Lithe or Large - displacement by the numbers

[caveman22]

My wife and I are planning to go water sailing">blue water sailing in around 4 years after kids finish school. Expect to take in low latitudes and stay out for as long as we enjoy it. We both have multi hull experience including ocean racing.

Looking at recent crop of cats circa 45- 50 foot which should be available 2nd hand round that time. I know we will be cruising and its not all about speed but seems to me light wind performance (10-15 knots) is an issue, at least for me.

I crew on a light (7200kg) 48 Atlantic cat that has had a number of performance upgrades. She will slide along at close to True wind speed even in light airs. This boat is probably too flighty to take around the world 2 up but an interesting reference point.

So running some numbers to get at least a sense of likely boat characteristics. The question is can the published displacement figures be trusted ? Are they light displacement, loaded displacement or just fantasy ?

I was at a weigh in for a number of cats before an ocean race and the variance from manufacturers specification was huge. The boats had reasonable amount of gear on and half tanks but several were over 50% heavier than manufacturers quoted displacement number.

Table below of some cats and their numbers sourced from a well know magazine (apology for wonky table columns):

BOAT LEN (F) DISP (KG) Disp (KG) / foot
GFORCE 1500 50.7 5,500 109
SPIRITED 480 48.4 7,600 157
CATATHAI 50 50.0 8,000 160
O YACHTS CL 4 45.9 7,500 163
SLYDER 47 46.9 8,200 175
OUTREMER 45 44.9 8,700 194
OUTREMER 51 50.2 10,000 199
PRIVILEGE 4.5 44.1 8,900 202
PRIVILEGE 4.9 49.0 11,300 230
VISION 450 46.9 11,000 234
CATANA 47 46.0 10,900 237
BAVARIA NAUT
OPEN 46 45.0 10,800 240
ST FRANCIS 50 50.0 12,500 250
SABA 50 49.1 14,000 285
LAGOON 450 S 45.8 15,100 330
LEOPARD 48 48.4 17,000 351
LAGOON 52 S 52.0 26,030 501

Are the above displacements for real ? Are the Leopards and Lagoon really that piggy ?

Love to hear your real world comments ?

[StuM]

Yes and Yes.

[Factor]

The displacement for the G force is optimistic for a cruising boat, Chill Pill & Mojo weigh in at around that (and that is weighed on rated load cells for the measurement requirement with all safety gear and stuff) but they are very much racer cruisers rather than cruiser racers. There is a 16 meter G force that is supremely built for couples cruising, heaps of fridges , beautiful finishes etc and it weighs around 9 tonne, still sails beautifully. Outremer will contract to launch the boat at the quoted weight, so you can rely on them, some others - maybe not.

[cwjohm]

These numbers are typically unloaded or racing weight. Andrew gives a good example of the Kato (Gforce 1600) which has a loaded weight of 9 tonne but is more cruiser than racer. You quote a Gforce 1500 which is more racer than cruiser.

Also, as Andrew says Outremer will guarantee weights, but the problem is that once the boat leave the factory then many people load the boat up with their own gear.

Simple math easily demonstrates that BY RATIO if you load up a light boat it will have more of a performance effect than loading up a heavy boat.

By way of an example in racing trim you could pretty much predict performance of the boats you quote by looking at the numbers you quote, but once you load them up fully this is no longer the case.

Before Andrew jumps in of course the lighter boats will perform better but not IN RATIO to the numbers. i.e. A Gforce will not be twice as fast as and Outremer which will be twice as fast as a production boat. These performance gaps reduce as the loads are increased.

You need to look at the Atlantic 48 loaded as you race it and ask if you would be prepared to long term cruise on such an equipped boat, as load carrying capacity is a prime criteria for many cruisers (not all by any means as Andrew will point out).

[Factor]

Chris and I are not far apart, but having said that, Attitude (the boat I was talking about) will still do 15 knots in 20 true fully loaded including dive compressor etc. The reality is that when loaded a slowish boat will get slower, a faster boat will get slower, but it will still be faster than the slow boat. I really dont care about the ration, I care about how many miles you can knock over in a day, or during daylight hours etc.

Also if a privelige 4.5 is 9 tonne i will walk backwards to bourke. (nice boat - but not light) Same for the Catana 47 - plenty of porkies being told there

[barnakiel]

They may be the heaviest, but I would not call them piggy. Look up their real life crossing times and you may like what you find.

They may not be performance boats, but they ARE comfort boats. About 2x the comfort of any given mono ...

Cheers,
b.

[44'cruisingcat]

Of course, weight isn't the only factor at work. Power it up well enough and you can make a heavy boat sail well. You just need big enough rig/sails.


The real advantage of light boats is they can sail well with modest sized rigs and sails. They're much easier to handle.

[Jeannius]

Originally Posted by Factor

Also if a privelige 4.5 is 9 tonne i will walk backwards to bourke. (nice boat - but not light) Same for the Catana 47 - plenty of porkies being told there

Correct. My Priv 435 (same boat as 4.5, different name) was never less than 30,000 lb (13,600 kg) more often 32,000 lb when lifted out fully laden when cruising.

[caveman22]

Gents,

Thanks for your comments and points taken:
1. A loaded light boat will always be faster than a similarly loaded heavy boat,
2. Performance is more about light wind mileage rather than setting speed records and
3. the Privilege numbers do look like fantasy.

Assume all goes well our boat will be our floating home for a number of years and so a reasonable level of comfort will be important.

I note that a number of you are from OZ and unlike our European or US cousins we dont get a lot of these boats down under to kick the tyres so Im trying to get a sense of likely performance VS comfort to narrow the list.

I just cant imagine that a Lagoon or even a Leopold at 501 or 351 kg/foot respectively could offer reasonable light wind performance.

The Francis 50 looks to be very seaworthy and well built and not at the extreme end of the porky scale. The Nautitech Open 46 looks to be a reasonable sail on the numbers and the reviews of its little sister look encouraging. No dagger boards on either but both appear to be beachable which theoretically sounds handy.

The dagger boards make a huge difference to the Atlantic Cat I race on which has had the mini keeps removed. They provide both lift and pointing ability. Wonder if they are worth the risk in a cruising environment ? Yes we hit a reef with a daggerboard down doing 14 knots and it was not pretty. We managed to get the board up and strapped to continue the race but a proper repair was a mayor exercise that I dont think would be possible in a remote pacific location.

The Outremer 51 looks a sweet boat and would probably be my first choice if the pricing eases a bit over the next four years.

[Factor]

Originally Posted by caveman22

The Nautitech Open 46 looks to be a reasonable sail on the numbers and the reviews of its little sister look encouraging.

The open 40 in Brisbane gets comprehensively spanked in the Local WAGS racing, not just by race boats but by plenty of smaller cruising multis.

The Outremer 51 looks a sweet boat and would probably be my first choice if the pricing eases a bit over the next four years

Price won't be easing but if the dollar gets stronger that will help.

[tp12]

Originally Posted by cwjohm

These numbers are typically unloaded or racing weight. Andrew gives a good example of the Kato (Gforce 1600) which has a loaded weight of 9 tonne but is more cruiser than racer. You quote a Gforce 1500 which is more racer than cruiser.

Also, as Andrew says Outremer will guarantee weights, but the problem is that once the boat leave the factory then many people load the boat up with their own gear.

Simple math easily demonstrates that BY RATIO if you load up a light boat it will have more of a performance effect than loading up a heavy boat.

By way of an example in racing trim you could pretty much predict performance of the boats you quote by looking at the numbers you quote, but once you load them up fully this is no longer the case.

Before Andrew jumps in of course the lighter boats will perform better but not IN RATIO to the numbers. i.e. A Gforce will not be twice as fast as and Outremer which will be twice as fast as a production boat. These performance gaps reduce as the loads are increased.

You need to look at the Atlantic 48 loaded as you race it and ask if you would be prepared to long term cruise on such an equipped boat, as load carrying capacity is a prime criteria for many cruisers (not all by any means as Andrew will point out).

Kato is a G-Force 1800C - so the cruise variant of design and also 18m, not 16. So a 9T 60 footer and she gets along very well. Zero is a lighter build than that, also at 18m, and is quicker than Kato. Zero's design is called the 1800SSS and it's a lighter design and I *think* it's meant to be quicker than the standard G-Force designs. There's a 20m version being designed right now and I understand it's being designed as a light, quick boat too. As in, more oriented to the SSS rather than Cruise or standard variants.

The guy who built Kato has sold her and is building a new one with a different design focus. I think Zero's appearance may have had something to do with that.

If you want more payload the Arrow designs are worth a look. There's 12m, 13.6m and 15m versions of the design and they're designed to carry significantly more payload than the G-Force and G-ForceC designs. They're also quicker to build.

[44'cruisingcat]

Originally Posted by caveman22

The dagger boards make a huge difference to the Atlantic Cat I race on which has had the mini keeps removed. They provide both lift and pointing ability. Wonder if they are worth the risk in a cruising environment ? Yes we hit a reef with a daggerboard down doing 14 knots and it was not pretty. We managed to get the board up and strapped to continue the race but a proper repair was a mayor exercise that I dont think would be possible in a remote pacific location.

It's easy to make the bottom 1/2 metre or so of a daggerboard "sacrificial", ie a foam core with light glass over it, which will just break off in an impact, and can be easily replaced.

Consider hitting a reef at 14 knots with a minikeel...


Come to that, you were sailing to windward at 14 knots? Don't you know cat's can't do that?

[44'cruisingcat]

The thing about weight is it feeds on itself.


On heavy boats the loads are higher, which calls for heavier construction, bigger engines, bigger fuel tanks, bigger rigs and sails, which generate higher loads....

[Symphony]

For the lighter cats, are there considerations for trim between hulls? Such as balancing
dive compressor, appliance and freezers, laundry machines, air conditioner compressor and pump, Battery bank.

[SVNeko]

Originally Posted by 44'cruisingcat

Of course, weight isn't the only factor at work. Power it up well enough and you can make a heavy boat sail well. You just need big enough rig/sails.


The real advantage of light boats is they can sail well with modest sized rigs and sails. They're much easier to handle.

Exactly. That's why you see many new performance cats with just scary big rigs. They have wider hulls for the stuff buyers want so have to have giant rigs to keep performance up.