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 Post subject: Active Ama Mod
PostPosted: Sat Sep 28, 2013 9:11 pm 
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Some of you may recall a tacking pros called the Raptor 16 that used a foil which could be swung out of the water entirely or lowered and pitch adjusted to keep the lone pros A
Ana from either flying out and capsizing the craft or submarining. Mostly it was for the former.
At anyrate Inknew if a guy who owned a Raptor 16 and did away with the foil - too much speed loss to drag. Instead he configured something that erased the speed penalty and kept his AMA from flying too high.

He gave his AMA the ability to gain and shed water ballist.

By means of a bilge valve and container within the ama and some hose he regulated the full to the sail loading and sped along all the faster. In a very short acceptable time he could empty the Ama per the bilge valve ( the kind used on onboard tanks for keeping fish alive till cleaning on large boats) and be set up for the next tack.

I thought it might be worth mentioning here as anything that can keep an AMA from burying too deep in heavy wind is all the better and faster. I don't have the particulars on the amount of water he used but it did the truck for him and anyone who knows this craft knows the generous amount if sail it carries required at least a couple gallons to keep it in the water.

For a tri its heavy sailing weather only when you dont or can't hike out. Unlike the Raptor of course the flying AMA would hold some water to counter act the sinking of the other. The full of course would be done prior to flying. I'd bet a gallon even (7lbs) could make a difference and its remarkably easy to to do (so it seems) .

Just throwing it out there.

Pete


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 Post subject: Re: Active Ama Mod
PostPosted: Sun Sep 29, 2013 5:06 am 
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Joined: Sat Nov 05, 2011 1:58 am
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Location: Forster, NSW, Australia
I tend to think that Islands are plenty versatile enough to handle high winds due to the ability to partially furl the sail. I find that, even without hiking out or ballasting the windward hull, that the limit is the state of the waves rather than wind strength. I have found the upper limit of sailing to windward is the roughness of the water (even on inshore lakes)

I recall that the Hobie dealer in Hawaii (sorry I forgot his name) added weight belts on the windward side of his TI when tackling the trade winds on a big inter-island trek, but I consider trhose conditions rather out of the ordinary for the rest of us.

While movable water ballast is a commonly employed feature of high-end competition yachts (eg Volvo round the world etc), by far the stand-out features of our islands are the versatility and simplicity, and the design was never meant to focus on outright performance,

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Tony Stott
2012 Tandem Island "SIC EM"
www.scenefromabove.com.au


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 Post subject: Re: Active Ama Mod
PostPosted: Sun Sep 29, 2013 6:36 am 
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Joined: Sun Apr 20, 2008 6:18 am
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Location: Sarasota,Key West FL
Interesting concept though it might get dangerous if you forget to empty the AMA when you tack. Personally it's easy for me to just hike out on the tramp and use my tiller extension ( a simple piece of PVC water pipe with a rope loop on one end that took all of two minutes to make and cost about $.50 cents to make.)
However if I were to design something like this I would use a two foot piece of 1/2 inch PVC and an elbow. I would drill and tap a hole in the center inside of the AMA wall about 1/2 or 3/4 up from the bottom. I would attach a line to the front of the 2 ft PVC so it can be raised. When you want to fill the AMA you lower the end if the pipe into the water before tacking. Your forward motion will fill the AMA with water. At the same time you would open a dump valve on the other AMA to start draining. It will likely take a while so will likely need to pedal for a while during your tack while all this water transfers. Once the AMA is filled you can adjust your sail for full power. Mounting the dump facing rearward near the back might create a vacuum to help drain the AMA faster.
If you wanted to get fancy you could have a weighted flexible hose inside the AMA attached to the inlet tube( like in a fuel tank). By doing this the AMA will fill while the 2 ft PVC is pointing forward, and drain while facing backward( via suction from your forward motion). This would eliminate the need for a separate dump valve. Basically it would all work with one control line that swings one tube forward and the other back then alternate. Might even work, but I'm not going to build one because it's just way easier to hike out.
In my opinion a much easier option would be to mount a 1/4" x 2" inch piece of polyethelene sheet about 4 ft long on the outside wall of the AMA side. It would be near the top of the AMA in the front and about 3/4 down from the top at the rear. With one on each side of the boat (outside of each AMA only), the foil in the water would create additional lift on your buried AMA. Totally automatic and simple ( no controls) with no weight penalty, no moving parts, and a lot less work to make.

According to my calculations a 2 inch wide foil would create about 32 lbs of additional lift at 6mph, and a 3 inch wide foil would create 47 lbs of additional lift at 6 mph. This is assuming the foil is mounted at 6 degrees angle of attack, and is a simple plank (1/4 " thick)

Image

Of course anything dragging in the water will create drag, and may effect steering especially on a TI, which has a smallish rudder to begin with.

With 47 lbs of additional lift on the AMA by using the 3 inch foil you could increase sail area by an additional 30 sq ft (like a jib for example) according to my calculations. It might be easier to move the AMA out one additional foot (so the boat would be 12 ft wide vs 10ft), which would give you a little more lifting effect (about 75 lbs) rather than adding the foil with less drag.


My two cents
Bob


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 Post subject: Re: Active Ama Mod
PostPosted: Sun Sep 29, 2013 2:30 pm 
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Joined: Sun Apr 28, 2013 4:26 pm
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Thanks for an informative reply.

You mentioned: If you wanted to get fancy you could have a weighted flexible hose inside the AMA attached to the inlet tube( like in a fuel tank). By doing this the AMA will fill while the 2 ft PVC is pointing forward, and drain while facing backward( via suction from your forward motion). This would eliminate the need for a separate dump valve. Basically it would all work with one control line that swings one tube forward and the other back then alternate.

That's exactly what the guy had rigged on his Raptor16. In his case the weight to keep the AMA from going airborne was the prime motivator and so it wouldn't apply equally to a tri hull configuration. I saw the ability to add water ballast as a way of fine tuning the balance over the main hull between two points. Optimizing wetted surface and the "footprint" of the submerged hulls.

The foil seems like the most carefree way to go . Unlike the tacking proa mentioned where a foil such as this would probably be more hazard than help it'd seem to an elegant way of dealing with excessive submersion with a tri hull design. Aside from polyethylene I think okoume shearhed in fiberglass might be a fine thing - a laminate of two 4mm sheets for stiffness . This might really really be the way to go here Bob. Looking at your numbers on the 47lb. lift it seems like it could be quite effective indeed. More so than spreading the amas farther apart simply because that extra foot out per ama is going to increase drag on its own. With the foil kept at 10' beam it acts as a reserve buoyancy of sorts that essentially is invisible drag wise until it is submerged enough to generate lift.
I like the 75 lbs lift over the 47 to be sure, but again the more slender foot print of the 10 foot beam (less of course per actual side of the vaka used) is a winning point .

As it is Ive got 70 sq ft. I'm looking at a Genoa type rig upfront - much like your rig. Have you any brands for the Gen? I know Hobie does jobs and so on.


Thanks again Bob - the clarity of information and creativity of your post was deeply appreciated.


Pete


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 Post subject: Re: Active Ama Mod
PostPosted: Sun Sep 29, 2013 3:39 pm 
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Joined: Tue May 18, 2010 2:31 pm
Posts: 2710
Location: Kailua 96734
Pete, the bilge idea is a waste of time, which we we did speculate on a couple years back...

Frankly, you can easily hike out in most conditions. No issue at all on a TI.

If you're gonna go extreme, rig some soft weight belts on a barber hauler and slide them in/out. Or throw a sandbag from side to side. Or a small person. :D

But it's funny you mentioned the Raptor! There is one parked right next to our boat on Kaneohe.

Image

I've checked it out a few times, after I noticed the retractable foil, but have never seen it used. I thought it was a custom built 1-man outrigger. Near as I can tell it broke a dagger outside the bay a couple years ago and has been sitting ever since.

The foil concept is cool and simple enough... one foil provides either lift or drag as required on different tacks.

Image

If I can chat with the owner, I'll post more feedback.


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 Post subject: Re: Active Ama Mod
PostPosted: Sun Sep 29, 2013 4:00 pm 
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Joined: Sun Apr 20, 2008 6:18 am
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Location: Sarasota,Key West FL
Pete:
My only reason for mentioning polyethylene sheet is it can be easily welded directly to the outside of the AMA with a hot glue gun and polyethylene filler. If you designed a slight bend into the foil so it is steeper near the front (like a sled rail), it will be slightly stronger. I would fill the AMA with water before welding. You could also probably go longer length as well if you wanted, I just used 4 ft for my calculations as an example.
Bob


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 Post subject: Re: Active Ama Mod
PostPosted: Sun Sep 29, 2013 4:58 pm 
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Joined: Sat Nov 05, 2011 1:58 am
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Location: Forster, NSW, Australia
Just one corrrection... increasing aka length so overall beam is 12 feet (or more) does not increase drag (well apart from the miniscule increase in air resistance) as the wetted surfaces remain unchanged (actually slightly reduced due to the ama floating higher in the water).

I would be really interested to see how a TI (or AI) would go with (say) 14 foot beam, with no other modifications. I gather that a few of you out there have a spare set of akas, and it would not be too hard to split them and add sleeving tube to extend them. Any volunteers?

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Tony Stott
2012 Tandem Island "SIC EM"
www.scenefromabove.com.au


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