Boat extension

It's a John's Bay Boat 32, with a proposed stretch to 35' 10" (12%).

 

I have to disagree with sharpii2
adding in a STRAIGHT section at the widest point.
The originator showed a boat with curved lines parallel to the waterline. To get a curved line, each frame is of different dimension. To add in a STRAIGHT section, you will loose the curve line.

Disagree, draw an oval on a piece of paper and cut a line perpendicular to the widest dimension, (the short cut) add in a straight piece. You will lose the curve. Certainly you could modify the frame to ensure some curve but will affect the shape of both frames ahead and behind the new inserted add on.

So the only way that you could just add a straight, by which I think you mean parallel section is that if you have two identical frames somewhere in the boat, you could add a straight new section between them

If you want a 30 foot boat to be 33 feet, a 10% increase in length, space the frames 10% further apart. The rate of change of the curves will go down, not much for 10% but this will affect CG and other dynamics.

I would stay away,( on a boat with curves ) from trying to fit in another section somewhere on the boat.

 

I agree w you Barry.

Adding a straight section to a curved one will not produce a fair line or a fair boat. More Frames will need to be slightly changed in size to make the whole affair fairly fair. (PI). The only really convenient boat to extend is a boat w multiple frames exactly the same.

One could approximate by adding 2 frames just a little bit bigger, as in 1/16" or perhaps 1/8". Three frames .. 2, 1/16" bigger and one (ctr) 3/32" bigger. Won't be fair but one hell-of-a-lot closer than three frames all the same.

However there may be times when getting a fair boat is less important than getting a longer or bigger boat.

 

http://forum.woodenboat.com/archive/index.php/t-157644.html
You shouldn't buy a wooden boat. If you don't already obsess about them, dream about them, hang the calendars on your wall, subscribe to WB and spend your every waking moment and spare bit of cash on them.
In this day and age, you don't just decide to be a wooden boat owner, it's already been decided for you by your inner makeup, and you do it because you can't help yourself. There's many more practical options for far less total outlay in cash, time or resources. If clearly don't have the drive or commitment. Count yourself lucky.
You got to really love everything about wood boats. Everything about owning them is tougher. Some yards won't haul them. Some marinas won't take them. Most insurance companies won't cover them.


http://www.frugal-mariner.com/Insurance.html
If you are purchasing an older boat, before you sign on the dotted line, check for insurance coverage availability. Many insurance companies will not insure boats over 20 years old, some over 30 years. Wooden boats are particularly difficult to insure so take that into consideration before you think about buying that classic wood boat.

 

Statistically two people of thousands of wooden boat owners plus one repeating stories he heard of slip problems is insignificant.

The fact is that you (apparently) nor I can name a single marina we've been at that turns away wooden boats as policy. I conclude slips for wooden boats are not a problem. There are some docks that even give preferential treatment to wooden boats because of their character. Most docks are only interested in maximizing profit by renting every slip.

 

There's no talking to Myark. He lives in a fantasy world of boats that don't corrode, where they all look the same and each has absolutely zero emissions too. His insurance link is one of the most biased on the web and it's full of just BS, much like him and most of his posts. Lastly guess what the largest (by a huge margin) hull material choice is used in the country he lives in? Yeah, I'm sure he's in denial about that too.

 

Why is it necessary to despise those who think differently?. As I am able to guess what someone else has done, guessing his training, his country and even the name of his grandmother, I consider myself entitled to assume that the "other" is a wretch.
Enough, gentleman ¡¡

 

Tansl
I agree with you.
I thought that this forums purpose was to allow people who have some time to learn from intelligently presented information garnered from the experience from a vast array of people rather than be personally attacked if you have a difference of opinion.

 

Excuse my insistence. What disadvantages do you see in lengthening a boat as shown in the picture?. No doubt that is but I would like to know your opinions, pros and cons.
(Thanks for your drawing PAR)

 

Not sure if this question was posed to me but
The two drawings imply that it COULD work . ie the gunwhale/gunnel? will be fine as viewed from the top, well as the keel and gunnel as viewed from the side,
but it is the surface area from the keel to the gunnel that would only work if every point along the cut is at the widest point of the boat at the position of the separation.

This cut as shown is at the widest point of the gunnel and looks fine but it is unlikely the widest point of hull at say 2 inches below the gunnel, or 4 inches or 6 inches all the way to the keel.

If you took horizontal crossections ( top view)across the cut and for each crossection, you were at the widest point of the boat then this section addition would be fine.

But it is unlikely that this is the case at which time the curves from the keel to the gunnel would possibly be unable to be fair

The way to check this is to make a pattern of the frame at which you are cutting the boat, make a pattern of the first frame bowside and sternside of the cut and see if the frame at which you are cutting the boat at is wider at every position. If the plan does not have patterns, then perhaps it has a set of tables that you could look at.

Or another attempt to explain this in words. If you took horizontal sections, top view, from the gunnel to the keel and if for EVERY one of the sections, you are at the tangent point of the curve of the boat, AT the Cut position, then your suggestion would work.

 

Should be feasible if the sheer and the hull surface is normal to the plane along the entire cut.

However if the sheer and hull surface are not normal to the plane of the cut as in the John's Bay Boat 32 which is the boat Albert is considering then a very peculiar hull shape with kinks would result by adding a cylindrical section.

Edit: I didn't see Barry's response before responding. He said the same thing in a different way.

 

Well a cylindrical body wouldn't work on the developed panels you're showing. Your method is used on ships fairly regularly, but cutting the widest midship section and adding a similar section to fair them in. In fact, and the part you wouldn't know about, because you've never actual had to take a torch to plate before is, it will not be fair. It'll be somewhat fair, as far as ships go, but not even remotely acceptable in a yacht. Both David and Barry have it correctly, in regard to adding a cylindrical section.

Simply put, you still can stretch a hull form this way, but you will have to line off again, probably over several frames bays past (in each direction) the lengthened area. This would be routine in a yacht, not so much in a ship.

 

This will only rarely make a shape that blends with the shape of the original. One reason, probably the main one, is that the widest part of the hull is not normally in the same place for the sheer, chine and middle part of the topsides. Often the widest part of the hull at the sheer is well forward of the widest part at the chine and the widest part of the middle is also somewhere else. Such variation is usually more prominent in planing hulls but is probably true to some extent in most boats.

Still it may be possible to cobber something that looks OK but it will not be a cylindrical section or a flat plane or anything that has the same section throughout.

If the cobbered section is a true cylinder, it will look just like that and undoubtedly be ugly in addition to any other problems that it may have. Straight lines inserted into an otherwise curved hull will always be wrong.

 

The forms of a yacht are not more complicated than an ocean fishing boat or a Voith tug or a supply vessel for oil rigs. Any shipbuilding professionals trying to do the forms of its boat perfectly smoothed and soft. Therefore, I believe that with my experience I can say that what is done in a large ship can can be done in a small one, call we it yacht or landing craft. The name does not indicate anything. Yachts can have very complicated shapes but usually not .
That said, I have to say that indeed a cylindrical body does not apply to any boat. But I can assure that any boat can be lengthened by cutting the center. Perhaps in many case, this section can not be a flat section, but you can cut the boat in many ways. For example following on the shell the lines joining the points of max breath at each water line.
On the other hand, add length in the central part of the boat is the most desirable because is there where you get much more volume, is to carry more cargo, is to make the living room bigger. Lengthen the boat astern, in my opinion it makes little sense, but sometimes it is the simplest way to increase the length.
On a boat that is already built not see more options. If the boat is in drawings the best thing to do is change the plans. It's that simple.
This is my opinion and I welcome your constructive comments that perhaps help Albert Jr.

 

The cut line in the shell should connect a series of points where a vector drawn from any point on the hull and normal to the hull surface has no longitudinal component. This may not be the same as connecting the points of maximum breadth at each waterline. A boat with a deep forefoot would have the cut line at the deepest point at the centerline, which would be forward of the widest point on most yacht hulls. This is approach hypothetically possible, but would be difficult to achieve in practice on all but the most simple of hull forms.