Sailboat calculations

[baart]

Looking at my boat's performance (30ft, 3.3t displacement) I have been trying to understand whether I can tell how a different boat would behave in similar conditions based on the numbers I can see on Sailboat data. So for example my boat's calculations :

S.A./Disp.:19.81
Bal./Disp.:43.30
Disp./Len.:234.00
Comfort Ratio:22.46
Capsize Screening Formula:1.91

If compared to Bavaria 40 Cruiser -
S.A./Disp.:18.88
Bal./Disp.:35.96
Disp./Len.:169.07
Comfort Ratio:23.67
Capsize Screening Formula:2.01

or Benateau 50 -
S.A./Disp.:17.62
Bal./Disp.:32.50
Disp./Len.:136.55
Comfort Ratio:26.35
Capsize Screening Formula:1.92

it seems that theoretically my boat should be more stable at least based on Bal./Disp i Disp./Len. I appreciate though that beam and weight play a part as well. I would think that for crossing the ocean Bavaria or Benateau should be way more comfortable than the difference in comfort ratio would suggest? But maybe not?

So what I am trying to undestand is whether my subjective experience from my boat can tell me what to expect on a different boat based on those figures. Or if I am looking for improvement in performance in certain areas what should I look for in those calculations?

Can anyone help?

 

[Chiara’s slave]

Our SA/Disp. Ratio comes out at 39. Today, in 15 kn of true wind we managed 9kn at 40 degrees true, and 16kn at 70 degrees true. Lwl is 28.5 ft. Comfortable? We didnt get wet, but you wouldnt want to open a bottle of champagne afterwards, it would go everywhere. Not sure if that is educational. We have no ambitions to cross oceans. We are at anchor currently, and have a virtual badminton court with the boom as a net. I think your gut is as good as the calculations, you can tell mostly by looking. Don’t over think/calculate, except as an academic excercise.

 

[Concerto]

They are only really just numbers. You just cannot compare a 30ft yacht's handling with a 50ft yacht. It is a bit like the crash safety results for cars. You cannot compare a small car with a large car, there are too many differences between them. Personally I would be happier in a larger car than a small box.

If you compare your 30ft yacht to other similar sized yachts you will certainly see some differences, but ultimately there has been a huge evolution in yacht design over the past 60 years making it is difficult to compare 50 year old boats with 10 year old boats, as the former rely on the ballast ratio and the latter on form stability.

 

[baart]

Ok, so how do I compare a modern design to the heavy boats from the past? Let's say I want to buy a bigger boat to cross oceans (not yet ) How something like for example Rival 41 ( if we can consider it an older design) would compare to the likes of Benateau and similar modern designs? Or at what point the heavy boat outperforms modern shapes and vice versa? Looking at the boats participating in ARC modern designs seem to dominate but I guess it will be very different when it comes to rounding Cape Horn. It would seem then that for an average cruiser a heavy displacement boat may not be necessary and a lighter newer design should do the job. So when would a heavy boat be justified?

 

[Tranona]

These figures need to be treated with care as they are often not comparable because they are based on data that is drawn from different sources and calculated by different methods. The best example is SA. Nowadays this is calculated usually as foretriangle area plus main but many boats (like yours I suspect) have large overlapping genoas and small mains and the sail area quoted is for the overlapping genoa. Your SA/Disp is high - the sort of figure that would indicate a performance boat, but your ballast ratio is high reflecting perhaps a narrow beam and relatively shallow heavily ballasted keel. Your L/Disp suggests medium displacement In other words a typical 80's cruising boat of that size with an IOR influenced foresail orientated rig.

"Comfort Ratio" is a Ted Brewer invention which attempts to capture comfort at sea. Ballast ratio and beam are big factors - narrow beam good, high ballast ratio good so not surprising that a light displacement low ballast ratio (because stability is derived from beam and greater draft and lower placement of ballast) of the other 2 you quoted result is the same comfort ratio and stability whereas you would expect a bigger boat to be more comfortable. In fact what it is telling us is that your smaller boat will be less lively (greater ballast, deeper canoe hull, narrower beam) but not necessarily more "comfortable" overall than the bigger, faster boats.

Many people going offshore prefer boats with stats like yours because they believe they are more comfortable "in a blow" - with some justification. However that does not mean that they are better cruising boats particularly when assessed against how people use their boats. "In a blow" conditions represent a tiny fraction of cruising time - as little as zero if you take care and a boat of the Bavaria/Beneteau style wins hands down in lighter conditions, at anchor/in a marina and in terms of domestic comfort.

Not surprising therefore that (almost) nobody makes boats with ratios like yours these days - even though thousands are in use with satisfied owners. Such boats exist because that is what most people can afford to buy (secondhand) and what is available, but those with the money mostly make different choices.

I have just sold a modern boat - smaller (33') version of you second examples with SA/D of 15, Ballast ratio 29%, Displ/L 209 comfort ratio 24.5, Capsize formula 1.99, for an old style 31' of roughly same displacement with SA/disp 14, Ballast ratio 36% Displ/L 270 comfort ratio 34, Capsize formula 1.6. The first is a reasonably lively boat, great in light airs did not like windward work in a sea, but was fantastic to live on with a spacious saloon 2 double cabins, huge head with shower, big cockpit and could be sailed easily by one person because of the all furling high aspect ratio fractional rig. Its replacement is narrow gutted, heavy, cramped, slow and ponderous, but in its day was probably the most popular small ocean voyaging boat on the market with over 40 transatlantics in the 1970s/80s and several circumnavigations. Can be bought for peanuts these days because that is not what people want out of a boat now.

As Concerto says things have moved on and while the sailboat type stats are useful for comparing boats of a similar type they are less useful comparing across boats designed to different principles. Things have moved on enormously in the last 30 years and boats are now designed based on different principles to the past.

 

[Tranona]

Ok, so how do I compare a modern design to the heavy boats from the past? Let's say I want to buy a bigger boat to cross oceans (not yet ) How something like for example Rival 41 ( if we can consider it an older design) would compare to the likes of Benateau and similar modern designs? Or at what point the heavy boat outperforms modern shapes and vice versa? Looking at the boats participating in ARC modern designs seem to dominate but I guess it will be very different when it comes to rounding Cape Horn. It would seem then that for an average cruiser a heavy displacement boat may not be necessary and a lighter newer design should do the job. So when would a heavy boat be justified?

This crossed with my more complete explanation. The answer to your question is if you like a Rival 41 then buy one. It will take you round the world, but so will an Ovni and you could not imagine 2 more different boats. The Rival was the epitome of what was considered the right sort of boat in the 1970s but nobody would buy a new one today. While some builders developed the Rival type design philosophy, particularly the Scandinavians over the last 20 years they have all moved away. Lots of reasons, not least because it has been shown comprehensively that you do not need a heavy narrow gutted boat for successful ocean voyaging, partly because technology and forecasting means unexpected heavy weather is a thing of the past and partly because of peoples' expectations of what comfort means has changed. Cruising is also now more about the destination than the journey and typically 80% of a world cruise is spent at anchor or in a marina. The sailing is the bit in between.

Another thing to consider is passage times, or more accurately daily runs. A Rival might make 130 miles a day (5,5 knots), a Bavaria 40, 150+ in similar offwind conditions - 15% greater. Yes, the Rival would likely be better going round Cape Horn if that is what you want to do, but it is a fact that several Bavarias have done that having been bought by Australians ex charter in the med and sailed home (to be sold at a profit!).

The reality is that older heavy displacement boats still have their advocates primarily because over the years our press and folk stories have built them up to a level of veneration and they are now available to people of modest means. However the people who had money to buy them new 40 or 50 years ago would now buy something completely different.

 

[baart]

Ok, that makes more sense now, thank you. I am not sure what the next step will be for us and at the moment what we have is sufficient. Although she requires reefing very early plus I struggle a bit with headroom, she is fast and goes upwind really well. Would I want to do a 3 day passage on her? Probably not. A few weeks ago we chartered a Dufour 360 in Croatia, felt more comfortable in waves, obviously better accommodation but lacked power and upwind ability in comparison. The amount of space was impressive though. So like you say cruising-wise way better. I used Rival as an example as read in many places that it is a go-anywhere type of a boat. It seems though I would be unlikely to use its true potential but would miss the modern cruisers' comforts. So if we ever decide to buy something different, which calculations etc. should we look into to assess the comfort and stability of modern boats?

 

[Tranona]

Stability is no problem. Although old salts go on about it, the reality is you are unlikely ever to get anywhere near having to worry about ultimate stability. As to comfort the Brewer ratio is as good as any but it is like any other composite measure it tends to reflect the weighting and choice of variables and Ted designed medium displacement narrower beamed, longish shallow keeled slack bilged boats which give a high comfort ratio. They do tend to be more comfortable in a seaway, but as I suggested that does not necessarily mean they are the only style of boat for cruising.

As you can see from the ARC and the dozens of yuotube cruisers people choose a wide variety of boats, but it is a truism that the boat is less important than the people in it and success in cruising is more to do with preparation and the crew's ability than the boat.

This is I think a good example of just choosing a boat and going for it. Perfectly ordinary middle of the road modern cruiser and look what he does with it. mjambo.de

One thing I have learned over the years is that Europeans, having been spared the diet of Hiscocks etc and the adoration of the long keel heavy displacement brigade of the post war years do not have the same hangups when choosing their boats. We forget that the early long distance cruisers chose those boats because that is what was available, Designers like Angus Primrose and Michael Dufour showed how a different approach worked better but many still hang on to the old ideas.

 

[baart]

That is a very thorough explanation. Thank you

 

[geem]

These figures need to be treated with care as they are often not comparable because they are based on data that is drawn from different sources and calculated by different methods. The best example is SA. Nowadays this is calculated usually as foretriangle area plus main but many boats (like yours I suspect) have large overlapping genoas and small mains and the sail area quoted is for the overlapping genoa. Your SA/Disp is high - the sort of figure that would indicate a performance boat, but your ballast ratio is high reflecting perhaps a narrow beam and relatively shallow heavily ballasted keel. Your L/Disp suggests medium displacement In other words a typical 80's cruising boat of that size with an IOR influenced foresail orientated rig.

"Comfort Ratio" is a Ted Brewer invention which attempts to capture comfort at sea. Ballast ratio and beam are big factors - narrow beam good, high ballast ratio good so not surprising that a light displacement low ballast ratio (because stability is derived from beam and greater draft and lower placement of ballast) of the other 2 you quoted result is the same comfort ratio and stability whereas you would expect a bigger boat to be more comfortable. In fact what it is telling us is that your smaller boat will be less lively (greater ballast, deeper canoe hull, narrower beam) but not necessarily more "comfortable" overall than the bigger, faster boats.

Many people going offshore prefer boats with stats like yours because they believe they are more comfortable "in a blow" - with some justification. However that does not mean that they are better cruising boats particularly when assessed against how people use their boats. "In a blow" conditions represent a tiny fraction of cruising time - as little as zero if you take care and a boat of the Bavaria/Beneteau style wins hands down in lighter conditions, at anchor/in a marina and in terms of domestic comfort.

Not surprising therefore that (almost) nobody makes boats with ratios like yours these days - even though thousands are in use with satisfied owners. Such boats exist because that is what most people can afford to buy (secondhand) and what is available, but those with the money mostly make different choices.

I have just sold a modern boat - smaller (33') version of you second examples with SA/D of 15, Ballast ratio 29%, Displ/L 209 comfort ratio 24.5, Capsize formula 1.99, for an old style 31' of roughly same displacement with SA/disp 14, Ballast ratio 36% Displ/L 270 comfort ratio 34, Capsize formula 1.6. The first is a reasonably lively boat, great in light airs did not like windward work in a sea, but was fantastic to live on with a spacious saloon 2 double cabins, huge head with shower, big cockpit and could be sailed easily by one person because of the all furling high aspect ratio fractional rig. Its replacement is narrow gutted, heavy, cramped, slow and ponderous, but in its day was probably the most popular small ocean voyaging boat on the market with over 40 transatlantics in the 1970s/80s and several circumnavigations. Can be bought for peanuts these days because that is not what people want out of a boat now.

As Concerto says things have moved on and while the sailboat type stats are useful for comparing boats of a similar type they are less useful comparing across boats designed to different principles. Things have moved on enormously in the last 30 years and boats are now designed based on different principles to the past.

You may recall the last ARC crossing of the Atlantic. A large Hanse had catastrophic steering failure. Guys we know on a Oyster 55 rescued them. The crew off the Hanse apparently remarked how much more comfortable the Oyster was than the Hanse even though the Hanse was slightly bigger. Hull shape makes a lot if difference to comfort. The two boats were built for different markets. One is a med boat the other is built for ocean sailing in comfort

 

[Tranona]

You may recall the last ARC crossing of the Atlantic. A large Hanse had catastrophic steering failure. Guys we know on a Oyster 55 rescued them. The crew off the Hanse apparently remarked how much more comfortable the Oyster was than the Hanse even though the Hanse was slightly bigger. Hull shape makes a lot if difference to comfort. The two boats were built for different markets. One is a med boat the other is built for ocean sailing in comfort

So, what is new? Their primary market is indeed different, but so is the price. Does not stop a lot of people buying Hanses and their like for ocean cruising aware of the compromises. No different from me fancying a car like a Jaguar FPace for long distance travel across Europe, but have been quite happy with a diesel Ford Focus for the job. Not as comfortable or as fast but gave no problems in the 90000 miles I had it for at roughly 40% of the price. If it had broken down and I had been rescued by a Jaguar I would have stroked the owners ego by complimenting him on his choice of car.

 

[geem]

So, what is new? Their primary market is indeed different, but so is the price. Does not stop a lot of people buying Hanses and their like for ocean cruising aware of the compromises. No different from me fancying a car like a Jaguar FPace for long distance travel across Europe, but have been quite happy with a diesel Ford Focus for the job. Not as comfortable or as fast but gave no problems in the 90000 miles I had it for at roughly 40% of the price. If it had broken down and I had been rescued by a Jaguar I would have stroked the owners ego by complimenting him on his choice of car.

The steering failed catastrophically on the Hanse? need I say more
You don't speak from experience having never sailed long distance but you are quite happy to quote 'others'. Armchair sailing springs to mind. How many of the Hanse owners might have wished they had bought an Oyster

 

[Tranona]

The steering failed catastrophically on the Hanse? need I say more
You don't speak from experience having never sailed long distance but you are quite happy to quote 'others'. Armchair sailing springs to mind. How many of the Hanse owners might have wished they had bought an Oyster

Steering breaks and not just on Hanses. Of course you have more experience then me - but are very fond of quoting others' experiences if they are negative as if they are typical and inevitable because of the boat they chose but seem incapable of seeing all those who do not have negative experiences in exactly the same types of boats.

Can't wait for you to tell everybody about the lovely people you met who are chuffed to bits with their Bavaria 40 which has taken them all round the world - but of course you would probably never talk to such people.

 

[geem]

Steering breaks and not just on Hanses. Of course you have more experience then me - but are very fond of quoting others' experiences if they are negative as if they are typical and inevitable because of the boat they chose but seem incapable of seeing all those who do not have negative experiences in exactly the same types of boats.

Can't wait for you to tell everybody about the lovely people you met who are chuffed to bits with their Bavaria 40 which has taken them all round the world - but of course you would probably never talk to such people.

Why would I never talk to such people? We have friends in the Caribbean with Bav46 that he calls the caravan. A good friend has a Hanse 575. Another good friend with a Jen 45 DS.
I also have a friend with a Grand Sol that he took across the Atlantic. He says it's too lightly built for ocean sailing. He said he could smell burning GRP as the inner and outer moulding ground together as the boat flexed so much. He wants to swap for a heavier more comfortable design.
The friends with the Jen had it from new. They shipped it across the pond to the Caribbean. They are scathing about the quality of the boat. Lots of bits falling off including all the pilothouse windows.
Our friends with a Ben 39 want a heavier boat. They say it's too bouncy for ocean sailing.
You will find few people want to talk about the bad purchases they made. It's natural human behaviour. Nobody likes to tell how they cocked up

 

[baart]

So thinking about youtubers - let's take Patrick Laine - I think he had Bavaria 40 previously and it seems to have served him well and the trips he did were clearly on the more advanced end of ofshore cruising, Not sure why he sold it though? The Bongo 870 he has now feels like a massive step down in comfort yet he still managed to go across and back. I know people have crossed atlantic in smaller boats so it is relative to an extent. But what to look for then if thinking of a boat that would allow a family/friends enjoy a 3-4 day passage offshore without the feeling of it being to bouncy/lively yet still offering quality accomodation - modern/light or older/heavy ?

 

[baart]

This is a good example I think. How different would it be in a heavy displacement boat like Rival ?

 

[geem]

This is a good example I think. How different would it be in a heavy displacement boat like Rival ?

We met a delivery skipper in the Azores in 2005. They were delivering a 60ft yacht to Europe. We spent quite a lot of time with him and his crew. Stokie had done 250,000nm as delivery skipper and we were out celebrating with him. I asked him what was the best small boat he had sailed across an ocean. His answer was a Rival 38

 

[baart]

This is really interesting, especially when you can get Rival 38 with some serious cruising history for £35k - Rival 38A for sale UK, Rival boats for sale, Rival used boat sales, Rival Sailing Yachts For Sale Rival 38A - Apollo Duck

 

[geem]

This is really interesting, especially when you can get Rival 38 with some serious cruising history for £35k - Rival 38A for sale UK, Rival boats for sale, Rival used boat sales, Rival Sailing Yachts For Sale Rival 38A - Apollo Duck

It's one guys opinion, albeit based on massive experience of sailing every kind of yacht. I find the cockpit a little cramped and the high bridge deck a pain. The cockpit is not a great space for entertaining. The motion is excellent and they track well. Accommodation is pretty nice. Set up with twin furlers I think they make a great short handed sailing yacht that will take you anywhere. Like every boat they are a compromise. If you spend your time in the Med hopping from harbour to harbour there are probably more suitable boats but if you want to sail over the horizon and keep going.....

 

[Chiara’s slave]

It’s a lot of money for a 45 year old boat. Unless someone’s spent serious money recently, every last system will be out of date, the sails will be knackered and the bog won’t work. It’s the way with older boats.