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Old 19-02-2015, 11:00   #661
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Re: Wave Induced Mast Failure, I don't think so

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Originally Posted by beiland View Post
I was just reading thru that subject thread a little, and ran across this posting....
Good technical explanation of the tradeoff between elastic and rigid materials.

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Old 19-02-2015, 11:18   #662
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Re: GUNBOAT Dismasting

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Its a Hall Spar problem, GB dont design mast not even build it, thats why you have spar makers, they design a rig for you , Gun Boat cant send the exactly especifications to Hall Spar , is obviously Hall Spar the boss when they design the rigging , mast, spreaders etc...who choose to go with a single diamond spreader set and no lowers? Hall Spar ....
As I have said on several occasions, it was likely the rig was designed by Nigel Irens
.
If you look back thru history of racing multihulls, both cats and tris you will find NUMEROUS instances where he has utilized 'minimal' diamond rigging and spreaders in his designs,...mainly for minimal drag.

And here is another recent design with single-spreader in a cat much larger than the gunboat 55

Allegra: Ready for Sailing Trials - Nigel Irens Design


(The sailplan has been developed in close cooperation between Future Fibres, Nigel Irens Design and North Sails to maximize performance for a shorthanded cruising crew)



Some more history for Nigel Irens
Nigel Irens Designs Some of the Fastest Racing Multihulls | Sail Magazine

http://www.stevencallahan.net/images...ns-feb2000.pdf
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Old 19-02-2015, 11:24   #663
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Re: GUNBOAT Dismasting

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The wave piercing hull is a common design outcome for power boats trying to beat the sail boat circumnavigation records.

Wave piercing offers comfort, speed and fuel consumption benefits. (at least during the modeling phase) A caveat is having a clean deck. Anything with a mast cannot be considered a clean deck.

Why would a wave piercing hull be a desirable feature on a cruising sailboat? Reserve bouyancy, the opposite of wave piercing, is a well understood benefit. (I'm an engineer but can't think of a practical hydrodynamic benefit)

Longer waterline length for speed and marketing spring to mind but these are racing concepts.

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You cant generalize with bow design. Many fine entry designs can be considered wave piercing because of entry angle of the bows without any flair. The profile of some wave piercing bows is plumb, some are reverse, these profiles increase waterline while reducing weight and pitching forces. Technically wave piercers don't lift up and over waves, so pitching is reduced, but things are usually a lot wetter. You can reduce bow submersion in conventional bows with flair while piercers usually rely on water shedding quickly.
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Old 19-02-2015, 11:34   #664
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Re: GUNBOAT Dismasting

Racing spars are like they say for Racing, minimal drag, minimal diameter, minimal scantlings.....i dont have a problem with that but can someone explain here how the frock!! they solve the mast pumping isue and bending in that particular área without checks stays, lowers or jumpers in the spreaders ????? because lowers or checkstays are not a requirement for multi rigs if they have jumper struts or the diamonds is a 3 spreader set, the other sweep back spreaders configuraton i deal with it have checkstays or lowers and even running backs in some configs....


Like the 20 meter spar i make a month agoo from Sparcraft for a 60 ft catamarán, uppers, checkstays , 2 diamond set, running backs , jib and genaker furler and even a solent stay for flying a storm jib... just wonder....Rigging projects 2015.
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Old 19-02-2015, 11:43   #665
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Re: GUNBOAT Dismasting

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Racing spars are like they say for Racing, minimal drag, minimal diameter, minimal scantlings.....i dont have a problem with that but can someone explain here how the frock!! they solve the mast pumping isue and bending in that particular área without checks stays, lowers or jumpers in the spreaders ????? because lowers or checkstays are not a requirement for multi rigs if they have jumper struts or the diamonds is a 3 spreader set, the other sweep back spreaders configuraton i deal with it have checkstays or lowers and even running backs in some configs....


Like the 20 meter spar i make a month agoo from Sparcraft for a 60 ft catamarán, uppers, checkstays , 2 diamond set, running backs , jib and genaker furler and even a solent stay for flying a storm jib... just wonder....Rigging projects 2015.
It is all dependent on the moments of inertia rated for the section. The section can be engineered for lots of stay support, minimal support, or none! (Free standing mast) It can also be dependent on whether the mast is deck stepped or keel/bridge deck stepped. But to engineer a mast in this size range that is stiff enough with pre-bend to not suffer from excessive pump or failure is not difficult. What matters is if the builder is pushing the envelope or being conservative. I for one like the idea of reduced rigging and stronger mast sections, not the other way around. I have a new design in mind with a round tapered section, three stays and no spreaders that should be much more reliable than many conventional catamaran rigs.
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Old 19-02-2015, 11:52   #666
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Re: GUNBOAT Dismasting

I dont think the RM mast scantlings score with that theory, multi rigs play in another game field, free standing mast for a multi hull??? could be solid diameter section , or really thick, im sorry mate but i dont put to much trust in those experiments until i see this stuff hanging around for a while, good for you , always good to see new stuff around, i remember those 47 from Catana with those horrible CF sticks with no spreaders at all, and the owners crying for a perfect tunning of the mast and rigging, but the overall goal is to keep the dam thing in column even in the worst shock loads , if you get that with plan A or B , then cool....
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Old 19-02-2015, 12:27   #667
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Re: GUNBOAT Dismasting

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I dont think the RM mast scantlings score with that theory, multi rigs play in another game field, free standing mast for a multi hull??? could be solid diameter section , or really thick, im sorry mate but i dont put to much trust in those experiments until i see this stuff hanging around for a while, good for you , always good to see new stuff around, i remember those 47 from Catana with those horrible CF sticks with no spreaders at all, and the owners crying for a perfect tunning of the mast and rigging, but the overall goal is to keep the dam thing in column even in the worst shock loads , if you get that with plan A or B , then cool....
I have been involved in the manufacturing of over 120 catamarans with single spreader rig, with tapered aluminum mast, and a custom 52 foot cat with freestanding carbon mast, both very well tested in conditions.
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Old 19-02-2015, 13:50   #668
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Re: GUNBOAT Dismasting

I am still waiting on more evidence, but as I mentioned I really thing this was a rig design problem. Sure a mast with this rigging could be fine, but my guess is that it would need more uni just below the spreaders (which is where I am guessing the mast snapped). It probably would be a better option to add running backs, but that's a problem for the engineer.

Is there any confirmation on who did the rig design? It's very possible it was in house from GB but I could also see Hall doing it, or printing in a mast expert.
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Old 19-02-2015, 16:18   #669
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Re: GUNBOAT Dismasting

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I am still waiting on more evidence, but as I mentioned I really thing this was a rig design problem. Sure a mast with this rigging could be fine, but my guess is that it would need more uni just below the spreaders (which is where I am guessing the mast snapped). It probably would be a better option to add running backs, but that's a problem for the engineer.

Is there any confirmation on who did the rig design? It's very possible it was in house from GB but I could also see Hall doing it, or printing in a mast expert.
Hall does the engineering based on the data the manufacturer gives them, if the boat weighs more than they said, then all bets are off. Also when these carbon boats with carbon sails, and dyneema running rigging accelerate or stop abruptly loads can go exponential and I don't believe there is enough data available to fully predict the loads.
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Old 19-02-2015, 16:52   #670
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Re: GUNBOAT Dismasting

Quote:
Originally Posted by neilpride View Post
Racing spars are like they say for Racing, minimal drag, minimal diameter, minimal scantlings.....i dont have a problem with that but can someone explain here how the frock!! they solve the mast pumping isue and bending in that particular área without checks stays, lowers or jumpers in the spreaders ????? because lowers or checkstays are not a requirement for multi rigs if they have jumper struts or the diamonds is a 3 spreader set, the other sweep back spreaders configuraton i deal with it have checkstays or lowers and even running backs in some configs....


Like the 20 meter spar i make a month agoo from Sparcraft for a 60 ft catamarán, uppers, checkstays , 2 diamond set, running backs , jib and genaker furler and even a solent stay for flying a storm jib... just wonder....Rigging projects 2015.
Not sure about the 20 meter spar you made, was it a rotating spar?

The thing about the rotating wing mast is that you can make it a deep as you want fore-and-aft to resist pumping without paying a drag penalty because the altitude is adjustable. Hence no runners and only three stays holding it up. Yesterday's news.

I have to dig up some photos of strip plank cedar and plywood rotating wing masts from some thirty odd years ago made by Gudgeon brothers who sell you expensive epoxy to fix yer boat. If I have it correctly they spun off a business making wind generator blades.

If you look at the pictures of the Newick Tri I posted, those are wood composite spars.

Funny thing about wood, it's got great fatigue resistance, what with those trees blowing around in the wind all the time. I know it's not as sexy but wood is more resilient than carbon fiber and if harvested responsibly, it's a renewable resource.

Carbon Fiber Fun Fact : Carbon fiber is made from burnt wood!
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Old 19-02-2015, 17:28   #671
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Re: GUNBOAT Dismasting

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Originally Posted by pbr View Post
Hall does the engineering based on the data the manufacturer gives them, if the boat weighs more than they said, then all bets are off. Also when these carbon boats with carbon sails, and dyneema running rigging accelerate or stop abruptly loads can go exponential and I don't believe there is enough data available to fully predict the loads.
The story is the boat was 250kg over design weight but well below max load weight when she set off. So I doubt that vessel weight was a factor here.

I agree with you about the shock loading. This is exactly the failure mode I think is most likely.
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Old 19-02-2015, 17:34   #672
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Re: GUNBOAT Dismasting

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Not sure about the 20 meter spar you made, was it a rotating spar?

The thing about the rotating wing mast is that you can make it a deep as you want fore-and-aft to resist pumping without paying a drag penalty because the altitude is adjustable. Hence no runners and only three stays holding it up. Yesterday's news.

I have to dig up some photos of strip plank cedar and plywood rotating wing masts from some thirty odd years ago made by Gudgeon brothers who sell you expensive epoxy to fix yer boat. If I have it correctly they spun off a business making wind generator blades.

If you look at the pictures of the Newick Tri I posted, those are wood composite spars.

Funny thing about wood, it's got great fatigue resistance, what with those trees blowing around in the wind all the time. I know it's not as sexy but wood is more resilient than carbon fiber and if harvested responsibly, it's a renewable resource.

Carbon Fiber Fun Fact : Carbon fiber is made from burnt wood!



Rain Maker have a rotating wing mast???
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Old 19-02-2015, 17:45   #673
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Re: GUNBOAT Dismasting

You know. I have to check my facts. That came from somewhere but maybe I am mistaken.
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Old 19-02-2015, 20:36   #674
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Re: GUNBOAT Dismasting

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Rain Maker have a rotating wing mast???
I am pretty sure the GB 55 doesn't have a rotating mast.

I just looked at the sailplan, and the specs from GB don't include a third reef. I wonder if this could have had any effect.
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Old 20-02-2015, 11:23   #675
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Re: GUNBOAT Dismasting

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Originally Posted by leftbrainstuff View Post
...

Why would a wave piercing hull be a desirable feature on a cruising sailboat? Reserve bouyancy, the opposite of wave piercing, is a well understood benefit. (I'm an engineer but can't think of a practical hydrodynamic benefit)

Longer waterline length for speed and marketing spring to mind but these are racing concepts.
..
You are wrong about less buoyancy, it is the opposite. When you do a wave piercing bow you extend it forward, that means that it will retain all the buoyancy of the previous vertical bow, adding some more buoyancy. As it was explained by the guy from the VOR, that helps to keep the bow up and diminishes water projections (that has to do also with a well designed one too).

Increasing LWL is fundamental to make a boat faster and has nothing to do with racing but with sailing faster. Compare the size of LWL between a contemporary designed boat and a same LOA boat designed 40 years ago and you will see a huge difference. Increasing the performance on a sailboat is a question of many factors that have been bettered through the years. Length of LWL is just one of them.
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