To scarf or not to scarf

[lazerus]

That is the Question.Well the latest question.:)
The boat I am going to build (in about 4 weeks now) calls for two layers of 3/8" mdo ply over a first layer of 3/4"x2" fir edge glued.Would I get any strength benefit by scarfing the plywood edges or the joints of the fir planks at least enough to make the extra work worth it?

[PAR]

In a word yes, but the real question might be, "is it necessary for this additional strength?"

With multiple layers of material, you can stagger butt joints and eliminate leak potential. Scarffing will make individual planks seem as one continuous piece, but again is this necessary.

An inch and a half of hull planking is fairly substantial, meaning a healthy size project. What is the boat and what do the plans suggest?

[lazerus]

Here it is:cool:
The designer admits its overbuilt.At first it was designed for 1 1/2" fir,plywood is an optional build and as I understand strong enough on its own.The 3/4x 2" fir is to help keep the hull stay fair when putting on unscarffed plywood.Cheaper and its easier than adjusting the blueprints for the change in hull thickness that ply allows.Quicker than scarfing too.
Yes The first post was badly worded

[Bob E]

I don't know about the rest of you but I'm going to be doing a whole lot of scarfing tomorrow. Have a great Thanksgiving all of you fellow yanks.

Bob

[Manie B]

Lazarus this may help a bit

i did scarf joints on my build and i lined the pieces up by drilling 3 holes right thru both panels and then inserted 8mm dowel sticks before epoxy. My scarfs were 8 to 1 some 6 to 1

it works well - strong and accurate

but is a lot of work

i now got a cheap router and started playing with step joints - to me its a WHOLE LOT quicker easier faster and accurate

i router to half the thickness of the plywood and 3x thickness in width so on 9mm ply the step is 4.5mm deep x 27mm wide

my hulls are now scarfed joints but all my decks and tops will be stepped joints

[Loveofsea]

Scarf every chance you get!

I built a 19ft skiff using the principles of aircraft construction rather than traditional boatbuilding design. Specifically, as FEW structural components as possible, each part being as big as it could possibly be...

Scarf splice to make all components 'one piece' then assmeble as few pieces as possible--(avoid butt joints!)

the less seam area, the greater the structural integrity.

When building aircraft, they go to extraordinary expense to use the biggest structural components as possible. one example i like to give is that we use wing stringers that are 90ft long. We could easily avoid the cost of transporting stringers at an oversized length by splicing the 5/16" X 2" X 2" angles together, but the result can never match a single piece....

"Every piece as big as it can be--as few pieces as possible..."

[PAR]

That a Buehler design, which means the scantlings are twice (or more) what they need to be. Frankly, if I were you, I'd use Geer's book and redo the whole set of scantlings, with a 10% higher fudge factor (Geer's book already produces a "healthy" set of scantlings as written), just to be on the hefty side and toss the remaining weight savings into ballast, which on that boat would be likely in the low 20% bracket as designed. You'd save a bunch of money on unnecessary materials and the increased ballast/displacement ratio will help considerably, holding that slack bilged double ender upright.

Let me guess, he suggests an 8" or bigger keel timber, 4" thick floors, 2x6" frames on 24" centers (or closer),1" thick gussets on each side of the frames, 2x4 stringers, double 2x6 chine logs, 1.5" solid lumber planking or three layers of 1/2" plywood for the planking, sawn 2x8 deck beams with the decking being the same as the hull planking.

Sweet God, that's way over kill. You can use it as an ice breaker during polar excursions.

If you're going to have a 17 to 18 ton boat and pay for the materials in it, wouldn't you like a fairly high percentage to be in ballast. By this I mean there is a direct correlation between the displacement of a boat and it's cost (and effort) to build. With a 20% ballast to displacement ratio (this boat is likely in this range, possibly lower) you're hanging the remaining 80% of the boat's structure by hand. If the scantlings were redone, still producing a strong, hefty boat, but with say a 40% ballast ratio, now you only have to build 60%, which is a big savings in effort. Yep, you still have to buy and install the ballast, but this is a one shot deal, not multiple tasks and assemblies.

I like George, but that old German is a bit anal about over building and under canvassing his sailboats. Check the SA/D on the design and compare this to your expected sailing area and average conditions. It's very probable you'll want to increase the sail area substantially. Some quick math with 1,000 sq. ft. of sail and a 17.5 ton boat, the SA/D is 14.9, which is pretty low, especially for light air or coastal work. In the trade winds this will be fine, but how often will you be sailing the trades.

[lazerus]

Actually The trade winds will fill the sails quite a bit.some of the destinations are going to be NewZeland australia the phillappines the carrrabean Holland...you get the Idea.It will be sailing constantly and I intend to cross many oceans.
Once the boat is built I retire.My sister in ST Kitts and her hubby own a house in Bassiterre and well goodbye snow.

[Tad]

Properly scarfed and bonded joints will produce a far superior hull, but it will not be easy to accomplish. I assume you are expected to clamp the ply to the inner (first) layer with screws or ring nails? Scarfing full sheets of ply in place on the hull will not go well for a small crew, much screwing around trying to get a good fit up in the air. Alternatively you could scarf on a table, but you'll need a big crew to handle a sheet of 3/8" ply 42' long! Yes it can be done, no it's not fun...

Why not just buy this boat....http://www.yachtworld.com/core/listing/boatFullDetails.jsp?boat_id=1503239&ybw=&units=Feet&currency=USD&access=Public&listing_id=11864&url=
She's only a dozen years old and all she needs is a new bottom. Been for sale for a number of years, they'll probably take less than half the asking.

[Boston]

Par
I loved the post
some funny stuff there

I think Buehler designs that way cause he is considering using basic framing lumber from the local yard
nothing fancy like white oak frames
or mahogany cabins
just low grade pine for cheep cheep cheep
the scantlings kinda make up for the inconsistencies in the material

laughed my ass off at

Sweet God, that's way over kill. You can use it as an ice breaker during polar excursions.

as for scarf joints
they are the bomb when it comes to strength
a but joint doesnt even come close
Tad's comments are right on the money
and Loveofsea made some good comparisons as well
thing about chine forms no one ever mentions is that the line of the chine is vulnerable to leaking and damage and tends to be a week point in the plan
overbuilding that area is a good idea
but being heavy above the line isnt
cielings, carlins, cabins and the like should be strong but light
bellow the line build a tank
it may come in handy some day
but being top heavy reduces your stability in a pinch
my two cents
B

[lazerus]

Sure just give me a hundred grand and ill by it of course it might take 15 or so to give it the new bottom.At 64 feet it is to big to solo and ill need a captains ticket. (sry for the sarcasm but Used boat means used problems)
There is no doubt in my mind that each of you have raised a valid point
but consider my needs for a boat.First and foremost seaworthy,it must be as seaworthy a design as possible and still be able to be built for as little as possible tough enough to stand 20-30 years of hard use in the south pacific and points beyond.I have no plans beyond living on it and sailing.A wind too strong to put up canvas in means a sea anchor and a cup of coffee.

[Boston]

I know the feeling
Im thinkin Ted Brewer's Sophia Christina as my first choice
but its a hundred for materials
40 just for the hull and thats not lead either
just wood and glue

I feel your pain mate

far winds and clear sailing
B

[Tad]

Laz...

Not trying to give you a hard time, only sharing some hard won experience. Building new with no money is a long hard road. Realize that you'll spend 8000 hours roughing out the 42' above. That is just construction time, finding materials is extra.

There are thousands of boats for sale cheap right now, no buyers to be found. Name your price, many are being given away. There's another Buehler (40+') on cragslist seattle for $6500.00 complete! The engine (good perkins) is worth more than that.

Yes, after 2009 all pleasure boat skippers in Canada must have a valid operators permit. Size of the boat does not matter.

[Boston]

my father
his father
and his father before him would rise from there graves and throttle me if I bought instead of build
but
I can salvage
I think
Ill let you know if I see any poltergeists

( good point Tad just Ive been wanting to build and retire for a while now )
( its the building part that lends so much satisfaction and peace of mind to the hole show so its hard to have economic realities thrown in )
( but appreciated none the less )

hey folks
go read my thread titled "the great race"

[lazerus]

I suppose I should mention my budget allows for $500 a month

[TeddyDiver]

just low grade pine for cheep cheep cheep
the scantlings kinda make up for the inconsistencies in the material

There's nothing wrong with pine especially when it's cheep:D
I'm building with fir and got it allmost free (couple of salmons 22 pounds each vs half a mile 2''x5'')

[PAR]

George Buehler's concepts are valid, though I don't buy into the execution and methods so much.

I'm pretty familiar with George's building style, for this type of design and if solid lumber, the bottom would likely be file planked, possibly with an exterior sheathing of plywood.

Yes, it would be stronger if scarfs were employed, but I don't think necessary on a triple planked build. Personally I wouldn't bother with the triple planking, just double it, maybe Ashcroft style, so both layers go down at the same time. Inner layer solid lumber, exterior layer ply if you like, though I see no advantage to this.

Yes, buying studs from Lowes/Depot can save funds, but not as much as you think when you have to buy twice as much, cut around lots of defects, etc., just to accommodate the design principles. With a 35,000 pound boat and assuming you can build it for $10 dollars (wishful thinking, honestly) per pound, the math is pretty simple as to the actual costs of this yacht. At $1,000 a month budget, that's a 30 year project to pay off the materials (at 10 bucks a pound). Lets say you can build for an astounding $2 per pound. This is still about a 6 year effort to pay off materials.

I think you could build a smaller Buehler design and still be comfortable. Again, the displacement of the boat can be directly related to the cost of the build. Maybe a "Hagar" (8,000 displacement), possibly a "Juno" (a lot of boat and about half of the displacement of the 42'er), maybe one of his "up graded" Juno's, which have different features, less deadrise and less displacement.

I agree with Tad, there are literally thousands of boats just waiting for a new owner, some free. I would be hesitant about buying a Buehler design unless I knew the builder well and the build was completely documented. With the cut rate materials and round the corner methods, you just can't tell what they used or did without full build documentation.

Lazerus, even if you do plan on lots of cruising, including a fair amount of trade wind runs, the vast majority of the actual sailing time will be in coastal efforts, where a higher SA/D would be welcome, even necessary. The most traveled cruiser will admit 90% of the time the boat is berthed or on a hook, with the remaining time divided up into 8% coastal hopping and 2% (or less) passage making.

Trust me I fully understand the need to build. Would it be much different if you found a sound, but worn out 1960's 'glass cruiser, for next to nothing. Ripped off the deck, gutted the interior and re-did everything, new rig, interior, decking, cabin, etc. The boat wouldn't look like anything but you own creation. It would have a solid, 'glass hull that is much less prone to leaking, caulking, springing planks, etc. and the satisfaction of doing damn near everything (including spending weeks fairing and fixing the 'glass hull) yourself.

I know of three 40'+ yachts in my area that could be had for less then $3,000. Okay, they have spent engines, need new sails, rigging a couple need masts and their interiors look like the Russian 3rd Army spent their last payday in there, but hay, what do you expect for 3 grand. Their hulls are sound, with minor damage, mostly cosmetic.

[Boston]

have you looked at dinghies :idea:

just kidding
ok well start collecting stuff then and stick it in storage
( Im buying white oak and storing it for now )
Tad's salvage boat idea was a good one if not to repair
then for stealing things like lead from
B

[lazerus]

Are you sayng that it will cost$10 pler pound of dispaced water?

[TeddyDiver]

Are you sayng that it will cost$10 pler pound of dispaced water?

That's about correct. Take a brand new boat closest to your project and reduce about 40% labour..

[lazerus]

No disrespect intended but after you get a set of his blueprints and you price things out as set out in his book (I have)you come up with a different figure.

[Boston]

if your talking Buehler's book on backyard boat building
then your referring to seriously substandard materials friend
he has some good ideas
but
there is a limit to what I trust my life to

[PAR]

I costed out a Buehler "Archimedes" (43', 42,000 pounds displacement) a few years ago, using construction grade materials and I'd be happy to compare the materials lists, privately through email. I did it a few different ways, one an all plywood build and also a solid limber build was included.

How much waste did you account for? Staging, cradle, templates, etc.? Fasteners, ballast, hardware, electrical systems, plumbing, other equipment, goo's, goop', fabrics and related supplies, shop supplies , engine, transmission, sails, etc.? How complete was your cost out?

[Ilan Voyager]

That a Buehler design, which means the scantlings are twice (or more) what they need to be. Frankly, if I were you, I'd use Geer's book and redo the whole set of scantlings, with a 10% higher fudge factor (Geer's book already produces a "healthy" set of scantlings as written), just to be on the hefty side and toss the remaining weight savings into ballast, which on that boat would be likely in the low 20% bracket as designed. You'd save a bunch of money on unnecessary materials and the increased ballast/displacement ratio will help considerably, holding that slack bilged double ender upright.

Let me guess, he suggests an 8" or bigger keel timber, 4" thick floors, 2x6" frames on 24" centers (or closer),1" thick gussets on each side of the frames, 2x4 stringers, double 2x6 chine logs, 1.5" solid lumber planking or three layers of 1/2" plywood for the planking, sawn 2x8 deck beams with the decking being the same as the hull planking.

Sweet God, that's way over kill. You can use it as an ice breaker during polar excursions.

If you're going to have a 17 to 18 ton boat and pay for the materials in it, wouldn't you like a fairly high percentage to be in ballast. By this I mean there is a direct correlation between the displacement of a boat and it's cost (and effort) to build. With a 20% ballast to displacement ratio (this boat is likely in this range, possibly lower) you're hanging the remaining 80% of the boat's structure by hand. If the scantlings were redone, still producing a strong, hefty boat, but with say a 40% ballast ratio, now you only have to build 60%, which is a big savings in effort. Yep, you still have to buy and install the ballast, but this is a one shot deal, not multiple tasks and assemblies.

I like George, but that old German is a bit anal about over building and under canvassing his sailboats. Check the SA/D on the design and compare this to your expected sailing area and average conditions. It's very probable you'll want to increase the sail area substantially. Some quick math with 1,000 sq. ft. of sail and a 17.5 ton boat, the SA/D is 14.9, which is pretty low, especially for light air or coastal work. In the trade winds this will be fine, but how often will you be sailing the trades.

You're gentle Par, with very soft words, trying to explain that's not a good boat. As I'm not well educated, as I do not sell plans nor I have acquaintance with any naval architect of sailing monohulls, I'll give my opinion "sans ambages" (straight).

It's overkill, heavy, surely expensive because 35000 pounds cost a lot and God, it's so old fashioned. It looks as an old De Knocker design in the fifties.

Even the Legh II designed by Manuel de Campos for Vito Dumas in 1942 looked more modern!

Vee shape, the best way to have a lot of wetted suface, and bad initial stability. Surely upwind in the breeze that heels nicely. Very useful to clean the deck.

Barn door rudder with a lot of inclination and not separated from the keel. The downwind stability won't be the best quality of this boat. When I think that Herreshof tried separate rudders around 1880-1890 to see it again in 2008, I'm in admiration of the stubbornness of some designers. Even Laurent Gilles abandoned that kind of rudders in 1970...

35000 pounds for a 42 footer and just 100 gallons of water...and a few drops of fuel. And less than 1000 sq feet to move all that. There is a problem; you can't use the engine except getting out and in the harbour, and there not enough water to cross the Atlantic as surely the journey will last more than 50 days...

35000 pounds with such scantlings means a heavy rigging, and low ballast ratio. The stabily won't be famous...

I can add more bad comments about the method of construction as naval engineer, but such scantling delirium gives me stomach aches.

Let's compare with a "normal" scantling for a boat of this size in plywood; 18 mm underwater, 12 to 15 mm at the top sides, idem for the deck in a good BS 1088 plywood with a good pine structure. Less expensive than two MDO plus wood. Less work.

Often I use the trick to use 6 mm (1/4 inch) or 9 mm (3/8 inch) plywood because it's a breeze to scarf them with a Scarffer form West System (70 bucks) attached to a good saw. Panels are light, bend nicely, do not spit the screws or nails brief it's easy for a lone man with only 2 hands and not as strong as a gorilla. Plus you can obtain a monocoque skin, and if you add composite joints at the chines it's practically unbreakable. Chines are always the weak point on classical chine building.

Before beginning the construction, and with your low budget you should think twice. Do you need a truly a 42 footer? Do you want to start a such hyper heavy boat (and thus expensive even with cheap materials) you'll never finish? Even physically it will be very demanding. Even with **** materials, heavy boats cost a lot. The price of the raw materials of the hull is a small fraction of the total cost. Even the work, that you think free costs, and a lot! Years and years of hard work, on weekends, nights, and holidays, what will become the relationship with girl friend, spouse, children, parents, friends ?

****last addition****
Par, you're wright again, refit a good glass hull is be a very good method. There is a lot of apparently rotten fiberglass sail and motor boats with sound, well made monolithic hulls. I'm rebuilding a 36 feet Cigarette for a dive shop. The monolithic fiberglass hull is good and straight, all the rest (plywood plus polyester resin) is rotten, they got the hull for free and they spent just 300 bucks, the price of the rent of the trailer...

[PAR]

Ilan, I see no need to piss people off, I'm quite adept at it with the other half, which is enough for me.

I have my eyes on several 'glass yachts, all making great "platforms" for a complete redo. I'm a bit picky on the hull form and type, so I'll wait some more. I just wish a Cherubini 44 or 48 would turn up derelict, so I can grab it up. Unfortunately, they made so few of the 48's, all of which are still sailing, that I'll be near death when one finally does come up for less then 3/4 of a million.

One thing I didn't mention and a point that has been hinted at, is the basic hull shell (planking and decking) accounts for about 8% of the build effort and costs on this particular yacht, even using budget materials.

1,400 sq. ft. of planking stock, 40 sheets of plywood per layer, another 500 sq. ft. of decking material, assuming 20 or so 2x6 frames, another 500 linear ft. of 2 by stock, of course you can double this amount to cover the structural floors, 600' or so of 2x10 stock for the keel and deadwood. This is just the most basic of materials list. A pro could get by with 15% waste, but a backyard builder would do well to keep it under 30%.

In the end, the project looks to be 100 sheets of assorted thickness plywood, several thousand linear ft. of assorted solid lumber, a couple of nice straight spruce trees for spars, then come the systems. Even going without an engine or any electronics, a fair bunch of money will get dumped into lighting, plumbing, rigging and a custom set of sails (wait till you get a quite on 1,000 sq, ft. of cloth).

It's an ambitious project, but certainly doable by a willful and determined builder with some experience. Of course it's not a first build.

About their sailing qualities, they're not as bad as you'd think. Anyone that could live with a Tahiti ketch could live with one of these. I've had the experience to sail a few different Buehler designs. They do seem tender initially, as he points out, but once the chine buries it stops and becomes a rock. A slow roll moment, gentle motion and yes you need a fair bit of wind to move them, all of which sounds very familiar to a Tahiti owner. In brisk winds, they can make a reasonably accounting for themselves, but the skipper must have had some sail plan changes as they're surely under powered. I don't think I've seen a Buehler design with a SA/D over 16, with most being 14 to 15 (this one is high 14's). Their high D/L makes for a comfortable ride in a confused sea. When being really pressed hard (read sailing in a half a gale) they drag a huge hole to windward. It's an amizingly deep one, that reminded me of a ride I had, on a last generation of the 12 meter AC yacht, which also pulled this type of huge hole.

Some of his later sail designs showed some promise, such as Dragonfly. Now there's a yacht with some potential. It would be cheaper to build then the one above and a lot faster. It's D/L is around 180 and with it's narrow beam, she'd propel easily, with smaller rags. He never completed his, though I understand a few have been built. His is for sale if I remember correctly and he wants 15 grand for the 15+ year old project that's not completed, nor ever splashed. Of course if I were to build Dragonfly, I'd make substantial changes to the under body and certainly the scantlings. I'd divide the appendages and firm up the bilges, particularly aft at the very least. I'd also take the weight savings and toss it into the ballast/displacement ratio, making a stiffer yacht that could carry more area. At this point it's no longer a Buehler, but a whole new design.

He's all but abandoned sail, now focusing on his successful "Duck" hitch.

As for the looks of George's yachts, they are what there are, working boat ancestry yachts. They have springy sheers, massive cutwaters, flat sided houses, all pretty typical stuff for a look-a-like coal hauler converted to pleasure use. I have an affection for this style of yacht, though having owned them, don't want to any more.

[lazerus]

THE QUESTION WAS ON SCARFING SINCE ALL THAT HAPPENS WHEN i TALK ABOUT AND ASK FOR CONSTRUCTION ADVICE ON HOW TO BUILD IT I GET TORN DOWN FOR MY CHOICE OF DESIGN i WONT BE BACK.

[Tad]

Laz....

Don't let life eat you man.....

If you think the detractors are bad now, wait till you start building the boat! Guys will come by every day to tell you how you're doing it wrong.

Don't listen, you don't even have to be polite, kick em out of the shop. Building a boat, any boat, is hard.....but people do it. It may be easier (I know it is for me) to treat the project as a journey rather than a destination. Set short-term goals every week or month. Don't bother setting a launch date, it's a long way out there. Then when people ask when you're going sailing, tell em, " when the boat's ready".

[Boston]

dont let it get to you Laz
we are all just a bunch of yachtsmen
each with his own tastes
Ive taken my share of abuse round here
water off a duck friend
just let it role away
B

[ancient kayaker]

If you have the time, strength, tools and skill, scarfing won't cost any more money. Can't remember where I read this but somewhere on this forum I would guess-

"build the best boat you can"

Looking at the pics, some places a scarf joint might not be worth the extra trouble, other places it might actually help get the ply go round the bend before you do. Scarf smart!

Par, try as you might, you still managed to piss off Lazarus. It's a gift you have ...

[Ilan Voyager]

Definitely yes, at least for the last ply to be sure of the continuity of the surface (no cracking joints and other ugly things) and to have the insurance of the smooth transmission of the stresses.
For the MDO in the middle layer, it's not mandatory as its role is similar to the foam of a sandwich: you can improve the quality of the joint, a good one has been described in this post. Inside, follow that says the designer.

You have enough scarfs to make that a special tooling is valuable. A Scarffer will help because it makes good feathers, the most delicate part, so it's easier to finish the scarf. A very good table bench, strong and straight is mandatory.

Par and I are too good guys; we have tried to warn you, as we know that you're embarking in a fateful project, specially with 500 USD/month to finance it. You are free to do what you want. But do not feel despised as that has never been our intention.

Together we have a few dozens of years (for my part 7 years as naval carpenter and after 31 years as naval engineer for the French Navy, my own shipyard, plus consulting in composite structures for race boats) of professional boat building and surely we have seen, expertized and built more boats that many of the people coming at this forum. I'm beginning to know what's a boat or ship, what works, and the most important : what never do.

I maintain that it's a bad boat, and if you like classical sailing boats you have Francois Sergent, a very nice man, Pierre Gutelle who made a very good book about sail boat design (you can find it in english worth the money), Dominique Presles, a specialist of the Colin Archer among the French architects, and a lot among the americains. Boats well and rationally designed, many beautiful, some truly astounding.

I conclude that as naval engineer, thus highly qualified to speak about this topic, the scantlings are a total delirium, an absolute foolishness, and the quintessence of the waste of materials and work. Spend 35 bucks, buy the good book "Boat Strength" by Gerr, read it...you'll be like St Paul on the road to Damas.

I won't enter in a discussion about the sailing qualities of this boat: to be short I'll say that 99 % of the earth, past and present production are better than this...I know that is your dream, nevertheless I hate to see someone run to the disaster while he can get better. That's all, folks.

[PAR]

I don't understand why someone can take this, an impersonal environment of opinions, voiced on an internet discussion forum to heart or as a personal attack. I don't believe this was what could be derived from my comments, nor to I think I stated more then reality for a project of this scope and build type.

I've built this type of project, single-handed and more then once. The last was a 48' ketch (which displaced just under 15 tons) which consumed 7 years and is currently afloat in Daytona Shores on the east coast of Florida. Previous to that was a "Spray" replica" (yep, a 41' replica). I do understand the issues associated with projects of this size and complexity.

I hope I don't have a "gift", though I'm sure I have pissed off more then one over the several years I've participated here.

Unlike many posters here, I rarely frequent the open discussion, nor entertain myself or other members with idle banter about what constitutes a proper head on a beer. This stuff just leads to misunderstandings and artificially inflated (or deflated) "reputation" points. My average since the turn of the century is about 1.5 replies per day. My attempt to pass along some of this stuff, 'cause I ain't getting any younger and there are few to fill the void. Some here post a dozen of more times a day (clearly needing something better to do in their lives) and have higher reputation values then me.

I also don't think I veer very far off topic, trying to stay on point and in focus for the most part. If folks find offence with this then I'm disappointed, though not particularly sorry (there I go pissing people off again) as it's a discussion forum, not your local pastor telling you to change your life or expect to go to hell. Thin skinned sailors should just watch videos.

[Boston]

well said

[erik818]

I've tried to avoid scarfing but found that plywood panels won't bend uniformly unless they are scarfed. Still I'd like an easier way to scarf than to plane and sand a stack of plywood sheet to get the 8:1 or 10:1 edges. (Last time 6:1 had to suffice.)

I've not seen any scarfing tools in the local shops in Stockholm. What are they, and can they be found on the internet? When buying floor boards, they always come with profiles at all four edges for scarfing. Would such profiles do for boat building as well?

Erik

[PAR]

I've found the fastest way to scarf is to quickly rough in with a power plane then come back with a hand plane. I can scarf a plank in the time it usually takes to setup a router jig.

Most scarffing is on a single plank or plywood edge. If multiple scarfs are necessary for the day, then it pays to set up a jig.

http://www.messing-about.com/photopost/data/500/619ScarfJig-med.jpg

This is a jig I use for making long scarfs, though it works on short ones too. It's very simple, has no moving parts and clamping isn't obstructed by the jig. It's not much more then a couple of 2x6's attached to the frame of a work bench. With a 7 1/4" circular saw, you get 10:1 on 1/4" plywood, 6.6:1 on 3/8" and 5:1 on 1/2".

There are several types of router jigs, but most I don't like because of setup time, clamping issues and actual bit in the work time as you plow through lots of waste material.

Maybe one day I'll find a way to swing a 10" blade in a similar rig as above. This would make 13.6:1 scarfs on 1/4", 9:1 on 3/8" and 6.8:1 on 1/2".

Honestly, unless you have a bunch to do at once, with just a little practice, you'll find a power plane, belt sander, sharp chisel and hand plane, the best tools to make up a scarf.

The joint can be intimidating, but after just a few, you'll be making good scarfs. If using epoxy to join the pieces then you don't have to be especially precise, in fact it's better if you're not. On brightly finished work, you should have some practice under your belt, before you sacrifice good lumber to the attempt.

[philSweet]

If I understand the build method correctly, you're going to use planks to get a fair hull shape, then apply two layers of ply over this. I would not scarf the plywood. The most important part of getting the skins on is to avoid voids, and smaller peices will be easier to install than larger ones. One option is to install all the sheets (one layer), then putty all the joints, then plane out a 3 inch by 2 mm dado and lay in one layer of 10 oz glass tape. the main advantage of this is it can all be done at one time rather than fiddling with each peice as you go. The putty and tape do a good job of preventing water from migrating along the joints.

At the risk of beating a dead horse, I don't think $500/mo. is going to get this boat built. $500/mo. isn't even enough to maintain the boat; so at some point it will be falling apart faster than you're building it. I recently planned out a build of a 38 foot plywood double-ender with an 18,000 pound displacement. I figured $400/ day out of pocket for 18 months; then figured it would have no resale value when completed. This didn't make much sense when I can trick out a Pacific Seacraft 37 for $110,000 and have a boat I can sell for $110,000. So in the end, I rebuilt an older boat which I bought six months ago (not a Seacraft), and I'm going cruising in about 10 days.

[erik818]

Thank you Par,
I'll arrange a jig similar to yours. It seems like a stright-forward solution.
Erik

[ancient kayaker]

Par, I could not open the picture of your jig, but I am interested in it as I have not been able to make decent scarfs with a regular hand-held power saw.

I have had a lot of success for repetitive scarfing of stringers using this jig for a miter saw. The jig is just a ply plate with a fixed guide and a 2nd moveable guide held by a wingnut that is set to the thickness of the wood. The blade is rotated to the desired angle. I used 7 deg, about 8:1. Once a cut is made the same angle must be used with the jig. I use a spring clamp to prevent the blade sucking the wood in as it cuts, that ensures an accurate cut. The scarfs do not need any further work before gluing.

Because it takes care of alignment and clamping it is very fast as well as accurate. However, it only does one at a time.

As shown it is only good up to about 1/2 x 1 inch because my saw is only 7-1/4 but if you are blessed with a 12 incher or a radial you can go bigger.

[erik818]

I'll help with Par's picture. I couldn't open i directly either but it was possible to follow the link in steps to reach it.
Erik

[ancient kayaker]

Thanks Erik! I remember that idea of Par's from another thread.

I tried it a couple of years back. It worked, but I was trying to scarf cheap 1/8 ply at the time. I had problems with the feather edge tearing and it was difficult to get a straight cut because the thin ply kept springing up in the middle of the cut, so I changed to a router/jig method. I have learned a lot since then; now I use proper marine ply. I also realized my saw bearings were worn beyond redemption. Mea Culpa.

As I now have a lovely thin-kerf blade and a new saw with ball-bearings I must try it again. Thanks for the idea Par, and the reminder!

[Boston]

looks dangerous
my old man had a jig for about a hundred pound Rockwell ancient router he swore by
was a simple flat plate of steal ( about another hundred pounds )
with two adjustable legs on it
the legs went on the high side of the cut and you adjusted em based on the thickness of the wood
once set
you just place the wood in the thing
bolt it in
and flip the router to airplane mode
would plow out a perfect joint
it even allows for a slight hook based on the angle of attack at the leading edge if you wanted one
my grand Dad hated the thing
and argued endlessly it was a piss pore excuse for craftsmanship
it was like alstar wrestling whenever they were in the boat house together
I could draw it for you if you want to see it

[ancient kayaker]

You confused me, Boston. Which jig looks dangerous? Par's is just a circular saw doing what a circular saw does best, and mine is just a miter saw ditto ...

Your Da's jig sounds neat; there are several around that use tubes as guides and work well by all accounts if you have the space and money. They have to be metal though; wood is not stiff enough to keep straight over a long distance. What I'd really like though is a video of your Dad and Granddad ...

[Boston]

you mean a video of em strangling each other

you should have tried being the kid in the middle
when Robby was in the shop you had best do it his way
when pops was working it was tow the line or tan your hide
take your pick it wasnt pretty

shoulda been there when my brother sliced the cord off Pops ww11 skill saw

[PAR]

Clamping is always an issue with a scarffing jig. With my jig, the blade turns and helps hold the lumber down. A sacrificial piece of plywood over the cut will make the edges clean and hold an unruly piece. I also use a vacuum table on full sheets.

Boston, your grand dad is right, craftsmanship is faster and more rewarding too.

[Boston]

well Par you're gonna have me beet on joining ply any day
I never really worked in the stuff much
would love to see the vacuum table

the kinda scarf joint we used was more like a hook scarf with out the hook
at least in the planking
we never brought it to a point but always kinda reverse cut the ends
if you leave a little meat there it keeps it from splitting
course we were dealing with 4/4 and up material pretty much all the time
ceder
so it was easy to chisel and clean up the birds mouth with a hand saw
least thats what Robby would do

Pops would take the planking and clamp it to the bench with a dog and wedge
then bolt the template down over the end of the plank and go to town
pissed off Robby no end when it got everything covered in dust
there would be a sacrifisial piece on the end were the template clamped to the table
Ill have to make you a drawing Mr Kayaker

[ancient kayaker]

Boston: please; sounds interesting.

Par: the vacuum table sounds like a good idea, I thought about it but so far haven't gone any further.

[Ilan Voyager]

A vacuum table is very useful and very easy to make. If I remember well there are the drawings of one in the Epoxyworks of West System. A little trick, use MDO as it's not porous at all with a very hard phenolic surface, and make at the perimeter with a router a 1/2 inch wide by a 1/4 deep line. Fill it with a liquid rubber like Thokiol or a very cheap polyurethane compound for filling the cracks in concrete like the Pennsylvania. It must remain slightly tacky, so the high quality polyus like the 3200 are just not good. Sand it to remain proud only of a 1/500 inch. It's too small to affect the precision of the scarf but that helps a lot the vacuum pump as you have a seal.

Car air conditioning compressors make good vacuum pumps for this kind of job (for more serious work a true vacuum pump is better, and with Ebay you'll find at any price) Venturi systems look cheap but have no good efficiency (about only 25-30%) and end to kill the air compressor.

In my shipyard as the fishing boats were made with 2 to 3 plies of marine plywood all scarfed, we used a modified Makita 8 inch with ball and roller bearings each side of the blade, the Makita was sliding on tracks and had a air cooling of the blade. Very precise and very fast, a 8 feet long scarf in a 9mm plywood was made in less that 3 minutes. With a good protection the system is very secure. In France you don't try to play with security in a shop, the fines are dissuasive...and you may go in jail.

For the other scarfs made "flying" we used another 7 inches Makita with a scarffer always modified to have ball bearings each side of the blade. If you're interested by this easy modification I'll make a rough drawing.

The saw must have a fast engine, and I've found that it's better to use cheap 40 carbure teeth blades and change them often. The glue lines in marine plywoods are killers. I think that the routers are dangerous and too slow.

Here I use the 7 1/4 Irving blade made in NZ sold at 125 pesos, about 12 bucks. It cuts also the fiberglass very well...

[Ilan Voyager]

I've tried to avoid scarfing but found that plywood panels won't bend uniformly unless they are scarfed. Still I'd like an easier way to scarf than to plane and sand a stack of plywood sheet to get the 8:1 or 10:1 edges. (Last time 6:1 had to suffice.)

I've not seen any scarfing tools in the local shops in Stockholm. What are they, and can they be found on the internet? When buying floor boards, they always come with profiles at all four edges for scarfing. Would such profiles do for boat building as well?

Erik

The profiles of the floor boards do not have to cope with high stresses nor bending issues. The lone good way is to scarf 6/1 is a mini with epoxy if you won't bend the ply. 8/1 is the good ratio with epoxy; if highly stressed the plywood will break rather than the scarf itself. That means that all the stresses are handled through the scarf until the ultimate strength of the wood.

Another advantage of scarfs is that do not develop cracks in the joint as the other systems, because there no concentration of stresses or hard points, or solutions of continuity. And do not hope that a 10 oz cloth will save the situation if your structure works at the maximum of its safe possibilities.

[ancient kayaker]

Does the vacuum have to be that good? I was planning to use my shop vac; 1 psi is 144 bl/sq ft which is a lot of force over a 4 ft wide ply sheet.

[Ilan Voyager]

Does the vacuum have to be that good? I was planning to use my shop vac; 1 psi is 144 bl/sq ft which is a lot of force over a 4 ft wide ply sheet.

No the vacuum has not to be too high, just enough to hold the panel and to keep it FLAT, not so easy with some cheap plywoods...it's why I use the trick of the slightly tacky polyurethane compound; with a very moderate vacuum the panel can't slide even on a MDO.

For short vacuum uses you can use a shop vac but only if you add a bleeder( a controlled leak) that limit the vacuum and permits to some fresh air to cool the shop vac. These animals suck an enormous volume of air, begin to scream over-revving and die prematurely by overheating or explosion of the ball bearings. Also the noise is horrible.

For short uses you have venturis you can install on the air compressor for about 50 bucks, so the use of a good vac shop, with the risk to kill it, it's no worth the saving. It's finally expensive being too greedy....

For less than 150 bucks in Ebay you'll get a small vacuum pump that will last forever and silent. It's not infusion, but just holding plywood for cutting or gluing. A complete kit cost about 400 bucks and has many uses as gluing plywood, making sandwich or honeycomb panels, veneering etc...Epoxy glue needs very little pressure.

The use of good meranti BS 1088 plywood is finally cheaper than a crappy fir plywood. It's flat with no voids in inner plies, or knots, holes or splits on the faces. Well smooth sanded so finishing it is a pleasure, nothing to fill. It can be cut, routed, scarffed and machined without chipping. And bends smoothly...

More, the consumption of resin is lower than on fir, it doesn't check so fiberglass covering is not needed in most applications, and it's stronger so a 1/2 replaces a 5/8 AC Fir.

Make the calculations in materials and work...you'll be surprised to find that a AC fir ends to be more expensive that a BS 1088 Meranti.

[ancient kayaker]

...you can use a shop vac but only if you add a bleeder( a controlled leak) that limit the vacuum

I had planned to run a large vac line to the vac table with a smaller hose to a dust chute on the saw which would proved the bypass as you suggest. Even my cheap little wet-and-dry vac will pull at least 2 psi, I used it to drain an underground water pipe last month; sucked it dry in seconds.

The use of good meranti BS 1088 plywood is finally cheaper than a crappy fir plywood ...

Agreed, in spades! And a thing of beauty is a joy for a damn long time if not forever.

[Ilan Voyager]

The best is to try as it's not dangerous nor expensive. I'm afraid that will be impossible to get vacuum and to suck the dust in same time with the same vac cleaner...It's curious but I've used very good fir plywood 30 years ago, what happened that all these plies have disappeared?

[erik818]

Any plywood from a respectable manufacturer is done to a specification of some kind. The questions is which. A way to find out is to ask, which I haven't done yet but intend to do before I use the plywood for any serious boat building.

I've found that construction fir plywood is crappy. "Furniture grade plywood" with pine at the surface and fir in the middle seems to behave very well on the other hand, and is available in several shops in the neighbourhood. All fir plywoods are not equal and BS 1088 possibly isn't the only spec for a usable plywood. "Furniture grade plywood" is much more expensive than construction plywood for the same dimension, but for the same strength I think the cost is almost the same. I haven't compared prices with BS 1088.

Erik

[ancient kayaker]

Construction fir plywood is crappy but fairly weatherproof, and it's about the only softwaood ply you can get from most lumber suppliers. We can get Baltic Birch ply here, lovely stuff but heavy; it's so good I planed the edge at a fine angle to expose the veneers as a decorative feature on one boat. It comes in 5 x 5 sheets insted of the usual 4 x 8 which is handy sometimes.

BS1088 isn't all it's cracked up to be at times I have sometimes found, but it's usually good. There's also BS6566, a bit cheaper with thinner outer veneers, and BS1088 Lloyds register approved, which is a bit over the top for most of us.

[Boston]

Kayaker's got a good point about not all plywood's, that may be rated the same, being up to snuff
you have to really watch what you buy
the mill's around here received huge fines for "mislabeling" there products as exterior when they had used interior glues and for not compressing the product during the manufacturing process sufficiently to meet industry standards
they accepted the fines and went on manufacturing substandard products

they were later found guilty of conspiring to sell fraudulently advertised products
http://papers.ssrn.com/sol3/Delivery.cfm/UVA-BP-0375.pdf?abstractid=907802&mirid=1

they were also found to be fixing prices
http://stage.homechannelnews.com/story.aspx?id=67661&menuid=305

and sued in a class action
http://www.bingham.com/PracticeMatter.aspx?PracticeID=223

I wont launch into a monologue on the use of ply in marine construction
Ild be frog marched outa here in a heartbeat
but I will second our Mr Kayaker with a song and dance you might remember

happy building
and clear sailing
B

[Ilan Voyager]

Thanks Boston for the very interesting infos you have given to us. A bit frightening....

About furniture plywood, no it can't be used in boat simply because of the glue; formol urea which is clear, and do not resist permanent humidity.

The BS 6566 has its place inside the hull, and in small boats where the stresses are low compared to the thickness. But in "big" boat it's better to use the BS 1088 or the Finlandese or Russian equivalent because the BS 6566 admits small voids in the inner plies, and the outer plies lack of thickness.

The BS (British Standard) is the best known in the USA, but there are a lot of national norms, civilian and military. The Russian norms are largely equivalent to the BS1088, and I'm happy of their commercial success with the baltic ply because they have worked very hard to get a very good product.

I bought many times pine and birch boat building ply to the Russians and I've never had the smallest problem even of the middle of the turmoil of the Gorbatcheff era. The quality is astounding. The ply imported in the States in in 5*5 because this size is handful in furniture and plywoods easier to fabricate so the price is kept fair. But you can get 12*6 (3.10m*1.53m) and 8*4 sheets.

Birch is heavy but very, very strong. If you calculate the structure in function of the characteristics of the birch plywood and better make a monocoque structure of 2 or 3 layers of plywood, vacuum epoxy glued, and all scarffed plus fiberglass you get a resilient structure that only can be beaten by high cost composites... but at 1/2 to 1/3 of the price.

To give you an idea of the strength the bottom of a fast pro fishing 40 feet boat, 25 knots @ heavy displacement (9 metric tons), Det Norske Veritas standards with a big safety margin is 1 1/2 inch (18mm) made of 3 plies of 6mm plus 2*6oz glass outside and 1*6oz inside. The weight@ sq foot is about one half of the same strength structure in monolithic fiberglass and far more rigid!
The oldest boat is 21 years old now, fishing every day, and is as pristine as the day of the launching. The boat is good to work 20 years more.

The method is very interesting because it doesn't need high tech tooling nor expensive materials at 100 US$ a pound.

Make a search in the Web about the Mosquito bomber and fighter plane, made by simple furniture shops during the WWII in Balsa and Birch plywood and you'll understand the possibilities of wood structures. With epoxies these structures are at the hand of the common boatbuilder.

Ok, carbone and kevlar, Nomex, infusion, post cure oven permit to get lighter boats but the technological level and the price are not the same...

To conclude you can make a crude test of a plywood to estimate its quality.
1-Buy a sheet and count the number of inner plies 7 for an 1/2" and quality and thickness 1/20" mini of the outside plies (knots, discoloration, splits etc...)
1-line glues must be dark brown (phenol)
2-cut the plywood in squares of 4*4 inches and look for voids and other defects.
3-with a chisel try to separate the plies: the glue lines must be stronger than the wood itself.
4-take ten squares and boil them 1 hour. Delamination while boiling is forbidden.
5-Destroy one boiled square with a chisel trying to separate the plies: the glue lines must be stronger than the wood itself at least at 80%.
6-take 2 squares and make it dry totally in a oven at 120 celsius degrees. Delamination while drying is forbidden.
7-Destroy one dried square with a chisel trying to separate the plies: the glue lines must be stronger than the wood itself at least at 70%.
8-meantime reboil one hour more the remaining 7 squares.
9-Destroy one re-boiled square with a chisel trying to separate the plies: the glue lines must be stronger than the wood itself at least at 70%.
10-take 2 re-boiled squares and make it dry totally in a oven at 120 celsius degrees. Delamination while drying is forbidden.
11-Destroy one re-boiled and dried square with a chisel trying to separate the plies: the glue lines must be stronger than the wood itself at least at 60 to 70%.
12-Clean the kitchen and buy flowers for you wife. Don't forget to open the windows because of the smell.

You bought this 1/2 inch at Home Depot for 29.99 bucks? Buy all the stock, you've got marine plywood for the price of crap.That happens, a friend of mine bought 120 sheets found in a Castorama (Home Depot similar) in Brittany France...mistake of a provider? The miraculous of miracles is that happens sometimes...

Seems stupid but I have done that on every new brand of plywood, even from a renowned provider. Better to destroy one sheet than to have a failure on a full size boat. There are also simple tests of bending and resistance.

Next time I can give you simple tests for evaluating the compatibility of the plywood with the epoxy, and the quality of the epoxy itself.

[erik818]

A comment about "furnitue plywood". The label put on the plywood at the store doesn't say anything about the glue used or the quality of the inner plys. I think the label focus on the cosmetic qualities. All "furniture grade" plywoods I've seen in my part of Stockholm have thin plys and are specified to have Water Boil Proof glue. This I have verifyed by boiling and splitting test samples of the plywood I used.

Thank you Ilan for tests you suggest. Plywood for boat building is a very small market and it is not available at many places. Testing the plywood that is locally available seems better than to order plywood according to a British Standard and hope that what I get meets the spec.

Erik

[ancient kayaker]

The Mosquito plane was a remarkable creation with an amazing performance for its time. It was a bit of a problem when used in the tropics, I have heard, due to local fungi and insects which found it delicious!

[Ilan Voyager]

Erik, you're wellcome. You're in Sweden, a country of high standards, and making some of the finest plywoods of the world,it won't be very difficult to get marine equivalent plywood. I've worked in a shipyard of Malmo in the seventies, and the plywood for concrete molds was good enough for long lasting fishing boats... You're a lucky man.

The plywood I find in Mexico is not worth to start a fire...Everything has to be imported at great expense after a fight with the Customs, and its corruption. French also are lucky, as the norms CTB are high and there are very good plywood makers, among the best of the world ( Joubert and Toubois are well known).

The Mosquitos were glued with casein, a protein from milk. You can imagine the feast for fungii and insects with a hamburger Royal of untreated birch plywood, balsa and cheese tasting glue, topped with oil paint...miam, miam...the king food for wood destroyers. But it remains that this plane made in war time by furniture shops and piano makers, with Canadian plywood of veneers hand ironed by women, was able of 755 km/h and was one of the safest and strongest planes of WWII. I knew one english naval engineer, Mosquito pilot, who told me they came back once from Germany with 30 shots of 20mm cannon in the tail, and a few dozens of 1/2" machine gun holes in the fuselage and the wings... good fail safe structure demonstration.

Now with epoxy glues and polyurethane compounds, plus treatments: no match...you'll get better quality, and best; within the skills of a home boat builder.

[ancient kayaker]

Many of the Mozzies were stripped to cut weight and sent over on reconnaisance flights. They were too fast to catch, at least until the Reich had jets. Lots of tall tales about the good old Mozzie.

[Boston]

I was actually talking about exterior grades used in the housing industry
they are worth about kindling when you get down to it
and that is about the extent of my knowhow on ply
as I said we always used some variation of plank on frame
dam its been a long time
the Mitsubishi Zero was also originally plywood and its still a hell of a plane
it was later built with metal skins but I think it remained wood framed through out the war
I could be dead wrong about that though
haven't been to the Smithsonian in ages
anyway that blurb about testing ply was perfect and I saved it so thanks
oh
and the ply that I was specifically relating to wasnt a marine grade ply at all but some oriented strand board I swore off when I first saw the stuff
so I got a bang out of there being sued over it being so bad
thank the Gods I didn't build anything out of it
regards
B

[ancient kayaker]

Speaking of the Mosquito and Mitsubishi Zero, wasn't there a mostly wood North Korean plane that caused the US pilots a bit of grief, partly because it was hard to spot on radar.

[Ilan Voyager]

Boston, you're welcome. I'm happy that the Testing Plywood Ole Smelly Recipe was useful for someone.

One of the purpose of a forum is to share experience, so I think that I'll start a thread about plywood, wood and resins, giving the information on how to test them for marine use, and I hope that some will add their salt grains.

There are a lot of myths about polyester and epoxy, and I see now companies marketing "cheap" epoxy resins claimed as of marine use (and there are some not truly naval) and others selling at too high price rather common resins, because of the brand written on the cans...

I did not know about the North Korean plane, maybe its was a copy of the Yak 2, made in plywood by the Russians in WWII. The Mosquito, because of its qualities, partly due to the wood construction, has been used in a surprising variety of difficult missions and it's true that it's only at the end of WWII that the German jets ME 262 were able to intercept the Mosquitos. A search in Internet gives a great deal of infos.

About the use of wood as a successful engineering material, there are a lot of examples as the German S boats, some Newick trimarans, a lot of small planes, a lot of yachts and also in building.

A look at the APA association, the US Forest Industry Laboratory and other internet sites is very instructive. It's unhappy that wood is linked to antiquated designs, sometimes very poorly and dangerously engineered, with lots of bright varnish. Anybody can christen himself yacht designer and sell plans...

For the home builder wood/epoxy/fibers composite is a material which needs common tooling, moderate skills, and very forgiving. It permits to work at its own pace, and best, you can get very good results, for a good price. I do not mean cheap, boats are always expensive, but lets say less expensive.

[PAR]

This is a highly over rated aircraft. It was quick, particularly unloaded carrying cameras. It could muster 390+ MPH which beat the ME-109, pissing off the German pilots that chased it. Then the FW-190 showed up and all bets were off, because it could get over 400 MPH with the last version capable of almost 440 MPH.

Against the ME-109 it could out run one in level flight, but if the ME-109 was one of the later variants like the E-7 and flown by a good pilot (most were dead by that point of the war) then the Mosquito driver was in for a surprise.

These were the only two German aircraft capable of giving the Mosquito a run for it's money, until the ME-163 and 262 showed up. In fact the FW-154 was the German attempt to make a Mosquito. Their result was slightly faster, but they couldn't keep it in production because of the glue used to bond the laminates (the glue factory kept getting bombed) so only a handful ever were built.

Compared to American aircraft of the era, it was pretty good, but we had several that could chew it up and spit it out their tail pipes. Fortunately, we were on the same side, as more then one of our aircraft had British engines (or copies) in them, of which they owed lots of they're stellar performance.

It's the wise builder that runs occasional tests on product combinations. I've tested several glues on different species of wood, subjected them to different loading situations and done so repeatedly, to insure reasonable accuracy.

The boil test is a good one, though I don't know many that will anchor their boat over active, underwater volcanoes. It does somewhat simulate long term submersion. I find wet/dry cycling a more informative test for trailer boats.

Saturation tests for coatings, like paint, epoxy etc. can offer some insight to what works better in your climate.

Ilan, though we usually agree on most things, I've yet to see a design that was compromised in any fashion by having excessive varnish work( :rolleyes: ). Of course I have seen some pretty poorly designed boats, from several angles of approach, engineering, hull form, rig selection, lack of building experience (a major issue, particularly with the new low cost and free software available now). Some designs can't be built as the plans show, simply because the designer didn't understand how much effort it would take, to bend in a piece of material to the shapes they'd drawn. Identifying these designs is very difficult for the novice, which I consider a very dangerous thing.

[Ilan Voyager]

Hi, Par
The Mosquito has its legend as the Spitfire. Remains that it was a remarkable achievement for a plane mainly made with simple non strategic materials by furniture and piano makers on concrete molds with steel straps to get the bonding pressure...Remains also its capacity of survival. That shows that wood is a good material with no high tech technics.

The Testing Plywood Ole Smelly Recipe is similar to the Italian RINA tests, it represents crudely the stresses induced in the glue joints by the dilatation and contraction of the wood, and also an accelerated aging of the glue itself. It permits also to control the quality of the inner plies. At least it permits to eliminate the badly made plywoods or/and with not waterproof glues. The test is simple and costs almost nothing.

I would be interested if the USA made MDOs are able to withstand this test as they look interesting for some parts in boatbuilding. I've tried with a Chilean MDO sold here and the auraco or radiata pine swelled so much that no glue in the world would withstand the stresses. Also these pines have not any durability, nor strength. Good for furniture, not for boats.

The tests I want to purpose for epoxies are principally informative. Saturation depth is not the best test, as any epox with solvent will soak wood. More interesting are adhesion, peeling, brittleness and water absorption. All tests easy to make.

I have seen ads for epoxies (specially a 1/1 mix resin-hardener- already suspicious as generally the 1/1 epoxies are not the best ones in boatbuilding-, which has poor elongation, and soaks as much water as a polyester) rather bothering because claimed as of marine use and I'm sure that a lot of people will try to save 5 bucks a gallon buying it... On the other hand some companies are selling at 80 $/gallon resins which are not better that the 45$/gallon resin sold by some honest guys.

About plans many are properly terrifying for a trained naval engineer. A lot are totally outdated, as if you wanted to remake a Ford T or 1908 Biplan, many have no idea of decent scantlings, worst you won't find any detail of scantlings, or use over-complicated or unsure methods, a few are totally crap/junk. In old good times the so called designers would be exposed to the infuriated customers provided with a good supply of rotten eggs and tomatoes :p

Yes it's too easy to produce a drawing with some freeware and to sell it, with a lot of bla-bla. I have just seen in internet the drawings of a multichine 7.5 meters trimaran with 4mm plywood hulls!!! Mamma mia!!!:mad:

[ancient kayaker]

The de Havilland Mosquito was designed originally as a fast, unarmed light bomber that could outrun fighters. It had an remarkable range and was also a highly effective night fighter with its load-carrying and loitering capability. However, there were quite a few legendary planes during WW2, British, German, Russian, US and so forth. It's not necessary to knock a legend in order to recognize another.

3 mm ply on a (fairly) big trimaran! Sounds risky. but some boats are built for speed, some for durability, then there's comfort, endurance, single handling ... hope it never hits a log.

That said, ply strength can be amazing; I built an ama for a sailing canoe using 3 mm door skin, that's really cheap luan ply, $10 for a 4 x 8 sheet. Lousy performance, but when it came to discard it, I wanted to see what punishment it could take. Think of a box, 9 inches (23 cm) square, 7 ft (2.1 m) long, pointy ends, two very light ply inner frames, no epoxy (Gorilla Glue), no glass (3/8" or 1 cm sq Poplar chine logs), a brick at each end to support it. I stood in the middle, no effect. Jumped up and down, nothing. Got my buddy to stand on it with me, about 440 lb/200 kg, didn't even creak! We even stamped on it (not enough room to jump) and this was crap ply! Swung a heafty axe at it; punched straight through the skin of course but bounced off the corners. To destroy the damn thing I had to cut it up with a saw.

Back to scarfing;

I made a series of test joints a couple of years back. varied the scarfing angle from 90 deg (butt joint) to 6:1. Then broke 'em. Only the test pieces with butt joints broke at the joints. Every joint with a scarf ratio 2:1 or better broke across the wood. I compared the strength of the butt joints (epoxied) to the wood, all fell in the range 55% to 70%. I did some more butt jointed pieces but added an epoxy fillet (no glass or fiber) to one side, about 30% of the ply's thickness, then broke them. This time they all broke across the wood except for one that turned out to be a dry joint.

As a result of that experiment, I concluded that the only reason for long scarf joints in plywood is, they are less inclined to slide apart when clamped. I now use 4:1 in ply, but I increase that to 6:1 for solid wood because the end grain can suck some of the glue out of the joint. I think the usually recommended ratios of 12:1 or even 20:1 is a hangover from the days before decent adhesives, when fasteners were used and the only thing inside the joint was sealer.

[Ilan Voyager]

The 7.5 meters trimaran looks like a daysailing one with possibilities of coastal cruising. The hulls are 4 mm MULTICHINES. That's a lot of pieces to cut accurately, joints to make, smooth and seal, and surely an dense frame of bulkheads and stringers to build. And nope, the skins are too thin.

I think that a 6mm, 2 plies of 3 mm, cylinder mold or even ployed or stress-formed will be stronger, with better hydrodynamics, and easier to make for a trimaran of same program. Kurt Hughes has some in his catalog, the Gougeon stressform tris were interesting, and the old original drawings of the Tornado in ployed plywood are avalaible at the Tornado Association for a few bucks. More: in Gougeon Bros book on boat construction (a bible) has the drawings in chapter 24 on tortured plywood the drawings of the panels for a 28 feet class C trimaran. A good base to start.

Plywood can be indecently strong. When I discarded the hulls of my first 18m2 sport catamaran like you I ended to use a chain saw. The last one made almost 20 years ago, in 3mm okoume plywood with 4oz glass cloth, sails always, but the owner has reduced the sail.

A 18m2 sail on a 30 feet wing mast on a 200 pounds 18 feet cat is a bit hard to dominate alone where you're softened by age...It was a wild beast. A 200 pounds skipper, able to run 5 miles singing and to lift 200 pounds smiling was required in a breeze over 10 knots. That gives an idea of the stresses held by this cat.

The Class C Yellow Pages (34 knots max, 12 knots in a 4 knots wind with rigid wing) used 3 mm okoume ply and stiffeners about 1/2 inch...

Some french aerobatic planes were all wood and cloth, and designed to stand 20 G stresses...So on a yacht no problem.

You're wright about the scarfs, the 12 to 20/1 are when glues were no better that boiled floor. The 8/1 has been fixed to give safety margin and to work on both hard and soft woods. Also for a smooth bending with no hard spots. On a deck a 4/1 or 6/1 is enough it depends on the wood used in the plywood.

[PAR]

I think most of the longer scarf ratios were to insure a fair bend, rather then a hard spot at a short glue line. On free standing masts, I'll use longer scarf ratios also on pieces that I want quick, but fair bend, other wise I'll use 6 or 8 to 1. The old school lapstrake builders used 8:1 on mechanically fastened planking and after many years of repairing these types, the method works very well and bend fair.

I didn't mean to suggest the Mosquito wasn't a cool ship, it was, but not as much as the legend suggests. The same can be said of the Spitfire, who's wing (tip) is highly touted as being the best. In fact, testing has concluded it wasn't. Every other aircraft of the era and since has ignored the benefit of less tip vortice generation in favor of slightly more drag, but much more effective area and lift at the tip, provided by a square plan form. The same is true of yacht appendages. Yes, the elliptical tip does generate less tip turbulence, but this benefit is offset, by the advantages of more lift (square tip) at the end of the lever arm. The bulb verses a fin keel debate have similar arguments and benefit trade offs.

When you look at the physical properties of well made plywood, it's difficult to rival it's attributes, especially in small craft. You have to go fairly high tech to beat it and the associated costs may be grossly out of scale in comparison. Repeated designs (including aircraft) have born this out.

[Ilan Voyager]

I agree with you, Par on a mast to get a fair bending better to go to 12 to 1. Scarfs on battens around the 1 to 1 1/2 inch are a breeze with a good circular saw and a jig (many designs). Mine are made with 1/4 thick 2 inches wide aluminum angles and incorporated press. Very simple and cheap with excellent results. Looks like a miter box.

At the risk to look like an old guy saying always the same thing, for plywood under 3/8 a Scarffer from Gougeon Bros make life simple. On thicker plies, you'll get a good feather edge, the most difficult part of scarfing.

No everybody is a king of the planer, able to shave the hair of a frog without damaging the delicate skin of this animal... A guide for a planer is not a hard project, but as hard glue lines have tendency to dull the planer blades fast and I'm very lazy so I prefer the circular saw, with "disposable" disc blade. The lone con is the vibrations of the blade and it's solved by adding a sealed ball or roller bearing on the other side, so the blade spins on bearings each side. That saves the main ball bearing of premature death.

I keep my precious planer blades (imagine the price imported from the states with a Fedex shipping of about 70 bucks) for the nice job on clean wood. Basic matter of taste, not worth of a discussion, as several methods are as valuable.

I agree totally with the conclusion, I'll add that the ratio price/efficiency is unbeatable with epoxies techniques and the last but not the least it has no hard smell and better: it is prefinished!

Work with polyester and breathe the delicate styrene fumes, that disinfect the lungs...listen with the impassibility of a zen monk to your neighbors complaining about the horrible smell that stinks up all the street...Smile to the city officials and policemen...Count the number of hard work hours and of unbearable itching while trying desperately to finish a polyester sandwich on male mold that looks like a battlefield after heavy bombing...the sanding of the inside of the polyester hull, ahhhh, what a sweet pleasure.:D I suspect that polyester amateurs do love also big women in black leather with harsh voices and whip at the hand...

[PAR]

The scarfer jig I show in an earlier post is now primarily used for those fast, thin plywood scarfs. Slap down the stock, toss a couple of drywall screws in it, maybe some vacuum or other clamping feature, fire up the circular saw, one quick pass and done. No attaching anything to anything (scarfer attachment) or fiddling around with setting up a router, just plow and go. With epoxy the feather edge isn't a concern, nor is neatness.

Ilan, what's wrong with loving big women in black leather with harsh voices and whip at the hand. Some of my best friends own whips and have enjoyed using it on me. Unfortunately, many have been clients and I couldn't show my pleasure as much as I'd have liked, without them expecting some sort of discount for services rendered . . .

[ancient kayaker]

Thanks for explaining why longer scarfs might sometimes be called for. I haven't needed joints near sharp bends yet, in fact my boats to date have scarcely stressed the ply or lumber during construction. I'll bear it in mind.

I'm always willing to learn. Speaking of learning, perhaps you can explain about the women in black leather as I've led a sheltered life.

[PAR]

I have a video I can send you . . .

[Ilan Voyager]

:eek: :) :p :D I can't see the screen because of the tears of laughing... Nothing wrong, all tastes are in nature...I have a tendency to whip the customers...some seem very happy.

[PAR]

But it's a reallllly good video . . .

[ancient kayaker]

Now I'm not a professional and I hesitate to offer advise but Par, it sounds like Ilan has a very good class of client. Maybe a move to Mexico ...

[Boston]

The old school lapstrake builders used 8:1
on a mast to get a fair bending better to go to 12 to 1

old Robby would be smiling, but I can hear it now
depends on the wood
for a fair bend in a dam hard wood you need to go with a higher ratio scarf
for a fair bend in a soft wood bla bla bla

Ilan feel free to start that thread and keep me posted
I wont be posting much but Ill be reading
I dont know **** about ply
nor do I know Jack about glue
wood and bronze I got down but I am not to slick with epoxies
thanks B

[Guest62110524]

Thanks Boston for the very interesting infos you have given to us. A bit frightening....

About furniture plywood, no it can't be used in boat simply because of the glue; formol urea which is clear, and do not resist permanent humidity.

The BS 6566 has its place inside the hull, and in small boats where the stresses are low compared to the thickness. But in "big" boat it's better to use the BS 1088 or the Finlandese or Russian equivalent because the BS 6566 admits small voids in the inner plies, and the outer plies lack of thickness.

The BS (British Standard) is the best known in the USA, but there are a lot of national norms, civilian and military. The Russian norms are largely equivalent to the BS1088, and I'm happy of their commercial success with the baltic ply because they have worked very hard to get a very good product.

I bought many times pine and birch boat building ply to the Russians and I've never had the smallest problem even of the middle of the turmoil of the Gorbatcheff era. The quality is astounding. The ply imported in the States in in 5*5 because this size is handful in furniture and plywoods easier to fabricate so the price is kept fair. But you can get 12*6 (3.10m*1.53m) and 8*4 sheets.

Birch is heavy but very, very strong. If you calculate the structure in function of the characteristics of the birch plywood and better make a monocoque structure of 2 or 3 layers of plywood, vacuum epoxy glued, and all scarffed plus fiberglass you get a resilient structure that only can be beaten by high cost composites... but at 1/2 to 1/3 of the price.

To give you an idea of the strength the bottom of a fast pro fishing 40 feet boat, 25 knots @ heavy displacement (9 metric tons), Det Norske Veritas standards with a big safety margin is 1 1/2 inch (18mm) made of 3 plies of 6mm plus 2*6oz glass outside and 1*6oz inside. The weight@ sq foot is about one half of the same strength structure in monolithic fiberglass and far more rigid!
The oldest boat is 21 years old now, fishing every day, and is as pristine as the day of the launching. The boat is good to work 20 years more.

The method is very interesting because it doesn't need high tech tooling nor expensive materials at 100 US$ a pound.

Make a search in the Web about the Mosquito bomber and fighter plane, made by simple furniture shops during the WWII in Balsa and Birch plywood and you'll understand the possibilities of wood structures. With epoxies these structures are at the hand of the common boatbuilder.

Ok, carbone and kevlar, Nomex, infusion, post cure oven permit to get lighter boats but the technological level and the price are not the same...

To conclude you can make a crude test of a plywood to estimate its quality.
1-Buy a sheet and count the number of inner plies 7 for an 1/2" and quality and thickness 1/20" mini of the outside plies (knots, discoloration, splits etc...)
1-line glues must be dark brown (phenol)
2-cut the plywood in squares of 4*4 inches and look for voids and other defects.
3-with a chisel try to separate the plies: the glue lines must be stronger than the wood itself.
4-take ten squares and boil them 1 hour. Delamination while boiling is forbidden.
5-Destroy one boiled square with a chisel trying to separate the plies: the glue lines must be stronger than the wood itself at least at 80%.
6-take 2 squares and make it dry totally in a oven at 120 celsius degrees. Delamination while drying is forbidden.
7-Destroy one dried square with a chisel trying to separate the plies: the glue lines must be stronger than the wood itself at least at 70%.
8-meantime reboil one hour more the remaining 7 squares.
9-Destroy one re-boiled square with a chisel trying to separate the plies: the glue lines must be stronger than the wood itself at least at 70%.
10-take 2 re-boiled squares and make it dry totally in a oven at 120 celsius degrees. Delamination while drying is forbidden.
11-Destroy one re-boiled and dried square with a chisel trying to separate the plies: the glue lines must be stronger than the wood itself at least at 60 to 70%.
12-Clean the kitchen and buy flowers for you wife. Don't forget to open the windows because of the smell.

You bought this 1/2 inch at Home Depot for 29.99 bucks? Buy all the stock, you've got marine plywood for the price of crap.That happens, a friend of mine bought 120 sheets found in a Castorama (Home Depot similar) in Brittany France...mistake of a provider? The miraculous of miracles is that happens sometimes...

Seems stupid but I have done that on every new brand of plywood, even from a renowned provider. Better to destroy one sheet than to have a failure on a full size boat. There are also simple tests of bending and resistance.

Next time I can give you simple tests for evaluating the compatibility of the plywood with the epoxy, and the quality of the epoxy itself.

Brilliant thanks

[Guest62110524]

thought this may be a good way for long joints, 2.4 m long. the saw is pulled along layed over a bit and dragged