Bruce Number Calculator

Matthew_Lingley · April 18, 2004, 3:59pm

<blockquote id=“quote”>quote:<hr height=“1” noshade id=“quote”>Originally posted by Dick Lemke

Not sure I can beat Matt with his big-roached MultiONE, however. His BN are too high
<hr height=“1” noshade id=“quote”></blockquote id=“quote”>

He He, I’ll give you a run, it thrashed a fullsize Contender by along way, and thats witht he T foil digging too hard and a bit too wavy for its liking…
The wind must be over a force 4, and consisting of only one beam reach of 100m from a rolling start, flat water! Oh, I dont reduce sail either, that BN has been held up to force 5…[:-bigeyes]

Luff 'em & leave 'em.

Dick_Lemke · April 18, 2004, 5:10pm

Doug -

(1) “AMYA Official” who has a viewpoint about multihulls?

(2) Circumstances regarding the conversation?

(3) “Pink-slip Race” - yes or no?

system · April 18, 2004, 5:32pm

You want me to agree to race your 18sq. (17-18’ cat) with my 48" X3? And the prize is the big boat? Sorry not interested: the fact that the X3’s BN with a spin is higher than an 18sq. has absolutely nothing to do with the X3 being able to beat such a large boat; though in lite air…
The AMYA official’s name and circumstances of my personal conversation are not important: what is important is his feeling that multihulls are held back because of their tendency to capsize/pitchpole. It was his personal opinion(and the opinion of several members of his club) not any form of official opinion.
It is an opinion held by a wide number of people I’ve talked to about the subject recently.
And it is a perception that we,as multihullers , need to address in order to get more interest in fast sailing on the water.
By compiling data such as Bruce numbers and working toward other methods of evaluating multihulls, perhaps thru a wider set of parameters, we are making a start on building an information base that will be added to over time. It may help us all see the relationships involved more clearly .

Doug Lord
–High Technology Sailing/Racing

Dick_Lemke · April 18, 2004, 7:14pm

<blockquote id=“quote”>quote:<hr height=“1” noshade id=“quote”>Originally posted by lorsail

what is important is his feeling that multihulls are held back because of their tendency to capsize/pitchpole. It was his personal opinion(and the opinion of several members of his club) not any form of official opinion.
It is an opinion held by a wide number of people I’ve talked to about the subject recently.<hr height=“1” noshade id=“quote”></blockquote id=“quote”>

Hmmm - seems that you better get going with some public relations, some information, some comparisons, and on-the-water demonstrations. Lot’s of work ahead of you. Will be fun to sit by and see how well you do at this. Don’t upset anyone <s>off</s> in the process, though.

Good luck !

Edited by Mod…Wis

system · April 18, 2004, 7:30pm

Thanks. I hope to be able to offer the new F48 Class Secretary, the multiONE Class secretary and anyone else interested more and more data that can be used to help understand how to better promote rc multihulls and to help owners , prospective owners,designers and builders to understand the boats better and to understand the technology that is available to everyone to improve performance-esp. control.
BN numbers are just a start so if you have details from other F48’s , mini 40’s or multiONE’s please add their BN’s to the information we have already by posting here.

edt:sp
Doug Lord
–High Technology Sailing/Racing

Roy_Langbord · April 18, 2004, 9:52pm

If the annonymous “AMYA Official” you quote was expressing a “personal opinion” why did you even mention his AMYA status?

Maybe the right thing to do here would be to go back and remove all of the references here to “AMYA”?

system · April 19, 2004, 6:52am

I was taken aback by this persons strong opinion on the subject; the fact of his AMYA position is a wakeup call that this perception must be dealt with.

This again reinforces the fact that collecting data such as BN numbers for rc multihulls with a perspective of using the data to help develop accurate ways of assesing an rc multihulls’ potential across the board including it’s proclivity to capsize/pitchpole (or lack thereof) is important. Going about promoting multihulls in the same old way just won’t cut it; there are solutions that can be developed.
BN numbers are a start…

edt:add info
Doug Lord
–High Technology Sailing/Racing

Peter_Birch · April 19, 2004, 7:44am

So am I to understand that this “official” knows nothing about multihull’s?

If this is the case the last person he needs advice from is you. You haven’t got a class registered boat on the water, so how are you the best person to talk to?

I don’t fit into the role as a good source of information relating to multihull’s in the US as I don’t have one there…Yet.

If anybody is interested the other thing that needs to be considered while trying to evaluate r/c multihull’s, is that the people who build boats build them to suit the “normal” conditions for where they will be sailed. Saying that a boat that has 2.034 is better than one that has 1.786 is rubbish. It comes down to many factors including “normal” conditions.

I don’t know why I am posting this.
My boat has a number of 1.779 but I have a customer boat that comes in at 2.064.

His boat is built lighter as it needs to suit his conditions.

Peter

system · April 19, 2004, 8:17am

Actually, I have one Formula 48 sailing now and one about to be! But that has nothing to do with one mans judgement based on his own experience-capsize of multihulls is widely considered by those that don’t sail them(and some that do), to be the biggest single handicap to getting widespread interest.
Much can be done to change this impression but it will involve new technology and not doing the same old thing boat after boat. Eliminating and/or drastically reducing the incidence of capsize /pitchpole will do a lot of good and that is why the accurate analysis of small multihulls is important and ,again, BN’s are just a start…
For instance, again, the only two manufacturer’s of rc multihulls in the US are experimenting with movable ballast; a major European race was won using movable ballast and people in the US , Spain and South Africa are experimentng with auto stabilizing foil systems. Many people worldwide recognize the problem: some are actually working on solutions!

Doug Lord
–High Technology Sailing/Racing

Dick_Lemke · April 19, 2004, 9:00am

<blockquote id=“quote”>quote:<hr height=“1” noshade id=“quote”>Originally posted by lorsail

But that has nothing to do with one mans judgement based on his own experience-capsize of multihulls is widely considered by those that don’t sail them(and some that do), to be the biggest single handicap to getting widespread interest.
Much can be done to change this impression but it will involve new technology and not doing the same old thing boat after boat. <hr height=“1” noshade id=“quote”></blockquote id=“quote”>

“JUDGEMENT BASED ON HIS OWN EXPERIENCE”??? Hmmm - perhaps he is one of those “unknown registered owners?”

As far as impressions go, you have posted a great example of why I feel the class needs to align itself with “True” multihull people. You know, those are the guys that actually sail and know about multihull tendencies and idiosyncracies? You don’t have to force an education upon them. AMYA currently is still a monohull organization. I don’t have the time effort or desire to try to change one person’s opinion if they feel multihulls are unstable. That education seems to be a Doug Lord goal, and more power to you. Why would this AMYA person be any different than someone who doesn’t like foils - or moving ballast. As I said, it looks like you’ve got your work cut out for you. But by posting that an “AMYA OFFICIAL” is down on a class he was elected to help support and promote makes me wonder why I am paying my membership dues? Must I now argue with an official that is supposed to be supporting the goals of the AMYA but has elected to make comments about something he seems to know little about - yet according to you he is basing his judgement on his “EXPERIENCE” - or is this just a way of starting your own conversation but trying to imply the original idea came from an unknown, unidentified, unregistered multihull owner?

If I am paying my AMYA membership fee each year to provide this level of discrimination, I sure would like to know about it, and perhaps an email to all of the AMYA “officials” might shed some light on the conversation, the views and the lack of understanding of this unidentified “official”. If this is truly a shared view by he and his club as you posted, I definitely see a need to look at the NAMSA (North American Multihull Sailing Association) affiliation a lot closer. Would much rather work with people INTERESTED in multihulls than those who feel they need to denegrate a multihull based on their “EXPERIENCE”.

Unless of course, as I question above, this is all really B.S. - and if it is, you have sunk to a new low to reference comments by someone in the AMYA administration that doesn’t exist.

system · April 19, 2004, 9:50am

To draw conclusions about the whole AMYA based on one mans opinion is ridiculous; to look at the problem realistically and work toward solutions is the best course of action…Hopefuly, the new Formula 48 Class Secretary will feel the same way.
Many people within and without the AMYA have been “educated” by years of poorly designed multihlls that can’t tack, can’t sail around a course faster than a monohull and that capsize /pitchpole in the blink of an eye. There is lot of work to be done to change that opinion.
So help gather BN numbers of various rc multi’s which is, at least, a start in gather data that can be used to help…

Doug Lord
–High Technology Sailing/Racing

system · April 19, 2004, 9:58am

<blockquote id=“quote”>quote:<hr height=“1” noshade id=“quote”>Originally posted by lorsail

To draw conclusions about the whole AMYA based on one mans opinion is ridiculous=
Doug Lord
–High Technology Sailing/Racing
<hr height=“1” noshade id=“quote”></blockquote id=“quote”>
you are so right

Wis

if it isn’t broken, don’t fix it!

http://wismerhell.esmartdesign.com/index.htm

Dick_Lemke · April 19, 2004, 10:30am

<blockquote id=“quote”>quote:<hr height=“1” noshade id=“quote”>Originally posted by Peter _Birch

So am I to understand that this “official” knows nothing about multihull’s?
<hr height=“1” noshade id=“quote”></blockquote id=“quote”>
Peter - according to Doug, this AMYA official has based his “opinion” on: <blockquote id=“quote”>quote:<hr height=“1” noshade id=“quote”>Originally posted by Doug Lord
one mans judgement based on his own experience<hr height=“1” noshade id=“quote”></blockquote id=“quote”>

What is extremely interesting, is that I’m not sure how this AMYA official could base it on “experience” - since I have no AMYA officials registered in the F-48 Class, and none appear in the “Open Class”. I also checked and there seems to be no one registered in the MultiONE Class that is an AMYA official.

Considering that no D4Z or X-3 multihulls have been sold/delivered, I question whether this conversation/viewpoint really took place? Considering that some “phantom owners” were registered with the F-48 Class (and never were able to be tracked down to confirm their ownership or registrations), it seems to me that Mr. Lord, may once again be using ficticious persons to futher his cause to promote and post his theories on foilers and moving ballast boats. After all, it lends credibility to his arguements if he can tie it to a “conversation” of an un-named AMYA official to the perception that multihulls are unstable. What a wonderful opportunity to bring forth (yet again) the subject of foils and moving ballast? I’m not suggesting that an AMYA official can’t have personal opinions, but when it is posted as it was, it gives me pause to wonder !

As Roy notes, to lay such a comment on an AMYA official, makes me concerned of how much discrimination is taking place within the AMYA administrative ranks.
Are efforts to develop a 1 Meter and a 1.2 Meter Multihull Class going to continue to be an uphill battle?
Will this AMYA official be helping or hindering our efforts to establish a class?
Why would not this official ask for clarification or voice his opinion directly from/to the classes that are trying to be developed? There are still acting secretaries for both MultiONE and F-48 Classes - and since we “ARE” associated with the AMYA “Open Class” it would seem he would be know to inquire or comment directly with the class.
Also, as Roy states, why would one add a “tag” to a personal conversation if not to elicit either an automatic acceptance of the statement by the reader, or to open the door to forward, once again stability solutions?

The persons on the forums who have had questions and opinions in the past have had the courtesy to sign their names to their undirected questions. It allowed me to at least respond. If some of them still don’t accept the concept of multihulls, I could care less, but at least they were mature enough to include their name with their opinions. To not include a name so further questions could be asked, or opinions could be shared does a great dis-service to those attempting to develop multihull classes here in the U.S., and it also casts negative shadows on the AMYA and it’s officials if they make “hidden” remarks such as this - regardless if in official or un-official capacity.

For whatever reason, I really have questions about the validity of the supposed comments, about who made them, and just “how” they happen to be about stablity and made to the person well known for trying to promote foils and moving ballast on multihulls. Of course, I’m positive that a solution to carry a more realistic (less) amount of sail, or add a lead keel while learning to sail was also discussed as an alternative. After all, it would allow this AMYA official to sail what he is used to sailing - an underpowered, lead-added monohull with side supports. Doubt that alternative was proposed or discussed - and have doubts about the conversation.

In conclusion Peter, I feel strongly that if true, we need to consider an alternative organization to align ourselves with that is “Multihull Tollerant”. If un-true, I guess we can simply chalk it up to the person who posted it, right? Isn’t it interesting the original post was a pretty straight statement that the Bruce Numbers compare weight to power of a multihull, yet when pressed, it is later admitted that it is NOT a conclusive number and is good only when comparing similar boats. Now to my way of thinking, if it isn’t a conclusive number, then the ONLY WAY to compare similar boats is on the race course. Posting numbers that really don’t mean much seems to more confusing to new owners, that helpful. Using the concept of comparison, we now are looking at boats with different platform dimensions, so again, the BN means little! Accordingly, my MultiONE shows more power to weight than your Mini40 - but it now looks like it doesn’t mean anything because the boats are physically different. Man ! [:-headache]

system · April 19, 2004, 10:50am

Dick,I’m sorry it’s hard for you to understand the way Bruce numbers work; they have some limitations as pointed out several times in earlier posts. They appear to be accurate when comparing rc multihulls in light air and based on European race results maybe in heavier air as well.

Doug Lord
–High Technology Sailing/Racing

Dick_Lemke · April 19, 2004, 11:45am

Doug - you are so full of yourself, you would never recognize important information if it bit you on the butt.

How about this ?

Instead of posting yet “MORE D.L.THEORY”, you just post facts that are verifiable. As I noted in my post to Peter, “My MultiONE has more power to weight than Peter’s Mini40” (1.779 vs. 1.819) SO WHAT? One is 48 inches and 1400 sq. <s>feet</s> inches of sail, the other is 39 inches and 1100 sq. inches of sail.

Sure there is a difference, BUT WHAT DOES IT MEAN? You keep saying how important this information will be - but in what format? In what context? Across what platforms? In what strength of air? With which skipper on the Tx?

How about posting something like a difference in BN should result is xx seconds per mile. NOW THAT could be useful. I did a scientifie study with a significant amount of data to back up my tests, and my F-48 is a 4 while my MultiONE is a 7. When compared to Peter’s multihull, his is 10. Unfortunately, I don’t have data on ANY Microsail products, but I am guessing they would rate a from a 3 to an 8 (maybe an 8.5) but until I know that data it is strictly speculative. It does however give a good indication of what can be expected - and in any wind strengths. It doesn’t take into account sail area, since that can be varied at the skipper’s choice, so it really doesn’t play an important role in the rating.

Now if you BN information would conclusively show a direct comparison, maybe I could get excited about your numbers. Simply show the boat type, the actual time to complete the course, the BN number, the wind strength and actual sail area or rig being used. Once you have this information, perhaps then others including my “uneducated self” would be able, at a glance, see exactly what the numbers represent - or don’t represent.

Back to my MultiONE, vs. Mini40, it appears that as you throw out more and more exceptions to the rules, it really doesn’t matter. I doubt my short MultiONE could beat a longer Mini40 - so what did the numbers really mean, except more hot air? Even Peter admits to have a wide descrepancy in his BN as reported/posted against a local competitors boat. If the lower BN boat wins - what does this say about the Bruce Numbers? It says they are a worthless bit of data, that is not needed and only clouds the issues even more.

Again, until a multihull is raced against a multihull, and it CONSISTENTLY wins, do any of these numbers mean anything. And then when (if) you look at wind strengths, even then the numbers may not much of anything. In the meantime, I’ll stick with my rated numbers shown above until such time as you can post numbers with details that really mean something.

Iwema · April 19, 2004, 12:41pm

Hi,

Basically the speed of a boat is the combination of :
length
weight
sail area
stability
hull shape

For a mono-hull a simple formula will give you (in some cases) a suitable speed indication.
But more imported is the length.
The maximum speed of the wave produced by the boat (= boat speed) is the square root of the length of the water line multiplied by 4.5.
This formula will give the maximum speed of the boat in km/hour.

Length will give speed potential!

A wider multi-hull with a lower weight can be more stable than a catamaran that is small and heavy.
The weight will also produce more drag and therefore it will give even less speed.

A multi-hull must be light and wide and also able to sail on one out-rigger.

For more info about this subject look at my web-site:
http://members.chello.nl/~t.iwema .

Look under: “boat info index”, “How to Sail”.

Regards,

Hugo

system · April 19, 2004, 2:14pm

Hugo, welcome to he forum and to this thread.I looked at your website-very nice. One boat really stood out-the F3!(Ha)
When you get a chance please post the Bruce numbers of any multi’s you are familiar with. We’re trying to collect as much data as possible on BN’s of various rc multihulls.
If you use rudder t-foils on any of your multi’s please post those area’s and angle of incidence settings when you have time.
Any other comments would also be welcome.

Doug Lord
–High Technology Sailing/Racing

Tranth · April 19, 2004, 4:43pm

The Bruce number has little real relevance to any design consideration. In most cases its just a “mine is bigger than yours” kinda thing which sound impressive to the layman but has little bearing on real world performance.

Troy

19 out of 7 people have trouble with statistics

system · April 20, 2004, 9:33am

In point of fact Bruce numbes are relevant for rc multihulls in light air when length(wavemaking resistance) and RM(righting moment) are not factors.
The number we’re looking for must factor in RM in higher wind strengths.Doing so with reference to an a rig will in most cases reflect the proportional reduction in SA as wind goes up. Ideally, it would reflect some measure of susceptability to pitchpole(for instance does the boat use ruddr t-foils and or anti diving planes?; does movable ballast move fore and aft as well as athwhartship?

Doug Lord
–High Technology Sailing/Racing

Iwema · April 21, 2004, 12:56pm

Hi,

I made a small program to predict the stability and the maximum speed of a multi-hull.

If you put the data of your boat or a boat you intend to buy in the program you can compare the boat with other boats.

Please put the data you generate on the forum.

This is the link: http://members.chello.nl/~t.iwema

Go to “Boat index” => “Plans of boats”.

Open: “Multi-hull speed figureV1”

Regards,

Hugo