Reading through the posts over the years I have noticed a trend of keel and stem failures occurring on many of the boats we build. The keel is the heart of most designs and I certainly have had more than my share of difficulties in this area. Is it caused by using improper materials? The debate rages between Fir, Southern Yellow Pine, MDO, ordinary exterior ply, and marine ply, or (insert your favorite wood species here). Cases for use can be made for all. What you use seems to be less important then how you use it. If that is so then is technique the problem? My choice was SYP and in retrospect it was a bit too wet. I glued it up with Weldwood water based glue making it even wetter. The recommended copper boat nails couldnât hold the wood as it moved and neither could the glue. It cupped as it dried. Glassing the keel just made this worse. I have seen SYP edge glued with epoxy actually tear itself apart as it dried out. The epoxy held but the center of the plank just split lengthwise. Rot in the stem is another common failure mechanism. I had to scarf in 80% of the outer planks and 50 % of the inner to get all the rot out of mine. The threaded bob stay runs down through the stem on my boat and it was not sealed with epoxy and re-drilled. It was caulked with 4200 but the water still got in. There has to be a better way to fabricate these laminated keel/stem assemblies. Are the butt joints the problem? Is the glue or epoxy issue the problem? Should the keel be made of solid sections and bolted together like a big ship keel? Should the laminated keel be cross bolted during manufacture? What are the best methods and materials and the issues involved with each? What are the engineering trades involved concerning cost, service life, ease of accomplishment, and availability of materials to the home builder?
Among our membership there are a couple NAs and at least two professional Boat Builders. Perhaps these folks could comment on laminated keel fabrication and provide us with methods and techniques to increase the life span of this critical component. Hopefully they can answer the questions above or at least share their experiences with us.
Gentlemen your thoughts please. 8) 8)
i have had a problem with the dead wood shrinking and leaving a space large enough to swim a dalphin through. but i have not had the keel problems that some others have. all i have for protection is a coat of paint and that is usually scraped off after a few outings. i sand and repaint every winter. i don't mind that though. i have not noticed any rott yet. i am voting yes but only because that dang dead wood won't stop moving.
i used the cheapest 1" b grade pine i could find. i usted plastic reson glue as per the plans and opted to use screws instead of nails. if i had it to do over again, i would have used epoxy. but i hated epoxy back then and the stuff i used worked well enough up till now.
I had some separation in the aft part of my keel fairly soon after completing the boat. I was able to repair it by through boltine the separates section and drawing it back together. I used Douglas Fir and resin glue as called for in the plans.
Looking back, I thing the problem was caused by my inexperience with the glue and the relatively low temperature (50s mostly) when I began that part of the boat. At that time, the keel had to be completed before I could join the BYYB and I rushed to get it done.
It would have been better to glue up some other less critical assemblies and learn how the glue worked before building the keel. I have often felt that by the time I completed my boat, I had the skills and knowledge to start.
Anyway, after 7 years, she still sails like a dream and, other than sailor induced breakage, she has held together well.
One of the engineering concerns over wooden laminates is the layer thickness and stability of the species used.
Hardwoods swell and contract more then soft woods. For this reason it's best to use thinner stock for the laminations. Width of the stock also affects the success of the lamination. Most buy flat sawn lumber, usually from relatively young trees. This means the cross section of the laminate layers will have heart wood, sap wood, pith, internal stresses and other less desirable features. In a house, where this lumber would stand, reasonably dry and without substantial movement, there's no problem. In a boat where wet/dry cycling, repeated loading cycles and load transfer requirements will test the glue lines and internal stability of the lumber selected, failure can be common. It's this reason, I'm so deliberate about choosing well suited lumber for the tasks demanded of it.
Buying over size lumber and milling it down to preferable dimensions and grain orientation can help a lot. Quarter sawn and vertical grain stock is much more stable, glues better and has advantages over the plan sawn stuff you see at Lowe's/Depot.
I'm currently building a popular 17' cat ketch for a client a few hours south of me. I feel guilty covering up so much pretty stock with paint. I can literally say there isn't a knot to be seen in any of the stock used and for the most part, the grain is straight and dense. The keel batten on this boat is about 14' long, will be bedded in thickened epoxy and covered in 'glass. It's got a beautiful straight grain, not a blemish, all quarter sawn and it'll be painted white with the rest of the bilge.
From an engineering stand point, there's much to consider. Some species of lumber take glue better then others. The same is true of natural internal stresses, hidden defects, combining sap and heart wood, tolerance of lamination, water absorbsion, etc. The reason the old timers had preferences for certain species was tried and true. Some just faired better so they continued using it.
When epoxy enters the picture, very few actually do it right. Done correctly, an encapsulated boat (keel included) will live many decades. Done improperly and it'll quickly shed it's plastic coating and spit wood pulp at you.
There's only one way epoxy works on wood, regardless of species and that's total encapsulation. By this, every face, cutout and fastener hole has to have a minimum of two coats (I prefer more) of laminating resin applied. Penetrating epoxy just doesn't cut it (it has to have regular epoxy over it to work). The stuff has to be laminating resin or you're letting in moisture. The stock can't be any thicker then .75" (typical one by stock) and it needs to be of a species that doesn't develop checks or other hidden internal defects (or you have to sheath it with fabric, to control the internal stresses). This is the down fall of most folks. Not applying enough epoxy or not insuring a complete and total entombing in plastic (epoxy). The wood has to be completely covered (I mean really complete) or moisture gets in, the wood swells and the coating is compromised.
If you elect to use epoxy as a coating (it can also be used as a glue, which is different), you have only one road to travel down and there are no side roads or short cuts, if you expect continued, long term success. This decision can dramatically affect the cost of a build. A Weekender could be built for $2,000 in materials. Add epoxy encapsulation and you've increased the cost by at least 25% with just the epoxy. This doesn't account for the supplies and other things that go along with this decision, like fabrics, fillers, solvents, gloves, mixing stuff, etc. The total for a truly encapsulate Weekender can increase by 50% pretty easily, when it's all said and done, meaning your $2,000 Weekender is now $3,000 in materials. (I'll use around 7 gallons of resin on that 17'er I mentioned)
I call this the "goo factor" and have recently strived to design things, particularly small boats, that don't require encapsulation, but just epoxy as a glue (for which it's unrivaled). The goo factor covers the messy nature of the process (especially to the novice), the cost and the related skills you need to master, just to do a good job.
Back to the engineering stuff. Sap wood and heart wood differ considerably in physical properties. If both are in a laminate, then the laminate is screwed and will eventually fail, unless the layers are very thin (3/8" or less). If you must use less then desirable lumber, don't use 1"x12" stock. Rip it down the middle (this will usually split the heart wood) and glue it up, alternating the way they lay against each other, as 1"x6" stock. Yep, that means more joints, but it also means you've "released" many of the internal stresses associated with the sap/heart interface. The extra glue lines will also help stiffen up the keel.
Most of you know about the edge glued type of centerboard and rudder laminates, being used on other designs. You rip the edge off a 2 by board, flipping every other one so the grain is opposing it's neighbor and glue it up. This is the same logic and it works in deadwood assemblies too. In the old days, when this keels where made from many pieces of big timbers, the same thing was done. Each piece was oriented so the natural cup tendency was opposing it's neighbor. Even though they didn't glue them (they were typically "drifted" with big ass rods), they knew the value of this simple trick.
The bottom line: use the best stock you can find. If using Lowe's/Depot stuff, then rip it into smaller sizes and alternate the layup so the grains oppose each other and that they are more quarter sawn then flat. Use wood that tolerates moisture, hasn't a tendency to split or check and accepts glue well. If electing to coat the boat or sheath the boat, then go the full 9 yards and get each piece that epoxy touches completely coated (screw holes are a common failure point). Use enough epoxy to form a complete embalming of the wood, at least 2 coats, preferably three, which includes fastener holes. Use good epoxy tactics, such as "bonding" all the fasteners that will be asked to hold something tightly or may be under the LWL. It's an extra step, but the results can be bullet proof if done right. Don't make silly substitutions, like replacing a piece the plans say should be oak with cedar (for example). Again in this example, maybe you can get the cedar easier, but it's less then half the strength of the oak, so you're asking for trouble. Substitutions have to be made some times, so attempt to match physical properties with a different species of wood or increase the dimensions of the weaker piece to compensate for the weakness. Using the cedar for oak example again, if the oak was a 1"x2" (.75"x1.5") stringer, then use a 1.5"x3" piece of cedar so you have the same relative physical properties.
And lastly, don't over build, usually in an effort to make things stronger. In the vast majority of cases, this doesn't make things stronger, it makes them weaker and heavier. Picture the bundle of straws thing. As a group of skinny pieces they are very strong, but if replaced by one big piece, then it's subject to a single failure (one crack and it's over), is less flexible (so it can't absorb loads as well) and is heavier. The bundle of skinny pieces can tolerate many broken pieces before failure, each piece can flex to it's own "drummer" without regard to it's neighbor and it's usually a lighter structure.
I restored a lapstrake runabout a few years ago. It was about as delicate a boat as you could imagine. 15' on deck, 9 planks each side of 3/8" plywood, 3/4" square bent oak frames on 6" centers, with two 1.25"x5/8" stringers in the bilge and a keel plank that was 3"x5/8". It carried an 80 HP outboard and had done so for the last 40 years of it's 50 year old life. The structure was all original! It had some age related stuff, like tension cracks in the frames, but this very dainty boat held up just fine and you could lift it with two average size guys (without the motor of course). We call this "light and tight", meaning the scantlings are small (light) and the spacing (structural elements) are close together. This simple engineering principle, has produced the lightest racing boats and most long lived yachts the world has known. When the World Trade Center was built, it was designed to the same principles. They required half the materials of a conventionally built, 110 floor, office buildings. The architect was a brilliant man, who understood this principle and took advantage of it, saving the cost of materials and the labor to build it.
I've also heard of this de-lamnination problem. In my case it happened long before she ever got on the water. My boat was upside down for so long (over a year) and outside that it de-lammed before I ever turned her over. In this case I mixed epoxy and filled it all in. On top of that I then proceeded to screw in a long metal plate almost the full length of the keel which has the screws set in epoxy and the plate bedded with Sikaflex caulk. I'm hoping this holds up for me. I am in the habit of inspecting every week and I'll be keeping a close eye on things down there.
No problems yet. I built out of white oak and I'm glad I did. It is holding up well after 3 years.
No problems w/keel or any other delaminations.
This issue all boils down to choices again. If you choose Plain sawn lumber, you will have cupping and warping that you will not be able to control. The movement of wood with seasonal changes is a powerful force. Not so noticable on thin strips, ie. stringers, gussets, etc. But when you get a wide board as is used on keels and stems or other places where it is joined with adjacent boards or plywood, the board(s) will warp and pull apart. That may or may not be noticable to the casual glance or inspection.
If it is hidden beneath a wrap of fiberglass, you will not notice it at all until after the rotting process has reached a stage that will require major repairs.
If you live in an area where the temperature variations are extreme, below freezing in the winter months to anything above freezing in the summer months, you will experience more damage caused by the moisture within the wood or sealed within the area by a glass coating. The moisture will expand when frozen thereby causing the wood to swell more than if it were dry and any moisture between layers caused by warping or cupping will expand even more and cause greater seperation between layers. The process continues with each freeze/thaw cycle. It only has to freeze and then thaw once and the damage can be initiated.
Encapsulate the keel and you won't even notice what has happened until much later when rot is a huge factor.
This can also happen under glass over plywood if there is any way that moisture can enter. ie. Holes drilled for fastening, edges not sealed, fresh water sitting in the interior of the boat.
Most builders are not aware of how wood moves with temperature and seasonal changes.
If you look at a wooden deck and look carefully at the boards covering them they become warped/cupped and what was a nicely laid covering is now uneven after one seasonal cycle with its temperature and moisture changes. The boards even if only 1 X 4 material will be cupped and warped and uneven. You can't prevent it from happening if it is plain sawn material.
That is the reason that experienced builders will choose and pay for quartersawn lumber of a species with greater stability to use for wide width laminations. There is less of a tendency to cup or warp with this stock. White oak is an excellent choice as is a fairly short list of other woods provided they are suitable for boat building use. Yes, they are more expensive and harder to locate. (You will not find them at a "Big Box Store.) But well worth the difference if you plan on having a wooden boat that will endure and not have as many issues with keels and stems.
Wrapping the stem or keel with glass is not recommended because any moisture that gets into the area will stay there and cause rot. This happens whether you are looking for cracks or not. Internal moisture and seasonal changes will result in the wood rotting eventually in small pockets or large.
Wooden boats require maintenance, they have to have an opportunity to in essence "breath with the seasons". If they have fresh water sitting in them they over the winter, there will be damage in the Spring. Count on it.
They live on a trailer, outside, exposed to the elements and condensation forming on the interior surfaces of covers as well as the boat surfaces. The boat is covered to keep moisture out, and that also keeps moisture in. It freezes and thaws in cycles and doesn't get a chance to dry out. Mildew, mold, rot, replacement is the result. They need to have drains open to allow moisture to drain from the interior. They need to have a way for air to circulate throughout the interior. Don't store things in the boat over the off season. If possible turn it over and keep it under cover, hard cover, like a roof, not tarps elevated off the ground. Water will not collect in the bottom of the boat, it will for the most part stay on the outside and there will be a chance for air to circulate within the boat to help keep it dry. This will also allow you to carefully inspect the keel for any cracks, scrapes or damage that will allow moisture to enter the laminations.
Crap, I thought you said "pneumatic keel".
Never mind.
My keel boards had "cupped" and there were big spaces between them. I poured a lot of epoxy in between the boards before it started dripping out the other end of the crack. I packed 'em full of thickened epoxy and repainted. When I originally built it, I used that powdered "pancake batter" glue and I picked a lot of that stuff out of the hole before refilling with epoxy. Disappointing, but it was the first thing I ever built and I learned as I went. My dad wondered why I didn't clamp it when I poured the resin into the void, I guess I didn't clamp it because I figured this would only make it want to "cup" again the next time it got wet. Maybe it's happier now and won't move as much next time. One thing's for sure, it's gonna get wet again and it will probably move again. No problem, I built it so I can definitely fix anything on it too.
My favorite kind of topic, good going Craig. 8)
I used recycled 16 foot by 12 inch SYP, glued with the yellow sticky stuff :lol: and they were beautiful. I soaked the outer layers with epoxy, before applying glass
The planks were probably twenty years old, used as shelving in the local HA garage. They had torn them out and leaned them up against the building out back. I had patched one them up in the ER, after a knife fight. His buddies told me if I ever needed a favor, ask. I did :roll:
I've keel hauled a couple of docks, maybe a few jet skiers too. Landed on rocky beaches and drug her across some sharp edged steel on the trailer. Not to mention bouncing her down the road on said trailer. The Wolf's still strong.
After three years, I stripped the keel due to trapped moisture causing the fabric to blister. I made the right choice, no rot so far. I just use alkaloid paint now.
I think the Auroawolf is eight years old, now. So far, my first build has held up. However, she needs caulking and paint on the upper deck. I also worry about the interior. I've had a chronic leak along the front cabin edge. The only water I ever get in side is from rain. The hull is tight.
I'm still dreaming of a twenty-six foot RV port to store her under.
Wow, Mike, your boat really is a pirate ship, what with her ties to organised crime and all...
I bought one of those "Garage Tents" from Canadian Tire, You know the ones with the steel tube frames and tarp-like covering. I keep my boat in there for the winter. Last winter it didn't work out so good because I forgot to remove all the snow from the roof of the tent and it collapsed...upsetting, but it still kept the boat dry. This year I paid the extra hundred bucks for the more sturdy model, and I will remember periodically to go knock the snow off. It will keep the boat dry and nothing will be touching it so air will be able to circulate around it in the winter.
I've decided I don't mind having to work on the keel every few years. I left the boat to its own devices for five years with no maintenance whatsoever, and the only trouble was some checking and cupping in the keel boards, so I guess the boat's pretty tough. If I had to do it again, I'd use epoxy in the keel and I guess I'd look into "quarter sawn" wood... I had never even encountered the term when I first started building. I failed grade ten wood shop... I wanted to build a model boat and the instructor wanted us to build footstools...