The Ideal Cruiser - a long range passagemaker

[Vega]

Originally Posted by Eric W. Sponberg

I should point out that Bagatelle is a daysailer and weekender and not meant for ocean cruising. However, if its dimensions were expanded to a bigger boat that would have the carrying capacity for an ocean voyage, then it would work. Of course, it would be more boat to handle in heavier conditions.
…..
I am struck by the similarities of Vega's design above to my Globetrotter 45 which was discussed at the beginning of the thread. The general flavor is the same, but Vega's has a cutter rig and a conventional transom. I firmly believe in the desireability of the features in the Globetrotter 45, and I think the whole design makes loads of sense for a long-range passagemaker.

Eric

Well Eric, that means that in what concerns long-range passagemakers we think along the same lines, and of course, I agree with you about the “Globetrotter”, even if I would prefer the conventional rig (more simple to repair if something goes wrong).

The reason I prefer a conventional transom is also an aesthetical one and because it also permits some more space on deck. But it is a more costly and less practical solution.

However, for me a beautiful boat is a must, and given the difficulty of obtaining that in a 45/47ft deck-saloon/pilothouse , and also maximize space for the Doghouse and space for the open cockpit, I will stick to a conventional transom.

I will not resist to post some drawings of the boat I am working in now (kind of a passagemaker “Bagatelle”).

I would prefer this boat over the one I have redesigned some months ago. It has a lot more of interior space, it is an overall better sailing boat, it can explore a lot of places not available to deep draft boats and with an AVS that probably will exceed 140º it will be a safer boat even if more uncomfortable in a seaway (we can’t have everything, can we?).

As Jacques Mertens says:

“The seaworthiness may come as a surprise to beginners or to those who have never sailed a shallow draft boat but experienced seamen know that the shallow draft boat is more seaworthy than a hull with a deep keel.
Unlike the deep boat, a centerboarder will not resist the sea. Instead of tripping on it's keel, it will dodge the waves or lift over them. Properly designed, a keel centerboarder will have the same ultimate stability than a boat with a conventional keel. …
But there is more to it than safety at sea. In case of real bad weather like a hurricane, a shallow draft boat can take refuge deep inland or in very protected coves inaccessible to deep boats. The centerboarder can, with only a small tide, be beached for repairs or to clean and paint the bottom. It can go on anchor where nobody else can and save on marina fees. “

http://www.amateurboatbuilding.com/a...sign/VG25.html

I believe that it is also for these reasons that the “traditional” French long range cruisers are aluminium boats of this kind, even if they have a lower AVS than this one, boats like the Ovni, Alliage, Allures, Garcia, etc..

Of course this does not mean that the Globetrotter (or the boat that I have redesigned) are not great passagemakers, it means only that there are several ways to look at the problem and different possible compromises and trade-offs.

There are some criteria that have to be met, but besides that, the way to go depends on the sailor priorities.

By the way, I loved the “stories” in your website.

Paulo

[Eric Sponberg]

Vega,

Thanks for the compliments, and absolutely, boat's are designed to sailor's priorities, and that is why we have so many solutions to a single question.

I do not necessarily agree with Jacques Mertens comments regarding a shallow centerboarder over a deep keel keel boat in heavy seas. I encourage everyone to read C.A. Marchaj's "Seaworthiness, the Forgotten Factor" for a lucid discussion of how hullform affects seaworthiness. Shallow draft and, particularly, wide beam encourage a boat to ride parallel to the wave face in heavy waves and thereby be prone to capsize simply because the waves flip the boat over--no keel tripping involved. Whereas a narrower boat with a deep keel will tend to ride much more upright in the waves and is much more difficult to capsize.

I agree with Mertens regarding the advantages of shallow draft and gunkholing.

Eric

[Vega]

Originally Posted by Eric W. Sponberg

Vega,

Shallow draft and, particularly, wide beam encourage a boat to ride parallel to the wave face in heavy waves and thereby be prone to capsize simply because the waves flip the boat over--no keel tripping involved. Whereas a narrower boat with a deep keel will tend to ride much more upright in the waves and is much more difficult to capsize.

Eric

Eric,
I agree with you that a boat with a wider beam and lesser ballast will ride more parallel to the wave than a narrow boat, reeling more on ballast than on hull form, but in my opinion that has more to do with comfort than with safety.

But I will disagree that this is of primordial importance to capsize the boat. Studies show that steep waves don’t capsize modern boats, breaking waves are what matter.

And of primordial importance are the dynamics, regarding stability. I mean what happens when 20 T of water crash on the side of the boat and push it sideways. If the boat has a large underwater keel, it is going to resist to a fast lateral displacement and it is going to trip on the keel and the 20T of force are going to produce a rotating movement.

In a boat without keel, but with a big interior ballast, the lateral push is going to be transformed in a fast lateral displacement and capsizing can be avoided (with luck).

Eric, I used to think like you (that’s why the boat that I have previously designed has “the same flavor” as the “Globetrotter”) and I know that there are not easy or complete answers about this, and there are a lot of other factors to be considered.

As Michael Kasten says : “If there is one absolute truth in all of this, it is that with regard to seakindliness and seaworthiness there are no absolutes, only tendencies. As a result, we may attempt to apply generalities to the problem. However generalities are necessarily prone to oversimplification, therefore they will nearly always be misleading if applied too broadly.... or too blindly...”

http://www.kastenmarine.com/beam_vs_ballast.htm

But a lot of very experienced sailors have testified about this effect. One of them is Mertens (that is also an experienced sailor) another is Eric Tabarly, one of the greatest sailors of the last century that in one of his books explains that effect with these pictures, comparing the effect in a boat with a long keel and in a boat with a narrow keel:

http://i19.photobucket.com/albums/b1...Penduick1a.jpg
http://i19.photobucket.com/albums/b1.../penduick1.jpg

Other experienced sailors have testified about this, even on this forum:

Originally Posted by Ilan Voyager

The "Deriveur integral" (inner ballast with daggerboard(s)) is in my opinion a better solution. You separate the problems of center of gravity and center of lateral resistance. You simplifly the study of the the foil(s).
That give sailboats with very gentle movements and very stable as you can adjust the surface of the center or daggerboard while sailing.

I've sailed on both kind of sailboats ( of similar size and weigth) and there is no match the deriveur is superior.

Against the common feeling the deriveur is very safe in rough weather and breaking seas. There is a proven record (on more than 30 years) of safety as these boats are used for long range travels and many have been in Artic and Antartic waters.

There are inconvenients; the ballast takes interior espace as does the case of the foil. It needs also more maintenance.

So, I guess that we should discuss this further when Jeff finally creates that Stability forum.

Fact is that you can find a lot of contradictory statements about stability made by responsible designers, specialized journalists and very experienced sailors.
The least studied and more controversial issues seem to be dynamic stability, roll moment of inertia and their importance to seaworthiness.

Jeff, what about that forum?

Paulo

[Eric Sponberg]

Hi Everyone,

I have posted new rendered images of my Globetrotter 45 on my website

http://www.sponbergyachtdesign.com/Globetrotter45.htm

and post a few of the images here. These show some details, and what it looks like sailing on the wind and off the wind.

Eric

[marshmat]

She's lookin' nice, Eric, real nice.
I'm looking forward to the day when the rating rules would allow such a boat to go head-to-head in competition against something with a more conventional rig. That could prove really interesting. Granted, the Globetrotter doesn't look like she's built for absolute maximum speed, but I'd be curious to see how she fares against more traditional designs of similar size and type.

[Guillermo]

Nice boat, Eric.
I loved this from your site:
"...Some of the features I would like on my next boat include a pilot house, an aft cockpit, and an aft cabin. When my wife, Arliss, and I were sailing Duprass, our Bianca 27, from England to California, we discovered we sorely missed not having a pilot house, such as we had seen on other cruising boats. It keeps cool and inclement weather off your back, especially during night watches, as well as the hot sun out of your eyes and off your head during the day. And on long voyages, you really do need inside steering in addition to normal outside steering."

Would it be possible to post the following: Hull draught, Cp, AVS, heeling arm, wetted surface and STIX?
I'd greatly appreciate that.
Also to know the GZ curves would be very interesting.

A final question: Will not be somewhat dangerous the big scoopy stern in a following sea?
All the best.

[yipster]

Eric, definitly a serious candidate for the best cruiser competition
i'm with Guilermo on the stern, sloping open steps perhaps or why?

had my say in this thread on advantages of multi's and now
like to ad a sketch of my idea of a trotting motor sailing cat

aft hinged A frame mast with planty sailplan possibility's
davids lift a small car in the hull, tender in the other
glued alu spaceframe, epoxy, airex, it can be done!

[westlawn5554X]

Nice Eric, I have found a hull with your special tandem twin keel, I was wonder which boat you put that in.

Is the GLobal 45 older design but now with a new add and rendering?

Thanks

[Eric Sponberg]

From Guillermo and Yipster:

Would it be possible to post the following: Hull draught, Cp, AVS, heeling arm, wetted surface and STIX?
I'd greatly appreciate that.
Also to know the GZ curves would be very interesting.

A final question: Will not be somewhat dangerous the big scoopy stern in a following sea?

Hull (canoe body) draft to the displacement shown (30,100 lbs) is 1.95' = 0.594 M.
Cp for hull with keel = 0.5144
Cp for canoe body only = 0.6025
AVS = 137 deg.
Heeling arm (Hce + Hlr) = 32.029' = 9.762 M
Wetted surface to displacement shown and including rudder = 562.037 sq.ft. = 52.209 sq.M.
STIX = 52.276

I estimate that the angle of downflooding would be 105 deg. which is the point at which the cockpit locker lids might start to seep water.

As for the stern, the platform itself is pitched down and aft slightly, and the volume contained in the whole aft end of the boat (foot steps are closed completely--no joints) is tremendous. The buoyancy would keep the stern high in most following seas. The cockpit coamings are high all around so the cockpit is well protected and there would be big drains from the cockpit to the swim platform. The area of the transom is no greater than portions of the area of the hull forward. And in following seas you are running with the waves so the relative speed between the boat and the waves is less than the bow sees going into the waves. Impact against the transom would be less than impact against the bow.

See below for righting arm curve.

From Marshmat:

A boat like the Globetrotter 45 could race PHRF against anyone else. All that it takes is someone with the money and interest to build one!!

From Westlawn5554X:

I don't know which hull you are referring to that would have a twin keel design from me. Can you please specifiy?

The Globetrotter 45 is my idea for an ideal ocean-going cruiser for myself. This design was originally laid out in 2004, and I would like to find a customer to build one. Construction is possible in fiberglass, wood-epoxy, or aluminum.

Eric

[westlawn5554X]

I may have seen the article wrongly but the picture might help as I have read is maybe one of your design Eric and I really forgotten the website. Dont feel offended ok. Cheers

[Eric Sponberg]

Westlawn,

Yes, those are bilge keels for the Moloka'i Strait 65, a 65' trawler motoryacht, not a sailboat. They actually turned out more problematic than they were worth--made the boat turn when it was not supposed to turn--so we deleted them from the design. Live and learn.

Eric

[Guillermo]

Thanks for the data, Eric.
Very nice GZ curve, with only an small amount of energy needed to upright the boat after a turtle turn.

I'm trying to compare 'old' parameters against STIX and its meaning. What is Bwl, please ? Displacement stated in your site is Mmsc or full load?
Also, if possible, may I know Cfl?
Thanks a lot in advance.

[Eric Sponberg]

Guillermo,

Bwl is 13.203' (4.024 M) at the design waterline (draft 6' 6", 2.016 M). The displacement stated at 30,100 lbs, which occurs 3" (75 mm) below the DWL. would be the MSC, although I have not yet run through a detailed weight estimate on this design yet, only estimates. The maximum displacement would be at the Dwl and is 36,640 lbs (16,620 Kgs).

What do you mean by Cfl? Is that Center of Flotation (Buoyancy?) in your terminology? If so, it is 1.006' (307 mm) below the waterline (at 30,100 lbs displ.). If that is not what you want to know, let me know.

Eric

[marshmat]

Another note on Globetrotter's GZ curve there.... I noticed on your website ( http://www.sponbergyachtdesign.com/Globetrotter45.htm ) you mention that her carbon masts would be hollow and sealed. Does the GZ curve you posted account for this extra buoyancy? (Either way, it'd prolly be awfully hard to get her to stay inverted for long, but I'm curious as to just how much a difference the light hollow masts make.)

[Guillermo]

Thanks, Eric.
Cfl is the coefficient of floatation (Area/LxB), sorry for the misunderstanding.
May I have Hce and Hlr separately? (I'm considering 8.76 and 1 resp.)

I attach here the corrected STIX spreadsheet posted before by SailDesign somewhere else, as it had a minor error when calculating Vaw (didn't work when flooding angles were bigger than 90)