View Full Version : Who's right Who's wrong? Is A Canoe Stern Better Performing Than A Double Ender?
I've been scanning this site trying to to get a firm answer to my question...IS A CANOE STERN A BETTER PERFORMING STERN THAN A DOUBLE ENDER???? It seems that there are many theories floating around, who's right...who's wrong???
Willallison
09-29-2005, 10:53 PM
It seems that there are many theories floating around, who's right...who's wrong???
Depends who you ask! :D
Forgive my ignorance, but what is the difference?
FAST FRED
09-30-2005, 06:35 AM
define better "Performing"
FAST FRED
SailDesign
09-30-2005, 06:57 AM
IS A CANOE STERN A BETTER PERFORMING STERN THAN A DOUBLE ENDER????
Neither, because a canoe-sterned boat IS a double-ender. :)
If you mena is a canoe stern better than a CRUISER stern, then we might have an argument to get stuck into. The canoe stern, generally, has "tumblehome" while the cruiser stern doesn't. VERY generally....
And the question has to be asked, as FastFred did, what do you mean by "performance" in this question?
Steve
Bergalia
09-30-2005, 07:54 AM
As my colleagues point out, Kudu, a canoe stern IS a double-ender.
And it's a valid question - what do you mean by performance. In a 'racing' hull there's no doubt that a 'fantail' creates less tumbleholme.
But in heavy following seas a double-ender gives a greater sense of security(or in my case it did). Which begs the question - where do you intend to sail her. Inshore sheltered waters - or blue ocean. :(
For an idea of a double-ender capabilities you might like to browse:
www.mavc2002.com/caledoniayawl/aegre
It is an account of a 20 foot Shetland foureen taking a 12,000 mile voyage acroos the Atlantic - well illustrated. :)
dougfrolich
09-30-2005, 12:21 PM
A heavy slower boat will benefit more from a double ended design intended for bluewater, than a lighter faster boat, The transom of a TP52 for instance has Lots of volume, much more than a double ended design of the same length, for that reason as a following sea approaches (usually you would be over taking waves though) the transome rises with the wave, even with an open transom green water does not rush into the cockpit- even backing down in 25kts. to free debris from the underbody. The configuration may not make "feel" secure though.
A heavier slower boat that finds itself being overtaken by waves and white water probably benefits from the back looking like the front for that reason- Strapped into a deep cockpit surrounded by high bulkworks adds to a "feeling" of security, But I think a modern cruiser will fall someware inbetween the two extreems.
JonathanCole
09-30-2005, 01:41 PM
How about for a catamaran for protected and inland waterways. Are there advantages to the double ended "canoe" type design. It seems to be that there would be less turbulence at the stern with a double ended design.
yipster
09-30-2005, 02:09 PM
that again depends on performance like forexample speed :D
Skippy
09-30-2005, 02:52 PM
A double-ender will have more turbulence above hull speed, which is typical of light catamarans, than will a squared-off transom. Water separates cleanly from the square stern, leaving only air and a smooth water surface behind it. Whereas the canoe stern pulls the water in toward the centerline, forcing it to turn again quickly once the water flows on the two sides of the hull crash into each other. Ultimately, the square transom will start to plane if it reaches a high enough speed.
safewalrus
09-30-2005, 05:46 PM
Double ended catamaran? is that not a proa? two 'sharp ends' and you 'tack' the rig not the boat. Apparantly goes like smoke!
Bergalia
09-30-2005, 08:47 PM
For an idea of a double-ender capabilities you might like to browse:
www.mavc2002.com/caledoniayawl/aegre
It is an account of a 20 foot Shetland foureen taking a 12,000 mile voyage across the Atlantic - well illustrated. :)
I love quoting myself...I'm that kind of chap...But as friend Skippy points out...I quoted wrong....
:mad:
The correct thread for the 'Aegres' Saga is: http://www.mavc2002.com/caledoniayawl/aegresum.htm
Still worthwhile all that keying in...
And thanks Skippy. You're a good man to have on the bridge ;)
Skippy
09-30-2005, 09:23 PM
Aw, shucks. *blush* :D
sw, a proa ama is usually narrower and at least slightly shorter than the main hull. On a Pacific proa, where the ama is on the weather side (lee side = Atlantic), the ama is much shorter and smaller than the hull. The hull is symmetric between the two ends, but can and ideally should be asymmetric between the windward and leeward sides. Whereas a canoe hull is symmetric along the centerline, and somewhat but often not quite symmetric fore-n-aft.
The rig has to pass through a plane perpendicular to the hull and ama rather than parallel. Proa rigs also tend to do things that are not necessarily tacking. The tack of a traditional oceanic lateen is moved from one end of the boat to the other, and the Gibbons rig swaps head and foot interchangeably. You need two rudders, one on each end, and usually two centerboards to control the helm balance.
Pacific proas reach fantastically because they're light and it's easy to fly the ama (hence the name "flying proa"). But I've been wondering recently whether they would point better than a cat, since the cat's big windward hull would provide more righting moment as long as you can fly it.
I'm feeling quite foolish...I was under the impression that a double ended sailboat has a hull similar to the Colin Archer "Redningskoite" type boat or an Ingrid, and that a canoe type hull resembled the much broader transom shape of the Aage Walstead. :eek:
A double-ender will have more turbulence above hull speed, which is typical of light catamarans, than will a squared-off transom. Water separates cleanly from the square stern, leaving only air and a smooth water surface behind it. Whereas the canoe stern pulls the water in toward the centerline, forcing it to turn again quickly once the water flows on the two sides of the hull crash into each other. Ultimately, the square transom will start to plane if it reaches a high enough speed.
This comment puzzles me...Does it really matter that the water from both sides of the hull crashes into each other? It seems, at that point of interference the transom would be one step ahead of it, no?
Bergalia
10-01-2005, 02:07 AM
This comment puzzles me...Does it really matter that the water from both sides of the hull crashes into each other? It seems, at that point of interference the transom would be one step ahead of it, no?
Ah Kudu - it matters not - until you come to a sudden stop - and then your 'transom' stern is 'flooded' whereas the canoe stern cleaves it to either side.. :D
BUT - a big but, it's an argument that is sure to rouse the hackles in either camp - double enders and transomers. Like throwing a stink bomb among the congregation...
Over here in Australia you get the 'petrol heads' arguing the merits of Ford versus Holden (General Motors). To the dispassionate they are much of a muchness... but both camps claim superiority (I drive a RangeRover Discovery) which is obviously far superior... :D
So when it comes down to it - each to his own. For me, double enders every time - for safety sake. (That's my contribution with a big spoon) :D
dougfrolich
10-01-2005, 02:42 AM
I'll second that, Bergalia---Though I do like those big butts. But then again I thought it was a good idea to sail this across the Pacific.
Skippy
10-01-2005, 03:03 AM
kudu: Does it really matter that the water from both sides of the hull crashes into each other? It seems, at that point of interference the transom would be one step ahead of it, no?
You always want the water flow to be as straight as possible. Curved flow/crashing is what creates wave drag. There's no transom on a canoe stern, the curved hull creates a low-pressure area that pulls the water toward the centerline. I'm not sure what you mean by one step ahead.
Bergalia
10-01-2005, 03:54 AM
Beautiful shot, Doug...but how do I know it's you hidden behind the sail...or if was you, did you hide because you were embarrassed at being caught wearing one of those multicoloured 'weekend yottie' bobble caps... :D :D
But bravely done Doug. ;)
safewalrus
10-01-2005, 04:44 AM
Skippy
That's what I said, two fronts/two a***s! Only without the gobblegook!
Skippy
10-01-2005, 11:06 AM
Gobbledygook is my specee-ality. :p
kudu: Does it really matter that the water from both sides of the hull crashes into each other? It seems, at that point of interference the transom would be one step ahead of it, no?
Skippy: I'm not sure what you mean by one step ahead.
Oh I know, you mean if the water is already past the hull, how can it have any effect? I guess the idea is that energy has already been imparted to the water, and that energy must have been drawn out of the boat. That occurs just before the crash, where the hull is curving inward so the low pressure exerts a drag on the boat. There's also an increase in displacement from the sloped underside of the hull, which I suspect adds to wave drag even more than the sides.
kudu: Does it really matter that the water from both sides of the hull crashes into each other? It seems, at that point of interference the transom would be one step ahead of it, no?
You always want the water flow to be as straight as possible. Curved flow/crashing is what creates wave drag. There's no transom on a canoe stern, the curved hull creates a low-pressure area that pulls the water toward the centerline. I'm not sure what you mean by one step ahead.
What I mean Skippy is...Isn't the stern moving away from the turbulance? Doesn't the action take place after the transom has moved forward? :confused:
dougfrolich
10-01-2005, 01:09 PM
Its like the pic.
Gobbledygook is my specee-ality. :p
kudu: Does it really matter that the water from both sides of the hull crashes into each other? It seems, at that point of interference the transom would be one step ahead of it, no?
Skippy: I'm not sure what you mean by one step ahead.
Oh I know, you mean if the water is already past the hull, how can it have any effect? I guess the idea is that energy has already been imparted to the water, and that energy must have been drawn out of the boat. That occurs just before the crash, where the hull is curving inward so the low pressure exerts a drag on the boat. There's also an increase in displacement from the sloped underside of the hull, which I suspect adds to wave drag even more than the sides.
I'm trying to picture this event...As momentum pushes the double ender forward the water sliding past each side of the hull folds upon itself (turbulence) at the trailing edge of the hull/rudder. At this point isn't it similar to the trailing edge of a sail or wing from a plane? Somewhat of a pinch point where the energy pushes one forward? In other words...a good thing, and after this event it becomes a moot point.
Its like the pic.
Hey Dougfrolich...In a cruising double ended hull, how fast could you be talking about? I'm assuming I'd be real lucky to do 8 knots. What do you think?
Neither, because a canoe-sterned boat IS a double-ender. :)
If you mena is a canoe stern better than a CRUISER stern, then we might have an argument to get stuck into. The canoe stern, generally, has "tumblehome" while the cruiser stern doesn't. VERY generally....
And the question has to be asked, as FastFred did, what do you mean by "performance" in this question?
Steve
Could you elaborate on the Cruiser stern vs a canoe? Thanks
I'm with you Bergalia...There is nothing finer, sweeter, sexier and oh yes, more pleasing to the eye than a double ender!!! I will happily deal with the loss of a + or - 1/2 knot of speed from a double ender, as FastFred describes! :)
Sean Herron
10-01-2005, 04:02 PM
Hello...
This is a funny thread for me - just recently I have been thinking about and doodling boats of 22 feet in length and shooting the poop at work with the 'guys' about double enders or transom sterns...
I have also decided that divorces are expensive because they are worth it - but my wife is still very attractive and she puts up with me so I don't go there... :)
She is a pain in the ass though - but thats better than fat, boring, and stupid looking I suppose... :)
So what have you...
I am suprised old Dave Gerr did not plant himself on this one as he seems to be the only contemporary designer doing proper canoe sterned yachts - which I think are ugly and stupid looking - and I am right - all the time - and in any place - because I am usually by myself there... :)
Happy wife - happy life - you can be right or you can be happy - you choose...
So canoe sterns are funny, ugly and weird - at least to me and MY wife - plus they are tricky to loft, fair and build - and hard to explain to people who ask 'why'... :)
You can draw and hide some flat aft sections into them per the discussion above - but something not mentioned thus far is the lack of bouyancy aft in both double enders and canoe sterned ulgies...
This is something to consider when taking into thought the use of the boat - how many people and things - gas tanks - water tanks - engines - outboards - rail mounted BBQ's are going to 'hanging' about the back end of the boat while sailing...
A transomed boat can load up asymetrically quite well for the daysail - and a double ender can load up very well for a long cruise - meaning you can sink the 'transom' of a double ender with little appreciable difference in performance or load waterline plans - sink a 'normal' transom below the DWL on a fatass boat and you get all those ugly eddies and little negative suction thingies... :)
Aside from all these thoughts - canoe sterns are just ugly and stupid - and I am always right when standing alone in an empty room... :)
Oh man - life is hard....
See http://www.donkrafft.com/gerr_boats.htm ...
SH
Skippy
10-01-2005, 05:46 PM
kudu: As momentum pushes the double ender forward the water sliding past each side of the hull folds upon itself (turbulence) at the trailing edge of the hull/rudder.
No, back up one step (actually, move forward :) ). As you can see in Doug's sketch, the hump of water is building up before it clears the stern. That's where the suction slows (and weighs) the boat down, where it's still in contact with the hull.
Sean Herron
10-01-2005, 05:51 PM
Hello...
Don't know if th is makes sense - but think of the tea dribbling down the side of a smooth lipped pot - it has been found that a pot with a sharp edged mouth (unfinished cheap metal) drips less - 'good release'...
Cheers - sun is out...
SH>
marshmat
10-01-2005, 07:29 PM
If you want to plane, you want as little drag as possible pulling you back. You also want as much lift as possible pushing you up. On most planing powerboats the bottom actually slopes down right up to the transom, usually about -5 deg., and so you get some lifting force at the stern. You then have a sharp corner so the boat and water can break away while maintaining more-or-less laminar flow right up to the transom. Curving the transom double-ender style works well at low speed, where laminar (smooth) flow can be maintained right up to the transom. But try to plane such a hull, and you get massive turbulence developing under the stern as the water tries to keep in contact with a boat that is moving faster than the water can adjust. Turbulence then prevents the hull from lifting and so it can't plane easily.
In general, the trailing edge should be sharper the higher the speed. (Note that this refers to the trailing edge of the hull-water interface; ie. the corner between the transom and bottom as viewed in profile.)
But in the scheme of things...Really now...How much of an issue is that mini wave at the stern of a double ender sail boat fully loaded for blue water sailing?
It's becoming apparent that this thread has hit a "Y" in the road...Speed and efficency vs safety and good looks.... :D
Sean Herron
10-01-2005, 08:22 PM
Hello...
Got back from a sail in my 'fatass'...
Here in Vancouver you 'reach out and run back' - I many times would like try a sail in a double ender over my boat when running wing on wing with a pole out on the jib - going home...
With the tide aft and running in with me - I cannot pour a whiskey without fear of a wild and crazy broach - bah...
Mind the boom...
My next boat will have two 'pointy ends' - and a pilot house against the damned rain...
Yup....
SH.
Bergalia
10-01-2005, 08:48 PM
With the tide aft and running in with me - I cannot pour a whiskey without fear of a wild and crazy broach - bah...
My next boat will have two 'pointy ends' - and a pilot house against the damned rain...SH.
That's because you're drinking whiskey with an (e). Either US, Canadian, or Irish...That stuff is only used for priming kerosine engines or curing worms in cattle. What you drink is whisky, preferably a single malt. :D
Bergalia
10-01-2005, 08:49 PM
With the tide aft and running in with me - I cannot pour a whiskey without fear of a wild and crazy broach - bah...
My next boat will have two 'pointy ends' - and a pilot house against the damned rain...SH.
That's because you're drinking whiskey with an (e). Either US, Canadian, or Irish...That stuff is only used for priming kerosine engines or curing worms in cattle. What you drink is whisky, preferably a single malt. :D
Hello...
Got back from a sail in my 'fatass'...
Here in Vancouver you 'reach out and run back' - I many times would like try a sail in a double ender over my boat when running wing on wing with a pole out on the jib - going home...
With the tide aft and running in with me - I cannot pour a whiskey without fear of a wild and crazy broach - bah...
Mind the boom...
My next boat will have two 'pointy ends' - and a pilot house against the damned rain...
Yup....
SH.
I just listed plans on this web site for a double ender with a pilothouse. They're for a 50 footer. Interested? :D
Skippy
10-01-2005, 09:50 PM
kudu: How much of an issue is that mini wave at the stern of a double ender sail boat fully loaded for blue water sailing?
When you're broad reaching in a nice fresh ocean breeze, it should make plenty of difference. But zipping along in perfect conditions is the least of your worries when cruising. I wonder if keeping that max speed down might reduce the chances of broaching?
Sean Herron
10-01-2005, 11:56 PM
Hello...
I don't drive a NASCAR to work and I don't run my Geo Metro on the track on weekends...
Form follows function - necessity is the mother of invention - glass is good if you need to look through it - all that stuff...
I think the one we need here is - 'play the game by averages'...
You can build the 'perfect' boat - the 'perfect' race car - but you cant guess at what (G)od is going to throw at you on any given day - or for a month at sea...
So that said - I like designs for average conditions with creature comforts for those less than good conditions... :)
Maybe thats why I stay married - and drink whiskEy... :)
SH.
MikeJohns
10-02-2005, 03:12 AM
A few comments here.
Latest research has shown the submerged transom to give lower drag BUT it depends on other factors in the UW hull form too mainly how the UW aft lines run.
Transoms that are entirely above the WL are essentially double ended hulls but the topside run aft gives a lot more usable space and counters one problem with pointed sterns, which is pooping in a following sea due to lack of reserve bouyancy.
Modern heavy weather tactics have changed with a quarter presented to the following sea and the hull allowed to run free rather than stern-to with warps and drogues to slow the boat down. Under these tactics a double ender has only the disadvatage of a lower bouyancy aft.
Another problem can be the hobby-horsing tendancy with similar sections fore n aft. Flatter aft sections damp the pitching oscillation better.
I have trouble with the loss of a decent cockpit or aft cabin with boats with a pinched stern, I favour a small transom to a true double ender any day.
Bergalia
10-02-2005, 03:14 AM
- I like designs for average conditions with creature comforts ...... - and drink whiskEy... :) SH.
Honestly...the man is incorrigible, even for a Canadian...do we decent chaps want to share a page with a man who boasts such uncivilised drinking habits... :D :D :D
Honestly...the man is incorrigible, even for a Canadian...do we decent chaps want to share a page with a man who boasts such uncivilised drinking habits... :D :D :D
You are a very humorous guy, Bergalia...I enjoy your input :D :D :D :D
tunnels
12-03-2011, 04:43 PM
This comment puzzles me...Does it really matter that the water from both sides of the hull crashes into each other? It seems, at that point of interference the transom would be one step ahead of it, no?
You dont see what is happening before the water leaves the bottom of the hull ,there lots going on as the hull moves through the water unable to be seen but its there . trail colored cotton thread throught the water that extends along and round and past a shape traveling through the water and see where the water actually starts to separate to go round a shape and what is happenig even up to a meter past the trailing end ! movment is still happening way behind the boat . its all interconnected and inter-related !. its what we cant see that we dont understand and just guess at and most time get it completely cocked up and wrong :?:.
Just remember it takes energy to move water !! a object moving through water is separrating and pushing aside the water to move forward and as it gets past the widest point the water presure +energy is pressing backinto fill the void being left behind as the hull moves forward through the water . this presure is taking place a long way fro the actual hull as well not only up close but up to a couple of meters away look at the wave alongside the hull as it moves !! the wave is water pressure up is pressure down is suction so take notice nexttime you see a boat going through the water . same applys to air with two cars passing at high speed they push eaach other aside and then immediatly draw each other into the other slipstream behind is more notice able in two highspeed trains traveling in opposite dirrections in a tunnel . theres high pressure before and suction after . water is fluid air just a lot more dense !:D
hoytedow
12-03-2011, 05:01 PM
Making boats is a[l]ways a passion never a chore!
I couldn't agree more.
Thanks for bringing this old discussion to light!
Yobarnacle
12-03-2011, 06:21 PM
aged sour mash...straight. smoothe with an E
rwatson
12-03-2011, 06:29 PM
........ Under these tactics a double ender has only the disadvatage of a lower bouyancy aft.
Another problem can be the hobby-horsing tendancy with similar sections fore n aft. Flatter aft sections damp the pitching oscillation better.
Surely this depends on whether
A) a canoe stern is a square transom with the edges cut off,
B) a transom with the hull extended out further
If it is A, then the hobby horsing is 'more', if it is B, then it is even 'less' :)
I like canoe sterns when a huge wave is chasing in behind you across the harbour bar.
I like square sterns when I am lounging around in the sun with friends, and there is more room on the end of the boat, while paying less at the marina per foot.
I hate canoe sterns when I have to build extra framing at both ends, and bend the timber at both ends, and paint/epoxy the narrow bits on the inside at both ends.
I hate canoe sterns when trying to hang a dinghy or an outboard motors of the end of the boat, or trying to climb in from the water.
So, I definitely prefer flat sterns unless canoe sterns are better - I think.
Yobarnacle
12-03-2011, 06:42 PM
I added a canoe stern to my wide transomed lil motorsailer, making her 30 feet long. Didn't lose any internal volumn, and faster hull speed because longer WL.She's a trailer sailer, so seldom incursrs dock fees. As for hobbyhorsing? Major cause of pitching is weight in the ends. Try to cram the same stuff in a pinch stern as a fat stern, and she's gonna pitch. IMHO
View Full Version : Who's right Who's wrong? Is A Canoe Stern Better Performing Than A Double Ender?