Hi Sven

I must say that this thread has been one of the most useful pieces of work I’ve seen. For example, I’m completely persuaded about the efficacy of daggerboards now that I see how to build a crashblock. Genius!

Also, the design work re the B/L ration on the new ama has been incorporated into my own model. Thanks heaps!

But here is a newbie qustion. What the heck is “CWL?” Also “CL-CL?” (Blank) waterline and (Blank) length are what my mind perceives.

I did a search before I posted this by the way. “CWL” is not in any glossary I can find, though I see it used here and there.

Cheers,
Rick

Aloha Rick,

Good to have some more added sense of humor around ,  that CWL would be the Central Water Line or 0 wl  or whatever other sortlike name the world has given it.

The CL - CL =  the distance from the centerline of the vaka to the centerline of the ama.  This is a figure which relates to the arm of the Rm (righting moment) , as in calculating the maximum stabilty of a proa , one can presume that the ama is just out of the water, and as such does is not “carried” by its own displacement, rather add all weights into one calculation sheet ,for simplicity sake.

Rm is further called by me Rm-var   which is Righting moment variable , because the “var” part is the amount of waterballast or any other shifting weight a pacific proa may carry, to vary its Rm righting moment.

I hope to have answered your questions , don’t hesitate to ask ,

Cheers Sven

Excellent Sven, and thank you. I appreciate your willingness to post these really detailed studies, and answer questions. I can see that if I really want to get serious about design, I’ll need to hit the books again.

But what I especially appreciate is theory which is balanced by sea miles. Major credibility there!

Best,
Rick

Hi Sven

Great write up and very clear. Additionally a couple of questions and remarks. On my designs I use 1:18 ratio on the main hull and 1;20 on the WW hull. You seem to favor 1;20 on the float ( as I do) but use a fatter ratio (1;5 of 1:20 is about 1:13 plus for the main hull. Marcaj speaks about ratio over 1;16 ( slimmer) not showing dramatic improvements on drag but I am of the opinion, as you also mentioned, that higher ratios ( up to a realistic point) that they could benefit the possible weather helm issue.
What are your feelings and comments about that?

PS on my 12m WLL is 12m and WLB 0,65cm. On the float at 7.55 LOA the ratio remains at 1:20 up to the start of scimming and a load of 350Kg. to 0 and above 350Kg moves to broader sections.
thank you for your time

Aloha Sven,

This is an amazing thread.  Thanks again!

Please excuse me if these questions are too broad or badly formed.  But I was wondering…

1. What’s a good way to figure out the spread (how far the dagger-rudders are from each other) and area of the dagger rudders?

Rudders that are further apart will shift the CLR more, for a given area.  And, the rudder needs to be a certain size to be effective.  What’s a good way of figuring out a that compromise?

2. Your discussion of weather helm caused by too much weight to windward was fascinating.  As a rule of thumb, how far to windward should the rig be relative to the centerline of the Vaka to balance well?  Is it proportional to the displacement of the vaka and ama?

Many thanks,
Chris

01 December 2011 04:04 AM #19   toni wrote;
Hi Sven

Great write up and very clear. Additionally a couple of questions and remarks. On my designs I use 1:18 ratio on the main hull and 1;20 on the WW hull. You seem to favor 1;20 on the float ( as I do) but use a fatter ratio (1;5 of 1:20 is about 1:13 plus for the main hull. Marcaj speaks about ratio over 1;16 ( slimmer) not showing dramatic improvements on drag but I am of the opinion, as you also mentioned, that higher ratios ( up to a realistic point) that they could benefit the possible weather helm issue.
What are your feelings and comments about that?

Hi Toni, 
Vaka L/B ratio’s is obviously very dependent on the purpose and size of the proa;

A. a daysailer or racer,  let’s assume 35feet, than I would go for a higher Vaka L/B ratio, as I would be less interested in the interior volume, so 1:18 would do fine.

B. A weekender/holiday 35feet version however , I need all that extra stuff on board to do proper cruising, now , you all of a sudden find the Vaka displacement, dictating the B/L ratio,s , to give you proper midship floor room, this together with the distribution of the displacement over that cwl, and the midsection shape and draft, I end up between 1:13.5 and 1:16.  To cover a 35-feet to 60-feet Pacific Proa design.

That said , narrower is likely to be only marginal faster on average base, but Pacific Bee IS already very fast for a cruiser, so I will give interior volume a more serious place within the total design, and so end up with a great roomy interior.

Furthermore I would pay loads of attention to overall(loaded) weight , and its distribution, I care less about having a very slim 1:18.5 vaka. , so the very first design work after you determine the all up size, is that excel weight/stability sheet , that is in my opinion the single most important factor in having a proper sailing pacific proa.

Look at the badly under-engineered and overweight samples you see out there, that is not what you want to end up with.  In general designers underestimate the true end weight of a cruising boat, they tend to calculate to the most optimum building weight,  I found plenty samples between 10-25% overweight by building, another 15% un-calculated for cruiser loading capacity.  hence they have no displacement to carry the load, so they are too deep in the water, especially an a multihull this is killing the concept, on top the beams and platform have barely enough clearance to the water.

So the pretentious Bruce numbers and SA/Displ. ratio , too weak building scantlings,etc.  flying through the air are all ridiculous,and dangerous .

Cheers Sven

PS on my 12m WLL is 12m and WLB 0,65cm. On the float at 7.55 LOA the ratio remains at 1:20 up to the start of scimming and a load of 350Kg. to 0 and above 350Kg moves to broader sections.
thank you for your time

04 December 2011 11:39 AM #20 Chris Luomanen wrote;

Aloha Sven,
This is an amazing thread.  Thanks again!
Please excuse me if these questions are too broad or badly formed.  But I was wondering…
1. What’s a good way to figure out the spread (how far the dagger-rudders are from each other) and area of the dagger rudders?

Hi Chris,

Were they are on Pacific Bee is clear. (to be honest I need to measure that if you like to know)
But I approach the matter a bit differently,  I think (also after doing a lot of studying, and playing around on the matter) that there is some very important other consideration to make first.
1.  what is the shape of your Vaka. ?
Is it deep V and very directional stable (after you setup your ama properly) than, the rudder serves mainly as a tracking board, and secondly as lateral area,  and only marginal rudder corrections need to be given. 
For this Vaka I would place the rudder in “solid water” where flow is relatively undisturbed. 
This is the way I design now; My 55 footer dagger/rudders are 2/3 of ½ cwl length forward from the CL.

Or;

2. Is your hull U shaped, and every directional (induced) un-balance will have to be corrected heavily,  (I can give you an example of a sort of proa (not a Pacific Proa) that rounded up into the wind , suddenly, each time the ama hit a bigger wave.) for such cases you can place rudders like doors what you want, that kind of rounding up can’t be stopped. actually they have 2 rudders constantly working hard to keep the whole circus on the road.

Rudders that are further apart will shift the CLR more, for a given area.  And, the rudder needs to be a certain size to be effective.  What’s a good way of figuring out a that compromise?

An U-shape is very very dependent on that extra lateral area and position, and foils in general, as one cannot expect too much lateral resistance from the U-shape.
I don’t like U shape for a proa, I know that it has less wetted surface over a V , but , I need the V anyway,  to beach and dry-out on the strong V shape bottom.  Besides its better in case of collision.
U-shape needs a separate outside wide keelplate , otherwise , small stones and sharp stuff will dent and/or penetrated your vaka skin.
You can try to establish the ideal rudder blade and position, but as I have written already,
you need ;  at speed             ; barely any rudder.
          manoeuvring in harbours ;  plenty area , so the manoeuvring will determine the area,not the sailing.
I stick to the relative sizes of Pacific Bee, as I found them just big enough to do the tight harbour stuff, at sea I don’t bother about the rudder , as long as the autohelm has no problem with it.

Your discussion of weather helm caused by too much weight to windward was fascinating.  As a rule of thumb, how far to windward should the rig be relative to the centreline of the Vaka to balance well?  Is it proportional to the displacement of the vaka and ama?

The amount of distance of the rig to windward has mainly two reasons
1. It provides an angle for the stays to leeward.
2. It sets the driving force in line with all other forces working on the total platform.(beating upwind) however this should not be overemphasized,  as you can understand if looking to all U-tube International Canoe class video’s ,its much the same,  see
  http://www.youtube.com/watch?v=3eLAsO2FxpQ&feature=related
as long as you manage to skim that ama, or discharge the waterballast , and so ride a light ama, you esentially sailing a monohull /international10m2 canoe.

A too short /displacing and so heavy riding ama is bad for any proa.

Note;
I notice that in general on all the forums, way too much small talk goes into all the “balancing forces” corner , I don’t dismiss that, only , you talk about marginal gains, in a cruising Pacific Proa.  Now if we go to a speed record Vector Proa, it obviously all of a sudden IS a big deal, for sure as all factors are magnified.

Many thanks,
Chris

Cheers Sven

Hi Sven,
Thanks for sharing all this great info.
I have one question about your skeg/rudders. Maybe I’m missing the obvious - how do you orient the rudders? Are both rudders facing toward each other, or do you pull out the “cassettes” and flip them whenever you shunt to orient the skegs in the new direction of travel? It seems that the skeg must be oriented in the direction of travel for the foam crash block to be effective. Please clarify.
Many thanks,
Curtis

Hi Sven,
Thanks for sharing all this great info.
I have one question about your skeg/rudders. Maybe I’m missing the obvious - how do you orient the rudders? Are both rudders facing toward each other, or do you pull out the “cassettes” and flip them whenever you shunt to orient the skegs in the new direction of travel? It seems that the skeg must be oriented in the direction of travel for the foam crash block to be effective. Please clarify.
Many thanks,
Curtis

Hi Curtis welcome to the proaworld, I attached a drawing ,I suggest it explains it all , if not , let me know.
you could also go to ;
http://www.clcboats.com/shop/boats/wooden-sailboat-kits/proa/madness-31-foot-pacific-proa.html 
http://www.wingo.com/proa/brown/jzerro-shop-l.jpg

cheers Sven

Duh, of course! I assumed both skegs needed to be lowered for lateral resistance. I guess the hull shape takes care of that.
Thanks for the quick reply,
Curtis

On the subject of asymmetrical vaka, isn’t there some merit in using it to prevent leeward slip in place of a daggerboard? Otherwise, the hull is going to be steered to windward—and therefore slide sideways—to a greater extent while implementing a fixed daggerboard.

hi, Adam,

quote my post #8 —-Downwind Yawing in a heavy seaway ; I never fight that motion let the waves take their cause, you likely to find yourself in the original path, ones the wave cycle has passed , and without aggressively having to correct.
I find a daggerboard to only disturb the easy vaka ama movement, more precisely it can bite and send you specifically into the direction you not intending to go. i.e. you get an easier motion without daggerboard,
besides the long narrow vaka/ama has plenty directional stability without that daggerboard.———unquote

furthermore—Russell Brown tried A-symmetric in Jzerro,  I have talked to him about it, to compare it against Pacific Bee behaviour , and as I was suspecting , he renders it not worth doing. 
-  1. to some extent it ruins the straight line tracking of the vaka. 
-  2.  the higher the speed the more force will be generated from that a-symmetric shape, as such that will generate a steering force, which a bearing-off result.
-  3. We do not have a lateral area / leeway problem, I often sail upwind without the daggerboard down.  So Its largely dependent on the lateral shape of your vaka, Pacific Bee is deep V. Jzerro is also deep V ,slightly bit flatter.

I can however imagine that very U-shaped vaka’s might have , leeway problems , here a correct placed daggerboard is essential. ( Iam currently experimenting with the correct placement of a good lift generating daggerboard.)

Cheers Sven

Post #  28.  AMA FOIL PLACEMENT
redirected from post ;  .............................................
Chris wrote; I’ve been wondering about the benefits of having a daggerboard or other foil in the ama.
Why have a third foil on a boat like Jzerro or Madness, where the dagger rudders *should* do the job?  Is it about having more foil in the water upwind?  Is it about having the a foil upwind of the rig?  What effect does it have on the handling of the boat?

Aloha Chris , the road i am travelling with the 52 footer below;

1. Chris; Why have a third foil on a boat like Jzerro or Madness. 

-I don’t want a foil inside or to weather of the vaka , it interferes too much with the vaka interior, center beam ,mast position, or surfacing the waterplane near the hull , let alone running such a strong foil aground at speed.
so automatically we end up either near or in the ama hull.
further I expect to gain eventually way more with foils out there, as we are also
experimenting with a hydrofoil setup, so the ama will be prepared for that. 

2. Chris;  where the dagger rudders *should* do the job? 

they not necessary do the job together, let me explain ;
Pacific Bee uses its aft rudder only, the bow one is totally lifted,as such blocked from turning. [on Jzerro I believe that Russell sails with the forward board down a foot or so ,also blocked from turning.

The thing is; I donot have a directional problem on Pacific Bee, so I have yet to try that, to see what happens , so you see even these slightly different Pacific Proas behave not alike. also it could well have something to do with Russell’s a-symetrical vaka, generating a slight bow to leeward force, I have to ask him if he is,and what he is correcting ,if anything.

3. Chris; Is it about having more foil in the water upwind?

I say yes , to point higher, I put the ama foil full down.  [same in tight quarters manoeuvring]

4.Chris; Is it about having the foil upwind of the rig? 

I think you mean for vector proa like?,
No , without extensive testing and measuring , I can’t see a way to suggest that it has something to do with balance   in the present boats.
I seldom use that ama foil now , [except hard upwind]  most times its fully up sailing, full down ; tight harbour manoeuvring .
On the new 52footer design, I planned to install 2 a-symmetric foils , angled to leeway, exiting the ama above the waterline. it will be a variable testbed to find out new balance, as not enough is yet known about the precise effects.
Some armchair theory can be put in , but I rather try this very complex set of variables, to see what works best.
I even suggest that the whole foil matter, is largely in relation with the shape of vaka/ama.
- deep V—versus—flat—versus—round—vaka/ama , I think they all react very differently to their foil setup.
also a schooner rigs configuration [Laurent, and Philippe ‘Des jours meullieur] will react ,more, controlled to the foils, relative to a sloop rigged Pacific Proa .

There is a lot of steering with sails i.e. Center of effort CE versus center of lateral resistance. CLR going on ,specifically important to control a slooprig version of the Pacific Proa. [steering w/ sails]
Hence an aerorig will never give you that flexible control , as its fixed very centrally in the hull. out there is a setup that has to correct its way of travel with 2 rudders steering, we don’t have to do that, as these proa’s are tracking like on railroad tracks. so for me its a nono to change that this balanced setup.

to be added further….....

cheers Sven

Post # 29         RUDDER SYSTEM DEVELOPMENT          on   34+ Pacific Proa’s .

[work in Progress,    ]

2. Chris;  where the dagger rudders *should* do the job?

they not necessary do the job together, let me explain ;
Pacific Bee uses its aft rudder only, the bow one is totally lifted,as such blocked from turning. [on Jzerro I believe that Russell sails with the forward board down a foot or so ,also blocked from turning.

The thing is; I donot have a directional problem on Pacific Bee, so I have yet to try that, to see what happens

3. Chris; Is it about having more foil in the water upwind?

I say yes , to point higher, I put the ama foil full down.  [same in tight quarters manoeuvring]

4.Chris; Is it about having the foil upwind of the rig?

I think you mean for vector proa like?,
No

First of all, thanks, Sven, for always answering our many, many questions.  Your advice is much appreciated.

So my question is; what is the difference in upwind performance between using the daggerboard in the ama compared with putting the front rudder dagger down a little.  Both change the CLR.  Is there a performance difference between those two options?  What is it?

I want to build as few foils as possible, but I also want to get to windward well.

aloha,
chris