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  #511  
Old 04-21-2017, 08:51 AM
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brian eiland brian eiland is offline
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First off before I forget it, perhaps have a look thru this somewhat long subject thread for ideas discussed that might be related to some you are contemplating.
http://www.cruisersforum.com/forums/...nted-8429.html

I've not had a chance to re-review it yet, but just ran across portions of the discussion I have saved on an older flash drive.
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  #512  
Old 04-21-2017, 09:05 AM
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brian eiland brian eiland is offline
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Quote:
Originally Posted by John Perry View Post
I agree that your design is looking much better now - the deep void you had below the bridgdeck was an obvious waste of space and resulted in unnecessarily high superstructure. I agree with your own sugestion that you should now consider some reduction in freeboard, if you can manage that you would save some weight and windage and I think improve the aesthetics, although that is of course subjective. But dont compromise the clearance under the bridge deck. I think there is at least one thread on this forum discussing bridge deck clearance.

Looking at your latest sketches I think you are in danger of not having sufficient torsional strength and torsional stiffness in your structure. The structure of a multihull needs torsional strength and stiffness to cater for situations such as the lee bow 'digging in' causing much of the total weight of the craft to be briefly supported at one corner of what is basically a rectangulr structure.

There seem to be two basic approaches to providing torsional strength and stiffness in a mulithull structure. The first approach, normal in cruising boats, is to have a single torsionally strong box like cabin structure connecting the hulls. The second approach, normal in lightweight racing craft, is to connect the hulls with fore and aft cross beams that are have relatively little torsional stiffness but which are stiff and strong enough in bending to transfer torsional loading onto the hulls which are capable of carrying that loading since they are much larger in section than the cross beams. Many multihulls do of course have more than two cross beams but in such cases you will usually find that only two of the cross beams provide the torsional strength and stiffness of the craft as a whole.

The cabin structure that you have sketched does not seem to offer much torsional strength or stiffness - being open at the rear and having almost continuous windows it is like a shoe box without a lid as opposed to a shoe box that has had the lid glued in place!

Since you have chosen not to have a torsionally strong and stiff cabin structure I think you need fore and aft cross beams. The front end of your bridge deck structure will act as a forward cross beam, but where is the aft one?! I suspect you have left that out because you fancy having a flat unobstructed deck right back aft. I suggest you need to make some compromise there by including an aft cross beam, but you may not like to have to step over it to access your tender which I suspect you will want to hang in davits aft. Actually, the bending moment on a multihull aft cross beam is minimal at the centre of the beam so there is an option to have a beam that tapers down in height towards the craft centreline, giving fairly minimal obstuction to strolling aft along the bridge deck - just a thought.
Good advice being offered on some of these latest postings. I can remember now a problem that occurred on the big Polish catamaran that entered that first 'RACE' around the world. It had to add diagonal cabling under the tramps between the fwd and aft crossbeams to obtain a better stiffness. (can't find that reference link at the moment).

But here is another discussion I started on that subject
X-Beam and the Giant
http://www.boatdesign.net/forums/multihulls/x-beam-giant-14679.html
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  #513  
Old 04-21-2017, 09:09 AM
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BTW, before you get set to accept those 'protuberances' into the wing deck areas to provide lower-bigger berths in the aft end of the vessel, take a look back at the old Prout designs that included such an item,...and the problems/complaints experienced.
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  #514  
Old 04-21-2017, 09:21 AM
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Vessel Substructure to Support Rigging Loads

Ah ha, I found this older posting (wonderful google search assistance)

Sail Loading on Rig, Rig Loading on Vessel

excerpt...
Quote:
The big Polish RACE catamaran "Warta Polpharma" added a cross X bracing of hi-modulus cable between the inner corners of its fore-beam and aft-beam in an attempt to stiffen itself in torsion and racking. Team Adventure was also contemplating the same arrangement (in fact I believe they did such an installation right after the finish of the RACE in preparation for a trans-Atlantic speed run). Of course these are non-bridgedeck cats.

Solid bridgedeck designs that we find with cruising cats are advantaged over the trampoline cats with respect to this cross-brace stiffening. But particular attention must be paid to the ‘flat-plate nature’ of most bridgedecks, and their construction composition, and their positive attachment to the main crossbeams in order that they are utilized most effectively.

Many cats are seen to have basically a flat bridgedeck structure with some attached fore-to-aft stiffening beam/ribs on the bottom side. These attached beams/ribs do act to cut down the unsupported panel size and give a stiffer walking deck to the saloon, but they only act in a small manner to prevent the bridgedeck from bending fore-to-aft. And they don’t contribute to the athwartships or diagonal bending problems at all. If we give a little camber shape and/or add a corrugated channel shape to the flat panel deck we improve things a little bit further.

Athwartships bending is a most serious concern as our rig’s shrouds are always acting to bend our vessel up in half around the mastbase pushing down. In open-deck cats the stiff crossbeams along with their dolphin strikers and gull strikers resist these bending loads. In our cruising cats it’s the main bulkheads we rely on to do this job. But so often we see vessels with less than desirable bulkhead arrangements. I believe it is very important that their be a minimum of two major bulkheads, one fore, one aft, and that akin to the open-deck boats these two bulkheads must be continuous across the whole beam of the vessel. And these bulkheads need some ‘beef’ rather than just be made of some ‘flat sheet’ of ¾ or 1 inch plywood or the sort. What’s wrong with a good stiff 2 - 5 inch thick panel of hi-tech sandwich cored material. Now you have a ‘bulk’head! Make sure you have a good bond between this super bulkhead and your bridgedeck and you are on your way to a stiff boat. Throw in a couple of ‘diagonals’ of hi-tech yarn (possible buried within the other structures, skins, and panels of the boat) to triangulate things.

Now you’ve got a stiffer boat and some good substructure to mount your sailing rig to.

In the particular case of my rather unusual mast-aft design, I tie the shrouds directly onto the same ‘super’ bulkhead that my mast is mounted on. And one of my backstays (the mizzen forestay) is tied directly to the same super bulkhead right at the base of the mast. Its upward force is countered by the downward force of the mast. The other two backstays are tied to another bulkhead at the stern, while the forestays are tied to the ‘flat plate’ rib structure down the centerline of the boat
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Last edited by brian eiland : 04-21-2017 at 09:35 AM. Reason: found the link to same posting on this forum rather than other one
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  #515  
Old 04-21-2017, 10:01 AM
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brian eiland brian eiland is offline
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video walkthrough of the new Saona 47

Here is a video walkthrough of the Saona 47 at La Grande Motte.

http://www.cruisersforum.com/forums/...ml#post2376120

...A LOT of boat in a 47 footer

https://www.youtube.com/watch?v=HNGGG8bsAd8
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  #516  
Old 04-21-2017, 10:39 AM
jorgepease jorgepease is offline
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Look at this catana, those bunk shelves look like they might slam. Aft I think it's less likely.

How high would you say the shelf is from the water in this pic? Looks much lower than what I am drawing.

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  #517  
Old 04-21-2017, 10:47 AM
jorgepease jorgepease is offline
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Quote:
Originally Posted by brian eiland View Post
Here is a video walkthrough of the Saona 47 at La Grande Motte.

http://www.cruisersforum.com/forums/...ml#post2376120

...A LOT of boat in a 47 footer

https://www.youtube.com/watch?v=HNGGG8bsAd8
Nice but that strays from the idea of being a lean mean fast machine. I would never have a fly bridge on a sail boat .. unless it's over 80' ... are you trying to push me in that direction???
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  #518  
Old 04-21-2017, 12:23 PM
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Quote:
Originally Posted by jorgepease View Post
Nice but that strays from the idea of being a lean mean fast machine. I would never have a fly bridge on a sail boat .. unless it's over 80' ... are you trying to push me in that direction???
For a lean/mean fast machine you are going to have to spend more than i think you plan on budgeting,...for both hi-tech hull materials, and hi-tech sailing rig equip. And you better plan on spending 2-5 years building it.

On the hand you could buy one of these, go off for some delightful sailing (perhaps a few knots slower), have some wonderful experiences exploring the MED, perhaps meet some wonderful ladies that would love hanging out on this vessel, and then turn around and sell it for a reasonable amount of money if you kept it in good shape. And I think this vessel has as much, if not more, room and amenities on it than what you are trying to put into yours.....just saying.

I would term that a 'raised helm station' rather than a flybridge, and I think you would come to really appreciate it. You need to go charter a few different
big cats to get a first hand look.
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  #519  
Old 04-21-2017, 12:34 PM
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Quote:
Originally Posted by jorgepease View Post
Look at this catana, those bunk shelves look like they might slam. Aft I think it's less likely.

How high would you say the shelf is from the water in this pic? Looks much lower than what I am drawing.

It's a little hard to tell from the dark shadows and the waterline, but I would venture to guess she is in a light-ship condition as it appears she is floating well up from her painted waterline. My guess is those protuberances are about 18 inches above the water at this point, and might go down to only 12 inches clearance once she is loaded up for cruising. It's their 'flat bottom surfaces' that bother me most,...that is a recipe for slap. I don't want any surfaces in that under bridgedeck are to be perpendicular to water impingement.

Maybe go on line and fine some owners of that design, and she what they have to report,...first hand info.

Here is a little discussion and a few photos from Richard Woods...
http://www.sailingcatamarans.com/ind...edeck-slamming
Quote:
......Furthermore, the water that goes in at the bow also has to come out at the stern, for as the bows pitch out of a wave the sterns will pitch in. So bridgedecks should also be high near the stern. Have a look at the stern of a Prout catamaran, you'll see there is very little space for the bows waves to get out. No wonder they are so noisy to sail - and the waves trying to force their way out must slow the boat down.
...and by the way those early Prouts had a tendency to pitch quite a bit as a result of their 'dbl-ended hull shapes'
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  #520  
Old 04-21-2017, 12:45 PM
jorgepease jorgepease is offline
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Originally Posted by brian eiland View Post
Maybe go on line and fine some owners of that design, and she what they have to report,...first hand info.
I did, they were complaints about it. I figured 18" too. Mine are about 36" above the waterline.

I just read that thread on the bending stresses, interesting, now I understand some more of the forces at play.

I think my bridgedeck is going to help a lot in that respect. By separating top and bottom panels and adding stiffeners in between it's going to be like a giant Ibeam and that stiffness has to be transferred to the hulls as best possible.

The upper and lower panels should be separated a minimum of 4" and the stiffeners have to run longitudinally.

Additionally I am thinking about the torsional forces that were mentioned. I am thinking that I can add that short return (enclosing salon) as first drawn with a beam that spans the space. This would be a carbon frame that would enclose very little but could help with the torsional support and tie in the roof as already mentioned, needs more support.
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  #521  
Old 04-21-2017, 12:56 PM
jorgepease jorgepease is offline
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Quote:
Originally Posted by brian eiland View Post
On the hand you could buy one of these, go off for some delightful sailing (perhaps a few knots slower), have some wonderful experiences exploring the MED, perhaps meet some wonderful ladies that would love hanging out on this vessel, and then turn around and sell it for a reasonable amount of money if you kept it in good shape. And I think this vessel has as much, if not more, room and amenities on it than what you are trying to put into yours.....just saying.

I would term that a 'raised helm station' rather than a flybridge, and I think you would come to really appreciate it. You need to go charter a few different
big cats to get a first hand look.
It has more amenities I think

The thing is what am I supposed to do for the rest of my life? A charter fleet is a perfect life style that will support me and allow 4 months per year to sail and fiddle around with innovations for years to come.
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  #522  
Old 04-21-2017, 05:21 PM
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The type of boats you see in charter fleets are like the boat shown in brians video. Thats what the industry wants, not high performance sailboats.... if thats the industry you want to be in jorge- then this boat you arw designing should be a floating palace- not a performer...

My needs and wants are very different to a charter guest. For me, i want a boat that can eat up hundreds of miles per day witg very good sailing performance so that i can cross oceans to get to new places all over the Pacific on an extended cruising adventure.

A charter guest im the med doesnt need ro cover many miles... they only have a short time available and just want to relax in comfort sippint cocktails and putting up their photos on instagram showing off to their friends back home. They want luxury. Most of them dont know how to sail or trim a sail.... they spend alot time motor sailing...

So you need to think carefully about what your designing Jorge....
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  #523  
Old 04-21-2017, 06:34 PM
jorgepease jorgepease is offline
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I have already thought about the business side of it. I don't want to cater to the masses, and there are quite a few SIG45's out in charter so I don't think I'm straying too far from the model. My craft will be much more luxurious than the SIG.

Also my angle is eco adventure, zero carbon footprint, this is at the peak of interest these days. )) and I can do some pretty beautiful things with my hands that I can't do on the computer. That is why I at least need a large topside.

And then after charter season, I'l be wanting to cover some miles myself.
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  #524  
Old 04-21-2017, 09:20 PM
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waikikin waikikin is offline
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If you check this ad there's a short vid that illustrates the step/blister on the Crowther boats
http://yachthub.com/list/yachts-for-...ther-47/188421

J.
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  #525  
Old 04-22-2017, 10:59 AM
jorgepease jorgepease is offline
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Quote:
Originally Posted by waikikin View Post
If you check this ad there's a short vid that illustrates the step/blister on the Crowther boats
http://yachthub.com/list/yachts-for-...ther-47/188421

J.
I checked it out, can't see from the front angle but I wonder why the 45 to the shelf? must be for a chase?

Anyway I decided to raise it a bit to be on the safe side, now my shelfs will be at 39" above waterline and rest of BD will be at 53.5 above waterline... It will raise interior bunks to 33" and I will see about the sheer but I think it's okay where it is.





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