CONTENTS                                                                                                 edited;  20th May. 2014
Post #  00.  GENERAL CONSIDERATIONS & DEFINITIONS                        
Post #  03.  RIGHTING MOMENT TABLES                
Post #  04.  HANDLING THE RIGHTING MOMENT            
Post #  05.  SCIMMING & WATERBALLAST       (to be edited soon)
Post #  06.  STABILITY IN PRACTICE , Sparring the Open 40
Post #  08.  POD DESIGN & RESERVE BOUYANCY
Post #  09.  CLARIFYING THE DYNAMIC HEELING   (updated 7 sept 13)
Post #  11.  STABILITY IN PRACTICE   Heeling test KAURI
Post #  13.  BEAMS, POD & COCKPIT CLEARANCE.
Post #  16.  HEIGHT of CG
Post #  31.  HOW LIGHT IS LIGHT ENOUGH ? [related to righting moment] 

_______________________________________________________________________________________________
Post #  00.  General Considerations

Aloha Proafans,

Disclaimer;
It is not my intention to claim this specific setup to be the best, or the only possible solution,  but the Russell Brown designs are well proven Blue Water Pacific Proa’s and so a very solid base , to develop the Pacific Proa into a even better performing craft.

____________________________________________________________________________________________
PACIFIC BEE (ex Cimba)  38 ft Russell Brown designed and build Cruising Pacific Proa. 

Pacific Bee   Just pulled onto the hard by Pick-Up truck                     Mobjack Bay, VA. 2009  

Thanks sven for sharing your knowledge with us. Its much appreciated.
My question relates only to the ease of completing a shunt.
Have you considered furling head-sails or do you feel the penalty of weight aloft and windage is too great a price to pay?. I understand the efficiency of a partially furled sail is poor so from a performance point it is not a good option. Would like to hear your thoughts on this.
Regards.

Hi ,Phillip,  please go to TECHNICAL       PACIFIC BEE   FOILS an SAILPLAN   Cheers Sven

Article # 2.  Pacific Bee Righting moment tables        

Aloha Proafans,  VWW   Variable Weight to Windward

For the interested Pacific Bee righting moment tables
Trim ; full cruising gear for 4 persons
      full Fresh water tank
      40 ltr fuel
      4 crew     and a   Jack Russell ,  she bites !!!
      dry food and freezer stores
      2 sets of anchors
      Zodiac & 3.5hp
      books
      etc etc

The First table is max Rm @ 30000 ft/lbs full waterballast (was never used at that amount, because its not neccesary
The Second table is   Rm @ 16000 ft/lbs
I could add a Third table in racing trim , but the only difference would be in the sailing displacement some odd 200kg less.
And of course I am happy to explain and discuss further Rm figures if there is any un-clarity.

Any combination in between is possible as such this is a;

VWW (Variable Weight to Windward) Pacific Proa.

Post #  04.  Handling the Variable Righting Moment RmVa

Quoted from Topic Pacific Bee sailplan & foils
James wrote;  I remember you saying that you shortened Pacific Bee’s beams to reduce RM and now i see you did it to conform to the optimal overall beam that the tank testing indicated. A good real world test for the experimental data.  Did the shortening of the beams live up to all your expectations?

Aloha James , Yes, but there is more to the issue, so I will answer it in a broader sense to clarify the outrigger workings by combining the reasoning behind the variable weight to windward on Pacific Bee .
By cutting the beams I was solving a combination of issues in one go;

1. The beams were cut to prepare them for this winters new ama.

2. The 27 year old ama beam bulkhead connection was damaged inside the ama, establishing a leak where the beam went into the ama, this came to light in a violent 24hrs 52 knot storm in the Med. In 2010. nothing serious but ,I had to do some surgery.
I have now the same beam to ama connection as Kauri & Jzerro instead of running into the ama. Bolted outside,  that’s way better and warrants the watertight integrity of the ama at all times.

Note; As I surveyed the ama beam bulkhead damage , it became clear to me that it was most likely caused by the missing brace wires linking the vaka bows to the beam ends. They were not there when I acquired Cimba,  I did not realize their importance enough when pushing Pacific Bee so hard in a seaway.  But in the new ama setup I will install those brace wires to keep the beam end rotational forces at bay.

3.This bolted beam connection is way more easy to attach when putting the proa together from trailer to water, instead of forcing the beams in their sockets and sealing them each time.

4. The total conceptual CL to CL width was over the intended number, so we narrowed the platform by 500mm .

5. The current ama was riding too heavy in a seaway, due to having too much Rm , a further prove that too much Rm is no good.

6. I feel confident to say that the new 1:20 B/L ratio ama will improve the overall performance significantly,  together with an as light and strong as possible construction, added water ballast system,  and so capable of adapting the RM to any condition at an instant.
———————————————————————————————————————
Reducing the arm of the outrigger = reducing the Rm .  How far you can go depends on the proper calculation , development and proper use of the Rm-var spreadsheet.

I hope to establish the understanding,  that there is a scope of Rm , to work between, and as such called by me Rm-var , as 2/3 of the Rm can be changed at will.

A. Light weather mode; you lighten up your ama by having no waterballast at all.
B. Heavy weather mode ; you have full waterballast .
And any modes in between, to enable you to scim the ama.

That’s in my opinion the beauty of the Pacific Proa, the total platform remains lightly loaded at all time.

A too heavy ama would result in a bad behaving uneven hull length catamaran, trying to drag its too short windward hull in a too heavy displacement mode through the water.

a few more considerations;
It is proven that a heavy too short ama is always dragging in displacement mode at a slow speed , so the first thing to solve is getting that ama displacement as low as possible , and to seek scimming,  in order to get rid of the platform “island” feeling , besides that being dangerous offshore or even inshore on a lee coast for that matter.
-.What I see often stated on other forums;  that it is a constant “struggle “ to keep a Pacific Proa on its feet, that is absolute ridicule non-sense;

It is suggested that you would constantly have to work hard on your righting moment,  this is simply not the case, as the weather condition do not change constantly and suddenly all the time, there are many,many hours of sailing without sail change , neither is the ballast figuration changed during sailing. [and for that matter not at all on the previous setup of Pacific Bee [without waterballast]]

If the platform is designed properly and handled accordingly by way of operating the waterballast system at convenient intervals.  ( see Post # 05 scimming &  waterballast)

More on the issue later……………or to anyones question and/or remarks…………………..
Cheers Sven

Post #  05.  Waterballast & Systems.

  Coming up soon   I have to edit that piece…....
Cheers Sven

Post 06.  Stability in Practice, sparring the Open 40.

Pacific Bee against the modern Open 40.

First of all Pacific Bee has NO RM issue whatsoever, and neither does the 36’ Jzerro , My family isn’t running around the net, to keep the proa on her feet, it’s just a matter of sailing properly, the combined forces act in a very docile way into the structure.
Even a sudden big gusts is easy to react upon, nothing new here, as easy as sailing any sportsboat.
In June I actually cut some 3ft of the beams to reduce RM.
I am only too glad to get rid of some RM to be able to scim the ama earlier, having a weather hull displacing any serious amounts of water is obviously the very wrong way to sail a proa .
Especially when Scimming the ama, the speed is astonishing, this summer going upwind with my family we could compare our performance against the newest French Open 40’s training outside La Trinite sur mer ,France.
Although we were in heavy cruising trim, I just wanted to know how we faired against them.

We started next to them, we a bit to leeward on porttack. The condition at that moment was moderate steep chop say; about 4ft by some 3/4 of Bee’s length, wind about 14knots true, nice and steady, full main and working jib we were doing between 8.5 and 8.9 knots on GPS, we could not maintain their height by about 5 degrees, but we went about 3/4 to 1 knot faster, so we gradually fell under them, the bearing on them seemed to remain the same, which means we had more boatspeed.

Some 4 miles upwind and some roughly 500 m below them, we decided to make a very quick shunt, to see how far we would pass astern of them, when we were tracking again I looked under the sail to see them, unfortunately they had tacked too ,but as I was going lower we would meet again later , some 10 minutes
later they tacked, oeps they had the right of way now, so I prepared to stop Pacific Bee to let them pass in front of me, keeping a close eye on them.

After looking a few times I saw the bearing shifting in favour of me , we cleared both Open 40 by 75meters, haha in the pocket…, ever since I owned this proa I was waiting for such a moment . although the shunting was clearly slower than there quick tacking.

Bee was handling the chop like a dream , slicing through the chop without slowing down, the GPS seldom changing the figures , you could clearly see them crash regularly in the crests. We shunt through 90 degrees , I think they were tacking through 80 degrees, well anyhow , I am used to sailing boats a bit lower ,finding the end VMG most often better, bit more miles , but way quicker.

Please Don’t forget that were comparing state of the art top 1/4 million dollar Open 40’s against a wooden 25year+ old cruising machine, I really regret not to have started this Pacific Proa fun earlier in life.

Later in the afternoon we had the code-0 up, TWA from the quarter reaching along, in the distance next to us we spotted a group of Open 40’s w/code -0’s up, racing back to the harbour, bit less wind about 12 knots true now, we were tracking at a sustained 15.5 knots , there was really no doubt about the performance difference now, we were on our mooring, cleared the decks, and sitting halfway through our first beer when the first came in. it’s always fun to clear the deck quickly, and sit down with a modest face .

They circled Bee to see what sailed so fast with barely any rig, later ashore (the French have a nice relaxed sailing attitude in there bars, without the general blabla, very refreshing !) one of them said that it’s an amazing sight to see such short rig go so fast in the distance, he admitted that they were first smiling a bit about Bee, till it start moving.
The French really love this machine……, and you’ll get all the help you want , Charlie Chapelle
http://www.technologiemarine.com offered his yard & tools might I need anything.
As for running sails ,I don’t know yet , we have to try that later. I specifically do not have any runners onboard at the moment, I rather jibe, and head up a little to get AWS over the deck, Jibe again down the lane ,etc. If any I
would suggest sort of 1/2 oz. floater/wind seeker might be useful, have to ask Russell someday.

Cheers, Sven Stevens “Pacific Bee”

Aloha Sven,

Thanks again for sharing all of this detailed info with us.  I have a stability question, or 5, about lee pods.

I understand that every design calls for a lot of tuning of these details, but in general, would you share your thoughts with us on the following;

At about what angle of heel should the lee pod touch the water?

At about what angle should it be fully loaded up to resist capsize?

How much is it loaded to resist capsize as a percentage of overall displacement?

What about the length of the pod.  Pacific Bee and Jzerro look like they have lee pods that are about 1/3 the overall length of the Vaka.  What are your thoughts about how long they should be?

You mentioned that your lee pod does not slam.  Any thoughts on pod clearance in a seaway?

If this is too simplistic a way of looking at these factors, what is the right way to look at them?

Keep the great information and pics coming, please.

Best,
Chris

Post #  08.  Pod design & Reserve Bouyancy

Hi Chris, Please first read   Stability Post # 09   for general info what happenes during sailing.

  (working on on your other question,  btw great stuff Thing-Tank)

Post #  09.  Clarifying the dynamic heeling

The Brown Pacific Bee is often attacked for lacking stability ,this due to misunderstanding the proces, for these individuals, a lot of dinghy racing hours would have helped, I found an interesting comparison between sailing an International 10m2 canoe and a Pacific Proa. I suggest that to get a better understanding on how a bigger Pacific Proa behaves, such videos should be watched at length.

You will notice that in general none of the IC helmsman change there position on the outrigger plank, instead they keep the canoe at speed, playing their sheet and tiller.  enjoy.

http://www.youtube.com/watch?v=zHwDRbIDPDY

PACIFIC BEE dynamic heeling
I speak about CLOSEHAULED only . Hard upwind means you have the sail wardrobe in the humble mast, for THAT specific weather condition.
So I presume in below sketched situation that we are sailing FULL sail wardrobe. [full main and 100% working jib.]
This give a true wind force of 12-15 knots.  Otherwise;  I would be out there in reefed condition.
the sweet spot of Pacific Bee is about 10-15 knots true, when going upwind.

Scimming the ama.      0 to 4 degrees heel,  [ total time at these angles ; 99.95%]
Note,  that we established already that we sail at a maximum heeling angle of 4 degrees, as that is the ideal scimming setting.
Actual “setting” might be the wrong word , as it is a constant heaving and lowering of the ama within this bandwidth, following the changing apparent wind-strength

now we have the sailing conditions as shown on this recent Jzerro video; enjoy
http://www.youtube.com/user/ptwatercraft#p/a/u/0/HevgDyupZeY

Flying the ama.      4 to 15 degrees heel [ total time at these angles ; 0,05%]
So from 4 degrees to 15 degrees (pod starting to touch the water) its called “flying the ama”  we Never fly the ama.  (unless we want to show off)

So we talk about upwind only, as any other course is a less interesting issue , due to the reduced overturning power vector, pointing more in the direction of travel.

At 15 degrees heel the pod starts to skid the water like a wing , now you are still at speed here, not a sitting duck, enabling you to correct that heel very easily , by slipping a bit of mainsheet or/and steering upwind.
Note; the wing adds to the righting moment, dynamically speaking, by its shape. i.e. it adds by pushing the pod out of the water. Still this is NO HIGH ALERT Status.

Heeling 15 to 24 degrees
Onwards from this 15 degrees heel ,the overturning force has to work against that pod , you really need a tremendous force to get that pod further submerged, as is logical and needs no further explanation .
By now the sails are spilling, both by its angle to the wind [reduced heeling force,], and by dumping some sheet. .,the water shooting under the podwing . is starting to push it upwards seriously
                                                                        CB =Centre Bouyancy
Heeling 24 to 43 degrees
At 24 degrees heel , the pod has taken over about half of the total displacement. Shifting the CB about 1000mm to leeward , as such increasing the Rm upwards again. [you are still sailing, so still able to dump sheet and
luff.] water shooting under the podwing is seriously pushing it upwards now. [fore and aft tip of that podwing are still 300mm above waterplane., so no stalling of that pod as I hear often suggested.]

Heeling 43 and onwards
At 43 degrees heel, the pod has taken over the TOTAL Displacement , as such shifting the CB 720mm outboard, Total CB shift further to leeward , its now at 1720mm from the vaka CL

I would not suggest that you are sailing now, neither will I suggest that you can steer now. ,or that it funny like that.
But regarding the available RM you are now again about at the max of it this , due to the shifted CB !!!
Added to that is the whole weight of the vaka starting to be lifted into the air.

How about that to comfort the Pacific Proa pilots mind !!

I will now continue to heel the proa over even further, although it starts to be Hypothetical as at say 43 degrees heel , 15 knots true there is simply NOT ENOUGH POWER to do so. , but anyhow I will do that for you…. For discussion sake.

At 90 degrees heel , near impossible to get to, due to the CB now in the high attached pod , vaka TOTALLY clear of the water by some 200mm.

At 105 degrees heel Statically speaking ; we arrived at the point of no return .(full ama waterballast tanks)
Dynamically, however, I suggest that that point can be anywhere between 90 and 105 because of unknown condition, to name a few, was there waterballast yes/no, was it only a huge gust , [storm is unlikely because you do not have any sail [bar stormjib] on that proa, at least if you had any brain particles left.]

POINT MADE; this sailing capsize scenario is unrealistic, as the helmsman was NOT, sailing in such severe conditions w/full sail wardrobe ,  remember full wardrope= 15knots True max.

Neither does a proa pilot pick his routes like that, he would have evaluated his Grib files already, staying away from this unrealistic scenario in the first place, or reefed down well in advance.

i.e the whole discussion /scenery as I see often suggested, regarding capsize is untrue , an near to impossible to contemplate or encounter.

Concluding, Yet another demystified fairytale , about the workings of a Brown pacific proa
Cheers Sven

Aloha Sven,

As usual, your explanation is fantastic and clear.  This is super useful information.

I laughed out loud when I read;

“I would not suggest that you are sailing now, neither will I suggest that you can steer now.”  As someone who has encountered an unresponsive helm when extremely heeled in all manner of boats, from big monohulls to my beloved Nacra 5.8, I hear you! 

There are so many pieces of information that are usefull here.  The very narrow range of flying before the pod engages is fascinating.  I really appreciated the details about the forward tip of the pod staying above the waterplane, even at high angles of heel.  This is really great, actionable info for my design noodlings.

Thanks, as always,
Chris

Post #  11 STABILITY IN PRACTICE   heeling test KAURI

PARK IT, DAD by Jim Brown - Russell and Jim Brown sail proa KAURI from Bermuda to New England
Chapter 18 of Jim Brown’s “Among the Multihulls, Vol. 2”

Mr. Jim Brown wrote; quote ;  I recalled how we had tested KAURI’s stability on our river in Virginia.

Using two anchors to position the boat near the river shore we then brought a line from the masthead to the bank, where Steve, Russ and I hauled as hard as we could, trying to pick up the float and heel the vessel over.

Indeed we were able to lift the outrigger float clear of the water, but as soon as the craft had heeled enough to press the pod down onto the surface, our continued efforts to tip the boat were to no avail.

I brought our old Pontiac station wagon into hauling position, and we tied the line to that. Then we hauled again, with 250 horsepower, and the boat heeled way over.

As the mast came down, the outrigger float climbed skyward. Surprisingly, as the pod was forced to submerge, the main hull was literally picked up by it, almost completely out of the water! It was now abundantly clear that the main hull acted as a powerful counterweight against the buoyancy of the pod, trying hard to re-right the vessel.

With the station wagon’s handbrake set and Steven blocking the wheels, I got out of the driver’s seat and noticed that the line from the wagon to KAURI’s masthead was bar taught, and furthermore, Russell was already half way between the shore and the boat. His feet were dangling in the water as he went hand over hand along the line, headed for the horizontal mast.

He reached it and pulled his legs almost free of the water. At this point, his weight, at the very top of the mast, finally overcame the knockdown stability of the vessel, and she continued heeling, which lowered Russ back into the water. When he let go, the craft snapped back toward upright until it was restrained by the line to the station wagon. It was an amazing demonstration.

I knew there were few multihulls of any size that would exhibit such ultimate stability.  ——un-quote

for further info on PARK IT DAD;  http://www.wingo.com/proa/brown/park_it_dad.html

Hey Sven, I want to thank you as well for your detailed and very informative posts! I’m a bit curious about the clearance question as well;

You mentioned that your lee pod does not slam.  Any thoughts on pod clearance in a seaway?

How much clearance do the lee pod, cockpit floor, and akas have from the waterline?

Cheers,
Marco

Manik - 06 September 2013 04:30 AM

Hey Sven, I want to thank you as well for your detailed and very informative posts! I’m a bit curious about the clearance question as well;

You mentioned that your lee pod does not slam.  Any thoughts on pod clearance in a seaway?

How much clearance do the lee pod, cockpit floor, and akas have from the waterline?

Cheers,
Marco

Aloha Marco,  All,

Just added another extended cruise in the Med.  Pacific Bee was set on a diet for this season, we removed all excessive weights & gear ,  replaced the pod by a super light carbon one,  it weights in a 34.4 kg now, the old wooden one was 78kg ,and near impossible to mount [when coming of the trailer, assembling the platform]

Ok, about your “clearance” question;

In general it makes a lot of difference how you want to use your Proa, for daysailing within the vicinity of a safe harbour , I suggest you could go for minimum height of these parts.
Not so for coastal [offshore use] ,  In sequence of importance ;  This in relation with very bad offshore weather.

1. Beam-ends.    most important the beams-ends shall stay well clear of the deck of the ama. i.e. running the beams with a bend into the ama , because if the ama submerges in a big wave , it can result in a violent roundup,  so a design requirement would be to have minimum frontal area beamends , for this look at the ancient pacific proas , they all had light vertical beamends, before connecting it to the vaka by way of a beam.
That roundup thing only happened twice to me, and this in very,very bad weather . But if you are designing from scratch I would tend it.

2.Cockpit.  the cockpit is the most vulnerable of all , as all heavy sea & breakers are approaching from the side of the ama.  I had several breakers hit the cockpit-vaka bottom corner, a few where able to lift the cockpit up off the beams.
At the same time the tail-end of the O/B will be hit,  the total engine getting very wet in the process , trying to drown it, but no damage yet, I really have to maintain the O/B frequently.
[note ; my extended cockpit is hanging over the beams,  as such not a construction part of the vaka, its tied down to the beams]

In the new 52ft design I minimized the exposed area of the cockpit to counter-act this inconvenience , on PB I will reduce PB cockpit width again this winter. 

3.Pod.  The pod [I often read] seems to be cause for a lot of discussion;
here is what it does NOT;
- reaching & running .  being hit by waves. [ as its in the lee of the vaka]
-  upwind               being hit by waves , while driving through waves. [ as its in the centre of pitch, the vaka bow has already heaved the centre of vaka way high enough]
                   
So any specific pod-height is merely related to; WHEN do you expect to get reserve RM in a knockdown, I think Russell has done a fine job of that in PB , as quoted earlier I manage to dip the windows of the pod under only ones, during a sudden big gust, while I wasn’t paying proper attention. no harm done here.

to give you a precise figure I would have to see what you are designing to give an opinion. 

Ballpark figure could be; that at 45 degrees heel I would want 100% displacement volume in my pod.

Cheers Sven.

Sven,
good reply, it is counter intuitive that the pod would not slam, but now we know better!
I had thought of a pod extending fore & aft to merge gently with the hull. Then saw a video of Russel, going fast, the spray comes off the bow, but lands well before the pod,  so yet again he got it right (and first time - Jzero, was this good luck or is he just a genius?!)
Mark
ps so your pod is detachable,  where does it divide?

Aloha Mark;

Sorry for answering so late, the pod can be detached for road transport , the cockpit will do so too, Pacific Bee width can be reduced for a 40 ft High Cube container to 2.34m width, as such its also narrow enough for normal permit free road transport. see Picture you can see both cockpit and pod loaded on foredecks.

the pod is bolted to the vaka near the lee vaka sheer , the only reason for using corecell & carbon in the pod is to have it as light as possible for lifting it in place. 

the cockpit rests on the beams, as such can be lifted off in a minute after removing the net.

Pacific Bee is dry-sailed because berthing placing are simply not available around here.  it takes 2 persons about a full morning to put him together,rig and launch.  and the afternoon to fit the mainsail , lee net/railing rigged.

cheers Sven