Sailboat calculations

[geem]

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 Unless someone’s spent serious money recently, every last system will be out of date, the sails will be knackered and the bog won’t work.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.

Any boat over 10 years old could be described like that. An old boat can easily be kept up to date. One that has been refurbished recently can easily be in far better condition than say a 15 year old boat with all original equipment.
Our own boat is 42 years old but there is almost nothing left of the original systems. They have either been refurbished or replaced.
For example, at 32 years old, I refurbished all the Whitlock shaft steering. Stripped the gearboxes and replaced bearings, seals and re-shimmed the gears. 35,000nm later I am doing them again. They have been done twice in 42 years. The boat isn't a museum piece. It's a working machine putting in the miles. It needs systems maintaining and rebuilding as necessary before they let you down at sea.
I am on my second genoa and third mainsail in 10 years. Now both Vectran so hoping to get more miles out of them than plain Dacron.
The boat had a new engine on 2007. It's now got 2700 hrs. It may have an old hull but with new Awgrip and new system all we get is positive comments from people about the boat and how well she looks. My electronics are now 14 years old. We will be doing an upgrade in the next couple of years.

 

[Laminar Flow]

There is an enormous difference between ocean cruising, which is the equivalent of full time living aboard, and a ten day charter in the Med. For one, the load carrying capacity and the degree of autonomy required for ocean cruising is in a completely different category. Light displacement does not do well here and the smaller the boat, the greater the disadvantage will be. Not only will any perceived performance benefit quickly evaporate, but you will also be overloading structure and rig beyond their design envelope.

I'm sorry, but the ARC, or indeed any West - East Atlantic crossing on the tradewind route is hardly the litmus test for seaworthiness or offshore ability. A downwind run in predominantly benign conditions. It has been done in any type of craft; barrels and kayaks included.

The really important numbers to look at are:

Displacement/length (D/L), it indicates the upper limits of speed performance and anything over 150 is not likely to plane in any kind of normal weather conditions.

SA/D: In simple terms: the power to weight ratio of any particular boat. Sail area used should be the entire SA the boat carries to windward, not just fore triangle. The reason the latter is predominantly used today, is because beamy, modern designs have a much wider shroud base to reduce compression loads on the rig and save weight aloft; this severely limits the sheeting angle for overlapping head sails and thus they cannot really be effectively carried to weather.
It should be noted, that when comparing two similar boats with the same SA/D ratio, one light and one heavy, the heavier one will be faster in light airs. They will both reach their respective (theoretical) hull speeds at the same time. Beyond this, the lighter boat has the performance advantage. In all practical terms, a heavy boat need not be slow.
In this context it might be noted, that displacement figures given by manufacturers are most often for a completely empty boat, without crew, and even then the numbers are frequently aspirational at best.

Ballast ratio: on it's own doesn't tell you much, if anything.
Beam has a much greater influence on (initial) stability than ballast or displacement.

Brewer's comfort ratio recognizes that high accelerations in a seaway lead to crew discomfort, seasickness and difficulty living on board. Wide beam and a large waterline plane, combined with light displacement, promote such higher acceleration. Heavy displacement on a smaller waterline plane dampens the motion and reduces acceleration.

 

[geem]

There is an enormous difference between ocean cruising, which is the equivalent of full time living aboard, and a ten day charter in the Med. For one, the load carrying capacity and the degree of autonomy required for ocean cruising is in a completely different category. Light displacement does not do well here and the smaller the boat, the greater the disadvantage will be. Not only will any perceived performance benefit quickly evaporate, but you will also be overloading structure and rig beyond their design envelope.

I'm sorry, but the ARC, or indeed any West - East Atlantic crossing on the tradewind route is hardly the litmus test for seaworthiness or offshore ability. A downwind run in predominantly benign conditions. It has been done in any type of craft; barrels and kayaks included.

The really important numbers to look at are:

Displacement/length (D/L), it indicates the upper limits of speed performance and anything over 150 is not likely to plane in any kind of normal weather conditions.

SA/D: In simple terms: the power to weight ratio of any particular boat. Sail area used should be the entire SA the boat carries to windward, not just fore triangle. The reason the latter is predominantly used today, is because beamy, modern designs have a much wider shroud base to reduce compression loads on the rig and save weight aloft; this severely limits the sheeting angle for overlapping head sails and thus they cannot really be effectively carried to weather.
It should be noted, that when comparing two similar boats with the same SA/D ratio, one light and one heavy, the heavier one will be faster in light airs. They will both reach their respective (theoretical) hull speeds at the same time. Beyond this, the lighter boat has the performance advantage. In all practical terms, a heavy boat need not be slow.
In this context it might be noted, that displacement figures given by manufacturers are most often for a completely empty boat, without crew, and even then the numbers are frequently aspirational at best.

Ballast ratio: on it's own doesn't tell you much, if anything.
Beam has a much greater influence on (initial) stability than ballast or displacement.

Brewer's comfort ratio recognizes that high accelerations in a seaway lead to crew discomfort, seasickness and difficulty living on board. Wide beam and a large waterline plane, combined with light displacement, promote such higher acceleration. Heavy displacement on a smaller waterline plane dampens the motion and reduces acceleration.

Brilliantly explained. I know all this from experience of sailing on a number of different boats but could not have explain it as well as you.
The one fact that always surprises me is how slow a modern lightly ballasted liveaboard boat becomes once all the worldly goods and creature comforts have been loaded aboard. We see so many yachts where you can't even see the antifouling paint. You just see green slime on the white hull. Alternatively the water line has been repainted 4 to 6 inches higher.

We were in Bonaire in the ABCs recently and we saw such a boat. A Bavaria 49. There was no sign of the bottom paint. They had a truly massive set of monkey bars to mount the huge solar array and their centre console rib. On deck in front of the mast were two huge chests full of gear and in front of the sprayhood was a massive petrol dive compressor. That lot did nothing for the centre of gravity, to say nothing of their forward visibility. They also lost their mast crossing the Atlantic. I wonder how much the overloaded boat contributed to the demise of the rigging?

 

[Tranona]

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

Nothing unusual about those stories Most people have some regrets about their purchase because no boat (in this case) is perfect). How about the things they liked about their boats - must be something otherwise why buy it in the first place. Suspect that those who say they would prefer a heavier boat probably knew that beforehand. If you want a 57' boat and want "weight" and quality then you have to pay 60-80% more than the Hanse to get you into an HR, Amel, Oyster etc. Same with a Bavaria - sure it is a caravan compared with more up market boats - that is why it is so modestly priced and does exactly what buyers expect as you can see from the Patrick Laine videos as well as Michael Jambo. I had the same decision to make when I bought my last Bavaria - heart said I should indulge (I had the money) in an HR310 but I just could not bring myself to spend £170k compared with the £100k for the Bavaria. 85% of the boat for 60% of the price. Splendid "value" did the job well apart from the bounciness in lumpy conditions but virtually trouble free for the 6 years I owned and sold it for not a lot less than I paid.

Of course your friends will tell you that they would prefer a heavier boat, after all they were talking to you! but will they act on their beliefs or explain why they did not buy a heavier boat in the first place. After all the choice was there.

 

[Roberto]

What is "ocean sailing" for you? Going round the world endless times, preferably around the Capes, hardly stopping anywhere, time spent at anchor insignificant, etc; or the odd transat either way and then mostly cruising in local areas, perhaps a few day sails with decent forecasts?
In both cases you might really wish you had bought a totally different boat for the same "ocean sailing"

 

[geem]

Nothing unusual about those stories Most people have some regrets about their purchase because no boat (in this case) is perfect). How about the things they liked about their boats - must be something otherwise why buy it in the first place. Suspect that those who say they would prefer a heavier boat probably knew that beforehand. If you want a 57' boat and want "weight" and quality then you have to pay 60-80% more than the Hanse to get you into an HR, Amel, Oyster etc. Same with a Bavaria - sure it is a caravan compared with more up market boats - that is why it is so modestly priced and does exactly what buyers expect as you can see from the Patrick Laine videos as well as Michael Jambo. I had the same decision to make when I bought my last Bavaria - heart said I should indulge (I had the money) in an HR310 but I just could not bring myself to spend £170k compared with the £100k for the Bavaria. 85% of the boat for 60% of the price. Splendid "value" did the job well apart from the bounciness in lumpy conditions but virtually trouble free for the 6 years I owned and sold it for not a lot less than I paid.

Of course your friends will tell you that they would prefer a heavier boat, after all they were talking to you! but will they act on their beliefs or explain why they did not buy a heavier boat in the first place. After all the choice was there.

You miss the point. They are doing similar sailing to us. That is where you lightweight boat is not at it's best. Now they know different.
My Belgium friends sold their lightweight boat. Now looking for a heavier cruising boat with .more load carrying capacity.
Our Dutch friends with the Ben 393 are also looking for a heavier boat. Not my influence. It's their experience

 

[geem]

What is "ocean sailing" for you? Going round the world endless times, preferably around the Capes, hardly stopping anywhere, time spent at anchor insignificant, etc; or the odd transat either way and then mostly cruising in local areas, perhaps a few day sails with decent forecasts?
In both cases you might really wish you had bought a totally different boat for the same "ocean sailing"

Absolutely not. No Capes for us. Most of our sailing is at anchor. Super comfortable boat. Doesn't roll when others do. Plenty of space for two and a couple of guests. All mods cons you would see in any modern 44 ft boat. We can take any weather and sail in comfort. It our idea of the perfect boat but we wouldn't expect others to agree. One man's meat is anothers poison. Find the boat that is perfect for you with the way YOU use it. Don't rely on others to tell you that a certain boat is perfectly good to cross oceans unless that the boat they use to cross oceans. Arm chair sailors never conquered an ocean

 

[baart]

It should be noted, that when comparing two similar boats with the same SA/D ratio, one light and one heavy, the heavier one will be faster in light airs. They will both reach their respective (theoretical) hull speeds at the same time.

Could you say a bit more about this ? I am not sure if I understand why heavier one would be faster?

 

[Laminar Flow]

Yes that is correct. The two main forms of resistance are frictional and form resistance. They do not increase at the same rate.
At slow speeds frictional resistance is predominant. It rises gradually and pretty linearly as speed increases.

Form resistance, on the other hand, rises exponentially, particularly at relative speeds over 1 (square root DWL x 1).

Form resistance is invariably linked to displacement. Frictional resistance depends on the surface area of the hull and surface area does not increase at the same rate as form resistance with increased displacement.

Therefore, for a heavy boat to reach hull speed at the same time as a lighter vessel, it needs more SA. Consequently, at low, relative speeds, the heavy boat has an abundance of power to overcome the slightly increased frictional resistance.



The reason lighter boats are faster at higher speeds is because their form resistance has a shallower curve.
At lower speeds the combined resistance curves for light and heavy boats are markedly similar.


This graph shows resistance curves for both a light and a heavy boat, relative speeds are in Froude #, a Froude # of 0.4 is the equivalent of 1.34 or nominal hull speed.

 

[Tranona]

You miss the point. They are doing similar sailing to us. That is where you lightweight boat is not at it's best. Now they know different.
My Belgium friends sold their lightweight boat. Now looking for a heavier cruising boat with .more load carrying capacity.
Our Dutch friends with the Ben 393 are also looking for a heavier boat. Not my influence. It's their experience

No I am not missing the point. They made the decision to buy their boats in the knowledge of the sort of sailing they intended. They may well have found that certain aspects turn out not as they expected (although I doubt it). In conversation with you, a believer in a different kind of boat I have no doubt they will focus on that aspect of their boats performance. Equally I have no doubt that in other conversations with different people they will be extolling the virtues of their boats - something like how good the built in barbeque is, how convenient it is to step off the hydraulic drop down platform into the Rib, how much space there is in the freezer, the neat installation of the washing machine, the constant supply of coffee from the machine, fresh bread every morning from the bread maker. That is why they spent £650k (or whatever it was) on their boat rather than buying an older more seakindly boat such as the Rival 38 for pocket money.

You more than anybody knows that ocean liveaboard cruising is maybe 80% stationary, 20% moving and of that 20% maybe 5% of it is uncomfortable weather - that is out of a time aboard for one year, uncomfortable weather may account for 1% or less than 4 days. Challenge for you - go over your logs for the time you have been cruising and see how close I am. Your post#27 suggests I will probably have overestimated .

That is why people buy big Hanse, Lagoon cats, big Bavarias and so on for their ocean adventures. It is really very little different from coastal cruising, short intense passages under sail followed by long periods doing nothing but enjoying your good fortune. Good planning means they avoid bad weather as much as possible. If ocean cruising was the obstacle course that some paint it as - off into the unknown worrying about whether your rig will fall down or you will be capsized by big seas etc few, least of all the couples that can afford it would sign up. Sure it was a bit like that 50 or 60 years ago when boats like the Rival were king, but it ain't now. I know there are people who do go off sailing like that, taking what comes and using a boat that is suitable for it, but that is not now typical and for them there is plenty of choice of old cheap boats like the Rival or my Golden Hind. However they soon discover that they are really not cheap - only the entry fee is low, the cost of bringing them up to standard is high but still a fraction of what a new build would be.

 

[geem]

No I am not missing the point. They made the decision to buy their boats in the knowledge of the sort of sailing they intended. They may well have found that certain aspects turn out not as they expected (although I doubt it). In conversation with you, a believer in a different kind of boat I have no doubt they will focus on that aspect of their boats performance. Equally I have no doubt that in other conversations with different people they will be extolling the virtues of their boats - something like how good the built in barbeque is, how convenient it is to step off the hydraulic drop down platform into the Rib, how much space there is in the freezer, the neat installation of the washing machine, the constant supply of coffee from the machine, fresh bread every morning from the bread maker. That is why they spent £650k (or whatever it was) on their boat rather than buying an older more seakindly boat such as the Rival 38 for pocket money.

You more than anybody knows that ocean liveaboard cruising is maybe 80% stationary, 20% moving and of that 20% maybe 5% of it is uncomfortable weather - that is out of a time aboard for one year, uncomfortable weather may account for 1% or less than 4 days. Challenge for you - go over your logs for the time you have been cruising and see how close I am. Your post#27 suggests I will probably have overestimated .

That is why people buy big Hanse, Lagoon cats, big Bavarias and so on for their ocean adventures. It is really very little different from coastal cruising, short intense passages under sail followed by long periods doing nothing but enjoying your good fortune. Good planning means they avoid bad weather as much as possible. If ocean cruising was the obstacle course that some paint it as - off into the unknown worrying about whether your rig will fall down or you will be capsized by big seas etc few, least of all the couples that can afford it would sign up. Sure it was a bit like that 50 or 60 years ago when boats like the Rival were king, but it ain't now. I know there are people who do go off sailing like that, taking what comes and using a boat that is suitable for it, but that is not now typical and for them there is plenty of choice of old cheap boats like the Rival or my Golden Hind. However they soon discover that they are really not cheap - only the entry fee is low, the cost of bringing them up to standard is high but still a fraction of what a new build would be.

That's a very confused post. You make it sound as though I recommend a Rival 38 over a modern £650k boat?
You don't have to buy a wreck of a boat. Boat are available in all conditions. Some of the best are those that have done lots of ocean sailing. The for sale section on the OCC website has some great boats for sale, already set up for liveaboard.


Why don't you stop telling us what ocean sailing is about. Go and try it then lecture from a place of experience.
I think of our experience as that of long term liveaboard.
We see lots of Rivals where people are cruising long term on a budget. Never seen a Golden Hind other than in the UK.

 

[Concerto]

Sure it was a bit like that 50 or 60 years ago when boats like the Rival were king, but it ain't now. I know there are people who do go off sailing like that, taking what comes and using a boat that is suitable for it, but that is not now typical and for them there is plenty of choice of old cheap boats like the Rival or my Golden Hind. However they soon discover that they are really not cheap - only the entry fee is low, the cost of bringing them up to standard is high but still a fraction of what a new build would be.

I know you loved your Bavarias for all the mod cons they provided at a keen price for the sailing you did. However, you do seem to have flipped on your choice of a Golden Hind, it is almost everything exactly opposite to what you have been preaching.

You and I have tussled in the past on the difference between modern and older boats, but I do respect your extensive knowledge on many boats and equipment. I certainly agree it costs a lot of time and money to make an older boat into a more modern standard of equipment. My Fulmar has cost a lot more to get it to the standard she is in now, than she cost to buy. It still only works out at a fraction of the cost of a new boat of a similar (if there is such a thing) size boat. You saw her at last years boat show and complimented me on how good she looked for her age, may be you realised I had not been talking total rubbish because you shortly afterwards bought the Golden Hind. Since the show I have done some other major upgrades to make living aboard much better including pressurised hot and cold water along with a shower, converted the original cool box to a fridge and having to change the electrical switch panel to accomodate extra switches (and get rid of fuses).

Most boats do have specific user profiles, driven by the chartering market, and too many of the modern designs are created arround being basically a floating caravan that only is used in light winds and when the sun is shining. For their owners this is just what they need and are happy with their boats. The trip round Britain I am currently doing is far different from that. It has been high winds, cold and wet, with long hops between ports, something I am glad the Fulmar seems to relish. Chatting with many other owners in these higher regions of our country, the modern boats are certainly less favoured. There are a surprising number who prefer steel yachts over GRP, a material that rarely gets mentioned in these forum discussions on yacht design. One couple I met in Stromness had a steel boat and they searched extensively to find the right one, eventually buying their secondhand one from Spain due to the limited number on the market. They live aboard almost permanently and prefer to anchor, they are able to produce enough electrical power through solar and wind, not to need shore power at all.

Over the decades I have been sailing I certainly have learnt what makes a good hull shape for a sea kindly boat. My boat certainly meets those needs and feels comfortable in rough weather, in a marina or at anchor (without the slap of waves under the transom). It was interesting at the boat show how many potential buyers at the show expressed a dislike for the modern "Ikea" type of yacht. These were all very experienced sailors, looking for something that just is not built any more. The way forward can only be to refurbish these older craft, and also save a lot of money in the process. Probably get the completed boat is less time than ordering a new one today with delivery in 2 to 3 years time with an unknown amount of guaranteed prices increases built into the contract. Yes it will be an older boat, but will be in demand for years to come by sailors who know what they want out of a yacht.

 

[Roberto]

our idea of the perfect boat but we wouldn't expect others to agree.

That's what I was referring to while asking the the OP what he considers "ocean sailing".
Fast back and forth ocean crossings with expert groups of sailor friends? JPK38
Ocean crossing then stop for weeks/months at an anchorage? Catamaran
Ocean crossings North/south Arctic to Antarctic and vice versa? Boreal 45
Ocean crossings on a tight budget? Google "Baluchon"
Ocean sailing for an elderly couple? Plenty to choose from
Ocean sailing/milk run for a family? (Almost) any AWB would do.
etc etc
There are always better boat options for a specific moment/activity, rather than start hunting for the "perfect ocean sailing yacht" one should delve into him/herself to find what he she really wants to do, the specific boat type will appear by herself

 

[geem]

That's what I was referring to while asking the the OP what he considers "ocean sailing".
Fast back and forth ocean crossings with expert groups of sailor friends? JPK38
Ocean crossing then stop for weeks/months at an anchorage? Catamaran
Ocean crossings North/south Arctic to Antarctic and vice versa? Boreal 45
Ocean crossings on a tight budget? Google "Baluchon"
Ocean sailing for an elderly couple? Plenty to choose from
Ocean sailing/milk run for a family? (Almost) any AWB would do.
etc etc
There are always better boat options for a specific moment/activity, rather than start hunting for the "perfect ocean sailing yacht" one should delve into him/herself to find what he she really wants to do, the specific boat type will appear by herself

Maybe. Did you watch this. Lightweight Pogo type of boat. Very little onboard
. He says how disappointed he is with performance. Puts it down to too much weight onboard. He is single handed with small fuel and water tank and some tools. Reckons he is 100kg over loaded. About the same as another person plus an overnight bag.
Guys we met sailed a large Pogo across the pond as a family. Very disappointed in his performance. Reality, these boats don't take weight. Load them up for an Ocean passage with more than one person and some tools and you can expect similar performance to a similar sized cruising boat. Take it a step further. Load up a modern production sailing boat for the same trip and an older design that had load carrying as part of its original spec just might do ok?

 

[Roberto]

Maybe. Did you watch this. Lightweight Pogo type of boat. Very little onboard
. He says how disappointed he is with performance. Puts it down to too much weight onboard. He is single handed with small fuel and water tank and some tools. Reckons he is 100kg over loaded. About the same as another person plus an overnight bag.
Guys we met sailed a large Pogo across the pond as a family. Very disappointed in his performance. Reality, these boats don't take weight. Load them up for an Ocean passage with more than one person and some tools and you can expect similar performance to a similar sized cruising boat. Take it a step further. Load up a modern production sailing boat for the same trip and an older design that had load carrying as part of its original spec just might do ok?

Good example of an uninformed decision, indeed one cannot load those boats. I know the Pogo interior designer, he sails a 1050 with friends (ok just to Azores and the like) they all limit their personal equipment to the size of an aircraft hand luggage, add a box of essential tools and off they go. Apart from performance, loading a light boat more worryingly decreases all design safety factors (rigging, hull scantlings, etc).
If one wants to sail fast on a monohull with all sorts of comfort, there is no substitute for size, the Dashew Beowulf and similar models etc are a good example of full comfort fast cruising American style (air conditioning etc etc) for a couple with the occasional couple of friends, sizes flirt with 18-20m. Loading a Pogo is like expecting regular double digit speed figures on a medium size HR, wrong choice.

 

[LittleSister]

Caprice, anyone?

 

[baart]

The discussion might have slightly deviated from my original question, in an interesting direction though. I like how my boat handles overall but being quite narrow (2.9m) in comparison to moder designs and with a lot of sail she gets overpowered quite quickly but is quite fast as well. So either I need more crew which I don't have or less sail. In F5 with full sails (135% genoa) and going close hauled the heel angle would be above 40 degrees. So not a very comfortable or efficient way of sailing. It still feels safe just not very entertaining for majority of the people.

But then for some reason D. Thomas decided to build her like that. In force 7 with 3rd reef in the main and a fraction of the jib she was still going but it was very exhausting physically definitely not something I would entertain for more than a few hours. Don't have fourth reef in the main and it felt I could do with one plus a storm jib, it was very gusty though. At the same time in 35knt of wind, broad reach no main, with slightly reefed genoa, she was very pleasant. The roll was manageble and predictable.

I am trying to understand then if I wanted to get a boat that would be more gentle to the crew in simmilar conditions still being reasonably fast do I aim for wider or heavier boat or what do I look for in the calculations?

 

[Fr J Hackett]

You need what I heard described as a 20 :20 boat

20 degrees of heel in 20 knots of wind forward of the beam wit all plain sail. Lots of traditional boats will achieve that

 

[baart]

You need what I heard described as a 20 :20 boat

Ok, that's a good start. which calculation then would tell me if the boat has this ability?

 

[geem]

You need what I heard described as a 20 :20 boat

20 degrees of heel in 20 knots of wind forward of the beam wit all plain sail. Lots of traditional boats will achieve that

In my head, that's an under canvassed boat. How's that same boat going to perform in a F3 to windward when there in no more plain sail to put up?
I would rather have sail area that can be reefed.
Any boat going to windward in F5 upwards is going to get knocked about. It's one of those things that you grin and bare rather than enjoy on long passages