Advantage and merits of Ama daggerboards

In looking at various designs of Tri's there seems to be some conflicting merits and disadvantages of Ama daggerboards rather than 1 large daggerboard in the hull.

Advantages are as far as I can tell are.
A smaller board can be used as it is always full length in the water and so can be optimum size.
It can be inclined to give lift making the possibility of a smaller Ama.
Cost, even though there are two boards, the overall cost is probably less than one large board.
More room in the Hull.

Disadvantages are
The risk of striking and damaging the boards maybe slightly higher as you won't always be in a position to view the sailing line of the Ama.
Once under way it is difficult to retract.
Heavily loaded including loading the connecting beams.

Hull Daggerboard Advantages
1 board only to build.
When the hull starts to lift the board length is shortened allowing the boat to slip sideways acting as a sort of safety governor.
Disadvantages
Not able to create lift vertically.
intrusive in the hull.
once damaged then there is a risk of damaging the hull.

Comments and views please

 

I think you pretty much hit them all, Wayne.

The singular and small observation that I would have has to deal with sailing the boat with ama mounted lifting foils while solo. Your comment about being able to adjust the foils while underway (leeward foil) is correct as they are heavily loaded in their trunks. For this reason, it makes for a fairly committed deployment unless you can comfortably tack/gybe off the foil to be adjusted. If the skipper has to get out on the leeward ama to effect such an adjustment while underway, then there's an obvious premium for staying on the boat.

A brief example of this consideration... The Trans-Atlantic solo sailing record for the Route of Discovery that was held, until recently by Coville, was set with his ORMA60 trimaran. That boat ran the full-tilt, ama mounted banana foils seen on all the ORMA60 boats before their demise as a class.

Interestingly enough, Coville chose to not utilize banana foils in the amas of his current trimaran, Sodeb'O, when going for records, even though he has a large amount of experience with the setup. Also to note... Francis Joyon on IDEC has also opted out of the ama foil setup.

They both may decide to alter that thinking in the future if they feel compelled to up the stakes in their record attempts and can find it prudent to do so. Only time will tell on that score.

I should think that Gary Baigent would be able to give you some really precise lowdown on the whole picture regarding this topic.

 

The largest -and potentially the fastest of the G-Class tri's will use ama lifting foils-Banque Populaire*. One thing has to be clarified ,though. Those that use ama foils for a large amount of vertical lift(70% of the all up weight on Orma tris) also use a daggerboard in the main hull since the ama lifting foils don't have enough area for just one of them to do the whole job. But ama boards don't have to lift that much and can be designed to work well with some lift and a primary job of lateral resistance. The pro's and cons you have down well as Mr. Ostlind said.
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Just because it is interesting: the boat that holds the outright 24 hr record is Groupama 3 at something like 33 knots. Oh, and she uses ama lifting foils......
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Just because its interesting 2: Check out this video-shows how much the ama lifting foils really do help-compare the footage of Banque Populaire with Sodebo at the end-you can see how close Sodebo comes to burying her lee hull when the foil clearly keeps BP's lee hull up-----
http://uk.youtube.com/watch?v=QTFLLZh-3Y4&mode=related&search=

 

Just because it's interesting 3... Banque Populaire is a fully crewed vessel and in no way reflects the realities that the solo skipper faces when going for serious blue water crossing records. This is especially important when one comprehends the inherent dangers and commitments of sailing solo for world class records in wildly varied conditions, sea temps and all that goes with the process.

While I was sailing on Sodeb'O in France in early September, I spoke with Coville's Boat Captain, Thierry Briend, (the only guy, according to Coville, who is allowed to tell him to sail faster) about BP's use of foils and the differences in a fully crewed boat, compared to a solo multihull designed for big time sailing records.

Thierry believes that a fully crewed boat can take far more chances than can a solo boat, especially when one considers in just what kind of waters these boats will be required to sail, while pushing it as hard as they can.

Keep in mind that I was an American guy trying like hell to form a full understanding of the comments from a highly accomplished French multihull sailor as he communicated with me in more than passable English, but this is the gist of the matter. There were hand and arm gestures, facial expressions and all sorts of wonderful methods for me to get the full measure of what he intended with his comments.

Here's the rather sketchy translation of Thierry's brief bio on the Sodeb'O site:
"Permanent member of the team of Thomas. Previously of the Foncia Trimaran at the side of Alain Gautier, Thierry is responsible for the Trimaran Sodeb'O in the absence of Thomas. He coordinates the engineering team and the outside contributors on the boat. He also deals with hydraulics. When he does not sail on Sodeb'O, Thierry runs in match racing."

Thierry is one amazing guy to talk to for any length of time and it makes me want to go back to France just to be a simple composite worker and dock helper just to get the complete picture over a longer period of time. In spite of the current effort by BMW/Oracle with their maxi racing machine trimaran in San Diego, the French are simply miles and miles ahead of our understanding of really fast multihull sailing boats… Cam Lewis, Pete Melvin and Randy Smyth notwithstanding.

Originally, in the press material, there was some vague representation that BP was going to be sailed as a solo machine. I asked Thierry about this option and he just laughed with a short wave of the hand and his comment, "no, this is just for many men. The boat is much too big."

Make what you will of this, but clearly, someone in the know with a high degree of multihull experience at the cutting edge feels that the case is closed as far as putting these boats in the same comparison category.

 

Now, without further distortion of your original summation; I'd like, very much, to get this back on the topic, in which you asked if there were any comments/views as to your take on ama mounted foils when compared to the typical vaka mounted daggerboard/centerboard-foil setup.

Perhaps you can share with us your own expanded understanding and your preferences in this regard...?

I'm anxious to hear your opinions beyond the summations above.

 

handling boards and foils

I don't kow about you blokes but trying to lift, let alone push down, any sort of loaded daggerboard or foil (whether in main hull or float) while the boat is moving above 5-7 knots, I have usually found impossible. Main has to be dropped and boat slowed or swerved about in my experience. I'm not talking about hydraulics or 24 to 1 tackle, just basic low technology, physically doing it on your own.
For conventionally setup angled in lifting foils in floats there is the added disadvantage of having to lean out in space to move them; however banana shaped foils are an advantage here because they curve inwards above the float deck and therefore you can get your body above the foil to move it. However again, on a trimaran configuration, both foils can be left down all the time anyway, they do NOT have to be lifted since the windward foil is mostly flying above water. In light conditions it can easily be hauled up a foot or so for those wanting to reduce the minimal drag of the foil tip skimming surface water.
Another alternative is angled out foils (which are even easier to handle since the top sections slopes inward) - but people have difficulty getting their heads around this foil configuration - or inverted T or Y foils (which have their blades verical or near vertical) - these can be movable or even fixed, and the latter has some excellent advantages on a tri.
IMO shifting a dagger or centreboard from the main hull to floats has the quite considerable advantage of de-cluttering the main hull but also, as you have mentioned Waynemarlow, producing a better shaped, smaller and more efficient foil that is always buried in non aerated water.
Your steering point that you are helming from a different line than the float, I have found to be not a problem - and if you're going to slam into some floating object with the float, not only is the foil going to be damaged but the float as well. Best not to hit things .... but a plus with float foils/boards is that you can have a watertight crashbox built around the cases so in worst case scenario, you only flood that small area. This is not the case with a conventional main board in the main hull.

 

Thanks guys for your comments. I was thinking more along the lines of the small Tri say up to 30ft or so rather than the full on 60's. Bannana boards to work well have to be really accurately made with the right wing section and incidence which probably excludes the small low volume builder. Mind you I think if they could be made to work cheaply then they have lots of advantages.

From experiance of racing small cats we are rapidly coming to the conclusion that to lift boards downwind costs more in time to lift than the extra drag, mind you the boat I sail is very flat bottomed and downwind we tend to be sailing apparant wind ( 90 gybe angle 45 to wind angle ) so a board down is almost necessary.

Keep the pros and cons coming guys & girls.

 

The Fastest Multihull in NZ line 7/Frantic Drift (a 30ft carbon tri) has the boards in the floats, however the designer and owner have said they would change that if they built the boat again, because its a pain to pull them up and down and you cant tack very well...

I have heard some F9Rs have had foils fitted and have had major structural issues... but been faster

 

Here goes- my opinion for what it's worth.

Advantages are as far as I can tell are.
A smaller board can be used as it is always full length in the water and so can be optimum size.
- I think you still need the correct amount of board area no matter where it's located. Very few tris really fly the main hull, the mainhull board is usually in the water.
It can be inclined to give lift making the possibility of a smaller Ama.
-it can be inclined to generate lift, but that's not a substitute for hulls, Ama volume is still needed for all around buoyancy unless you're building a single purpose weapon.
Cost, even though there are two boards, the overall cost is probably less than one large board.
-Don't forget the structure in the ama and the beams to support the added loads. I bet it's either a wash, or cheaper to build in a mainhull board.
More room in the Hull.
-YES! (which make a swing-centerboard attractive.)

Disadvantages are
The risk of striking and damaging the boards maybe slightly higher as you won't always be in a position to view the sailing line of the Ama.
-perhaps, and the smaller boards will likely be easier to damage.
Once under way it is difficult to retract.
-No need to retract it anyway, the windward one should be out of the water anyway. A mainhull daggerboard won't retract once under weigh either, under load its not gonna move, and really, you don't need it to.
Heavily loaded including loading the connecting beams.
-Indeed.

Hull Daggerboard Advantages
1 board only to build.
-And probably lower tech/easier to build too.
When the hull starts to lift the board length is shortened allowing the boat to slip sideways acting as a sort of safety governor.
-Disagree with the whole concept. If you're pushing hard enough to even begin to lift the mainhull, you want Control! That board should be deep enough to remain workable. If you lift so high that it quits working, then *maybe* there's some safety benefit.
Disadvantages
Not able to create lift vertically.
intrusive in the hull.
once damaged then there is a risk of damaging the hull.
-All true.

I'd add, amas mounted boards are generally considered to make the boat harder to tack, and offer interesting tracking/handling issues in some conditions. Are simply harder to 'get right.' But can obviosuly work well.

 

I personally believe that if the mast is properly positioned then there would be no need for ama lifting foils - I'm talking ORMA-60 tri's here - when these boats crash down & almost submarine from going around a bouy thru the "zone-of-death" this is quite apparent - Nigel Irens mentioned moving the mast position aft on ORMA designs would make the boats safer - he has done just that in some of his recent designs - on the ORMA re-build that we are in the middle of right now - the mast will be moved aft 5' 6" - I don't intend to instal cases & boards in the amas - just the 30 degree daggerboard in the main hull - - - Dale S.V. VOODOO SCIENCE Miami

 

on the subject of smaller trimarans - I built & cruised for 15 years on an antique design 37 foot trimaran - early sailing in SF I got real tired of the small fixed fins on the floats - (they were known as floats back then) - I hauled out on the beach in SF & installed daggerboard cases in the same location of the original fins - cases were bulletproof & toed-in 6 degrees to eliminate hunting - could put 4.5 foot of board below the float keel - (about 3.4:1 aspect ratio) - boat handled much better - would point higher & would get up enough drive to tack without sloshing thru the tacks - this board/case design was right out of Rudy Choy - 38 years later this boat is still sailing - (Marathon Florida) - on the same float daggerboard configuration - 3rd owner - - - 1n 15 years I only sheared 2 boards - I built them to shear - - - much better to shear a board than to tear apart the float - - - Dale S. V. Voodoo Science Miami

 

Ama mounted daggerboards

I'm building a hybrid 6.2 metre tri using modified beach cat hulls as the amas -naturally these have the boards already installed and I should much prefer leaving them in the amas rather than having to build an entirely new case and board for the main hull.

When researching the merits versus diadvantages I found a most interesting old thread on this forum There were some excellent suggestions but I was especially impressed by Gary Baigent's comment:

However again, on a trimaran configuration, both foils can be left down all the time anyway, they do NOT have to be lifted since the windward foil is mostly flying above water. In light conditions it can easily be hauled up a foot or so for those wanting to reduce the minimal drag of the foil tip skimming surface water.​

Bearing in mind this will be a small single handed cruising tri never to be raced, the simplicity would seem to vastly outweigh the minimal drag.

Any further comments would be greatly appreciated

Alan

 

I think Gary is right- as are you. No mods at all is pretty simple....



Pix from Derick Reynolds site: ( http://www.derickreynolds.co.uk/sailboats.htm )

(click on image)

 

Thanks Doug

It is good to have positive feedback from someone as experienced as you.

Shortly, I'll post some pictures of the modified amas, where the displacement of the original A Class hulls has been increased from around 300Kg to over 1500kg and they look great. Maybe then you could comment on whether it might be best to make new, longer boards to fit the existing cases.

Regards

Alan

 

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5 times more?! Wow..... gotta see those pix... Its hard to conceive of those trunks still being accessible. It could change the assessment of what is the simpler way to proceed....