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Old 16-05-2016, 00:49   #181
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Re: Pilothouse Variations -- Boreal

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Originally Posted by TJ D View Post
This is a great thread.

It's interesting to read the different perspectives here. All I can say is that I have been indoctrinated since childhood that heavy boats with small rigs, and lots of overhangs were the real 'sea boats'. Then in 2013, an amazing thing happened. I sold my 43' steel Roberts tank, and switched to the exact opposite end of the spectrum.

We've sailed RS about 11,000 miles since then, in conditions mild and robust, and I can state without reservation that I will never voluntarily embark on a passage on a boat with a waterline substantially shorter than the LOD.

Now, I would also not choose a boat like ours for the kind of expedition sailing that Dock is contemplating. For that, I would incorporate a lot of modern design elements, but would build heavier, out of aluminum, with a lot of watertight compartmentalization and a proper inside watchkeeping station.

For the rest of us, I submit that a well-built modern hull is superior to the older heavy boats in just about every way. (Emphasis on well-built).

TJ
I agree with all of this, except only one thing -- there is no such thing as a "modern hull". The design tradeoffs have not disappeared.

Some kinds of hull types -- heavy, full keel -- have almost disappeared, but the other choices are very much alive and well, and as hard to make as they ever were.

Only on the pages of glossy magazines is there only one type of "modern" hull type. The advertisers don't want you to think about the tradeoffs, because they want you to get rid of whatever you have which was fashionable last year, and buy and buy and buy, what is fashionable this year, just so that next year you'll repeat the whole cycle. Obviously a real depth of understanding impedes this natural process of commerce.
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Old 16-05-2016, 00:59   #182
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Re: Pilothouse Variations -- Boreal

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Originally Posted by Dockhead View Post
To illustrate what I'm talking about --

Attachment 124403

The designer deleted that part of the bow shown in red here, with no savings in LOA. With it, he deleted all the buoyancy which that part of the bow would have provided when the bow is depressed in an oncoming sea.

That boat might or might not need the deleted buoyancy. With a long empty forward section it might have a low enough polar moment of inertia that the bow pops up quickly and stays dry enough in any case, and/or the use of this boat probably doesn't care so much about dry decks.

Such a bow will be faster -- it will "cut" through the waves with no loss of fineness. It will also save some windage, and a bit of weight forward. But at some point it will have a tendency to submarine, as there is NO reserve buoyancy.

Cruising boats designed to be used in weather other than balmy, who are packed with gear and do not have empty forward sections, imitate this approach as a fashion statement -- at their peril.
If the boat was designed as you have drawn, then the forestay would have moved to the bow and a new bowsprit added for the asymmetric increasing the LOA

Given that a lot of the inverted bow yachts tend to be race oriented, I wonder if the design is some how related to the current rating system. Perhaps hull length is a factor in the calculation and fixed bowsprits are not penalised

For cruisers an inverted bow with a retractable bowsprit, will maximise speed and minimise dockage costs.
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Old 16-05-2016, 01:02   #183
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Re: Pilothouse Variations -- Boreal

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Originally Posted by Dockhead View Post
I agree with all of this, except only one thing -- there is no such thing as a "modern hull". The design tradeoffs have not disappeared.

Some kinds of hull types -- heavy, full keel -- have almost disappeared, but the other choices are very much alive and well, and as hard to make as they ever were.

Only on the pages of glossy magazines is there only one type of "modern" hull type. The advertisers don't want you to think about the tradeoffs, because they want you to get rid of whatever you have which was fashionable last year, and buy and buy and buy, what is fashionable this year, just so that next year you'll repeat the whole cycle. Obviously a real depth of understanding impedes this natural process of commerce.

Yes, I should have been more clear. My definition of a 'modern' hull generally brings a particular shape to mind.

Basically, I'm talking about a long waterline, broader stern sections, and modern materials with a high strength to weight ratio. There isn't much downside to this formula in my experience. The minutiae are all subject to the naval architect and the builder's own vision. I may agree with them or not, but generally, the above is what I meant.

TJ
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Old 16-05-2016, 02:35   #184
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Re: Pilothouse Variations -- Boreal

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Hi Dockhead,

Some numbers for you on RS.

Length of fairbody (does not include the bow prod for anchor and housing for some of the retractable sprit)--54'6"

LWL--52'11"
Beam-- 14'8"
Disp--24,000 lbs(she used to be 21,000-this reflects her actual 'cruising' dry disp.
Ballast (most of which in a bulb nearly 10' down) 9480 lbs. This does not include water ballast
Upwind sail is about 1500 square feet, downwind around 3000 with the big asym.

Righting moment is 62kip@ 20deg, 83 at 30, max is 129. IIRC maximum positive stability is 137 degrees.

D/L is 72.

Water ballast tanks are 200 gallons, located in triangular tanks outboard of the cockpit area. There seems to be some misconception among some in the group on this front. These are generally kept empty, and they are certainly not intended to be used as additional FW storage! The displacement hit only takes place at a time of one's choosing, when it benefits the boat. We have them empty most of the time.

She is built to DNV/ABS slamming standards for high speed motor/military craft. This spec calls for the structure to take 7.5 psi. Panel testing was conducted and failure of the hull panels occurred at 54psi. 400,000 cycles at 20 psi produced no damage. The deck will take 34psi.


svrocketscience.com has a very good technical details tab if you're interested further. We plan to be in the UK for a year or so, perhaps our paths will cross.

TJ
A really interesting, unusual, and beautiful boat

I would love to see her when you're in the UK, if you don't mind showing me. And I'd love to pick your brains about the custom build process if you don't mind sharing. Gin and tonics on me

We can exchange contacts offline. When are you coming, and where do you plan to be? In the Solent?
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Old 16-05-2016, 03:07   #185
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Re: Pilothouse Variations -- Boreal

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Originally Posted by TJ D View Post
Yes, I should have been more clear. My definition of a 'modern' hull generally brings a particular shape to mind.

Basically, I'm talking about a long waterline, broader stern sections, and modern materials with a high strength to weight ratio. There isn't much downside to this formula in my experience. The minutiae are all subject to the naval architect and the builder's own vision. I may agree with them or not, but generally, the above is what I meant.

TJ
Yes, I understood and don't really disagree, but your own boat contradicts the idea that there is only one approach to hull form -- you have a totally different underbody shape from recent fashion (if I understand the description) with a deep "v" shaped forefoot and without the flat sections (maybe you could post the drawings?).

One thing which puzzles me, however, is "high strength to weight ratio", as part of the "modern formula". I'm not sure there is any such formula. Obviously this is a very desirable quality on just about any boat, but it typically costs money. You certainly don't get it on modern mass produced boats which on the contrary have simply much weaker construction, with extensive use of very thin single skin GRP. This is the result of "value engineering" and is not necessarily bad for the average user -- better engineering and techniques like FEA allow the designers to reduce the weight and cost of different structural elements while maintaining an acceptable level of strength, because they better understand exactly how much strength is typically required. Some boats have gone too far with that probably, like the Benes and Hunters with eggshell bows, but this is a natural evolutionary process IMHO. Really higher strength to weight ratio comes in expensive boats with techniques like coring, and with exotic materials like carbon.


I do agree that there is such a thing as "Progress". There are some concrete improvements which are discovered which have broadly applicable and widely accepted advantages. What I am railing against is confusing Fashion with Progress -- they are different things, which sometimes coincide but often do not.

In my opinion, the biggest change in hull forms of cruising boats since the '70's is simply SIZE. Cruising boats have gotten much larger -- from average 32' to about 45' now.

Don't think that the designers of the '70's didn't know how to build light boats -- by then there were already light cored hulls, very strong using balsa, and other techniques. But you couldn't have a light 32' boat with any degree of seaworthiness, so they built them heavier. There has not been any vast improvements in materials since then, other at the very high end with carbon (still used only in a tiny percentage of total boat production), and more durable coring techniques making cored hulls less risky.

The difference is that when you're designing a 45' boat you can afford to make it far lighter than a 32' with no loss of seaworthiness, or even a net gain.

Some of this is simply better -- lighter may be less expensive (unless you go to exotic materials, and not counting any efficiency gains from robotic assembly, cost of the structure of a boat is nearly constant per kilogram) so the cost of this 45' boat may not be so much greater than the 32' heavier boat of yore, it is no less or even more seaworthy, and vastly much faster -- so that is something like real progress, with hardly any advantage to the old 32' boat. The only problem is that to get the cost down to what the old 32' cost corrected for inflation, you have to greatly cheapen the fitout and other things, and use all the efficiencies of mass production. So that's how we end up with the very cheaply built Bavarias and so forth -- that's the bigger boat at the old price point (which is a better deal than the old 32' boats so probably even that is real progress -- yes, if I had to choose between a Contessa and a 45' Bav, I'd take the Bav, however much I admire the Contessa). Meanwhile, however, the average price of a cruising boat in inflation corrected money has increased as sailors have become more affluent than in the 1970's, so part of the "modern" larger, lighter and faster boat just reflects the deeper pockets of today's sailors.


But there is no consensus around the "wedgie" form with very sharp entry and beam brought all the way back to the transom, and flat bottom aft of the keel, and an extreme high aspect torpedo keel. That is only one of several directions. Your own boat is not like that at all. There is also a lot of variety in current boat designs around fineness ratio, and even Polux claims to like narrow beam boats (he didn't quite drink all his Kool Aid, apparently). So if there is a general movement towards larger and lighter boats, with shorter overhangs (but by no means always NO overhangs), which are (depending on how extreme you go with those) mostly better for most sailors and most conditions, other aspects of hull form -- bow form, beam, shape of forefoot, shape of aft sections -- have no clear "one size fits all" direction, despite what you might gather from reading certain glossy magazines.

Also, not every sailor needs SA/D of 25 or more. One rig size definitely does not fit all uses and latitudes. A larger rig has more weight aloft and more windage -- it's very good in light conditions and very bad in heavy ones, so different sailors, will have different priorities.

Likewise with keels -- ludicrous to suggest, as some have, that the extreme high aspect torpedo keel is the only "modern" one. What is great for a high performance boat in controlled conditions may be terrible for sailing the uncharted rocky coasts of the Eastern Baltic. If we might agree that the ancient full keel is pretty much obsolete (Island Packeters may protest here), and we might agree that some kind of bulb on the keel is good for nearly everyone, that doesn't mean that the ONLY modern keel is a torpedo on a whisp of a whip like on a pure racing boat. Cruising boats made for a wide range of conditions will give up some aspect ratio for sturdiness and tracking, and the torpedo doesn't suit anyone who sails where there are likely to be fishing nets and pot lines about and no towing service for hundreds or thousands of miles.


Few of the boats shown in Polux's posts in this thread have anything to do with normal cruising boats. They are like the Lamborghinis, F1 cars, and fantasy concept hot rods taped to a teenage boy's bedroom wall.
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Old 16-05-2016, 05:05   #186
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Re: Pilothouse Variations -- Boreal

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Wow that's a big windsurfer.

I wonder if they have thought of doing away with the keel and hanging lead ballast off the windward rail on a trapeze, maybe supported by spinnaker poles (analogous to the body weight hanging off a harness on the windsurfer).

All that will be needed then to go sailing is the daggerboard, rudder and mast and off you go. No need for a bow to behave well in waves when it is flying over them with only foils in the water.

Things seem to be going this way. I wouldn't be surprised to see one on the circuit soon.
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Old 16-05-2016, 06:34   #187
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Re: Pilothouse Variations -- Boreal

Snow--good post.
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Old 16-05-2016, 06:50   #188
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Re: Pilothouse Variations -- Boreal

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Originally Posted by hoppy View Post
If the boat was designed as you have drawn, then the forestay would have moved to the bow and a new bowsprit added for the asymmetric increasing the LOA

Given that a lot of the inverted bow yachts tend to be race oriented, I wonder if the design is some how related to the current rating system. Perhaps hull length is a factor in the calculation and fixed bowsprits are not penalised

For cruisers an inverted bow with a retractable bowsprit, will maximise speed and minimise dockage costs.
Well, it would not NEED to be moved that far

By the way, forestay further forward (and not necessarily all the way out) increases foretriangle area and is yet another advantage of that configuration.

An inverted bow will have negative progressivity of buoyancy and will be very wet compared even to a plumb bow. The resistance to plunging will be reduced as the bow goes down, so will have a tendency to pierce into the waves. Whether it's faster or not depends. In sea conditions where there's no problem with water over the bows it might give you some efficiency gain because of less pitching. Slightly less windage and a bit less weight, but at the expense of foretriangle size, and God help you if you have to go upwind in bad weather, or surf downwind on big waves.

I doubt that an inverted bow will bring any practical benefit to any cruising boat other than looking unusual and so "cool".

On an EXTREMELY light, long racing boat, which just barely floats on top of the water and has no weight in the ends, the savings of windage and weight of an inverted bow might be worthwhile.


But this is how a reverse bow tends to behave:

Click image for larger version

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That's the "wave piercing" effect of a reverse bow in action, when you definitely don't want it, and that's not even a difficult sea condition.

So the risk of THIS would go hand in hand with any advantages -- a tradeoff like so many others. This profound disadvantage would be poorly bought on a cruising boat which couldn't enjoy any of the advantages.
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Old 16-05-2016, 07:58   #189
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Re: Pilothouse Variations -- Boreal

We did not discuss the HYDRODYNAMIC effects of different bow forms -- only buoyancy. But the hydrodynamic effects are also very important. Here's what it looks like:

Click image for larger version

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The reverse bow tends to push the bow down, and the effect increases as the bow is immersed, even while buoyancy is being reduced.

This is simply terrible for rough sea conditions -- just the opposite of what you want. It tends to drive the bow into the sea, and this will make the boat far wetter and greatly increase the tendency to pitchpole.

On a racing boat this effect might be desirable as pushing the bow down might reduce squat at hull speed and give the boat a boost. But on a cruising boat intended for rough weather? Gack.

There's a good article on it here: Reverse Bows — Pros & Cons

from where I took the images.
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Old 16-05-2016, 09:34   #190
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Re: Pilothouse Variations -- Boreal

Boat designers can calculate stability curves based on the hull shape of a boat. We could have other similar curves too, like a curve describing the behaviour of a boat when it hits a wave.

One should take into account the shape of the boat (from bow to stern), weight distribution, speed of the boat, and a simplified model of the waves. From the curves it could be easy to see if some boat will survive hitting a large wave or if it will pitchpole. One could also see e.g. how much hobbyhorsing to expect with different size and frequency of waves.

Few curves could tell quite a lot, and give some basis for comparison of different bow and hull shapes. No need to debate them very long if it is all on paper . I wonder if designers already use such calculations or if they do it all (= the dynamic aspects of buoyancy) based on experience only.
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Old 16-05-2016, 09:38   #191
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Re: Pilothouse Variations -- Boreal

Gack
To get messed up in the process of putting the team on your back and still going out like a champ.

Thank you DH for enlarging my lexicon

This is meaning nr.5

(I spare all the other 4, all worth a ban... :-))
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Old 16-05-2016, 09:46   #192
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Re: Pilothouse Variations -- Borealis

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Also on a metal boat, an integral bow spirit pushes that space even further fwd to improve forestay angles and to keep chain from fouling bow.

My small bulwark around the bow spirit creates a very strong box structure and a secure location when working there.
How large!? 1'1/2"
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Old 16-05-2016, 10:04   #193
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Re: Pilothouse Variations -- Boreal

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Gack
To get messed up in the process of putting the team on your back and still going out like a champ.

Thank you DH for enlarging my lexicon

This is meaning nr.5

(I spare all the other 4, all worth a ban... :-))
The correct meaning in this context is "'Gak' -- ejaculation; an exclamation of disgust. Poss. onomatopoeia; from the sound of a cat spitting up a hairball."

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Old 16-05-2016, 11:32   #194
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Re: Pilothouse Variations -- Boreal

Hi Dockhead,

I will send you a PM. We expect to be in the Solent area for the winter. I would be happy to meet you and show you Rocket Science.

By the way, I did not commission this build. Building that thing would have been WAY out of my budget. I'm merely looking after her for as long as I own her.

Mr.Bieker has been very generous with his time, so I've been able to get some pretty good insights into his thinking about the design. I think that he probably talks to us mostly because he's amused. Typically, when his phone rings, it's the likes of Russell Couts, so when we get in touch after some long trip to somewhere odd, (and just 2 of us with no racing cred at all), I think that he's mostly just happy that his creation's out there being sailed as intended. Well, we probably sail her a lot slower than he intended, but we're out there.

The 'high strength to weight ratio' is something that is not really achievable without dropping some coin substantially in excess of a 'normal' boat.

But, since we're talking custom builds and hypotheticals here mostly, I think that higher end materials would be on the table for the purposes of this thread.

You are right about there being no 'right' hull shape. My only real bitch about RS's sailing characteristics is that when we're surfing, that deep bow tends to offer some steering resistance this way and that. She would track far better if she was sporting a flatter forward section.

However, there's a very good reason for the 'V' up there, since without it the boat would pound mercilessly going to weather. We don't have the pounding, but downwind suffers.

There is no free lunch.

For my part, I would not want to own a flat-bottomed boat for general cruising. I'm guessing that sailing a VOR boat to weather is not something that your normal cruiser would find acceptable!

I do think that a torpedo bulb keel is an acceptable way to go for cruising, probably even desirable, but again, probably not if one's unwilling to drop a lot of cash on the engineering. I would be uneasy owning one without really knowing how well it was done.

I am a fan of SA/D in the 20's. You can always reef, and it's nice to have the horsepower there when you need it. Spec a carbon rig, and weight becomes less of an issue. Make it a low aspect rig with a sprit, and it's even better, keeping the CE low. RS, for example, has a SA/D in the high 20's with a mast tube length of just 60 feet. Windage is quite low, as is the weight.

You're already way ahead since you're trying to design for one particular region's conditions. I think you're going to have a great time with this project.

PM on the way.

TJ
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Old 16-05-2016, 12:32   #195
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Re: Pilothouse Variations -- Borealis

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How large!? 1'1/2"
With pipe section on top...almost 3"
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