Shoal draft keel versus regular fin keel - SailNet Community

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  #1  
Old 08-06-2007
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Shoal draft keel versus regular fin keel

Is there a distinct tradeoff in performance between the two if they are on the same model boat?

I assume that the weight is the same except with the shoal draft version it is spread out along the hull instead of below the boats center of gravity.

There must be some difference in the "moment of inertia" between the two but is it enough to make a big difference?

I certainly do not need a shoal draft boat but there is a very clean looking one for sale that I'm looking at.

Thanks for any knowledgeable input.
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Old 08-06-2007
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Often shoal draft boats will have a slightly heavier keel to make up for the shorter lever arm. Generally, the deeper draft fin keel will also have slightly better to windward performance.
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Old 08-06-2007
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Check PHRF ratings to compare

I looked at a couple of boat's rating with deep keels and shoal keels and the difference seemed to be 6 to 9 sec/mi. Not a huge difference really.

I would prefer the deep draft version except for docking. I am looking for a boat in the 40 - 43 foot range for Lake Ontario (initially) and anything beyond 6' is a problem. Hence a shoal draft version would be the choice here.
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Thanks....... I'm enjoying looking at boats!
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Old 08-06-2007
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GB,

Regardless of what the numbers say, my experience is that fins ALWAYS perform better. Period. That being said, I am a fan of wing and sholad draft boats because of my cruising grounds. A fin on the same boat would keep me in the dock. Wings are also tougher to get out of the mud/shoal, but the argument could (COULD) be made they are less likely to get stuck in the first place.

In the end, it will all come down to the cruising grounds. Buy a boat where draft will be a minimum issue, or no matter how good your fin sails when moving, it will be wortless at the dock.

Did that make sense?? Others may bave other opinions.

- CD
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Old 08-07-2007
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CD -

Yeah, makes sense.

Thanks
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Old 08-07-2007
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Hello,

I think it's a little more complicated than just your cruising grounds. If you are buying a used boat, and you find a great one, but it has a shoal draft, do you skip it or buy it even if you don't NEED shoal draft? If you are a racer you skip it. If not, then what?

Do you ever anchor out, or anchor and swim off the boat? The shoal draft will allow you to get closer to shore.

If you really value performance, the shoal draft won't point as high. Is that going to bother you?

For me personally, my last boat had a deep draft (5' 2"). My current boat has shoal draft (4' 6" or so). My last boat would point higher. My current boat allows me to anchor 20' off the beach.

I wasn't looking for a shoal draft boat. In fact, the listing on my boat stated it had the fin keel (5' 6" draft). When the boat was hauled for the survey I told the surveyor that the keel looked like the shoal draft version (wider and shorter). He took his tape measure and measured it at 4' something. The owner said something was wrong, she KNEW it was the deep keel. The surveyor gave her the tape measure and said "measure it yourself." It IS the shoal draft.

I still don't know which one I like better, but I have the shoal draft.

Barry
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Old 08-14-2007
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change the keel?

As a follow up to BarryL's comment about it not necessarily being an option for used...

Given that many boats offer shoal and deep draft versions, would it be possible to change the shoal version to a deep draft version? Would that prohibitively expensive? I understand the rudder may need to be changed out too.

This is assuming it's not poured in place, and is rather attached with keel bolts, and that the ballast is the same type of material between fin and shoal draft. (in order to stay within the original manufacturers design parameters).

It seems totally nuts, but this is sailnet, so maybe someone has tried it?
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You should be able to point a bit higher as the deep keel acts like a lifting foil or so the mythology goes.

I would think that the shoal draft might be a bit more tender and being a bit longer track a bit better and turn a bit slower on tacks. But the differences in performance are probably so small that the advantages of the shoal draft outweigh all the advantages of the deep draft.

And you need a shorter ladder when you are at the boat yard!

jef
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Maybe in NY.. here in the northwest there are really no advantages to having a shoal draft. Being higher up in the yard means a taller ladder, but it means you get a nicer view too!

From what I understand the differences in performance are more than minor though I'm sure it varies wildly from boat to boat.
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