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  #171  
Old 04-15-2013
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Re: Modern Hull forms and Motion Comfort

One:
No, I've been at this some time now with a design or two to my credit. I understand it all pretty well. Yes, as you immerse the boat the WPA will increase making the lbs. per inch immers greater for the next inch. But if we are talking about a 3" range in immersion you can use one number for convenience.
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  #172  
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Re: Modern Hull forms and Motion Comfort

Quote:
Originally Posted by bobperry View Post
One:
No, I've been at this some time now with a design or two to my credit. I understand it all pretty well. Yes, as you immerse the boat the WPA will increase making the lbs. per inch immers greater for the next inch. But if we are talking about a 3" range in immersion you can use one number for convenience.
I wasn't disagreeing with you on the whole. I was making sure you understood that we were talking about the same thing, albeit with different wording. It's not exactly rocket science, regardless of the fact that one of us are designing boats to be build.

I mentioned Archimedes for a reason.
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  #173  
Old 04-15-2013
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Re: Modern Hull forms and Motion Comfort

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Originally Posted by chucklesR View Post
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.
Sorry but we are not talking about the same type of boats or hulls. Giulietta is a cruiser racer able to get good results in regatta and the hull is on the line of those boats. It requires a crew to go very fast and as all regatta boats is a nervous boat.

The Pogo comes from a line of solo racing boats. that is quite the opposite in what regards behavior: while a regatta boat is a nervous boat solo racing boats are designed to be forgiven boats and boats to be steered on autopilot, while a regatta boat has always someone at the wheel.

Regards

Paulo
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Re: Modern Hull forms and Motion Comfort

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Originally Posted by chucklesR View Post
Stepping off the pier onto her transom step my modest 180 pounds sank the stern a full inch.
I hope you're aware that steeping onto the scoop is not the same as the whole hull immersing?

Quote:
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).
Apparently not.

Step onto the stern of a skerry cruiser or otherwise relatively slim boat and/or one with "flared" ends looking at it in profile, and you'd get even more of that zee-zaw motion. That is not the same as lbs/inch immersion.
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  #175  
Old 04-15-2013
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Re: Modern Hull forms and Motion Comfort

I will stop trying to use my boat to defend heavy disp and/or full keel boats because as it turns out it's performance is not typical of such boats. And yes I can't do hull speed sailing up wind, but it doesn't take much to 6.5kt, a1/4 of a knot less than the theoretical hull speed (6.75kt). I use my boat more as an example to try and beat down over generalizations "all full keel boats...." "all heavy disp boats....".
On a different note a Cape George 31 pulled into the marina here, it is 1' longer not quite a foot wider but is extremely similar (a lot more emphasis was put into accommodations, cabin trunk was carried further forward and aft).
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Re: Modern Hull forms and Motion Comfort

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Originally Posted by One View Post
I wasn't disagreeing with you on the whole. I was making sure you understood that we were talking about the same thing, albeit with different wording. It's not exactly rocket science, regardless of the fact that one of us are designing boats to be build.

I mentioned Archimedes for a reason.
One - you ARE aware that you are talking to one of the preeminent yacht designers in the world aren't you?

Tip - the Maestro is someone you ASK questions of, not someone you explain yacht design details to.

Also, in some ways boat design is more difficult than rocket science - it requires a big component of artistry whereas rocket science is almost pure math.
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Re: Modern Hull forms and Motion Comfort

Because there are only so many things you can do to a hull, yacht design is getting harder, as with any effective marketing you have to make anything prior seem inferior to what you are offering....when in this case alternatives should be offered and the huge accumulation of knowledge over the years should allow for more customization for an individuals personal uses.
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Re: Modern Hull forms and Motion Comfort

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Originally Posted by SloopJonB View Post
One - you ARE aware that you are talking to one of the preeminent yacht designers in the world aren't you?
You ARE aware that I have REPEATEDLY said we're saying the same thing, only with different wording, right? I mentioned that when Perry was unable to see that. He is now aware that I'm not disagreeing with him. He even "admitted" that the water plane area, WPA, was just a simple way to look at it (i.e. it's two-dimensional, while my explanation went with three dimensions).


Quote:
Tip - the Maestro is someone you ASK questions of, not someone you explain yacht design details to.
Tip: Understand what you read before you tell others to be in awe of someone. If you had, you would have seen we were talking about the same thing, only with different wording. I'm sorry I added to the two-dimensional explanation, because we are in reality dealing with volume. I should have taken what Perry said as gospel without attempting to explain things a bit less, well, simplistic.

Quote:
Also, in some ways boat design is more difficult than rocket science - it requires a big component of artistry whereas rocket science is almost pure math.
"Artistry"? Pfft. It's about compromises and solutions to given problems. If you want to call those things "artistry", be my guest, but you might as well go "It's magic". It's not.

"It's not rocket science" is a figure of speech. I could have gone with "It's not neurological research". Now, better?
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  #179  
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Re: Modern Hull forms and Motion Comfort

I was thinking more along the lines of respect than "awe".

I guess we mere peasants just don't have the subtlety of thought or understanding to grasp the concepts you seemingly have at your fingertips.

I mean, a mere 40 years of sailing, boatbuilding and studying design isn't that much of a base of knowledge is it?
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  #180  
Old 04-15-2013
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Bob Perry's take on Wolfenzee's dream boat

Way back in Post # 142, Wolfenzee said "BOB: take a close look at the lines of my boat and tell me could a fin keel have been designed in relatively easily http://atkinboatplans.com/Sail/image...inCicero-3.gif ."

And in Post #152 and #153 Bob Perry Responded:
(#152)"Damn it Wolfer!
You made me think.
I hate it when that happens.

Sure I coud do your boat with a fin keel and a nice skeg hung rudder or better yet a spade rudder.

It would look just like your boat,,,above the water. Under the water you would not recognize it. I would have to shave away all that deadrise and reduce displ while carving away some volume forward and reducing some hollows aft.

But in the end you and me would love it. It would be a WOLF in sheep's clothing like NIGHT RUNNER."


(#153) "Wolfy:
Next Wednesday post your hull lines again and a photo or two of your boat.
When I start thinking about a new boat I need to see it and I think it would be fun for all of us to see what your boat would look like with a more modern hull combined with that traditional Atkin look.

I have to do this to get it off my mind. I'm built like that.

Or, Jeff could do it. I know he could.
Or, Jeff and I could do it together.
He'd do the hard work and I'd do the pointing and gesturing.

Either way let's see if we can produce a boat that will get your juices flowing."

And I am bowled over by that.

Bob,
As a SailNet Moderator, I can only thank you for that generous offer to come up with a design that explores Wolf's question. That is a true gift to this forum. Normal folk rarely get to see a custom design process and so this should prove interesting.

And I am truly honored that you would be willing to do this with me. I truly appreciate your willingness to give that a try.

Rather than hijack this thread, I have started a thread for that purpose here: Bob Perry's take on Wolfenzee's dream boat

I'll be very interested in where this ends up,

Jeff
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Last edited by Jeff_H; 04-16-2013 at 09:22 AM.
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