Reply
 
Thread Tools Search this Thread Display Modes
 
Old 02-14-2019, 10:55 AM   #301
Art
Guru
 
Art's Avatar
 
City: SF Bay Area
Vessel Model: Tollycraft 34' Tri Cabin
Join Date: Feb 2011
Posts: 10,829
Pulling or pushing a D hull fast enough over water trying to get it on "plane", in semblance, is not too unlike pulling or pushing a person fast enough over ground trying to make them "fly".


End result is neither form actually accomplished "planning" nor "flying". Just forced alterations to their physical forms' intended stance-results. And, both items are likely wrecked at close of the grossly overpowered pulling/pushing endeavor.


Why o' Why - would any adult for any reason want to pull or push a D hull fast enough to try to get it on plane???? Makes no sense!!


This thread kinda reminds me of playing with model boats in bathtub when very young... Little intention for actuality nor care for reality!
__________________
Advertisement

Art is offline   Reply With Quote
Old 02-14-2019, 11:10 AM   #302
Guru
 
Fish53's Avatar
 
City: Pitcairn Island
Join Date: Jul 2015
Posts: 716
Quote:
Originally Posted by Art View Post
Pulling or pushing a D hull fast enough over water trying to get it on "plane", in semblance, is not too unlike pulling or pushing a person fast enough over ground trying to make them "fly".


End result is neither form actually accomplished "planning" nor "flying". Just forced alterations to their physical forms' intended stance-results. And, both items are likely wrecked at close of the grossly overpowered pulling/pushing endeavor.


Why o' Why - would any adult for any reason want to pull or push a D hull fast enough to try to get it on plane???? Makes no sense!!


This thread kinda reminds me of playing with model boats in bathtub when very young... Little intention for actuality nor care for reality!
Well said, that's why design is the key, at least in the bathtub there's bubbles.
__________________

Fish53 is offline   Reply With Quote
Old 02-14-2019, 11:15 AM   #303
Grand Vizier
 
Delfin's Avatar
 
Join Date: Jan 2010
Posts: 3,464
Quote:
Originally Posted by Baker View Post
Yes it does. There is no flat sections to provide lift. Just because a boat goes planing speeds does not make it a planing hull.
The flat sections are quite visible in the photo. At speed, it doesn't take much to get a very light rig up on plane. For older Hobie designs that don't have the "at rest" flat sections you can see in the picture I posted, the planning surface becomes the hull side when the Cat gets up on one sponson and you have to hang way out to windward to keep from capsizing.

But as I said, if one wishes to call a hull that planes a non planing hull, it's fine by me. To paraphrase the Red Queen, hull type is whatever she says it is, regardless of what it actually is.

In that spirit, since all hull designs of whatever shape displace water at rest, and at displacement speeds push the water out of the way rather than riding on top of it, I declare that the answer to the OP's question is that anything that touches the water is a full displacement hull, whether wineglass shaped blue water cruiser, a rock, a Hobie Cat skimming the warer at 30 knots, an inner tube being pulled by a hydroplane, the hydroplane itself - these are all full displacement hulls.

I personally have always wanted to own a hydrofoil, so the one exception to the above definition is going to be Delfin, which henceforth will be referred to as a hydrofoil. The fact that it lacks foils is no deterrent anymore than the ability to plane indicates a planing hull, which no longer describes anything anyway.
Delfin is offline   Reply With Quote
Old 02-14-2019, 11:29 AM   #304
Guru
 
City: Carefree, Arizona
Vessel Name: sunchaser V
Vessel Model: DeFever 48
Join Date: Apr 2008
Posts: 9,047
Quote:
Originally Posted by Delfin View Post
I personally have always wanted to own a hydrofoil, so the one exception to the above definition is going to be Delfin, which henceforth will be referred to as a hydrofoil..
In the two latest America's Cups the arguments over wings vs hydrofoil language and definitions is prodigious. Even the top designers argue over the minutiae of the definition and guard their curve linear differential equations carefully.

Flat vs round bottoms vs exposed aft sections seems more, well, gentlemanly.
sunchaser is offline   Reply With Quote
Old 02-14-2019, 12:55 PM   #305
DDW
Guru
 
City: San Francisco
Join Date: Apr 2018
Posts: 1,453
Quote:
Originally Posted by Delfin View Post
Got it. This vessel is behind its bow wave because as you say, a boat never gets ahead of it.
The vessel in that picture is certainly not ahead of its bow wave. The only parts of the hull that have any effect on hydrodynamics are the parts that get wet. Everything else can be cut away without effect. In that photo the effective bow of the boat is where the water and fiberglass meet. You might as well say a heavy tub with a long bowsprit is "ahead of its bow wave" since the end of the bowsprit is - which would be ridiculous.

Quote:
Originally Posted by Fish53 View Post
"A non breaking wave in deep water and no current is never even close to vertical" As water molecules travel in a vertically circular pattern in non-breaking waves I find it difficult to imagine that at some times they aren't moving vertically at two points in the circle, say maybe 3 and 9 o'clock?
The surface is not vertical, and 3 and 9 o'clock positions are not on the surface. In any case the water motion is insignificant compare to the boat speed - do the calculations.

Quote:
Originally Posted by Delfin View Post
The flat sections are quite visible in the photo. At speed, it doesn't take much to get a very light rig up on plane. For older Hobie designs that don't have the "at rest" flat sections you can see in the picture I posted, the planning surface becomes the hull side when the Cat gets up on one sponson and you have to hang way out to windward to keep from capsizing.
A Hobie (and any cat) sails fastest with very little heel. Sure you can have fun with one like the picture shows, but that will not win any races. Even with both hulls in the water, a Hobie 16 will do 16 knots easily - that is 4 x WL ^ 0.5. It is not planing as anyone would define it. Even the fastest cats in the world ( non-hydrofoil) have no flat planing sections, they are semi-circular bow to stern. (Hydrofoils are not bound be wavemaking drag and are a whole different subject.) The most recent ocean racing cats have wave piercing bows as it is quicker to go through waves, rather than over them.
DDW is offline   Reply With Quote
Old 02-14-2019, 01:21 PM   #306
Guru
 
Nomad Willy's Avatar
 
City: Concrete Washington State
Vessel Name: Willy
Vessel Model: Willard Nomad 30'
Join Date: Oct 2007
Posts: 17,660
Baker wrote;
“Originally Posted by Nomad Willy View Post
There are boats that have no flat planing hull surfaces that exceed hull speed considerably. Old sub chaser’s do come to mind.
But they have some lengthly straight lines aft and a well submerged transom. And lots of power.
__________________
Eric

North Western Washington State USA
Nomad Willy is offline   Reply With Quote
Old 02-14-2019, 01:30 PM   #307
Guru
 
Fish53's Avatar
 
City: Pitcairn Island
Join Date: Jul 2015
Posts: 716
Quote:
Originally Posted by DDW View Post
The vessel in that picture is certainly not ahead of its bow wave. The only parts of the hull that have any effect on hydrodynamics are the parts that get wet. Everything else can be cut away without effect. In that photo the effective bow of the boat is where the water and fiberglass meet. You might as well say a heavy tub with a long bowsprit is "ahead of its bow wave" since the end of the bowsprit is - which would be ridiculous.


The surface is not vertical, and 3 and 9 o'clock positions are not on the surface. In any case the water motion is insignificant compare to the boat speed - do the calculations.


A Hobie (and any cat) sails fastest with very little heel. Sure you can have fun with one like the picture shows, but that will not win any races. Even with both hulls in the water, a Hobie 16 will do 16 knots easily - that is 4 x WL ^ 0.5. It is not planing as anyone would define it. Even the fastest cats in the world ( non-hydrofoil) have no flat planing sections, they are semi-circular bow to stern. (Hydrofoils are not bound be wavemaking drag and are a whole different subject.) The most recent ocean racing cats have wave piercing bows as it is quicker to go through waves, rather than over them.
So if it's "insignificant" then why even say it much less bother to correct others? I apparently didn't understand your original comment correctly, for that I'm well, apathetic.
Fish53 is offline   Reply With Quote
Old 02-14-2019, 01:52 PM   #308
Art
Guru
 
Art's Avatar
 
City: SF Bay Area
Vessel Model: Tollycraft 34' Tri Cabin
Join Date: Feb 2011
Posts: 10,829
Quote:
Originally Posted by Fish53 View Post
So if it's "insignificant" then why even say it much less bother to correct others? I apparently didn't understand your original comment correctly, for that I'm well, apathetic.
53 - There must be a 12 step program for addicted hull shape persons!!
Art is offline   Reply With Quote
Old 02-14-2019, 02:27 PM   #309
Guru
 
Fish53's Avatar
 
City: Pitcairn Island
Join Date: Jul 2015
Posts: 716
Quote:
Originally Posted by Art View Post
53 - There must be a 12 step program for addicted hull shape persons!!
12 steps will take too long. As there is apparently no end in sight for this thread I'll declare my boat with it's 5000 pounds and 18hp a wicked slow boat and let it go at that. I did enjoy your posts however.
Fish53 is offline   Reply With Quote
Old 02-14-2019, 03:02 PM   #310
Grand Vizier
 
Delfin's Avatar
 
Join Date: Jan 2010
Posts: 3,464
Quote:
Originally Posted by DDW View Post
The vessel in that picture is certainly not ahead of its bow wave. The only parts of the hull that have any effect on hydrodynamics are the parts that get wet. Everything else can be cut away without effect. In that photo the effective bow of the boat is where the water and fiberglass meet. You might as well say a heavy tub with a long bowsprit is "ahead of its bow wave" since the end of the bowsprit is - which would be ridiculous.
Another new term. A bowsprit is now a hull, and not a, well, bowsprit. But on the chance that hull still means what it did before this thread, and the bow of the hull still means the same thing, then yes, in the picture the bow is ahead of any wave associated with the bow.

Quote:
Originally Posted by DDW View Post
A Hobie (and any cat) sails fastest with very little heel. Sure you can have fun with one like the picture shows, but that will not win any races. Even with both hulls in the water, a Hobie 16 will do 16 knots easily - that is 4 x WL ^ 0.5. It is not planing as anyone would define it. Even the fastest cats in the world ( non-hydrofoil) have no flat planing sections, they are semi-circular bow to stern. (Hydrofoils are not bound be wavemaking drag and are a whole different subject.) The most recent ocean racing cats have wave piercing bows as it is quicker to go through waves, rather than over them.
Of course a semi-circular hull generates lift, and with a long narrow hull, the Hobie under sail generates more lift than drag, so planes. Which is something a full displacement hull cannot do, except with physics that don't seem to apply to this space/time envelope. Again, you can redefine the language to your heart's content to make your point, and as I said, I am a ok with that.
__________________
Delfin
"Dad always thought laughter was the best medicine, which I guess is why several of us died of tuberculosis." - Jack Handy
Delfin is offline   Reply With Quote
Old 02-14-2019, 03:21 PM   #311
Guru
 
Nomad Willy's Avatar
 
City: Concrete Washington State
Vessel Name: Willy
Vessel Model: Willard Nomad 30'
Join Date: Oct 2007
Posts: 17,660
Delfin I think I'll pass on a counter post.
We've got enough balance on this thread now.
__________________
Eric

North Western Washington State USA
Nomad Willy is offline   Reply With Quote
Old 02-14-2019, 03:48 PM   #312
Art
Guru
 
Art's Avatar
 
City: SF Bay Area
Vessel Model: Tollycraft 34' Tri Cabin
Join Date: Feb 2011
Posts: 10,829
Or... imbalance!
Art is offline   Reply With Quote
Old 02-14-2019, 05:11 PM   #313
Senior Member
 
bgillroy's Avatar
 
City: Marathon, FL & On Loop
Vessel Name: Maka Honu
Vessel Model: Ta Yang, 42 Tayana PH Trawler 1976
Join Date: Mar 2014
Posts: 258
simple no flat sections aft. P and SD have flat sections aft.
bgillroy is offline   Reply With Quote
Old 02-14-2019, 05:16 PM   #314
Guru
 
Airstream345's Avatar
 
City: Seattle, WA USA
Vessel Name: FORTITUDE
Vessel Model: Kadey Krogen 54-8
Join Date: Jul 2017
Posts: 799
At the risk of putting another log on this fire, I found this article comparing KKs FDs to Fleming's SDs (on KK's site) offered a practical explanation for those of us not interested in being towed by aircraft carriers.

http://www.kadeykrogen.com/articles/...esignprobe.htm
__________________
FORTITUDE
Blog: mvfortitude.com
Instagram: @mvfortitude
Airstream345 is offline   Reply With Quote
Old 02-14-2019, 06:45 PM   #315
Guru
 
Nomad Willy's Avatar
 
City: Concrete Washington State
Vessel Name: Willy
Vessel Model: Willard Nomad 30'
Join Date: Oct 2007
Posts: 17,660
bgilroy,
Simple eh?

314 posts and there’s only some agreement at this point.

But probably 49 out of 50 you’re right. But then it gets complicated. Very very few boats are perfectly flat. Flat fore and aft or athartships or flat at an angle. Or several combinations of flat.
__________________
Eric

North Western Washington State USA
Nomad Willy is offline   Reply With Quote
Old 02-14-2019, 07:44 PM   #316
Grand Vizier
 
Delfin's Avatar
 
Join Date: Jan 2010
Posts: 3,464
Quote:
Originally Posted by Airstream345 View Post
At the risk of putting another log on this fire, I found this article comparing KKs FDs to Fleming's SDs (on KK's site) offered a practical explanation for those of us not interested in being towed by aircraft carriers.

http://www.kadeykrogen.com/articles/...esignprobe.htm
Interesting article, although out of date based on the new physics discovered on this thread, since we've learned that the reference to a speed limit for a full displacement hull is obsolete. KK should have consulted with Hobie. Perhaps then they could have built a full displacement hull that planes.
Delfin is offline   Reply With Quote
Old 02-17-2019, 01:30 PM   #317
Guru
 
City: Carefree, Arizona
Vessel Name: sunchaser V
Vessel Model: DeFever 48
Join Date: Apr 2008
Posts: 9,047
If I saw an M30 sitting at the dock, looking at its stern would suggest an FD vessel. 43 knots out of this beauty.
http://www.mooresyachts.com
sunchaser is offline   Reply With Quote
Old 02-17-2019, 02:32 PM   #318
Guru
 
caltexflanc's Avatar
 
City: North Carolina for now
Vessel Name: Small Incentive
Vessel Model: Boston Whaler 130 Sport
Join Date: Aug 2011
Posts: 6,307
Here you go, have fun discussing this one and all its brethren:



__________________
George

"There's the Right Way, the Wrong Way, and what some guy says he's gotten away with"
caltexflanc is offline   Reply With Quote
Old 02-17-2019, 03:25 PM   #319
Guru
 
Fish53's Avatar
 
City: Pitcairn Island
Join Date: Jul 2015
Posts: 716
Quote:
Originally Posted by caltexflanc View Post
Here you go, have fun discussing this one and all its brethren:



Almost every dragger I ever worked on had an immersed transom, including my own but it's important to remember that these vessels are designed to take on a considerable amount of load, far more than a pleasure boat of similar size. In practice minus ice and fish that may or may not be immersed. Oh boy this thread isn't dead after all.
Fish53 is offline   Reply With Quote
Old 02-17-2019, 04:31 PM   #320
Grand Vizier
 
Delfin's Avatar
 
Join Date: Jan 2010
Posts: 3,464
Quote:
Originally Posted by sunchaser View Post
If I saw an M30 sitting at the dock, looking at its stern would suggest an FD vessel. 43 knots out of this beauty.
http://www.mooresyachts.com
Cool looking boat.
__________________

Delfin is offline   Reply With Quote
Reply

Thread Tools Search this Thread
Search this Thread:

Advanced Search
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off



» Trawler Port Captains
Port Captains are TF volunteers who can serve as local guides or assist with local arrangements and information. Search below to locate Port Captains near your destination. To learn more about this program read here: TF Port Captain Program





All times are GMT -5. The time now is 05:36 AM.


Powered by vBulletin® Version 3.8.8 Beta 4
Copyright ©2000 - 2021, vBulletin Solutions, Inc.
Search Engine Optimization by vBSEO 3.6.0
Copyright 2006 - 2012
×