Desirable and Undesirable Characteristics of Offshore Yachts

MikeJohns

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Hobart
sigh . . . I  dont really want to engage in a debate about 'general' answers to the desirable/undesirable/seaworthy question  . . .because it is damn complicated and there is no one answer, they 'all depend' on compromises one wants to make. 

But, let me just point out that the design space is rather not generally moving toward narrow/heavy/full keel/barn door rudders - it is rather moving in exact the opposite direction (wider beams, lighter, fin-er keels and spade-er rudders).  And that is NOT because the clients and their NA's are complete morons, but because that direction makes sense in the totality of the sailing they do. And there is no evidence that direction is particularly 'unsafe'. Just to quote from the official Sydney to Hobart report "There is no evidence that any particular style or design of boat fared better or worse in the conditions. The age of yacht, age of design, construction method, construction material, high or low stability, heavy or light displacement or rig type were not determining factors."  

As to the expedition centerboards - that feature is primarily for the important task of being able to sneek into shallow enough water that truck size ice bergs can't follow you.  They ground outside you.  And for being able to take the ground well.  It also DOES happen to make those boats (generally) run really well, with really good directional stability - which means they (generally) dont round up and they dont need to even test whether keels are a primary or secondary or contributing cause to roll overs.  But, I would suggest it is rather clear that keels can and do have complicated hydrodynamic effects on capsize.

MikeJohns  seems to like narrow/heavy/full keel/barn door boats and that's just fine.  They can be fine boats.  But they bring their own set of compromises. And they are NOT (at all) immune to breaking waves, and he continues to rather overstate what the tank testing determined. No-one (that I know) is 'against' RM or AVS - they just bring compromises.  There are rather a wide range of people 'against' full keels and barn door rudders - but again they just bring compromises.  Narrow vs Wide is honestly the most interesting discussion - there are great boats along that whole spectrum from pencil thin ones to square multihulls - all seaworthy.

Anecdotally, the only boat I know which has been knocked over (and then abandoned near S Georgia)) while streaming a series drogue was in this general (heavy/full/barndoor) design space - this happened primarily because it was a single hander trying to a solo RTW, who was just too fried and tired and was making mistakes.  Which to my mind points out the more important contributing factors than boat design - skipper skill and knowledge and raw (bad) luck, and in the 'design space' raw size is the only thing (yea in the general middle of the design space, if you go to a corner of the space you can ofc create problems) which systematically effects outcomes (both in tests and empirically). 
 I am not advocating that boats that exhibit extremes in seaworthiness should be sought just that awareness of the compromises be acknowledged.

There's a common theme in these sorts of discussions where individuals try and subvert research. That research has been done for a long time. It's repeated and validated, it's not highly theoretical.

Of course skill can make up for deficiencies and compromises in vessel design.

No one has ever suggested anything about designers as you said "being morons" , but they they are designing for a commercial market that dictates the compromises.

Performance influences designers more than seakindliness or inate seaworthiness. Performace is more easily achievable with a light boat. There's nothing inately slow about a heavy boat. It's the sail area ratios and the power to carry sail that determine speed. But heavy boats performance are expensive to produce......

For example, design trends; you use the terminology "a Barn Door" for a lower aspect rudder.  That a lower aspect rudder stalls at much higher loads than a high aspect rudder. But a high aspect rudder has a more desirable lift/Drag ratio and a lower wetted surface area.

If you ask for the most seaworthy controllable hullform they will or should design something else. Because they design they design a Pogo and they are skilled qualified designers doesn't mean the design trend is necessarily desirable.

Seaworthiness and seakindliness especially aren't current trends in the majority of production boats.

The plumb stem is a really good illustration of current trends.

As for the 1998 S-H the outcome was well predicted by the research done on the Fastnet. It's a pretty clear example of people misled about the level of safety of the boats they are buying.

Just look at the data. There was a clear trend of the less seaworthy boats being rolled ( fully inverted) and the more seaworthy boats coping very well.

 

estarzinger

Super Anarchist
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I was lucky enough to see the famous Taleisin up close once - Larry (and Lin?) Pardey did extraordinary, detailed work on that boat.
you should look up Noel Barrott - very low profile but I guess google might find something. A kiwi wooden boat builder - took two of his boats Masina and Sina - rtw generally in decently high latitudes (higher than the Pardeys generally used).  The first one was engineless.  Super impressive guy - one of only a handful that I know who I think would have thrived on one of the old cape horn tall ships.  

we had Larry and Noel on board for some nice Chilean red.  Larry did not know Noel's background/experience and it was a bit funny to watch, both excellent seaman but such different personalities - the discussion came around to heavy weather at one point and Larry started with 'well I wrote the book on heavy weather', and Noel just sat and nodded his head - nothing to prove.  I really liked him.  He got laid low later on by bad metal in his blood, we assumed from the boat building, but he also ate a lot of fish up in Iceland/Spitzbergen and there was apparently also a lot of toxic Russian metal in those.

On the first boat Noel broken his rudder off with an ice impact, and sailed 1500 miles to a pin point landfall on a Chilean port with no rudder (and this was ofc pre-gps).

 
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CapDave

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Antigua
I have 6 boats (with various stages of designs) I would like to build.  I hope we get the opportunity to build one of them. I doubt we will go south again, but I have some unfinished business north.
Hear that tick tock noise?? Building boats takes too long, and you have to make a lot of decisions about things you don't care about that much. So many boats for sale.....

That may be my delivery skipper background talking - take them as I find them, go sailing....

 

estarzinger

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No rudder, hard. Latitude sailing to a North-South coast by sextant, easy. 
hmmm, sure they were pretty sure to hit something . . but  . . . 'easy' . . idk if that's the word I would use, Someone else here used the word 'easy' for a different passage in the 40's and 50's and I was not so confident about that usage of the word either. . . . . The rudder came off in the '50's - so it was a NNE course to Valparaiso. There is often not much sky down there and it is generally pretty rough in a small boat.  And if you get in too close you are on an ironbound lee shore.

Hear that tick tock noise?? Building boats takes too long, and you have to make a lot of decisions about things you don't care about that much. So many boats for sale.....
I hear you.  I have told many people exactly that.  But I personally am perhaps a bit spoiled by having had a custom boat - I find most of the used stuff pretty uninspired. A few of my 6 'concepts' I could find something, but for a few others I dont think anything exists I would be happy with.  Look up mv Polar Bound - how many of those do you think are on the used market?

 
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CapDave

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Antigua
but  . . . 'easy' . . idk if that's the word I would use,
Yeah, this is where internet forums fall so far short of conversation - because if we were talking I'd agree with you, and then qualify my agreement with some further observation, etc. But even in near real time (or generally with more latency), it gets old quickly....

 

Cruisin Loser

Super Anarchist
On a tangent . . . good wood is a truly marvelous material.  If it were 'invented' today it would be hailed as a wonder material. And careful wood construction is quite awesome.  
I can attest. My previous boat was nearly as good as glass gets, a Hinckley, carefully built and very well sorted.

My current boat is cold molded by Brooklin BY, and, so far as I can tell, better in almost every way. Plus beautiful beyond imagine. 

She's not everybody's cuppa. Since my size limit on boats is driven not by money but by what my wife and I can easily handle by ourselves. She's a 48' with the pricetag of a 60' and the accomodations of a 40' or less, but she is perfect for us, now, while I am still doing a little offshore racing, but mainly cruising with my love of 47 years. 

She finds the aesthetics, inside and out, of the woody to be simply irresistible. I find the sailing characteristics downright addictive. With this  boat I have a boat that sails like I think a boat should sail, looks how I think a boat should look, treats her crew how I think a crew should be treated. 

Back to the original topic, the book really only has a couple of sections on hull design. Jim McCurdy, designer of my Hinckley, I think wrote the section on scantlings, while we have much advancement in materials science, that is still worth reading.

A much neglected area in modern boats, I think, is interior ventilation. My current boat has 4 large dorades and 6 opening hatches with integral bug screens. The Dorades have interior plugs so they may be sealed from inside in the event of truly horrendous weather. The result  is a boat is a joy to be abaord during rainstorms. A stuffy boat is not my idea of fun, but I see so many with only hatches for ventilation. We have a spray over our forward hatch, which allows us to keep it open in moderate conditions offshore, and makes sailing quite pleasant

 
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shaggybaxter

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As for the 1998 S-H the outcome was well predicted by the research done on the Fastnet. It's a pretty clear example of people misled about the level of safety of the boats they are buying.

Just look at the data. There was a clear trend of the less seaworthy boats being rolled ( fully inverted) and the more seaworthy boats coping very well.
G'day Mike,

I thought the summary from the 98 S-H was the yachts getting into trouble was more about the locale the boat found itself in rather than the seaworthiness of the boat? I do believe there were some new boats that simply were too focused on speed vs manners for those conditions but a lot of good boats got caught out too.  

Winston Churchill springs to mind, a Percy Coverdale wooden cutter that IIRC was immaculately prepared and loved heavy weather, it was simply in the wrong spot. 

Happy to be corrected! 

Cheers,

SB

 
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estarzinger

Super Anarchist
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My current boat is cold molded by Brooklin BY, and, so far as I can tell, better in almost every way. Plus beautiful beyond imagine. 
yea, your current boat in fact fits smack dab in one of my 6 concepts - a 'gentleman's boat' - Beauty and style, but also fast enough to (at least potentially) crush the competition.

When I was planning Hawk, I had dinner with two of the Maine high latitude fraternity, and they tried to talk me into thick wood. They had compelling arguments, and I'm sure something excellent would have resulted.

 

DDW

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For example, design trends; you use the terminology "a Barn Door" for a lower aspect rudder.  That a lower aspect rudder stalls at much higher loads than a high aspect rudder. But a high aspect rudder has a more desirable lift/Drag ratio and a lower wetted surface area.
Not really technically correct - a low aspect rudder stalls at high angles of attack. It does not necessarily generate higher loads, other things equal it will generate lower loads. The lower lift slope and less distinct stall can be a benefit if you are under ruddered or have a ham fisted helmsman (or autopilot). 

 

CapDave

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Antigua
'gentleman's boat'
This Bowman is in better shape than the Nic....

https://www.yachtworld.com/boats/1979/bowman-corsair-3661882/

Or Jim Clarke might let you borrow Hanuman?

CA26D797-7E4B-433C-A952-0C9980A18957_1_105_c.jpeg

 

MikeJohns

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Hobart
G'day Mike,

I thought the summary from the 98 S-H was the yachts getting into trouble was more about the locale the boat found itself in rather than the seaworthiness of the boat? I do believe there were some new boats that simply were too focused on speed vs manners for those conditions but a lot of good boats got caught out too.  

Winston Churchill springs to mind, a Percy Coverdale wooden cutter that IIRC was immaculately prepared and loved heavy weather, it was simply in the wrong spot. 

Happy to be corrected! 

Cheers,

SB
For a start the organizers hired a professional public relations damage control specialist. That influenced the media, a lot of people's opinions and set the theme for the language used.

There was a lot of mention  about the awesome and unpredictable power of the sea, It was also loudly promoted that it was a once in 100 year storm.

Localized storms of that magnitude occur in that area 4 to 5 times a year. The records of the oil platforms and testimony from Naval commanders and commercial boat operators who were there were different.

The conditions were well forecast the day before and warnings were current. The coronial inquest revealed that many participants didn't properly understand marine forecasts and that the wind and wave height were not expected maximums.

As for Winston Churchill; The Displacement was 21.4 tonnes Length On deck 50.6 ft Built in 1942 as a performance craft.

At 56 years of age and plank on frame the quality of the plank fastenings was poor  Importantly she was partially refastening but the job was not complete She lost a topside plank along with her Bulwark after a wave strike and sank from water ingress. The boat was lightly built and had a prior history of major damage in rough weather.  It had nearly sunk some years prior when the mast pushed through the bottom of the hull and was only saved when it was run aground. Similar damage to old plank on frame boats has been very common over the years. 

Also WC was not what you'd class as very stable with a LPS of only 124 degrees. It certainly wasn't a traditional solid, heavy displacement, highly stable craft.

Here's a plot showing S-H boats that were  rolled ( as in fully capsized ) overlaid on the UK MCA commercial requirement for sailing craft produced by Wolfston. This is from Kim Taylors paper on the event.

rolled sydney Hobart.JPG

 

MikeJohns

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Hobart
Not really technically correct - a low aspect rudder stalls at high angles of attack. It does not necessarily generate higher loads, other things equal it will generate lower loads. The lower lift slope and less distinct stall can be a benefit if you are under ruddered or have a ham fisted helmsman (or autopilot). 
Sure with the same foil section and planform scales just for AR but  lower aspect rudders are commonly skeg partial skeg and even flat plate.

Fully attached rudders like the flat plate "barn door" also work quite differently, they move Cp of the keel rather than being a lifting foil.

Rudders are interesting,  do you have you read Molland's Marine rudders and control surfaces ? Look at Flat plates and even Naca sections used backwards you get more lift for a given angle and more robust control at the cost of Drag....... 

 

shaggybaxter

Super Anarchist
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Australia
For a start the organizers hired a professional public relations damage control specialist. That influenced the media, a lot of people's opinions and set the theme for the language used.

There was a lot of mention  about the awesome and unpredictable power of the sea, It was also loudly promoted that it was a once in 100 year storm.

Localized storms of that magnitude occur in that area 4 to 5 times a year. The records of the oil platforms and testimony from Naval commanders and commercial boat operators who were there were different.

The conditions were well forecast the day before and warnings were current. The coronial inquest revealed that many participants didn't properly understand marine forecasts and that the wind and wave height were not expected maximums.

As for Winston Churchill; The Displacement was 21.4 tonnes Length On deck 50.6 ft Built in 1942 as a performance craft.

At 56 years of age and plank on frame the quality of the plank fastenings was poor  Importantly she was partially refastening but the job was not complete She lost a topside plank along with her Bulwark after a wave strike and sank from water ingress. The boat was lightly built and had a prior history of major damage in rough weather.  It had nearly sunk some years prior when the mast pushed through the bottom of the hull and was only saved when it was run aground. Similar damage to old plank on frame boats has been very common over the years. 

Also WC was not what you'd class as very stable with a LPS of only 124 degrees. It certainly wasn't a traditional solid, heavy displacement, highly stable craft.

Here's a plot showing S-H boats that were  rolled ( as in fully capsized ) overlaid on the UK MCA commercial requirement for sailing craft produced by Wolfston. This is from Kim Taylors paper on the event.

View attachment 442512
Thanks very much for the very informative response. Albeit I need more coffee to absorb the chart, is the vertical axis intended to be the AVS? 

 

DDW

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Sure with the same foil section and planform scales just for AR but  lower aspect rudders are commonly skeg partial skeg and even flat plate.

Fully attached rudders like the flat plate "barn door" also work quite differently, they move Cp of the keel rather than being a lifting foil.

Rudders are interesting,  do you have you read Molland's Marine rudders and control surfaces ? Look at Flat plates and even Naca sections used backwards you get more lift for a given angle and more robust control at the cost of Drag....... 
None of which is particularly relevant. A fully attached flat plate is not going to develop more steering moment than a proper spade rudder on any vaguely normal hull form. This has been known for 100 years. Nat Herreshoff knew it. Running sections backwards isn't going to give you better control, the lift slope is slightly increased at the cost of greatly reduced stall angle - not at all what you want. Molland does not appear to address sailing yacht rudders, rather ships. They have very different requirements from rudders. If you're reading stuff, Vacanti's writings would be far more relevant to sailing yachts.

 

MikeJohns

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133
Hobart
None of which is particularly relevant. A fully attached flat plate is not going to develop more steering moment than a proper spade rudder on any vaguely normal hull form. This has been known for 100 years. Nat Herreshoff knew it. Running sections backwards isn't going to give you better control, the lift slope is slightly increased at the cost of greatly reduced stall angle - not at all what you want. Molland does not appear to address sailing yacht rudders, rather ships. They have very different requirements from rudders. If you're reading stuff, Vacanti's writings would be far more relevant to sailing yachts.
I like to gauge peoples reaction to the foil reversal... ;-)  And yes for equivalent areas.

Molland spent a lot of time with small craft including sailboat rudders, did a lot of free stream tests that have useful data on a raft of different forms.  He really pioneered current empirical  methods for load derivation used by class societies for small craft as well as ships.

I'd like to come back to your claim that  "although  low aspect rudder stalls at high angles of attack. It does not necessarily generate higher loads....." what  AR.e are you considering there ?

Also Vacanti and his code are all about ideal free stream flow.  The problem I have is that in a seaway the inflow is nothing like ideal.

 




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