WishBone Sailing Rig

[yipster]

thinking of wind, inertia, seaway etc how di or un-desirable would it be to strike a mast altogether, any rough guesses?

 

[Kojii]

I would have to say this is a drastic measure given the weight involved, wire attachments, etc. My point is simply that with a bipod it does become a real option because of the stance of the mast step - both feet on the deck as it were. So here we are again with the trade-offs. This is simply not an option with keep stepped masts and probably not with most deckstepped mast because they "stand" on one leg. This would only be feasible in a situation where you could get it down before the winds hit. It could not be done in the middle of the blow. One would have to know what was coming well in advance. A good designer could put this together on this rig without much trouble I am sure. Once on deck, strap it down and enjoy the ride....

 

[brian eiland]

Rigs for Storms

Striking a mast while at sea should NEVER be considered, regardless of its being a single mast tube or bi-pod....besides its near impossible.

Good seamanship is the key to surviving a storm. There have been many different types of vessels that have been taken to sea and survived big storms. Each of these different type vessels have their own 'quirks' that must be accounted for in extreme conditions.

Some vessels may be better off running with a storm, some better off facing it. Look at the multitude of arguments for drogues verses parachute anchors. And look at the multitude of storm sail deployments that have been utilized over the ages. And how about the variety of multi-masted vessels. Or the differences in handling multihull vessels verses single hull ones.

So to condemn one vessel design in favor of another based just on its mast placement is not a fair assessment. If we did this we might have to proclaim that a aft-masted vessel would perform better in a sea-anchor (para-anchor) off the bow attitude than would a fore-masted vessel....probably so, but not necessarily.

I personally much prefer the concept of a bow deployed sea anchor in an extreme storm to that of running off under drogues. Eventually I am going to get real tired, and I much prefer some rest to constantly steering down the face of waves.The key is knowing your vessel and how it best reacts to the conditions of the sea.

Parachute Anchors, Para-Anchor, Sea Anchor

 

[brian eiland]

Bowed Wishbone Legs

...The wishbone legs are bowed (cleverly), and require pre-loading, if you will, by the shrouds at the mid-arc to keep them from springing (they are afterall bows of carbon/kevlar/plastic). The wires do the trick as designed. As such the bowlegs of this mast act as shroudmasts with the wires performing the role of the string on a bow, only this string is attached in the mid-arc...

Dear Kojii,
You mentioned at one time about the possibility of getting in touch with someone who knew the designer, Mr Greenway from Boeing Corp. I wonder if his widow would have some info? It's often that such papers of the deceased get lost to the world, as no one takes the time to dig them out from obscurity. Have you checked to see if he had a surviving spouse. I'm sure she would be more than willing to see her husbands work go to good use.

I would be very interested to see his observations on why he chose to use a 'bowed frame' for his bi-pod, and the subsequent use of additional shrouds and spreaders?? We might even run across his mast construction details. It would be interesting to see these details, as well as if there are differences between the tall rig and your shorter rig versions?

 

[rob denney]

thinking of wind, inertia, seaway etc how di or un-desirable would it be to strike a mast altogether, any rough guesses?

G'day,

Extremely desirable. weight and windage would be lowered, the boat would become a whole lot safer. However, getting it down at sea is not to be recommended and there is the problem of what to do if you need the rig in a hurry (ship, man overboard,etc).

My solution to this is a telescoping mast. This allows you to have as much mast as you want, when you want it. In a good breeze you reef the mast at the same time as you reef the sail. Many cruisers do not go upwind with a reef due to the drag of the rest of the rig.

The concept only really works on an unstayed mast, and is perfectly suited for a wing mast, There is a harryproa under construction at the moment that will have such a mast. Should be sailing by Xmas. I will keep you informed.

regards,

Rob

 

[yipster]

stil wonder how far striking and raising mast(s) stretches and can be really used in various conditions
thanks for speaking out guy's and yes plz do keep me informed on that or any telescopic mast rob
pete gosh is going to write a book on team phillips, guess he will also go into the masts in more detail

 

[Pericles]

The Lateen rig, when lowered, considerably reduces top hamper, which is why it has withstood the test of time. Dipping lugsails are also good in that respect, but in both cases, crew numbers are important. Short masts are easier to manage and be made freestanding

http://en.wikipedia.org/wiki/Lateen

http://en.wikipedia.org/wiki/Lugger

Old forms of sails and rigging systems are easily revived, if implemented using modern materials such as carbon fibre spars and Spectra.

Perry

 

[MikeJohns]

On a ballasted mono-hull lowering the mast in heavy weather is not a good idea since it will make a knockdown or inversion far more likely.

Some of these comments need to be clarified as to what sort of vessel they refer to mono or multihull.

I'd be interested if anyone has a cruising Cat say 40 to 50 feet Weights and moments. What happens to the radius of gyration with and without the mast? I presume that the loss will not be anything like the reduction for a monohull.

Typically a light 40 foot mono-hull roll period will drop from 4 to closer to 2 seconds without the mast. Even a heavy displacement 60 footer will drop to a 3 second roll period sans masts. Pretty uncomfortable and dangerous. The loss of inertial damping also makes the vessel more prone to violent roll knockdown etc.


As for aft masts, drogues helming running off etc:
Tactics must vary as the storm progresses and the sea conditions change. There’s no hard and fast rule for survival in extreme conditions. Surely every deleterious ‘quirk’ is just that, if the CLR is fwd of the COE for bare poles then the vessel is dangerously unbalanced in that situation IMHO.

Running under bare poles has been shown a very necessary tactic in some storm conditions, . Most vessels survive 'normal' heavy weather, some don’t, analyzing and making sense of the lottery has seen a lot of effort from people like Marchaj and more recently Cloughton et al at the Wolfston unit in the UK and Renilson and Deakin here at the Australinian Maritime college in Tasmania.

There has been some study on drogues in the wave tank here by Deakin I think. They have their time and place but they are not a total panacea.

I'd seriously think about some proper testing. My own opinion is that if the vessel has a strong inclination to swings bow into the wind then it has a very strong disposition to get into irons if bare headed. I don't like that thought since there are conditions that preclude carrying anything.
Solutions? I suppose you could use dagger boards right aft.

The iron topsail would be needed to you back after a broach, what about some high drag device for the forestay to shift the windage fwd in survival situations. Flog resistant and sheetless would be good. Of course you might go too fast then you'll need that drogue


Cheers

 

[Nordic Cat]

what about some high drag device for the forestay to shift the windage fwd in survival situations. Flog resistant and sheetless would be good. Of course you might go too fast then you'll need that drogue


Cheers

2 or 3 halyards to the bows would give some windage. About 45 N/meter at 40 knots for a ½" wire, so 3 halyards of 20 m each = 60 m x 45 = 2700 N

Maybe add some rode for a bit more?

Same effect as streaming lines

Regards

Alan

 

[Kojii]

Striking mast monohull

Curious about the inertial changes with mast struck. Would the 50 % ballast be an advantage in this case. My seasense was that this vessel will roll badly (9' beam) with or without the mast up, but I can't see it being worse with the mast struck. Please explain. Thanks, K

 

[MikeJohns]

Kojii
It is a damped oscillatory system The frequency of oscillation depends on the mass moment of inertia. Inertia is the mass times the distance from the roll axis squared consequently the rig has more effect than you might initially consider.
It is also the reason a heavier rig can add considerable comfort by reducing the roll accelerations (designed for not retrofitted).

9 ft beam and 50% ballast then I think your rig is going to be even more important since the vessels GM is going to go through the roof sans mast. In other words it will become not just uncomfortable but even dangerous to be on deck.

In a W&M spreadsheet it’s easy to add the vertical components, calculate and sum the total rotational inertia.
Natural period is then easily calculated but you need to find GM pref from a hydrostatics package and add a hydro damping coeff based on keel area & hull-form.

 

[Kojii]

Thanks Mike, I suspected it would be something like that ...I tried computing the underwater profile once but ran out of steam. I estimated the full rig with furler - the whole - at around 1,100 lbs. I guess from my limited experience with the boat in a sea way I sense it would tend to do as you predicted with the aftmast in big following seas/winds. I always have felt very comfortable driving into the seas/wind so far on this boat because it does none of the pitching and slamming and reverberating that I have felt on most conventional "broadbeam", production boats.
Mast is only 48'. Does the two-footed, gunnel mounted aspect improve or diminish the roll concern? Thanks. Appreciate everyone's input much. K

 

[MikeJohns]

Kojii
You are welcome.
Gunnels, Bulwarks aren't going to make much difference to this.

 

[kenJ]

Location

I haven't read the whole thread so this may be a duplicate. The original picture you posted was taken in Bremerton, WA. Hope that helps in the search.

 

[catsketcher]

Broken masts

Hello,

I remember reading an article in Australian Sailing about masts and roll moment of inertia. It is pretty common supposedly for people to become seasick after breaking masts as the boat then rocks like a motor boat. One quote came from a bloke who found it very hard to keep his footing after the mast broke.

My little folding cat can be rocked really easily when folded with no mast. Put the mast up and the period becomes much longer. Like a long rope on a swing rather than short one.

Think of the high wire trapeze artists. They hold a long pole to increase their roll moment of inertia. They take much longer with the pole to start falling either way and so can react to any unbalancing forces they experience.

cheers

Phil Thompson