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JimD
02-13-2004, 12:51 PM
In the recent Tursiops thread there is some discussion on the merits of a skeg in the stern that retracts into a trunk inside the boat. My question is how about a sort of kick up skeg hung off the back like a rudder although it could only be raised or lowered for tracking but would not turn like a true rudder? Sounds like it might be simpler to build and maintain than an internally housed skeg.

Don Maurer
02-13-2004, 05:22 PM
If you are going through all of the trouble to install a kick up skeg, why not just intall a rudder? My advice is to build the kayak without a skeg or rudder and spend a season learning to paddle it. Then if you decide you need a skeg or a rudder, install it next winter.

Todd Bradshaw
02-13-2004, 05:24 PM
You mean a "stuck rudder"? It will do some of the same stuff, but generally not as well. Skegs are usually farther inboard, which helps keep them from popping out of the water in waves. Another nice thing about them is the ability to use as much or as little as you need hanging down to really dial-in the windage. This is more difficult on a rudder-like fin and most of them bend side to side enough when not vertical to preclude using a raked angle as a means of partial deployment. Unless I could come-up with some really good reason not to add a skeg-box instead of a stern-mounted fin, I'd bite the bullet, build the box and never look back. In terms of adjustability, minimal drag, beachability, effectiveness with the smallest fin possible, least amount of junk hanging off the back end of the boat, effectiveness in rough water, etc. they're pretty hard to beat.

Todd Bradshaw
02-13-2004, 05:44 PM
Don, I don't think learning how to paddle is the whole key here. I don't care how good you are, there are some designs which have very annoying tendencies in a crosswind. You can spend all afternoon compensating for them (with paddle and/or rudder) and wasting a lot of energy in the process, or do it by changing the windage of the hull with either a skeg or a means of adjustable trim - like a sliding seat. I can't say anything specific about this boat and how well it does in adverse conditions, but I generally put rudders in the same category as training wheels. I've never seen one make someone a better paddler. A skeg, on the other hand, strikes me as more of a boat-tuning tool. This will be my 32nd season of kayaking and by now, I can pretty much get my boat to go just about anywhere I want it to go, with or without rudders or skegs but I have one kayak with a sliding seat and one with a skeg and I use both of them to tune the boat. You wouldn't start a symphony on an untuned violin and compensate by bending the strings on all the off notes. Why start across a three-mile stretch of open water in an untuned kayak that wants to constantly twist to weather?

JimD
02-13-2004, 06:56 PM
Todd, I found a website of someone who built the Turpsiops and says they installed a retractable skeg mounted one metre ahead of the stern but there are no pics of the skeg so its hard to say exactly where it is or what shape was chosen. Does that mean the end of the skeg is a yard from the end of the boat? A skeg isn't part of the plans so I'd just be making a guess anyway. So tell me, about where does one put the skeg?

Don, I'd rather not have to retro fit a skeg next year, much rather make a decision before the deck goes on.

Todd Bradshaw
02-13-2004, 09:36 PM
Jim, tomorrow when it's light, I'll go out and do some measuring and shoot a couple pictures of the skeg system on my Gulfstream. That measurement is probably fairly accurate, but I'll be able to get dimensions from a couple boats to compare it to.

Don Maurer
02-13-2004, 11:46 PM
Todd,
I've only been paddling kayaks for 17 years, so I don't have near your experience, but I have paddled sea kayaks with and without rudders or skegs across open water in crosswinds. My first sea kayak had a rudder. After a while I quit using it, preferring to use paddle strokes, balance and shifting ballast to trim the boat. The 2 cedar strip kayaks I built have no rudder or skeg, but have fine entries and a deep forefoot and tracks straight as an arrow in as much crosswind and waves as you would care to paddle in. It seems to me boat builders always want to modify a boat design before they know how it performs as designed. All I am suggesting is that you get to know the boat as designed before you make a lot of changes that will affect the performance characteristics of the boat.

[ 02-13-2004, 11:49 PM: Message edited by: Don Maurer ]

Todd Bradshaw
02-14-2004, 03:40 AM
I also generally share your basic aversion to builders changing designs before trying them out.
In this case though, other than taking up some storage space inside the stern hatch, I can't think of any harm that adding a skeg will do and it's likely going to be a neater and easier job to do it now than later. I also think that there is a good chance that it will get used.

In a way, a kayak hull in a crosswind is much like a sailplan. It has both a Center of Effort for the exposed portion and a Center of Lateral Plane for the submerged portion, which it will pivot on. When the two are properly lined-up, the boat doesn't weather-cock. When they don't, it can be a pain to paddle efficiently. Even though designers strive to eliminate weather-cocking, sometimes a fairly small variation in paddler weight and submerged hull profile can make a substantial difference in the amount that a boat will or will not tend to do it. The amount of "bite" that the ends, especially the stern, get on the water will then affect how much it pivots and provide various amounts of tracking.

One of the truly fun parts of being good in a kayak is learning to stand a long, skinny hull on it's ear and make it really carve tight turns. Sometimes the addition of a skeg will allow stiff tracking when desired on a somewhat more maneuverable hull. Some of us find this type of boat more interesting and fun to paddle and a skeg then comes in handy when you're faced with two miles of open water to cross. Like I said, I don't know much about this particular design or how good the designer is, but I can't see how a skeg would really compromise the design and I'd certainly rether fit it before the deck goes on.

[ 02-14-2004, 03:42 AM: Message edited by: Todd Bradshaw ]

LeeG
02-14-2004, 08:38 AM
Jim, I'd still put off the installation of the skeg unless you've already paddled one and know exactly what the skeg is correcting for and what it'll do. For example I went on a trip with a friend who has a glass Caribou without a skeg and if I were to get one I'd get it with a skeg because I've seen how it works in long distances with beam winds.
If you place the aft hatch about 2' from the coaming it'll give you enough arm reach to install a skeg box 2' further back which is "in the ball park" should you decide.
You'll spend more time learning how to rotate your torso with relaxed hands holding a paddle than you will take installing the skeg. The other self-correcting aspect to reducing the number of tracking/turning aids is that you'll tend to paddle within conditions that you can controll the kayak. If you are in conditions where having a skeg will make the difference between getting home or not then you're over your head to begin with,,and a skeg would probably not make a difference.

Todd Bradshaw
02-14-2004, 12:05 PM
Kind of makes me wonder how many skeg-retrofit jobs you guys have actually done. It sounds so easy, doesn't it? Personally I find that even retrofitting and properly glassing-in a locking eye on the back deck can sometimes be a real P.I.T.A. when working through a hatch and a skeg that has to be neatly tabbed in, straight and plumb could be another one. What techniques have you used to do it successfully?

Again, the point of the skeg is not to save your bacon when paddling in conditions which are over your head, it's to save your energy by making the hull do more of the work when tracking is a problem, which allows your energy to be used for moving forward. I don't care who you are or how good you are, if you're spending energy making the boat track in a crosswind, you're wasting energy. The ability to instantly add or remove skeg-power and change how the boat tracks saves energy and beats the hell out of trying to shift cargo around with your feet, choking-up on one side of the paddle or just trying to muscle the boat in a straight line.

Todd Bradshaw
02-14-2004, 07:53 PM
Sorry Jim, I got burried in other stuff today and by the time I got to the garage it was too dark to shoot pix. I'll try tomorrow.

JimD
02-15-2004, 12:29 PM
Originally posted by Todd Bradshaw:
Sorry Jim, I got burried in other stuff today and by the time I got to the garage it was too dark to shoot pix. I'll try tomorrow.I'll be here! :D

One nice thing about the Turpsiops which I didn't even know until I got the plans is that it has a flat bottom about 5 or 6 inches wide at the beam and tapered to the ends. That will make installing a skeg a little simpler than were it a V. The design calls for adding an expendable 'wear plate' on the bottom so when its gets chewed up from beaching and launching it can simply be sanded smooth and replaced or reinforced as wear dictates.

Hans Lassen
02-15-2004, 01:21 PM
http://www.atlantickayaktours.com/Images/Retail/Kayaks/VCP/Nordkapp/Jubilee-M-side-w550.jpg
http://www.nanuk.de/inhalt/kayaks/image/nordk_s.gif
VCP says (Valley Canoe Products, Nottingham - they don't have an own homepage. You may want to look at http://www.atlantickayaktours.com/) : "The Nordkapp is the premier example of the West Greenland Eskimo kayak style and is used worldwide for the most demanding sea kayak expeditions. It is a long and narrow kayak. It tracks well without a rudder and is very fast. It has a low deck and fine bow and stern: these features present minimum resistance to the wind and the boat continues to track straight and remains maneuverable under all conditions, whether loaded or empty. Valley Canoe Products now have produced the second generation of Nordkapp, called "Nordkapp Jubilee". It refines the original highly successful design by slightly changing the stem and stern contours. Moreover, a new anatomical design of the cockpit was incorporated into the Nordkapp Jubilee, which includes recessed rear coaming. This allows the paddler to lean well back while executing an Eskimo roll or just plain relaxing. There are several variations of the basic Nordkapp design. The most popular is a modified (M) hull with built-in skeg as a part of the hull. This boat tracks like a train, but requires good kayaking technique, such as edging, in order to turn. Another variation of the Nordkapp is the standard (S) hull, equipped with a retractable skeg. Such a configuration adds great versatility to the kayak - just dropping the skeg will instantly change a maneuverable kayak into a straight running one for difficult quartering seas.
Not many kayaks are in a museum, but the Nordkapp is on display at the National Maritime museum in Greenwich, England. The Nordkapp is a classic. The Nordkapp has been on expeditions around the world. With each new Nordkapp generation it becomes an even better kayak. Fast, good tracking (with the skeg or modified hull) and handles rough conditions great. It is a long kayak, so it will not turn like an Avocet, but if you are paddling longer distances, the Nordkapp is a great kayak to be in."
The photos above show the skeg and the modified hull (integral skeg) version.
I think it might be very tricky to build the fine skeg at the rear end in a stripbuilt or plywood kayak, so I would opt for the integral skeg version but try to find out from the designer where to put it. Better than trial & error IMHO. (Owner of a very fine Pintail kayak with retractable skeg. Wouldn't want to miss it.)
Hans

[ 02-15-2004, 01:23 PM: Message edited by: Hans Lassen ]

JimD
02-15-2004, 02:16 PM
Thanks for the link, Hans. Here's an excerpt from the site. There was also an image of a kayak with its skeg lowered (So now I know what they look like :D )

How does a Skeg Work?

The kayak skeg may be the most misunderstood piece of kayak equipment. Many people think the skeg is used to make the kayak track, but its function is to "trim" the boat when conditions affect its performance.

The skeg should be part of the kayak design, not an addition to fix a poorly designed boat. Kayaks with skegs should be designed to slightly weathercock (turn into the wind).

With the Skeg up, the kayak weathercocks.

With the Skeg down, the kayak turns downwind.

With the Skeg half way down the kayak turns crosswind.

Watch the Flash Lesson above for a visual lesson on how a skeg works.

The dominant force (Wind or Current) influences how the skeg works i.e., down current is the same as down wind.

The two main types of skegs are rope controlled and cable controlled. The rope controlled skeg is more reliable, as it does not damage easily and can be fixed in the field. The disadvantage of the rope controlled skeg is that you can't fine tune the skeg position. The cable controlled skeg is easier to fine tune, but it is more vulnerable. If you leave the cable skeg down when you run up on land or over an object, the cable can kink. Most cable skegs are easy to fix with tools and an extra cable, but you don't usually carry these in the field. If you own a kayak with a cable skeg, you should always have an extra cable at home to do a repair. Our personal preference is the cable controlled skeg, for the fine tuning that it offers.

A skegged boat can be packed a bit bow heavy, since the skeg will help to compensate, but a trimmed kayak is always best.

Todd Bradshaw
02-15-2004, 03:13 PM
Gee, it's cold out there. These are about the best I could get without jockying boats around and freezing my posterior off. The top boat is my C.D. Hutchinson Gulfstream and is 16'10" long. The trailing edge of the skeg is 35" forward of the stern end of the boat. The skeg when fully deployed is 14" long along the hull bottom and 3.75" deep at it's back edge, which is plumb.
http://www.imagestation.com/picture/sraid103/pd8caaea6a56da8cc2d37244e16b7bc88/f99d5fde.jpg

It's made from 1/8" anodized aluminum plate. The box inside the hull is just big enough to hold it. There is a glassed-in pivot pin of some sort forward and the control cable feeds into it through the top, aft corner (well above the waterline).
http://www.imagestation.com/picture/sraid103/p9ec5185561a0428400b459750ba3637b/f99d5f91.jpg

My boat has a rubbery gasket glued into a molded recess on the hull's exterior around the fin. Both my wife's Slipstream (lower boat in the photo) and the Avocet we owned just had a narrow slot cut or molded into the hull on the outside.

This is the third or fourth boat I've owned with a cable controlled skeg and I have yet to break anything, so the predictions above about the potential problems of cable control may be somewhat over-stated. I do usually retract the skeg for beaching, but if I don't, it will retract itself pretty easily and I'm not sure how one would put enough strain on the cable to break it in normal use. These cables slide inside a tight fitting tube, like a bicycle brake cable, but the inner, working part on mine is 1/8",1x19 SS rigging wire. If you break it, you'll probably be lucky to live!

Notice the reflective deck lines on my boat caught by the camera flash. The stuff is called something like "Glow-Cord" and is used for rescue work and tent pull-outs that won't trip you when navigating through camp at night with a flashlight. Current Designs started using it for deck lines last year and when caught by a beam of light in the dark, it really shines. Nice safety feature. MSR among others sells some of it, but I'm not sure which diameters.

JimD
02-15-2004, 04:06 PM
Thank for the pics, Todd. I've been in my own garage working on a mild case of frost bite while cutting the last of the 10 station molds for Tursiops. This kayak is quite heavily framed. Probably more than is necessary. I'm not going to bother with half of them.

The skegs on your boats look about as I had imagined but the skeg illustrated on the website posted by Hans show a very different skeg, a deep fin. Any thoughts on the difference?

Hans Lassen
02-15-2004, 05:06 PM
Haven't got a clue - the physicists among us (I've been to that kinetic energy thread... wow tongue.gif ) should be able to tell... What's interesting though is that my skeg when fully lowered starts to "sing" when I'm surfing on the wave. Must be the vibrations of course, but it's really great!
Good night for now (5 to 11 pm over here). Thanks for those photos, Todd!

[ 02-15-2004, 05:09 PM: Message edited by: Hans Lassen ]

JimD
02-15-2004, 05:47 PM
What's interesting though is that my skeg when fully lowered starts to "sing" when I'm surfing on the wave. So that was you? I thought I heard The Beach Boys: 'Let's go surfin' now, everybody's learnin' how...' :D

Todd Bradshaw
02-15-2004, 07:54 PM
I don't know much about proper skeg shape and as long as those on my boats work great, I don't think I'll worry much about changing their shapes. Those which I do have are capable of doing so much with so little exposure, drag, hull draft etc. that I can't see much reason to need longer ones and possibly increase their vulnerability in the lengthening process. It seems possible to "over-think" some topics and this strikes me as though it may be one of them. Even the section posted above about the boat having weather helm with the skeg in one position and lee helm with a different amount of skeg lowered strikes me as both a bit much and quite possibly, extremely inaccurate. If the boat behaves that way at rest, it's certainly going to change as soon as you start moving and if it behaves that way when moving at any given speed, it's going to change when you change speeds. Different paddler and cargo weights are also certainly going to have an effect on this by burying different amounts of the hull and it's ends in the water, which is extremely likely to throw the whole thing out of kilter. I just don't think it's that complicated.

LeeG
02-15-2004, 08:12 PM
Todd, I have never installed a skeg nor paddled a Tursiops. I think skegs are great,,I'm making a big assumption that if Jim is new to kayaks then if the Tursiops is his introduction then he'll be making another kayak. Installing a skeg seemed like more complication than necessary. If I was sure that I wanted a skeg it would make sense to install it before the deck is on. Have you paddled a Tursiops?

George Roberts
02-15-2004, 08:34 PM
Hans Lassen ---

In general, a skeg resists sideways movement. A reasonable relative approximation to that resistance is:

The area of the skeg * the distance from the center of the kayak

The further back the smaller the skeg needs to be for the same effect.

A paddle works as a skeg along the lines of

The area of the paddle * half the length of the paddle.

Rob Hazard
02-15-2004, 10:46 PM
If you are looking for a simple internal skeg design, you might take a peek at Rob Bryan's _Seguin_ , available from the magazine.
It has an adjustable skeg in a box that is carried up and glassed to the deck, open-topped. The skeg drops in and is tensioned downward by a length of bungee along the deck, and pulled up by a simple cord running forward to the cockpit. Extremely simple.
I hardly ever use the skeg, preferring how the boat handles without it, but when open water conditions make the boat want to weathercock, dropping the skeg an inch or so is all it takes to tame it.

Todd Bradshaw
02-16-2004, 03:48 AM
Lee, I haven't paddled, or even seen one. From WB's cryptic little drawing, basic dimensions and the boat's construction method, I imagine it is quite stable and not terribly fast as sea kayaks go, but should be a reasonable recreational touring boat. It obviously wasn't intended for either expeditions or big-water tripping but it's got enough volume that it should bob like a cork in big waves. With that kind of beam, it's comparitively short length and a multi-chine hull, I certainly don't expect it to track like it's on rails, so I suspect a small skeg may be a worthwhile addition and at times be quite handy.

LeeG
02-16-2004, 09:55 AM
I've been intrigued with QCCs skeg system. It's adapted from a Sealine rudder with a spring deployment. The blade is tapered and I'm guessing that might reduce the pebble jamming characteristics of some skeg designs. That Gulfstream is a perfect "do-all" design. I was somewhat surprised to find that the Scirocco skeg doesn't correct for weathercocking as efficiently as the Gulfstream.
Likewise paddling a Necky Elaho,,to discover a big plate of a skeg that didn't eliminate weathercocking with full deployment.