The last thread on the "ultimate beach cat design" talked a lot about sail area versus righting moment and why a 10' Tornado has such a huge advantage over the 8' wide boats of the same length (some even carrying more sail area). The generalization that I interpreted out of it was: "if you want more sail area, make the boat wider". O.K., this makes a lot of sense but at what point does that additional sail area begin to make your hull length susceptible to pitch polling. Certainly, I couldn't make my 6.0NA 12 feet wide, add another 100sq ft of sail area, and expect to keep from hearing "eeerrrrr-EEEEEEE...DIVE! DIVE! DIVE!" everytime I turned the thing downwind. What is a reasonable ratio of sail area to boat length? Do the new taller higher aspect ratio sail plans lend themselves to more submarining problems off the wind?

I don't know about sail area to beam issues, but in a recent Multihulls Magazine article, a designer (and I forget off the top of my head who this was) related that for catamarans, there is an ideal length to width ratio of 2:1. The claim being that more than 2:1 (like a 20' x 8.5' boat) doesn't have the ideal righting moment, while less than that(like a 20 x 12+ boat) leads to a potential for pitch-poling. The designer was talking about big boats, not beach-cats. But at 20' x 10' a Tornado would seem just right. That all doesn't take trapezing into account, of course.

The last 20 foot design was Marstrom's M20. He made the width 9 and 1/2 feet. My understanding is that with 340 lbs on the wire, you could burden the leeward hull and increase your drag... so he made the boat a bit narrower to optimize the design.

I am not sure how choices in hull shape influences this calculation for beam width given a fixed crew weight.

Hi Jake,
First let's review a little bit.
Using the Tornado Sport as a chinning bar, to have equal speed in light winds a boat,X, must have equal sail area to weight ratio than the TS. That means if boat X is heavier than the TS by 10%, for example, then boat X must have 10% more sail area than a TS just to be equal in sail area to weight ratio or power to weight ratio. The highest performance way of adding sail area for sailing to windward is to add mast height and increase sail aspect ratio at the same time as the sail area increase. Let's say this results in boat X having a mast 10% taller mast than the TS. The centerboard area on boat X needs to go up by 10% also to keep the sail area to centerboard area in balance. Now we have boat X powered up to the same sail area to weight ratio as the TS and it took a 10% increase in sail area, mast height and centerboard area to get there with no further increase in weight.
Now let's look at the righting moment situation. The TS with a 10 ft beam has 6100 ftlbs of righting moment and 251 sqft of sail area for a righting moment to sail area ratio of 24.3. Now we want boat X to have at least an equal righting moment to sail area ratio as the TS so it will have equal speed when the wind blows over 12-15 knots. Boat X has 10% more sail area than the TS, therefore its max righting moment must be 1.1x6100 = 6710 ft lbs. If boat X is 8.5ft wide and the compliment in righting moment is gained with wings, then the wings must be an additional 3.6 ft outboard of the hulls and not weigh anything. So at this point boat X, which is 10% heavier than a TS, must have 10% more sail area, 10% taller mast and 10% more centerboard area and also have 3.6 ft wide wings on each side to be competitive with the TS in 'all' wind conditions. Now we have a boat X that might stand a chance of being competitve with the TS.
So how about the pitchpole tendency of boat X??? Boat X has 10% more sail area than the TS and that sail area is 10% higher above the center of bouyancy than the TS. Is it more prone to pitchpole than the TS???
First let's understand pitchpole. Two criteria must be met before pitchpole can occurr. 1) The pitching moment from the forward component of the sail force must be equal to than the restoring moment from the hulls. This is called 'verge of pitchpole'. 2) A very sudden and abrupt increase in hull drag occurrs and trips the boat and makes the boat rotate in a violent forward cartwheeling motion, sterns over bows. When this happens, we sailors call this pitchpole. This very sudden and abrupt increase in hull drag occurrs when the fore deck goes underwater and the sleek bow that was splitting the water becomes very blunt as the foredeck becomes the bow and parts the water. The cartwheeling motion of pitchpole is a result of the the conservation of momentum, Physics again. The boat system mass times velocity of translation is converted into rotational momentum, mass times rotational velocity. This can only occurr when criteria #1 and #2 are met. Now let's go back and look at criteria #1 again.
Boat X has 10% more sail area and that sail area is 10% higher above the center of bouyancy in the hulls. This tells us that boat X has 21% more max pitching moment than the TS. This is pro pitchpole for boat X. Now let's look at the max restoring moment of boat X relative to the TS. The restoring moment is the sum of the platform restoring moment plus the people restoring moment. The restoring moment, in general, is equal the the weight times the distance from that weight to the center of bouyancy in the hull. Now the boat naturally tries to resist pitchpole. As the forward component of sail thrust increases, the resulting moment forces the bows down and this makes the center of bouyancy migrate forward in the hull and increase the distance between the center of bouyancy and the weight, platform and people. This is an automatic increase in restoring moment. If boats were long enough and bows were tall enough, catamarans would never pitchpole. (Look what they did to Playstation's bows.) Back to boat X and the TS: Let's assume that boat X and the TS have similiar bow heights, therefore both boats, hull shapes, can make the center of bouyancy migrate the same distance forward toward the bows. If the rigs, main beams, on both boats are at the same fore and aft location along the hull, 10 ft for example, then it is likely that the center of gravity of the two platforms are in the same place. Now remember that boat X is 10% heavier. This means that boat X has 10% more platform restoring moment, platform weight times distance from the center of bouyancy to the platform center of gravity, than the TS. This is more pitchpole resistance for boat X. Now let's consider the people restoring moment. At the verge of pitchpole the sailors are usually as far aft as they can possibly get on the boat. Let's assume that the sailors are at the same aft position. Since the centers of bouyance of these two boats are equally forward at verge of pitchpole, the restoring moments, people weight times distance from center of bouyancy to their center of gravity, are equal.
So in summary on the pitchpole question we can say that boat X has 21% more max pitching moment due to the larger sailplan and 10% more restoring moment due to its heavier platform which is only 3% in total restoring moment. Therefore Boat X has an 18% greater tendency to pitchpole than the TS. Another way to put it is to say that boat X will pitchpole with 18% less forward component sail thrust than the TS.
Bill
PS Jake, there is alot more to this which I will get into another time.

Mark,
When any catamaran sails on one hull, the total boat plus people weight is carried by the leeward hull. It doesn't matter if the boat is 5ft or 10ft or 50 ft wide. The total weight carried by the leeward hull is the same.
Bill

*I am not a boat designer or a physicist, the following are merely my thoughts on the matter*

What some people are maybe forgetting in this wide vs narrow debate, is that with a wider boat the weight of the hulls is also futher out, helping increase righting moment. That's why it's not the same as putting 2' wings on each side of the narrow boat so the crews can trapeze at the same distance from center.

Also, when the comment was made that the easiest way to make a boat faster was to make it wider, they weren't talking about increasing sail area or anything else, because the point of making the boat wider was to help it say upright in heavy winds in the first place.

Width shouldn't effect a boats ability to pitchpole all that much, since it doesn't help you move further aft to keep the bows up. However a boat that is so wide that capsizing is unlikely can be pushed hard enough to get the bows to dig in instead.

One designer's comment that I remember well: "When you're not sure wether the craft will first capsize or pitchpole, you've got it right." Granted, he was talking about maxi cats.

Another great post by Bill. Keep this up and you will have material for a book. I would appreciate your comments on the new generation of wave piercing designs. It would seen these boats seek to avoid that sudden increase in drag you spoke of rather than providing more boyancy in the bows. The most extreme examples I have seen is Morelli and Melvin's new A cat and perhaps "Team Phillips"...Thanks Dan

at some point the boat becomes more stable side to side and less stable fore and aft. my boat is 13' 6" and she will drop the
bows before she will fly a hull. she has enough reserve buoyancy to resist a pitch pole at this point, but it feels weird to have
the transom flying by 3' or so and the bow just inches off the water.

Hi Keith,
I don't know who wrote the article you read but there is no 'ideal' or perfect length to width ratio for catamarans. Catamarans of all length to width ratios can be pitchpoled and turned over sideways. The responsibility to avoid these undesireable situations belongs to the sailors on the boat. For turnover the sailors on the boat can see and feel the windward hull lifting out of the water and the boat tilting prior to turnover. They are being given notice. The wider the boat the more slowly this action occurrs and the more time is available to take corrective action and avoid the turnover.
Pitchpole is more subtle but there are signs that the boat is getting close to pitchpole such as the bow being driven lower and lower until it goes under solid water, not foam or spray. At the moment the bow and foredeck go under solid water there is an abrupt increase in hull drag and the boat stops quickly and does a forward cartwheel maneuver. So to avoid pitchpole, watch the bow!
Hull design has much to do with pitchpole. The taller the bows, the more wind it takes to make a boat pitchpole. The more streamlined the foredeck is, high arch side to side, the smaller the increase in hull drag when the foredeck is pushed underwater. Hulls designed with a flat foredecks pitchpole with a snap roll, very quickly. Hulls designed with a foredeck that is shaped with a high peak in the center will pitchpole much more slowly, sort of a mushey pitchpole. Sometimes this hull shape will recover from a near pitchpole situation even when the transoms are 4 or 5ft up in the air if the sailors can hold their positions on the boat and not fall forward.
Bill
PS. I put a SC20 together once that was 20ft wide and it sailed fine. To windward it was a rocket. Reaching don't trapeze. Downwind same as a normal SC20, watch the bows.

Boat X center of drive from the sailplan, with 10% taller mast, is only 5% higher, unless I'm badly mistaken?

Hi Andrew,
I'm trying to keep the math and logic easy to understand. Let's say that our base boat has a 30ft mast and that the center of effort,CE, in the sailplan is at 40% of mast height plus 3ft above the hull center of bouyancy,CB, to the bottom of the sail. The CE of this sailplan is located at 40%x30ft + 3ft = 15ft above the CB of the hulls. Now our 10% taller mast on boat X will be 33ft tall with a CE at 40% of mast height plus 3ft from the hull CB to the foot of the sails. This measuerment is at 40%x33ft + 3ft = 16.3ft.
The ratio of 16.3/15 = 1.087 or about 9% higher center of effort in the sailplan of boat X.
If I ignore the height from the CB to the bottom of the sailplan and simply take the ratio of the heights to the CE in the sailplans based on mast length alone, I would take the ratio of 40%x33/40%x30 = 1.1 or a 10% higher CE in the sailplan with the 10% taller mast.
You are right in that the CE only moves upward half as much as the top of the mast did but since we are taking the ratio of the two CEs, the 40% factor cancels out. So the CE moves up the same percentage as the mast top moved up.
Good Sailing,
Bill

Hi Dan,
Thanks for the compliment. First I want to say that in my experience 'all beach cats are wave piercers'. I sail in the ocean so that is what I see. The foredeck of a boat can go underwater for two reasons. 1) A wave taller than the bows, two times as tall or more for example, can pass down the hull, bow to stern, and put the foredeck underwater for a short period of time. If there is enough bouyancy in the forward sections of the hull, the bow will lift and the wave action will actually push aft on the hull for a moment. When the bow is being lifted higher than the transom as the wave passes, the transient bouyant force actually has an aft component to it relative to the forward velocity of the CG of the boat. There is some recovery of lost boat speed as the transom goes higher than the bow as the wave passes but the loss, bow up, is greater than the recovery, stern up. Also the sail/rig is made to pitch, changes relative velocity rapidly, as the boat goes over and through the waves and this reduces sail thrust.
We can reduce the hull pitching up action due to waves by reducing the volume in the front end of the hull. If we reduce the width of the hull, we upset the displacement distribution of the hull. So how else can we reduce the hull front end volume? Reduce the height of the hull at the bow! Doing this will reduce the response of the hull to wave action; it will reduce hull windage while sailing to windward; it will reduce hull surface area which will reduce hull weight. These are the plusses, +++. There is one big minus, ---.
2)There is one very important situation which occurrs while sailing downwind where hull volume in the front end is very valuable. This situation is "verge of pitchpole". The max forward sail force, maximum pitching moment, that a hull can support occurrs when the waterline is at the top of the bow. As the forward sail force increases, the bow is pushed downward which causes the transient center of bouyancy to migrate forward in the hull. This increases the distance between the hull instantenous center of bouyancy and the boat plus sailor center of gravity. This is the "restoring moment" which opposes the "pitching moment". The taller the bows are the deeper they can be driven into the water and the further forward the transient center of bouyancy can be made to migrate so the larger the restoring moment and the larger the sail force can be and the faster the boat can be driven downwind in windy conditions. So there's the trade off, reduced response to wave action vs reduced restoring moment to prevent pitchpole. A noteworthy point relative to A cats is that 18ft is a 'long hull' for a 'one man boat'. With that in mind it may be possible to reduce bow height some without too much loss in restoring moment. Note that Marstrom has not lowered the bow on his A cats and his are amoung the best and fastest.
One other comment: If we take an 18ft hull and put two people on it and double the sail thrust which doubles the pitchpole tendency, we probably should not consider the downward sloping foredeck and reduced bow height trade off on this size boat. A downward sloping foredeck is still draggy when forced underwater if it is flat on top. A high crown foredeck is much less draggy when forced underwater and it is inherently stronger and stiffer.
Good Sailing,
Bill

>>But at 20' x 10' a Tornado would seem just right. ratio 2:1

How about a a 16,4 ft X 8,2 ft ? Yes we have this area covered.

Wouter

Hi Wouter,
I'm not sure what 'just right' is. It is not a nautical/boat design term that I am familiar with. I don't follow what it means unless it means 2:1 boat length to beam ratio. There is no magic ratio or perfect ratio or just right ratio that I know of.
If a Tornado was 12ft wide, it would be the same speed/performance as today's Tornado in light and medium winds. When the winds go higher than 15knots, the wide Tornado would be faster to windward, faster on a close reach, faster on a beam reach and the same speed downwind.
Any time there is enough wind to utilize the additional 20% in righting moment, the 12ft wide Tornado will be faster.
Now, there are some conditions where the over use of righting moment can drive a boat to pitchpole. This is no different whether the boat is 10ft wide or 12ft wide or 20ft wide. You still have to watch the leeward bow and make your decision. The sailors operating the boat have to make the call as to how much righting moment to apply. Righting moment to a sailboat is just like horsepower to a race car. The operator has to make the decision as to how much power to apply. In a highly powered race car sometimes the driver has to back off the throttle to maintain control. So it is with a high powered catamaran sailboat. Sometimes you have to get out of the throttle a little to maintain stability. That's part of the skill and fun. Monohull sailors don't know what we are talking about.
Bill

Bill,
I believe the article was by Malcom Tenant (sp?), but I haven't had a chance to dig in and retrieve it. Again, he was dealing with larger boats where trapezing crew didn't come into the equation. And I think the meaning of 'optimum' was a balance of righting moment and perceived safety for pitchpole, in that there would be other hints to depower before driving a bow in - so this also was related to the level of skill in the crew. Again, this was for larger boats where the consequences of going over are larger. Still, I found it to be an interesting take.

I know you have way more research and design time on the bow/deck shape thing with respect to pitch pole, but I feel (and this is from my very limited pitch-pole experience) that the deck lips of a shoe-box style construction method seem to contribute way more to the pitchpole causing drag than the flatter decks. In the absence of the lips, flatter decks are certainly next in the order, but now having been on boats without the lips I'm of the opinion that they are the bigger evil. The tripping drag seems to initiate far sooner and in situations where the flatter deck itself wouldn't be as much a problem due to the angle of attack in the water.

I've been toying with the idea of widening my NACRA 5.8. It seems that the bow shape is pretty resistant to pitch-pole (lots of volume and narrow on the top), and that with some extra righting moment it could handle a fair bit more horsepower. Any thoughts on the NACRA 5.8 design in this regard?

I noticed that Performance Catamarans sells 11' cross-bars for converting a NACRA 5.5 to an 18sq. It seems like they would go on a 5.8 pretty easily. Has anybody else tried this?

Hi all,
To Bill and all the other posters, I would just like to say Thanks for posing and answering such stimulating questions.
I have one of my own. We have pretty much established the relationship between centres of effort, buoyancy, hull and deck forms etc in their effect on PP resistance, but I was wondering about one aspect of dynamic lift. O.K I have seen threads on foil assistance either in the form of T foils (as seen on the Australian moths, the Stealth F18HT and F16 and on many I14 skiffs) and inclined foils as used on the ORMA 60 tris. There is no doubt both these devices will allow the boats to be pushed harder downwind although in extreme conditions the foils may work against you. But what about concavities in the hull under the waterline forward of the main beam. Sailbooards have being using subtle concavities for some time to promote early planing and recently I tested a seakayak with slightly concave rear sections to help lift the stern when paddled hard. This very fast kayak the result of computer modelling and tank testing. Could the acceleration of water under the hull on a beach cat provide enough useful lift at speed to hold the bows higher and so allow the boat to be driven harder? Bill have you done any work on this?

Cheers

Simon Fisher

great question! Kinda like this?




And this?



This is all from an earlier thread located HERE

>>>If a Tornado was 12ft wide, it would be the same speed/performance as today's Tornado in light and medium winds. When the winds go higher than 15knots, the wide Tornado would be faster to windward, faster on a close reach, faster on a beam reach and the same speed downwind


Every kid knows that there are two limits to how far he can push his parents. -1- His mother -2- his Father. Often his mother is the more strickt but when his father gets angry it is often the most severe. Now every kid now knows that either one blowing up limits his range of pushing the boundery. Which ever he reaches first will stop his gains. I mean he know that his farther still gave him some slack when for example his mother reaches her liit of patience sooner. So some potential has been lost. Now what is he can shift some burden towards his father in this situation and move the apparent limit up while keeping the limit of his father the same. Now teh kid can make more gains.

Now what is he shifts alot of burden towards his father and go easy on his mother (very wide beams) will he get even further still. NO, because now the patience ofhis farther is more limiting than that of his mother. He still reaches one single limit before the other. Best ratio is when both reaches their limit at the same time than you have maxed out how far you can go given the kids stuff resistance potential of both parents.

Boats are much the same. And I've found this happens indeed. For example the 13,5 ft by 7 ft wide Hobie Dragoon is imposibble to trapeze of as an adult. as soon as you do that the noose goes down and you can't get aft enough to get it back up. It sprays like crazy and goes slow. Slower than than hangin out like on a monohull and keeping his noose up.

Now different course have different ratios that is true but each course has a ration beyond which extra width is waste,

Wouter

Hi Wouter…I think there is a flaw in your analogy…Bill has already stated

“PS. I put a SC20 together once that was 20ft wide and it sailed fine. To windward it was a rocket. Reaching don't trapeze. Downwind same as a normal SC20, watch the bows.”

Therefore, based on his testing, (even when taking it to the extreme of beam=Loa) I would come to the conclusion, that when factoring in all points of sail , the wider boat may not have a increase in usable speed down wind…but it will not be at an disadvantage either. While on the upwind and reaching legs it would have a clear advantage.

If you can advance performance on many points of sail, and keep performance of your slowest point of sail equal…I believe that is increasing the performance of the boat overall.

Maybe this would be a better analogy:

When Son goes to Dad for date Money…Dad gives him $20.00

Then Son goes to Mom for date Money…Mom gives him $20.00

Son tells Dad he has a date with the most beautiful girl in school and asks for more money….Dad says “that’s my boy”…gives him an extra $20.00 (beam increased)

Son tells Mom he has a date with the most beautiful girl in school asks for more money…Mom says I gave you enough already...no more money……$0.00 (length stays the same)

So originally the Son had $40.00 (original performance with original beam) but after approaching his parents again he picks up an extra $20.00 from Dad (increase in beam) he now has $60.00 to spend instead of $40.00.

$60.00 is greater than $40.00 no mater how you spend it…

Bob

Hmm. Wouter, what I THINK you`re saying is that if you widen a boat`s beam you put more load on the leeward hull in strong breeze, perhaps so much that the bouyancy of the leeward hull is not enough to support the additional load, so the whole hull starts to submerge, never mind the bow ?
So in order to take an existing design & widen the platform, first you would need to re-design the hulls to have more bouyancy in general, preferably with a healthy percentage of it up front, unless the hulls are very bouyant to start with. So in effect you start again, and design a complete new boat. There has to be a limit as to how much width you can put on an existing hull design. Making a Hobie 16 wider will only increase the distance you fly after that inevitable pitch-pole !

Steve

Bill

Did you ever try poling the jib, i.e. using a pole to move the jib in front of the bows? I mention this because in one way the Wave is like the 18 sq, it tends to pitchpole before it flips and this helps

I have been experimenting with Rick's super Wave concept and found if you pole the jib out, the lift from jib torques the bows up and stern down. This makes the Wave sail like a real boat rather than bobbing along like a fishing float.

It is amazing how much lift a jib produces. The little 15 ft2 Wave jib bent the original 8 ft x 1 1/4 in Al pole like it was a batten and a Tornado jib broke it, on lift alone.

The reaction of the boat is different, with a poled jib. Instead of the bows burying in a puff, they stay the same or lift a little.

The main problem is forestay sag. With the pole and the mast bending it is difficult to keep the forestay tight enough to work upwind. The new pole is carbon and a lot stiffer I will have to see how it works.

Steve, …Bill Robert’s had the foresight to address the pitch pole problem right from the outset with his Super Cat designs. They are extremely resistant to pitch poleing. They incorporate the very things you are proposing in your “new boat”.

If the basic platform is flawed (such as the Hobie 16’s, with it’s propensity to pitch pole) then that “flaw” has to be addressed before one can fully take advantage of these other performance enhancements. Widening a Hobie 16 might lead to a totally false conclusion concerning the benefit of increased beam…blaming it (increased beam) instead of the of the Hobie’s innate tendency to pitch pole.

Simon,

Bill answered in previous posts that he did some experimenting using two different hulls in a cat: a normal one and a planing one. He tacked to compare the relative performance in identical conditions.

Apparently there was about 5% gain downwind but the slaming and pounding upwind was terrible.

One solution seems to be a variable geometry hull, with flaps or something alike extending from a normal hull to provide a greater planing area.

Foils are another approach. The inclined foils in open 60s provide only limited lift, but the figures seem to be increasing lately. The Catri 27 foils lift up to 90% of its displacement to assist it in planing. The downside of foils is the poor light wind performance.

Cheers,

Hello 5.8 sailor,
Going from 8.5ft beam to 11ft beam is one big jump in hprsepower, like 29%. This also means the max loads in your boat are going up by 29%. As max righting moment goes up, so does sail force and sail cloth tension especially leech tension. Mast compression goes up. Main beam loads go up. Centerboard bending loads go up. Sheet loads go up. If all the forces acting on the boat didn't go up, then the boat wouldn't go any faster. There are no free lunches.
But, if you want to go faster, do it!
Bill

Wait a minute...I gotta admit, I got lost in all that parent child relationship stuff . It's an easy misconception that making the boat wider loads the leeward hull equally more but it just 'aint so. For the most part (there is a small exception when considering the foward drive of the sails on the bow) I believe the leeward hull's buoyancy is only supporting the weight of the boat and the sailors. The additional righting moment only induces less rotational moment around the leeward hull. The mast, rigging, beams, boards, rudders, etc....just about everything else on the boat DOES carry more loading as the stresses go up but this stress exists between the sail and it's contact points to the windward hull where all the extra righting moment is. The leeward hull is supporting the same weight - it just has more advantage because it's farther out.

Hold on. A wider beam lowers mast compression for the same sail driving force, because the shroud is anchored further out and therefore pulls less "down" for the same "across". Imagine an infinitely wide boat. The shroud would come at the mast horizontally, and there would be no mast compression. Beam windage would be a bitch though.Maybe you could go upwind at the speed of light though? Jake, you could then check your results for RTI before you left, and make your decision to go!

yeak, I stand corrected...but you lost me when you started talking about RTI results???

AHHH, but reread the following phrase again.

“PS. I put a SC20 together once that was 20ft wide and it sailed fine. To windward it was a rocket. Reaching don't trapeze. Downwind same as a normal SC20, watch the bows.”

Don't you notice that little "Reaching don't trapeze" thingy ?

Why is that bit included ? Why can't you trapeze on this course ?

And Steve; I wasn't saying that the total volume of the leeward hulls needs to increase; just that the longitudal pitching restance needs to be increased in order to make effective use of the extra width.

What have you won when you've replaced capsizing with pitchpoling ? Either way you can't transform the sailpower that you have into speed.

But by all means guys, if you believe that you can make boats indefinately faster by making them wider and that no other design aspect will limit you gains to something far less than expected then widen your boats.


Wouter

Hi David,
What you say is true, but that is not the object. The object is to INCREASE SAIL DRIVING FORCE. At the same sail driving force there is no increase in boat speed. Our basic objective is to increase sail driving force by increasing righting moment. This will make the boat go faster. The same sail driving force on a wider boat does nothing to make the boat go faster and it does reduce shroud tension and mast compression.
Bill

Understood, Bill. Just wanted to reiterate that beam and its associated wider shroud stance has that advantage of allowing further rig loadings with not immediately increasing mast buckling load. You can go faster for the same mast compression...

Wouter...the boat was 20'wide X 20' long...what in the world do you need to trap on a reach for? You already have plenty of righting moment...

Bob

Hello Luiz,
The planing hull bottom that I tried was one design, one effort. I do not think it was optimized. I was primarily concerned with getting the boat to plane at all. Therefore I used a planing surface that was probably larger than optimum and easy to build, flat. To plane at lower speeds requires a low planing surface loading, pounds of lift per square foot of planing surface area. The combination of 'flat bottom' and low planing surface loading led to a hull that pounded severely sailing upwind in chop. The pounding problem can be attenuated with a vee shaped hull and less planing surface area, higher planing surface loading. This would lead to a higher displacement speed before planing began. I guess my point is that this planing hull thing is a large study and development program on its own. If I were to put more effort into it, I would try a vee shaped hull with concave surfaces forming the vee, very much like the hull surface of a sea plane. To support two people with a light hull loading, vee shaped hull, might take a longer hull than we are used to seeing for a two person boat. If we can keep the hull narrow. I think the pounding thing can be brought under control.
Bill

>>Wouter...the boat was 20'wide X 20' long...what in the world do you need to trap on a reach for? You already have plenty of righting moment...


So you are actually saying here that a narrow craft with trapezes could be just as fast on this course as their is more righting force available than is needed ? Doesn't this in a way underline the notion that going wider beyond a certain width is useless ?

Now answer the following question ; what will happen if you did trapeze off that 20 ft wide beam in 20 knots of wind and a sailarea to match your width ?

Wouter


(I see only two possible outcomes ; you dive - pitchpole and get beaten by a Hobie 14 as no sailboats sails as slow as an upside down sail boat. OR you let out your traveller and mainsheet to depower you rig which means that you do not make full used of both the available sailarea and width. At 8 knots of wind the extra width is useless as every design is stabil enough.)

Think about it.

I think I have found a better analogy :

Picture two guys facing eachother pulling on a long piece of line. Put a load on the middle of the line pulling down. If the load is small enough than the two guys are both strong enough to lift the load by pulling on the line. Than there is a load where both guys can just pull hard enough to lift it. Lets now put an even heavier load on the line. Both can not pull hard enough. Can we lift the heavier load by replacing just one of the guys by a much stronger one ?

No substitude one guy for "maximum sailforce at which the boat capsizes" ; the other for "Maximum sailforce at which the boat dives" and the load for sailarea. See the system ?

Or here another one ; some people think you can drive harder through a bend when you increase the friction tires have an the road. Others know that at some point you will just flip the car or hit the ground with you foot rest. Either way your not making the bend anymore.


Wouter

Hello Bill,

I simply can't resist comparing your simple statement:


with that of another famous designer when he justifies the absence of foils in his (excelent) designs with one single bad experience a long time ago. It simply fails to recognize that one try is not enough - especially when you do not have access to the best research available.

In my opinion this says a lot about your own idoniety and credibility (but I don't mean he isn't - just that he adopted a more sales-oriented position in this case)

Today many multihulls are experimenting with flat bottoms, steps, foils, etc. The only place I saw a "V" bottom was in the preliminary drawings of a 60 ft cat for a French skipper (Kersauson?). It looked like the float of a hidroplane, exactly as you say.

I guess by now they should already be testing the concept in smaller scale. We will soon find out if it worked.

Thanks for your time,

Question,

How does a Catri 27R's speed

http://www.multicascos.com/ingles/catri_english.htm

compare to an approximate equal size Farrier/Corsair?

Hello Luiz,
I don't follow what what you are saying in your comments.
The thing that stopped me from further testing/developing of the planing beach cat was that I could see it was going to be a long road, possibly without success, and I have other interests to follow.
The real world situation is, at least where I sail, when there is enough wind to plane, the surface of the water has waves on it 2 to 3ft high. Go for a ride in a flat bottom power boat and drive it into these waves even on a slow plane and the ride is very jerky and unpleasant and would probably damage the rigging of a beach cat. Drive a Vee bottom power boat into these same waves and the ride is more tolerable but the vee bottom power boat requires more horsepower to go the same speed as the flat bottom boat on flat water. Here in South Florida when the water is flat, there is no wind. The flat water situation is useless to consider because there is not enough wind to get a boat up on a plane. I'm sure the reason the seaplane has a Vee bottom is because frequently they land and take off on choppy water, real water, and they don't want to pound the bottom out of the airplane. There are many many variables to optimize on a planing beach cat hull shape by itself and I don't have a few years to devote to that.
With my brief experience with planing beach cat hull shapes, I now think the answer is a long slender planing hull shape that does not even attempt to plane to windward but runs displacement mode. Then when the boat speed doubles while reaching and going downwind with a spinnaker, the hull will climb out on a plane and really go fast when it is going along the waves or downwind with the waves and crossing them slowly. I think a narrow Vee hull shape with hard chines and lifting strakes is the way to go.
Bill

Bill
Planing surfaces are of course most efficient as very wide and very short, for much the same reasons wings are. But even power boats have longer and stepped "pads" for more versatility. Foils look a lot more attractive when you bring in the pounding. Also, I spoke to a guy in SA who has an about 30 foot beachcat (Whiplash)I remember him saying something about planing upwind, but bow burying preventing downwind planing. Back to the foils or my personal favorite, Racking hulls, which bring the buoyancy forward when sailing off the wind.

Wouter,
Sailors on a racing beach cat have several things to control. They trim the sails with the sheets. They steer the boat with the helm. They trim the hull out fore and aft by moving their weight forward or aft along the hull and they move their weight athwartship to balance the angle of heel. Which ever team can do these tasks in the best concert usually has the best boat speed.
On the angle of heel point: It doesn't matter how wide the boat is, you always want to barely fly a hull. So if you are on a very wide boat you may not trapeze or you might ever have to sit in the middle of the trampoline to get the hull to fly. In the same wind conditions on a narrow boat the team might be trapezeing to acheive the same goal. The point is to get the most boat speed out of your boat you place your weight where ever you need to to acheive the optimum goal. It is possible to trapeze when you don't need to and that is slow on a wide boat or a narrow boat. It is also possible to overtrim the sails on both boats and that is slow also. The wide boat offers the option to go very fast when the wind blows hard and you can't do that on a narrow boat. I've been there and done that, Wouter.
Bill

Luiz...I dont understand either. It seems to me that it is for Bill to decide what he spends his time and energy researching and to abandon any line of investigation for whatever reason. It says nothing about his idonity (had to look that one up) or his credibility...Dan

Hi David,,
Your planing experience is very different from mine. On a short trick water ski, to slide the ski across the water sideways is much more drag than to plane with the ski parallel to the direction of motion. I used to water ski alot. Back in the old days, 1950's, when a 60 horsepower Gray Marine inboard engine was a big engine, the boats planed and they were long and slender, skinney boats. Look at old Christ Craft and Correct Craft power boats. They were all long and skinney because they had so little power to work with and they wanted to get the most speed out of their boats with limited horsepower.
As far as foils go, I'm glad to let Sam Bradfield fight that battle. He is a long way down the road from the rest of us and the trip isn't over yet. You don't see foil boats zipping around on 'real water'. They run good in flat water and strong winds but I don't know where to find that condition except in that ditch full of water over there in France.
Be careful of rhumors from guys in SA. A sailboat will always plane on its mid hull section out to its bow. The thrust from the sails is up in the air/rig at the CE and this creates a downward pitching torque which forces the boat to plane on its forward sections, like a seaplane. On a power boat the thrust is down in the water at the propellor. The thrust being generated in the water below the hull creats an upward pitching torque which lifts the bow and makes the boat plane on the aft sections of the hull.
Bill

Hi Carl,
Screechers and Hooters and Genoas all flown from the end of or the middle of a spinnaker pole are forms of 'poling the jib' as you put it. The old square riggers hundreds of years ago flew their jibs from structures called bow sprits, poles. For more information you might try a guy in Italy named Christopher Columbus.
Bill

The last report I received came from the owner of the first prototype, now sailing in Sweden. He told me the following:

QUOTE

...talked to the Catri folks in San Fransisco, they have new topspeed of 30.7 knots and continious runs at 28-29 knots for more than 5 minutes, with no reefing...

UNQUOTE

Dan,

Bill tested a planing hull once and as a result he decided not to use this feature in his designs.

In his post he described his test, noted that it was limited and that the idea could be put to work, pending further development and tests. He even offered suggestions on how to develop it. He is not bashing a feature only because it didn't work once.

Compare this to the other designer who tested foils once and now says that he doesn't use them because they didn't work at that time.

This is true, but not the whole truth. He tried only once, had limited experience with foils, probably did not have the resources for further experimenting, was not aware about relevant ressearches on the subject, etc. - all this is ommited.

The difference is that Bill told the truth with great simplicity, without fear of this affecting the sales of his designs, with genuine interest in the development of faster boats.

The other designer simply skiped those details, in my opinion only because it could hurt business.

Bill's posts on theoretical issues tend to be those of a scientist: totally unbiased.
The other guy's are those of an educated salesman: correct but partial or biased.

That's why I affirm that Bill's post says a lot about his credibility (no dictionary now).

Cheers,

Bill,

The moto of my previous post was your disposition to discuss and question features and ideas with objetivity, without omissions aimed to leverage sales. In my opinion this means that you are self-confident and honest.

Your sales-oriented posts are usually focused in "new ideas" which are actually your inventions or were already present in your designs 20 years ago. You fundament the claims with scientific objectivity but simple sentences, helping people understand the toys and tricks of our sport.

There are very few people who can claim to have invented and put in practice so many relevant solutions, improvements, inventions and ideas in sailing. Of those, even less are available for open discussion (and questioning!) of their ideas. I admire your work and your atitude.

Cheers,

Luiz...I got it now. Thanks for the clarification...Dan

Wouter thingy,
Why do you do things like this? You know that all you are doing is confusing some readers. You know that any beach cat can be made faster by increasing righting moment as long as the boat is not pitching moment limited. I know of no beach cat design that is pitching moment limited sailing to windward so on this point of sail, speed can be increased. Do you know of a beach cat design that is pitching moment limited sailing to windward?
On the SC20 by 20 we could double trapeze it sailing to windward standing aft on the hulls. Our feet were on a hull 20ft away from the leeward hull.
Reaching and flying a hull we would sit on the windward hull 20ft away from the leeward hull. We would not trapeze because the boat was near its pitchpole limit with us just sitting on the windward hull 20ft away from the leeward hull. We were still generating much more righting moment and sail thrust than a team trapezeing on a 12ft wide boat. Downwind the overturning/righting moment doesn't require the use of the trapeze, just watch the bows; trapeze out the back of the boat if necessary to keep the bows up. This is no change. So on two out of three points of sail you can make most boats faster by making them wider than the highway width limit. Making a boat infinately faster was only mentioned by you and as you know is not possible and only serves to confuse.
This wider boat thing sounds like an opportunity for invention to me, Wouter. Even your little F16hp could be made faster. How about a boat or a version of an existing boat for handicapped persons wide enough that handicapped persons could generate as much righting moment as a trapezeing team? Then they could race together, boat for boat.
Bill



AHHH, but reread the following phrase again.

“PS. I put a SC20 together once that was 20ft wide and it sailed fine. To windward it was a rocket. Reaching don't trapeze. Downwind same as a normal SC20, watch the bows.”

Don't you notice that little "Reaching don't trapeze" thingy ?

Why is that bit included ? Why can't you trapeze on this course ?

And Steve; I wasn't saying that the total volume of the leeward hulls needs to increase; just that the longitudal pitching restance needs to be increased in order to make effective use of the extra width.

What have you won when you've replaced capsizing with pitchpoling ? Either way you can't transform the sailpower that you have into speed.

But by all means guys, if you believe that you can make boats indefinately faster by making them wider and that no other design aspect will limit you gains to something far less than expected then widen your boats.


Wouter

I don't know if this has been mentioned before, but these wider boats (10',12', and up) have an important disadvantage. This is the fact that it takes more wind to get them up on one hull. And in most parts of the US/Canada in the summer the wind is quite light. So, a standard width (8.5') boat will walk away on all points of sail, everything else being equal, in light wind, say 12 knots or less.

Bill, can you tell us how much wind was required to get your 20x20' beast flying a hull?

Bill,

I think I may have the invention you talk about, I am building a four hulled "catamaran" this has the advantage that if the boat is built longer and wider it does not really increase in weight too much i.e the hull weight is the same in a 16ft version as a 20ft version. Just the gap between the hulls get bigger.

My calculations indicate that a 16ft boat has 15% higher for and aft stability (pitching moment) than a conventional cat, because the volume is in the four corners.

It is designed to go on a car roof rack, and because of the way it folds it can be made almost any width without any trailer width restrictions.

See the link for a drawing of one of my designs.
http://www.fourhulls.com/xcatdrawing.pdf

I would be interested to hear your thoughts on this design?

All the best

Gareth
www.fourhulls.com

Hi Dave,
There is no rule or law that says just because a boat is xft wide or 20ft wide that in light winds the sailors must sit on the windward hull and or trapeze from the windward hull in all sailing conditions. Both sailors can sit on the leeward hull and fly a hull in 5 knots. Both sailors can sit in the middle of the trampoline and generate righting moment using a 10ft lever arm. Both sailors can sit on the windward hull and hike with a 20ft lever arm and fly a hull in 15 knots of wind. Both sailors can trapeze from the windward hull, 20ft lever arm, and fly a hull in 20 knots of wind and go like a rocket to windward. Just because your boat is 20ft wide you don't have to use the full width until you need it. Just because your boat has an 8:1, or 10:1, or 12:1 mechanical advantage mainsheet, you don't have to sheet your sail in as hard as you can pull it and make the sail board flat in light winds. The same is true for righting moment. You trim the boat out to what you need for best speed. That goes for sail trim, fore and aft hull trim and righting moment trim.
Bill

Hi Gareth,
Good luck with your project. A four hulled quadramaran was built and sailed out of the Miami Y C for a few years about four years ago. I never saw it sail so I don't know anything about its performance or other characteristics.
Good luck,
Bill