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Full or fin keel?

192K views 846 replies 107 participants last post by  mstern 
#1 ·
Can somebody pro/con a full vs. fin keel for a newbie (will learn to sail on said boat) and taking it thru the Caribbean? All I can seem to come up with so far is fin keel is better to the wind, and a full keel will protect your rudder.
 
#465 ·
Doug Peterson?!?!?!?!?!

oh yeah, the guy the designed the peterson trapezoidal keels on many boats from the late 80s into the 90's. This included my mid 80s Jeanneau........

I would still take a current day fin/bulb over my current keel if I had a choice. Not sure if the boat I have would like the keel or not, ie do better per say. I would like a bit more ASSet if you would, for a bit more room in the cockpit.

At the end of the day, ALL boats are compromises! as to how the end user wants to fill certain uses etc of the boat.

marty
 
#467 ·
And some do not, its not about the keel or the weight of the boat, but the shape of the hull and the distribution of the buoyancy and weight. But more significantly, a properly designed, longer boat with the same displacement as yours would feel the waves even less than you do since the impact would be less, but the momentum the same.
 
#469 ·
Certainly while loading has all to do with reserve buoyancy, I believe that the CG has more to do with keel design. A long broad keel offers a more forgiving ride yet becomes more stiff on the reach, regardless of reserve buoyancy. Designers alleviate this by cutting back the keel. Reserve buoyancy may have more significance in boats with finely shaped fin keeps where the shape of the hull changes the shape of their hulls at speed, but displacement is displacement.
 
#470 · (Edited)
Some boats are just well designed and well balanced -

It is a careful balancing act between wetted surface area vs. trim vs. center of effort vs. center of lateral resistance. There is quite of bit of art in balancing the oft conflicting parameters.

For example Steve Schock designed the Harbor 14,20,25, and 30 to have low wetted surface and balanced helm. He spent a lot of time adjusting the keel shapes and location to achieve the neutral helm these boats are known for.

A Harbor 25 sailor on SF Bay single hands most of the 100 days a year he sails. He sails out of Sausilito so he spends a lot of time in and around the slot. No autopilot. He says the boat is so nicely tuned, that he can leave tiller unattended for minutes at a time.

The longest he left the tiller unattended was 20 minutes ! He says the boat just tracks along.

 
#471 ·
Sea Hunter- Could you please explain what you are talking about? It may be a linguistic issue but much of what you have written has little, if anything, to do with the way that these terms are normally used in yacht design or design theory, or with the behavior of a vessel.

For example: "Certainly while loading has all to do with reserve buoyancy" The way that the term "reserve buoyancy" is classicly used, loading has little, if anything t0 do with reserve buoyancy. As I read your sentence, I would suggest that you are mistaking (reserve) "carrying capacity" for "reserve buoyancy". These are two very different and not necesarily related concepts.

Or, "I believe that the CG has more to do with keel design." CG is only affected by weight distribution. While the type of keel and the profile and section of the keel affords the designer more or less ability to move the CG around, the type of keel and the profile and section of the keel does not in and of itself impact the CG of the boat. To provide an example to explain this, you could have an three boats the identical type of keel and with the same profile and section of the keel, but one uses cast lead, the second cast iron, and the third has a timber keel. Obviously each of these materials would move the CG around vertically, and in most cases, longitudinally as well.

Similarly, "A long broad keel offers a more forgiving ride yet becomes more stiff on the reach, regardless of reserve buoyancy." A broad, meaning a transversely wide keel in conventional yacht design useage, while more forgiving in terms of stalling has litte or nothing to do with stiffness (form stability), reaching ability or reserve buoyancy.

None of the rest of "Designers alleviate this by cutting back the keel. Reserve buoyancy may have more significance in boats with finely shaped fin keeps where the shape of the hull changes the shape of their hulls at speed, but displacement is displacement." makes any sense or has any accuracy, except that "displacement is displacement."

Respectfully,
Jeff
 
#474 · (Edited)
Sea Hunter,

I am glad that you clarified what you are thinking. At least as you are describing it, (i.e. "Reserve buoyancy is a hulls ability to carry a load over and above displacement".) that is not in keeping with the way yacht and ship designers use the term, "Reserve buoyancy". What you are describing rarely if ever is considered as a part of yacht design. To some extent you are describing something like the total displacement of the submerged vessel less its normal buoyancy, which is not terribly relevant even in an extreme seaway.

More relevant in understanding the behavior and characteristics of the vessel is carrying capacity which is the amout of weight that a vessel can carry before the load has a significant impact on performance and safety. Also more relevant is the impact of hull shape on reserve stability, the angle of vanishing stability and area under the stability curve.

But none of these are inherently associated with whether the boat has a full or fin keel.

Jeff
 
#481 ·
Sea Hunter,

I am glad that you clarified what you are thinking. At least as you are describing it, (i.e. "Reserve buoyancy is a hulls ability to carry a load over and above displacement".) that is not in keeping with the way yacht and ship designers use the term, "Reserve buoyancy". What you are describing rarely if ever is considered as a part of yacht design.
"Reserve of Buoyancy" is a term that come from time begin of yacht design. Sometimes shortened to reserve buoyancy. There are a number of chapters in this subject and the importance of reserve of buoyancy in yacht design. Here is a quote from page 12 of "Naval Architecture" printed 1877.

".. commonly used to express the volume and corresponding buoyancy of the part of the ship not immersed, but which may be made water tight.."

"The under water, or immersed, part of a ship contributes to the buoyancy; the out-of-water part the reserve of buoyancy, and the ratio between the two has a most important influence upon the safety of the ship against foundering at sea."

It sounds like Sea Hunter described it correctly.
Bryce
 
#476 · (Edited)
And just to be clear for someone trying to follow this, as the terms are normally used, displacement and Center of Gravity have little to nothing to do with 'reserve buoyancy' either. But when evaluating motion, carrying capacity and stability of a vessel, weight distribution and buoyancy distribution are far more critical than the overall displacement of the vessel, or its keel type.
 
#477 ·
jeff_h:905984 said:
and just to be clear for someone trying to follow this, as the terms are normally used, displacement and center of gravity have little to nothing to do with 'reserve buoyancy' either. But when evaluation motion, carrying capacity and stability of a vessel, weight and buoyancy distribution are far more critical than the overall displacement of the vessel, or its keel type.
+1
 
#487 · (Edited)
I'm really glad you admited to being a weekend sailor, as that fits in my view of fin keelers :). We intend to liveaboard, on the hook as much as possible, traveling to different areas harvesting resources, with a shoreside plot for backup, though indeed we could be a small minority, that's okay :), oh ya ferrocement full keeler mmm, sooo good :-D.
 
#488 ·
After scanning this blog, it is apparent that there are a quite a few folks out there who are able to rationalize their positions on fin vs. full keel based on what they own. "Love me, love my boat."

My current boat is is a 35' sloop with a weighted swing keel. It has other parts than the keel that impact its performance, like substantial form stability (less heeling) and inboard shrouds (allows better performance to upwind). It--like every boat--is a compromise and has its negatives, like less interior space to accommodate the keel trunk and more moving parts (swing keel and also a swing rudder). All of this allows the boat to float in less than 2' of water, but with drastically reduced maneuverability. I've sailed her from the Gulf coast to Maine over a period of 16 years and have found myself in a wide range of conditions and have to admit that I'm rather comfortable with the compromise. I've had her offshore and I've been in various conditions from light winds to sustained winds of 40+ kts.

On the other hand, I've sailed on many full- and modified full-keel boats ranging from a 26' Dolphin to a 42' Island Packet over the past 40 years. Most of my experience on full keel boats was as a bareboat skipper for a minimum of a week at a time and a lot of that was in the Caribbean, from Puerto Rico to Antigua. These keel boats were noticeably less responsive than the fin keel boats I've sailed. This could make for a challenge when tacking, for example, especially with the cutter rigged Island Packets. They also didn't do as well going to weather or in light air. On the other hand, they were more comfortable when the wind picked up to 20+kts, but some of that was due to their higher displacement. For some reason, all of the Island Packets I've been on (350, 370,380, 40, 420) required a heavy hand to steer. This might have been due to the steering design, rather than the keel, but the net result was fatigue and sore shoulders, so whatever tracking advantage is claimed for full keel boats was nullified. When going to weather, I would just use the motor. The fin keel boats--mine included--took a much lighter touch on the wheel and were more weatherly. This is a big deal on longer trips or in higher winds.

The one serious reservation I have about fin keels is their deeper draft, which makes anchorages smaller and some "shortcuts" unavailable.

There is no boat that does everything, so you pick your parameters and live with a compromise in either case. In my case, the swing keel and swing rudder needed an expensive upgrade (to make sure things move when necessary). These expenses would not be incurred with a traditional full keel (non-centerboard) boat. On the other hand, I have never needed help to get ungrounded.

My bottom line on fin vs. full keel is that to each his own.
 
#489 ·
I agree,

I have a cutaway forfefoot keel and while they turn on a dime when the wind is just right, they are sluggish at low speed and I have had a few problem tacking when the wind was really strong just like I had on cape cod mercurys so it's not just the shape.

I approach my boat rationaly, it's a machine with nice features and flaws too. It's a little disconcerting to see people swear by the design they happen to have (sometime by luck) and get into pissing contest about the shape of their keel. All this talk is nonsense, the only persons I would trust in this matter are boat designers and naval architects. Let them discuss the merits of such and such configuration. The rest is legend and fable.
 
#490 ·
I agree,

I have a cutaway forfefoot keel and while they turn on a dime when the wind is just right, they are sluggish at low speed and I have had a few problem tacking when the wind was really strong just like I had on cape cod mercurys so it's not just the shape.

I approach my boat rationaly, it's a machine with nice features and flaws too. It's a little disconcerting to see people swear by the design they happen to have (sometime by luck) and get into pissing contest about the shape of their keel. All this talk is nonsense, the only persons I would trust in this matter are boat designers and naval architects. Let them discuss the merits of such and such configuration. The rest is legend and fable.
Well, if you take it that way it is rather simple: Naval Architects, I mean reputable ones, have long abandoned full keel configuration even for blue water cruising purposes, even the ones that once, far in the past, designed full keel boats.

Regards

Paulo
 
#491 ·
And it might very well be.

Like I said, I do not feel like I belong to Team Long Keel just because it happens to be the design of my boat. Honestly the main reason I got a longer keel boat was because I felt that they would be mechanically better connected to the keel due to its length and because the other fin keeled boat I had surveyed had a little flexing problem there (it was an encapsulated keel)

Come to think of it now, with the experience I got on this one, that would probably have been repairable in a few week-ends but that's another story.

Bottom line is I could have gone for a fin keel.
 
#492 ·
One doesn't have to be a boat designer or naval architect to understand the mechanics and hydrodynamics of keels. There are lots of sailors who aren't naval architects, but have enough technical savvy to clearly understand the characteristics of different keel shapes. The keel is only one part of an assemblage of often interactive parts, so it can be presumptive to label a boat as a "full keel" or "fin keel" boat, as if that is sufficient to characterize the boat.

Take the Island Packet (IP)cutters, for example. All the ones I've sailed had a modified full keel, but their shortfall in tacking related as much to getting the genoa through the narrow slot between the inner and outer forestays when coming about. The keel/rudder combination doesn't allow you to pivot through the wind as crisply as a fin keel/ spade rudder arrangement would. This problem would be mitigated if you had a sloop rig (as some IPs are configured). The IPs probably do better in higher winds because of that cutter rig vs. a higher sloop rig--not because they are full keel boats.

That said, there is a loyal IP following, not necessarily because their customers are fond of a full keel, but because the total package fits their lifestyle. I have been going back to IPs for Caribbean charters because the IPs work for me in that venue. In southeastern New England, however, I am happy with my own boat for a variety of reasons--not just because is has a fin keel.

If folks are passionate about their boats, so what? Putting down someone else's, however is another matter.
 
#493 ·
One doesn't have to be a boat designer or naval architect to understand the mechanics and hydrodynamics of keels. There are lots of sailors who aren't naval architects, but have enough technical savvy to clearly understand the characteristics of different keel shapes. The keel is only one part of an assemblage of often interactive parts, so it can be presumptive to label a boat as a "full keel" or "fin keel" boat, as if that is sufficient to characterize the boat.

Take the Island Packet (IP)cutters, for example. All the ones I've sailed had a modified full keel, but their shortfall in tacking related as much to getting the genoa through the narrow slot between the inner and outer forestays when coming about. The keel/rudder combination doesn't allow you to pivot through the wind as crisply as a fin keel/ spade rudder arrangement would. This problem would be mitigated if you had a sloop rig (as some IPs are configured). The IPs probably do better in higher winds because of that cutter rig vs. a higher sloop rig--not because they are full keel boats.

That said, there is a loyal IP following, not necessarily because their customers are fond of a full keel, but because the total package fits their lifestyle. I have been going back to IPs for Caribbean charters because the IPs work for me in that venue. In southeastern New England, however, I am happy with my own boat for a variety of reasons--not just because is has a fin keel.

If folks are passionate about their boats, so what? Putting down someone else's, however is another matter.
 
#494 ·
I can't believe this went on for 50 pages.

Apples, oranges - which is better?

I love the technical discussions, the opinions I take with a grain of salt (and then a shot of tequila).
Here's my opinion -
On my Gemini (catamaran) with the boards up it was akin to a long shoal keel - 32 feet long, but only 18 inches deep - and it sucked to leeward, I mean drifted. Board down and it was 5/12 feet of asymmetrical lifting pointy-ness.

On the Irwin 38 Mk II I have the shoal keel, 4.5 feet of stubby. I don't care about the extra 2 degrees of leeward drift in 5 knots of wind - because I'm probably going to be motoring in 5 knots
Once the boat gets to speed it points just fine.
I don't care about the 3-5 degrees of extra point I might get out of a fin keel (6 foot, optional on the boat) - because I'm not racing for the buoy.

I might care about the extra degrees on a 500 mile off shore leg but only because it will save me a half day on the trip. Then again so will being able to cross that sand bar without dragging or bouncing off the coral.
 
#495 ·
I can't believe this went on for 50 pages.
Yes, amazing, isn't it??

And probably no converts either.. in any event it's been interesting, entertaining and vexing, all at the same time.

Compromise and setting priorities is what it's all about.. and always has been.
 
#496 ·
We could go for 51 pages.

Agree with Faster that its about compromise and priorities: rarely does a single parameter, like the keel, decide the matter.

My wife was enamored of the Island Packets we have chartered from Florida to the Caribbean for quite a while. She liked the roomy cabins in particular and the large galley and all the storage. Our own boat, by comparison, has a narrow cabin and wide side decks and a keel trunk that splits the main cabin and runs all the way to the coachroof. Our storage is probably a third that of an IP of the same length (35').

Our boat has a retractable, weighted fin keel that allows us to go from 5'11" draft down to 1'10" (with keel and rudder retracted), but normally she is sailed with everything down until we come into a shallow anchorage or negotiate a "shortcut".

What really makes the difference worth it is that we can keep the boat at our shallow water dock, yet we can sail to weather better than most. In our area in southeastern New England, weatherliness matters when you are heading west against the typically southwesterly breeze.

Well, we were beating from Cuttyhunk to Mystic (about 50 nm) several years ago when we passed a larger Island Packet that was motoring in the same direction. The IP skipper saw us, unfurled his sails, and took up the challenge. Unfortunately, he could not point as high and soon enough had to come about, unable to maintain a competitive velocity made good to Watch Hill Passage. He rolled up his sails and continued to motor. The difference was primarily the keel (full vs. my fin) and the fact that the IPs have outboard shrouds and don't allow sheeting the genoa as close. We made it on the same tack all the way to the Mystic River. My wife--who would rather sail and absolutely hates to motor--stopped bugging me about the IP accommodations after that.

That said, we continued to charter IPs in the Caribbean, where she can enjoy the bigger cabins and larger water tanks (we like our showers at the end of the day). The longest legs we've motored are about 15 miles--she can put up with that. (You really don't want to sail a full keel boat from St. John to Virgin Gorda.)
 
#497 ·
We could go for 51 pages.

Agree with Faster that its about compromise and priorities: rarely does a single parameter, like the keel, decide the matter.

My wife was enamored of the Island Packets we have chartered from Florida to the Caribbean for quite a while. She liked the roomy cabins in particular and the large galley and all the storage. Our own boat, by comparison, has a narrow cabin and wide side decks and a keel trunk that splits the main cabin and runs all the way to the coachroof. Our storage is probably a third that of an IP of the same length (35').

Our boat has a retractable, weighted fin keel that allows us to go from 5'11" draft down to 1'10" (with keel and rudder retracted), but normally she is sailed with everything down until we come into a shallow anchorage or negotiate a "shortcut".

What really makes the difference worth it is that we can keep the boat at our shallow water dock, yet we can sail to weather better than most. In our area in southeastern New England, weatherliness matters when you are heading west against the typically southwesterly breeze.

Well, we were beating from Cuttyhunk to Mystic (about 50 nm) several years ago when we passed a larger Island Packet that was motoring in the same direction. The IP skipper saw us, unfurled his sails, and took up the challenge. Unfortunately, he could not point as high and soon enough had to come about, unable to maintain a competitive velocity made good to Watch Hill Passage. He rolled up his sails and continued to motor. The difference was primarily the keel (full vs. my fin) and the fact that the IPs have outboard shrouds and don't allow sheeting the genoa as close. We made it on the same tack all the way to the Mystic River. My wife--who would rather sail and absolutely hates to motor--stopped bugging me about the IP accommodations after that.

That said, we continued to charter IPs in the Caribbean, where she can enjoy the bigger cabins and larger water tanks (we like our showers at the end of the day). The longest legs we've motored are about 15 miles--she can put up with that. (You really don't want to sail a full keel boat from St. John to Virgin Gorda.)
Is it a secret what kind of boat you have?
 
#500 ·
One of the LAST boats I would want to be on is an IP in higher winds......but that is me.

My wife would also prefer one a bit less cramped than what we have. BUT, even a full keeler would not have a lot more room. I was on boar an Eric jr awhile back. Half the room of my boat, with the same length etc. Not sure it would do any better in a blow either.

As said, one needs to decide WHICH keel will work best for that persons circumstances. Be it a fin, full, something in the middle, or for that matter, a CB style! Along with for kicks and giggles, lets throw in a canting keel with dagger boards! ie a V70 or equal style boat! Schock built a 40' canter for awhile.......you could probably still get one if you really wanted it!

At the end of the day, choose based on where you are going, how you wish to sail etc. For me, it would not be a full keel, not matter where I was going! IF I needed shoal draft, I would go with a CB or lifting keel of some sort. then put it down in deeper water for the additional pointing etc they offer over full keels. Then an appropriate hull form which is probably more important for comfort etc. than keel shape or form.

Marty
 
#513 ·
One of the LAST boats I would want to be on is an IP in higher winds......but that is me.
Marty
200 years of yacht Architects would vehemently disagree with you. The IP is not as wide as most big cruisers, and coupled with the full keel tends to make the hull less stiff. As we all know the lower the stiffness, the better the rough water capability.

The huge keel mass coupled with the heavy hull results in a quite low CG further enhancing its rough water capability. And as everyone knows the IP is extremely respected in its rough water capability.

Bryce
 
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