Following Seas and Cockpit Height

[tp12]

Let me rephrase my post ...

You're talking about whether the manufacturer claims the boat is light displacement and whether 10t over 40 feet is light displacement. But compared to what? Compared to other multi's? No, it isn't.

[Sailing55]

Originally Posted by tp12

According to the designers ...

Light displacement refers to the boat being empty, nothing else. The lightest that boat will ever weigh, according to the manufacturer. I'd wager that it would actually weigh more. The heavy displacement is at it's maximum loaded capacity. As determined by the designers.

You're confusing two separate things here. A 40 foot catamaran weighing over 10t (and that's 'manufacturer claimed' remember) is not a light catamaran.

Thanks for being civil...much appreciated. But I just cannot see how those numbers do not equate to anything but light displacement. When the boat is loaded it in effect becomes a heavy displacement boat, but as designed it is considered, even by the builders and designers, as a light displacement boat. [referring to the Lagoon 400]

Any way, thanks again for being agreeable.

[Sailing55]

Originally Posted by tp12

Let me rephrase my post ...

You're talking about whether the manufacturer claims the boat is light displacement and whether 10t over 40 feet is light displacement. But compared to what? Compared to other multi's? No, it isn't.

I think in an odd sort of way we actually agree. Let's just say that I have understood multi's in general could be considered to be light displacement boats, even if you feel that 10T is heavy for a multi?

I feel that the numbers and ratios are just a way to compare boats and get an idea how they would handle and what the motion would be like. How a given boat would be able to carry stores and what the effect of the added weight would be.

[tp12]

I see my edit was too slow!

I guess people are getting short with you because a number of people are telling you the same thing and getting no traction with you.

In any case, IMO you need to treat the claims from Lagoon as marketing and the pinch of salt that goes along with that. I think you also need to understand that you're getting advice from experienced people in the multi world who understand what is a light boat and what isn't a light boat - sans marketing bumpf.

What we're really interested in is how light is the boat. That is a comparative metric and needs to be compared to like. Cats to cats etc ... Off the top of my head 44c's boat is around the 5t mark and is 44' .... is a cat weighing over 10t and 4' shorter a light boat? No, by a long way and hence my comment about a boat of that weight being a light boat would need to be big ... probably 50'-55' actually.

[tp12]

Originally Posted by morven55

I think in an odd sort of way we actually agree. Let's just say that I have understood multi's in general could be considered to be light displacement boats, even if you feel that 10T is heavy for a multi?

I feel that the numbers and ratios are just a way to compare boats and get an idea how they would handle and what the motion would be like. How a given boat would be able to carry stores and what the effect of the added weight would be.

Not all boats are equal and therefore not able to be compared in the manner you're suggesting. At least not meaningfully. You're not going to get an understanding of motion, payload etc the way you're going about it.

My telling you that a 40' cat over 10t is heavy isn't my feeling, it's based on comparison to other multi's.

If you want to understand the motion, you're going to have to get on one because there's an awful lot more to it than D/L. Same goes for payload as every manufacturer goes about things in different ways. For that you need to look at the specs for each boat.

[44'cruisingcat]

Originally Posted by morven55

Ballast is irrelevant. If a cat or a mono hull has a D/L in the 150 to 200 range it is a LIGHT DISPLACEMENT boat.

You're wrong. Simple as that.

You can't simply dismiss ballast as irrelevant. It usually represents around 40% of a monohull's displacement. Versus ZERO for a multihull.

My boat's D/L comes in at around 70. (44' LWL, 13,400 lbs)

It's a performance cruiser. THAT'S a lightish displacement multihull. There are plenty that are lighter.

A cat in the 150-200 range is NOT a light displacement multihull. In fact it's a heavy one.


A lot of the "traditional" calculations for mono's simply don't apply or work for multihulls.


Hull speed, comfort ratios, righting moments etc - they're all done differently on multi's.

[StuM]

Originally Posted by 44'cruisingcat

You're wrong. Simple as that.

You can't simply dismiss ballast as irrelevant. It usually represents around 40% of a monohull's displacement. Versus ZERO for a multihull.

My boat's D/L comes in at around 70. (44' LWL, 13,400 lbs)

It's a performance cruiser. THAT'S a lightish displacement multihull. There are plenty that are lighter.

A cat in the 150-200 range is NOT a light displacement multihull. In fact it's a heavy one.

A lot of the "traditional" calculations for mono's simply don't apply or work for multihulls.

Yep my cat's D/Ls are 116 lightship and about 144 in cruising mode.

According to all the monohull D/L guides that makes me a "very light ocean racer" even in cruising trim. (And approaching "ultralight" in lightship trim.)

I can only repeat, using the commonly accepted monohull D/L values/descriptors is not applicable to catamarans.

[Sailing55]

Originally Posted by StuM

Yep my cat's D/Ls are 116 lightship and about 144 in cruising mode.

According to all the monohull D/L guides that makes me a "very light ocean racer" even in cruising trim. (And approaching "ultralight" in lightship trim.)

I can only repeat, using the commonly accepted monohull D/L values/descriptors is not applicable to catamarans.

Nowhere can I find any reference that states monos and multis have different values for DLR. And I will go so far as to contact a Naval Architect that I have been acquainted with for many years.

If I prove myself to be wrong I will gladly admit it.

DLR's are for boats, not monos or multis. Your boat is considered to be light displacement by every standard I can find and I have researched a lot this evening. It may be heavy by multi standards but it is still a light displacement boat.

In all honesty I do not understand the controversy, but I will not stop until I have a definitive answer. And believe me I will let you know my conclusion.

[Sailing55]

Originally Posted by tp12

Not all boats are equal and therefore not able to be compared in the manner you're suggesting. At least not meaningfully. You're not going to get an understanding of motion, payload etc the way you're going about it.

My telling you that a 40' cat over 10t is heavy isn't my feeling, it's based on comparison to other multi's.

If you want to understand the motion, you're going to have to get on one because there's an awful lot more to it than D/L. Same goes for payload as every manufacturer goes about things in different ways. For that you need to look at the specs for each boat.

Not all boats are equal and that is the reason for non-dimensional ratios...a means of comparison.
I am comparing BOATS and you are comparing MULTIS...big difference.

[Sailing55]

Originally Posted by 44'cruisingcat

You're wrong. Simple as that.

You can't simply dismiss ballast as irrelevant. It usually represents around 40% of a monohull's displacement. Versus ZERO for a multihull.

My boat's D/L comes in at around 70. (44' LWL, 13,400 lbs)

It's a performance cruiser. THAT'S a lightish displacement multihull. There are plenty that are lighter.

A cat in the 150-200 range is NOT a light displacement multihull. In fact it's a heavy one.


A lot of the "traditional" calculations for mono's simply don't apply or work for multihulls.


Hull speed, comfort ratios, righting moments etc - they're all done differently on multi's.

For a Ballast/Displacement ratio, ballast is indeed relevant, but for a Displacement/Length ratio it is irrelevant. Remove the ballast and you have a boat with a BDR 40% less to use your example. Load a big cat with 5 tons of consumables and you now have a moderate to heavy displacement boat until such time as the stores are used up. The PPI [pounds per inch immersion factor] goes up drastically for a mono with that much of a load but much less for a cat of the same displacement.
A cat with a 150-200 BDR may well be heavy [for a cat] but it is still a light displacement BOAT.
The other ratios you reference are indeed different for a multi's...two hulls separated a great distance have a tremendous effect on righting moments, speed, etc.

[StuM]

> Nowhere can I find any reference that states monos and multis have different values for DLR

Of course not D/L is D/L regardless of the type of vessel.

Once again:

"I can only repeat, using the commonly accepted monohull D/L values/descriptors is not applicable to catamarans."

A 150 D/L monohull is only "light" compared to a median monohull.
A 150 D/L catamaran is "heavy" compared to a median catamaran.

Light/Heavy are comparative descriptors and type dependent. There is nothing absolute about those descriptors.

We who sail catamarans know what a light or heavy catamaran is. A "heavy" catamaran has a D/L ratio much lower than that of a "heavy" monohull.

[44'cruisingcat]

Originally Posted by morven55

Nowhere can I find any reference that states monos and multis have different values for DLR. And I will go so far as to contact a Naval Architect that I have been acquainted with for many years.

OK you win. I am cruising on an extreme racing boat.

[Factor]

Why does this continue to happen, people with no knowledge of multihulls make definitive and unequivocal statements that are frankly just wrong. An Oram 44C is a great, lightish comfortable quick cruising boat, extreme race boat it most certainly isn't.

Why does it happen, why do people feel the need to make these statements when they clearly do not know what they are talking about, why?

[tp12]

Originally Posted by morven55

Not all boats are equal and that is the reason for non-dimensional ratios...a means of comparison.
I am comparing BOATS and you are comparing MULTIS...big difference.

Yes, I know, and this is exactly where you are going wrong. You asked, you got the answer, but you don't like it and are acting all defiant about it.

I gave you the benefit of the doubt but you're being obtuse now.

Good luck with it but maybe stick with the monos.


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[Training Wheels]

It's always seemed to me that to be accurate, when comparing D/L ratios from monos to cats, the L for the cat should be for the total waterline length of both hulls, since the displacement is carried on 2 hulls.


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