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  #121  
Old 05-12-2009, 08:25 AM
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Spiv Spiv is offline
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Fanie,
you're right, I remember, you had great result with your rig.
One more proof that it does work.

I agree with Alik thet forestay tension is important, but good sail performance could also be achieved with designing the sails for 'not so tight' a forestay as they have in the racing rigs.
In any case, I believe I can achieve good forestay tension as I have two backstays on winches.

My challenge is with engineering the CF mast. Any FE designers out there??
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  #122  
Old 05-12-2009, 04:27 PM
masalai masalai is offline
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Bob Oram is suggesting I go aft (well further than standard design) mast for my "hitch-hiker rig" - but at present I am happy with where it is - as it looks like I am just too lazy/broke to buy/put a standard "mainsail" - but actually I want to use the space for PV solar panels (up to 10kW) - Bob is apparently considering an aft-mast rigged design somewhere down the track...

I will probably cant the mast aft a bit to get more sail area from the twin genoas and put the centre of effort a bit further aft - just ideas at the moment...
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  #123  
Old 05-13-2009, 01:30 AM
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my 2 cents

Quote:
I have serious doubts if aft mast rigged boat is capable to tack due to sail area distribution. Aslo there are serious concerns about windward performance. Anyway soon we will have chance to test it on one of our designed cats.
most of my sailing experience is on 35 to 39 foot bermudan sloop mono hulls with full keel and "barn door" style rudders
then also PLENTY dinghies and lasers and hoby cats

i can assure all of you that after i sailed on Fanie's little tri i was completely blown away by it's excelent performance to windward and its ability to tack. Admitted this was on inland waters but it was a gusty blow.

the system that Mas intends to use with twin head sails is a very good choice for cruising and Fanie's experiment clearly shows that the aftmast concept works exceptionally well - absolutely nothing to worry about
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  #124  
Old 05-13-2009, 01:46 AM
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Manie, it is common knowledge that cats with 'Prout rig' are more difficult to tack compared with conventional rigged cats. This is because of big genoa that blows out and creates yawing momentum that prevents the tacking motion. Small mainsail is not capable to balance the genoa. Of course, it could be different on different boats depending on many other factors.

Anyway, this is just talks. Brian's rig should be built and tested before we can make conculsions and actually before it is marketed. He needs at least a 20-30' cat built with this rig... instead of hundreds of pages written on the subject during many years. I mean that prototyping and engineering are important before someone start investing real money in 50-60' boats with this unproven rig.
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  #125  
Old 05-13-2009, 02:10 AM
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I'm building two boats where the aft mast rig goes on. One is a 8m cat the other is a 10m cat. Both will have double aft mast rigs similar to what I had before. Needless to say there are changes, but not much.

I don't like referring to this sail as a genoa, a genoa seems to be clumsy and less controllable.

We should find a proper name for this.
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  #126  
Old 05-13-2009, 02:16 AM
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Fanie, but You built a prototype before start building bigger boats. This is right way to go, really appriciated!
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  #127  
Old 05-13-2009, 10:43 AM
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Yes well the way things are going here financial wise it seems I'll only get one finished in about 250 or so years
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  #128  
Old 05-17-2009, 09:24 PM
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Quote:
Originally Posted by Alik View Post
....I have serious doubts if aft mast rigged boat is capable to tack due to sail area distribution. Aslo there are serious concerns about windward performance.
Almost makes you wonder how this vessel ever manages to tack or go up wind
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Aftmast rigs???-3.jpg  Aftmast rigs???-4.jpg  
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  #129  
Old 05-17-2009, 09:45 PM
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Quote:
Originally Posted by Alik View Post
..I just stated that Brian's aft mast rig has never been built and tested. It is aerodynamicaly excellent (if we neglect slack of forestay ) but structurally weak, and mainsail does not seem practical.
I agree Alik, my rig is not to be put on many boats as it needs a good foundation to accept the high loading. Creating this good foundation may add considerable to the engineering and the price of the vessel. So its not for all.

I wrote a few discussions with reference to a few situations where 'unusually' high loading is involved:
Sail Loading on Rig, Rig Loading on Vessel

Vessel Substructure to Support Rigging Loads
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  #130  
Old 05-17-2009, 09:45 PM
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Brian, You have to put big disclaimer on Your website saying that these concepts have never been built.

For years, You are talking about these 'aft mast rigs' instread of building and testing a prototype. Sorry to say, but without engineering, prototyping and testing Your ideas have zero value.

As to the photos You post above - completely different situation, pls note the position of mainsail to CLR of boat.
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  #131  
Old 05-17-2009, 09:55 PM
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Quote:
Originally Posted by Alik View Post
I never said 'aft mast has never been built'. There are few boats built most known is 'Prout rig'.
Reference Posting #7 above
...for a moment look at the profile drawing of my rig and picture it as though the mast was standing straight up vertically with its masthead in the same location as mine now is. Contrary to Tom’s statement, my forestays are really no longer than a conventional sloop rig, in fact they are likely shorter. And his comments about the angles between the backstay & the mast and the forestay & the mast are not quite correct. In reality it’s the horizontal (not vertical) component of the tension forces in these two stays that determines the ability of the rig to resist sag in the forestay……my masthead backstay has a more advantageous (rearward pulling) angle than does my forestay pulling forward. Interestingly, this phenomenon was probably most detrimental to the Prout mast-aft rig. Their short vertical mast at the aft position resulted in a highly sloped forestay that was both too long for the rig’s overall height, and it could over-exert a forward pulling force on the masthead that was indefensible by the shallow-angled backstays…..result, big time sag, sails too full. This rig had other problems as well….not an example of a successful mast-aft rig, but a case study in some things to avoid.
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  #132  
Old 05-17-2009, 09:56 PM
masalai masalai is offline
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It is not, it is sailing downwind faster than the wind
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  #133  
Old 05-17-2009, 10:03 PM
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Quote:
Originally Posted by brian eiland View Post
Reference Posting #7 above
...for a moment look at the profile drawing of my rig and picture it as though the mast was standing straight up vertically with its masthead in the same location as mine now is. Contrary to Tom’s statement, my forestays are really no longer than a conventional sloop rig, in fact they are likely shorter. And his comments about the angles between the backstay & the mast and the forestay & the mast are not quite correct. In reality it’s the horizontal (not vertical) component of the tension forces in these two stays that determines the ability of the rig to resist sag in the forestay……my masthead backstay has a more advantageous (rearward pulling) angle than does my forestay pulling forward. Interestingly, this phenomenon was probably most detrimental to the Prout mast-aft rig. Their short vertical mast at the aft position resulted in a highly sloped forestay that was both too long for the rig’s overall height, and it could over-exert a forward pulling force on the masthead that was indefensible by the shallow-angled backstays…..result, big time sag, sails too full. This rig had other problems as well….not an example of a successful mast-aft rig, but a case study in some things to avoid.

Talking again... Show us the boat!!!
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  #134  
Old 05-17-2009, 10:13 PM
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Quote:
Originally Posted by Alik View Post
..As to the photos You post above - completely different situation, pls note the position of mainsail to CLR of boat.
I'm unsure as to what you are insinuating here...the balance of the CE over the CLR, I assume??

Are you claiming the main on the tri is of a larger area than my mizzen, and located more rearward, and that is more balanced?

If you look at my original design I think you will find that me CE for my full rig (all 3 sails), and the CE for the combo genoa/mizzen (2 sails) are both very close to one another fore-to-aft. and both are almost directly over the CLR of my centerboard

..and you might also refer to the illustrations in posting #98 above
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  #135  
Old 05-17-2009, 10:20 PM
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Quote:
Originally Posted by brian eiland View Post
I'm unsure as to what you are insinuating here...the balance of the CE over the CLR I assume??

Are you claiming the main on the tri is of a larger area than my mizzen, and located more rearward?

If you look at my original design I think you will find that me CE for the full rig (all 3 sails), and the CE for the combo genoa/mizzen (2 sails) are both very close to one another. and both are almost directly over my centerboard CLR.
The geometric CLR/CE relation is basic thing and it seems correct from Your sketch. To be accurate, this is simplified repersentation that works only for proven rigs. I mean that CE of sails will move during tacking motion of boat, and this will seriousely effect tacking performance.

I say again: reference to posts, guesswork and basic geometry are not sufficient to prove feasibility of this rig. Show us working boat, at least a dinghy, with Your rig!
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