Shoal Draft v. Full Depth Keel

[malbert73]

Originally Posted by bmz

My keel is less than one square foot at the bottom with almost vertical leading and trailing edges; a shoal draft is usually around 4 ft.² with a sloped leading edge. When I run aground, my boat stops, and all I have to do is back off(in 32 years I have only needed help once); when a shoal draft boat runs aground, it continues a way until it is hard aground, and hardly ever can simply back off.

I think a smaller keel tip may facilitate spinning the boat to get off of a shoal and may have less keel friction. I don't know why a shoal draft keel would run harder aground. That generally has to do with displacement of boat, speed and momentum. I suppose a sloped forward section of keel may be like a sled and glide onto a shoal more?


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[Cheechako]

[QUOTE=bmz;1697654]

Originally Posted by malbert73

5'8" isnt that deep a draft for bigger boats. Sailing on the chesapeake, though, you have ruled out quite a few coves and harbors in northern part of Bay,"

Darn--that limits me to around a hundred (seriously, sailing out of the South and Severn rivers, I have never wanted to anchor that far north)

" How do you explain the last sentence? Aground is aground. If you mean wing keels or long full, then yes I agree with you."

My keel is less than one square foot at the bottom with almost vertical leading and trailing edges; a shoal draft is usually around 4 ft.² with a sloped leading edge. When I run aground, my boat stops, and all I have to do is back off(in 32 years I have only needed help once); when a shoal draft boat runs aground, it continues a way until it is hard aground, and hardly ever can simply back off.

Yeah... I thought this way for years. Then after plowing along much of the ICW thru muck with no issues... I finally ran aground on a hard sand "peak" south of Miami. Nothing would get the boat off. Finally Tow Boat came to help. After several attempts including pulling with the main halyard (as well) to tilt the boat the skipper told me "one more try or it will have to be a salvage". Fortunately we dragged the boat, bumping along off on that try.

[Group9]

My first full size sailing vessel was a Cape DOry 25D with a full keel. I ran that baby aground on hard sand, and had to kedge it off, so many times I lost count. I finally learned that 3.5 feet of draft did not mean I should sail in 4 feet of water.

[Boatyarddog]

Upwind performance is the biggest consideration.
Ketch rigged boats, don't use a keel the same as a sloop does.


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[Randyonr3]

Originally Posted by Boatyarddog

Upwind performance is the biggest consideration.
Ketch rigged boats, don't use a keel the same as a sloop does.


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Now this I've got to hear....please explain......

[Boatyarddog]

So, without a bunch of technical stuff, sloops yaw alot more than Ketch rigged boats.
The reason, a long keel tracks better.
The Mizzen also helps this.
You can typically point higher with a deeper keel, as well the capsize righting moment is a bit faster.

[Polux]

Originally Posted by Boatyarddog

So, without a bunch of technical stuff, sloops yaw alot more than Ketch rigged boats.
The reason, a long keel tracks better.
The Mizzen also helps this.
You can typically point higher with a deeper keel, as well the capsize righting moment is a bit faster.

I did not understood that explanation about the keel working differently on a ketch or in a slop and I now of Ketches that were transformed in sloops with significant sailing advantages and no keel change.
Longer keel means a deeper one or a modified fin keel?
But I am even more confused with that thing about the capsize righting moment being faster? what is the capsize righting moment? Do you mean the righting moment? and by faster do you mean bigger?

[Boatyarddog]

I'm very sorry but due to explainable issues with boat technical knowledge.
I will refer you to research more the different keel designs ,and reasons for multiple masts or reasons for rigging types.
It really hard to learn online, better to study why these designs are what they are.
Happy sailing.��

[Randyonr3]

Originally Posted by Boatyarddog

I'm very sorry but due to explainable issues with boat technical knowledge.
I will refer you to research more the different keel designs ,and reasons for multiple masts or reasons for rigging types.
It really hard to learn online, better to study why these designs are what they are.
Happy sailing.��

Sounds like a "bail"
I also would like to know why a ketch uses a keel differently than a Sloop.
And this "Yaw" you speak of, I'm wondering why My FIRST 42 sloop with a "High Aspect" rig will have more "yaw" than the Feji Ketck setting next to me..

[Randyonr3]

Concerning the different type of keels, Dont make any rash judgments based on the keel type before you sail the boat.
On one hand, ours tracks very well and we have no complaints, But again
On our last trip up the west coast, I had a 60 foot, what looked like a Garden Style Ketck with which I would presume, had a full length keel, slowly disapear over the horrizon in front of us, Sailing to weather.
As for the depth, chose the area you'll be sailing, and the depth to match..

[bmz]

I understand what Boatyarddog is saying. Fin keels definitely have less tracking stability (yaw) than longer shoal draft or full keels; whereas a ketch has greater tracking stability than a sloop. Additionally, for any given weight, a deep keel will have greater righting moment than a shallow keel.

[Boatyarddog]

High aspect refers to the shape of a foil as it cuts through its fluid. A deep keel with a short chord where it attaches to the boat, and a tall mainsail with a short boom would be high aspects. Gliders have long, narrow wings: high aspect. A shallower keel with a long keel/hull joint, a mainsail on a short mast with a long boom would be low aspect. Supersonic fighter planes have short, wide wings: low aspect. A solent jib is considered high aspect. A genoa would be low aspect. The term is relative. It comes from "aspect ratio", which compares the leading edge length of the foil to its chord length. CCA rigs were designed typically with low aspect mainsails. IOR boats with their short booms generally have high aspect mains. High aspect foils develop more lift for their size than low aspect foils. This is one of the reasons deep keel boats do better to windward than full keel boats. There are points of diminishing returns however. If the keel's too deep, you start to hit things with it. If the mast's too tall, you heel too much, and the weight you have to carry to compensate for it slows the boat down. It's all a balancing act.

Keel design and sail, mast combinations, will vary results with regards to windward performance.
Full keels track better because of the length of the keel under the boat.
Ask the guy with the Fuji Ketch, the hull on his boat is the same as the Mariner ketch.
I don't know what 40 your referring to as "your last boat".
There are many different keel designs out there. Why? Because they allow the boat to do certain things better than other designs.
Otherwise they would all have the same keel design.
Nuff said.

[Polux]

Originally Posted by Boatyarddog

High aspect refers to the shape of a foil as it cuts through its fluid. A deep keel with a short chord where it attaches to the boat, and a tall mainsail with a short boom would be high aspects. Gliders have long, narrow wings: high aspect. A shallower keel with a long keel/hull joint, a mainsail on a short mast with a long boom would be low aspect. Supersonic fighter planes have short, wide wings: low aspect. A solent jib is considered high aspect. A genoa would be low aspect. The term is relative. It comes from "aspect ratio", which compares the leading edge length of the foil to its chord length. CCA rigs were designed typically with low aspect mainsails. IOR boats with their short booms generally have high aspect mains. High aspect foils develop more lift for their size than low aspect foils. This is one of the reasons deep keel boats do better to windward than full keel boats. There are points of diminishing returns however. If the keel's too deep, you start to hit things with it. If the mast's too tall, you heel too much, and the weight you have to carry to compensate for it slows the boat down. It's all a balancing act.

Keel design and sail, mast combinations, will vary results with regards to windward performance.
Full keels track better because of the length of the keel under the boat.
Ask the guy with the Fuji Ketch, the hull on his boat is the same as the Mariner ketch.
I don't know what 40 your referring to as "your last boat".
There are many different keel designs out there. Why? Because they allow the boat to do certain things better than other designs.
Otherwise they would all have the same keel design.
Nuff said.

This is an incredible amount of disinformation. Alright I see that you have an old ketch, that has probably to do with that.

The main reason there are many types of keels around has to do with the boats on the water having being built over almost a century and the main reason they have many shapes has to do with sailboat design evolution.
If you look at contemporary designs the keels are not that different and have a lot more in common between them than with 30, 40 or 50 old designed keels.

[El Pinguino]

Originally Posted by Polux

If you look at contemporary designs the keels are not that different and have a lot more in common between them than with 30, 40 or 50 old designed keels.

Is that right.... golly... I thought there was quite a bit of difference between -frinstance - an Island Packet, an Ovni, and something like...say... 'Rio 100'

I guess I need to go to Specsavers......

[Polux]

Originally Posted by El Pinguino

Is that right.... golly... I thought there was quite a bit of difference between -frinstance - an Island Packet, an Ovni, and something like...say... 'Rio 100'

I guess I need to go to Specsavers......

Island Packet have not a contemporary design, OVNI is an integral centerboarder. I am talking about boats with a deep keel and in what regards that the top racer Rio 100 (ex Konica), a Luxurious ketch maxi cruiser like Hetairos and a modest Hanse 415 have something in common:

Rio 100 - Yates Cup on Vimeo

https://www.youtube.com/watch?v=xmAkXwWkzAQ

https://www.youtube.com/watch?v=kNiLzUdAKcM