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Old 09-03-2007, 13:16   #1
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deep vs shoal production

I read a few threads on general keel design, full vs fin vs wing.

On production boats they seem to often offer a deep or shoal option. Am I correct in thinking the difference in deep vs shoal on the same boat is as follows?
  1. deep keels point higher
  2. deep keels have better light wind performance
  3. deep keels offer slightly better righting motion
  4. shoals can go in shallower water
Are there any other differences?

I'm not trying to start a debate on keel types. There are threads here that have answered a lot. I just wonder which option most people choose and why.

~Brett
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Old 09-03-2007, 13:44   #2
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Quote:
Originally Posted by bmanley
...
2. deep keels have better light wind performance...
For this to be true it should say upwind performance. Downwind the two should be same or the shallow draft maybe better.

Paul
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Old 09-03-2007, 13:44   #3
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I just wonder which option most people choose and why.
Shoal draft boats are most popular where the water is shallow. Along the Pacific coast they have almost no shallow water. Here on the Chesapeake the average depth is only 6 1/2 ft. The only good reason to have a shoal draft boat is so you don't go aground.

As far as any other properties go things get very unclear without considering other factors in the design. Draft alone is just one factor but in the case of local conditions I sure wouldn't own a 9 ft draft boat where I live no matter what it could do. I would only have a few hours twice a day to get in and out of the slip.

Your first three factors might be considered true but there are enough examples of exceptions and draft alone is not even most of the issue at best. Your 4th reason is why they make them in the first place and the only serious point to be made about the benefits of a shoal draft vessel.
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Old 09-03-2007, 20:08   #4
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Hi Brett,
You didn't mention size of boat so I assume you are talking about displacement boats?
You didn't mention swing keel vs daggerboard or combination shoal and swing keel.
Lots of options.
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Old 09-03-2007, 20:23   #5
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I was really asking concerning the big production boats. Most of those are just "deep" or "shoal". I know there are tons of keel variations. And I know that the keel alone is just part of a hull's hydrodynamic character. I assume though that a hunter 380 deep and a hunter 380 shoal have mostly the same hull lines (minus the keel). Am I wrong about that?

Thanks

~Brett
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Old 09-03-2007, 21:04   #6
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I assume identical. Keel options are just that - options. The trade off comes in how that shoal keel performs. You are moving the weight up and adding more to compensate for the loss of draft. Most shoal keels are a marketing option to meet specific shallow draft needs, but may not perform as well as the deep fin. Bristol was designed as either fin keel or keel centerboard so the boat would sail well either way but the centerboard option is a little tender. On a specific boat, you can look up the PHRF and see if the keel options affect performance.
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Old 09-03-2007, 21:44   #7
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Unless you are serious about racing your boat, you're not going to notice a real difference between the two types of keel. The fin will provide you with better upwind performance, but you pay a little bit of a price downwind for that. Absolute righting moment (exclusive of any wind or wave factors) will be almost exactly the same, as most of the shoal keels are within 12 inches of the fins. The shoal keel may heel a couple of degrees more than the fin.

Buy based on the depth of the water you are planning to sail in.
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Old 01-12-2007, 11:48   #8
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I've owned both shoal and fin keel boats of similar design and size and must say that from my experience the extra weight of a shoal draft provides for a stiffer boat hands down. With regards to sailing upwind, sail trim and captains ability will outpoint every time regardless of keel type. Where I sail there is a very well equiped shoal draft boat that will point as high if not higher than many pure racers.
I'm not quite sure what would enable a shoal draft boat to go better off wind? Perhaps a shoal wing type woud provide more lift?
George
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Old 01-12-2007, 11:56   #9
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Your going to be quicker uphill and point higher with a deeper keel. If you can accpet the draft, deeper is almost always a better way to go.
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Old 01-12-2007, 11:58   #10
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My last boat had a fin, and now I have a modified full. I'd like to say I can tell the differences, but the displacement, sail plan, rudder, size, and spar all changed too.

I like a full because now when I ground the boat I feel like "the boat grounded", which is a lot more comfortable than "the tiny little fin is holding the boat up on the sand bar now".

On the topic of smacking into stuff and keels, I like knowing that my rudder is aft (and protected by) my keel. When I see rudders dangling freely it scares the crap out of me. Maybe someone here knows the answer, but a loose ("spade"?) rudder seems like it would rip right off if you smacked it into something.
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Old 01-12-2007, 14:27   #11
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We have a wing keel on our boat draws 4' and it's handy for gunkholing. We can get in places no one else goes. Our boat also has a better capsize ratio than the same boat with the fin keel because they put 300 lbs more ballast in the keel and the wing is very big thus a larger percentage of the weight is carried lower than in the fin keel. The fin keel gets smaller as it goes deeper. Owners of the fin keel version like to think they go upwind better than the wing keels, but last summer we proved one owner wrong upwind and then really smoked them downwind. I'm not sure you can generalize about keels at all anymore there's too many other factors at work. IMHO.
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Old 01-12-2007, 15:05   #12
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While you are more likely to hit bottom with a deep fin keel than with a wing keel, you are also more likely to get off, as you can turn the boat with the propellor pushing against the rudder and plough back through to deeper water. Long keels and wing keels are more likely to require some outside means of getting off, like setting kedge anchors or (dare I say it) TowboatUS$$$.

I also saw one boat with the wings being cut off in a yard--the owner reported that the boat was really scary with the wings in big seas, like they were trying to drag it under. Anyone else have that experience??
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Old 01-12-2007, 15:21   #13
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I also saw one boat with the wings being cut off in a yard--the owner reported that the boat was really scary with the wings in big seas, like they were trying to drag it under. Anyone else have that experience??
Nope, and I've sailed on 3 boats besides ours with wing keels in pretty decent seas. But if you stick one in mud you are likely going to be needing a tow lots of suction effect to deal with. And I wouldn't try pulling from the masthead with a wide wing like ours, the load on the keel would be mighty huge I think.
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Old 01-12-2007, 15:26   #14
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As stated, it depends entirely on the use and location of the vessel.

For long ocean passages, the deeper the keel, the better.

Kanani draws 7' and I have taken her all over the Bahamas, including over the flats which are 6' at low water. She's been up & down the ICW a few times without incident. She's been up & down shallow rivers in Australia & Africa and over coral reefs all over the world without incident.

Never make a decission on a hull design for it's ability to get off after a grounding . Just don't go there and it shouldn't be a concideration. Grounding a vessel is all about lack of seamanship and nothing to do with hull design.
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Old 01-12-2007, 18:12   #15
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I got to agree with that last post, I didnt buy my boat planning on it setting on a sand bar.. With all the equeptment avalable now days for underwater sonar or a depth finder,its pretty hard NOT to see where you're going, and why would you take a chance on even going where you might run aground.
I draw 8 foot and when I get below 20, I turn the probe on and slow the speed down to a crawl. Never have run aground, and I dont plan to....
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