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Thread: Can we discuss outriggers?
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9th October 2012, 07:08 AM #1
Can we discuss outriggers?
Please excuse me if this has already been discussed
(I'm reading the archived articles as fast as I can!) ;
I've been looking at commercial and home-built outriggers for canoes
and am puzzled at the apparent lack of either rhyme or reason
regarding the optimum size of the equipment.
The amas (dismissing the crab pot traps and the swimming pool noodles)
appear to be anything from one quarter the length of the boat
to the full boat length.
I have not seen any reference
to the length of the floats produced by your plans
(though your pdf file "outriggers drop in Eureka version b"
shows the ama as about one half the boat length)
nor have I seen the function of ama length discussed anywhere.
Is there no formula for the relative lengths of boat to amas?
And aside from the effect on bouyancy,
does the width and depth of the amas affect sailing performance?
What about the effective beam of the outriggers
relative to the beam or length or displacement of the 'host' boat?
And we haven't even touched on
the fore-and-aft placement of the amas
and, separate but related, the akas.
I did see a brief mention of fine vs blunt ama entry
when someone considered scaling down his Quick Canoe plans
to one-third for use as amas,
but I don't recall any conclusions being drawn,
other than a mention of lateral resistance when the ama is submerged
(No doubt one must consider the intended purpose of the outriggers,
whether they are part of the sailing equipment or merely 'training wheels').
How about it-
can someone contribute some wisdom on outrigger design,
or is it a case of 'any size fits all'?
If this has all been discussed previously
I would be satisfied with a link...
Thanks.
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12th October 2012, 02:40 PM #2
Howdy,
I started writing a reply. And it was so current compared to what I was doing the last week I just put it straight on my website.
Hope it helps explain some of the background choices.
Michael.
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14th October 2012, 11:49 PM #3
Adding to MIK's comments, a quote from Phil Bolger's "Boats with an Open Mind"
regarding his contribution to the 3M Multihull Class. Bear in mind these thoughts
relate to a racing class, where every last possible bit of boat speed is being
wrung out of it. I think his comment about being buoyant enough to aid entry/exit
is well made across the board.
Bolger 3M tri.jpg
"Since all the boat's power to carry sail comes from the buoyancy of the lee-side float,
the floats are designed to bury to the deck without prohibitive drag: slim-lined, round-bilged,
with sharp canoe sterns. (appreciation is given to the memory of Arthur Piver, who first perceived
that a trimaran's floats should be as long as the main hull since they should move at the same speed.
For an embarrassingly long time, people who should have known better kept imitating flying boat
wing-tip floats.) These floats will support 270lbs to the deck amidships, with a lot of sheer above
that for reserve. Apart from driving through squalls, it's handy to be able to step on a float to get
into or out of the boat."
Once upon a time, when I was too broke to afford MIK's outrigger plans let alone the materials
to make them, I built some amas for a 16' canoe from 6M of 90mm storm water pipe. Approx
buoyancy was 10kg to bury the centre section with another 5kg reserve in the canted tips.
I broke the main mast (40mm sq laminated pinus crapiata trellis laths) before I ever buried
one of the floats. The boat was plenty stable enough for my wife & (then) little kids to feel
secure, & the skinny floats had no appreciable resistance to forward movement on this slow boat.
1997-09-07 Wingham1.jpg
Of course, one needs to consider that this extra stiffness makes for a very rough ride if
travelling across a chop rather than into it or with it. The leverage of large amas can
roll the the boat quite violently through an admittedly limited arc. With attendant stress
on the structure of the main hull. I'm guessing that's the reason behind the very small floats
seen on (UK) touring canoes: there just to buy time to react to wind changes, and give some
respite from actively balancing the boat for long periods.
swings... roundabouts...
So in the end, the ama design depends on what you want it to do...
hope his helps.
Alan J
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15th October 2012, 07:32 AM #4
Good information
Yes, that helps, Alan.
Thanks.
And thanks to you, Michael,
for the great response you posted on your page.
I have a much better picture of the purpose and function of outriggers now.
Speaking of pictures of purpose and function,
I found this photo on the yahoo 'sailing_canoes' forum.
I have had no success in contacting the photographer
but maybe a peek for the sake of education could be permitted.
A sunbathing platform/ dining table might induce
many a reluctant mate to join the fun!
ShasLast edited by Shas Cho; 15th October 2012 at 07:35 AM. Reason: Punctuation error
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15th October 2012, 08:27 AM #5
Nice Article AJ,
The logical problem with Bolger's statement is that a 16ft catamaran can touch on 20 knots (while barely under control) but an 18ft can get there with some stability intact. So observation would lead us to say that shorter amas are not necessarily a handicap.
If you want to get up to 20 knots anything up from 18 feet can do it. Bolger seems to be hinting the large hull will be limited by the small hull - which is a flawed argument.
On a trimaran they will have a higher slenderness than a longer main hull so have a larger speed potential. But be aware of excessive slenderness - a knife bowed ama with straight deck edge back to the crossbeam is pretty inefficient. The reason is that it displaces too little - and will sit much deeper in the water than a hull of same length, beam (and thus same slenderness) for more wetted surface and less ability to stand up to the sail or deal with trim changes.
It is interesting looking at the development of Lock Crowther's cats and tris. Many had very wide convex decklines and were regarded as very fast but nice to handle. It seems the most important criterion that overarches everything - if you want a fast multi - it has to be built light. Then more volume gives you better handling and better average speeds (as opposed to top speeds).
It's average speeds that are important cruising and racing
MIK
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