List of boats with skeg and sugar scoop

[OneHullPaul]

Perhaps you could draw me a canoe stern keel form with a swim platform, I really can't picture it. A swim platform requires compromises in keel design, keel design requires compromise in swimming options.

All design is compromise, I know where I'd like the compromise to be when I come back to an anchorage to find my anchor dragged and the boat lying on the beach being picked up and dropped repeatedly by the waves.

Originally Posted by Dockhead

No, I'm not trolling. I seriously don't understand what swim platforms have to do with rudder or keel form.


In fact I would stick my neck out and say that these things are totally unrelated to each other. Why in the world could you not have a nice swim platform with a full keel, or a plumb transom with a bulb keel?


If I'm missing something, I'll be glad to be enlightened.

[Ericson38]

Originally Posted by Dockhead

You are blowing my mind here. Why???


My boat (Bill Dixon design) has a partial skeg. I always thought that this is inferior hydrodynamically in every way to a spade rudder.


But I will say that in tens of thousands of miles of sailing, many of them in tough conditions, I have never once stalled this rudder. I always put it down to the sheer size of it (which is also a tradeoff in terms of drag).


Why would a skeg extend the range of AOA? I don't understand.

I have a hardcopy of Technical Yacht Design by Hammit. I also have Marhaj's books. On pages 168 and 169 of Andrew Hammit's book in the chapter on Directional Control of a Sailboat he explains this very point. The term he uses is Rudder Deflection Coefficient.

Example he gives:

For a spade rudder of with a 2 ft chord and 4 ft span at 10 kts water flow velocity, and a skeg setup of identical total area with 50% area in the skeg and 50% in the attached rudder, 1st determine maximum side force at 13 deg AOA and torque required (rudder post 25% back from leading edge of rudder, post is vertical in hull, hull is upright) for the spade:

Rudder side force is 2200 lbs, and rudder torque is 110 ft lbs. This turning moment is applied through the lever arm distance to the center of the boat's natural rotational center point (close to leading edge of keel). Rudder's lift coef is 1.35 (for infinite aspect ratio)

For Skeg rudder, the torque required to deflect the flap (rudder part of skeg-rudder) is higher at 410 ft pounds, as all the flap is behind the skeg (full skeg...not a partial design like Dixon's). The AOA required was also higher than the spade (16.6 deg) for the same 2200 lb side force. The rudder-skeg lift coef is 2.2 (for infinite aspect ratio)

The difference with the Skeg is that the rudder AOA could be set all the way to 21 deg without stalling, and at this angle, the side force of the Skeg configuration was higher than the spade rudder could develop, due to resistance to laminar water flow separation.

The Hammit book is considered essential reading in this course:

Theory & Design of Sailing Yachts

I'm not going to type out the equations.

[NevilleCat]

Originally Posted by OneHullPaul

Perhaps you could draw me a canoe stern keel form with a swim platform, I really can't picture it. A swim platform requires compromises in keel design, keel design requires compromise in swimming options.

All design is compromise, I know where I'd like the compromise to be when I come back to an anchorage to find my anchor dragged and the boat lying on the beach being picked up and dropped repeatedly by the waves.

I think I too am not understanding the relationships you are talking about, but am interested. Perhaps I am not understanding the specific definitions...I am not too au fait with the technical terms; are you talking about a waterline "sugar scoop" type of stern? Is there a hydrodynamic reason this couldn't be incorporated with a full keel (apart from tradition)? Or any other type of keel (or centerboard)?
After all, as a layperson it seems like a sugar scoop is pretty much where the hull should end but the designer has opted to waste a portion of the boat so you can have the undoubted relief of dangling your toes in the cold water after you have just damaged them on a poorly placed cleat whilst struggling around the shrouds.

[sck5]

I had a Caliber 40 with sort of a sugar scoop and a skeg. I would sail that boat anywhere.

[Dockhead]

Originally Posted by OneHullPaul

Perhaps you could draw me a canoe stern keel form with a swim platform, I really can't picture it. A swim platform requires compromises in keel design, keel design requires compromise in swimming options.

All design is compromise, I know where I'd like the compromise to be when I come back to an anchorage to find my anchor dragged and the boat lying on the beach being picked up and dropped repeatedly by the waves.

What does a canoe stern have to do with the keel form? You see double enders with both full keels and fin keels.



And what does any of this have to do with anchoring?


I am more and more confused.

[Leighpilot]

Dix Coquette 39.

Fast ,light and great in light and strong winds.

https://www.dixdesign.com/coquette.htm

[jvonsenden]

Have you checked out the Island Packet 350 or similar?

[Ericson38]

Originally Posted by Dockhead

You are blowing my mind here. Why???


Why would a skeg extend the range of AOA? I don't understand.

Here's an illustration of the principle in general.

https://www.bing.com/images/search?v...=23&ajaxhist=0

With the Dixon implementation, a partial skeg allows for a large degree of the lower rudder to be in front of the post, which greatly lessens the turning torque needed. In addition, stalling starts at the top and works its way down, since water pressure is less and the turbulence around the bustle generates bubbles which reduce the water density further, increasing stall tendency in difficult conditions. So the skeg is there closer to the surface, where it can delay stall best.

[Dockhead]

Originally Posted by Ericson38

Here's an illustration of the principle in general.

https://www.bing.com/images/search?v...=23&ajaxhist=0

With the Dixon implementation, a partial skeg allows for a large degree of the lower rudder to be in front of the post, which greatly lessens the turning torque needed. In addition, stalling starts at the top and works its way down, since water pressure is less and the turbulence around the bustle generates bubbles which reduce the water density further, increasing stall tendency in difficult conditions. So the skeg is there closer to the surface, where it can delay stall best.

That is all absolutely new information for me. I thank you for the education.


I have noticed of course that all the boats with spade rudders I've sailed, have been much easier to stall the rudder. I always put that down to high aspect ratio of those rudders, because the boats were all performance oriented (I used to charter Salona 45's for example).



My rudder is just about stall-proof. I have never stalled it in tens of thousands of miles of hard sailing, sometimes foolishly overcanvassed. I always put that down to the sheer size of it, not to the little skeg.



But I see that it's all more complicated than I thought.

[slug]

Originally Posted by deCarabas

Good day all,

I have been searching far and wide for a list of boats that have a skeg rudder and a sugar scoop with no luck. Anyone know where I might find such as list or if one even exists? Perhaps a site with an extensive advanced search?
Thanks for taking the time.

Look for boats designed by Ron Holland

[OneHullPaul]

Care to provide a pic or name to those fin keel canoe stern boats? A canoe stern would seem like the opposite of a pizza slice shape with most of the width carried aft. If such machines exist, I have no beef with them but I've only ever seen a swim platform or an encapsulated keel, never both on the same boat. Given that, I'd pick the encapsulated keel and sleep better than my home being reliant on a handful of keel bolts to stay upright.

Originally Posted by Dockhead

What does a canoe stern have to do with the keel form? You see double enders with both full keels and fin keels.



And what does any of this have to do with anchoring?


I am more and more confused.

[Les Noble]

I haven't read all.posts, but I have the last built (33) Via Marine 42. Got it all plus Aluminum hull.

[slug]

Originally Posted by Dockhead

That is all absolutely new information for me. I thank you for the education.


I have noticed of course that all the boats with spade rudders I've sailed, have been much easier to stall the rudder. I always put that down to high aspect ratio of those rudders, because the boats were all performance oriented (I used to charter Salona 45's for example).



My rudder is just about stall-proof. I have never stalled it in tens of thousands of miles of hard sailing, sometimes foolishly overcanvassed. I always put that down to the sheer size of it, not to the little skeg.



But I see that it's all more complicated than I thought.

Semi balanced rudder

[Dockhead]

Originally Posted by OneHullPaul

Care to provide a pic or name to those fin keel canoe stern boats? . . .

You've never seen one? Really? I think Bob Perry designed more canoe-stern boats than anyone. A lot of his were fin keel. Some even with spade rudders. Like Sliver:







Perry's Valiant 40 is a double-ender with Fin keel:




Perry did a lot of full keel double-enders, but many of them had fin keels.

So again -- what does the form of the stern, have to do with the type of keel or rudder? Now that you know the question is not "trolling".

[OneHullPaul]

Your first example isn't encapsulated, your second isn't a fin keel. I'm an owner of a Perry design FYI.

https://www.merriam-webster.com/dictionary/fin%20keel

I'm asking for an example of an encapsulated keel with a swim platform. I don't believe one exists.