Blue Water

[Auspicious]

Originally Posted by StuM

Nabla: ∇

That's it. Karma points to you sir.

[Adelie]

Originally Posted by Auspicious

Wait - let me check the wall - yep - still there. Bachelor of Science in Naval Architecture and Marine Engineering from Webb Institute.

First, non-dimensional means all the terms cancel out. You have to carry all the units. Tonnes (or pounds)/cu ft (or any unit of volume) is proportional to a non-dimensional metric but is not itself non-dimensional. If you use MT and cu m the number is different. That isn't non-dimensional.

It really doesn't matter a lot as it is an indicator and not something that is deterministic of performance. It's only useful in comparing similar hull forms.

Not useful at all. Looking at multiple conditions is indicative but not deterministic. How often does a ship or boat go to sea in lightship conditions? We look at full load, full load depleted stores, in ballast, and in ballast depleted stores.

This is why launch conditions (lightship minus a bunch of outfit) is always treated as a special case. It's also why a lot of work goes into inclining experiments to see how the builder's planned steel weight worked out. You'll find my signature on a lot of stability books. Lightship is only a reference point. No one goes to sea that way, at least not for long.

Oh wow, you have a shiny pretty piece of paper that more or less says your are pretty good at math and physics and you take tests really well.

I got one that say "Engineer" on it so I know how that works. One of the 50 states let me get an embossing stamp to go with my shiny pretty paper.

I took a year of naval architecture but didn't pursue it professionally.



Moving right along. Let's start with a little history. 1910 David Taylor published the formula DLR = Displacement/(Lwl/100)^3 in a book discussing model testing of ships. He discovered that for models with the same DLR as a full size vessel moving at the same Froude number (dimensionless analog to speed) through the water, the pounds of resistance per ton of displacement would be the same for both the model and the full size vessel. Thus you could use model testing to very accurately estimate the resistance on a full size vessel and therefore how big an engine it required for the speed desired.

Onward. Dimensionless means all the units cancel not all the terms. Sorry couldn't help myself from being a word nitpick.

Next. For solids and liquids near STP weight is also a very good proxy for volume. The density of water or saltwater can generally be considered a constant for use in the DLR and for that reason has historically be ignored. Turns out that 2240lb (a long ton) of seawater is 35cf (to about .1% accuracy, 63.9lb/cf density).

So even though the dividend in the equation is in lb, by application of a constant the units become cubic feet which is the same as the divisor. Since the constant only changes the absolute values of the results without changing their proportionality, applying that step is skipped since it introduced another source of mathematical error without adding anything to the final result. The absolute values of the ratio has no physical meaning, so skipping that conversion step was a no brainer. Since displacement is also a very good proxy for volume, the results of the equation can be considered dimensionless.

On to Lightship. There are 2 main uses for the DLR, design and comparing boats in the field.

For design one would consider all the cases of loading in evaluating DLR. That would be an appropriate thing to do if we were on https://www.boatdesign.net/forums/. We aren't.

Here people want to compare boats for speed potential and strength of construction when they argue with each other about the relative merits of each other's boats or when they are comparing boats they might buy. Feeling that weight per size of boat is a good proxy for strength folks latched onto DLR. They also latched onto it in the belief that it is inversely related to speed potential. Unlike you and me, most of these folks are laymen/laywomen/laypeople who if they DLR is not already calculated for them are going to have enough trouble calculating it using the readily available info (lightship displacement and LWL). Expecting them to be able to adequately estimate loaded displacement stretches credulity. Likewise the change in LWL as the boat is loaded. Also most people are just looking for a boat's DLR relative to other boats and the relative positions in a ranking will not change that much between lightship and loaded conditions. So for the purposes of comparison in general the OP's question in this thread in particular, the lightship displacement works just fine when calc'ing DLR.

As an aside DLR does a pretty poor job of estimating relative structural weight and by implication strength and in estimating speed potential. You need to have difference of 50 between boats to be sure you have even a small advantage in strength or speed, alternatively at 50 you might have a huge advantage but you really don't know because DLR is so poor at estimating relative strength or speed.

For strength the equation should use LoA, Displacement - Ballast and Beam.

An equation estimating speed potential should use LWL and SA/D (Sail area/Displacement^0.66).

However DLR is what everybody currently uses and I don't currently have the time or energy to tilt at that windmill.


https://www.ericwsponberg.com/wp-con...ign-ratios.pdf

[FV Black Pearl]

still looking, now that I know how the google search works it saves on questions 3 boats that consistently fit the bill is the Westsail, Island Packet and the Halsberg Rassy all 35-40 range. I was real leery of the older boats but there is very few original older boats. Most have been upgraded many times, some with new sails and rigging. I haven't ruled other boats I like the Aluminum ones but always just out of budget. At least the search is becoming more sane

[ranger58sb]

Originally Posted by FV Black Pearl

still looking, now that I know how the google search works it saves on questions

And you're looking on yachtworld, too, yes?

Info from there might not speak directly to seaworthiness, but you can find boatloads o' info about features and layout and so forth...

-Chris

[JPA Cate]

You know, Black Pearl, another source of info is <sailboatdata.com>.

Glad you got the search working for you.

[Auspicious]

Originally Posted by Adelie

Moving right along. Let's start with a little history. 1910 David Taylor published the formula DLR = Displacement/(Lwl/100)^3 in a book discussing model testing of ships.

ADM Taylor did not create the Δ/L ratio; it greatly predates him. ADM Taylor is best known for the Taylor Series that explored the variation of one parameter at a time for the empirical evaluation (model testing) of a series of hulls to better understand the implications of design changes. Even today with the benefits of some pretty spiffy algorithms running on power computers the Taylor Series has application in preliminary design.

Not of recreational boats of course, but ADM Taylor’s Series is conceptually applicable.

I had the privilege twice of leading test programs at the model basin that bears ADM Taylor’s name for platforms well outside the Taylor Series. Science marches on. Froude scaling with corrections for Reynolds number of course still apply. Depending on the application elasticity and surface tension may be factors. Surface piercing foils like those I worked on at Hyrdonautics (another model basin) are very hard to scale.

Originally Posted by Adelie

Onward. Dimensionless means all the units cancel not all the terms. Sorry couldn't help myself from being a word nitpick.

Correct. Tonnes/cu ft does not cancel the units. It certainly is an empirical measure but not non-dimensional. That it was used for many years doesn’t make it non-dimensional. If you have to convert between Imperial and SI it isn’t non-dimensional.

D by the way is not displacement. Δ is displacement. There are few “reserved” variables in naval architecture but D is one of a few that are not used for other than a fundamental parameter: L – length, B – beam, D – depth, T – draft.

Originally Posted by Adelie

On to Lightship.

If you only are interested in speed potential you will be hard pressed. L/B, prismatic coefficient, and Δ/L may cast some light but are far from deterministic.

Δ/L has very little to do with strength of construction. First we would have to agree on what strength of construction means. Stiffness? Toughness? That “people” may have latched onto Δ/L as a proxy for strength doesn’t mean it’s appropriate. Consider the progression from wood to fiberglass to carbon fiber or from wood to iron to steel to aluminum.

Originally Posted by Adelie

An equation estimating speed potential should use LWL and SA/D (Sail area/Displacement^0.66).

SA/Δ is another measure that is overused. It’s interesting. It may even be useful in preliminary design. In comparing boats it is a very poor measure compared to looking at polars for each combination of sails.

Originally Posted by Adelie

https://www.ericwsponberg.com/wp-content/uploads/the-design-ratios.pdf

I think well of Mr. Sponberg and his paper on design ratios is interesting. I do take issue with embracing hull speed (professional naval architects have long since left the concept behind for speed-power curves) and playing a little loose with nomenclature.

[MartinMV]

Blue Water is not only about seaworthynes but about independence from a habour for a long time especially crossing oceans.

Thus you need large fuel tanks, water maker and/or large water tanks, means for energy, room to carry tools, equipment, spare parts, your household and food.

Also blue water usually goes for boats to be sailed with a small crew of usually two or one.

That means selfsteering. Simplicity. Redundancy in important parts and so on. Professional anchoring gear.

Not to forget about good rescue gear and long distance communication equipment like satelite telefone or short band radio.

[atlantical]

My boat is a southern cross 31, which (if you see my post on budget atlantic crossing) I bought in Carolina Beach NC for 8500 dollars. Its a full keel, and on my own, I got a good seven hours sleep every night crossing the Atlantic, I bought the boat because an American woman sailed one round the world, she wrote the book "by the grace of the sea" Pat hendry.

The size of a boat does not guarantee its strength, but in my own opinion, fin keels are not great, there is a huge amount of stress on those bolts, and a huge amount of stress on the hull, especially on racing boats.

Hull deck joint, you want a bolted joint, a lot of the boats, the deck is held down with self tapping screws, and a bit of ticky tack.

The chain plates need to be good, I had an irwin citation, that had one port and starboard chain plate, going through the deck, and anchored onto the plywood bulk head, I had a lancer that had chain plates that would just pull against a plate that was only being stopped from going up by the deck, which was held on with self tapping screws, My current boat, has four independent chain plates either side, all anchored to integral ribs on the hull of the boat, its as solid as you get.

Hull thicknesses ten to be eight and twelve mm, modern production boats tend to be eight, but the lay up process defines the strength, not the thickness, older boats were laid up without any consideration to humidity, or temp, modern boats are laid up in controlled conditions, but, due to how thin they are, the hulls are prone to flexing.

When I was crossing the Atlantic (well I was in Bermuda at the time) a big Beneatua went down, as I understand, the steering cables broke, and free rudder, tore the back end out of the boat. My boat has a tiller, and rudder mounted on the canoe stern, which makes it much stronger. The lancer I had suffered from a bent rudder post, due to the rudder being deeper than the keel.

Everyone has there own opinion of what makes a good boat, to me, its what its record is, and how it feels when I sail it, and you are likely to more confident of a build that you know has been round the world, than one that you don't know of any that have been sailed far.

[daysgoneby]

Ocean Yachts Endure More Load Cycles
Distance alone doesn’t tell the whole story, though. Many of the loads on a yacht are cyclical, rising and falling with each passing wave.

Our club racer only has to worry about this for perhaps 150 or so of the 520 miles a year she sails. The rest of the time, the waves are less than half a metre, and so can be ignored for our present purposes as the cyclical loads they introduce are rather small. With a typical wave period of perhaps two seconds and an average speed around six knots, she might hit 45,000 waves of appreciable size each year, and therefore see 45,000 significant load cycles on her rigging, mast, keel and other key components.

The ocean-going yacht sees much larger waves (and therefore much larger cyclical loads), and is exposed to many more of them.

John’s experience with the Bermuda passage suggests that we’ll see significant wave heights of 1.5 to 2 m for about 40% of the trip, and 2 to 3 m for about 50% of the trip. While we’re in the Gulf Stream, we might have a day of being tossed around by 4 m waves.

The cyclical loads this boat experiences, then, will be of much greater amplitude—a larger swing between high and low load than the club racer would see. (While Lake Ontario, Long Island Sound and many other popular areas routinely whip up four-metre breakers, no sane inshore sailor goes out in that stuff when there are plenty of safe harbours available. Ocean boats just have to slog through whatever comes their way.)

The ocean waves also have a longer period than the lake chop did—approximate calculations suggest a period of perhaps 3 seconds for the rough stuff in the Stream, and 4 seconds in the open ocean. In one trip to Bermuda and back, then, we’ve seen on the order of 230,000 load cycles—the equivalent of five years of racing and day-sailing back home, and they’re much larger load cycles to boot.

https://www.morganscloud.com/2013/04...ard-on-a-boat/

[barnakiel]

Originally Posted by MartinMV

(...)

Thus you need large fuel tanks,

(...)

100% with you thru the rest of your post. I would make an exception for fuel tanks though as they are more equipment choice than a must. A sailing boat does not need a fuel tank at all, per se.

But in respect of 99% (?) of cruisers you are right. Many of them cannot sail a boat that is anything but a car. Which is odd, since sailing boats seem to sail better than heavy sailboat/tank hybrids.

It is a great shame. We are losing the sailing thing as much as we are gaining more democratization of this once noble (and most unfortunately elitist) pastime.

Cheers,
summer b.

[GTom]

This Monsun 31 established a new category: whitewater sailing boat:

https://www.youtube.com/watch?v=qKBGizcD1uY

[rostyvyg]

Originally Posted by Jim Cate

FWIW, Island Packets are "production boats" every bit as much as Catalina et al are. They don't manufacture as many as the big name guys do, but t hey are series production vessels.
Jim

Well, there are production boats and there are production boats. Island Packets are designed and built with no expense spared and no corners cut. Heavy displacement, full keel, low draft, lead ballast, solid hull (no core), excellent glasswork, keel stepped mast, bronze thru-hulls, deep bilges, huge tanks under floor (low center of gravity and lots of room left above for stowage), tinned numbered electrical wires, solid teak cabinetry, all doors louvered, great galley layouts, superinsulated ice boxes, rack-and-pinion steering, no balsa or plywood in deck to rot (they use some proprietary resin fillers), stainless steel portholes, snug well drained cockpits, first class deck hardware, oversized winches, all lines lead to cockpit, excellent bow platforms for dual anchors, cutter rig... They part waves as opposed to other "production boats" slamming their fat bottoms, they are comfortable downwind, they smile on wind gusts and do not care of "small craft advisories." And, contrary to popular belief, 3 digit models from IP420 and above do sail pretty well in light air or close-hauled. As a matter of fact they are so good that the company almost went bankrupt because it was next to impossible for them to compete with their own used boats. I am glad they are through the hard times and are ramping up production now. And, BTW, their factory support is unbelievable good.

On this note, Amel's are also "production boats", but who would want an ...eau if they can afford an Amel 55?

[Jim Cate]

Originally Posted by rostyvyg

Well, there are production boats and there are production boats. Island Packets are designed and built with no expense spared and no corners cut. Heavy displacement, full keel, low draft, lead ballast, solid hull (no core), excellent glasswork, keel stepped mast, bronze thru-hulls, deep bilges, huge tanks under floor (low center of gravity and lots of room left above for stowage), tinned numbered electrical wires, solid teak cabinetry, all doors louvered, great galley layouts, superinsulated ice boxes, rack-and-pinion steering, no balsa or plywood in deck to rot (they use some proprietary resin fillers), stainless steel portholes, snug well drained cockpits, first class deck hardware, oversized winches, all lines lead to cockpit, excellent bow platforms for dual anchors, cutter rig... They part waves as opposed to other "production boats" slamming their fat bottoms, they are comfortable downwind, they smile on wind gusts and do not care of "small craft advisories." And, contrary to popular belief, 3 digit models from IP420 and above do sail pretty well in light air or close-hauled. As a matter of fact they are so good that the company almost went bankrupt because it was next to impossible for them to compete with their own used boats. I am glad they are through the hard times and are ramping up production now. And, BTW, their factory support is unbelievable good.

On this note, Amel's are also "production boats", but who would want an ...eau if they can afford an Amel 55?

I'm really glad that you like your boat (if you own one), but IPs are still production boats. YOu like their features, other folks don't. They are still production boats.

It sounds like you have memorized their glossy brochures. Such enthusiasm is cool, but they are still production boats.

I prefer other designs, but that does not make me right or better. I have owned two production boats, one semi production and now one one-off. I have some ideas about what a cruising boat should be and there didn't seem to be any production boats around that filled those boxes... hence my choice.

I could have purchased an Amel if I had wanted one... I didn't.

Jim

[thomm225]

[QUOTE=Glenn.Brooks;2407752]One interesting thing to me is to look at the boats that have been entered in the single handed Transpac, Transpac, and Vic Maui Races over the years. These boat lists will give you a good idea of what constitutes a proven "blue water" sailboat, versus a coastal cruiser.
QUOTE]

Actually this isn't quite true. I look at the list of the boats that have raced the Single Handed Transpac (which is from San Francisco to Hawaii) and am quite amazed that folks would sail some of those boats in that race the 2100 miles or so

Examples:

Cal 20
Olson 30
Hobie 33
Cal 2/27
Merit 25

Merit 25 spec's:

MERIT 25 sailboat specifications and details on sailboatdata.com

http://sfbaysss.net/archive-shtp-web...tsThru2012.htm

[MartinR]

Originally Posted by FV Black Pearl

Yes I looked last night and again just now... Im not sure if its older boats or if its blue water boats but they seem so cluttered on the deck. theres no outside area but the cockpit with just feet space. I also think Im going to have to get used to the idea that my bed may not be square I do notice some things I like about the bluewater boats Ive been looking at is there is larger fuel and water tanks. I don't want to rule out a Westsail, and not knocking them...but Im not there yet...

I love flush-decked boats, but for heavy weather this is not a good solution. All the "clutter" on deck gives you something to hold on to.