What to do that Amas (Outriggers) aren't "dead space" for a Tri ?

[Skip JayR]

Since couple of weeks I have this question in mind:
"How to use the Amas (Outriggers) on cruising Trimarans best ?"


... as we see Amas which are just "dead zone", nothing else than floaters with the function of "righting moment" connected by cross beams (akas) with the main hull.

I have seen amas on 30-40 Footers with no single space in side.... even no single hutch window. Just a screwd plate as "inspection hole", e.g. for the rudder pole.


... simply glas fibre epoxy, carbon or marine plywood wrapping "space of air" for uplifting moment.... eventually with some trimming units, e.g. uplifting foils.

What to do with kind of bigger cruising trimaran, one gets the chance to buy ???

Taking the saw, open the ama for creating some extra storage room with installing 1, 2 or 3 hatch windows ?? (In the picture its a Farrier F-82 in Turkey)





If possible... what kind of storage ?? - Packing each two of 4 heavy weighted gel batteries into the port and starbord ama to get more space in the centre hull ? Or just keeping it light weighted for storage of little things like fenders and sheets in it ? - Or just glue some solar panels on it ?



Or creating something more valuable space, e.g. integrating a berth (as known from Wharram Catamarans) or a toilet ?



No joke... the toilet is seen on the starbord ama of Trimaran Tritium ... see vid starting at 02:49...

https://www.youtube.com/watch?v=9-0iZpVv8R8

Feel free to share how you expanded your amas into some valuable extra space... without damaging the sailing abilities and substance of the boat.

[44'cruisingcat]

I think I remember seeing on a Dragonfly tri, the amas had an opening transom which allowed for storage of bulky but light items like sea kayaks etc.

[Stumble]

The amas need to be kept as light as possible. Anything that is stored in the has a huge negative effect of sailing capability and sea keeping.

That being said large bulky items that don't weigh much are generally acceptable. So things like lifejackets, bumpers, spinnakers, ect. But for heavy items like batteries there is nowhere worse you could put them.

[Kowloon Breeze]

@Stumble
What would be a good way of putting a number to the effect of weight in the amas, to approximate the desired max weight for amas given a certain trimaran structure ( ex issues with the robustness of the structure itself)?


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[Stumble]

I am not an engineer far from it, but just work the RM numbers and it's pretty clear.

Let's take a Corsair 31 as an example, and put a couple of batteries in each of the amas as an example. The max beam is 19', so let's assume our batteries are pressed right up against the outer hull just to make the math easy.

There are a few problems I see, but there may be more.

1)we have added tremendously to the load the. Windward beams have to carry, since when the windward ama lifts there is now 9.5*200lbs=1,950foot-lbs of static torque to the windward hulls. We have also added the same to the leeward hull, which adds the same force trying to push the same amount into the water.

Conversely if the same load was carried in the center hull 1' off centerline the number would be 1'*200=200ft-lbs. Or a reduction in torque of 90%.

2) this assumes static load, but the amas also move vertically the most. Figure the impact force of 200lbs being slammed down as the boat rocks from waves passing by. The math is beyond me, but the forces involved can be tremendous.

3) this extra load also increases flex load in the beams. Which can cause all sorts of problem.

In short the only advantage to a a storage is that it's a lot of 'free' space. But it has dramatic negative effects on the way the boat sails.

[Skip JayR]

Originally Posted by 44'cruisingcat

I think I remember seeing on a Dragonfly tri, the amas had an opening transom which allowed for storage of bulky but light items like sea kayaks etc.

yep... its on a Dragonfly 35 Tri.... because I have seen it there it kept running my question in the head. As the Danish constructors build sportive Tris I suppose they know what they are doing. :-) Cant be wrong...

Just did some screenshots from the promo video...





Here the video you can see the astern hatch opened from 01:49 min.

https://www.youtube.com/watch?v=oh4q2bt61EY

Such paddling kayaks can have a weight between 65-85 pounds roughly. This would be the equivalent for round about two leight-weighted A123 Military Batteries (round about 20 kg each) for long term use.

The Dragonfly 35 has another hutch window on deckside of the amas... so some more storage there...


Just by feeling I'd like to have on a 35-40 foot Trimaran extra storage weight of 150-200 kilogrammes, each side port + starbord. - It can be compensated by a higher mast, bigger main sail for righting moment, e.g. a 40 Foot Trimaran has a 60 Foot Mast... and some uplifting foils in the amas plus more stiffy construction materials to connect the cross beams safely, e.g. using foam-kevlar-epoxy.

Would be interesting to make some detailled cost calculations. Having 300-400 kg more transportation volume in the amas makes sense for long distance cruising Trimarans, isnt ? I'd like to get free 300-400 kgs more volume in the main hull using for other equipment. :-)

With wave piercing bows the negatiely bumping effect of heavier weight shouldnt be too extreme. I will ask some multihull naval architects I know to get a more clear picture about such items...

[Sailingcouple13]

Don't forget putting the batteries equally that far out from center the additional weight of cables and all the other negative results due long runs.

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[Sailingcouple13]

By the time you make your amas large enough to clear your center hull, beef up your supports you might as well lift the center hull out of the water. I think it has been done.....

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[Skip JayR]

Originally Posted by Sailingcouple13

By the time you make your amas large enough to clear your center hull, beef up your supports you might as well lift the center hull out of the water. I think it has been done.....

No need to make big Amas for lifting up the centre hull.... and yes... already done, as "mad human brain"'s creativity can find out the most crazy solutions... like that of the Proteus Catamaran (150 ft. lenth x 60 ft. width).

Officially it is called WAMV = Wave Adapting Module Vehicle...







I should think about that concept more seriously ... so I could expand my then "no more to be called living Trimaran" into a Cargo Lifter to earn some extra money, e.g. with island hopping ISO Container delivery services. Proteus Cat has no keel, so it can do beaching easily.

E.g. I could install an ISO Living container regularly under the cockpit for own living with some clamps (or kind of hydraulic cheek pliers or crane as you can see in the last video bottom down)... and when getting the order for some carrier services, I deposit my own living floating container and pick up some cargo ISO containers...

The cabin on its own is demountable... very cool...




Might work as business model... just wonder, why the Proteus Cat never made it into series... it stayed in the phase of "proto-typing" for nearby 10 years.

I like the idea... cool "boat". Just thinking about how to install sails ???

https://www.youtube.com/watch?v=qp3Ykf98Pcs

Amazing perspective from cockpit to see the water flowing under.... with an inteview of the engineer Ugo Conti who created this vessel because he suffered of seasickness as circumnavigation sailor...

https://www.youtube.com/watch?v=q0MZzFT3XpQ

Google is collaborating with Ugo Conti they created a smaller 16 foot "drone boat" (self driving robot) on the basis of the Proteus Cat concept for Google mapping the coastal areas...

[S/V Alchemy]

Originally Posted by Sailingcouple13

Don't forget putting the batteries equally that far out from center the additional weight of cables and all the other negative results due long runs.

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Not to mention the need to box said batteries, to make the hatch utterly watertight, and to keep the cable runs utterly watertight. It's like putting the jet engines of an airliner at the ends of the wings: possible, but pointlessly complex.

[Sand crab]

Once you get to about 50' then the situation changes. Frequently there are wingdeck berths and the amas are used as companionways. These tris are a bit slower than the ones in your discussion.

The Neel 50 had rear hatches for storage like the Dragonfly. The N45 has an option of beds in the amas so it can be done.

[GrahamHO]

I always thought the ama were meant to be kept light with boyancy as the designer intended.

[cabo_sailor]

Don't really know anything about cats. A zillion years ago I had a Hobie 16 and now have a TakaCat dink.

But you multi sailors are teaching me stuff all the time. If I wère younger I might be considering one.

Don't mind me lurking but I think my Cabo will be my last boat in this world. 😎


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[Skip JayR]

Originally Posted by cabo_sailor

Don't mind me lurking but I think my Cabo will be my last boat in this world.

Never say never... :-)

[Skip JayR]

Originally Posted by GrahamHO

I always thought the ama were meant to be kept light with boyancy as the designer intended.

Sure, we have to follow the ideas of the designer. A truck is a truck and cannot be used as a formula1 racing car. Same with boats.

But there are parameters we can handle flexible. E.g. calculate that many of the Trimarans have to 4-6 birth. Its part of the stability and sailing plan.

Lets say we take a 35 or 40 foot Trimaran, regularly 6 birth, e.g. 1 double bed in astern cabin, one double cabin in foreship and two single beds each in the wings beside the saloon.

So the construction itself is designed to transport maximum 6 people... with all the personal stuff (weather clothes, luggage etc. ...) and food capacities (water + regular food) I suppose we can calculate minimum 100 kilogrammes each person, right ?

Not to mention, that during day sailing we see 8-10 people hanging around on the trampolins of such boats :-) Never heard about that one of the amas has broken off. :-)

Even on a small 24 Foot Trimaran, e.g. a Kurt Huges Design which is used in Italy for Charter, there hang around 6 people on board with all that stuff (e.g. surf boards)... and they sail very tough MUFFOLO as you can see in the vid... no problem with stability...

https://www.youtube.com/watch?v=9ldeuwTuQaA

If you reduce the crew for a regularly crusing to a two handed one, which is in tendency very typically nowadays... we get free 4 birth = 400 kilogrammes "trimming weight"... to invest in other equipment or to manage the storage places differently. Right ?

Naturally it is a very normal thing for a designer, that he expects these 6 people jump around on board as they like, not all sit all time in the cockpit. Some hang around on the trampolins, another sits on the bow to enjoy watching dolphins etc. .... very normal way for leasure sailing on Multihulls.

So the boat itselfs has a stiffness to handle such crew weight of more than 500-600 kilogrammes easily.... not loosing its sailing ability.

If I take such kind of boat, reduce it to a maximum crew of 2-3 people I get free 200-300 kilogrammes of weight I can use differently, e.g. storage of batteries into the amas...

I am very confident about that in very close future, we will see such kind of concepts, to have electro motors in the amas and the whole battery bank... there.

In small there exist already a US patent for an electro motor driven Trimaran designed by inventor Ronald A. George (owner of company THE OCEANSCIENCE GROUP which shortly was sold to TELEDYNE RD INSTRUMENTS, INC. in California)
Patent US20140158037 - Trimaran having outriggers with propulsors - Google Patents



The Finnish company OceanVolt installed shortly a pure electro engine into a bigger Cruising Trimaran... it has a water cooled sail drive, too (only 44 kgs weight). More details here: The yachting future is silent… new & powerful Electro Motor Systems from Finland.



I am in contact with the folks of OceanVolt and waiting for some more details... will report as soon I have more details.

We just need to become flexible in our mind to handle the parameters given by the Multihull designers... and find a good way for compromize: Speed + Space. :-)