crazy idea???

[terabika]

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Hello, I have a 31ft westerly longbow. She was sunk and now is up. I need a longer boat. I do not have the money so I propose to cut shiloh in two at the fullest part under the water line of the hull. at this point the water flows parrallel to the waterline. I then hope to spread her for and aft sections some ten feet and fill this space in with mutible layers of 1/4 inch plywood epoxied to eachother ( I use this because it is easier to curve thinner wood. there will be no attemptat compound curvature. SO, in profile she will have a ten foot flat section. I will glass over this with some number (I am thinking thre now)of layers of epoxy inside and out. I will use common exteior grade playwood and layer it up to a thickness of 1.5 inches to be sure it is strong enough. This should more than compensate for the voids in wood. Exterior 1/4 inch is 10 bucks a sheat, marine is 40, thats why! 1 foot of overlap inside and a scarf on the outside will ensurebonding. Any thoughts would be appreciated. Yes, it is wayyyy cheaper then buying a 41ft boat and it should be faster as its hull length to beam ratio will be thin and it will still be wayyy lighter than comparable boats. She has a 4k lb keel I will reinstall and make lower for a draft of 6 ft or so...toying with idea of retractable. thanks!

[PAR]

You'll be making a 132% adjustment to her length and I'd strongly advise you against such an endeavor. I know it seems an easy thing, but it's way beyond the scope of the average backyard guy. Not that it's to hard to accomplish, but the can of worms, you're unaware of opening, will be quite significant, likely ruining the vessel and your hopes of a 41' yacht. This can of beasties isn't the cutting, attaching new low grade plywood and cloth skin, but the balance, stability, longitudinal stiffness and a host of other issues you're unaware of and simply not easily obtainable information.

I'll let everyone else beat you up (be kind folks he's a new guy) for trying to engineer a substantial structure, one that will take you much farther from shore then you can swim back to, with the lowest grade of materials. Generally it's wise to have a strong grasp of the concepts, principles, physics, chemistry and engineering to insure a reasonable expectation of success.

How hard can it be? I bill out at over $200 per hour, take a quick guess.

[Sean Herron]

Hello...

So long as you are not buying from the police - ah - can I come to your next BBQ...

SH

[marshmat]

What PAR said.

What you propose will totally screw up the stability and hydrodynamics of the yacht. It can be, and has been, done successfully. I've seen 800ft cruise boats lengthened like this. But it's done by carefully analyzing the current structure, completely redoing all the hydrostatics and dynamics numbers, computing thousands of stresses on the joints and filler module, and then cutting, dismantling, building and finally reuniting the hull with millimetre precision. Done as you propose, you will have a huge weak region amidships that will be most likely to fail in high winds and high waves, perhaps the least desirable place to have your boat go Titanic on you.

Sorry to bash the idea so hard, but I'd rather you be alive and crowded than on the front page of a Coast Guard report.

[terabika]

Originally Posted by PAR

You'll be making a 132% adjustment to her length and I'd strongly advise you against such an endeavor. I know it seems an easy thing, but it's way beyond the scope of the average backyard guy.
GOOD THING I AM NOT THE AVERAGE BACKYARD GUY
Not that it's to hard to accomplish, but the can of worms, you're unaware of opening,
HOW DO YOU KNOW i AM UNAWARE? will be quite significant, likely ruining the vessel and your hopes of a 41' yacht. This can of beasties isn't the cutting, attaching new low grade plywood and cloth skin, but the balance, stability, longitudinal stiffness and a host of other issues you're unaware of and simply not easily obtainable information.
i HAVE RESEARCHED LATERAL RESISTANCE BALANCE ETC. IF SHE HAS A BIT OF WEATHER OR LEEE HELM I CAN ADJUST FOR THIS IN SAILS. CABINETS AND OTHER THINGS INSIDE WILL ALL BE STRUCTURALLY INTEGRATED. BOATS WERE GOING TO SEE LONG BEFORE CALCULUS. BY OVER BUILDING THE CENTER SECTION WITH PLENTY OF OVERLAP, I AM NOT CONCERNED ABOUT LONG STIFFNESS. HAVING SEEN THE SKIN OF 41 FOOT BOATS AS I HAVE REPAIRED HULLS IN THEM, I FEEL CONFIDENT I CAN MAKE SOMETHING AT LEAST AS STRONG...OBVIOUSLY, I AM NOT SO CONCERNED ABOUT WIEGHT TWIICE THE THICKNESS OF CHEAP (BUT WATER PROOF GLUED) PLY IS STRONG AS THE BIG BUCKS STUFF ACCORDING TO SEVERAL NAUTICAL ENGINEERS I QUEERIED

I'll let everyone else beat you up (be kind folks he's a new guy) for trying to engineer a substantial structure, one that will take you much farther from shore then you can swim back to, with the lowest grade of materials. Generally it's wise to have a strong grasp of the concepts, principles, physics, chemistry and engineering to insure a reasonable expectation of success.

How hard can it be? I bill out at over $200 per hour, take a quick guess.

PEOPLE SEEM TO NOT REMEMBER THEIR HISTORY ABOUT JUST WHAT TYPE OF CRAFT PEOPLE WENT SUCCESSFULLY TO SEA IN HUNDREDS OF YEARS AGO. OF COURSE, I WOULD GRADUALLY WORK HER UP TO LARGER AND LARGER SEAS NEAR SHORE AND ACTUALLLY HAVE A LIFE RAFT WITHME... CAPS ONLY FOR CLARITY, NOT SHOUTING I WAS REALLY LOOKING FOR SOME MORE PRACTICAL ADVICE ABOUT THIS (OTHER THAN DONT DO IT, IT IS BEYOND YOU), THANKS :-) tERRY

[terabika]

WANTING TO RE USE THE 4K LB KEEL THAT NOW DRAWS 4.5 FOOT, IS THERE ANY EASY ( i KNOW THERE ARE MANY EQUATIONS FOR AN EXACT ANALYSIS) "GUESTAMI" FOR HOW MUCH DEEPER SHE NEEDS TO GO TO INCREASE RIGHTING BY "Y" FT POUNDS AT 30 DEGREES LIST?.......CAPS ARE STUCK ON AND i AM AFFRAID TO TURN THEM OFF :-)

[terabika]

Originally Posted by marshmat

What PAR said.

What you propose will totally screw up the stability
HOW DO YOU KNOW THIS WHEN YOU HAVE NOT ASKED HOW MUCH DEEPER I WILL SINK THE KEEL....ANOTHER 4.5 FT DEPTH AND IT WOULD SEEM TO BE A LOTT MORE STALE
and hydrodynamics of the yacht.
YES FLOW WILL NOT BE AS SILKY SMOTH AS BEFORE BUTGUESS WHAT? i DO NOT CARE AS SHE WILL HAVE MUCH MORE HULL LENGTH AND HER BEAM TO LENGTH RATIO WILL BE BETTER THEN ANY YATCH FOR SALE I HAVE SEEN.....EVERYTHING IS A TRADEOFF
It can be, and has been, done successfully. I've seen 800ft cruise boats lengthened like this. But it's done by carefully analyzing the current structure, completely redoing all the hydrostatics
THE WATER WILL GO AROUND IT AS THE WIND PUSHES IT. A CONAINER WHICH FALLS FROM A SHIPP IS A SAILBOAT AND GOES WHERE THE WIND PUSHES IT....NO HYDROSTATICS ETC. and dynamics numbers, computing thousands of stresses on the joints and filler module, and then cutting, dismantling, building and finally reuniting the hull with millimetre precision. Done as you propose, you will have a huge weak region amidships
ALL CABINETS BERTH ETC IN THIS REGION WILL BE STRUCTURAL AND 1.5 INCHES OF THICKNESS IS WAYYYY FATTER THAN I HAVE SEEN ON MEGA YATCHS I HAVE WORKED ON that will be most likely to fail in high winds and high waves, perhaps the least desirable place to have your boat go Titanic on you.

Sorry to bash the idea so hard, but I'd rather you be alive and crowded than on the front page of a Coast Guard report.

WELL GEE, DID YOU THINK I WOULD GO OUT IN 30 KNOTS FIRST TIME OUT WITH NO LIFERAFT, NO EPERB ETC??? IF SO, I DESERVE TO NOT BE AROUND TO MUDDY THE GENE POOL :-) ALL CAPS FOR CLARITY, NOT YELLING

[PAR]

My intent wasn't to get you pissed, but more to an understanding that there is a great deal of information you will need to absorb, so you'll have a reasonable level of success. This isn't the best place to attain this information (on a wholesale level), not to mention most will need a few years of schooling to acquire it and I'd expect you'll have a similar route, if you elect not to use a designer or NA.

The ideas in your original post (exterior plywood, lowering the existing ballast, etc.) suggested a less then reasonable knowledge of the forces involved.

Your boat can be lengthened, to 41', but much needs be accomplished, before the first sheet of 1/4" ply (good idea to laminate thin ply into thick) gets cut. It's very probable you'll need to add ballast, which will require a redesign of the sail plan, plus a number of other issues, such as appendage concerns, hard points, localized stresses,etc., all quite normal for such a major revision to this hull configuration.

In direct answer to your questions, yes it can be done, there isn't any calculus necessary in the redo of this craft and the math skills can be accomplished by any high school grad that had good grades, the 1/4" box store ply isn't near as strong, but more importantly is very prone to rot and usually is of poor construction, those NA's you "queried" should be consulted about your plans and ideas, a heavily built, stiff midship section will cause the ends to snap off the boat (honest), loading has to be matched, the additional displacement (of the added midship section) will require a substantial ballast increase, appendage reinforcement if not redesign and any significant drop in the resulting CG will typically require a new rig be designed and installed, generally it's not wise to "guesstimate" the stability calculations in ocean going vessels, containers that fall overboard do have hydrodynamic qualities (hydrostatic too) I'm a bit of a history buff and am well aware of the ships that went to sea a hundred or more years ago, they were very well engineered structures and surprisingly clever to boot, using formulas and calculations for thousands of years, the ALL CAPS doesn't help the clarity, much like this run on sentence . . .

If my data base is correct (it usually is) you have a Laurent Giles penned cruiser. LOD 31', LWL 24', beam 9' 6", draft 4' 6", 442 sq. ft. sail area, 7,600 lbs. displacement, 3,600 ballast, 245.4 D/L, 18.3 SA/D The SA/D indicates she's a good light air boat and the mid 200's D/L shows she's a pretty easy going craft, in spite of the weather going south on her. A solid cruiser.

With the healthy displacement, short waterline and generous overhangs it's understandably a little cramped by current standards, which could squeeze in an aft cabin in that length, though wouldn't be near as pretty as your yacht.

Lets see what happens if we use just a little math on her and add 10 feet to her waterline length at 54% of her LWL, the point of maximum beam on the rail, which is different then the bottom of the keel and the LWL, but hey, it's just for fun. She now has a 34' LWL, LOD 41' and everything else is the same. The SA/D drops into the mid 12's and clearly you'll need a new sail plan, the once comfortable mid 200's D/L is now mid 100's making the motion much more violent then before and the comfort aspect of this yacht is gone, she's nearly a racer, but will fair quite poorly against one. This is factoring a very modest 5,000 lbs. additional displacement. In reality, you'll be gaining in the area of 175 to 250 cubic of extra immersed volume. If you multiply that number by the weight of a cubic foot of sea water, you'll get a pretty quick picture how much we're talking about. Frankly, you'll be quite lucky if you can bring this yacht in (with the proposed 10' addition) at double it's current displacement. Nothing on this boat is designed to withstand the tremendous increases in loading this would bring on. I didn't need to do the math to understand this, but the quick demonstration for you, I felt was necessary.

This doesn't mean you can't do it, you can, but you'll be building a new boat, probably with over twice the volume of the old one and none of her wonderful qualities will shine back through, except the cosmetic ones.

[terabika]

[quote=PAR]
Oh, It takes much more than that to get me pissed! lol, if I got pissed every time someone laughed at an idea of mine I would have gone AK a long time ago! I should refine my position though, I am not trying to make something on par with a Gozard or any other boat. I am just trying to own a larger live aboard sailboat which will take me places. Life has risks, I am much less risk averse than most. I do not wear a seatbelt... or helmet when I cycle on cocoa beach roads clogged with retired new yorkers.

Why doesnt lowering balast increase stability? Isnt it harder to move something on a longer beam? I know the initial stability is form related.
with regards to ext plywood, What does that have to do with my understanding of the forces involved? You obviously look at wood in a ratio of thckness to strength which is good when you have lots of money or are using others money but I look at it as a ratio of dollars per unit of strength and ext. playwood wins this hands down. you buy 40 dollars of you super duper marine ply and I will spend the same on ext. and see which box is stronger! ...think outside your box, lol. Yes, mine will rot before yours will but that assumes leakage which I do not detect. Maybe I cannot afford a boat which will last 40 years! according to several sources, the glue is nearly identical, Mine has more viods but, dollar per strngth, mine wins easily. I have decided to make the addition only 3ft though because, given the width, It was ompossible to incorporate the extra berth. So, 3 ft seems easy....why just three? Because , short of another berth, I only care about adding some conter space ( I love to cook)and enough room for a fridge....a FULL sized fridge which does not use elctricity/ run my bats down...PROPANE! cheap and effective and I do not have to tend it often ( I must have at least two types of Chardoney at the ready at all times). Difference between boat and yatch? ICE CUBES!! I will have plenty!
This will free up a dedicated nav station and so an extra 3 ft is all I need. and 3 ft down below in a 31 ft boat makes a HUGE phsychological diference...plus, 31 is a prime number and people who sail these boats are 34.8% more likely to be victims of alien abduction! The boat is , at this point , near worthless as it was sunk but the hul is good and so,WHy NOt? extra ballast: I will have a water tank in the bildge area to compensate for extra flotation...lead is to expensive...water is free. I will also add twoo feet on her backside as she has a flat butt (transom goes to waterline) and I date niether boats nor chicks with flat butts! I dig that swoppy look...I willl move back stay and maybe add sail here....I will also add a bow sprit cause they look cool and add some sail up there......now before we get all touchy about moments and lateral resistance, I have sailed enough boats with non stock sails and other oddities to know that this is not so exact a deall as some would make it....the wind pushes the boat...I may need to power one sail a bit more on a certain point of sail but this tuning I do even on a "Proper" boat. Also, A fin keel is more forgiving of this than a drop blade so this gives me 5000 slack points!.. I caugt a big trap on the keel one time and sailed almost an hour before I figured it out (it was my first one), WHen she sudenly changed, I adjusted sails and she kept going! even though forces where way out of alignment. I could drop a 5 gallon pale off a poll, 5 ft to port and she would still sail....not nicely but these forces can be delt with ( this was a rather extreme case)and I can make longer sprit or shorter boom to move sail area around as need be...used sails are cheap and easy to experiment with and make great backups!
and about all that fancy math and stuff....I recall a certain mega buck cup boat in NZ which broke in half????how many million dollars? and a certain wave peircing cat which broke a hull off??? If I need to span 10 feet with a forces in the center of 100 lbs, an engineer may calculate I need a 2x4 on edge to do the job.....I look at it and say " I know a 2x6 will do the job". this is how I think with exterior playwood. an inch and a half of it certainly is strong enough....stress risers? Yes, I had thought of this but you argue in one area that ext. playwood is not strong enough and now you say it is tooo strnog and makes a stress riser and nose will break off....which is which? bulkheads make stress risers also! every thing makes stress risers!...in drag racing, a crank with radiused filets where the bearing journal meets the cheek was the trick to mitigate this nafarious scourge. Stress risers are only bad if they creat a place which will fale WITHIN design load parameters
...I hope spelling dosnt count! ...about my sailing philosofy. in big weather, I am disinclined to drive a boat hard and I do not even like hoaving to but rather prefer to throw out a sea chute....much nicer to the boat!...and people.

Rot, yes, my playwood will rot sooner than yours but only if my glass job fails and I do not ketch it.....tapping with a mallet will expose soft ares which is why I do not plan on going any thicker on the layup than needed to ensure playwood stays dry...( I am thinking 4 /8oz epoxy....give me props for not saying I will use polyeter in any of this!)thinner is easier to find weakness underneath of.
appendage concerns: yes , I had thought of this (I actually have thought through this more than you realize , I seem to think) by bringing the small bildge bulkheads up to the floor and out to the edge of the floor/hull joint, I will make this very very strong....with big stress risers :-)
Rol stability: I see many yatchs with multible keel configurations for various uses. They obviously have different roll curves but everything is a trade off....Maybe I do not fully understand the relationship between depth of ballast and roll stabilty, ddoesnt lowering ballast make boat more stable? I know there is more but...
yes, it is a giles but I had numbers of 4k ballast and 9620lb disp......mine are from two net sources but who knows....isnt everything on here true?? :-)
generous overhangs???her butt has no overhang (she has worn a braw from early on) I have a 1971 westerly lonbow, maybe you thought of something diferent?
compared to most yatchs her point of max beam and max dpth are very close. cut will be somewhat of an ark but concentration will be on underwater section's fullest point.
obviously 3 ft is easier than 10 ft to add and I await you response! :-)

[woodboat]

I will not address the design principals. I will however address the exterior plywood. First off you assume fiberglass is "waterproof". In fact blisters are water finding it's way in through solid fiberglass. There was a test posted recently were the person used different coatings on a piece of wood like west system epoxy and submerged it for several days. He then weighed the wood and noted the increase in weight. every coating showed some increase in weight meaning that water was getting in. The voids in exterior plywood will cause it to rot quickly.
An observation: all the lenghtening jobs I have seen have been at the stern and occasionally the nose as well. I have not seen a boat your size lengthen in the middle.

[terabika]

one of the good things about going to the 3 ft lengthening is that I can afford to use super duper ply! I was under the impression that marine ply had actually been treeted against rot though ...
another thought about the water/ballast. this may not be the optimal way of keeping her at her waterline but almost all things come with tradeoffs...in this case, it is that , once grounded, I can lighten my boat by some1500 lbs and get her off easier!....every cloud has its silver lining! If I undertake this, I shall make a websight and post url here..... it is a choice between this project and a cat which I am goingto make a post about now. I appreciate all the input! thanks much! And I am going to duplicate this experiment covering wood with 4 layers of 8 oz and epoxy (not West though, they are part of the united nations plot to take over the free world) and submerging it to check wieght. Great idea!!! I must see it to believe it....probably a marine plywood manufactorer said they did this just to sell more marine ply!...not that I am cynical or anything :-) Have a HAPPY day!!
Terry

[marshmat]

You seem to have a pretty nice boat now. If I were in your position I'd sell her and use the $$ to buy a 40-footer with the qualities you want. One in need of repairs can probably be had fairly cheap, and you could then repair and outfit it to your needs. From what PAR was kind enough to calculate earlier, it's pretty clear that stretching your current yacht would make her tricky to handle and uncomfortable to ride in. You'd be miles (and dollars) ahead to start with a hull that already has the dimensions you want.

[water addict]

Since you started this thread with an interrogative, you are soliciting opinions, so don't be surprised if people respond with opinions you don't want.

I'd also restate what others have said- this is a bad idea. Big difference going from 31 to 40ish feet. Loads will be more than double. IF - you analyze and engineer the structure for the new design, compute stability, etc., then have at it. If you are pasting in a plywood midsection at the zone of the boat that is most highly loaded without crunching the numbers, you are asking for trouble.

Feel free to yell back at me with the caps lock on - for clarity of course.

[JEM]

From a costing point of veiw, sounds like a lot effort. You might be better off building a similar design from scratch. Will use be using the same sails?

Lot depends on how much you're attached to your current hull. It can be done. Just have to figure out the cost/benefit ratio.

[terabika]

I did have caps on for clarity as it was easier for me to respond within the quoted material...if no caps mine would be betwixt his and no one would know which was which.Hope it did not offend! I really am not the type to yell :-) You maybe missed my post of yesterday where I said that I downscaled to a 3 ft section (see post for reasons). I like guessing! lol The hull I have could not be readily sold for much and a bigger boat is at least 9 thousand bucks. I know I can do this for les than that! For instance, I use galvanised wire for all stnding rig and thimbles and U bolts. All gotten from a power line support company. I rigged the whole deal for less than 200 bucks! 4 staylocks would eat that much! Galvanized wire is 10 % stronger than stainless! Electrical: I use regular old speaker wire of the appropriate gauge and solder all conections, then I use sealant from conector to insulation. I can wire a boat way cheaper than this and as a live aboard I have not had a failure yet! There are many ways to go cheap! The system is agaiinst it though and so people are educated (indoctrinated) that I shall surely die a hideous death for afronting the gods of greed! :-) Have a happy day! (this was the first time I had posted anything anywhere and have found out how not to intersperse my repley, sorry again for the caps :-)
God bless, Terry