A Glass Sheathed Hull

[Boardy]

Hi,

I have a 1907 Carvel planked Gaff Cutter. The boat is under restoration at the moment and this will probably be one of many posts over the restoration period.
The boat was epoxy sheathed before i took her on and i don't have any intention of taking the sheathing off and hasn't been in the water since. The boat has been out of the water for a good 20 years to my knowledge possibly more.
I am confident the sheathing has an excellent bond on the hull, however i'm well aware of the problems associated with sheathing and want to make sure there is no possible way for water ingress.

This then brings me to my 1st question.

The Sheathing ends half way down the iron keel, this is a slight concern because the sheathing doesn't appear to be finished in this area. I would like to know peoples opinion, whether the whole keel should be encapsulated, i sand the sheathing back and epoxy bond it to the keel or whether the keel has to come off, which is a whole new project in itself. Any other ideas would be greatly appreciated.

Many thanks

[Thorne]

Welcome to the Forum.

More info and photos will be a big help. Did you get a survey? What is the planking, and what was it sheathed with? At that time polyester resin was popular and was not a good choice - has adhesion problems amongst others.

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[kc8pql]

I'm not sure you're going to like most of the opinions you're going to get. Sheathing a carvel hull is generally considered to be the worst thing that could be done to an old boat.

[Joe Lambert]

Just spent last winter with a crew of 2 peeling really well applied sheathing off a carvel hull. 10 years old and the rot damage it caused was almost terminal. Get the survey if you haven't and try to figure out why it was sheathed in the first place.

Oh yea, and the idea of making sure water can't ingress is a fools errand. Water will enter the hull, make sure it isn't going to ruin the hull when it does.

[paladin]

and 20 years ago and not back in the water may mean it was done with polyester resin....which ain't agonna hold for long on that hull and water vapor will pass right through it.....

[RFNK]

The question of whether an old hull should be sheathed or not is moot. It's not right to say that this should never be done as it's proven to be such a successful method for many boats, including most cold-moulded and so many strip planked boats. However, the caveat on that is that the hull must be strong and tight, with no rot, for sheathing to be considered. Seawater ingress probably can be prevented if sheathing is done properly to a tight hull but, probably more importantly, something must be done to prevent fresh water from lying in a wooden hull and sheathing, if not done properly, could exacerbate this problem. As far as the seal at the ballast goes, this seems to be a problem area. I have a Twister with a splined hull that I'll probably sheathe, either with glass or a combination of timber strips and glass. I'll remove the ballast so that I can wrap the sheathing right under the timber and make up epoxy plugs for all keel bolts so that there's no bare edge to the sheathing.

The point about the old sheathing possibly being polyester is a good one - it's unlikely that polyester resin impregnated glass will be in good condition after 20 years and you cannot expect there to be a good bond to the timber with this. Rick

[Bob Cleek]

I've never been one to walk on eggs. We do no one any service by blowing smoke up their ass.

Buck bet your 102 year old boat didn't last that long because she was coated in plastic. RFNK is not correct. Sheathing has hardly proven itself a successful method over the long haul. For cheaply built boats, it works... for a time. ("Cold molded" or laminated hulls, which are essentially resin impregnated wood, or "fibre-wood" boats, are something different again... and have their own collection of unique problems.) You can often get a decade or two out of a sheathed carvel hull... longer if the boat is dry stored indoors. In the marine environment, however, over the long haul, it doesn't last and promotes rot like all get out. Sorry, but epoxy, and more so polyester resins, are NOT WATERPROOF. Not at all. They are moisture permeable. "Encapsulation" is a fantasy, a fool's errand, and a slick salesman's pitch to the uninitiated. (And yes, I've owned a fibreglass sheathed plywood boat or two over the years and seen dozens and dozens more worked on.)

On sailboats with external ballast, sheathing is always a problem. Some have sheathed the hull, and then attached the ballast, which makes the most sense. You will never get anything close to a decent seal between an iron ballast keel and the sheathing. The iron will rust and flake and the resin won't stick to it long. Some carry the sheathing down around the entire ballast keel, but soon find the keel corrodes anyway and eventually cracks the sheathing off, if it isn't scraped off the first time she touches ground.

The answer is very simple. If you want your 102 year old boat to see birthdays number 110 or 120, you must remove the sheathing and repair or replace what needs repair and replacing to maintain her structural integrity. Otherwise, be content with a few years of diminishing returns and then try to sell it to the next sucker that comes down the pike.

[RFNK]

The point I made is that the question of sheathing is moot, i.e., debatable. To suggest that sheathing hasn't proven successful on many boats, particularly cold-moulded and strip planked boats is a bit silly isn't it Bob? There's no reason why, if a hull is repaired or built to be tight and dry, whether it's carvel, splined, or whatever, that sheathing can't be used to strengthen a hull. Of course the sheathing's not going to last forever and of course the epoxy will eventually allow water ingress but sheathing's not going to cause accelerated rot while it remains in good condition, and as long as the sheathing's done properly, this is likely to take a very long time. It should be replaced before it gets to that point - like paint.

To me, the question is more about the potential advantage of sheathing for a carvel boat. If it's being done to tighten up the hull then, personally, I think this is a mistake as the inherent movement will damage the sheathing and you'll get Bob's scenario. However, if it's being done to fair a very rough hull that's been repaired very strongly, or it's simply being done to thicken thin planking or light planking, then it can be an alternative to replanking that should at least be considered. Some people sheathe carvel hulls so that the seams don't open up when the boat is hauled out or otherwise dried out from time to time. I don't know whether it's worth doing this for this reason or not. In the case of my Twister, I have a splined hull. When the boat is taken out of the water for a while, a few of the glued seams split away from the planks, damaging the splines. I'd like to stop this from happening. This boat is also built from a type of mahogany that is too light, in my opinion, for a cruising yacht so I'm keen to strengthen it - probably with sheathing or a combination of `cold-moulding' and sheathing.

Because sheathing is a method that's worked well on many boats (i.e., not carvel), it's a method that has potential to provide solutions to other issues as well, such as the need to strengthen a carvel or splined hull, IMHO. That's not to say it's the best method and there are many, many examples of boats that have been damaged by improper sheathing or inappropriate assumptions about what sheathing will or won't do. Typically the boat wasn't built or repaired properly and the sheathing was added as a stop-gap measure.

I suggest to Boardy that he should get a copy of the Gougeon Bros manual on uses of epoxy and consider the points they make carefully. I've also been told that these people are very helpful in relation to technical matters when contacted.

I respect the opinions of those who've been around boats for a while but I respect the opinion most of those who've managed to retain a willingness to learn something other than the first method they were taught and refrain from ridiculing those who think we haven't learned everything just yet. Rick


PS I just went to the West System site and couldn't find the section on sheathing that I thought was there - sorry! I am pretty sure there is a Gougeon Bros rundown on sheathing around though. I'll post it if I can find it. Rick

[Bob Cleek]

"The point I made is that the question of sheathing is moot, i.e., debatable. To suggest that sheathing hasn't proven successful on many boats, particularly cold-moulded and strip planked boats is a bit silly isn't it Bob? There's no reason why, if a hull is repaired or built to be tight and dry, whether it's carvel, splined, or whatever, that sheathing can't be used to strengthen a hull. Of course the sheathing's not going to last forever and of course the epoxy will eventually allow water ingress but sheathing's not going to cause accelerated rot while it remains in good condition, and as long as the sheathing's done properly, this is likely to take a very long time. It should be replaced before it gets to that point - like paint."

Sorry, but no, there's no debate about it. The facts are absolute: Wood moves. Epoxy don't. (And it gets less flexible and more brittle as it ages.) We are talking about a traditionally built carvel planked boat here. Sheathing such a hull is purely a very short term solution and a very labor intensive, and expensive, one at that. I suppose one could quibble over what is "short term" and what is "long term," but the outcome of that discussion will be dictated by whether or not one cares at all how long their work will last. "Good enough" is often just that, but let's not polish a turd. If "quick and dirty" is one's objective, they should acknowledge that.

The fact that there are traditionally planked boats over a century old is because they are engineered to take into account, and, indeed, to employ, the natural movement of the wood to hold themselves together and remain watertight. Given the forces created by the movement of a wooden hull, sheathing it in fabric and epoxy doesn't add any more "strength" to the structure than wrapping it in toilet paper would. Granted, it may stop major leaking for a short while, but only until the movement causes the coating to crack along the seams, which often happens with amazing rapidity, although your mileage may vary.

"...if it's being done to fair a very rough hull that's been repaired very strongly, or it's simply being done to thicken thin planking or light planking, then it can be an alternative to replanking that should at least be considered. Some people sheathe carvel hulls so that the seams don't open up when the boat is hauled out or otherwise dried out from time to time. I don't know whether it's worth doing this for this reason or not. In the case of my Twister, I have a splined hull. When the boat is taken out of the water for a while, a few of the glued seams split away from the planks, damaging the splines. I'd like to stop this from happening. This boat is also built from a type of mahogany that is too light, in my opinion, for a cruising yacht so I'm keen to strengthen it - probably with sheathing or a combination of `cold-moulding' and sheathing."

There are many less expensive and labor intensive ways to fair a wooden hull than slathering it with plastic. Oil based fairing compound is the industry standard. If a plank is so shot replacement is indicated, no amount of epoxy piled on top of it is going to replace the structural weakness caused by that plank's deterioration. Sheathing it is just putting a Band-Aid on a laceration that really requires stitches. When a planked hull dries, it WILL shrink. That's a given. Short of laying up what amounts to a separate epoxy and fabric hull outside the wooden one (essentially laying up a fibreglass hull using the wooden hull as a plug), the wood will crack and rip the epoxy sheathing when it shrinks. The sheathing does NOT have sufficient strength to overcome the shear forces of the wood movement. This is what is happening to your splined hull when it is hauled out, except, given the inherent engineering defects of splined construction, you have splines splitting in addition to your sheathing.

Sheathing plywood is somewhat more practical in small boats because plywood doesn't have the same movement dynamics. (Since the laminates in plywood run at right angles to each other, it is continually trying to tear itself apart, moving in opposite directions, as it swells and shrinks, of course, much less so than plank... but that's a story for another time.) Again, sheathing a planked hull of any type, splined or otherwise, will NOT add ANY structural strength (although it may add perhaps some measure of abrasion resistance if laid over soft inferior wood.) To solve the problem you describe with a splined hull by sheathing as you contemplate, you will have to add enough of an epoxy and fabric covering to afford enough structural strength to exceed the combined forces of all the wood in the boat moving as it naturally does. If you succeed in that, your boat (now really a fibreglass shell enclosing a wooden structure) will tear itself apart internally as the forces generated by the planking that cannot overcome the resistance of the sheathing structure are transferred through the plank fastenings to the frames, floors and deck beams, which will likely start cracking, beginning at the weakest point and moving on from there.

"Cold molding" is something altogether different from sheathing with resin and fabric. It is essentially a wood lamination process, using the resin as adhesive, and any sheathing is merely for cosmetic fairing purposes. A cold molded boat is essentially a plywood hull formed to shape in place. The wood's natural movement is distributed through the thin laminations running at right angles to each other and the forces managed by directing them in small amounts against each other. This dramatically reduces apparent movement at the seams, which essentially don't exist, at least directly through the laminate section. The forces are still there, but they aren't going anywhere except against the adjacent lamination and, owing to the thinness of the laminates, they aren't in any one plane sufficiently powerful to do much damage. Again, if one intends to cold mold a sheathing onto a traditionally built hull, it will have to be strong enough to overcome the shear forces generated by the planking movement... and the hull will then have to absorb them, usually with disasterous results.

"Because sheathing is a method that's worked well on many boats (i.e., not carvel), it's a method that has potential to provide solutions to other issues as well, such as the need to strengthen a carvel or splined hull, IMHO."

Again, what's "well" and for how long? However humble your opinion, I'm sorry, but it's incorrect. Sheathing, for all the reasons explained above, simply does not "strengthen" anything, at least not until it becomes so thick it becomes the structure of the hull itself, at which point I don't think it can be any longer considered "sheathing." To the extent sheathing has "worked well" on "many boats," those hulls have been plywood and laminated (cold molded) hulls designed without regard to the natural movement of wood. Such contruction methods are be cost effective for boats that are not intended to last as long as traditionally constructed hulls and are priced accordingly. The Chris Craft line is an excellent example of how that cost/benefit analysis can be done well. There is no dispute, however, among both the industry and the marketplace that such vessels are of a lesser quality, cost versus longevity considered, and are less desireable (and hence less valuable), than traditionally constructed wooden boats.

[Bob Cleek]

"I respect the opinions of those who've been around boats for a while but I respect the opinion most of those who've managed to retain a willingness to learn something other than the first method they were taught and refrain from ridiculing those who think we haven't learned everything just yet. Rick"

Rick, it isn't about ridicule at all. Nor is it at all about any unwillingness to learn "something other than the first method they were taught." Maybe the fundamental difference lies in the misunderstanding that "everybody has a right to their opinion." To the extent they do, they also enjoy the "right" to be dead wrong. Some things are fact. They are true. They just are. Other things, whether one calls them "opinions" or not, are just flat out wrong. Simply "having an opinion" or "being open to try new things" conveys no franchise to being correct. It's like playing jazz (about which I know practically nothing). Somebody can teach themself to play "by ear" and produce something that sounds pretty good, but they aren't going to ever be an accomplished jazz improvisationalist unless they have a firm grounding is classical music theory and practice. Neither is anyone ever going to "invent" or "discover" a new wooden boatbuilding technology without a firm grounding in the understanding of wood as a structural material in the marine environment.

You have before your own eyes the consequences of the dynamics I've described. Your splined hull is splitting when it dries out because the wood shrinks and those forces are greater than what is holding it together. The splines simply do not have the strength to overcome the shear forces generated by the planks and so, when the planks shink, the splines are torn apart. There are many fine ways to form a large shape full of compound curves like a hull. Strip planking or glued splines are among these methods. What they don't take into consideration is the wood's natural MOVEMENT. The same goes for a piece of fine furniture. It will last for centuries, so long as it remains dry and is kept in a relatively stable environment. Leave your 250 year old Chippendale desk out in the weather for a year or two and it will likely become a rotten pile of sticks. We put the wood in our boats to the ultimate in abusive environments. If that abuse isn't planned for when the boat is built, it won't fare much better than any other piece of wooden furniture left out in the weather. A carvel or lapstrake hull will open up when it dries, but it will swell back up tight when launched. It's planks are designed to press against each other, and where used, against the caulking between them, when they swell, such that the hull is watertight. The problems you are encountering with your strip planked hull are inherent in that construction method. The splines were an attempt to make a solid wooden structure without regard to the wood's natural movement, relying on splines and adhesive to hold it together. When the wood moved, it tears itself apart, usually at the splines, which are softer and weaker than the adjacent planks. While splining may provide a short term fix, perhaps more easily, so some say, than traditional planking practice, there's no free lunch. It's always a trade off. Glued splined seams always bust up and, at best, the spline ends up being just something to fill a gap that could have more easily been filled with caulking material.

Guys who have built a boat with one of the "new" (most have been around forever) techniques are often attached to the method they selected. It's natural to dance with the girl ya brought. However, she's either the "prom queen," or she's not. A man's gotta know his limitations.

[RFNK]

Bob, whether you like it or not, declaring that someone is blowing smoke up someone's rear end is ridicule. If you left these kinds of gratuitous quips out of your posts you'd make fewer enemies. But let me add, I'm not your enemy!

I appreciate the many points you make and the time you've put into it. I agree and I think I understand just about everything you've written (especially your jazz analogy). I accept that there's sheathing and there's sheathing which is more of a structural replacement and could, probably should, be regarded as something other than sheathing, like as you put it, creating a replacement hull using the original as the plug. Where I think your predictions go astray is in the idea that if a glass or composite hull is constructed around a wooden hull that is strong enough to be considered a new hull, or where this `new' hull acts in concert with the original planking, that it will somehow cause all the internal structure to fail. The stresses in the splined hull (and I agree, by the way, that's it's not a good way to build a boat) that cause cracking at the seams are from timber saturated at sea shrinking upon drying out on land. If the boat was sheathed once the boat was quite dry and this sheathing is maintained and eventually replaced so that it retains it's water resistant qualities, then these stresses from the drying out process no longer exist. Of course all timber moves through humidity changes but simply not to the extent that it's going to rip the boat apart. Sorry, but there are just too many strip-planked boats around in good condition where the sheathing has worked well in combination with the structural planking for this to not be regarded as a sound method.

I completely agree that sheathing a carvel hull that's not tight, that really needs replanking, sounds like a bad idea, for all the reasons you've noted, and I wouldn't do it. But, if someone is considering sheathing as a protection or strengthening of a new or really well-repaired carvel hull, it simply seems to me that sheathing could be done successfully as long as it's properly done and maintained. I've already suggested to the WB editors that they develop an article about this - if it can be done, what is the best way to do it? Your answer is, it's never going to work. Maybe you're right but then again, in my short life, I've heard that said about a lot of things.

Let me ask this question. I have a Twister with a splined mahogany hull. There are split splines below the waterline but these seem to be only in the proximity of some suspect planking which I'll be replacing. The mahogany planking is mostly fine except that, personally, I don't think it's a very good timber for a cruising yacht - I understand that mahogany varies a lot so bear in mind that I'm only referring to the species that I have - switenia something or other I think it's called (don't have my notes with me here in Vietnam). Anyway, I plan to replace all suspect planking and splines, replace about half the frames (laminated instead of the traditional steamed frames which mostly cracked at the turn of the bilge) and then strengthen the hull somehow. I plan to cruise around the Great Barrier Reef and Tasmania so I want a strong hull. My choices in strengthening the hull are - replace all planking, sheathe with two layers of double-bias glass or `sheathe' with two layers of timber strips and a layer of double-bias. On the other hand, I could simply repair all planking and splines and imagine that I won't ever hit anything or be caught in a storm. What would you do? Rick

[S B]

Glassing a carvel planked hull is common practise here, sometimes to save an aging hull or to strenghten a new one.The old ones are stripped of caulking and rope soaked in epoxy replaces it. If it didn't work, the practise whould have been abandoned long ago. BTY epoxy doesn't cure rot.

[RFNK]

Boardy, just to take this discussion back to your original question (I plead guilty to causing the thread to wander off a bit) and to the statement you made that you're not going to remove the sheathing anyway. The simple answer is that it's highly unlikely that you'll get sheathing to successfully encapsulate the whole keel. From researching this issue fairly extensively (but not exhaustively, of course!) the advice I have is that you should remove the ballast and wrap the glass right around the remaining keel. As Bob points out above, you'll never get the glass to bond to the ballast. If it's an iron ballast keel, it'll rust under the epoxy but, anyway, there's always going to be significant movement between the keel and ballast. This will definitely cause the sheathing to tear or delaminate.

I think you'll probably need to create some sort of epoxy plug where the keel bolts go through so that you can ensure that the edges of the glass at the keel bolt ways are really bedded in well, although, logically, this may depend on how the join between the keel and ballast will be sealed or bedded. I'm sure that wrapping the hull without the ballast is the right way to go but I'm still unsure of the best way to deal with the glass at the keel bolt ways - it's one of the things about sheathing that I'd like to learn more about. Rick

[Boardy]

Well that definately caused some debate.

Thankyou to everyone who responded. To be honest the replies were kind of what i expected. I did however definately learn some new consequences of sheathing.
I know the hull was restored to a solid state before sheathing i.e. it wasn't done to cure rot. She was splined with a soft pine then sheathed. I believe the sheathing was done to cut down on the usual maintenance of a wooden boat. I am still in contact with the previous owner who applied the sheathing so will endeavour to find out his reasons for sheathing.
Ultimately this restoration is about having the boat back in the water, being used for what she was originally intended and lasting as long as possible.
Before i make my final decision on to peel or not to peel. Would anyone care to comment on good ventilation preventing rotting out from the inside if she was to stay sheathed. By the way i haven't dismissed the other valid points made by the obviously very knowledgeable people on the forum. I have a learnt a great deal and would just like to explore every avenue. Once again thankyou to everyone for responding.

[RFNK]

If the boat's now splined anyway you're probably going to have to either keep the sheathing if it's okay, replace the sheathing if it's not or re-plank unless the splining is really up to exposure to sun and sea.

As far as ventilation goes, it's just a matter of achieving through-flow. Dorades up front and mushroom vents up back will achieve that but you need to go through the hull and clear any real blocks to ventilation, especially anywhere where moisture, water or moist air are likely to sit. Clear limber ways, make sure any ceiling/panelling doesn't prevent air flowing past all planking and frames, cut holes in bulkheads if they prevent flow, etc. Some people recommend keeping salty water in bilges - I think this is a serious mistake as it increases the humidity in the boat. Bilges should be dry. Those little solar-powered ventilators work really well but if you use them, only put them at one end as you really want to achieve through-flow, e.g., dorades or a solar vent up front and a mushroom or two at the back or dorades or mushrooms up front and a solar vent at the back. Rick

[Bob Cleek]

Let me ask this question. I have a Twister with a splined mahogany hull. There are split splines below the waterline but these seem to be only in the proximity of some suspect planking which I'll be replacing. The mahogany planking is mostly fine except that, personally, I don't think it's a very good timber for a cruising yacht - I understand that mahogany varies a lot so bear in mind that I'm only referring to the species that I have - switenia something or other I think it's called (don't have my notes with me here in Vietnam). Anyway, I plan to replace all suspect planking and splines, replace about half the frames (laminated instead of the traditional steamed frames which mostly cracked at the turn of the bilge) and then strengthen the hull somehow. I plan to cruise around the Great Barrier Reef and Tasmania so I want a strong hull. My choices in strengthening the hull are - replace all planking, sheathe with two layers of double-bias glass or `sheathe' with two layers of timber strips and a layer of double-bias. On the other hand, I could simply repair all planking and splines and imagine that I won't ever hit anything or be caught in a storm. What would you do? Rick

Sorry about the "blowing smoke" comment... sometimes the internet leads one to forget it's real people with feelings that one is talking to... I realize I tend to be a bit caustic now and then. As for friends vs. enemies... well, as a divorce lawyer, I pretty much automatically acquire one enemy for every friend I make anyway, so I stopped counting a long time ago. (That's a joke, actually. It is not all that uncommon for an opposing party in a case to call some years after its over and ask me to represent them in their NEXT divorce because they thought I really did a good job for their "ex" and was still a nice guy!)

As for your question... what would I do? Well, that's somewhat hard to answer, given that I don't have the boat to look at. However, I would say that if the boat was built by someone who knew what they were doing, as opposed to a home-built boat where the builder decided he had a lot of better ideas, the mahogany planking is probably just fine. There are a lot of woods that are called "mahogany," but if it is one of the better ones, it is suitable. (Swietenia mahogani... also known as West Indies mahogany, is native to Florida, the West Indies and the Bahamas. It is the most valuable of all true mahoganies and has been pretty nearly harvested to commercial extinction. It survives in parks and cultivated plantings these days. This is the stuff fine furniture was made of and I'd be surprised to find it used as boat planking in any boat built in the last fifty years.)More determinative of strength is the thickness of the planking. I'll assume it is of the usual proportionate thickness. I'm not sure why the seams were splined. Sometimes, somebody gets scared of caulking and figures gluing splines in between the seams will serve as well. We've already established that not to be the case, although it sounds like you are stuck with them at this point. I'd mention that there is a spling method that is sometimes used when plank seams become worn from improper caulking or old age. In this method, the spline is glued only to one side of the seam, thus creating a new sharp sound plank edge and then the seam is caulked traditionally. This method will not cause spline splitting because the planks can shrink and open up the caulked seam (and close again upon launching) without a spline trying to hold them together with glue.

Now, if your cracked splines are otherwise in decent condition, I'd expect if they are well and tightly fitted, that the planks will swell up when the boat is in the water and the seams will close up, splines and all, with the splines essentially serving as caulking material. If so, that's probably as good a fix as one can expect. The splines can be routed (or sawed out with a specially machined circular saw blade shaped to be more narrow at the edge than back towards the arbor so as to cut a "V" shaped kerf) and replaced, of course, but you'll be right back where you started from the next time she dries out.

Replacing steamed or grown frames with epoxy laminated ones is a good solution, especially where replacing a steamed or grown frame would require tearing up the decks and covering boards to set the replacement frames. Usually, one can rig jigs to lay up a laminated frame right up against the planking itself without having to tear out too much joinerwork. If the lamination is done well, I think the laminated frames will be superior to the traditional ones, especially where there are sharp turns in the bilges.

As for "strengthing the hull" because you plan to cruise in hazardous waters... well at the risk of sounding like a smart ass, I'd say the best solution is to keep a good weather eye out and stay off the reefs! Seriously, though, there's no point in trying to make a hull strong enough to withstand running up on a coral reef. I don't think anybody's ever accomplished that. Your best insurance against grounding is a big lead keel, which will absorb a lot of shock in a hard grounding. Iron is next best. I'd say that if a boat lacks the "strength" to withstand whatever the sea might be reasonably expected to throw at it, then it isn't a boat suitable for offshore work and one would be best advised to sell it and buy a boat that is proper for the task intended.

That said, there is very, very little meaningful "strengthing" that will ever be accomplished by adding anything to the planking of a hull. Strength is a function of the underlying structure of the vessel. The primary relevant "strength" factor to planking is simply impact resistance... what does it take to punch a hole in it? If you consider the weight of the vessel applied to a given point on the "skin" of the vessel, most every boat starts looking a lot like an egg, which shares the same structural features. There is really no way to sufficiently strengthen the skin of a boat to the point where it's "puncture proof." A metal hull is the best bet in that regard, but, as I expect you know, those South Pacific reefs are strewn with as many, or more, metal hulls than wooden ones. To judge the "strength" of a boat, look to its structure. What are the keel, the frames and the deck beams like? How well do the floors and knees hold all that together? A suitable ocean cruising boat is built to do that job from the ground up. While many have taken remarkable ocean voyages in a boat designed for another purpose, beginning with Joshua Slocum, trying to make a boat which is lightly built (lightly meaning structurally, not weight wise) for sheltered waters serve as an offshore boat is a dubious, and even dangerous, proposition. Nor is the hull structure alone the sole factor. Far more ocean cruising boats have come to grief due to rig and fitting failures than have because their hulls weren't "strong" enough.

If you haven't done so already, read the Hiscock's book, "Cruising Under Sail," and Donald Street's "The Ocean Sailing Yacht" volumes I and II, for openers. They will explain the principles very clearly and in great detail.

I'm not sure what your "Twister" is. I know of a Twister line that was built in England back in the late sixties and early seventies. It is a full keeled 28' fibreglass cruising sloop, which looks like it would be a fairly decent offshore boat, but I don't know of any built in wood. I think what you might want to do is really look at your boat critically and decide if it is suitable for heavy work. If it isn't, you really aren't going to be able to turn it into something it isn't and your money would be better spent exchanging it for what you need. If your cruising plans are as you say, having a proper boat can indeed be a matter of life or death.

[CharlieCobra]

I'm going to jump in here because I have a sheathed carvel planked hull. She was done in '94 because electrolysis killed the latest set of fasteners that had only been in 18 months. She was done in C-Flex and they did a nice job. There are issues to deal with however. Ingress of fresh water caused some problems when a lousy repair was done. I'll probably have to peal a section to replace part of the sheer plank. There are some ribs aft that are gone, again from past crappy repairs. Replacing those, though they aren't needed structurally, will be a monumental PITA. I'll have to figure out a different method for attaching them to the planks, not to hold fast the planks (they ain't moving) but to hold fast the ribs.

[RFNK]

Thanks Bob, a lot of helpful advice there. I have a thread on the Twister restoration. I'll bump it up to make it easier to find as I'm currently in Vietnam and the boat's in Australia, so there's not much action! You'll see a few shots of the hull and the extent to which I've already removed almost everything except the hull! You'd be a welcome contributor if willing.

The original Twisters were all wood and there are still quite a few around. The design was modified for glass a few years after the wooden ones hit the water. It's a Kim Holman design. My hull was splined from the start. The builder was regarded as very competent. He was a Danish guy who was brought to Australia to work on an America's Cup challenger called Dame Pattie (the name of a former prime minister's wife). He also built our Folkboat. I also have a thread in the Resouces section where I asked if anyone knew where I could obtain a splining blade. Clearly I'll need to get one made, as I thought, but that thread provided some valuable advice. Rick

I


Rick

[Bob Cleek]

I saw your Twister thread "bumped up," Rick. If you restore her well, she looks like she should be more than up to the task of taking you offshore. As for the planking, you may want to replank without caulking or splines. It is a particularly high quality planking method favored at one time by the Scandahoovians (who else!) There was an article in WB on it years ago. The planks are perfectly fitted so that no caulking is necessary. It's easier than it sounds, although probably tedious. The WB article had a plan for a little measuring "fid stick" that one used to measure and spile the plank shapes. I've seen boats planked that way and they stay rather tight. It would avoid the need to install splines or partially caulk, which I don't think you'd want to do. That would build up uneven tension in the planking.

Yours is the Twister design I had in mind. I didn't know there had been wooden ones built.

Looks like you've got your work cut out for you there. Nothing money and time can't cure, though.

I've never actually done it, but you might try taking a cheap circular saw blade, NOT one with carbide teeth, just a plain old really cheapo one, to your local brake shop and see if it is possible for them to turn it down to a wedge shape on a brake lathe. I've never used a brake lathe, but as I understand it, they use them to turn brake drums and, I believe, to true up disk brake disks. A circular saw blade can't be all that much different from a brake disk, or so it would seem. Otherwise, you could perhaps find someone with a lathe with a tool post grinder. You could chuck the blade in the headstock and use the grinder to take the edge down. You wouldn't have to remove a lot of metal. Just enough to form a wedge the depth of your splines. When it's mounted in a skillsaw, you tack a batten in place to fit the seam and run the saw down the seam with the batten as a guide. The only tricky part is making sure the batten is accurately placed. You can make up a block as wide as the distance between the edge of your saw and the blade with a strip of overhanging metal tacked to its edge and put the metal lip into the seam. You can then butt the batten up against the block edge and you should get a perfect fit all along the curve of the seam. I presume you know that if you're going to reinstall battens, you want them softer than the plank species so the batten will split if that's going to happen and not the plank!

Now, given as much planking as you'll probably replace, if what is left is fitted tightly at the inboard edges, i.e. the splines are "V" shaped, you might consider finding a knowlegeable caulker around to look at her and let you know if he thinks it's possible to saw out the splines with a shaped circular saw that would leave a suitable bevel to allow traditional caulking. You could then cut caulking bevels in the existing planking and hang your new planking with caulking bevels planed on them and caulk her up the regular way. This assumes your plank fastenings are suitably strong, which they look to be. (Sometimes they skimped on plank fastenings in splined hulls, which was possible, providing the glue holding the splines together worked as it was supposed to work.) There IS ONE way to "strengthen" a carvel planked hull and that's to caulk it properly. The tension generated by all those caulking mallet blows just gets stored up in the hull structure, pushing it all tight against itself. If you've ever hammered any cotton, you know how much it will harden up a hull structure. You can hammer in splines pretty tight as well, but it's just not close to the same.

Splined planking was in fashion for a time about when your boat was built, so the fact that she's splined doesn't indicate poor construction. Like a lot of techniques that come and go, splining fell out of fashion once the inherent cracking problems became obvious. At the time, it was thought that splining would eliminate the need to recaulk and, in new construction, it certainly is easier to glue splines than hammer cotton. As usual, or so it seems, they went back to the old fashioned carvel caulking after the "experiment" was done. Boats are nothing but collections of compromises. The trick is to find the compromise that doesn't cost more in the end than it is worth in the beginning.

[RFNK]

Thanks again Bob. I've thought about replanking but really I don't think I want to go quite that far, so my plan is to replace all suspect planking and splines and then, as discussed, I've been considering whether to add any other reinforcement to the hull. The fix it up well and then don't hit anything approach certainly appeals but let me explain something. I've been fortunate to have come across several boatbuilders in my local area - an area with a pretty long history in traditional boatbuilding and more `contemporary' methods, who've given me loads of advice and assistance in work related to boats. All the suggestions I make to others on this forum and pretty much everything I've done to my own boats is based on knowledge gained from these guys, none of whom ever participate in this forum, unfortunately. I've seen the work that these guys have done and it's really impressive. They know a lot about boats. The advice they've given me in relation to the Twister hull conflicts. Please bear in mind that these guys do know what they're doing: They all say replanking is unnecessary - don't even think about it. One guy says that the mahogany is a bit light so why not turn it into a much stronger hull by cold-moulding with double diagonal layers. Another guy says that's overkill, do a full wrap with two layers of double bias after removing the ballast. The third guy says it just needs to be patched up - don't hit anything!. However, when I've discussed the recommendations from the other guys with the third guy, he simply says, well, either method would certainly make it a much stronger boat - if you can afford the money and time, do it! These guys build and have built carvel boats, strip-planked boats, cold-moulded boats etc. They all have a lot of faith in sheathing as a structural component.

In the end, I'll have to make a decision about which way to go with the Twister, of course. So, I'm going to simply replank where necessary and replace splines as necessary and then see how it looks! Most of the splines are pretty much as new. Your point about using a softer material for the splines makes sense to me although it wasn't done originally. The splines are the same timber as the rest of the planking. Thanks for the tips re shaping the saw blade and batten marking gauge. Rick