Modern Hull forms and Motion Comfort - Page 9 - SailNet Community

   Search Sailnet:

 forums  store  


Quick Menu
Forums           
Articles          
Galleries        
Boat Reviews  
Classifieds     
Search SailNet 
Boat Search (new)

Shop the
SailNet Store
Anchor Locker
Boatbuilding & Repair
Charts
Clothing
Electrical
Electronics
Engine
Hatches and Portlights
Interior And Galley
Maintenance
Marine Electronics
Navigation
Other Items
Plumbing and Pumps
Rigging
Safety
Sailing Hardware
Trailer & Watersports
Clearance Items

Advertise Here






Go Back   SailNet Community > On Board > Boat Review and Purchase Forum > Sailboat Design and Construction
 Not a Member? 


Like Tree60Likes
Reply
 
LinkBack Thread Tools
  #81  
Old 04-10-2013
grumpy old man
 
Join Date: Apr 2011
Posts: 3,793
Thanks: 1
Thanked 81 Times in 77 Posts
Rep Power: 4
bobperry will become famous soon enough
Re: Modern Hull forms and Motion Comfort

Wolf:
We can do better than a Hans Christian. I would suggest for you a Tashiba 36. It's a little brother to the Baba 40 but an even better design. If you want bigger with a full keel the Baba 40 is hard to beat. It will surprise you with it's performance under sail, especially hard on the wind.

Under power, in reverse it will just surprise you period.
__________________
Please visit my blog. It's fun to read.


To view links or images in signatures your post count must be 10 or greater. You currently have 0 posts.

Bob's Blog ....

To view links or images in signatures your post count must be 10 or greater. You currently have 0 posts.


Please also visit my new web site
To view links or images in signatures your post count must be 10 or greater. You currently have 0 posts.
Reply With Quote Quick reply to this message Share with Facebook
  #82  
Old 04-10-2013
Senior Member
 
Join Date: Dec 2012
Location: new england
Posts: 1,881
Thanks: 34
Thanked 35 Times in 32 Posts
Rep Power: 3
outbound is on a distinguished road
Re: Modern Hull forms and Motion Comfort

Tank you Bob. You expertly elucidated my thinking. Clearly, ther are good and bad designs in all hull forms. Hardest part for me is to be realistic about my capabilities and the true use of the vessel and not be influenced by my pipe drearms. Spent a lot of time talking to the admiral before making the ultimate decision. Be in Norfolk May 23 HOOOO WOOO.
__________________
s/v Hippocampus
Outbound 46
Reply With Quote Quick reply to this message Share with Facebook
  #83  
Old 04-10-2013
wolfenzee's Avatar
Senior Member
 
Join Date: Jul 2008
Location: S/V Waltzing Matilda, Port Ludlow, WA (NW Puget Sound)
Posts: 497
Thanks: 2
Thanked 2 Times in 1 Post
Rep Power: 7
wolfenzee is on a distinguished road
Send a message via ICQ to wolfenzee
Re: Modern Hull forms and Motion Comfort

Quote:
Originally Posted by bobperry View Post
Wolf:
We can do better than a Hans Christian. I would suggest for you a Tashiba 36. It's a little brother to the Baba 40 but an even better design. If you want bigger with a full keel the Baba 40 is hard to beat. It will surprise you with it's performance under sail, especially hard on the wind.

Under power, in reverse it will just surprise you period.
I though that post of mine would goad you into giving me more info about the type of boat I like, thanks =).
But they are all theoretical because I doubt I will ever be able to afford another boat, to make it worse my boat is my home and I would have to sell it before I could afford another.
Those two have alot fuller keel than mine and are proportionally alot beamier, but my boat is my home. Comfort is the most important thing either at anchor or at sea be it calm or nasty.
The Cape George 36 has the same lines (with out that beautiful shear) as my boat. It's amazing how much 6' extra feet in length and a couple extra feet in beam really are, not to mention the lazarette was alot smaller on the CG36. Yacht designers can't/don't live in a vacum, William Atkin was given credit along with Ed Monk for the Cape George 36.

Last edited by wolfenzee; 04-10-2013 at 02:21 PM.
Reply With Quote Quick reply to this message Share with Facebook
  #84  
Old 04-10-2013
grumpy old man
 
Join Date: Apr 2011
Posts: 3,793
Thanks: 1
Thanked 81 Times in 77 Posts
Rep Power: 4
bobperry will become famous soon enough
Re: Modern Hull forms and Motion Comfort

Wolf:
Good eye. The Cecil Lange Cape George Cutter has a modified freeboard from the original Atkin design. Cecil raised the sheer, destroyed the beautiful original sheer spring and called it good. I have zero respect for Cecil. The original design from Atkin as I recall was TALLY HO MAJOR. I could be wrong. I lent those bbooks and pof course I never got them back. Bastard! You can see the design as Atkin intended if you can fuind pics of Doug Fryer's old boat AFRCAN STAR. This is the boat I used as an inspiration for Doug's next boat NIGHT RUNNER.
Attached Thumbnails
Modern Hull forms and Motion Comfort-night-runner-lin.jpg  
__________________
Please visit my blog. It's fun to read.


To view links or images in signatures your post count must be 10 or greater. You currently have 0 posts.

Bob's Blog ....

To view links or images in signatures your post count must be 10 or greater. You currently have 0 posts.


Please also visit my new web site
To view links or images in signatures your post count must be 10 or greater. You currently have 0 posts.
Reply With Quote Quick reply to this message Share with Facebook
  #85  
Old 04-10-2013
wolfenzee's Avatar
Senior Member
 
Join Date: Jul 2008
Location: S/V Waltzing Matilda, Port Ludlow, WA (NW Puget Sound)
Posts: 497
Thanks: 2
Thanked 2 Times in 1 Post
Rep Power: 7
wolfenzee is on a distinguished road
Send a message via ICQ to wolfenzee
Re: Modern Hull forms and Motion Comfort

Quote:
Originally Posted by bobperry View Post
Wolf:
Good eye. The Cecil Lange Cape George Cutter has a modified freeboard from the original Atkin design. Cecil raised the sheer, destroyed the beautiful original sheer spring and called it good. I have zero respect for Cecil. The original design from Atkin as I recall was TALLY HO MAJOR. I could be wrong. I lent those bbooks and pof course I never got them back. Bastard! You can see the design as Atkin intended if you can fuind pics of Doug Fryer's old boat AFRCAN STAR. This is the boat I used as an inspiration for Doug's next boat NIGHT RUNNER.
The Tally Ho Has about the same shear as the Cape George but below the waterline is alot fuller, sort of in between the Captain Cicero and the Tally Ho
Below are the Tally Ho, Cape George and Captain Cicero in that order



Last edited by wolfenzee; 04-10-2013 at 02:58 PM.
Reply With Quote Quick reply to this message Share with Facebook
  #86  
Old 04-10-2013
Faster's Avatar
Just another Moderator
 
Join Date: Sep 2005
Location: New Westminster, BC
Posts: 15,361
Thanks: 88
Thanked 243 Times in 234 Posts
Rep Power: 10
Faster has a spectacular aura about Faster has a spectacular aura about Faster has a spectacular aura about
Re: Modern Hull forms and Motion Comfort

Quote:
Originally Posted by bobperry View Post
For the record, I love all kinds of boats, power and sail. I love nice row boats.
........ Another favorite of mine is WHITE EAGLE ( now WILD HORSES). This is a 62, very light cruiser with a fin and bulb keel, spade rudder and a very tall cutter rig......
We shared an anchorage at Jedidiah Is. with Wild Horses a couple of summers back.. a beauty!

__________________
Ron

1984 Fast/Nicholson 345 "FastForward"

".. there is much you could do at sea with common sense.. and very little you could do without it.."
Capt G E Ericson (from "The Cruel Sea" by Nicholas Monsarrat)
Reply With Quote Quick reply to this message Share with Facebook
  #87  
Old 04-10-2013
wolfenzee's Avatar
Senior Member
 
Join Date: Jul 2008
Location: S/V Waltzing Matilda, Port Ludlow, WA (NW Puget Sound)
Posts: 497
Thanks: 2
Thanked 2 Times in 1 Post
Rep Power: 7
wolfenzee is on a distinguished road
Send a message via ICQ to wolfenzee
Re: Modern Hull forms and Motion Comfort

oops the pic I posted was the Cape George 31, which differs very little from the 36
Reply With Quote Quick reply to this message Share with Facebook
  #88  
Old 04-10-2013
Jeff_H's Avatar
Moderator
 
Join Date: Feb 2000
Location: Annapolis, Md
Posts: 6,684
Thanks: 5
Thanked 105 Times in 81 Posts
Rep Power: 10
Jeff_H has a spectacular aura about Jeff_H has a spectacular aura about Jeff_H has a spectacular aura about
Re: Modern Hull forms and Motion Comfort

Bob,
First of all, I want to say that I completely agree with my fellow moderator, Ron (Faster), when he says, "that's one cute little girl!" Bob, she's a charmer. I can only imagine that Violet must bring you a vast amount of joy.

Outbound:
Quote:
Originally Posted by outbound View Post
Still, have a question. Seems a given to assume ultra modern designs sail faster in more circumstances but is there a limit imposed by the design parameters as regards comfort motion. I see the light hulls, beamy aft hulls flying in semi displacement mode and wonder if a wave slaps against the usually unwetted portion of the aft canoe body ( except when running) will it produce a snap heave or corkscrew motion that many find most unpleasant. I also wonder about the sensitivity of the ultra modern hulls to the weight cruisers impose on their vessels. To what extent does the skipper need to attend to "trimming ship" when loading and is there a risk that overloading with stores or that 300' chain rode will screw the whole thing up. Lastly even when operated within design displacement ( with weight central/aft and low)given the semi planning behavior, decreased wetted surface with the boat on the water instead of in it -are these designs evolving to approximate the ride of a cigarette boat with a testosterone drunk driver.
To start my reply, for the sake of clarity, I want to make it clear that when I was commenting that current 'modern hull forms' have gone in an unexpected direction, I want to note, that I was referring to the general direction being taken in some of the more extreme grand prix level race boats, by which I mean the boats like the TP 52's, Open Class Boats, or the Volvo Boats. I believe that these represent much of the leading edge thinking in race boats, and that some of the thinking that created those boats is filtering into production coastal cruisers, if not into offshore cruisers as well.

To put my comments into a fair perspective, I suggest that it is important to also understand that I have never sailed these latest boats, and so much of my commentary is conjectural at best. My opinions are mostly shaped by studying at footage of these newer boats under way, observing a few examples on the water and also talking with people who have designed and sailed them.

With that in mind, here are my initial conclusions. I have watched a lot of footage of these boats in a range of conditions, and was especially interested in how they behave in transitional conditions, either being hot by a gust or in waves. I initially thought those conditions would be the Achilles’ heels of boats with this kind of extreme beam. It is amazing how much footage is out there, and with the ability to stop frame these images there is a lot that can be learned, albeit at the price of spending way too much time staring at a computer monitor rather than actually sailing.

I came away with a range of impressions. First of all, to get the most performance out of these boats, for any given wind and sea state, and for any given course, there appears to be comparatively narrow range of idea hel angles. On courses where the boat cannot plane, that angle appears to be roughly 10 to 15 degrees, just steep enough to allow the boat to sail on the turn of its bilge and lift one rudder blade mostly out of the water. Looking at shots from astern, it appears that at that heel angle, these boats actually have a comparatively narrow and symmetrical submerged hull form. I would expect that ignoring other factors for a moment, in that mode, these boats could behave like a long narrow hull form; meaning easily transitioning into semi-displacement (small wave making) mode, being balanced, producing minimal drag and perhaps even generating a fair amount of directional stability.

That conjecture seems to be borne out in shots from astern where you can see the helmsman’s hand, the elevated rudder and/or wheel, and see that there does not appear to be a lot of course corrections taking place, and that the helm appears surprisingly neutral, even as heel angles, wave impact, and sail plan forces cycle up and down. But also long narrow hull forms are prone to less heave and pitch, albeit with a more sway and roll. (The roll seems to get dampened out by their muscular sail plans and their ability to stand up to a huge amount of sail area relative to their displacement.)

That behavior is striking to me. Before these boats, the prevailing wisdom was that beamy boats were subject a lot of ‘roll steer’, meaning as a beamy boat heeled, she would change fore and aft trim, and the plan sections of the hull in the water would get very asymmetrical, and that combination would cause the boat to develop weather helm and wander, requiring a lot of course corrections, sail trim changes, and so on to maintain a straight course in waves or changeable conditions.

The lack of fore and aft trim change is truly amazing to me, and in some ways this is the seeming miracle that the science, coupled with advances in computer analysis, allows so effectively. To explain, when almost any boat heels, there is some amount of static change in fore and aft trim. Even on the majority of traditional designs, that trim change may be imperceptible, but its still there. As speed increases, trim also changes due to dynamic rig, hull and keel forces as well.

But if you study pictures of these boats in wind and waves, the way that their hulls are shaped, they do not seem to go through the kinds of major bow down stern up changes that you might expect meaning that the point of entry remains about the same height on the stem, and the corner of transom at the waterline remains at about the vertical height at the water. That should not be mistaken for ‘rolling up’ or ‘rolling down’. These boats clearly roll up, meaning that their vertical center of gravity rise vertically with heel angle. (Many traditional designs roll down, which historically was seen as better for tracking and motion.)

That kind of behavior would have been extremely difficult to predict in the days when boats were drawn by hand and calculations were manual, since the iterative process to analyze at trim change, let alone dynamic force distribution, with heel angle would have been wildly time consuming drudgery and would not represent real behavior when completed.

Where it gets harder to predict without sailing the boat, is what happens when meter or so wave hits one of the flats (topsides or bottom) when heeled. My sense is that these boats would behave about as well as any boat of their displacement. The impact would be felt, but for a boat of their weight nothing better or worse would happen.

But that begins to drift into the discussion of weight carrying. What tends to happen in many of these discussions is to say something like, “How can a 9,500 lb, 40 footer carry enough ‘stuff’ to be a good cruising boat?” But the answer really lies in the 9,500 lb part. Regardless of length, excess weight carrying capacity is somewhat proportional to design displacement, and to a lesser extent to the waterline plane of the vessel. So if you ask about carrying capacity in the abstract, I would say that a 9,500 lb boat of the current modern hull form can tolerate as much excess weight as any 9,500 lb boat, including a traditional design. And in theory, the long water plane should be reasonably tolerant of loading fore and aft.

But when you start asking about carrying enough weight for a couple to go off and do some serious voyaging, I would expect that the boat would minimally need something like 16,000- 20,000 lbs of displacement, designing around the types of hull forms in question, that gets to be a pretty long boat, probably a 50 or more footer. And also the current design trends really are dependent on efficient foils and bulbs carried very low meaning a lot of draft, or the complexity of a lift keel.

And that gets to some of my reservations about the wider range applicability of the current design trend.


To answer Ppvajko’s Question: "Would you mind giving us a few of these ideas (Whitbread 60-IMS style hull forms) filtered into cruising boat designs, that resulted in some wonderful cruising boats? Boats that are fast and forgiving, with comfortable motions and so on."

A few example of these designs to which I was referring that come immediately to mind are the Morris Ocean Series, or Coast Guard Training Boat, the current Hallberg-Rassey 40, and to a lesser extent the Malo 37 and as a coastal cruiser, perhaps something like the Xp 38.

Re: JameWilson’s comments: When you look at these videos, you are mostly seeing these boats racing and being pushed to the limits. Much of the “hit by a fire hose blast of water every 30 seconds, where water runs over the deck and the cockpit is constantly awash, water draining out of the open transom, where every gust translates into an additional 10 degree heel angle, where I am forced to concentrate on minute adjustments continually in order to stay out of trouble.” is the result of being over canvassed for the conditions and pushing to get the absolute max out of the boat. What is more revealing in those videos are the moments when they are not being pushed into the high drama shots that you describe.

But by the same token, my concern with this model translating into production cruisers, is that much of the advance in performance on these boats come from being able to carry enough sail to overpower their potential for generating very high drag for their weight. And I worry that like the old CCA boats which needed to heeled in a very narrow range to perform, requiring constant trimming to stay at speed, as these designs translate into cruising boats, they will also need care in sail trim to keep them loaded up enough to perform anywhere near as advertised.
jameswilson29 likes this.
__________________

To view links or images in signatures your post count must be 10 or greater. You currently have 0 posts.
Curmudgeon at Large- and rhinestone in the rough, sailing my Farr 11.6 on the Chesapeake Bay
Reply With Quote Quick reply to this message Share with Facebook
  #89  
Old 04-10-2013
Jeff_H's Avatar
Moderator
 
Join Date: Feb 2000
Location: Annapolis, Md
Posts: 6,684
Thanks: 5
Thanked 105 Times in 81 Posts
Rep Power: 10
Jeff_H has a spectacular aura about Jeff_H has a spectacular aura about Jeff_H has a spectacular aura about
Re: Modern Hull forms and Motion Comfort

Opps, I was so busy banging away my lunch hour that I had not noticed that Bob had gotten to explaining the waterplane aspect of carrying capacity.

The one thing that I might respectfully disagree with in Bob's example, is that sail area is generally proportionate to displacement, and so even if the lighter boat only submerged the same amount as the heavier boat, and even if the lighter boat started out with more sail area relative to displacement, there is a good chance that the larger proportionate loading would hurt performance more on the lighter boat than might simply be expected from comparing submersion inches.
__________________

To view links or images in signatures your post count must be 10 or greater. You currently have 0 posts.
Curmudgeon at Large- and rhinestone in the rough, sailing my Farr 11.6 on the Chesapeake Bay
Reply With Quote Quick reply to this message Share with Facebook
  #90  
Old 04-10-2013
Senior Member
 
Join Date: Dec 2012
Location: new england
Posts: 1,881
Thanks: 34
Thanked 35 Times in 32 Posts
Rep Power: 3
outbound is on a distinguished road
Re: Modern Hull forms and Motion Comfort

Jeff- great post. I actually understood most of it ( grin) and it addressed the question beautifully. Have a 46' with 28000 disp. coming. Have sailed others of same hull before ordering this one. Issue of wt., beauty, functionality as a place to live long term addressed without significant hardship in loss of vmg. Some penalty with 6.5' draft but can't have everything. Think there will be a place for heavy and light for the foreseeable future. My thinking is if you're going light multi hull vessels may make more sense for the cruiser if you can find someplace to "park" them. Something "high" performance not a broadblue or French production vessel ( although they function very well in their element).46'scares me anything larger I'd be terrified coming in for diesel/water/pump out. Anything deeper lose too many harbors. Anything wider like a multi have troubles with the yards/marinas etc. They say different strokes but I think different boats for different folks is equally true as Bob pointed out.
One likes this.
__________________
s/v Hippocampus
Outbound 46
Reply With Quote Quick reply to this message Share with Facebook
Reply

Quick Reply
Message:
Options

By choosing to post the reply above you agree to the rules you agreed to when joining Sailnet.
Click Here to view those rules.

Register Now

In order to be able to post messages on the SailNet Community forums, you must first register.
Please enter your desired user name, your email address and other required details in the form below.
Please note: After entering 3 characters a list of Usernames already in use will appear and the list will disappear once a valid Username is entered.
User Name:
Password
Please enter a password for your user account. Note that passwords are case-sensitive.
Password:
Confirm Password:
Email Address
Please enter a valid email address for yourself.
Email Address:

Log-in

Human Verification

In order to verify that you are a human and not a spam bot, please enter the answer into the following box below based on the instructions contained in the graphic.




Currently Active Users Viewing This Thread: 1 (0 members and 1 guests)
 
Thread Tools

 
Posting Rules
You may post new threads
You may post replies
You may post attachments
You may edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is On


Similar Threads
Thread Thread Starter Forum Replies Last Post
Seakindly Boats vs.the rest rmf1643 Boat Review and Purchase Forum 14 04-10-2013 04:26 PM
What can you tell from the numbers? brazilnut Boat Review and Purchase Forum 10 07-01-2009 05:09 PM


All times are GMT -4. The time now is 03:41 PM.

Add to My Yahoo!         
Powered by vBulletin® Version 3.8.7
Copyright ©2000 - 2014, vBulletin Solutions, Inc.
SEO by vBSEO 3.6.1
(c) Marine.com LLC 2000-2012

The SailNet.com store is owned and operated by a company independent of the SailNet.com forum. You are now leaving the SailNet forum. Click OK to continue or Cancel to return to the SailNet forum.