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  #161  
Old 04-14-2013
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Re: Modern Hull forms and Motion Comfort

Quote:
Originally Posted by bobperry View Post
Wolfer has it correct.
I think you mean PCP.

Quote:
The amount of weight it takes to sink ANY BOAT 1" has NOTHING to do with displacement. NOTHING. Say it three times.
LOL, no, I got it.

Quote:
"lbs. per inch immersion" is all about waterplane or the boat's "footprint" in the water.
I think "Archimedes" when I think that. We can even measure the weight of boobs that way

In any case, the more "spread" the waterplane is the more it's immersed, or the faster the plane grows in area, the more it will resist immersion (simply because the volume grows proportionally faster). I know you know that, but, I thought I'd attempt to explain it with my own words.


Quote:
Two 40'er of grossly different displs can have very similar water plane areas so they will have very similar lbs. per inch immersion.
Yes, but when adding or subtracting lbs, the change of shape of the waterplane matters (again, think vertical cylinder vs. inverted cone shape).


Quote:
No sailing vessel short of a Mac 26 or a radical trapeze dinghy is designed to be a " truly planing boat". If they were they would look like power boats that ARE designed to be truly planing boats.
I don't disagree with regards to keel boats not being truly planing boats, but I disagree that if they were, they would look like planing powerboats. They wouldn't, as the propulsion of a powerboat (center of effort for want of a better term), is below the waterline, and at the back. A sailboat, or kite boat or whatever, doesn't have the propulsion down there.
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  #162  
Old 04-14-2013
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Re: Modern Hull forms and Motion Comfort

I think most agree that boats should be compared by displacement rather than length. If we compare 2 designs of the same displacement, one an older design and one much newer, the comparisons are interesting.

The Westsail 32 is part of this thread so it can be the older design. For a newer design one of my favorites and one that Bob is very familiar with as it is his design, the Saga 43.

Westsail 32 Disp 19,500 lbs
Waterline 27.5 ft
Hull speed 7 (1.34 x sq rt waterline)
34% ballast ratio
1064 lbs/inch immersion

Saga 43 Disp 19,843
Waterline 39 ft
Hull speed 8.7
39% ballast ratio
1634 lbs/inch immersion

The Saga can carry about 1.5 times as much weight before it is 1" lower in the water than the Westsail. It sails faster and gains all that 11 feet of boat and more than that in increased waterline length allows.

I know which one I would sooner cruise in.
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Modern Hull forms and Motion Comfort-saga43.jpg   Modern Hull forms and Motion Comfort-westsail32.jpg  
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  #163  
Old 04-14-2013
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Re: Modern Hull forms and Motion Comfort

Quote:
Originally Posted by bobperry View Post
... While many modern, high performance boats can plane when the conditions are right I have yet to see a cruising boat of any flavor do this. ...
Well, there is always a first time





This was the sailing boat that won was the 2012 European boat of the year on the performance cruiser category, the Pogo 12.50. the boat is not even a cruiser racer since is rating is so bad that would be pretty useless in handicap racing. The same builder has a racer that had inspired this boat, the racer is much lighter and has much more sail (it is a class40 solor-racer). The success of the boat as a cruiser has been huge. They have a waiting list of more than a year. Many are bluewater cruising extensively on this boat.

There are a member with one (first time he cruised he has done 16K easily) and another one is on that waiting list. Eric only uses the boat to cruise with the family, no racing involved or planned.

Quote:
Originally Posted by bobperry View Post

The fact is that it takes so much effort and skill to make a sailing vessel sustain a plane that this kind of performance is way beyond the crew of the average cruising vessel regardless of design. Maybe if you cruise with a crew of twelve 20 year old guys, preferably in their off season from rugby, you could do it. But that does not sound like my idea of cruising.
" You, what's your name, get the number three kite on deck."
Not on a cruising boat that is derived from a solo racer. This one, like the solo racer can plane on autopilot. The solo racers sleep while the boat is planing and they took the knowledge that allows them to do that to the cruising world. The cruiser Pogo comes with a top autopilot, similar to the ones of racing boats.

Regards

Paulo
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Last edited by PCP; 04-14-2013 at 07:54 PM.
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Re: Modern Hull forms and Motion Comfort

That Pogo looked like it had very nice motion to me. I realize they were not sailing in the roaring 40's but on long passages across the pacific we have far more days where the seas look just like in the video than days of lousy seas. Put a dodger and spray skirts on her and she will be pretty dry in conditions like that. How would the Pogo sail if seas were rough and you slowed her down to 7 Kts? Can she be slowed down and still sail as well?
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Re: Modern Hull forms and Motion Comfort

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Originally Posted by hannah2 View Post
That Pogo looked like it had very nice motion to me. I realize they were not sailing in the roaring 40's but on long passages across the pacific we have far more days where the seas look just like in the video than days of lousy seas. Put a dodger and spray skirts on her and she will be pretty dry in conditions like that. How would the Pogo sail if seas were rough and you slowed her down to 7 Kts? Can she be slowed down and still sail as well?
Yes I am sure but the one more indicated to tell you about that is Eric. I find amazing that boat has that performance and has the ability to go near to the shore for safer anchorage, due to his swing keel. I was deleting old emails and found one reply from the shipyard to a request for information that I had made some years ago when the boat has only a project. It turned out that the swing keel is lighter than the torpedo keel for a similar RM. That is only possible because the torpedo keel for practical reasons cannot be as deep as the swing one.

The boat you are seeing on the the first movie is a charter boat, not for racing but for cruising.

http://www.fastsailing.gr/sailing.asp?catid=4271

On the second movie testers are testing it, among others boats, for the European 2012 Boat of the year contest. On the beginning of the movie we can see a sail faraway, going on the same course. Later we can see the Pogo catching it and leaving it behind with a big speed differential. That boat is a big and fast cruiser racer, a Grand Soleil 50

And they have improved the interior to the point that it is quite nice, light and practical one:













Regards

Paulo
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Last edited by PCP; 04-14-2013 at 10:06 PM.
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  #166  
Old 04-15-2013
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Re: Modern Hull forms and Motion Comfort

I didn't invent geometry.
Understand it or not.
Thant's your choice.
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Re: Modern Hull forms and Motion Comfort

Quote:
Originally Posted by bobperry View Post
I didn't invent geometry.
Understand it or not.
Thant's your choice.
Oh, I do. It is you who fail to understand that I'm describing the same thing you're describing. Perhaps you should read the posts again: The only difference between our explanations is that you're describing a static load, while I'm also describing how to make it even more difficult to submerge the next inch (i.e. enlarging the waterplane area the higher on the shape you go, which translates into "More volume has more resistance to immersion" and by extension "The faster the volume grows, the more resistant to immersion it will be").

Last edited by One; 04-15-2013 at 07:18 AM.
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  #168  
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Re: Modern Hull forms and Motion Comfort

Paulo, those videos of the Pogo 12,5 are really impressive. She looks quite comfortable in those mild sea conditions. I'd like to see how that hull configuration does when the sea kicks up into 6' square-faced waves and also how she handles in a big following sea. I can't help but think the bow might tend to be underwater a lot (to the point of pitchpoling) and make control a bit difficult. It looks like a wet ride but going that fast, it's understandable.
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Re: Modern Hull forms and Motion Comfort

I've had the good fortune of sailing on one of those 'modern' hull forms - in blue water and configured for 'cruising'.
Namely Alex's Guilietta - a modified Del Conde 42 https://www.facebook.com/pages/Marin...00589133310358

She didn't do 20+ on the two days we sailed her down the coast of Portugal, but she did break 14 on a regular basis. IIRC she weighed in at 12000 pounds. Her assym was the now old big blue - 1500 sq ft. The afternoon of the first day saw winds in the 20-30kt range.
Her interior (at the time) was fully outfitted for short term cruising. She has since been stripped and is now dedicated to racing.

Day two was mostly light winds - sailing until the schedule got in the way then motoring.
I the time I likened her to a 42 foot cruising dinghy.
I still do.
Stepping off the pier onto her transom step my modest 180 pounds sank the stern a full inch.
Bottom line for me - boats like this are not suitable for long range cruising. I repeat, cruising. She bobbed, she bounced, she required constant and nitpicking attention at the helm to maintain performance - Something no cruiser is going to put up with.

Did I mention we rounded up 7 times (assym in the water) and broached once- boom in the water?
I've only been sailing 11 years but I only know of one 'cruiser' who has ever put a boom in the water.

I'll stick with my old fashioned almost full keel, moderate displacement (20k) Irwin 38 CC with a SA/D of 16.7, with a pounds per inch of immersion of 1390 lbs (per Irwin).
I might get to the anchor a little later than others, but I'll get there.
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Re: Modern Hull forms and Motion Comfort

Quote:
Originally Posted by smurphny View Post
Paulo, those videos of the Pogo 12,5 are really impressive. She looks quite comfortable in those mild sea conditions. I'd like to see how that hull configuration does when the sea kicks up into 6' square-faced waves and also how she handles in a big following sea. I can't help but think the bow might tend to be underwater a lot (to the point of pitchpoling) and make control a bit difficult. It looks like a wet ride but going that fast, it's understandable.
You can ask Eric (EricKLYC), he is quite honest in his assessments and he has one of those. For what I know this is one of the best boats to have on a following sea, big or not. Very steady and able to go very fast even with big waves (that diminish the speed of the waves regarding the boat). Regarding frontal waves this is not the best boat around. This is a voyage boat for the trade winds.

Eric had already posted about that on the interesting boat thread comparing the performance of his boat with boats like mine that are good on those conditions. The motion is more uncomfortable, the boat experiences a bigger wave drag, he has to open more its course regarding to the wind but the boat has lot's of power so it can get a very good speed that somewhat can compensate its poorer pointing ability with waves.

Without waves or small waves the boat points well upwind (for a cruiser) and has a very good speed (lots power for a small wet surface - the boat weights only 5500kg )

Pogo 12,50 | Chantier naval STRUCTURES, constructeur des voiliers POGO (site officiel) :: STRUCTURES Shipyard, construction of sailing boat POGO (Oficial website)

Regards

Paulo
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Last edited by PCP; 04-15-2013 at 09:47 AM.
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