Ok to go up mast whilst in cradle ?

[guernseyman]

I've noticed that, when the boat is is the water, stationary at her mooring, movement of someone at the top of the mast has virtually no effect. On the other hand, if someone on deck moves to one side the boat rolls noticeably and there is usually a shout from overhead "Oy, stop that!"

I can't imagine what someone up the mast would have to do to cause a problem.

 

[Victoria Sponge]

It's certainly not allowed in Burnham YM.

 

[Scotty_Tradewind]

It's not the distance swayed when in shores rather than the fact that there is no absorbtion of the mini forces involved.
When the boat is in the water then small horizontal movements up the top of the mast are absorbed and supported by the hull in water, rather like a shock absorber.
When the boat is firmly supported on shores there is next to no give and so the small movements and forces that are sent to the hull are putting the shores under stress.
When I've been ashore sleeping in my boat supported by shores it often shudders when there are high winds as there is nowhere for the vibrations to go, they are effectively kept within the structure of the boat until they gradually die - albeit in a matter of seconds if not fractions of a second. The shores can occassionally require their wedges to be knocked in to tighten after a storm and the ground has shown no sign of the shores digging a hole into it.
When I've slept aboard my friends boat (a Nic 38', some 9+ tons) in its cradle, the whole boat has often done a 'micro' sway as the gusts come in and as the cradle absorbs the forces, again a bit like a shock absorber.
The smallest amount of movement 30ft+ up a mast, can also generate movement on my friends boat when in the cradle, again the cradle absorbs this.
It may be that the heavier the boat the less risk there is. I have just changed from a 4.5ton long keeler, to a 9.7 ton long keeler, so it will be interesting to see what differences there are when up top and swaying about.

 

[Scotty_Tradewind]

The weight of the ballast is not lending anything to the boat's propensity to fall over.

Is that why the lighter boats propped with shores in my yard are seen to have more props and crossed braced from one end to the other than the heavy displacement boats then?
If you blow a gust of wind at an empty cornflakes box, it will blow over more readily than a full box.
What you have to remember is that with any horizontal movement at the top, the forces involved at the bottom are tremendous even though movement at the bottom is a fraction of that at the top. 'O' level fizzics!

 

[doug748]

Hi Nigel,
I shin up mine most years, a similar boat to yours, on legs and shores. No problems so far, better than on the water with no fears of a motor boat coming by towing the idiot.

 

[Lakesailor]

Is that why the lighter boats propped with shores in my yard are seen to have more props and crossed braced from one end to the other than the heavy displacement boats then?
If you blow a gust of wind at an empty cornflakes box, it will blow over more readily than a full box.
What you have to remember is that with any horizontal movement at the top, the forces involved at the bottom are tremendous even though movement at the bottom is a fraction of that at the top. 'O' level fizzics!

You argue elegantly the same case to that which I suggest. The ballast is not making the boat fall over.

The OP asked, in his title if it was safe to go up the mast with boat in a cradle.
The answer is yes.

 

[noelex]

I am coward with heights, but my wife has spent some time aloft while we were in a cradle. One day it was over 4 hours (what a champion ) while we were replacing wind instruments.

 

[KellysEye]

Ask the yard some allow it many don't (no insurance for it).

 

[vyv_cox]

Your boat and mine are pretty similar in terms of size, weight, ballast ratio, rig, etc. I have been to the top of my mast countless times, far more often on the hard than on the water.

Search 'Mastclimb' for recent discussions on the various types of equipment and techniques for doing it.

Some yards have rules saying it is not allowed, frequently ignored.

 

[jdc]

some quick sums

The wind exerts a force on the mast, and thus a heeling moment (moment only - it doen't heel becuase it's shored up)

The human suspended from the top of the mast exerts a heeling force if the mast isn't excactly vertical.

Let's compare the two:

1. wind
Force per unit area, F/A = 1/2 rho * v^2 * Cdrag
Heeling moment integrated up the mast is 1/2 w * L^2 * F/A

Cdrag = 1.2 (super aerodynamic car = 0.3 or so, radio mast typically 1.2)
rho = 1.2kg/m^3
v, wind velocity = 20m/s (40kts - a good gale but not exceptional)
w, width of mast and rest of rigging, so 20cm?
L, length of mast = 10m?

Moment due to wind = 1/2 * 1/2 * 1.2 * 1.2 * 0.2 * 10^2 * 20^2 = 4100Nm

2. Human up mast
Moment = L * T * sin(theta),
where T is weight of human (in N) = 1000 say
theta = list, or angle from vertical = 2.5 degrees say (much less usually I think)

Moment due to weight up mast = 520Nm, a factor of 8 less than that due to wind.

So I agree with the others saying that one does not have to worry about the boat falling over if you go up the mast when ashore: if your boat is well enough supported to survive the winter winds it can take you up the mast.

 

[Scotty_Tradewind]

The OP asked, in his title if it was safe to go up the mast with boat in a cradle.
The answer is yes.

Safer!... Possibly!!

 

[Lakesailor]

erm... yes, better still if the mast is down.

 

[noelex]

The wind exerts a force on the mast, and thus a heeling moment (moment only - it doen't heel becuase it's shored up)

The human suspended from the top of the mast exerts a heeling force if the mast isn't excactly vertical.

.

From a practical point of view I can verify the validity of those calculations. I have never noticed any difference with the weight of someone up the mast, but I did experience one storm while on the hard. I would have rather been at anchor !
I went around the boatyard at 3am looking for extra supports. In retrospect it wasn’t a wise move as there was lots of debris flying around combined with the hail and lightening I think I would have been safer on board even if the cradle had collapsed.

 

[NigelFortune]

Thanks

Many thanks to all with a reply/opinion. Seems like No.1 son has a job for the weekend !!

Nigel

 

[Graham_Wright]

If the cradle or shoring is good then not a problem. A yacht onshore has to, or should withstand storm force winds which will exert forces far in excess of what a man aloft will.
As with all these things if you aren't happy doing it then don't. I recently went up a 60ft mast in a yard.

I was explaining our MastaClimba to a professional rigger at Bursledon and showed him the video of my speed ascent.

He was absolutely horrified. I could not understand his problem but he was adamant that you should not ascend a mast with the boat on the hard.

He explained that the weight of a man swinging at the top of the mast can easily dislodge the shores due to the large lever involved.

I then pointed out that my demo was on bilge keeler. He was then happy and apologised for assuming the shores.

He was still very much against ascending a boat in a cradle for the same reasons.

 

[Graham_Wright]

I've been up the mast of a 19 foot boat on the water and there is very little turning moment. I had a mate ready to apply his weight to the side decks to counteract any heeling, but there was none.

Au contraire!

At the top of the mast on my Four 21, I asked my dear lady wife (girl friend at the time) to pop back below for a screwdriver. With alacrity ( more common then than now!) she stepped on to the side deck and made her way aft into the cockpit.

You can guess the rest. Her ability to synchronise the back-swing at the end of the swing could have been admirable had it been a challenge. I made a very good upside-down pendulum although I did stay dry.

 

[Lakesailor]

Yeah. I know people who have all the training but have no ability to work things out for themselves.

As for your Au Contraire. You argue for my case. Your example shows exactly the effect my mate was there to provide, should it be needed. To counteract any heel that I induced.

 

[Scotty_Tradewind]

many thanks to all with a reply/opinion. Seems like no.1 son has a job for the weekend !!

Nigel

cleaning the bilges out?

 

[guernseyman]

I was explaining our MastaClimba to a professional rigger at Bursledon and showed him the video of my speed ascent.

He was absolutely horrified. I could not understand his problem but he was adamant that you should not ascend a mast with the boat on the hard.

He explained that the weight of a man swinging at the top of the mast can easily dislodge the shores due to the large lever involved.

"swinging" ?

How?

 

[Lakesailor]

Some bloke he learned his trade from told him that and he never bothered to think it through.