Sail area/Displacement #s

[JustMurph]

Yep. That is, if it's an apples to apples comparison with similar DLR and SA/D.

There really are a huge number of variables that all play in, as Tupaia says. But DLR, SA/D and LWL are where you start.

As an example, people have been a bit disappointed the performance of the HH44. This is because they swallowed the marketing material and didn't look at the numbers. It performs exactly as you'd expect for a boat of its LWL, displacement and SA. A 9.5 ton, 44' boat will simply never be that fast, no matter how good the naval architecture is or how many times you write performance in the brochure.

The caveat here is that this is in ideal conditions on a reach. The "base speed" calc gives a good indication of downwind, milk run, ocean crossing performance. None of them tell you how well the boat will do VMG upwind!

[Wpg3ut]

Yep that marketing for the HH's is something. Practically sells itself I've heard!
Thank you for the detail and insight, extremely helpful. You read so much about performance and the delta between "performance vs production" and I do believe that delta is substantial but there is just so much hyperbole in all the marketing, etc. So it is a gift to get to gather firsthand information from sailors on this forum. Priceless really. Thanks again for the insight! Currently deep diving into the Nautitech 46 open and the Outremers.

[Tin Tin]

The "Base speed" above is the formula

Base Speed = 1.7*(Lwl^0.5)*(SA^0.352)/((Disp*2240)^0.253). Using Ft, Sq ft and Tons.

Supposedly to represent 24 hours in racing conditions. It is used to handicap multihulls apparently. It is highly dependent on what displacement number is used as manufacturers "Light Ship" is nothing like what the boat actually displaces with any sort of load. So when I use this formula I used the lightship and then the gross max (per manufacturers specs) so there are two numbers - no load and full load. The answer for a live aboard cruiser would be full load and the part time weekender with a bare boat around light ship + 2T approx + - a Ton

[Wpg3ut]

Thanks TinTin, So instead of having 2 baselines for the boat could you use the mean of the the high and low displacement #s and have a somewhat accurate idea of disp/LWL # ?

[JustMurph]

I do similar tintin. I run my numbers for a light ship weight and a cruising weight.

Probably another thing worth mentioning here, is the numbers you use for sail area. The "proper" way is to use the main plus the 100% foretriangle area, but I really don't agree with that. Use the number for the actual upwind sail are the boat uses. The difference between a small self tacker and a 110%+ genoa is significant.

[Tupaia]

Originally Posted by Wpg3ut

Thank you for the detail and insight, extremely helpful. You read so much about performance and the delta between "performance vs production" and I do believe that delta is substantial but there is just so much hyperbole in all the marketing, etc.


Currently deep diving into the Nautitech 46 open and the Outremers.

Another thing to be aware of is that "production" boats, performance or otherwise have to have a level of internal finish that appeals at boat-shows. This is most easily achieved using linings of various sorts all of which add significant weight. An out and out racer will have no such linings at all. A compromise has to be reached on a "performance" boat the older Outremers were regarded as being very primitive internally the newer ones and the Nautitech's have much more luxurious interiors by comparison and are consequently heavier as a result.


It is very very expensive to achieve a lightweight yet acceptable interior that very few production boats succeed in achieving. Compare for example a Dazcat 1495 (15m) empty weight 7700kg with a Nautitech 46 (14m) empty weight 10800kg , 1m sorter and 40% heavier.

[Tin Tin]

Originally Posted by Wpg3ut

Thanks TinTin, So instead of having 2 baselines for the boat could you use the mean of the the high and low displacement #s and have a somewhat accurate idea of disp/LWL # ?

Of course. However in the early example of the Leopard 46 and Outremer 51 the LS and GS of the Leopard was approx 10T and 17 T so you would pick 13.5T. However the loads for the O51 were 10T and 13.7 so the middle would be 11.85. The thing is cruising full time on an O51 with only 1.85T of gear on board would mean a tiny dinghy and outboard , a small anchor, no spare anchor, no guests, no washing machine or water maker, small freezer, small battery bank etc etc etc - you would have a much more comfortable slower paced life on the Leopard with 3.5T and if you wanted to splurge go to 7T. Of course an O51 could be loaded past the 13.7 but then it will slow down somewhat as the fine hulls sink much further into the water increasing wetted surface as a % vs the Leopard. So my suggestion is to draw up a list of equipment you would like to have on your boat + people and their gear and toys and provisions, add that to lightship of the boats you are looking at and see what the number is.

[sw34]

Originally Posted by JustMurph

I do similar tintin. I run my numbers for a light ship weight and a cruising weight.

Probably another thing worth mentioning here, is the numbers you use for sail area. The "proper" way is to use the main plus the 100% foretriangle area, but I really don't agree with that. Use the number for the actual upwind sail are the boat uses. The difference between a small self tacker and a 110%+ genoa is significant.

But that is why SA is supposed to be 100% foretriangle and not random sails, so you compare apples to apples and not with oranges. The numbers are already fake as the inputs generally come from marketing material and not actual builds/engineering plans, no reason to add even more fake data.

Either way OP, try chartering any one of these or all that your interested in. There was still a Nautitech 46 Open chartering in the BVI, but not sure when its phase out is. There are a couple of Nautitech Open 44's and 40's and tons of Leopard 42 and 45's.

Chartering multiple boats, plus doing a demo sail on a "performance" cat helped seal the deal that we wanted to stick with performance and give up some creature comforts while spending about 20-30% more!

[JustMurph]

Originally Posted by sw34

But that is why SA is supposed to be 100% foretriangle and not random sails, so you compare apples to apples and not with oranges. The numbers are already fake as the inputs generally come from marketing material and not actual builds/engineering plans, no reason to add even more fake data.

My point is to not use random sails (or an imaginary number), but use the actual numbers for the actual boats you're comparing. Comparing configurations that don't exist on the real boats is not apples and apples.

[Wpg3ut]

Thanks for the info Tupuai.

[Wpg3ut]

Thank you SW, what did you end up going with?

[barnakiel]

Leopard is heavy. Outremer (new) is medium-heavy (=lighter than Leopard).


Probably someone messed up the calc.


b.

[Tin Tin]

Originally Posted by sw34

But that is why SA is supposed to be 100% foretriangle and not random sails, so you compare apples to apples and not with oranges. The numbers are already fake as the inputs generally come from marketing material and not actual builds/engineering plans, no reason to add even more fake data.

Either way OP, try chartering any one of these or all that your interested in. There was still a Nautitech 46 Open chartering in the BVI, but not sure when its phase out is. There are a couple of Nautitech Open 44's and 40's and tons of Leopard 42 and 45's.

Chartering multiple boats, plus doing a demo sail on a "performance" cat helped seal the deal that we wanted to stick with performance and give up some creature comforts while spending about 20-30% more!

Yes, what boat did you get?