# Fin vs bulb vs wing keels



## Pegu club (Jun 10, 2012)

Here I am again, I'm asking about sailing characteristics of the different keel designs. The Bristol 20 that the admiral and me have been sailing on Narragansett bay since spring is a full keel boat, it would appear that most of what I have looked at is a fin or wing keel, less so the bulb keel.

So there it is, you folk have forgotten more about sailing than I have learned, so I'm asking your opinions on these keel designs. What do you guys and gals think about this as applied to sailing characteristics. I understand that fin keels point better and wing keels with a more shallow draft are good for getting in to shallows better. How do they compare one against the other on 32 to 36 foot Catalina's or Hunters while under sail.

Thank you for your knowledge and insight on this question.


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## Faster (Sep 13, 2005)

OK.. presuming you've read all 54 pages of this?

http://www.sailnet.com/forums/cruising-liveaboard-forum/83221-full-fin-keel.html

and now to the various 'fin/short' keel discussion. You may have started another unwinnable argument.

IMO from a pure sailing (esp upwind) perspective, draft "rules". If you can get around with it the maximum draft your boat can be engineered for would be 'best'.. but what's best and what's practical won't likely align so nicely.

Plenty of sailing areas are so shallow that a good deep draft boat would spend more time stuck than sailing. Hence the current popularity of the various shoal draft designs. To a degree I think the current crop of wing keels is as much marketing as design refinement, but moving the ballast into wings does lower the CG and improve righting moment. The various keel/centerboard configurations can offer the 'best of both worlds' for some.

Concentrating the ballast in a bulb hanging off the tip of a short chord low drag fin is most efficient of all, but it can be a difficult thing to properly engineer, and they require a lot of skill to maximize the performance benefit. If such a boat doesn't keep the flow 'attached' there will be ridiculous amounts of leeway because such a keel has little lateral plane to resist sliding sidewise in the absence of hydrodynamic lift.

Most cruiser/racer type boats today will either have a standard deep fin (many new designs do have bulbous keels that get the ballast down low) or some version of a wing/shoal style keel. I think the difference between the two will only be seriously noticed if two equally well sailed similar boats line up, one with fin and one with wing. For the average cruiser/casual racer I think it may be a non issue, and the shoal draft may work to advantage overall.

For ourselves our cruising grounds don't really have any draft restrictions so a deep fin would be my preference. Ten feet of draft would be extreme, of course, but a 6 feet we rarely need to worry about where to go.

Another issue is that not all models even offer both versions.. some manufacturers seem to have concentrated on the shoal draft 'version' exclusively.


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## peterchech (Sep 2, 2011)

I have the shoal keel version of a hunter 25. It's got a very high ballast/displacement ratio of 50% (2200 lbs lead to 4400 lbs overall displacement. Most boats have around 40%). This is, I believe, to make up for having the weight up higher than a standard fin keeled boat (draft is 3', I think the fin keel version would have 5' draft). 

I haven't sailed on the standard fin keeled version of my boat, but I have sailed on several similarly sized boats with fin keels and I must say they point significantly higher than my shoal draft boat. I can rarely tack through 90 degrees, 100-115 is usually what I can do while maintaining good speed (always speed first, then pointing). I do a little better with the working jib but not much. The shallow draft has not been much of an advantage for me. I have anchored in shallow water a few times, and I rarely worry about draft, but from sailing my fathers boat with a 6' draft I can say that there is absolutely nowhere I can go with my boat that we can't go with his, at leat in this area. And that extra pointing, and more importantly that extra vmg that the deep keel gives you with its proper foil profile, really make a difference ESP when fighting a current upwind.


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## SchockT (May 21, 2012)

Faster sums it up nicely. Essentially if you sail in an area where there are a lot of shallow waters, then you will benefit from a shoal draft, but you will definitely get better performance out of a deep draft fin. So if depth is not an issue, go deep!


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## Pegu club (Jun 10, 2012)

Thank you for the info and advice everyone.


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## Stumble (Feb 2, 2012)

The one thing I would point out is that a bulb keel is really just a modified fin. 

But instead of being restricted to the chord required to get that much mass, they just sling it at the bottom ( I am simplifying, it's tricky to do right). But what this allows is the ideal fin shape for the given hull, while allowing less mass to give the same righting moment. 

Basically bulbs are much faster than either a fin or a full at any given draft. The more draft you can allow for though the more efficient the mass can work, and therefore the less you need. 

The formula is:
Distance from pivot around which the hull heels that the mass is located -D
Weight of the mass - M

Righting moment =DM. 

Note that this is just a specialized application of the general torque formula. So the two ways to get more righting moment are 1) increase weight, 2) increase distance (draft). Because in all instances righting moment is directly related to the amount of maximum available horsepower


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## SHNOOL (Jun 7, 2007)

Probably the most concise answers I've seen this group give out. Could not agree more with any of them. Fin keel is good, light fin with a bulb even better (cause it puts the weight where it can be most effective), shoal keel/wing keels are more about making due (therefore increasing weight, to give the same righting amount) for easier access to shallow waters (and/or easier trailerablity).


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## Stumble (Feb 2, 2012)

Actually wing keels are an attempt to reduce tip vortex creation by effectively having a longer keel. If they worked as intended you could have the lift gains of a deeper keel on a shoal draft. Sadly what works on planes doesn't work very well on boats. In practice wing keels can't keep the water attached due to subtle water currents, yaw and roll, and attitude changes as a boat goes through the waves.

The only advantage a wing keel has over a fin, is the lower mass, but in practice a streamlined bulb will always be better.


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## bobperry (Apr 29, 2011)

Not sure I agree with your police work there Lou/Stumble.


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## jimrafford (Jan 7, 2011)

Stumble said:


> Actually wing keels are an attempt to reduce tip vortex creation by effectively having a longer keel. If they worked as intended you could have the lift gains of a deeper keel on a shoal draft. Sadly what works on planes doesn't work very well on boats. In practice wing keels can't keep the water attached due to subtle water currents, yaw and roll, and attitude changes as a boat goes through the waves.
> 
> The only advantage a wing keel has over a fin, is the lower mass, but in practice a streamlined bulb will always be better.


Tell that to the Aussies.
We used to own a trophy til they showed up w/ a wing


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## bobperry (Apr 29, 2011)

We may be on thin ice here lumping all wing keels into one category. There is no question that when you are up gainst a hard draft restrcition a wing can work quite well.
The Aussie winged keel worked well in conjunction with the upside down profile of that keel and the extra long tip chord with it's vortex problems.

When I designed the Islander 34 we did a 5.5' draft wing keel and a 7' draft straight fin. Islander built one of each as hulls 1 and 2. They were launched the same day with sails from the same sailmaker. I flew down with one of my helpers, a very good sailor, and for two days we raced these two boats against each other. The difference in speed was minimal if present at all. And, I was a skeptic to begin with. But after trading boats and sailing them upwind and down. I came away a believer. The wing keel boat was a bit slower off the wind, not much. Up wind the two boats were pretty much identical in VMG. This is not theory. This is first hand sailing experience with two identical boats.

But wings to be effective have to have aspect ratio just like fins. Short, thick stubby wings, like we have seen on many production models, are not efficient. They may do a nice job at lowering the VCG but they can be a lot of drag and be wonderful Bruce type anchors if you get stuck in the mud.

All I'm saying is to treat wings on keels on an individual basis.


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## jimrafford (Jan 7, 2011)

Every foil section is different. Some of the production wings just look wrong. 
CS called the wing on my boat a hydrofoil. It is larger than any other wing I have ever seen. W/o measuring it's about 6' wide and 5' deep.
I have yet to meet another cruising boat that can out point w/ me and there has yet to be another similar boat I can't catch off the wind.
But that's my foil section. I think Tony Castro did some research.
Jim


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## CBinRI (May 17, 2004)

As to shoal keels, fin is best for performance, and the deeper the better. You will point higher and track better. And if you race, whatever handicap you are given for another form of draft will not be enough. Don't have any experience with bulbs.


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## RobGallagher (Aug 22, 2001)

After I decided what boat I way buying, I chose a wing keel over the deeper fin keel model because of draft restrictions.

Does that make me a draft dodger?


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## Faster (Sep 13, 2005)

RobGallagher said:


> Does that make me a draft dodger?


... or it just means you're a bit shallow.....


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## BryceGTX (Sep 7, 2011)

I view the differences between these keel designs from a number of angles:

First is the performance issue to to change in resistance. Rather than calculate actual resistance, I can look at wetted surface. It is interesting to compare the wetted surface between the wing keel version of my boat (Catalina 400) to the fin keel version.

When I crunch the numbers, I find that the wetted surface of the wing keel version is less than 4% higher than the fin keel. Granted, the resistance is probably less; however this shows how little effect the wing keel has on the overall resistance.

A rough calculation of the difference between a bulb at the same draft, with the same righting moment, I would find the difference between the bulb and the wing to be a similar 4%.

One has to wonder if the 4% difference is significant. It might be interesting to look at some of the advantages of the wing keel versus the others. A quick look at Wikipedia gives a bit of insite:

http://en.wikipedia.org/wiki/Wing_keel


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## BryceGTX (Sep 7, 2011)

Now comes the interesting possibilities of a wing keel.

One aspect I find intriguing is the possibility that a wing keel is capable of increasing its leway resistance as the boat heels because its effective vertical surface area increases as it heels (as long as the wing is large enough). Neither the bulb nor the fin keel provide this benefit. Rather both the fin and bulb keels reduce their vertical surface as the boat heels. This increase in leway resistance can be quite dramatic for a wing keel designed to optimize this effect. The wing must be a resonable size. Also, as stated, the dynamic effects of water at the root of the keel.

The next aspect I find intriguing is that the wing keel is the only keel of the three that actually creates damping in the vertical direction. Furthermore, it can damp in the rising motion of the boat! This damping could be advantageous in reducing the dynamic motions of sailboats. Obviously, the hull creates damping as the hull falls, but the wing (unlike the hull) additionally provides damping as the hull rises.

The third aspect of the keels is damping to rolling. The wing keel also provides damping benefit to rolling due to its overall surface area and flow resistance at the root. The bulb keel provides no damping benefit from the bulb design, only due to the vertical area. The fin keel provides more damping benefit to rolling than the wing keel only if it is deeper.

I have a wing keel as I want shallow water capability. In the numerous times I have grounded, I have not ever needed to be pulled off, nor have I required a kedge. One interesting advantage, is that my wing keel increases draft as the boat heels (to a point). The result is that I suspect I am less likely to sail onto a shallow without my keel hitting. And when it hits, the large frontal area does not allow the wing to travel much into the shallow. These two effects, I suspect may make it less likely to get heavily grounded.

However, I appeciate the viewpoint of the wing acting as a disadvantage on a heavy grounding.


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## bobperry (Apr 29, 2011)

GTX:
Amazing, How scientific.
I do it the Neantherthal way:
I build two identical boats.
I give one a deep draft fin
I give one a shoal draft wing keel.
It's kind of hands on.
I give them identical suits of sails.
I give each boat a very competant crew.
I sail the two boats against each other for a couple of days.
I report on my findings.

Somewhere along the way I forgot to "crunch the numbers".
I was too busy sailing the boats.

But I am lucky. I have the benefit of testing these things in the real word.


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## bobperry (Apr 29, 2011)

My last post was made after a long and hard and succesful day of racing in lots of wind. I was tired and re-reading my post it now seems a bit snotty. My excuse is, I was feeling snotty. I'll work on being nicer next time.


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## RandyonR3 (Oct 2, 2005)

bobperry said:


> My excuse is, I was feeling snotty.


 Its a result of putting up with Idots all your life Bob.. In my 60s, I've delt with 
many of the same.. and just the other day, I had someone at the Yacht Club Bar compairing his Full keel, Hans from the 70s to my First 42, in "race" criteria..
After about 10 minutes of his ramble, Instead of a rebutle, I just told him he was full of crap and I got up and left.. 
At one time, it was the chalange of the argument, Now days, dont have time for it..

sorry for the drift, now back to the origional channel..............


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## bobperry (Apr 29, 2011)

R3:
Sometimes you are just not going to be able to apply reason to the performance argument. Yesterday we had a long race with every condition and heading imaginable. We saw almost 30 knots TWS and TWS down to 2 knots. It was the Race Your House race for liveaboards and we had a fleet of 50 boats that covered all but the very top end of the performance and type spectrum. Racing a pilot house baba 35 we managed a second in class being beat by 22 seconds on corrected time and 2 minutes on elapsed time by a well sailed ( damn it) Cat 30 raced by a very good sailor and old pal of mine. The HC''s, Ingrids and Cape George Cutters were well behind us. I think we amazed a lot of sailors, including myself. That puts a lot of the talk to rest.

Sometimes I like to point out to an owner of an "antique" type design (and I have design a few of them) that he should check the PHRF rating for his boat. PHRF ratings are usually very good indicators of a boat's potential performance. Kind of like this, "If your boat is that fast why does it rate 255?"

At the end of our race I could not even see either of the two HC's in the race. Mind you, we pushed the Baba 35 very hard and we had very good sails (thank you Carol Hassey) plus an Aussie pal of mine called tactics and sail trim. We raced for fun and our attitude is winning is the way to have the most fun. Several boats dropped out of the race including a Cape George cutter. I'm not sure our performance did much to promote the "full keel boats are slow upwind" argument. We seemed to hold our own and maintain very good VMG's upwind. But I am not so blind as to think a full keel boat has the same upwind potential or even downwind, in most conditions, as a well sailed fin keel boat.

Maybe, "You're full of crap" was the only way to end that argument.


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## jrd22 (Nov 14, 2000)

bobperry said:


> R3:
> Racing a *pilot house* baba 35 we managed a second in class being beat by 22 seconds on corrected time and 2 minutes on elapsed time by a well sailed ( damn it) Cat 30 raced by a very good sailor and old pal of mine.


Like a ray of sunshine, it is

The Baba PHs were my dream boat for years and years Bob.


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## BryceGTX (Sep 7, 2011)

bobperry said:


> My last post was made after a long and hard and succesful day of racing in lots of wind. I was tired and re-reading my post it now seems a bit snotty. My excuse is, I was feeling snotty. I'll work on being nicer next time.


Hi Bob.. Not sure about anyone else, but I did not take your post as a bad post.

I found your post about the two boats quite useful as I have often wondered the real performance difference between the two keels. It seemed a very well controlled test between two boats. Would be nice if all comparisons between boats was so well done.
Bryce


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## bobperry (Apr 29, 2011)

GTX:
Thanks and you are correct. But in all fairness that was a different time and money was more available for experiments like that. It was fun. We had fun. We all enjoyed the process and we all understood the results. We flew back to Seattle satisfied and feeling like we had learned something.

It's a different world today. 

Ok, I deleted the rest of this post because it got political and if I thought you had any interest at all in my political opinions I'd think you were idiots. I know better.


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## blt2ski (May 5, 2005)

Bob,

Did not know you were out there yesterday. Did you like that squall about 3pm or there abouts! about 1/3 of the fall regatta folks dropped out in the third race! Was real happy about our finish, only had three on board, could have used 2 others, got a 1st and 2nd, last a 5th........wore out the crew on that one, so went easy when the squall came thru, took them awhile to want to put the jib up, but once we did, could not catch the others in front......oh well, was afraid we would have a 3rd overall from that fiasco!

Sloop was packed afterwards last night too! Were you at the party?

Marty


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## blt2ski (May 5, 2005)

Waterspouts on north Puget Sound - Local News - Seattle, WA | NBC News

Good thing we were not in Everett! or there abouts eh! It was more PHUN weather wise near BP's house!


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## SloopJonB (Jun 6, 2011)

blt2ski said:


> Waterspouts on north Puget Sound - Local News - Seattle, WA | NBC News
> 
> Good thing we were not in Everett! or there abouts eh! It was more PHUN weather wise near BP's house!


I saw one of those once on English Bay. Has anyone here ever been hit by one?


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## blt2ski (May 5, 2005)

Not sure which would be worst, a water spout, or an actual cyclone/dust devil type thing. The water possibly, since water would should have more solid mass to it!


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## chef2sail (Nov 27, 2007)

We were chased back to our home port by a spout in earlier September by a waterspout off off Baltimores North Point on the nChesapeake Bay and the Patapsco River.

We had made our way back to the Bay that day from Cape May as it was the last day of our NE/ LI Sound trip and the wether had been threatening all day with TStorms. As we approached the Patapsco the clouds lowered, got greenish purple and we saw a funnel drop sideways out of the hook like looking cloud. It hit the water about a half a mile away, and we could hear the low rumble of it. We had our sails down and engine on ull blast as we saw it moving parallel with us for 5 minutes. We finally hit the river and were able to veer away as it continued SW. 

That was close enough for me. 

Dave


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## bobperry (Apr 29, 2011)

Marty:
My wife was at the shack all day Saturday and she was a bit concerned about the weather we would have on the race. It was pretty damn nice actually. Much worse at the shack.

We had a really good race and got 2nd in class in a tubby, pilot house double ender that had a lot of bigger, more modern boats looking slow. I drove the boat harder than it had ever been driven according to the owner but I had a ball and the boat responded very well. The Carol Hassey sails were new and a good part of the key to out performance. All in all a satisfying day on the water.


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## skygazer (Sep 3, 2011)

BryceGTX said:


> .... The next aspect I find intriguing is that the wing keel is the only keel of the three that actually creates damping in the vertical direction. ...


I found this to be an interesting idea (vertical dampening). I'd never been on a wing keeled boat until I rebuilt a Hunter 23 this spring/mid summer. When I finally tried it out on a local lake to see if it would sail and if everything worked, I was surprised when I first hit some motorboat wake. I expected the normal up and down hobby horsing I've always had, throwing the wind out of my sails, but instead the boat seemed to flatten the wave and go through almost on the level. I was thrilled each time I went through wakes - which was constantly, every motor boat seems required to alter course to pass just in front of a sailboat. (Partly I think it's interest, I heard one kid yell over the motor, "Dad, could we get a sailboat?".)

When I got it on the ocean I noticed the same effect, although of course it rode up and down the swells, but it still seemed to flatten smaller waves and continue on without losing the wind in the sails.

I attributed it to the modern almost straight, unsexy, uncurved, no sheer hull shape, but it's entirely possible the smallish wings did have some effect as well. The idea never crossed my mind, and I appreciate you pointing it out.

Must be my early childhood experiences, but I still seem fixated on deep, full keels on curvy boats as "stomach grabbing" beauty. I admit to lusting after boats shaped overall like a Contessa. I only bought the Hunter because it was close by, low priced, and had a trailer with broken brakes that could be wired and fixed. (OK, the fin keel/ full keel pages also made me curious.)

Sailing the Hunter was a very pleasant surprise. My first day on the ocean was also my first day with a GPS. Just a pocket model, had to change screens to see my speed (in MPH, not knots). With a theoretical hull speed of something like 5.9 knots, I was surprised to change screens and see I was going 6.2 MPH against a very strong tide between islands, tacking into the moderately brisk wind. Days later I found that the GPS had saved a trail and showed my top speed at 8.3 MPH. Further, the interior has no liner, just carpet glued to the hull. Almost no bilge. Sounds bad but actually makes it deep and spacious and comfortable for such a small boat. We stayed on it for a week, sailing on and off our anchor except for one very tight boat filled anchorage. I now actually like it a lot (coastal sailing). Just got it out of the water last weekend. Glad, because there is a possible huge storm coming at the end of Oct/start of Nov.


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## D. Skipper (May 15, 2021)

Pegu club said:


> Here I am again, I'm asking about sailing characteristics of the different keel designs. The Bristol 20 that the admiral and me have been sailing on Narragansett bay since spring is a full keel boat, it would appear that most of what I have looked at is a fin or wing keel, less so the bulb keel.
> 
> So there it is, you folk have forgotten more about sailing than I have learned, so I'm asking your opinions on these keel designs. What do you guys and gals think about this as applied to sailing characteristics. I understand that fin keels point better and wing keels with a more shallow draft are good for getting in to shallows better. How do they compare one against the other on 32 to 36 foot Catalina's or Hunters while under sail.
> 
> Thank you for your knowledge and insight on this question.


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## D. Skipper (May 15, 2021)

bobperry said:


> Marty:
> My wife was at the shack all day Saturday and she was a bit concerned about the weather we would have on the race. It was pretty damn nice actually. Much worse at the shack.
> 
> We had a really good race and got 2nd in class in a tubby, pilot house double ender that had a lot of bigger, more modern boats looking slow. I drove the boat harder than it had ever been driven according to the owner but I had a ball and the boat responded very well. The Carol Hassey sails were new and a good part of the key to out performance. All in all a satisfying day on the water.


There is an advantage and disadvantage in every keel design. We all know and accept that. As an example in the Abacos sailing from West End to Great Sail Cay across the Great Bahama Bank can be very difficult with a keel of 6ft. In my experience in both not step vessels (power boats) is almost impossible at 5.5 feet due to the irregular bottom contours. It is a little less difficult in a heeling sailboat.

I delivering boats in deep water and trade wind sailing deeper keels are a big advantage. Pointing high when actually related to leeway is important. If one loses a .5 nautical miles per hour over a 24 hour period is 12 nautical miles. In pure terms that equals 336 nautical miles in some direction. There are so many design factors that come into play when traveling long distances. In good wind conditions down wind bulb and shoal keels do well. But, as wind force effectively doubles or quads then lighter displacement vessels become unmanageable. Because of potential broaching at higher speeds downwind becomes a real issue. We all know or should know going to wind in lighter boats can be a real issue when making runs of 500 to 1,000 miles.

All boats have their advantages and disadvantages based on their planned use. A simple mathematical formula is required. If you race around tetrahedra buoys in a lake you can have an advantage in lighter displacement vessels. This is also true in ocean racing if you have too, if you have enough capital and guts to race light displacement vessels made of carbon fiber.

Without formulas for the last thirty years, I can tell from the design of the boat I am skippering what the macro challenges my crew and I will encounter by virtue of where we are going and the time of year. In the right hands all keels and displacement usually get there.

C.John


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## D. Skipper (May 15, 2021)

D. Skipper said:


> There is an advantage and disadvantage in every keel design. We all know and accept that. As an example in the Abacos sailing from West End to Great Sail Cay across the Great Bahama Bank can be very difficult with a keel of 6ft. In my experience in both not step vessels (power boats) is almost impossible at 5.5 feet due to the irregular bottom contours. It is a little less difficult in a heeling sailboat.
> 
> I delivering boats in deep water and trade wind sailing deeper keels are a big advantage. Pointing high when actually related to leeway is important. If one loses a .5 nautical miles per hour over a 24 hour period is 12 nautical miles. In pure terms that equals 336 nautical miles in some direction. There are so many design factors that come into play when traveling long distances. In good wind conditions down wind bulb and shoal keels do well. But, as wind force effectively doubles or quads then lighter displacement vessels become unmanageable. Because of potential broaching at higher speeds downwind becomes a real issue. We all know or should know going to wind in lighter boats can be a real issue when making runs of 500 to 1,000 miles.
> 
> ...


ps://m.youtube.com/watch?v=dFeTd5falps&t=3s


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## jtsailjt (Aug 1, 2013)

The OP asked about the sailing characteristics snd I think that’s been very well answered here. But I’d like to add for cruising I’d stay away from wings because of the potential of getting really stuck in a grounding situation and here in Maine they can be a nightmare if you get a lobstermans pot warp wrapped around it.
Often we discuss various configurations of hull appendages and sails in pretty extreme terms, as if a fin/spade is the only answer if you’re interested in performance and you’re guaranteed to finish last if you have in mast furling, etc., etc. but as Bob pointed out in this thread, even a full keeled boat with well trimmed sails, if skillfully helmed and crewed can do very well, and that’s especially true for cruising. I’m not suggesting that there aren’t some pretty significant differences in performance between different boat types but there are well designed and executed full keel boats and there are some horrible tubs with fin keels. So, in addition to the OP’s question about keels, when choosing his next boat I’d suggest that he pay pretty close attention to its overall design and how it actually sails. The type keel that it has won’t even begin to tell the whole story.


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