Aligning CE with CRL on a Multi-Hull

[@MattTucker]

More amateur Proa designers need to watch this. I've learnt the mechanics of it through trial and error but so many Proas are designed and built with balance issues because they design them from looking at 99.999% of boats (which aren't Proas). Great explanations thanks!

[@markpalmquist]

Thanks! I agree, the traditional proas work better than some of the modern proas. I spent 3 years making test models and sailing them across the local duck pond. Some of them sailed better backwards. You learn a lot when a boat sails better backwards.

[@zooknut]

Thanks Mark, great explanation. I’m a monomoran sailer about to come over to the dark side and sail multi’s for convenience. I’m looking to build a small 18’ tri and downsize from a bigger 26’ trailer yacht as I don’t have the ability to get crew much these days. Launching and retrieving single handed with a bigger yacht is hard, especially if the wind is up. With the small tri I wanted to move the rig aft to align more with the centre boards on the hulls of a Hobie 18 so I didn’t have to build in a keel trunk on the main hull and use a Hobie 18 instead of building amas. Looks like I should be able to work it out now and then get the designer to approve the mod. Thanks again, Nick.

[@markpalmquist]

Sure, glad it was helpful. Your outriggers will be Hobie 18 hulls? The general rule with trimarans is to position the center of pressure of the sails 10-12% back from center of main hull. I’ve seen large racing trimarans with the combined sail area 13% back.

[@laurentfournier561]

Thanks for this clear explanation. Loved to hear about "Cheers" and praos in general. Cheers, Mark

[@markpalmquist]

Thanks. I am a big fan of the Atlantic proa because of its greater righting moment. With a windward pod, they are also very safe.

[@robertlaird6746]

As a young kid, I went to sailing school in the summer time for racing Naple Sabots and then Lasers. I learned one of those first principles but not the rest of the stuff you spoke about. That's great information to know. Thanks.

[@markpalmquist]

Glad it was informative. I cringe when I watch it. There were a few omissions and misspoken words but in general it’s all accurate. Hobie shortened the length of the Hobie 18 side stays twice in order to rake the mast back. 1 thing I failed to mention is Mono hulls move their sails forward to account for asymmetric waterlines when heeled.

[@robertlaird6746]

@@markpalmquist Not sure why you said Hobie when nothing in the video showed that. I've sailed a few of the original Hobie cats but you could only go so fast before you pitch poled because of not having enough positive buoyancy. The Tornado catamarans also had that same issue. I had a Tornado and sold it because of that. I then got a Nacra 6.0 with a spinnaker but that boat had more power than I could handle so I sold that and got a Nacra 5.8. Both the Nacra 6.0 and the 5.8 had the right amount of positive buoyancy which made me not have to trapeze out over the rudder. With the right amount of positive buoyancy, you could easily get out on the trapeze amidships without burring the bow of the leeward hull. If you want to cut down on spray than you would have to have a knife edge bow but somewhat quickly blend the shape into a wider shape so that you had enough positive buoyancy. I hope that explains it but again, why did you use the name Hobie?

[@markpalmquist]

@@robertlaird6746 In the video, I say that more recently (in this century) tri and cat designers have moved their sail rigs backwards on new models. Hobie modified the design of the 18 without making new molds and without shifting the mast step backwards by tipping their rigs backwards by shortening the length of their side stays. So depending on the model year, a Hobie 18 mast will either be vertical or raked backwards. The newest Nacras all have mast positions and dagger board positions much further back which allows the boats to attain higher speeds before the lee hull digs in. The Tornado was designed in the late 60's and therefore also has a problem with digging in as you said. The new Nacras are excellent boats. I just used Hobie as an example of the trend which is to move the sail rig further back. And as you also said, the newer hulls tend to have more volume in their cross sections in the front 1/3.

[@robertlaird6746]

@@markpalmquist That's pretty amazing how you know this stuff. I've always wondered how a boat was designed. I'd actually like to know more.

[@robertlaird6746]

@@markpalmquist I'd like to build a proa. Is there any plans available?

[@daveamies5031]

Awesome video, great explanations, deserves many more likes 👍🏼

[@BalkanShipyards]

Always happy to meet again Dave.... yeah, great video! My best Proa Make O'Break and the new HAVAYA are exactly like this video explains. It's a great Video, deserves many more likes.......

[@daveamies5031]

@@BalkanShipyards I agree, I was watching this thinking about you le shunk and how your junk rig moves exactly into the position described, hopefully us commenting here with help the YT algorithm promote this video to the status it deserves.

[@BalkanShipyards]

@@daveamies5031The Force is strong with Mark, for he shares wisdom.....

[@pakde8002]

This really filled in a lot of holes in my knowledge of sail physics. I want to build a multihull here in Bali but I'm more interested in utilitarian use (fishing > trolling) as opposed to racing, so stability and ease of operation are more important than speed for my design considerations. I'm sure you're familiar with the Balinese jukung, which is a traditional fishing trimaran but they also hold races each year with speeds over 25 knots using huge crab claw sails that are flown pretty much horizontal with the end of the sail even running on top of the water. I haven't seen any using a keel or lee board and I'm assuming the deepish knife shape hull is how they manage without one. I never see the crew hanging out the side as counter balance either as you would on a western style multihull. The sail is basically the same length as the boat with the short "mast" (actually a sail hanger I suppose) towards the bow approximately one quarter of the boat. What I'm trying to say is these boats break every rule you mentioned yet are very stable,, run extremely fast, handle heavy winds and seas, and tack very quickly using a very interesting maneuver that is better seen than described. I've been trying to find information on how its possible but it seems a lot of naval engineers are also perplexed.

[@markpalmquist]

I just watched a video of a Balinese jukung. A few comments: 1) a deep V center hull suffices for a keel or dagger board 2) a crab claw sail flown more horizontally creates less heeling because its center of effort is lower 3). the sail is slightly inclined to windward, which also reduces heel 4) the lift on a crab claw sail is different from the lift on a tall high aspect ratio sail. Instead of attached flow, you get a rolling vortex on both edges of the sail which create low pressure. 5) according to the findings of Marchaj, this sail will outperform a bermuda rig of similar sail area when going on a beam reach but not when pointing. I have no way of knowing how well these point, but I doubt they point as well as a modern racing trimaran with a bermuda rig and dagger boards.

[@BalkanShipyards]

Good Stuff, well put!

[@daveamies5031]

No surprise to see you here Rael 👍🏼

[@vgaulin]

Very interesting !

[@doyouwanttogivemelekiss3097]

Around the 11:00 mark: "you can't really move the sail" - wasn't this the point of many traditional rigs with masts that tilt slightly and/or bend?

[@markpalmquist]

On a shunting proa, yes, but usually on a tacking outrigger there is a fixed mast step.

[@doyouwanttogivemelekiss3097]

@@markpalmquist awesome!

[@TheErmerm999]

I have been pretty interested in proa's for awhile, a lot of the pacific proa's use a ballestron rig balanced by design, with imbalance achieved using trim or reefing, I have also seen schooner rig as shown by your Atlantic proa example. My question as the windward outrigger lifts this moves the CLR toward the leeward hull could a head sail help move the CE forward, to reduce the moment and if so why do you never see that favouring the ballestron rig instead . The second confusion a lot of modern yacht proa's seem to build shorter but heavy windward hulls which would seem to me to make it harder to move lift them moving the CLR into the leeward hull, is this to increase the potential power in the size of rig or something weird going on.

[@markpalmquist]

I believe the Ballestron rig is better at pointing than a traditional crab claw sail. It is basically a swiveling bermuda sloop. Question 1 when the CLR moves towards the windward hull, this puts the CE automatically more in front, so no putting more sail area in the front is not needed, except on larger heavier proas that never fly the windward hull. Question 2. most traditional Pacific Proas have a pivoting windward hull which greatly reduces drag. You may be referring to the Harry Proa which is a larger, modern Pacific Proa. Correct, having most weight in the smaller windward hull allows more surface area in the sails. Personally, I prefer tacking outriggers and Atlantic proas. Proas work best in open ocean going on a beam reach. Shunting takes more time than tacking. It was developed as the best method to get between 2 islands where the wind was always blowing perpendicular to the course of travel. A well designed modern pacific proa like Jzerro has a proven track record and can track well on all courses although upwind is not its strength.

[@chrispalmer1255]

Great video! Around the 12:20 mark you say that Pacific proas often have the sail pushed forward. But isn’t the outrigger always on the windward side? So, I’m confused as to how the pacific pros could sail 180* opposite of your pic while keeping the outrigger on the windward side? Would the sail then be located aft of center?

[@markpalmquist]

Pacific proas shunt their sails. Shunt means to uproot. They literally slide the sail to the other side so that the bow and stern switch sides. That is the traditional way. Modern versions of pacific proas rely on furling head sails to keep helm balance, for instance Jezerro, made by Russell Brown.

[@chrispalmer1255]

@@markpalmquist thank you for your response! That makes sense.

[@chrispalmer1255]

@@markpalmquist so I recently learned that there are some outriggers that can tack? Would love to hear you explain this. Please and thank you!

[@markpalmquist]

@@chrispalmer1255 I cover that at 8:32. For a tacking outrigger with a fixed sail, you need a way to shift a vertical foil forward or back. Most people use a pivoting Lee board. I use a sliding track. On larger boats having 2 dagger board slots is best, use forward position when outrigger is to leeward and backward position when outrigger is flying or lifting.

[@chrispalmer1255]

@@markpalmquist thank you!

[@antoniorospujante3821]

hi, I have a question, where do u get the 60% and 40% from the main and the jib? I mean, is just a relation between sail area for ex. 40sq meters from the jib and 60 sq meters from the main sail? thank you! such a interesting video!

[@markpalmquist]

Yes, I was just giving an example. It could be 70% main and 30% jib, depends on your boat. You calculate the area of the main and the jib. You add them together. Then you divide the jib by the total. This gives you a percentage. Then you move from Center of main towards center of jib exactly that percentage. The CE is often just behind the mast. One more thing I failed to mention, on a monohull you usually move the sail plan forward 10% and on a multihull you move the sail plan back 10% (with respect to the dagger board or keel). This has to do with differences in heeling. Monohulls tend to turn into the wind when heeling due to increased curvature of leeward waterline and multihulls tend to turn away from the wind when heeling due to increased drag from the leeward float. I hope that makes sense!

[@antoniorospujante3821]

@@markpalmquist wow thank you for the explanation, I am finishing naval architecture and unfortunately there is not much content on the web since the community is not very large and there is usually a lot of mysticism and not sharing too many Info. Thnks, you have a new suscriptor from Spain

[@markpalmquist]

@@antoniorospujante3821 I agree, there are a lot of books. Some of them are helpful and others just give formulas with no data. I plan on writing a sailboat design book some day that distills everything down to easy to follow concepts with simplified formulas.

[@markpalmquist]

@@antoniorospujante3821 also, the big naval architectural firms do not share their secrets. Too much money to be made. I go to sailboat shows and ask questions and have learned some of their secrets that way.

[@tsanakou]

Great! Thanks ;-)

[@stefantornblom1555]

If you want to learn about yacht design try to find another source. This is crap.

[@markpalmquist]

Oh really! Enlighten me.

[@stefantornblom1555]

What do you think happens when the keelboat heels. Look at the boat from a top view, the resistance is in the center of the boat and the driving forces is in the center of effort out to leeward. This results in a rotating moment to windward. It is not possible to establish the balance from a two dimensional side view. You describe the center of the sail area that is not the same as the center of effort. On a high aspect keel or daggerboard the cf is 25% of the cord. The driving force from the sails is divided in two forces one longitudinal driving force and one transverse side force. The driving force is balanced with the resistance of the boat and the side force is balanced with the lifting force from the daggerboard and rudder. Best regards Stefan Törnblom.

[@markpalmquist]

@@stefantornblom1555 this video is about multihulls, not keel boats. I agree I over simplified the process of finding the balance of a keelboat, because I wanted to focus on multihulls. As far as I know there are many videos on keelboat balance but none on cats, tris, proas, and tacking outriggers. Even so, most keelboat designers disregard the difference between center of area and center of pressure (on both the sails and the keel) and simply move the sail plan forward 6-14% of the keel depending on which kind of sail rig they plan to use to make up for the asymmetric waterline caused while heeling. Regarding separating the total effort of the sail into 2 components, heeling and pitching, that is much more confusing than showing the force as 1 diagonal line. I used the illustration of the string of a kite because it’s much more clear, the force acts through the string. Without this visualization method it’s impossible for most people to know where to place their vertical foils. It looks like you took classes on the subject, congratulations, however I have learned incites that have not been put into any book yet. I have over 40 books on sailboat design. Most of them are carbon copies of each other. Most focus entirely on monohulls or entirely on cats and tris. Multihulls are very different from keelboats. They don’t suffer from asymmetric water lines while heeling but they do suffer from leeward hull drag while heeling.