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Old 02-12-2019, 08:40 PM   #261
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Originally Posted by Delfin View Post
So, does that mean that a boat builder who states physical reality with respect to hull design can't be trusted because you can buy their boat? Interesting perspective, Fish.
Delfin,
Boat builders are business people. Sure they hire engineers and designers but they have a lot to say that they don’t pass through the engineering department. And they are primarly in the business of selling boats. And the boat building business being what it is few have no worries about making money. So what boat builders have to say about boats may not be something to take to the bank.
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Old 02-12-2019, 08:45 PM   #262
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As distinct from the "pissing people off" contest. A clear winner there!
Quite so and I appreciate that it's appreciated, just getting a laugh out of the scrum at my own expense, as is appropriate.
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Old 02-12-2019, 08:49 PM   #263
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T
Some people have great dificulty with things that can’t be positively identified and classified. This is one of those things.
Those people wouldn't include boat designers, apparently.

And yes, a full displacement hull can "start to climb their wave". Problem is, it can't ever get to the top. If it can, it isn't a full displacement hull because it is no longer travelling at displacement speed.

But if it makes anyone feel better, we can define full displacement as whatever one wants it to be. Kind of like gender these days. You get to make up whatever definition you like, and you don't have to get pinned down to a definition, classification-wise.
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Old 02-12-2019, 08:52 PM   #264
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Fish

A read of the voluminous Nordhavn website can prove illuminating, plus the hundreds of available pages of first hand blogs from world cruisers. Don't forget to browse their in house written and then published "update" to Beebe's Voyaging Under Power. Then direct your curiosities and questions to them in well thought out written correspondence that should elicit a cogent reply.
I'm actually not very likely to take you up on your invitation, while it is very gracious of you to offer I'm in fact not the subscriber that brought the hallowed name of Nordhavn into the "conversation".
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Old 02-12-2019, 08:58 PM   #265
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Delfin,
Boat builders are business people. Sure they hire engineers and designers but they have a lot to say that they don’t pass through the engineering department. And they are primarly in the business of selling boats. And the boat building business being what it is few have no worries about making money. So what boat builders have to say about boats may not be something to take to the bank.
So Nordhavn doesn't know the difference between a FD and SD hull? If they don't, I guess we shouldn't be buying their boats. If they do, I guess I'm not sure of your point.
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Old 02-12-2019, 09:32 PM   #266
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But as I said it’s prolly the marketing dept talking so who cares?

The only Nordhavn that interests me is the 46.
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Old 02-12-2019, 11:55 PM   #267
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But as I said it’s prolly the marketing dept talking so who cares?

The only Nordhavn that interests me is the 46.
Eric - Sorta looks like your boat... all grown up! No wonder you like her.
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Old 02-13-2019, 05:56 AM   #268
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So...

What is the definition of full displacement.

Is it a specific hull design? Where no matter the engine HP it will always stay within the FD formula. Hull Speed = 1.34 x √LWL

Or

Is is a boat with a limited hp power plant that can never exceed FD speeds based on the LWL? Even if that hull design with bigger engines would result in a boat that would exceed the formula!

Can you even describe a FD bottom?
It was such a simple question.

Seems the answer is somewhat along the lines of: "if you ask a hundred doctors..."
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Old 02-13-2019, 06:42 AM   #269
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Because that formula doesn't take into all the factors that affect the 1.34 factor and obviously it applised to vessels in "the displacement mode"...not necessarily "just" full displacement hulls.


Exceptios to theory such as a full displacement hull with trim tabs as someone mentioned... might have been altered enough to now be a displacement hull (maybe not full displacement by definition) that now can travel in the semi displacement mode.


The catamaran hull. like the Hobie 16, even though it may have the characteristics of a full displacement hull, it has a prismatic coefficient and draft to beam ratio off the normal design scales...and when it lifts a hull and presents a nearly flat side to the surface...the wave making formula obviously no longer applies.


I have never seen what exactly the Hobie in hydrodynamic terms is all summed up as.... but like many simple concepts..... change but one of a few elements and new formulas now apply.


That said....Delfin repost of the boatdesign comments is pretty much what I have always heard and understood....and like my comments...the more I learned (like pretty much everything in life), exceptions exist.



The question ultimately is, does a basic definition include or exclude these exceptions?
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Old 02-13-2019, 09:41 AM   #270
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It was such a simple question.

Seems the answer is somewhat along the lines of: "if you ask a hundred doctors..."
Folks can make it as complex as they wish to, but a FD boat is one that cannot exceed a speed close to ideal hull speed because the lift generated by forward motion is more than offset by the drag created by the waves generated. In other words, they can't get ahead of their own bow wave. The reasons why this is so are complex. The phenomenon is not.

Their advantage in an ocean cruising is fuel efficiency at a high percentage of hull speed and most will after, a more comfortable motion while underway.
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Old 02-13-2019, 10:09 AM   #271
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Do we now need a definition of 'possible'?

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Yes that boat in the picture can be made to do that. It isn't practical, but it is possible. I've already referenced the power source that will do it. 418,000 lbs of thrust, weighs only 7700 lbs. The fuel pumps alone generate nearly 100,000 hp. Mileage will be poor though.
Why keep resorting to the ridiculous to prove a ridiculous assertion?

No, it's not 'possible', because (apart from being ridiculous), the combined weight of the engine >>and<< fuel for the power source you 'already referenced' would, would (a) sink the boat instantly before the engine starts, and (b) fuel would be totally consumed in less than 9 seconds. During that nine seconds, the boat would still not plane, it would sink, the same as it would if it was simply towed too fast. Also, you didn't include the weight of the "100,000 hp fuel pumps" in your calculation.

Maybe we could use a definition of 'possible' that means "possible in the real world".

re: "I said a displacement hull can be made to exceed "hull speed" by applying enough power. Pretty much every NA will agree with me on that."

Of course we'd agree, because it's a platitude. I'm not challenging that. If you read more carefully...I was responding to your subsequent post...where you said: "most normal hull shapes will eventually plane". A full-displacement hull is definitely a 'normal' shape and it will definitely never plane. Just like a sailboat being towed too fast, it will sink before it planes.

2) Re: "What do you mean when you say "planing"?

I attached a link to a definition from boatdesign.net in my post, maybe you didn't catch that? You should check out that website. There are real naval architects there.

3) Re: "sailboats...and on the face of a wave will do a pretty good job of planing."

Also false, and yet another ridiculous analogy. Think. If the force of gravity is no longer perpendicular to the water on which you are 'planing' (as it will be on the face of a wave), then the upward forces on the hull (hydrodynamic and bouyancy) will be less than the downward force of gravity on the boat. In this state the boat will be 'falling' down the surface of the water. On a hull that is capable of planing, this is known as surfing. Now...as the face of the wave approaches vertical, the weight of the boat relative to the wave's surface approaches zero. So...falling is not planing, and we don't need a definition to know that. It occurs to me that if you had actually experienced this, you'd already know that you were falling because you can feel it in your stomach, just like you can anytime you lose altitude rapidly.

Now...setting aside all of the impossible nonsense scenarios, here is why a full displacement hull can NEVER plane:
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Old 02-13-2019, 10:18 AM   #272
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Why keep resorting to the ridiculous to prove a ridiculous assertion?

No, it's not 'possible', because (apart from being ridiculous), the combined weight of the engine >>and<< fuel for the power source you 'already referenced' would, would (a) sink the boat instantly before the engine starts, and (b) fuel would be totally consumed in less than 9 seconds. During that nine seconds, the boat would still not plane, it would sink, the same as it would if it was simply towed too fast. Also, you didn't include the weight of the "100,000 hp fuel pumps" in your calculation.

Maybe we could use a definition of 'possible' that means "possible in the real world".

re: "I said a displacement hull can be made to exceed "hull speed" by applying enough power. Pretty much every NA will agree with me on that."

Of course we'd agree, because it's a platitude. I'm not challenging that. If you read more carefully...I was responding to your subsequent post...where you said: "most normal hull shapes will eventually plane". A full-displacement hull is definitely a 'normal' shape and it will definitely never plane. Just like a sailboat being towed too fast, it will sink before it planes.

2) Re: "What do you mean when you say "planing"?

I attached a link to a definition from boatdesign.net in my post, maybe you didn't catch that? You should check out that website. There are real naval architects there.

3) Re: "sailboats...and on the face of a wave will do a pretty good job of planing."

Also false, and yet another ridiculous analogy. Think. If the force of gravity is no longer perpendicular to the water on which you are 'planing' (as it will be on the face of a wave), then the upward forces on the hull (hydrodynamic and bouyancy) will be less than the downward force of gravity on the boat. In this state the boat will be 'falling' down the surface of the water. On a hull that is capable of planing, this is known as surfing. Now...as the face of the wave approaches vertical, the weight of the boat relative to the wave's surface approaches zero. So...falling is not planing, and we don't need a definition to know that. It occurs to me that if you had actually experienced this, you'd already know that you were falling because you can feel it in your stomach, just like you can anytime you lose altitude rapidly.

Now...setting aside all of the impossible nonsense scenarios, here is why a full displacement hull can NEVER plane:
Amen, brother....

What makes internet forums so much fun is that any proposition, no matter how mundane or grounded in physics, will be challenged for pages and pages.
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Old 02-13-2019, 10:26 AM   #273
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Why keep resorting to the ridiculous to prove a ridiculous assertion?

No, it's not 'possible', because (apart from being ridiculous), the combined weight of the engine >>and<< fuel for the power source you 'already referenced' would, would (a) sink the boat instantly before the engine starts, and (b) fuel would be totally consumed in less than 9 seconds. During that nine seconds, the boat would still not plane, it would sink, the same as it would if it was simply towed too fast. Also, you didn't include the weight of the "100,000 hp fuel pumps" in your calculation.

Maybe we could use a definition of 'possible' that means "possible in the real world".

re: "I said a displacement hull can be made to exceed "hull speed" by applying enough power. Pretty much every NA will agree with me on that."

Of course we'd agree, because it's a platitude. I'm not challenging that. If you read more carefully...I was responding to your subsequent post...where you said: "most normal hull shapes will eventually plane". A full-displacement hull is definitely a 'normal' shape and it will definitely never plane. Just like a sailboat being towed too fast, it will sink before it planes.

2) Re: "What do you mean when you say "planing"?

I attached a link to a definition from boatdesign.net in my post, maybe you didn't catch that? You should check out that website. There are real naval architects there.

3) Re: "sailboats...and on the face of a wave will do a pretty good job of planing."

Also false, and yet another ridiculous analogy. Think. If the force of gravity is no longer perpendicular to the water on which you are 'planing' (as it will be on the face of a wave), then the upward forces on the hull (hydrodynamic and bouyancy) will be less than the downward force of gravity on the boat. In this state the boat will be 'falling' down the surface of the water. On a hull that is capable of planing, this is known as surfing. Now...as the face of the wave approaches vertical, the weight of the boat relative to the wave's surface approaches zero. So...falling is not planing, and we don't need a definition to know that. It occurs to me that if you had actually experienced this, you'd already know that you were falling because you can feel it in your stomach, just like you can anytime you lose altitude rapidly.

Now...setting aside all of the impossible nonsense scenarios, here is why a full displacement hull can NEVER plane:
The sailboat towing analogy I presented twice on this thread to no avail, thanks for providing some documentation. I also provided the accepted naval architecture definition of the three primary hull forms but again we wandered off into the absurd. In the practical world with the vast majority of boats this subject is no where near as bizarre as presented here. The same book I referenced elsewhere, Dave Gerr's the Propeller Handbook, explains this subject in an easy to understand form. Perhaps those with a serious interest might find illumination there, I'd also suggest William Van Dorn's Oceanography and Seamanship.
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Old 02-13-2019, 10:30 AM   #274
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The question ultimately is, does a basic definition include or exclude these exceptions?
Sure there is. If the hull can get ahead of its bow wave, it isn't a FD. If it can't, it is.

The only way this is not true is if the proposition that I can get Delfin to plane with enough horsepower is true. In this thread there have been numerous references from builders, designers, sites on boat design, etc. that this is false, so I guess I'm sticking with that.

Now, if I stick some garage door sized trim tabs plus the engine for the Boeing 787 on her, then she could plane, in the which case, she's no longer a FD boat. Absent the trim tabs, she'd be a 65 ton submarine.
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Old 02-13-2019, 10:30 AM   #275
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Amen, brother....

What makes internet forums so much fun is that any proposition, no matter how mundane or grounded in physics, will be challenged for pages and pages.
Where have I seen that? Hmmm.
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Old 02-13-2019, 10:43 AM   #276
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Where have I seen that? Hmmm.
Oh, I wouldn't be too hard on yourself Fish. You only spent 3 pointless posts suggesting that Nordhavn, because they sell boats, don't know anything about boats. No one paid much attention, so no harm done.
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Old 02-13-2019, 10:45 AM   #277
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OMG... boredom strikes deep. and, must be attended in some manner!! - LOL
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Old 02-13-2019, 10:52 AM   #278
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OMG... boredom strikes deep. and, must be attended in some manner!! - LOL
I'm not bored, I just came in from plowing snow off of 1600 feet of driveway and two parking areas in 23 degrees and 30kt winds on a tractor. Yippee.
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Old 02-13-2019, 11:07 AM   #279
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Every hull in the world is exactly the same and only fits into 3 categories...you have seen it right here on the internet as proven by a few.
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Old 02-13-2019, 11:20 AM   #280
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I'm not bored, I just came in from plowing snow off of 1600 feet of driveway and two parking areas in 23 degrees and 30kt winds on a tractor. Yippee.
Mid 70's to mid 80's in winter I ran my two snow plow trucks at 5K to 6K feet elevation - in Sierra Nevada mts. Being a masonry, concrete and tile contractor... had to keep my two best installers busy during winter! Man, did we ever have some fun snow plowing... The Stories!!!...
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