Deep Keel vs Shoal Keel

markwbird · Dec 4, 2014

Yes. There are no shoal keel racing boats. The keel is a huge part of what makes the boat perform and what makes it point. A shoal keel boat is all about cruising convenience.

Tom J · Dec 4, 2014

keithdeller said:
Thank you markwbird,

Some sellers are stating that the shoal winged keel is as effective as deep keel.
They say that the wing increases the counter force to be equivalent to a deep keel..?..
I am doubtful.

Something to consider is that as the boat heels more, the wing on the shoal draft will resist side-slip more, whereas the long fin keel will resist side-slip less. As we have seen with the new swinging keels, as the keel approaches a horizontal position, it becomes necessary to deploy a dagger board.
It might be useful to know what the America's Cup designers were thinking when they introduced the wing keel.

Gunni · Dec 4, 2014

The purpose of the winged keel was to keep the underwater foil engaged in the flow and the boat on it's feet (upright) so that the sails can lift the boat to windward. The winged keel is a foil aspect multiplier. Everything is a compromise, including the value of your desire to boat into shoal water.

Gunni · Dec 4, 2014

keithdeller said:
What about shoal keels that have a bulb at the keel base.
Is it used only for additional leverage?

The bulb is designed to avoid the wing keel propensity to act like a well-set anchor.

...and it puts the ballast where you most want it - low.

JRacer · Dec 4, 2014

I have a 310 WITH THE SHORT KEEL - that's my only complaint with the boat. Doesn't point worth a darn. I got the short keel because we have depth issues here - droughts drop the lake levels. My preference was to have the deep keel. If water depth isn't an issue and you want to be able to point well get the deep keeled boat.

Gunni · Dec 4, 2014

keithdeller said:
..So, there should not be a significant difference in performance when sailing upwind, between a bulb shoal keel vs a deeper fin keel...

No, a deeper underwater fin foil provides better lift to windward, and hence better upwind sailing. ...if you have the depth.

Chief RA · Dec 4, 2014

The only fallacy in all this discussion is how good a sailor is skippering that wing keel! It's kinda like the guy who thought you didn't really need a boom vang to sail well.
Chief

Jackdaw · Dec 4, 2014

Ah, topics near and dear to my heart.

First, a deep keel will give better performace than a shoal or wing keel, full stop.

Better windward because it generates more lift. And better on all points of sail because the deep keel boat will be lighter than a more shoal boat, always. Deep, high aspect keels are the lift champs. Like low speed airplane wings. Long and narrow. Think U2 spy plane. Ever see one of those take off?

BUT, given the choice, I might take a tall rig 310 over a deep keel 310. Bepends on local weather. The big rig will always give more horsepower. The keel helps mostly going pure upwind. And the standard 310 is slightly underpowered. We race against a regular 310 and in light airs we simply crush it, by way more that the 50 seconds difference in handicap. Minutes difference.

Deep vs shoal matters most on direct boat on boat (One Design) racing. No way a shoal 36.7 sails with us. We spit them out the back. But in a handicap race, a shoal boat sailing it's own race will do OK.

Now saying all that, I see there is a deep keel 310 with a tall rig and a TILLER on yachtworld. That's pure sex with sails. I'll send you a case of beer of you buy that one!

JohnShannon · Dec 4, 2014

phrf ratings will give you a clue as to the performance impact of various options like tall rig or shoal keel lower number = faster

Jackdaw · Dec 5, 2014

JohnShannon said:
phrf ratings will give you a clue as to the performance impact of various options like tall rig or shoal keel lower number = faster

Indeed. Three configurations of the First 310 show up in the detailed US Sailing PHRF rates guide. Only one region rates them all, namely Eastern Connecticut.

standard rig, standard keel = PHRF 144
standard rig, shoal keel = PHRF 153 (9 seconds/mile off the pace)
tall rig (assuming std keel) = PHRF 135 (9 seconds/mile faster)

There is no record of a tall rig shoal keel being ever raced in PHRF, you could assume it would be near the baseline boat at 144. Note this is in 8 knots of breeze. In light air I would expect the tall rig (even with a shoal keel) to be faster than the (deep keel) base boat.

You can see how the tall rig torches the shoal boat (all else being equal), on a W/L 2 course with 1 mile legs, it would finish almost 2 minutes ahead.

Chief RA · Dec 5, 2014

Jackdaw: It is interesting you mentioned a tall rig, wing keel as I have one. I have no interest in racing or would not have bought this boat but am aware that it can do 7 knots and that did impress me. Chief

Jackdaw · Dec 5, 2014

Keith, I figure that the 310s shoal bulb is equal or better than a wing on the same draft. I've owned wing keels; they really are another way to get ballast low without the draft. Just like a bulb. They offer nothing in terms of extra lift. That's why nobody makes them any more. But they DO catch stuff! ;^)

Chief, my thinking is that any boat can make 7 knots on a reach, given a reasonable enough breeze. The measure of how 'quick' a boat is is measured by its ability to make progress to windward (VMG) in a wide range of breeze. Some boats are a lot better at that. Your boat rates PHRF 222, not bad for a 25 foot mostly-cruiser.

A month or so ago I was bored and wrote a post on this stuff.

http://forums.sbo.sailboatowners.com/showthread.php?p=1151452

Jackdaw · Dec 5, 2014

keithdeller said:
Thanks Jackdaw,

Looking at the PHRF ratings, the Beneteau 310 has a median rating of 138, whereas the
310 SD is 159, (a difference of +21). The 310 Tall is 132, so one would factor +21 for the 310 Tall w/ SD to be approx 153. Correct?

Apologies for harping on this subject, as I need to make a decision whether to purchase a First 310 with deep fin keel, or a First 310 tall with Shoal bulb keel.

As I will be sailing on the west coast, either keel will work.
My sailing will be mixed, with cruising and racing.
When cruising, I enjoy tweaking for higher performance...

Which one would you choose?

The median ratings you used average all reporting areas. This works for comparisons when boats are well represented, but not so much in this case. I was looking at the detailed report for US Sailing members, where are clubs/areas are reported as line items, and it shows that in only one area do all three 310 varients race. Because of the difference in the ratings between zones, its hard to make a meaningful comparison of say a F310 rating from SF bay to a 310 TR from the Chesapeake.

Complicating all this, there is no mention of a tall rig-shoal draft boat racing.

In light airs, the tall rig will for sure help you. In a breezy area, the regular rig will power-up just fine, and the deep keel will be faster. So now its up to you to figure whats more typical for you, and maybe in what season you will race vs cruise. For me, I would also factor in that you do not know what rating that TR/SD boat will end up with; I cannot see mention of it in the US sailing database. You might get stuck with the F310TR rating for your area, and that would suck. All else being equal, knowing the standard f310 is slightly underpowered as it is, I would go with the TR/SD boat, and see where the chips fall!