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Old 13-05-2016, 06:05   #121
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Re: Pilothouse Variations -- Boreal

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Originally Posted by Panope View Post
. . . However, the ability to make progress to windward increased greatly with the addition of the pilothouse because the crew is more comfortable/ less fatigued. . . .
This is a very important point, and true.

Imagine trying to get 1000 miles dead upwind, in 20 to 30 knots true and 5 to 10 degrees temperature, and short handed.

Unfortunately I've done this.

The boat you need to do this, is very different from an average cruising boat. This is not playing around in the bay.

You cannot hang out in the weather for a 1000 miles constantly microtrimming the sails, unless you have a crew of 8 on two hour watches. So you need a boat with very little windage and an easily driven hull, so that you don't have to produce heroic amounts of power to keep the boat moving. You need a modest sized rig and lots of stability. You set the pilot on wind mode, and let the boat sail herself so you can retreat to the pilothouse and keep an eye on everything from there. You'll lose a couple of degrees AWA compared to actively steering in the puffs and lulls so the boat needs to be so good upwind that you can afford this.

It's a tough set of design criteria.
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Old 13-05-2016, 06:42   #122
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Re: Pilothouse Variations -- Borealis

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Originally Posted by Dockhead View Post
The point of a raked (and flared) stem is to increase buoyancy as the bow is immersed. It's like a variable rate spring on an off road vehicle where the spring rate is mild at first but goes up when the spring is compressed.
Interesting, also my understanding that raked bows help to stop the boat being stuffed into the back of a wave when going down wind in big seas. Achieved as you say by increasingly greater volume and the bow goes in. In addition there is something about the bow not being tripped if its raked. Not so much end over end, but sideways and being unable to recover if the bows goes sideways and the stern starts to over take.

Having submerged a 19ft rib completely by stuffing it into the back of a wave to the point that when we and the boat stopped the only thing to see were 4 heads just above the sea level and somewhere beneath us a boat. We did eventually surface looking much like a US submarine in a Hollywood movie and I learnt some valuable lessons.

So whilst upwind might be very uncomfortable, downwind is the one that scares me.

Pete
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Old 13-05-2016, 07:06   #123
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Re: Pilothouse Variations -- Borealis

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Originally Posted by Pete7 View Post
Interesting, also my understanding that raked bows help to stop the boat being stuffed into the back of a wave when going down wind in big seas. Achieved as you say by increasingly greater volume and the bow goes in. In addition there is something about the bow not being tripped if its raked. Not so much end over end, but sideways and being unable to recover if the bows goes sideways and the stern starts to over take.

Having submerged a 19ft rib completely by stuffing it into the back of a wave to the point that when we and the boat stopped the only thing to see were 4 heads just above the sea level and somewhere beneath us a boat. We did eventually surface looking much like a US submarine in a Hollywood movie and I learnt some valuable lessons.

So whilst upwind might be very uncomfortable, downwind is the one that scares me.

Pete
Indeed. Bow vs. Wave is a battle fought in different situations, most terrifyingly while surfing downwind at the edge of a broach.

The bow on my present boat looks like the one on your boat in your avatar --

mildly raked and no flare.

I would like for the next boat to have a bit of flare in addition to a mild rake.

The flare has another advantage, a serious one, of giving a bit more deck space there where you are handling ground tackle, working on furlers, dropping sails, climbing on and off the bow when moored Baltic-style.

My present boat has rudimentary bulwarks which I really like. I think the bulwarks might be a bit higher at the bow. This might cost a bit of windage, or then again maybe not -- it could be that properly shaped bulwarks could smooth the air flow over the deck and reduce the net windage forces. Air doesn't like to flow over randomly shaped objects.



I guess you didn't have a GoPro with you when you tried that U-Boat maneuver? Would be pretty cool to watch.
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Old 13-05-2016, 08:52   #124
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Re: Pilothouse Variations -- Boreal

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Originally Posted by Panope View Post
B, I was just clarifying things as there seemed to be some erroneous responses to Dockhead's statement "Nor do I like the hull form at all, which resembles a Hanse with the plumb bow (no extra buoyancy)..." from post #81, above.

You will have to ask Dockhead why he prefers 'reserve buoyancy' but I will guess it has something to do with not getting washed overboard.

Regarding the bow that you posted above: I agree, that is a beauty. However, the boat would be unusable for me in its current state as there is no provision to handle a proper anchor. Give me a couple days time and some aluminum pipe and I could cobble up something real shippy ......

Steve
I see. Plenty depends on what the boat is doing and where. Even clippers had their bows for a reason.

You are right with my 'perfect bow' boat likely utilizing a soft rubber anchor. I should consider posting more sexy stern shots as clearly I get caught out with the bow ones ;-)

Most interesting the opinions in this thread. I am amazed to see that some sailors actually like sailing boats without dodgers, pilothouses and other un-seaman-like inventos, while I would pay big bucks for a fine hard dodger let alone a cozy pilothouse. Apparently, South Pacific rains are something one most suffer thru, to develop some amount of arthritis, to cure all the romance of the sea ... ;-)

+Big hug,
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Old 13-05-2016, 10:53   #125
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Re: Pilothouse Variations -- Boreal

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Originally Posted by Terra Nova View Post
Water ballast simply does not seem practical for a cruising boat. Makes no sense to me.
I'm with you. I fail to see how water is ballast since it has about the same specific gravity as the sea. I guess it does displace air. I can't see water for more than fresh water needs and since it is used up can't be considered ballast. Furling also becomes a problem with free surface.
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Old 13-05-2016, 11:28   #126
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Re: Pilothouse Variations -- Borealis

Light sails and fuel. In high latitudes you don't need the former if you have enough of the latter.

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Another thing, for high latitudes -- "flying enough sail in light air to make speed" is not necessarily a high priority. You're not racing. I don't have any light air sails whatsoever at the moment, and I'm not really suffering -- I just use the motor in wind too light to move the boat (often, under 10 knots if the wind is behind the beam). A very high level of strength is 1000x more important than light air sailing ability, for me. I do want to improve light air sailing ability, just because I love to sail, but this is just not the top priority, and I sure as hell am not going to sacrifice strength for this.


Quite so - You rarely have very long without wind, especially in the summer. If you have light wind it is just a lull before the next low comes through so you motor. I am in the tropics now and suffering from not having light sails but never ever an issue in high latitudes


Sure, I didn't say it's not possible. But Novak's boat looks like a trawler underneath and carries 2 1/2 tons of fuel. It's probably the most practical approach for truly extreme high latitude sailing, exploring really, but again this is also not exactly what I'm looking for.

7 Tonnes on the bigger Pelagic The Pelagics are pretty much the only boats using swing keels in the south these days apart from one or two of the old hands/boats built when they were fashionable.


Ah, water ballast. I had forgotten about that.

Tranquillo - a Dykstra job has very effective water ballast. I haven't seen it in use sailing but fantastic with a cross wind on a mooring
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Old 13-05-2016, 13:50   #127
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Re: Pilothouse Variations -- Boreal

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I should consider posting more sexy stern shots as clearly I get caught out with the bow ones ;-) .........
barnakiel
All sexy photo shoots should include both bow and stern shots.

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Old 13-05-2016, 13:53   #128
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Re: Pilothouse Variations -- Boreal

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Polux, I think you might be mistaken when you used the word "LOA" above. I you sure you did not mean "LOD" ?

...
Steve
Yes you are right. I was using the term in a lose way. I should have said hull lenght.
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Old 13-05-2016, 14:04   #129
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Re: Pilothouse Variations -- Boreal

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A quick sketch to go with the above.

The raked stem boat will likely have:
-more reserve buoyancy
-drier decks (because of flare)
-more deck space
-stronger anchor roller support
-head-stay can be placed further forward (unless the plumb stemmed bowsprit is stayed).

The need for a large over-hang of the anchor roller is often overlooked on modern designs. A dangling anchor on a pitching boat, will cause great damage to the topsides.

That makes no sense. Consider hull length and the advantages are all on the plumb bow (that is why they are used in modern boat design).

Yes the LOA is bigger but the easiest and more used cruising downwind sail is a geenaker and a gennaker needs a pole. The modern tendency is to have a pole that incorporate an anchor stand. Here another aluminium passagemaker with that type of pole/stand, the Allures 52:
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Old 13-05-2016, 14:19   #130
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Re: Pilothouse Variations -- Boreal

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Yes --

Plumb bow does not give any GRADATION of buoyancy -- when the bow is raked and flared, the buoyancy increases sharply with immersion in a wave and lifts the bow over.

...
That is pretty simple: Bow buoyancy has to do with the volume of the bow and the biggest volume on a bow regarding hull length is given by a plumb bow. If we consider the deck length than an inverted bow it will offer even more buoyancy.

Besides plumb bows (or tendentially plumb bows) that are used pretty much on all modern designs were efficiency is the major factor in design (not looks) the more interesting recent development are the use of chines to increase dynamic lift (that has the same role as buoyancy) and to prevent spray and water to come to the deck, contributing to drier boats.
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Old 13-05-2016, 14:28   #131
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Re: Pilothouse Variations -- Boreal

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I'm with you. I fail to see how water is ballast since it has about the same specific gravity as the sea. I guess it does displace air. I can't see water for more than fresh water needs and since it is used up can't be considered ballast. Furling also becomes a problem with free surface.
Water ballast makes sense if the boat is used for passage making and if it has a beamy hull. It does not make sense on coastal sailing were change of tacks are frequent. Water Ballast is used on some high end fast passage makers and on many ocean racers specially the ones solo sailed (that are the ones more similarities with cruising boats).

How it works? The same way the weight of a crew sitting on a rail works on a racing boat. Body weight is not very different than water weight. Just imagine instead of having 10 crew sitting on a rail having 1000kg of water on the side of the boat. That water can be moved from side to side, it can be fresh water and used as drinking water if needed.
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Old 13-05-2016, 14:48   #132
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Re: Pilothouse Variations -- Boreal

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Water ballast makes sense if the boat is used for passage making and if it has a beamy hull. It does not make sense on coastal sailing were change of tacks are frequent. Water Ballast is used on some high end fast passage makers and on many ocean racers specially the ones solo sailed (that are the ones more similarities with cruising boats).

How it works? The same way the weight of a crew sitting on a rail works on a racing boat. Body weight is not very different than water weight. Just imagine instead of having 10 crew sitting on a rail having 1000kg of water on the side of the boat. That water can be moved from side to side, it can be fresh water and used as drinking water if needed.
Probably works on expensive long range racers, singling. I hope tanks are well baffled. Not my cup of tea. I want all tankage as low as possible and well baffled. Sloshing water can transfer a bunch of weight quickly.
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Old 13-05-2016, 14:53   #133
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Re: Pilothouse Variations -- Boreal

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That is pretty simple: Bow buoyancy has to do with the volume of the bow and the biggest volume on a bow regarding hull length is given by a plumb bow. If we consider the deck length than an inverted bow it will offer even more buoyancy.
Nah, I disagree . In a static object possibly but charging down the face of a wave then dynamic stability is far more important as you state later.

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Besides plumb bows (or tendentially plumb bows) that are used pretty much on all modern designs were efficiency is the major factor in design (not looks) the more interesting recent development are the use of chines to increase dynamic lift (that has the same role as buoyancy) and to prevent spray and water to come to the deck, contributing to drier boats.
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Old 13-05-2016, 15:26   #134
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Re: Pilothouse Variations -- Boreal

Just a point for clarity on the Boreal in in regards to all the keel talk. Boreal places all of its ballast in the hull. The swing centerboard is a hollow aluminum, proper NACA foil that pivots, typically by using a mechanical winch (although power is an option). I haven't seen what the centerboard weighs but it can't be more than a few hundred pounds on the 47 I'd guess. It's not there for stability; It's there to give you better pointing ability upwind.

IMO that's a much more robust system than the Adventure 55, although I have no doubt the Adventure will be a much higher performance boat. The difference between pivoting a relatively light weight centerboard and hydraulically lifting a ballast keel is enormous.
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Old 13-05-2016, 15:34   #135
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Re: Pilothouse Variations -- Boreal

Quote:
Originally Posted by Polux View Post
That is pretty simple: Bow buoyancy has to do with the volume of the bow and the biggest volume on a bow regarding hull length is given by a plumb bow. If we consider the deck length than an inverted bow it will offer even more buoyancy.

Besides plumb bows (or tendentially plumb bows) that are used pretty much on all modern designs were efficiency is the major factor in design (not looks) the more interesting recent development are the use of chines to increase dynamic lift (that has the same role as buoyancy) and to prevent spray and water to come to the deck, contributing to drier boats.
You're missing the point -- it's the "progressive spring" effect of rake and flare, not the total amount of buoyancy. A flared and/or raked bow will have more and more tons of buoyancy for every inch of immersion, as it is pressed down (or wave rises up), compared to plumb bow, which has a constant rate.

An inverted bow has negative progressivity -- it will resist less and less, as it is immersed, and quickly dive.

Plumb bow is fine for racers and for mild weather, but less so for keeping the decks dry in really nasty weather. There are different kinds of "efficiency" and different design priorities for different types of sailing.

Rake and flare is not the only way to keep the decks dry of course -- you can just have a whole lot of buoyancy forward and keep weight out of the bow and that can also work. But it's "inefficient" at this, because it requires more vertical space to achieve a given amount of extra buoyancy, when it's needed, and so you really need more freeboard.

Boats with plumb bows -- and now I'm speaking from experience, not theory -- "cut" into the waves relatively more than rising up over them, and this is also fine under certain conditions and may even make for a more comfortable ride with less pitching. But when conditions are really bad, "cutting" into the waves is bad and can be very very bad.

My present boat has mild rake and fairly high bows but is absolutely inadequate from this point of view -- not infrequently, where I sail, the nav lights are under water and green water sweeps the decks. This happens in steep sea conditions especially with wind against tide. To avoid that on my next boat, I will either have to have much more freeboard, which is undesirable from point of view of windage, or much less weight in the bow -- which is all good from all points of view but hard to achieve -- or have more rake and/or flare.

Rake and flare make it much harder to "run out of" freeboard exactly because of the progressivity of the buoyancy effect. Not "running out of" freeboard is extremely desirable sailing up here, in these conditions.
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