Pivoting Amas for Sailing Canoes

[tink]

Re: Pivoting Amas for Sailing Canoes

You might need to worry more about toe in with an inflatable - no real sideways strength.
On a rigid ama you should be able to control the toe in by having wide enough attachment brackets at the aka.

What I see is something to pull the nose of the ama down. Since it's a rope it cannot pull the nose up.

So it looks like the anti dive planes and the aft rope control are doing two different things.

Perhaps his slightly reverse raked bows on the amas did not help with nose diving.

Anyone who spends 3 days in one of these has my sincere admiration, and 18 days is just insane.

My inflatable has a ridged spine so does not bend sideways, the attachment to the ama was not ideal and the likely contributed to the toe in. Obviously though there is a stress in this area which would be good to understand and reduce.

Yes fully agree that the control nad the dive planes are doing opposite tasks. I would like to eliminate both however.

And 18 days does show signs of insanity, might explain why he tried to sell it as soon as he finished.

[upchurchmr]

Re: Pivoting Amas for Sailing Canoes

Gary,

What is your opinion of the different benefits for pivoting amas and more rigidly attached amas?

[Gary Dierking]

Re: Pivoting Amas for Sailing Canoes

Gary,

What is your opinion of the different benefits for pivoting amas and more rigidly attached amas?

They both work and I don't really see much advantage in one or the other. My first priority with an ama is to have a veed deck so that it can come out of the water easier when it becomes submerged into a wave face.

[Todd Bradshaw]

Re: Pivoting Amas for Sailing Canoes

My first priority with an ama is to have a veed deck so that it can come out of the water easier when it becomes submerged into a wave face.

That was exactly my first thought when I saw that wide flat top on the forward part of that new ama drawing.

One thing about trimarans in particular is that at times, and with chop coming from certain directions, they can develop a very uncomfortable, semi-nauseating wobble that a lot of folks find pretty uncomfortable.The pivoting ama might go a long way toward reducing that effect.

[Woxbox]

Re: Pivoting Amas for Sailing Canoes

The general trend in ama design has been to go with wave piercing hull shapes as opposed to the old-style amas that are intended to stay above the water always. For this reason, they are also designed to pop back up onto the surface very easily. I seem to recall those Adrenaline amas as being described as cigar shaped. This was an innovation at the time (OK, in Western boat development) -- the combination of a wave piercing hull and a pivoting structure so that the ama would provide lift but be otherwise free to move through the waves fishlike with very little drag.

But keep in mind that the volume and length of any ama will determine how much speed you can get out of a trimaran. When pushed hard, the boat sails on the leeward hull and the other two hulls pretty much go along for the ride. If the ama is short or of low volume, you'll place a real limit on performance. When putting the whole design together, the ama needs to be able to support the full sail plan -- it's not just a secondary support for added stability.

Also, when it comes to safety, the bigger the amas, the harder it will be to capsize the boat. Not the other way around as suggested high up in this thread. And if ever she does wind up keel in the sunshine, then an easy folding system might help sort things out. But of course it's better to have a boat that wants to stay upright in the first place.

[upchurchmr]

Re: Pivoting Amas for Sailing Canoes

So Woxbox,

You don't subscribe to the theory that if the ama is 50% of the total boat weight, it will submerge, spilling the wind, and the boat will not end up with the keel to the sky.
Coming back up when the wind abates, or you let go the sheet(s).

Seems to be obvious that is the plan for the Gougeon sailing canoes. My wag is that those amas are around 100# bouyancy.

[tink]

Re: Pivoting Amas for Sailing Canoes

They both work and I don't really see much advantage in one or the other. My first priority with an ama is to have a veed deck so that it can come out of the water easier when it becomes submerged into a wave face.

Fair point about the veed deck. For my application, flat water, I am hoping the buoyancy forward of the aka and weight aft of aka will prevent the bow becoming submerged- I will experiment with some vee deck shapes.

[tink]

The general trend in ama design has been to go with wave piercing hull shapes as opposed to the old-style amas that are intended to stay above the water always. For this reason, they are also designed to pop back up onto the surface very easily. I seem to recall those Adrenaline amas as being described as cigar shaped. This was an innovation at the time (OK, in Western boat development) -- the combination of a wave piercing hull and a pivoting structure so that the ama would provide lift but be otherwise free to move through the waves fishlike with very little drag.

But keep in mind that the volume and length of any ama will determine how much speed you can get out of a trimaran. When pushed hard, the boat sails on the leeward hull and the other two hulls pretty much go along for the ride. If the ama is short or of low volume, you'll place a real limit on performance. When putting the whole design together, the ama needs to be able to support the full sail plan -- it's not just a secondary support for added stability.

Also, when it comes to safety, the bigger the amas, the harder it will be to capsize the boat. Not the other way around as suggested high up in this thread. And if ever she does wind up keel in the sunshine, then an easy folding system might help sort things out. But of course it's better to have a boat that wants to stay upright in the first place.

Firstly let apologise to Matt Young who started the thread which I have hijacked. I am ill at the moment so have a lot of chair time and love a design challenge and new amas is likely to be my next build.

I imagine that Matt’s, Meade’s and SOS have design requirements are different to mine more in line with the the advice given above.

I have no intention of designing a trimaran, it has a main hull and two outriggers but that is where the similarity ends.

While sailing the amas are a mainly redundant feature to give a vital few seconds to release the mainsheet should there be a change in wind force but more likely direction- for river sailing. I sail solo on a very quiet river so want to eliminate the capsize risk . My canoe sails just fine without any additions in open water. They are also useful when stationary for stability moving around the canoe to reef etc.

I am sure Paraw use there outriggers in a similar way, primarily for static secondary stability while at anchor or fishing.


In addition to my above requirements are simplicity and reliability which is why I am exploring an idea based on the well proven BSD BOSS system.

https://tinkboats.wordpress.com

http://proasail.blogspot.co.uk

What I get up to
https://youtu.be/X9NZEyvpb_Y Streaker dinghy
https://youtu.be/oni-3rJzxqQ Sail Canoe
https://youtu.be/eW078PPgJak Proa

[Frank!]

Re: Pivoting Amas for Sailing Canoes

Dive plates are not liked on surf skis
Dive plates work just as well negatively if water flow comes from above - ie in waves, bars, surf etc
Suggest a raised prow - even just an extended stem post - could go a foot or more above the deck. The advantage is that it parts The water and ensures air not water on the foredeck.
A Viking longships prow is probably the most effective configuration
Any pivoting float on a cruising canoe must surely have to cope with worst case scenarios
2 bobs worth,
Frank

[tink]

This is still very rough model but give the best weight behind buoyancy of all the models I have done

https://tinkboats.wordpress.com

http://proasail.blogspot.co.uk

What I get up to
https://youtu.be/X9NZEyvpb_Y Streaker dinghy
https://youtu.be/oni-3rJzxqQ Sail Canoe
https://youtu.be/eW078PPgJak Proa

[Rob Hazard]

Re: Pivoting Amas for Sailing Canoes

The last time I saw Meade's canoe I noticed he'd added a pair of small disc-shaped weights to the sterns of the amas. He said it was to make them hang level, though he also said he'd never had one "stuff a wave". I might have quizzed him about that, but he was surrounded by people asking him about all the clever details of his little speedster.

[tink]

Re: Pivoting Amas for Sailing Canoes

The last time I saw Meade's canoe I noticed he'd added a pair of small disc-shaped weights to the sterns of the amas. He said it was to make them hang level, though he also said he'd never had one "stuff a wave". I might have quizzed him about that, but he was surrounded by people asking him about all the clever details of his little speedster.

I am rapidly coming to the conclusion that a good low drag hull design with a bit of weight in the back is much better than a very compromised hull that weighs the back down by the design alone.

[Woxbox]

Re: Pivoting Amas for Sailing Canoes

So Woxbox,

You don't subscribe to the theory that if the ama is 50% of the total boat weight, it will submerge, spilling the wind, and the boat will not end up with the keel to the sky.
Coming back up when the wind abates, or you let go the sheet(s).

Seems to be obvious that is the plan for the Gougeon sailing canoes. My wag is that those amas are around 100# bouyancy.

First off, let's be clear that trimarans are fast because they replace lead for stability with beam, lots of beam -- so they can carry lots of sail on a a very light platform. The speed comes from a high sail area to weight ratio. There rest is detail.

If you decide to improve the stability of an established and workable sailboat by adding akas and amas, but don't add any more sail area, you will not magically get a faster boat. Indeed, it will have more weight and windage and most of the time will be a more cumbersome and slower boat.

If the starting boat is dangerously tender in certain conditions, the question is this: What's the best solution to improve safety? The usual and traditional step is to add some deck so water over the rail doesn't come into the cockpit, or to add some ballast, or both of these. This improves safety without adding the windage and complexity of going the trimaran route. It also leaves the boat clear for rowing or paddling. This is what I did last year to improve the safety of my Wisp. (Thread here.)

The Everglades boats are a fascinating study, but keep in mind that they are developed for a very specific race, and aren't necessarily ideal setups for other uses. They are made to be light and portable and in most cases are designed to be rowed or paddled as much as they are sailed. If a boat is going to be sailed almost all of the time, then going to a minimalist trimaran design with a small rig and low volume amas doesn't make sense. For this use, you'd want either a well developed monohull or a fully developed trimaran. Going halfway will tend to combine the disadvantages of both types.

Which brings us back to the question. If you submerge a 50% displacement ama -- and this won't be hard to do -- it will immediately increase the drag to leeward and the boat will want to turn downwind. You may or may not be able to counter this tendency with the rudder. The boat will stall out and the ama will come back up if there's a fairly level sea state. If we're talking big waves, the hull may be driven over the submerged ama by a combination of the wave action and the boat's momentum and you'll have a capsize. Keep in mind that the submerged hull is a massive tripping point for the moving boat. This is why 100% is the smallest volume amas you'll find on full-fledged tris, and most designers go to 150% or even 200%. (My F27 had 100% displacement amas and it was not hard to drive them under in 20 knots and more wind.)

But there's more to be considered. If a boat is well balanced under sail as a monohull and you turn it into a trimaran, there's a very good chance that balance will be thrown off because the drag of the hulls is now centered in a different location. Specfically, lee helm may be introduced and you'll now need to adjust the position of the rig or centerboard or both.

So retrofitting a mono into a tri risks becoming a downward spiral design exercise. It can and has been done, of course. But one needs to be aware of the drawbacks.

[Matt young]

Re: Pivoting Amas for Sailing Canoes

There has been good suggestions in this thread so far, thank you everyone. There is a world of experience more here than my own.

Upchurchmr, cheers to you for trying to tract down the details of Meades canoes. Too bad it hasn't bee very fruitful. I also have guessed that Meade's amas are 100 pounds displacement. Tink hijack away, as you are still talking about a pivoting ama. A smaller ama but an ama non-the-less, an E-ama(emergency ama) is how I am starting to think of that type, the Soloway style. The flexible rear aka is very interesting to me as an option, if dive stop proves necessary. The V-shaped deck makes sense to me, thanks for that Gary and Todd.

Woxbox, how do you calculate the displacement needed in the amas? When you say 100%-150% are you referring to, sail force or vessel weight? Or something else.

As to the of hull I will be using these on. I have three now, none of them are tri-specific designs. But I think they all will be interesting to sail with amas. One as an interesting way to sail them, and two as a way to test run the amas. I will later build a new hull (long and narrowish) to work with the amas. I am taking this route as I already have the three vessels, want amas on at least two of them, and don't have the time to build a new vessel right now. This may seam a backward way of approaching it, but its how I am going to do it. I have referred to them as canoes, but really only one is a true canoe, its a 15.5' x 33" beam x 31" WL-beam plastic canoe(lots of wooden parts added, deck, rudder, mast, and leeboard). One reason I want to fully develop this plastic canoe as a sailing canoe is I have local trips planned. Where I will run a somewhat mellow river of .5 to 3 days into a large reservoir then sail across it. I have been sailing it mono and have had a blast. It sails better the flatter it sits, it has quite straight sides, by better i mean I can sail it healed but the balance changes drasticlay. This will be the first to get the amas. And my plan is to have the amas allow me to keep more sail up in heavier winds. Here the conditions will quickly go from 5-8 mph to 25+ mph. Often with nice mid-range work to windward or beam-reaching in the first half of the day, to lakes end, then a screaming run back as the afternoon system cranks up. I would prefer to do all this without reefing, for fun. I have sailed this canoe a number of times, fully rigged, in the 25 mph range. Its fun, fast, and take constant vigilance on the sheet and rudder. The 14.5' x 31" beam x 27" WL-beam, is my Sail-SUP-SOT. Narrow flat bottom, lap multi-chined shape. Fully decked double-ended and with a fine entry. This is an experiment, it have had a good time sailing and paddling this on lakes, open ocean, and trough breaking waves. I want to try it with amas, making it a wave-piercing trimaran. It will be wet, but in the summer that is nice. But will need to get a better sail for this first. And third I just received an older Folbot 17.5" x 38"? beam kayak, this one is wide well rounded sides. I will be re-skinning in, I am considering cranking a little more rocker into it, I will then give this a go with the sail and the amas, lets see how this goes.

So, at this point these are the details of the amas I am thinking of. Longer then I was initially thinking, going to the trimaran set up and not the E-ama. More volume forward in the ama and some rocker to the run. Sides narrowing to the stern. Single pivot with the option, or not, of a sprung-stop on a rear aka, and a V-deck. Specs and rough sketches below. I still have two different sections, on with more volume. Drawn is a 9' long version, on the 15.5' canoe. But a 12' long version makes sense also to my eye. I am gong to re-draw it today, most likely with more bottom shape, curvier rocker. I haven't calculated the volume yet.

length - 108"
depth - 10.5"
beam - 5" or 5.5"
volume - ?

ama.plan.1.jpg ama.section.2.jpg

[tink]

First off, let's be clear that trimarans are fast because they replace lead for stability with beam, lots of beam -- so they can carry lots of sail on a a very light platform. The speed comes from a high sail area to weight ratio. There rest is detail.

If you decide to improve the stability of an established and workable sailboat by adding akas and amas, but don't add any more sail area, you will not magically get a faster boat. Indeed, it will have more weight and windage and most of the time will be a more cumbersome and slower boat.

If the starting boat is dangerously tender in certain conditions, the question is this: What's the best solution to improve safety? The usual and traditional step is to add some deck so water over the rail doesn't come into the cockpit, or to add some ballast, or both of these. This improves safety without adding the windage and complexity of going the trimaran route. It also leaves the boat clear for rowing or paddling. This is what I did last year to improve the safety of my Wisp. (Thread here.)

The Everglades boats are a fascinating study, but keep in mind that they are developed for a very specific race, and aren't necessarily ideal setups for other uses. They are made to be light and portable and in most cases are designed to be rowed or paddled as much as they are sailed. If a boat is going to be sailed almost all of the time, then going to a minimalist trimaran design with a small rig and low volume amas doesn't make sense. For this use, you'd want either a well developed monohull or a fully developed trimaran. Going halfway will tend to combine the disadvantages of both types.

Which brings us back to the question. If you submerge a 50% displacement ama -- and this won't be hard to do -- it will immediately increase the drag to leeward and the boat will want to turn downwind. You may or may not be able to counter this tendency with the rudder. The boat will stall out and the ama will come back up if there's a fairly level sea state. If we're talking big waves, the hull may be driven over the submerged ama by a combination of the wave action and the boat's momentum and you'll have a capsize. Keep in mind that the submerged hull is a massive tripping point for the moving boat. This is why 100% is the smallest volume amas you'll find on full-fledged tris, and most designers go to 150% or even 200%. (My F27 had 100% displacement amas and it was not hard to drive them under in 20 knots and more wind.)

But there's more to be considered. If a boat is well balanced under sail as a monohull and you turn it into a trimaran, there's a very good chance that balance will be thrown off because the drag of the hulls is now centered in a different location. Specfically, lee helm may be introduced and you'll now need to adjust the position of the rig or centerboard or both.

So retrofitting a mono into a tri risks becoming a downward spiral design exercise. It can and has been done, of course. But one needs to be aware of the drawbacks.

Some very valid points but I think there are many other considerations and routes.

The Solway Dory outriggers are a point in case, they have been around for over ten years, are popular and people have done some challenge journeys with them.

They are not intended to be used as sailing stability being canted 9 inches upwards they allow the sailor to sail push the boat with a bit of safety. Not the best quality but a picture is worth a thousand words

http://www.solwaydory.co.uk/products/sailing-canoes/mini-outriggers/

In addition the outriggers make recovery much easier, especially re - entry and being able to sit in and bail a swamped canoe.

http://www.solwaydory.co.uk/articles/capsize-recovery-with-outriggers/

the prime use of my canoe is to paddle without any sailing kit at all. When it is a good day to sail I go sailing in my racing dinghy. Now and then I like to sail the canoe, it is a potter for the pure joy of it, the joy comes from knowing I am not going to go for a swim. I also enjoy trying something new and who knows where that may lead.


So in this case

https://tinkboats.wordpress.com

http://proasail.blogspot.co.uk

What I get up to
https://youtu.be/X9NZEyvpb_Y Streaker dinghy
https://youtu.be/oni-3rJzxqQ Sail Canoe
https://youtu.be/eW078PPgJak Proa