40' Bluewater Cruiser Choice

[MJH]

I was in error on the Capsize Risk Ratio for the Cal 40. At 1.77 the Cal 40 is within the acceptable criteria of "less than 1.80".

~ ~ _/) ~ ~ Mike

[Adelie]

Originally Posted by MJH

I was in error on the Capsize Risk Ratio for the Cal 40. At 1.77 the Cal 40 is within the acceptable criteria of "less than 1.80".

~ ~ _/) ~ ~ Mike

Where did 1.80 come from as a cutoff, CCA used 2.0. Not arguing, less is better, but still curious?

[Likato]

I was using 2 as a cutoff - I was just looking at a Beneteau 45F5 (Farr design) - my heart says yes but....capsize ratio is 2.06....

[Likato]

There's a nice Cal 40 in CT but rigged for racing - road trips are for later - right now I'm looking at a "variety" of local boats including Tartan 40SD, Morgan 43, Jeanneau 42, Wauquiez Amphitrite 43....

[MJH]

Adelie,

I took my lead from an article written by John Holtrop for "Cruising World" magazine in their April 1998 issue entitle "Crunching Numbers For A Quality Cruiser". Visit his site at johnsboatstuff.com for a full explanation of his technique.

I found his approach interesting, educational and expanded the database fields and number of boats to suit my own search but preferred a pure comparison and less "Fuzzy Logic" as he calls it. I did use his criteria which for Capsize Risk which stated:

"CAPSIZE RISK = beam/(disp/(.9*64))^.333 A seaworthiness factor derived from the USYRU analysis of the 1979 FASTNET Race, funded by the Society of Navel Architects and Marine Engineers. Values less than 2 are good. The formula penalizes wide boats for their high inverted stability and light weight boats because of their violent response to large waves. All multi hulls, some modern coastal cruisers and many racing designs have problems meeting this criteria. Since safety is a very important feature in a cruising boat, I selected values less than 1.8 for full credit Anything over 2 scores zero."

I would recommend anyone seriously interested in buying a "cruising sailboat" to visit his site even if you disagree with his approach. I hope this helps.

~ ~ _/) ~ ~ Mike

[speedoo]

If you are willing to look at a center cockpit boat, the Kelly Peterson 44 would probably meet your needs, including a few 200 mile days. But I think you would be fortunate to get one at your $110k budget, ready to go.

[Adelie]

Originally Posted by MJH

Adelie,

I took my lead from an article written by John Holtrop for "Cruising World" magazine in their April 1998 issue entitle "Crunching Numbers For A Quality Cruiser". Visit his site at johnsboatstuff.com for a full explanation of his technique.

"CAPSIZE RISK = beam/(disp/(.9*64))^.333 A seaworthiness factor derived from the USYRU analysis of the 1979 FASTNET Race, funded by the Society of Navel Architects and Marine Engineers. Values less than 2 are good. The formula penalizes wide boats for their high inverted stability and light weight boats because of their violent response to large waves. All multi hulls, some modern coastal cruisers and many racing designs have problems meeting this criteria. Since safety is a very important feature in a cruising boat, I selected values less than 1.8 for full credit Anything over 2 scores zero."
~ ~ _/) ~ ~ Mike

I looked at Holtrop's page and found a page with the paragraph you cite, http://www.johnsboatstuff.com/Articles/estimati.htm.

I tried to get hold of the USYRU/SNAME report. The closest I got was 'Desirable and Undesirable characteristics of offshore yachts' by a CCA technical committee which I believe was also was involved in the research with SNAME and USYRU.

The formula cited there was CAPSIZE Screening Formula = beam/(disp/64)^.333 which differs from Holtrop's by the .9 multiplier on the seawater weight of 64 pcf. Using the .9 multiplier results in an easier formula to pass. It appears he modified the formula, or typo'd it and didn't proofread.

In his explaination he indicates beam is used in the formula because it penalizes boats with high inverted stability then later in the paragraph on the website he indicates it is because beam gives white water a longer lever arm to roll the boat. My reading of the CCA book indicates it is only there for the longer lever arm. Inverted stability is an important but separate issue.

I noted he made no mention of multihulls in the paragraph I found on his website. I assume you found the modified paragraph somewhere else on his site, I am too lazy to look further. In any case the screening formula does not apply to multihulls, the research was only done on mono-hulls so the conclusions can not be extended to them. In any case the basic assumption of using weight as a proxy for roll moment of inertia would fall apart because the weight in the amas is so separated that the roll interia in the mast makes up a lot less of the total (my guess would be 5-25%), verses a mono-hull where the mast can be almost half the roll inertia. Research on this topic is needed if it hasn't already been done.

Finally I noted his paragraph appears to be word for word the same as a paragraph in a 2007 post on this forum (http://www.cruisersforum.com/forums/f47/capsize-ratio-5964-2.html#post65060). I am curious as to which one plagerized the other, or if they both plagerized a 3rd party or if Holtrop is the 2007 poster. If the website is word for word from the 1998 article then the poster plagerized.

I haven't looked at much of the other info on his site but this would be enough to make me a little leary. If he can't get get basic things straight and clear, then how much should I trust his deeper conclusions based on those things?

[barnakiel]

And what is the capsize ratio of boats safely moored in the local marina?

All formulas are nice, still they are just formulas - nice to compare things or sort out the handful of boats that are simply a designer's failure to think (for boats NOT moored in the marina the process of sorting out is natural though).

Very easy to be lured into a 'good CR' boat and then load her up with all sort of cruising junk that will render the boat much less safe than the 'bad CR' boat not loaded up! Cruiser beware.

b.

[Bash]

Originally Posted by barnakiel

Very easy to be lured into a 'good CR' boat and then load her up with all sort of cruising junk that will render the boat much less safe than the 'bad CR' boat not loaded up! Cruiser beware.

+1 on that. I'll put more faith in waterline than "capsize ratio" any day.

[MJH]

Adelie,

Your catch of the formula mentioned in the introduction is noted. However, on visiting his web site and noting the Capsize Risk calculations of boats included there, the formula used was the correct one.

More importantly, I would encourage any prospective buyer of a cruising boat to do their own research which should include a comparison of available boat specifications and their resultant ratios. The task is not an end in itself but can only assist a buyer into making a knowledgeable decision, something I think many new buyers need help with particularly those planning to make an safe offshore passage. Most sailboat manufacturers have had to cater to the mainstream market to survive which has been predominantly charter and racing oriented. Cruising offshore raises the bar as to what is acceptable because the conditions can be more extreme.

~ ~ _/) ~ ~ Mike

[Adelie]

Originally Posted by MJH

Adelie,

Your catch of the formula mentioned in the introduction is noted. However, on visiting his web site and noting the Capsize Risk calculations of boats included there, the formula used was the correct one.

More importantly, I would encourage any prospective buyer of a cruising boat to do their own research which should include a comparison of available boat specifications and their resultant ratios. The task is not an end in itself but can only assist a buyer into making a knowledgeable decision, something I think many new buyers need help with particularly those planning to make an safe offshore passage. Most sailboat manufacturers have had to cater to the mainstream market to survive which has been predominantly charter and racing oriented. Cruising offshore raises the bar as to what is acceptable because the conditions can be more extreme.

~ ~ _/) ~ ~ Mike

I opened his spread sheet, the formula I saw there had the .9 in it.

Something that occured to me is that Holtrop is using the formula title Capsize Risk instead of Capsize Screen which is the CCA title. Maybe he is using the title and equation from the USYRU/SNAME paper and the CCA decided to tighten things up slightly and removed the .9 before publishing.

I sent him an email asking about the difference.

The issues with the formula aside, I agree wholeheartedly that a searchable database is a boon to boat buyers. Holtrop seems to have come up with a good start towards such a database, decent layout with lots of source info and lots of calculated info.

The one thing I worry about is the accuracy of some of the source info, specifically weights for displacement and ballast which are not readily measurable. I am researching boats to buy with my wife currently and know that there can be conflicting values from different sources. I have generally been seeing 2 values for Cal34 displacement which would be my first pick for a boat. I have found a 4th value this eveing for the Cal40, my wife's preference, plus Holtrop's value makes 5. I don't know how to resolve this for any database except maybe to average all available values or to declare a standard source like sailboatdata.com and tell people that source may not be accurate.

Once again, I agree with you that such a database is a boon to new boatbuyers and that at the very least Holtrop has a good start on one.

[MJH]

Adelie,

I ran into the same problem when I built my database. I would give the manufacturer "specifications" first choice whenever possible unless I discovered an obvious error but never trusted the ratios they provided. Boats that are out of production can be more difficult but I found that owner associations and racing association handicap listings valuable in locating "raw" data. Additionally, there are a couple of web sites (sail lofts I believe) that contain I, J, P, E measurements listings when you can't get them from the manufacturer; that is where I learned that some boats offered optional mast lengths and rigs (sloop, cutter, yawl) just as some offer optional keel designs (fin & shoal keels weights will differ). Taking these and other variables into consideration can become a mission, perhaps obsession, unto itself. Like Topsy, your database just grows and grows as you discover just one more variable that you must consider...but it was always educational.

~ ~ _/) ~ ~ Mike

[Dockhead]

Originally Posted by savoir

Until reading this thread I had never even heard of the Avance 40. It sure is similar to a Swan. If it is rigged like a Swan then there will be mountings for an inner forestay on both the mast and deck. Get some wire made up and fix a staysail furler to it.

True cutters are hard to come by so you may have to settle for a cutter rigged sloop.

I think the difference has become purely academic. "True cutters", in the sense of a boat with its mast further aft than a sloop and a really big set of headsails, with the foremost one on a long bowsprit, and probably gaff rigged, have not been made in decades, as far as I know. Modern "cutters" would probably be called "double-headed sloops", if we used our terminology according to the standards of 1935.

But we don't use our terminology that way unless we're showing off. When we say "cutter", we mean something which is just the same as a sloop, except that it has a staysail in addition to the regular headsail. And just maybe it has a high-cut jib called a "yankee", instead of a genoa (the primary headsail can be high cut because the staysail picks up the wind at deck level, making it easier to trim than a genoa). That's it; otherwise these days sloops and cutters are exactly the same.

Here a "true cutter": http://en.wikipedia.org/wiki/File:Li...Brest_2008.jpg

I don't think Beneteau makes any of these.

By the way, I don't think the phrase "cutter-rigged sloop" is correct according to classical terminology, either. If it's a sloop, how can it be cutter-rigged? It doesn't have a bowsprit, its mast is in the same place. It's got a big headsail to forward and a little staysail. The foremost headsail is carried on the forestay. It's just a sloop with a staysail; that doesn't make it a cutter or even "cutter-rigged", using the classical definition. I think the ordinary usage -- cutter for double-headed, single-masted sailboats, sloop for single-headed sailboats -- is fine, personally.

[Mule]

Howcome no one mentions the Pearsons, such as the 424? I saw one recently with in mast furling, new engine, new genset needing some cosmetics for around 75?

[MJH]

Dockhead,

The differences between a true sloop design and a true cutter design are significant enough that a buyer should be certain as to what they are getting.

When I was doing my boat search Pacific Seacraft offered a number of their boats (true cutter designs) as either a sloop, cutter or even a yawl. I asked them if they moved the mast forward for the sloop version and they said that the mast location was the same for all. That is cost effective for manufacturing but not what designer Bill Crealock originally had in mind. Other things being equal, a true sloop will generally sail closer to the wind than a cutter because the mast is further forward. The tradeoff with the cutter are the smaller dual forward sails made possible by the mast being further aft. Someone buying a single forward sail rigged cutter design will not be buying what the designer initially intended and it will not perform as a true sloop would have. The hybrid, a true sloop design with a removeable inner stay for bad weather, offers the best mix of both rigs...but it will never be a cutter and should not be called one.

~ ~ _/) ~ ~ Mike