What makes a "Blue Water Boat"?

What's wrong with modern, small designs?

Having sailed two traditional long-keeled boats, one 45' and one 55', across an ocean with the usual mix of good and bad weather, my personal experience says it is the crew that makes a "blue water boat".

As long as the boat is well built, and the crew is knowledgeable, then many boats that traditionalists call unsuitable may be used for offshore sailing. My personal preference in size would be about 37-40 ft LOA, a modern deep fin and spade rudder underbody with a cutter rig.

Over the years, I've had two lower shrouds break, both of them were rod and one headstay clevis pin sheer - that was no fun, but we didn't lose the rig in any case. Inner forestay and double spreader with separate shrouds, not the modern setup of discontinuous seems to be the best for offshore - in my opinion.

Sufficient water is probably the most important requirement, in at least two, if not more, tanks - and the crew knowing how to ration water usage.

 

John, (post #25) your question invokes the all important matter of damping.

Without damping all boats would capsize eventually given randomly generated surface oscillations.

Generally, damping is augmented by large lateral planes and 'flats' in the sections.

When lying ahull there is almost no remaining aerodynamic damping (unless the wind is strong enough to effect damping on remaining windage) so hull damping is crucial to heavy weather survivability.

Most modern double wedge canoe forms with small high aspect appendages afford scant damping which is an issue of concern for all weather passagemaking.

It is therefore fairly obvious that the forms that were in favour at the height of sailing (pre motorisation) were full keel designs with large damping factors to be able to carry on with business as usual regardless of weather. The full keel has been shown to be one of the superior forms for consistency of performance across a broad spectrum of conditions.

If on the other hand ( as in racing , or racing scene inspired yachts) the operating conditions are anticipated to be within a certain window, then of course a fin keel can result in performance benefits.

 

Good points. Talking once with one sailor that survived 2 big hurricanes he said that sooner or later the final resting position for a boat is ahull -- meaning that when drogue bridles break, or you are too exhausted or hurt, etc... you will end up ahull; therefore how the boat behaves ahull is important if you think you might end up in extreme conditions. Your dampening thoughts make sense. Thanks

 

Blue water boat is a matter of dreams, pocket book, preparation, living with less, enjoying the moment and not being in a hurry. Personally, I don't know if I would cross at mid ocean in anything smaller than 80 feet. Island hopping however is a different thing.

 

Tcubed wrote:
"Without damping all boats would capsize eventually given randomly generated surface oscillations.

Generally, damping is augmented by large lateral planes and 'flats' in the sections. "

I think you are missing the importance of mast inertia in damping roll of sailboats in a seaway. Marchaj's investigations showed how the same hull with a rig was far more stable than without.

Add this to the wind resistance at high wind speeds of the rig (mast and shrouds) and modern sailing craft with less keel surface area may not be as unstable as you think.

I've only tried lying ahull one time, winds 50 to 65kts, for about 12 hrs, when the wind dropped below 45kts, the boat started to bounce around uncomfortably so we got back to sailing. This happened on passage from Azores to Bermuda, so we had plenty of searoom and I had enough crew that one could sit in the companionway to keep watch.

 

Let me gently correct your very good point .<<<<I think you are missing the importance of mast inertia in damping roll of sailboats in a seaway.>>>>

The increase in rotational moment of inertia about the roll axis (rmoiara) due to the mast is not the same thing as damping.

The windage of the mast is a powerful damper in strong winds. In no wind it is a negligible damper as it does not have enough area, but of course you would then hoist the sails which do damp very strongly in no wind, provided they are sheeted in, of course.


The 'rmoiara' will slow the roll period, in fact it slows it twice, because it also raises the boats CoG, lessening the righting moment. (based on the laws of simple harmonics)

This is very apparent when unstepping a mast and a passing motorboats' wake makes the now mast-less boat roll. It is immediately obvious the boat rolls much faster.

This correlates exactly with your experience that it damped the motion effectively with the strong wind but stopped being so effective once the wind eased off somewhat.

***

Now to this i would add two points;

The first is pedantic but valid nonetheless in certain situations, namely when in a strong left over sea but no wind. (These can be very terrifying as the sails seem like they will tear the rig out of the boat but to take them down makes the motion even more dangerous)

The second is something i do think is quite important and that is the boat with less rig windage would still be able to carry some sail and make way. What i mean is lessening rig windage is crucial to increasing the wind strength ceiling of positive VMG to windward, an often under appreciated feature of seaworthiness i feel.

So therefore, yes, spar windage will significantly damp a boat forced to lie ahull due to wind strength + other factors , but it is much better to have the damping come from elsewhere as per my above two points. Imagine you could still keep up a little trysail in that same wind?

 

misunderstandings

Your point about mast inertia slowing the roll period as not being the same as damping -

"The increase in rotational moment of inertia about the roll axis (rmoiara) due to the mast is not the same thing as damping. "

appears to be a matter of definition. I think that in your initial post you were talking about form stability as a means of 'damping' a vessel's roll period. Being pedantic, I think that damping is used as a general term describing a reduction in vessel motion by any of several means.

I'm not a big fan of traditional hull forms, and my personal experience has not shown increased damping owing to those hull forms. In fact, just the opposite is what I've seen. The roll period may be extended but the angle of heel to either side has been much greater which I think may be attributed to the more V-eed hull form of the traditional craft.

More later

 

Phew!! that god for that I was thinking I was the only one.

 

Somerville,

It is indeed important to define terms if one wishes to communicate ideas clearly.

I was and am using the same definitions as used C.A. Marchaj in his textbooks.

That is damping is how effectively roll energy gets dissipated (just talking about roll for now).

Roll moment of inertia / righting moment defines roll period. (this is an integral)

Form stability is not damping.

Maximum roll amplitude and roll damping are two separate things.

Myself i am a boat design atheist. Science and real experience are my guides. The working boats of the 19 th century proved themselves to be extremely able in all kinds of conditions and who knows where the evolution of boat design would be at today where the motor to not have made working sail almost extinct. We nowadays live in an age where all recent sailboat evolutions have been made with racing (note i say racing, not speed) and recreation in mind. This has made it difficult to remain objective and not influenced by current design fashions. Within the minute fraction of sailboats which can be considered serious blue water cruisers one observes a vastly larger proportion of 'traditional' forms however, which is hardly a coincidence. Keep in mind too that few of even the most adventurous cruisers consistently sail in as poor conditions as working sail, since they could rarely afford the luxury of staying at anchor. You do have Marchaj's book?

I cannot speak for your own personal experiences whatsoever, but there are certainly well accepted norms to augment hydrodynamic roll damping, such as large lateral planes, sectional flats, hard chines and other. This is one of the reasons freighters etc have slab sides and flat bottom. Observe the midsection of the great tea clippers and it's the same.

 

Hey I know more than you do . I read a book N stuff, you must listen to me because I am done everything on bots.

The question is --What makes a blue water boat?

Not rolling or floating or mast inertia.

In simple terms --what size Tv do I need? how mush water to wash my T shirt?

Where is the authur? what do you mean by "blue water"?

 

What other waters there is so we can exclude and the rest is blue?

White water? Kayaks and raft boats.. been there done that etc..for 25years
Sweet water? The main raw material for Grey water & black water? Hopefully only inside tanks.. but unfortunately also been there done that up to my neck bcs 've been a plumber
Ice water? Hey! I'm living 70deg N so got even a t-shirt..
Muddy Waters?

More?

 

You see some people dont read the question. they think the question is what makes a seaworthy boat. Or what makes comfortable boat. Both those questions and the answers are important in a Blue water boat but not only.

Some read the question as how small a boat can I got to sea in, Or what conditions could you tolerate for extended periods of time.

What is a Blue water boat is personal, and to me comfort is of paramount importance and comes along with size, fuel, water, bathrooms etc etc

Cruising will involve you being in harbour 99% of the time.

 

Seriously speaking there's no excact length as you suggest to have those qualities if we just don't restrict our choices to mass production boats (which, in my books anyway, aren't true bluewater boats). However there are trade offs both in short and long hulls. One of the worst comes with long hulls trying to find an appropriate and affordable mooring for that 60' hull. It just restrict's the options to a fraction what can be gained with 30'er.. and as you say that's 99% of the time..

 

I tell people that usually buying a new boat for cruising is a waste of money. You usually have to start by removing a lot of stuff and getting bigger versions of everything. And invent new storage places for more things. I think I have like 5 anchors, 3 huge hurricane rope, 2 huge dock lines, multiple chains, almost 2 spares for every running part. Super duty windlass, multiple electrical systems, at least 4 vhf radios, like 10 bilge pumps, 6 fuel/water filter separators, emergency suits, 2 outboards, 2 dingies, 3 vhf antennas
A computer and log book to keep track of everything. Multiple charts, tech manuals on every piece of gear. And I personally know every wire, hose and clamp on board..... Boy, I am just tired of talking about it.

And this is just to be ready for Murphy to happen somewhere unexpected. So you need a boat big enough to carry all this stuff across the ocean and the fuel to get there with a reserve.

Oh, food, water , freezer, stores, stove, heating....

And we need low center of gravity, stability and everything needs to take jump 5 feet in air.

 

Yes Frosty, the question is what ultimately makes a blue water boat, explicitly? In my original question I was curious to know if a more solid vessel ultimately makes a Blue Water Boat? Is it ultimately the strength of the vessel? Is it a bobbing vessel that can withstand tumbling in the seas and being dropped 15 feet or 50 and stay intact? Worse case seniors at sea, physically? ?If I construct a huge indestructible 20-inch thick carbon fiber airtight barrel with tons of water and food, is this blue water?. Forgive the ignorance but I would think a sinking vessel is pretty dramatic and probably lethal far at sea without help. One should and can plan how to conserve water and food reasonably. Not knowing if the boat will crack up is a little bit more out of your control I would think. (I saw a program on the Discovery channel of rouge waves being real). I?m all for science and I cannot even begin to express the value of which I have stumbled across here hence absorbing as much form the apparent and extremely experienced. Anyway, most beer is 90% water.