. The pole is tensioned on either side back to as near the pivot point of the mast as possible. I rig temporary mast stays back to the same point. My wife lowers the mast and I guide it.

The tackle I use is all a bit heavy, and heavy duty. I have used 7X3 inch timber to form a U section which is ratcheded to the front of the mast. The rear roller pole is again support by a bracket made out of 7X3 inch; which goes over the transom, the tiller and rests on the cockpit sole a diagram is here and pictures here .

I want to make it simpler to rig by fitting a tabernacle, fitting a socket in the front of the mast to take the forward pole and some sort of socket at the back to take the resting pole with roller. Raising the pivot point will mean I can get the mast down lower at the transom. I also want to use smaller section tubing if possible I have a spinnaker pole that I may be able to use instead of the scaff tube but want to know if it is strong enough, it is about 30mm diameter and fairly light gauge.

What is the maximum compression load the stand off pole at the front of the mast will be under ?
and hence what diameter and gauge of tube do I really need?

What diameter and gauge pole should I be looking at for the rear support?

What sort of loads are the side supports for the pole and mast under?

What sort of forward load would the mast foot be under when the mast is at its lowest height.

Many thanks

David

 

[Lakesailor]

I made a similar thing for my much shorter mast look at the pics from 07 onwards Mast lowering

On my current boat I went for an "A" frame hoist which worked well.

 

[tyce]

phil,
that is a genius idea, i always planned to lower mine using the spinnaker pole ring but worried about the load on the ring and if it was upto it with the weight of my mast.
never thought to use the tabernacle pin as the pivot.
well done that man

 

[William_H]

David here in Fremantle (up river) mast lowering is a big thing on masts and boats much bigger than yours. Granted on the bigger boats the mast is only lowered to go under bridges for an air draft of about 6 metres. The method you use is pretty much standard however...
Most of us find it is easier to use 2 spin poles forming an A shape to the forestay bottom as this doesn't need to be braced by guys and they usually snap onto rings mounted on the deck near the gunwhale abeam the mast. I have never heard of anyone having a pole fail under compression but using trig the compression load could be calculated.
I presume you have a fractional rig such that the side stays go very slack as the mast goes down. This is a major problem in Fremantle as the mast is lowered on the water with Mobos often going past causing the boat to roll.
I use a tackle to a point on the side stays about 1.5 metres up from the chain plate which pulls the stay forward so maintains tension as mast goes down however often this is omitted in lieu of dropping and raining the mast quickly with a person on the cabin top guiding it into a crutch on a pole at the transom.

A local rigger (Rolley Taskers) are promoting a system which has a sliding car (on wheels) which runs up the mainsail track. Two poles (spin poles) are attached to carefully chosen points on the gunwhale about midway mast base to transom. This car is attached to the main halyard and also a downhaul line.
So release the forestay pull on the mainhalyard the car goes up the track pulling the mast back. The downhaul is carefully paid out to stop it falling. When the car reaches the top of the track it will stop the mast falling and support the mast at a suitable lowered angle. To raise again you pull on the down haul forcing the car down the track so pushing up the mast.
Now the mast is very well supported sideways in its traverse. However I would want the poles on the front on a tackle on the forestay as well and a crutch to rest the mast in at the back as the loads could be very great on awkwardly angled back poles. In other words I would lift the mast as you do not forcing the car up the track.
Now to your questions. A higher tabernacle would enable the mast to be lowered in the tabernacle down to near horizontal. However I find that with a tall pole crutch (such that I can just reach to lift mast out of the crutch) is best. (near horizontal the pivot point will be closer to the mast base so the unbalance of weighty mast aft of the transom will be much worse. At the higher angle there is somewhat less upward force at the mast step so it is easier to fit and remove the pin. (I have a low crutch pole for towing on the road.) The higher mast crutch means it is much easier to raise the mast from 30degrees to the horizontal than near horizontal.

If you want the mast base higher it could be raised a few inches by wood blocks under the mast base. You will need to shorten the mast at the base or shorten the stays.

So basically the way you are doing it is best. I think you would find 2 spin poles pivotted to the deck a little easier but at the cost of another spin pole (or similar)

Lake sailor's arrangement is great for keel stepped masts and may be worth a try but I reckon you are doing it the best way.

I realise your mast is a lot heavier than mine but I have many friends with really heavy masts who do it as you do at least to lower it if not remove it.
One thing I find very valuable is a high field lever to allow me to retension the forstay and whole rig in a second. (while making an intial reattachment of the forestay easy. PM me to discuss. olewilll

 

[davidpbo]

Thank you both for your fulsome replies.

Phil
What do you believe the advantage of the A frame system you use now to be over what you had previously?

Tyce,
Yes it is a fractional rig.
To brace the mast I use 1 ton rated ratchet straps attached as far up the mast as I can reasonably reach (2m or so) by a strap going a couple of times around the mast. At the bottom the other end is attached to a loop of rope which is attached to the aluminium toe rail in such a way that hook of the strap is as near in line with the pivot point of the mast as possible.

You are right about a higher tabernacle. As things are at present with the tall crutch on the transom the mast is fairly well balanced on it although in danger of slipping forward, this does make getting the pin in easy.

What I have works, I just what to make it lighter and need some indications of the forces involved. I giving more thought to an a frame to the the bottom of a the forestay rather than a guyed pole.

 

[Lakesailor]

[ QUOTE ]

What do you believe the advantage of the A frame system you use now to be over what you had previously?


[/ QUOTE ]There is no advantage at all, but I was forced into it by my current boat which merely has a mast step shoe on the cabin roof. There is no pivot at all.

I would always prefer the pivot in a tabernacle. Using my home made pole I don't need stays as the bracket on the pole locates on the pivot bolt and provides enough lateral control. I made one cheek of the bracket with a hinge so that slipping it over the pivot bolt was easy.

The point that Will made about keel-stepped masts was probably made with knowing that my mast wasn't pivoted.

 

[davidpbo]

Aha, I see,


David