Wave-Piercing, Pitching damping or marketing?

[Erwan]

Hi Everybody,

I try to find out the actual advantage of pierce-wave design for catamaran.
As these designs are usually combined with larger beam section, it is not clear wether the supposed advantage comes from less hull drag as "pierce-wave" suggests, or from less pitching and therefore better rig efficiency ?

Thank you in advance.

[frosh]

My understanding of the wave piercing design which has been done much more in power cats than in sailing craft is mainly to allow higher average speeds through rough sea conditions. In sailing catamarans there is the very considerable risk of capsize by pitchpole which is not a factor in power cats. A bouyant bow section will lead to a very rapid slow down of the leeward hull if it suddenly is pressed hard by the rig forces, especially if a large wave is also encountered simultaneously by the leeward bow. The rig has considerable momentum and wants to continue it's forward motion at the same speed it was travelling at just prior to the burying of the leeward bow. A capsize over the nose may result, and at the least, a shuddering de-acceleration with huge stresses being created especially on the mast and the staying system, and also the forward hull sections.
The wave piercing bows will in theory de-accelerate much less, and all the bad events described above will be minimized. Also in theory the hulls should continue sailing even when the bow(s) are fully under the water surface. It doesn't always work and the notable maxi cat Team Phillips did break up in trials even though it was a definite wave piercer.
See story in this link: http://www.solarnavigator.net/team_phillips.htm

[MalSmith]

While it is true that wave piercing bows have been used on power cats to achieve higher average speeds in rough conditions, the reason has nothing to do with reducing hull resistance. A limiting factor for high speed ferry operation is seasickness. Wave piercing bows are used in an attempt to reduce the passenger seasickness incidence by reducing the pitching motions of the vessel. I am not aware that there is any significant reduction in resistance due to wave piercing. In fact the reverse may be true, but it would depend on the details of the design. I was involved in some early development work for wave piercing catamarans, and I can state that for a wave piercing bow to be effective, a very significant reduction in reserve bouyancy above the bow is required. Most sailing multihulls I have seen which are touted as being of wave piercing design, do not even come close to being true wave piercers.

I do not know for sure why wave pieercing bow on sailing multihulls as are fashionable at the moment, but the two potential benefits which come to mind are reduction in crew fatigue and, as mentioned, reduced rig motion. Both of these benefits will be realised only on upwind legs.

On downwind legs I would think that wave piercing bows would tend to be a liability rather than a benefit, as pitchpole resistance is considerably reduced due to the necessary reduction in reserve bouyancy. I doubt that any reduction in decelaration when stabbing into the back of a wave would offset the loss of longitudinal stability and hence sail carrying ability.

Mal.

[Frosty]

So-- what is the definition of a wave piercing hull?

Semi displacement bulbous bow?

[MalSmith]

I guess a wave piercing bow is one such that the shape provides the kind of wave piercing behaviour that you desire!! Personally I think that an effective wave piercing bow could be defined in very broad terms as a bow shape for which the enclosed volume above the waterline is less than the volume below the waterline, for at least 20% of the waterline length aft of the stem. The effectiveness of any wave piercing bow is effected by the sea state. i.e the wave height and encounter frequency, and the dynamic properties of the hull, i.e the radius of gyration and the damping effects of the hull shape itself. Any given wave peircing hull will be most effective in one particlar sea state, and less effective to varying degrees in most other sea states. The trick is firstly to pick the right design sea state, and then be able to tune the hull shape for that condition.

Mal.

[Erwan]

Thank you very much , your references and comments are very usefull. The definition you provide for wave-piercing bow is an interesting benchmark to keep in mind. I primarily look at A-Cat hull shapes which seem to associate wave-piercing features with larger and flatter hull (U shape) with maximum beam a bit forward (55% vs 61%) and in addition to dynamic lift these hull shapes seem to be designed in order to dampen pitching motion. But on the other hand in choppy water it seems that the boat rebound on waves like a tennis ball, it has been noticed by competitors at the last F18 World in Australia. But F18 Cats are twice heavier than A-Cats for the same lenght: 18 feet. I think I have too investigate further on relationship between pitching, center & area of flotation and so on.

[frosh]

I found this interesting link written by highly respected yacht designer and multi-talented, Meade Gougeon. It looks at the extremely competitive A class catamaran, a devolopment class with only a few restrictions. There is also a photo of the Nacra A2 showing very obvious reverse bows, where bouyancy below the waterline is significantly greater than bouyancy towards the deck in the bow sections. This trend has been the class standard for a few years now, and is still a feature of the world's top A class designs. The article by Meade is the second link.
http://www.a-cat.org/id59.htm
http://www.sailingworld.com/article.jsp?ID=34924&typeID=395&catID=635

[MalSmith]

Another practical, but more obscure example of wave piercing hull forms can be found in the amas of traditional Polynesian proas. These are usually made from solid logs with a specific gravity of about 0.5, which gives a 50/50 volume distribution above and below the waterline. It has been speculated that one advantage of this, apart from simplicity of the solid log construction, is that the resulting wave piercing nature of the ama reduces torsional loads on the aka structure by minimising movement due to independent pitching of the ama, which would wear out the structure more quickly.

It makes sense that for good wave piercing properties the volume distribution should be about 50/50 above and below the waterline, since the upward buoyant force of the fully immersed hull section will then be equal to the downward weight force when the section is fully airborne. Our findings from tank testing that we got better performance with less than 50% volume above the waterline in the bow region were probably due to the practical restriction that we had to have significantly more that 50% volume above the waterline from about 20% LWL aft of the stem.

One interesting observation from the tank tests was that for a conventional bow, the average running trim in waves was a few degrees bow up, whereas with the wave piercing bow, the average running trim was closer to zero. From this one could speculate that the improved average running trim may result in lower average hull resistance.

Mal.

[Otter 33]

I am definitely not the “resident expert” on this subject – But I’m currently building a small “wave piercing” power cat that I have designed… and hopefully these comments can be of use to someone. Please correct any misassumptions I may have about this subject.

To me, wave piercing effectively means:
Length to beam ratio of the hulls are near 20:1 and as high as 40:1.
Very fine forward entries of the bows.
Very low volume bows
Forward bow sections (roughly first 1/3 of hull shape) elliptical/symmetrical or have a low drag section. To create a low drag section for the bow you would consider the conditions that will exist on the bow when they travel into a large wave. Imagine slicing the bows off, and then using them as a keel, with the “deck” surface now acting as the leading edge of the keel. This is a good thought experiment to create an efficient bow section. A low drag shape in this condition will reduce the tendency to nose dive. A high drag section in this condition (like the bows of a Hobie 16) will increase the tendency of the boat to trip.

In regards to the radical looking hull shapes on newer A-cats: To me it seems A-cat’s have been wave piercing for some time now. The newer radical looking bow shapes may increase the speed of the boat through wholesale reduction of windage as opposed to changing the wave piercing affects of the hulls. For a boat like the A-cat- you may be seeing performance gains from a design decision to remove any parasitic, above water, unnecessary hull surface.

Also, the trend in A-cats of moving the underwater volume of the hull forward may also be of benefit only to the A-cat and not larger catamarans. It is there to counteract the sailing forces on the boat as opposed to creating a more efficient hull shape. A more efficient wave piercing hull shape would bring the underwater volume further aft- that’s if you did not have to consider the rig. Note that A-cats have very high aspect ratio rigs with the center of effort a lot higher than any other sailboat I can think of, while weighing proportionally less than any other sailboat I can think of. This creates a huge lever arm which pushes the bows down… while the boats have very little comparative weight aft to counteract this (even with the one crew trappesed near the windward rudder). Also note that the tendency in A-cats is to move the rig further and further aft. For these reasons, I would have to conclude that the tendency to move the underwater hull volume forward is to counteract a very high aspect rig on a very lightweight platform, as opposed to having any “wave piercing” or hull drag benefits.

[frosh]

Hi Otter, your reasoning seems quite sound re the A cats and the need to reduce the tendency to depress the leeward bow, and reduce parasitic aerodynamic drag. This might be as, or even a more important reason as wave piercing for the unusual reverse bows seen almost universally on this class of cat.

[Erwan]

Thank you everybody for your relevant and very interesting comments. As for many boat, the issue is the optimum trade-off with many criterias to be considered, and difficult to modelize, that is why Yacth design is still and art.

Regards

EK

[Retired Geek]

not quite ready for the water (one or two weeks away yet) but hope to have the LR2 competing shortly...btw, design waterline is where the unskinned hulls were joined

[Erwan]

Great boat, obviously, according to the carbon beam and high aspect ratio daggerboard it seems to be a A-Cat. Hulls seem to be made with carbon or dark foam ? limited area for the hulls must lead to light weight
Is it your own design ?
The place you live seems to be near the water, happy man !!!

Thank you again

Cheers

EK
erwankerauzen@free.fr

[Erwan]

Sorry for the misspelling in the former msg

[Retired Geek]

Yes, its an A-Class, core is corecell with carbon inner and outer skins, weighs about 34 kg as shown before paint, boards are very high AR (just 140mm chord and draw about 1.15m), rudders are just shorter versions of the boards.

[Erwan]

I guess that 34 kg is for the whole platform. As you are in NZ, you probably know Murray Philpot (not sure for the spelling), 15 years ago he came to the A-Cat world with his own design and building method, light &fast.
Did you made a master shape and a mould for your hulls?
Your hull section seems thinner than current design like Flyer, is it correct ?
Did you make the design yourself, which kind of software did you used ?

I stop there, I don't want to harass you with too much question, and probably your time can be used for another purpose.

On my side I work on a morphing wing section for A-Cat, it is not easy especially with transportation issues to be addressed.

Good luck for the last steps before sailing.

Best regards

EK

[patrik111]

Hello Erwan,

I have read some of your earlier posts and would like to know absolutely as muych as possible from what you are understanding, what are your assumptions when designing the morphing wing, what are your expected benefits etc etc. All that you can possibly muster.

I do believe that when asking this I am doing so on behalf of quite many A-cat sailors.

Looking forward to reading about your project.

Best regards

Patrik

[Erwan]

Thank you four your interest in my project. I focuse on a A-Cat wing primarily because I have just enough space to make the top part of the rig (above the hound: 3.50 m).
The lower part will be a copycat of the upper part but much more simple.
My assumptions are a map of reynolds numbers according to APPARENT WIND in different conditions: winward, downwind ...and with different true wind speeds.
The twist control will be similar to the Cogito system.
A control line will limit the camber, to tack will be the same than for C cat with a hinge effect in order than the wing section reverse.
I guess I will gain in maximum lift at low reynolds numbers and will have far lower drag windward at high reynolds numbers.
My main issue is to meet the measurement rules and therefore the double trailing edge must be fixed at the same point without any possibility to drift and increase sailing area at for high camber section.
As a result the problem is to allow the sail cloth to move around the leading edge fromone side to another, I dont think it is actually possible.
Also another problem is to avoid wrinkles on the sailing cloth with the twist of the underlying structure.
The wing will be a simple one, without flap.
Probably we are not at the right place for this topic, we are in the wave-piercing topic ? I am not so familiar with forum.
Regards Erwan

[Retired Geek]

The 34 kg is just for the hulls and beams, the minimum weight for an A-Class is 75 kg, so once its finished we will be adding corrector weights.
Don't know many A-Class guys here, the boat was built in the USA using female frames on a jig, then strip planked with foam, then glassed internally, hull halves are then joined and the outer shape is faired using templates then glassed. The hulls are about 12% narrower than a Flyer and the LCB is more than 200mm further forward.

[mydauphin]

You might get stopped by Homeland Security.... It looks like a couple of 2000lbs bombs strap together... Very Aerodynamic :)

[TTS]

not quite ready for the water (one or two weeks away yet) but hope to have the LR2 competing shortly...btw, design waterline is where the unskinned hulls were joined

That must be John out there. I was going to add to this thread that out of all of the A-Class designs that I have seen recently, the LR2 that you and Ian are building is the closest to what a wave-piercing design should be. I cannot wait to hear how the trials on the water go with Ian and Fred. Good luck and the workmanship looks great.

Tom

[TTS]

Retired Geek,

Just caught up with the rest of the thread. Realized you are not John and are not here in the US. Sorry for my presumption. If you are interested in A's there is a lot coming down the line right now. Ben hall also evidently has a new designed boat going in the water in the next couple of weeks. Also have you checked out the NZ A-class site http://a-class.org.nz/ ?

[Retired Geek]

Hi Tom,
Im just the designer.
John says its the best A-Class he's ever sailed, Ian's not quite as sure as the helm loads up a bit in the stronger air to weather, but it appears to go fast downwind, and probably uphill as well, but they have yet to sail it against other A's to be sure. That test will come this coming weekend. The pitch damping we designed into it appears to work extra well, with no vetical motion at the bow in any chop sailed in so far (prolly 12 knots max) and no pitching with gusts up to the same....you'll have to wait and see what happens in harsher conditions.
Enjoy the attached pics
Retired Geek

[TTS]

Retired Geek,

Nice shots of the boat. Will fred's be in the water this week as well? Looking at the design, my thoughts were that the most difficult part of the boat to get comfortable with will be just how weight sensitive it will be. That is just my thought in looking at the design. Understanding just where and when to move your weight as well as how much difference even a few inches will make in the way the boat handles as well as its speed. Good luck with the project.

Tom

[TTS]

Also, maybe just change the mast rake an inch or two forward might take some of the load off.

[Retired Geek]

Tom,
the boat shouldn't be weight sensitive at all....and at least with the range of weights that have sailed it so far that appears to be true, the same goes for where you are on the boat, other than moving too far aft...in fact both John and Ian have commented on how difficult it is to get the bow down...such a nice problem to have :-)
As for mast rake, we want it further aft, not fwd for reasons that have nothing to do with helm load, but we think we have a solution for that now also. Like I said before....real performance is yet to be proven, but this coming weekend should give us a better idea of how well or badly we have done.
RG

[Retired Geek]

Tom
just a few pics to show the difference between Ian's boat (red) and a Flyer (green)...pic's are a comparison at full load (i.e sailing on one hull)
RG

[TTS]

RG

Well, good luck this weekend. Where is Ian sailing it this weekend? Had they wanted another test platform, I would have let Fred keep his Boyer for another couple of weeks. I can see the loads that you are reffering to, what program is it that you are using to track, quantify and pinpoint the loads so accurately?

Tom

[grob]

Nice boat, I like it when people go out on a limb and try something different.

I posted a link to this thread over at catsailor.com and a few people said the hull shape reminded them of a "sizzler" an aluminium catamaran from the 70's.

go to this page for a picture
http://www.thebeachcats.com/index.php?module=pictures&g2_itemId=3391&g2_imageViewsIndex=1


Hope it all goes well this weekend.

Gareth

[TTS]

grob,

I actually said the same thing to Fred Smith who is the owner of the second LR2 to hit the water.

Tom

[Erwan]

RG, Tom

I guess the picture shows the volumes not the loads ?
It is a great idea to think outside the box. Since a few years it is nearly monotype, and it seems that in a near future a new Martin Fischer A Cat shape is on the track. I have been told hull could be flatter and larger than the flyer.
Instead your design is in another direction and I can tell you that the Hobie Tiger designer Mr J; Valer has a new shape for F18.
Big difference with the Tiger are a narrower hull, the maximum draft has moved foreward and the stern is much thinner in order to allow the crew to put bow up easily moving its weight aft.
As a result the boat is much more foregiving and safe with spinneaker in strong winds. The hull has more freeboard than the Tiger and is not pierce-wave.
Despite 5% more wetted area than its competitors, thinner hull allow the boat to fly a hull earlier with spinneaker in light wind.

A special question for you RG, do you think pierce wave beam would provide more freedoom for the hull design (beam could move aft, or less freeboard at the beam:hull connection..)
Here is a link for a such a beam build for F18 HT, the picture is far from perfect and the beam are circular with 100 mm diameter in the middle and become flat elliptical with 60 mm thick and around 200 mm long.
In addition the beam is curved and the middle is 120 / 150 mm higher than the sides.
http://18ht.free.fr/Avancement/V016/Calculs/DetailsCalculsRDM.html#PartieRDM1

[grob]

I have been thinking recently about how the new trend of fitting T foil rudders to catamarans might affect the hull design. I think your hull might be a good way forward. You don't need large bows as the pitch control is done by the T foils. Tall bows are a prblem with drag from windage.

Gareth

[Retired Geek]

Tom,
program we use was developed as a collaboration between 16 people for applications like this and others you haven't seen.
Gareth
The program sorta negates the need for a T-foil, not to mention that its illegal in A-Class (google the hydrofoil debate in A's). See the attached files (sorry they aren't too clear as I had to zoom and crop some pics for examples)..the 1st thru 3rd show increasing speeds, note how we have achieved no bow wave in the traditional sense, but that it climbs slightly with speed and provides variable displacement at the bow and only on the leeward side of leeward hull. This solution appears to work quite well downwind, the jury is still out on how well this works to windward....this is all part of the solution to keeping the bows more or less vertically fixed regardless of sea state or driving force...again jury is out as I don't think the boat has seen much more than 12 knots of wind so far, but its encouraging that it does what it was designed to do up to this point so far.
Erwan
Our hull while thinner than a flyer, also has less wetted area but not by much (2% or so). Curious as to why you'd say thinner hulls fly earlier? (assumming all other things are equal)....whats your rational there? As for the beams, they don't affect our hull shape at all...we are designing to specific pressure distributions which in turn determines the shape and the forces in play...the hard part is getting the flow to behave as the pic's show over a range of speeds and chop/wave sizes.
Hope that answers most of your questions
RG

[Erwan]

RG

Sorry my former msg was probably a bit confusing.
That is true only for F18 with spinneaker,in light winds; its seems that thinner hull provide more lateral "grip" at low speed with high aspect ratio daggerboard, than other fatter hull sections.
That is why I guess you could expect to sail "the wild thing" earlier than the Flyer shape.
In addition, as far as I have understood correctly some theory, I believe that thinner hull creates less "spray drag" which is supposed to change according to the cube of the hull's width, above the waterline.
So your thinner hull than the Flyer's will be faster downwind, and your little volume in the aft part of the hull and the related ability to put bow up should enable the crew to push the boat further downwind, in strong winds.

For windward speed, I think that the Aerodynamic drag is the point and hull drag plays a minor role, but stabilizing the rig for a better average efficiency.
Hight aspect ratio centerboard combined with the rig provide most of the
efficiency windward.

It is what I have discovered so far, studying A-Cat.

But of course I will not compare my research to your team work of rocket scientists, I am unabled to create a spreadsheet with some Navier-Stock formula, or pressure distribution ...I am a second league player.

Congratulation for this great job, I look forwards for news after sailing tests.

Best regards

EK

[Retired Geek]

EK
first...no one is "second league" .... there are only those who try and those who whine <grin>....and if you don't know the answers at first, at least by the time you try a second time your a whole lot smarter for having tried :-)
As for our effort...it might look cool, but believe me, it has asked more questions than it has answered.
As for narrow hulls, by definition for a given displacement, a narrower hull is deeper, this will of course increase the lateral area which will generally increase the windward drag unless you design around that. Our narrow transoms are about drag, not allowing the bow to rise...in fact ours don't unless you stand on the transom...our optimum crew position for downhill is approx half way between the fwd beam and the centerboard....at least till its blowing 12 knots.
As for high AR boards...ours are very high....about 17 if I recall correctly...and the rudders are only slightly smaller....look at a Discus 2 sailplane....we use a similar planform....compared to tacticalz boards, you can get about 30% better LD,s and more lift, improved sections help a lot also with the use of 3-4 different sections over the span also.
While your correct about the aero drag of the hull being important, its not the major drag element, so don't ignore the hulls hydro contribution ever.
RG

[TTS]

RG,

Any reports on how the racing is going at Silver Lake?

Tom

[TTS]

Thank you four your interest in my project. I focuse on a A-Cat wing primarily because I have just enough space to make the top part of the rig (above the hound: 3.50 m).


Erwan,

I would love to be brought into the loop as you continue development of the wing. What are you going to use as a platform for the wing when completed?

Tom

[Retired Geek]

Tom
Ian just sent a quickie note saying he blew the Flyer away and he's very happy.
RG

[Retired Geek]

This is a cut and paste from Ian....

Today was 4-7 knots and the boat performed great. Flew a hull as quick if not quicker which is something I have not been able to do on any other boat in light wind like that. As soon as it would start to fly a hull you could really feel the boards start lifting to windward and I would separate from all other boats. The only other boat that stayed with it was the flyer. He is a good sailor and weighs 165 pounds so the fact that I was able to still keep pace and sail higher is very promising. Downwind I was evenly matched until the wind would get up to the 7 knot range and then I would start to pull away. I am sure my weight was a factor in that. As far as my bow down comments. It is an adjustment in sailing a boat with as much volume forward along with the rocker. After this weekend I have found that I have been over sheeting and not allowing the boat to drive down and ride on its lines. It is just a rigging issue and me learning to sail the boat. I can say this. I intentionally drove the bows down downwind to see if it would want to pitch and it does not. Waterline goes just beyond the forestay attachment and then pops right back with out slowing down a bit. Today was choppy also and it cuts through waves very nicely. All in all with a bit of time this thing is going to be a rocket ship.

RG

[TTS]

RG,

Way to go. Cannot wait until Ian gets comfortable with the boat, learns what it can and cannot do and figures its subtleties out. Then if it already is tearing up the course, it will even perform better.

tom

[Retired Geek]

try this link...nice video
http://sl-acat.blogspot.com/

[bobdarbygso]

RG,

Is the design optimized for a particular weight range?
Any thoughts on how it would respond to crew in the 100 kg range.

Thx
Bob

[TTS]

Bob,

I cannot respond to the LR2 on crew weight, but one of the A-Class platforms to look at is the DK-17, designed by Dirk Kramer. This is the email for the person who right now is in possession of those molds. pointfarm@verizon.net
This is a copy of the email he posted on the usaca.info website.
United States A-Class Catamaran Association List Server e-mail:
Some information:

The DK 17 was designed by Dirk Kramers for sailors who weigh more than 200 lbs ( 90 kg)

I bullied him into actually completing the design after his Boyer Mk4 died in an accident with Ben Hall’s A2.

We have built 5 platforms. Dirk and I have them, George Saunders has one (which was featured in a photo in Seahorse last month)

Oliver Moore has one and Bill Vining has one.

Mine has probably seen the most miles at this point, and I generally think the boat is very satisfactory. It does not make up completely for the fact that I weigh over 100 kg, but I think I am more competitive than I was on either the Mk4 or the Flyer.

The molds live in my shop, and Dirk, George and Bill have all come, pulled the 4 necessary halves and taken them away for completion.

Oliver, being my nephew, finished his in my shop recycling bits of old catamarans as much as possible.

I expect that I will be starting a new platform for Dave Penfield in the near future to replace his A2.

We did a day of boat swapping and he is pretty convinced that the larger displacement/ higher water plane inertia of the DK 17 is a better fit for his weight.

The boat will be Carbon/ Nomex/ Epoxy, we post cure things a bit, but the tooling can’t be allowed to get too hot.

All the boats have been well under minimum weight and remarkably stiff.

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[bobdarbygso]

RG,

Thanks. I'm actually familiar with the DK-17 and that lead to my question to you re crew weight. It also has it's displacement low in the hulls but your sections appear rather more elliptical and clearly you've moved well beyond Kramer in reducing volume above the w/l in both ends.

I assume the beams (on your design) are bonded into mouldings that are bonded in turn to the hulls i.e. no fasteners?

Thx
Bob

[Retired Geek]

RG,

Is the design optimized for a particular weight range?
Any thoughts on how it would respond to crew in the 100 kg range.

Thx
Bob

Bob,
The boat is designed around a 75kg crew and at a stretch might accommodate 100kg, but thats just a guess. To my knowledge no one who is that heavy has sailed the boat yet. One of the things we set out to do was model the dynamics of the boat in waves and get the pitch rate way down to just a fraction of that of the other boats which we appear to have achieved, but that coupling is very mass dependent, so I'm not sure how that would be affected with a heavier sailor as I never modeled that situation...perhaps something I can look at on a rainy day.

As for the beams, yes they are bonded in place and the sections of the hull change the entire length, they vary from ellipses with major axis in y & z to round to veed sections aft, plus we have chines aft also. In contrast to the larger waterplane area that was mentioned for Dirks design, ours has the smallest waterplane of any A-Class by quite a lot, that I'm aware of.
RG

[Steve Clark]

"that person" is me.
SHC

[Retired Geek]

Bob,

one of the A-Class platforms to look at is the DK-17, designed by Dirk Kramer.

Tom, as I have never seen the DK-17, is there any chance you could post a pic here of it ? would be nice to see what we are talking about.

RG

[Steve Clark]

Two views:
USA222 is DK17
USA323 is A2.1
15392

15393
SHC

[Retired Geek]

Thanks Steve, nice looking boat :)
RG

[Retired Geek]

RG,

Is the design optimized for a particular weight range?
Any thoughts on how it would respond to crew in the 100 kg range.

Bob

Bob,
we have now sailed the boat with up to 120 kg and using a Mk1 butt as a speedo, appears to go just fine, but its definitely sliding sideways and probably needs bigger boards. When you put it in the computer, the numbers tell a different story, none of which looks good. As luck would have it someone just appeared who is willing to produce a "larger" version of the boat and while the details remain to be dealt with, its possible we may have something sailing sometime in the Q1 2008 if all goes to plan.
As a preliminary estimate, I'd guess it will be optimised for a 105-110 kg crew.
RG

[bobdarbygso]

RG,

Thanks for the update.

I'm curious if these are designs you're doing on a commission basis, or will they be offered as plans?

Bob

[Retired Geek]

RG,

Thanks for the update.

I'm curious if these are designs you're doing on a commission basis, or will they be offered as plans?

Bob

Bob,
the boats (either version) will only be available in the US thru John & Ian Lindahl as finished boats, you can contact them at jlindahl_lcd@yahoo.com
RG

[bobdarbygso]

RG

Thanks!

Bob

[Triman]

Hy to all,
I'm an A-Cat sailor and of course followed with big attention the discussion. First of all,congratulation for the nice LR2 project. This is really other than mainstream, that points at the moment generally to flat and mainly fat bottom, with a straighter scoop-rocker line (flyer MkII, The Tool, Scheurer S5, BIM XJ). I would really try once this cat! The only doubt I have is about the rear beam, that seems to be very near the water; with this thin stern I wonder if it will hit soon the water downwind in weavy conditions (this was a major problem with the flyer MkI).
I love very much all these new boats after flyer MkI opened the doors for new thinking in cat design; but I must recognise that people are still going very fast with older designs like Marstrom (http://www.marstrom.com), wich is all but a wavepiercer or a low-drag cat (people call it CC - Container Cat). So it seems we have very different hull designs with not so big differences in performances.
So I'm always wondering if the design of the hull can make a real difference between the new A-Cats, or if the mast-sail (and boards) combination and the weight (and of course the sailing skills) of the sailor have a much bigger influence.
The reasons could maybe be described from the practical experience: since A-Cat can't plane, upwind you reach soon the maximum speed (ab. 9.5 - 10.5 knots; 11 knots in flat water) and then you have to maintain it with stonger winds; so you must have a very adaptable rig. The differences in speed between good trimmed and sailed boats is then very little. Downwind is the effect of sail-mast combination and sailor weight much bigger: with a powerful rig and/or a light sailor you fly the hull much earlier, and then the speed difference is huge. In my personal experience, +/- 7-8% of body weight makes you flying or sitting in the water...:D
So we can guess that at the moment, a good trimmed and developed mast-sail combination wich can provide good allround performance, and a regular diet for the happy A-Sailor :p can be at least so decisive as the hull shape itself.
Good Wind!
Marcus

[Retired Geek]

Hi Marcus
while the pic's of the LR2 might make it seem like the rear beam is low, it is infact a little higher than the Flyer MkI and in the worse chop we have sailed in so far hasn't hit the water yet.
In designing the boat we concentrated on 4 things, damping the pitch rate, minimising the hull wake, improving the rudder and board performance and developing a sail profile for minimum induced drag. If you accomplish the first then the rear beam issue vanishes and you end up with more usable power, the 2nd and 3rd hopefully give you the difference in hull performance that seems be missing between all the other designs and the last part is an attempt to eek out a bit more horsepower.
Personally I think that breakaway performance for any design is going to be extremely difficult, the best you can do is probably incremental small improvements....if you do enough of those increments, then perhaps you'll win a few races.

[Aerynt]

On a slightly different tack, if any of the other designers are in this forum, what are the things that they try and improve on when designing a new A-Class?

[Erwan]

Hi Everybody, Hi Triman,

You are in the right place to investigate solutions to improve A-Cat perf,
For the rig I highly recommend you to read the threads: "Soft Wing Sail"
and ' & "Sail Aerodynamic".

But you can get a good picture with a customized "Tornado Polar" and basic calculations:
1- You know at which true wind speed you just fly a hull winward, full trapeze.

2- You know your sailing weight, the boat speed, and the apparent wind speed, average angle of attack, and your righting moment full trapeze.
Of course, you assume that you trim the boat perfectly, especially the twist...and so on

3-If you are at constant speed (for the purpose of the computation, you hold everything constant especially the wind), the total drag=total driving force.

4- with your righting moment, you derive the lateral component of the sail lift

5- Then, combined with the angle of attack, you search the "implicit" lift coefficient which provides the appropriate aerodynamic force in order to balance your righting moment.

6-With the Lift Coef, and the angle of attack, you compute the total driving force.

7-With lift coef again and aspect ratio, and under the assumption you have the perfect twist, with elliptical ..... you can compute, the induced drag.

Of course, it is not VPP/CFD, it looks more like (KFD: Kitchen Fluid Dynamics) but when I did it, I realized that the outcomes were surprising for a basic cat sailor who has never computed anything.


Very quickly, if you consider the sail section drag + the sail friction drag+ the stays drag+ crew aero drag+ hull aero drag, you will find nearly more drag from air than from water (windward).

But hydro drag is alos important and Retired Geek provide us with interesting insights: The centerboard is made with 3 or 4 different sections. Probably, you need a special section for the part of the centerboard which is just under the hull, and has to deal with the boundary layer of the water flow around the hull.
At the rudder level, it is even more important as the boundary layer is thicker.
Then another section is required for the flow not affected by the hull boundary layer, the part with the largest chord.
Then for the centerboard elliptical tip another wing section is required for the large chord and a different one for the small one.

Good Wind

Regards

[TTS]

[QUOTE] I love very much all these new boats after flyer MkI opened the doors for new thinking in cat design; but I must recognise that people are still going very fast with older designs like Marstrom (http://www.marstrom.com), wich is all but a wavepiercer or a low-drag cat (people call it CC - Container Cat). So it seems we have very different hull designs with not so big differences in performances. [QUOTE]

Marstrom for one, is also testing a new wave peircing platform, Ben Hall has a new design being tested, Martin Fischer has a new design as well and all of them are one form or another of a wave peircing design.

[QUOTE] So I'm always wondering if the design of the hull can make a real difference between the new A-Cats, or if the mast-sail (and boards) combination and the weight (and of course the sailing skills) of the sailor have a much bigger influence. [QUOTE]

So now to the rig. I think that it is going to take a while for the hull shapes to settle down and work themselves out, so it is fair to say that the mast-sail dynamics are extremely important to the boat's performance. I think that Ian's boat is Hall Mast, Glaser Sail, Fred's boat has a Hall Spar with Fiberfoam parts (spreaders, gooseneck and so on), I do not know which sail he is using. My sails are Brewin, Ullman (Charlie Ogletree), Brewin, Goodall (Ashby) and will soon be a Glaser as well

[Doug Lord]

I saw TTS's posting of the A class rules in another thread. I was curious if anybody in the class remembers how long the "hydrofoils are permitted" rule was in effect before the "hydrofoils are not permitted" rule took effect?

[TTS]

Doug,

I think that you can find that answer on the http://www.usaca.info/ website under the blog. If not there, follow the link to the international website and follow the postings back. http://www.a-cat.org/ one link is http://www.a-cat.org/id93.htm .

[Doug Lord]

Thanks Tom. I followed the "foils,no foils" debate on the Aussie A class forum. Unfortunately, most of that debate(something like 6 of 8 pages) was lost a year or so ago. I don't remember ever reading how long that foils had been legal and am not sure it was ever mentioned.
I'll do the research you suggested.
-------------
EDIT: In doing research tonight I discovered this head on pix of Glen Ashby's(former world champion at least twice and 2nd in this regatta) boat showing a clearly canted in foil-the only purpose for which I would assume is to develop a small amount of vertical lift with angle of heel. Scroll down -you'll see it . There is a question and comment there as well that seems to say the matter is undecided -whether or not this violates the "no hydrofoils" rule. Anybody know anything more up to date?
Catsailor.com: Pete Melvin Wins the A-CLass Worlds
Address:http://www.catsailor.com/forums/showflat.php?Cat=&Board=Test&Number=52254&page=0&view=collapsed&sb=5&o=&fpart=1
---------------
EDIT #2: ANSWER
Again, thanks Tom-its been very interesting learning about this! I found the answer here where you suggested:
hydrofoil rule 2006
Address:http://www.a-cat.org/id93.htm Changed:4:09 PM on Monday, January 29, 2007
Apparently, the inward cant angle depends on the length to beam ratio of the hulls and the length of the board. Just for the heck of it I tried the rule on a set of hulls with an 18/1 length to beam ratio and came up with a max inward cant angle of about 15° on a 3' board and 11° on a 4' board.

[Triman]

Thanks RG for your answer; as I can see, you are developing a very complete concept; I would very pleased to train together and test the boats! Unfortunately is Switzerland a bit to far from US. If you have new informations (and pics) about your very nice boat, please post it. I'm now at the moment at the swiss Champ. in Silvaplana, near St. Moritz (very cold, rainy and shifty conditions!), so you can see every kind of boats from the marstroms to the Niels Bunkenburgs Nikita with round daggerboards, through Flyer mkII and Scheurers S5. About daggerboards, as i can see from the pictures, yours are straight, whilst trend is to have cantered daggerboards; that's of course not really to promote lift (it is always a simmetric profile), but to have it orthogonal to the water when both hulls are in the water (cantered hulls) and to have a little drift in the gusts. What are your reflection about that?
About hydrofoils on A-Cat: the international Ass. (IACA) promoted 2 years ago a task force to decide about that; they can't accomplish the task because the first problem couldn't be solved: to define what an hydrofoil is (it is much more complicate as what it seems!!). So we have at the moment a regulation that you can find on the IACA site (http://www.a-cat.org/), wich says that foils must be simmetric, and they can't not exceed boat BWL and can't be more near than 1,50 m; that is a limitation to cantered boards, and gerally, to hydrofoils.

[Retired Geek]

Triman....personally I don't see that canting the boards provides any benefit and probably increases the hull pitch rate a bit when you look at all the forces in play when sailing in a chop. Also don't see any good reason to allow drift in the gusts if your able to turn that into boat speed.
RG

[bobdarbygso]

RG

I'm curious how you approach the design displacement of a vessel such as an A-Cat given that the cat weighs 75kg with a moveable ballast (crew) of 75kg.

With 5 to 6 degrees of heel needed to fly one hull the rig must also be generating about 10kg of downforce so the lee hull is going to displace about 160kg versus 75kg with both hulls in the water in light air. In rough terms, can one assume that the one hull flying waterline corresponds with the extreme point of the bow and the bottom of the transom for the LR2?

Thanks
Bob

[MalSmith]

RG

With 5 to 6 degrees of heel needed to fly one hull the rig must also be generating about 10kg of downforce so the lee hull is going to displace about 160kg versus 75kg with both hulls in the water in light air.

Bob

The downforce from the rig can be ignored because it is counteracted by the upforce from the centreboards etc which are also heeled.

Mal.

[bobdarbygso]

At low angles of heel the lee board is vertical and the other is canted at about 10 to 12 degrees so that may well be the case but it doesn't substantially change the problem described; a change in loading from 75kg to 150kg or perhaps 175kg in the case of heavy crew.

This raises one other question; how effective is the windward board when the hull is flying? Is ventilation (perhaps wrong term) of the board a problem?

Thx,
Bob

[Retired Geek]

Bob,
I you go back thru the thread to the first pic's of the boat, DWL is where the hulls were joined...which is the extreme nose of the bow with the transom in the water a bit. In reality, with the boat trucking along the hull rides slightly higher than this. When on both hulls, both the bow and the transom are out. As for the weather boards, the tip chord is so small that they don't appear to have any problems and Ian tells me that he can't tell the difference between having them in or out of the water, although I'm sure that they still produce some drag.

[bobdarbygso]

RG

Thx
Bob

[kach22i]

Another practical, but more obscure example of wave piercing hull forms can be found in the amas of traditional Polynesian proas. These are usually made from solid logs with a specific gravity of about 0.5, which gives a 50/50 volume distribution above and below the waterline. It has been speculated that one advantage of this, apart from simplicity of the solid log construction, is that the resulting wave piercing nature of the ama reduces torsional loads on the aka structure by minimising movement due to independent pitching of the ama, which would wear out the structure more quickly.

It makes sense that for good wave piercing properties the volume distribution should be about 50/50 above and below the waterline, since the upward buoyant force of the fully immersed hull section will then be equal to the downward weight force when the section is fully airborne. Our findings from tank testing that we got better performance with less than 50% volume above the waterline in the bow region were probably due to the practical restriction that we had to have significantly more that 50% volume above the waterline from about 20% LWL aft of the stem.

One interesting observation from the tank tests was that for a conventional bow, the average running trim in waves was a few degrees bow up, whereas with the wave piercing bow, the average running trim was closer to zero. From this one could speculate that the improved average running trim may result in lower average hull resistance.

Mal.

Great stuff, I enjoyed the perspective.:)

[Retired Geek]

It makes sense that for good wave piercing properties the volume distribution should be about 50/50 above and below the waterline, since the upward buoyant force of the fully immersed hull section will then be equal to the downward weight force when the section is fully airborne. Our findings from tank testing that we got better performance with less than 50% volume above the waterline in the bow region were probably due to the practical restriction that we had to have significantly more that 50% volume above the waterline from about 20% LWL aft of the stem.

Not that we design according to such ratios but it peeked my interest to see how our design compared... on total volume ours is 36.1% below DWL, Flyer is 30.7% and our hull has only 84.9% of a Flyers volume.

I think that an effective wave piercing bow could be defined in very broad terms as a bow shape for which the enclosed volume above the waterline is less than the volume below the waterline, for at least 20% of the waterline length aft of the stem.Mal.

At 150mm aft of the bow we are almost the same at 36.3% and Flyer is much lower at 25.36% while our section area is at 88.1% of flyers. Waterplane for the first 150mm is 115.7% of section area for Flyer while ours is at 222.8%.

Section area at the transom is also interesting, we are at 8.1% and Flyer is at 22.5%, while our section area is just 29.5% of Flyers.

With all that said I doubt you can read much into or infer much from these numbers...ultimately its the forces in play that count...the trick is being able to calculate them.
RG

[Retired Geek]

Has been a while coming, but we finally got some GPS data off the boat, at times the wind was 10-12 knots and very shifty, but the average was 8.2 with the lows around 3 knots and the highest gust at 14.8 knots. Not a particularly good day for results but it will give you an idea of whats possible. (see the polar)

[Retired Geek]

forgot to mention the outer dashed and shaded area represent max speeds and vmg's and the inner darker shaded area and dashed lines represent averages over 500m of distance.
RG

[Retired Geek]

A couple more screen caps from the GPS trace from today, set to 101m averages
RG

[Daniel Gut]

I sail an A cat (Scheurer G5) weigh 90 kg and cast a fair sized shadow. Wind resistance increases exponentially with increased wind velocity, I believe there is substantial room for improvement in the aerodynamic characteristics of the large lump of ballast at the business end of the trapeze wire, who in 15 knots of wind probably has more wind resistance than his boat. Keeping the boat flat when the breeze gets up helps keep that lumpy ballast in the turbulent wind affected by the water and waves, once you get higher up, you the windward hull daggerboards and rudder get into the stronger more laminate air and that must be slow.

Is the LR2 entered at the worlds in the US?

@ Triman; Were you a spectator or sailing in Silvaplana?

Regards from Zurich
Daniel
SUI 208

[Retired Geek]

Hi Daniel,
your right about the lump on the end of the trapeze, and their may be some sort of advantage to clothing similar to what downhill skiers use, but I doubt that it will change your uphill VMG that much. The other alternative would be an aerodynamic "body bag" but I'd guess that would be a pain to wear and quite dangerous if you fell in the water. Attached section is a midships slice thru a couple of older designs at normal AWA's uphill, this I think can provide some advantages, but I know that it doesn't produce enough of a gain to change the VMG's by more than a few 10ths of a knot.

Right now we will definitely have 2 LR2's at the worlds, possibly 3.
RG

[Retired Geek]

here's a couple of video's of the boat out practicing today

http://www.youtube.com/watch?v=MRdBQY8YHj0
RG

[patrik111]

Nice to see modelling followed through!

Yes, its an A-Class, core is corecell with carbon inner and outer skins, weighs about 34 kg as shown before paint, boards are very high AR (just 140mm chord and draw about 1.15m), rudders are just shorter versions of the boards.


Some specific questions regarding your building method
Is this weight achieved with hand layup and vacuum? Or is it infused?

Heatformed in a female mold? If so, how did you make shure to avoid leaks from the heatforming? (screws from outside but not through?). Have you managed to scarf join the corecell sheets? or did you manage to find Very long sheets?

Very impressive project!

All the best

Patrik

[Retired Geek]

Nice to see modelling followed through!




Some specific questions regarding your building method
Is this weight achieved with hand layup and vacuum? Or is it infused?

Heatformed in a female mold? If so, how did you make shure to avoid leaks from the heatforming? (screws from outside but not through?). Have you managed to scarf join the corecell sheets? or did you manage to find Very long sheets?

Very impressive project!

All the best

Patrik

Hi Patrik,
boat was strip planked and hand layed with a vacuum, attached pic shows the strips used....other than that all credit goes to Ian & John for doing a brilliant job
RG

[TTS]

The second LR2 on it's first sail with Fred smiling on the helm.Way to go Fred! Great scenery too. Tom

[DSmith]

Hi Daniel,
your right about the lump on the end of the trapeze, and their may be some sort of advantage to clothing similar to what downhill skiers use, but I doubt that it will change your uphill VMG that much.
RG
I would have throught that it would have made a bit of a difference to windward where you have the highest apparent wind speed and your VMG depends on the overall lift to drag ratio. It always surprises me to see the amount of aero drag from the crew and hulls that comes out of the VPP.

[TTS]

Just a reminder to everyone! The new Roake/Lindahl LR2 will be racing at the lake Hoptacong A-Class fall regatta on Sept. 28-30. There will also be an on/off the water seminar put on by current NA champion Lars Guck. This should be a great clinic and an interesting and fun regatta. There will be two new designs at the regatta. Ian Lindahl and Fred Smith's new LR2 as well as the new Ben Hall/Peter Cogan designed A-class featuring a rigid wing sail. John Lindahl is the primary builder of the LR2 with assistance from his son Ian. John has been a builder for over 25 years and has built a few A's in his time. He has extensive building experience from Melges Boatworks to his own designs and many more. the molds for the new Hall/Cogan design were built at Vectorworks marine in Florida, but I am not sure who built the boats themselves. I will try to get this information. There currently are two of these boats on the water. Ban Hall of Hall Spars is the driving force behind this new project and is one of the stalwarts of the A-Class. So to round it up, there should be 2 LR2's and 2 Hall/Cogans at the regatta. If you are anywhere near the area, it should prove to be an exciting and informative weekend.

Tom Siders

[TTS]

Some Lake Hopatcong Pictues from LesBurn on catsailor.com.
http://mysite.verizon.net/vze28w8n/

[Retired Geek]

As predicted, it was very shifty at Lake Hopatcong so I doubt you can read much into any individual boats performance.
Finals places were 1st, Lars Gluck, 2nd, Ian Lindahl tied with Michael Gruber
RG

[TTS]

Since RG has not yet updated this thread here is his news. There will be three LR2s at the 2007 ronstan A-cat Worlds. Ian Lindahl will sail hull number three, Fred Smith on hull number two and for the real news here, Randy Smyth will be on hull number one. Randy will also be bringing newly designed and "radical" sails to the event. This should add some spice to what is already turning out to be an exciting event and a great place to debut a new platform on the world wide stage.

[Retired Geek]

Randy will also be bringing newly designed and "radical" sails to the event.

I'm not sure radical is the right description, but it is different from the current crop of competitive sails that are available.

Attached pic is boat #3 in primer, will post some sailing pics tomorrow.
RG

[TTS]

The beams are imbeded on this one without the little stub ends hanging out. boat looks great RG.

[Retired Geek]

Tom....you missed the fact that the whole of the hull fwd of the front beam has been changed slightly, less volume and waterplane area. Had to get rid of a little excess lift we had (see below).

ygyssdsy...for a conventional wave piercer you'd be correct, but what if you could have a variable radius of gyration ? and the damping effects were dynamic and not static ?

Attached a couple of pics of Ian (approx 1 sec apart) out practising a few weeks back, where he came up a bit too high looking for speed, the gust hit, bows go down and then our design comes into its own and spits the bow out....all in around 1 sec....note....no significant waves to help or hinder the process
RG

[PI Design]

Can anyone describe the Smythe sail?

[Retired Geek]

Here's a couple of pics from Boat #3's first sail
RG

[bobdarbygso]

RG, TTS, Steve Hall

Having had time to digest the lessons of the A-Cat worlds, can you comment on the performance of the various new designs (LR-2, DK-17, Ben Hall's new hull, etc.) versus more "traditional" hulls, trying to factor out differences in rigs and crews?

Thx,
Bob

[TTS]

I do not want to address the designs today because time is short for the next couple of weeks. What was shown more clearly than anything else at the regatta was the old adage, "time on the water". You can state that the more traditional hulls did better, but that is not correct either. None of these hulls were of traditional designs. What was dominate were the 2-3 platforms that were dominant in the class over the prior 2-4 years. Ben's boat is a further evolution of the XJ platform designed by Peter Cogan. What made Ben's boat interesting was the rigid wing. In terms of wing technology, it was a simple rig and more refinements can be made to improve it's performance. Again, time on the water was critical with this boat. It would have been great for Ben to have had 12-18 months on the water with it. Randy had less than a month on the LR2 before the worlds. The top sailors in the class were the top finishers.

[Retired Geek]

I'll post my own thoughts shortly, but the following is John Lindahl's thoughts

Comments on the LR2 A design:

This new design is one of the best feeling boats I have ever been on. From the first time I sailed it there was a unique feel that separated it from any other boat I ever built and/or sailed (and that includes over 25 different A's and 18 Squares).These hulls have the ability to stabilize the platform and give it a most solid feel, with the fear of pitchpole nearly eliminated. This design kept the surface area very low, which led to the lightest weight boat at the Worlds (150 pounds). The only down side to the design that I can see is the possible increase in wave drag on the hull topside when it gets into the heavy chop conditions that were prevalent in Islamarado. All of our sailing had been done in flat water lake conditions and the wave drag was not evident there. Since there is plenty of buoyancy forward I think the nose could be fined up some for a sharper entry as long as the flow remains attached.There is an upwind feel of the boat being pulled to weather and downwind it likes to be driven low.

The boards and rudders contribute in an "effortless" way. There is a "no-load" feel, with no cavitation or stall characteristics. This "no-load" feel allows the board to be easily raised, even when sailing upwind. The boards all weighed less than 3 pounds. The only problem with the boards is the tapered tip does not allow for weed removal when the boards are raised. But the boat can sit on the start line and jump into point mode very quickly.

The hull cross section, with no apparent deck allows the sailor to get out on the trap very easily as it's just a slide down the hull and there is a very comfortable feel when on the wire because of the hull side angle to the feet. The "no deck" design, with the resultant egg shaped cross section is structurally superior to anything else and provided the builder natural strong points to make tang and tramp attachments. The minimal area forward sections were not blown around when the wind piped up, so aero drag was dramatically reduced. A condition that has not been encountered yet is the ocean swell and I would anticipate this platform just loving that (going both uphill and down).

The boat build was exceptionally strong and stiff. Hull design (the egg) contributed a lot to that.The hulls were built with 9mm Corecell 5.5# density foam, which I'm sure is the thickest core of any, and then sheathed in and out with Hexcel 5.8 oz. carbon bedded with West System Epoxy. Hull weight averaged 31 pounds prior to primer and paint. Standard Hall beams were attached with carbon and epoxy which gave the platform a very solid feel, with no racking or twist. Integrated rudder gudgeons, recessed tramp hooks and minimal tangs presented an extremely clean appearance, especially when the beams were recessed into the hulls. Even when the beams were recessed there was no evidence of wave slap on the beams or even the dolphin striker. I feel the profile height could be reduced slightly.

For a boat that did not come out of a machined female mold the fairing and finish was excellent. Attention to detail was evident in the appearance. The fact that this design did not get a lot of trial time leads me to believe it has an excellent future.

[Doug Lord]

Congratulations RG, thats quite a testament!

[bobdarbygso]

RG & TTS

Thx for comments!

Bob

[Retired Geek]

Bob,
here is what Fred Smith had to say about his LR2

MY problems and I emphasis my.

1. I did not sail the boat enough prior to the worlds.

2. I should have used the old sail

3.Just to many new things to learn in a short time.

4.Not in good enough shape.(to much work not enough sailing)

5.Start of the regatta accident didn't help.

Wednesday of the regatta I started to sail better.I was reaching the first
mark in the top 25.I just sucked downwind.Boards are excellent I could
outpoint most everyone.I will experiment with pulling up the boards next
spring going downwind.

Thursday ,the boat was even faster upwind,I rounded in front of Pete Melvin
,Ben Hall,I think I was in the top fifteen,couldn't keep up on the downwind
but I was getting faster on the run.

[TTS]

FOLLOW UP ON THE LR2

After finishing the A Class Worlds an evaluation of the LR2 was made by builder, John Lindahl; builder/sailor, Ian Lindahl; designer, Richard Roake; sail maker/sailor Randy Smyth; and sailor, Fred Smith. Input was also received from several others and the conclusions are noted here.

For a brand new boat (both design and build) there was a general feeling of success. The boat itself performed very well, for as little time as the sailors had to learn it and tune. Roakes hull shape put some lift in the bow and got the weather hull out of the water very quickly. Everyone commented about the fact that this design does not want to pitchpole. There is plenty of volume forward. One nice attribute of the design is the boats ability to go into “point mode” and maintain speed. The best VMG downwind seemed to be achieved by heading down rather than doing the “wild thing”. The unique bows did not dive and trip, like a lot of people thought they would. Instead they stabilized the platform and at times there was a feeling of too much bow. This was felt in the accelerations coming out of a wave or when a gust hit you. The hull shape above the waterline reduced air drag, so you didn’t feel the bows getting pushed around in the wind. Boards and rudders were excellent with extremely good getaway from the starting line and a no drag feel when underway. It was possible to easily pull them up, even when “loaded” on an upwind beat.

When the building project began there were two overriding parameters: integrity and weight. The platform had to be strong and light. Hull panel stiffness was achieved by using a much thicker core than anyone else (9mm). The thick core was shaped by strip-planking the foam core inside CNC cut female frames. The core was then carefully laminated with carbon and epoxy inside and out. Beam junctions were glued and carbon wrapped for an exceptional joint. The first three LR2’s built are all under class minimum weight, with the third boat being 15 pounds under). Minimal fairing and attention to resin use kept the hull weight very low, as well as there only being 63 sq.ft. of surface area on a hull. The platform was stiff, strong and surprisingly light, with the added bonus that the boats finished out looking good.

All agreed that time on the boat is all that’s needed to put this boat up at the front of the fleet. All also agreed that the rig tune (mast-sail combination) was the area that needed the most attention. This of course goes back to time on the boat. There was also a feeling that the platform could take on more power.

This exercise was intended to get some new ideas in design and building technique introduced to the A Class community. We feel successful in doing that and will continue custom work on the boat. Complete boats are available as well as kits for those interested in doing their own. Board and rudder speed kits are available as well. R & D will continue with Richard Roake in the New Zealand design studio and Lindahl Composite Design here in Michigan.

A website is in the works but for now information is available from:

John Lindahl
LINDAHL COMPOSITE DESIGN
6002 Cedar St.
Fennville, MI 49408
269.650.5900
jlindahl_lcd@yahoo.com

[waynemarlow]

Any further update / views on the design