stabilizers

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john allsop
Brotherhood of the Golden Paddle
Posts: 1255
Joined: Mon Apr 18, 2005 3:40 pm
Location: isles of scilly UK

stabilizers

Post by john allsop »

I see "sail boats to go" have 10 foot long pontoons to make your boat "sail only i expect" or make a sort of "cat". They are inflatable, I don,t know if they are any good. Our expert will tell us.

Alm

Re: stabilizers

Post by Alm »

10 ft is too long for inflatable thing to be rigid enough to have a good hydrodynamics. The most rigid ones I've ever seen are from Balogh (yes, long waiting times and steep price, and they aren't indestructible either). They are about 5 ft long, torpedo shaped. After one multiday trip one of them has developed some tiny leak, which I can't find (the belly got abraded when I landed at a slow speed on shallow beach with small rocks, so it was dragged for a while before I could stop the boat). Don't know what to do - I have a spare, but may be will paint the sponson belly with Aquaseal glue. With 10ft sponsons your footprint will be huge, difficult to maneuver when landing, not to mention mooring at floating dock (often the case in marinas).

Cactus

Re: stabilizers

Post by Cactus »

I disagree that the length of the float/stabilizer/outrigger is factor in either rigidity or performance.

As far as rigidity is concerned, volume and pressure are the key. I ordered my 10 footer from tseeker.com and they are AWESOME! My 6-year old can stand on one between the two chairs, without much bending. It's 100% custom, so be sure you know exactly what you want. However, they work fast and are inexpensive.

From personal experience, I would say that it's a combination of volume and attachment strategy that are critical to the float's performance.

I definetely would advise against using 2 outriggers in a trimaran configuration. Unless those would be perfectly centered, very little forward progress would take place when under sail. Instead, one may try a single, longer and higher volume outrigger. Think of Hawaiian outrigger canoes as a reference.

Believe it or not, stability would only increase with such configuration. While your boat seaworthiness would get significantly better.

As far sealing the air leak on your outrigger, covering it with glue would not help.
I suggest getting a piece of the same material it was made of from the manufacturer and some of the glue that he used. Then, I would completely inflate the float and glue a wide strip of that material on the bottom of it. Full length.

The important thing here is that the float has to be completely inflated, while the strip should not be stretched (no wrinkles though). This would likely take care of your air leak and make the outrigger virtually indestructable.

Alm

Re: stabilizers

Post by Alm »

Thanks for the tips on repairs! I think I found the leak - it's a tiny rip on the top, not on the bottom. Probably caught some thorns when dried/stowed ashore or towing it on the cart away from the high tide line for the night. Reinforcing the entire belly with one large piece of fabric is a good idea. getting such a piece from Balogh will be long wait (and probably expensive), so I think I'll get a piece of Urethane deck fabric from Feathercraft Kayaks factory - Balogh sponsons are Urethane too, and almost same yellow colour.

Yes, volume and way of sponson attachment affect the rigidity. It should have 4 points for each sponson (2 points on each side of each sponson), with the distance at least 1 ft between the fore pair of attachment points (i.e. fore of the crossbar), and the aft pair. For a 10 ft sponson I would think - minimum 1.5 ft or 2 ft distance between the two pairs of attachment points. This might result in a double aka, i.e. 2 crossbars to support lengthy sponsons, which in turn results in much incontinence for occasional paddling strokes, not to mention more bulky package in transportation. And there is no need to have sponsons that long, really. Also, - sponson shape matters.

I doubt that sponson on one side makes the boat more stable than sponsons on both sides - port and starboard. These inflatable sponsons are not the same thing as solid wood "amas" in Polynesian canoes - the latter rely on the "ama" weight for stability, while the former - mostly on Archimedes force of the displaced water volume, so light inflatable sponson only provides stability when it's in contact with water. With a strong wind coming from the side where single inflatable sponson is installed, it's light weight will not stop the boat from leaning to the other side (where there is no sponson) and eventually - capsizing. You'll have to hike out every time in this situation, and the probability of capsizing is much higher than with 2 sponsons. Yes, a "trimaran" style (i.e. sponsons on both sides) is a beast in terms of additional water resistance due to the 2 sponsons, compared to the rig with sponson on one side only. And the larger is the sponson, the more water resistance.

John Monroe

Re: stabilizers

Post by John Monroe »

Hi,

The quote below is from Chris Ostlind who designs fantastic boats. Several years ago I saw a picture of him sailing with huge sails and two 10' amas. For performance information you could contact him. I have run into him on different forums where he has guided me in my attempts to achieve better sailing.

I came across one guy that told me the Balough Amas were blown up tight with air pressure to perform better. I have the Folboat Amas as John has but I don't know if I would want to blow it up that tight or not.

John
Brad's a great guy and has built many sailing kayaks, this being his most recent effort. Brad got his 10' amas from Attila at Custom Inflatables in West Virginia. They're duplicates of the inflatables I have used on my boats for many years and work like a charm. They're made from super durable, 32 oz. PVC impregnated polyester with Halkey-Roberts valves.

I haven't seen this boat in action yet, but I suspect it cooks along with a defined degree of liveliness.

Chris Ostlind
http://www.lunadadesign.com


mje
Site Admin
Posts: 1918
Joined: Thu Apr 14, 2005 12:34 pm
Location: Southeast Michigan

Re: stabilizers

Post by mje »

If an inflatable ama is large enough in diameter it'll be stiff. It's the ratio, and not the absolute dimensions, that determines stiffness.
Michael Edelman
FoldingKayaks.org Webmaster

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