Question about lofting

[John How]

I am in the processs of lofting the new Gartside 18' double ender "SjoginIII" and have a couple of questions.

First when lofting the mold station, is it common to do just one side and mirror both sides of the mold station from the same line or should I loft the whole section of each station.

In the offset table, the dimensions are listed as feet, inches, & eighths, pretty straight forward but some of the eighths have a plus sign behind them and I am assuming that this means to add a sixteenth to the dimension. Is this correct?

I'm sure to have more questions but I hope this will get me started.

[Peerie Maa]

You can do both sides if you have the space, but most lofting puts all three views on the same loft floor. That is actually more accurate as you avoid errors in waterline spacing and in replicating the mirror lines on the floor. You should be able to build symmetrical moulds from one side only.
As to the eighths +, yes I believe that you are correct.

[skaraborgcraft]

What Peerie said. But the + and - after the 1/8th is not neccesarliy 1/16th ,but wherever the fairing batten takes a fair swoop,which may be just a fraction under or over the 1/8th figure given. May not seem much unless you are used to working to a tolerance of 1/64. Let the batten speak.

[Bill Huson]

What Peerie said. But the + and - after the 1/8th is not neccesarliy 1/16th ,but wherever the fairing batten takes a fair swoop,which may be just a fraction under or over the 1/8th figure given. May not seem much unless you are used to working to a tolerance of 1/64. Let the batten speak.

What skaraborgcraft said - let the battan speak.

[John How]

Thanks guys, my lofting floor is a 4x8 sheet of plywood large enough to loft the stations in full but I'd prefer to make the molds from one set of lines so that is the plan. I figure to do the mold stations on one side, then flip it over and do the stems on the other. There is sure to be lots of sorting out once the stations and stems are on the strongback.

[davebrown]

This thread solved one of the oddities of lofting that I have encountered from time to time. I lofted a Culler Butternut and then what is known as the Culler SheepBoat and I came across minus signs in both (-). This confounded me. Why did the designer write, 1-3-5- instead of 1-3-4+? It makes sense that the battern will land on an edge that might not be exact.

[Eric Hvalsoe]

Of course always let the batten speak. For simplicity sake think a plus or minus as a 16th.
Rarely would you be working beyond a tolerance of 1/16 in the laying out of the lines. Things come and go in the wash. Which side of the pencil line are you calling good.

[St.J]

Thanks guys, my lofting floor is a 4x8 sheet of plywood large enough to loft the stations in full but I'd prefer to make the molds from one set of lines so that is the plan. I figure to do the mold stations on one side, then flip it over and do the stems on the other. There is sure to be lots of sorting out once the stations and stems are on the strongback.

John,
Are you just going to loft the stations and stems or will you loft the buttock lines and diagonals as well to check the stations against?

How are you going to find the bearding line without the half breadths? Or will you try to cut the rabbet with the stems on the strongback?

Or does the fact that you're building in glued clinker ply mean that none of this is relevant?

St.John

[mcdenny]

When people ask about lofting I always wonder if they know that "lofting" means drawing all three views and being sure waterlines, buttocks, diagonals and sections are all reasonably fair and agree with other. It often sounds as if the original poster is just drawing out the sections full size from the table of offsets. That will get you a set of frames and/or molds but it is unlikely the resultant hull surface will be fair, at least without lots of sanding and filling. Just wondering....

[John How]

Yeah, I'll do glued ply. The plan calls for a stem/keelson backbone to be planked and then outer stems and keel to be attached after planking. Pretty typical I think for glued lap ply.

[Rick Nardone]

+1 for mcdenny

If you are building a boat that requires lofting, then draw it out as accurately as you can, ALL IN ONE PLACE. If space is a concern, then do the long lines on the floor and the body plan on a separate sheet hung on the wall. It's a PITA, but not as bad as having to tick off a dimension and flip the lofting over every time you need to transfer from one view to the other.

I hate to sound overly dramatic, but a shortcut in lofting is the boat builder's equivalent of deliberately infecting your child with a disease in the womb. This is your only chance to accurately determine the fair and proper hull shape before you start making shavings. It is much easier (and cheaper) to solve problems when dealing with pencil lines than with wood, not to mention the goops and fasteners. The finest joinery skills will not compensate for a hull that is not lofted and set up properly.

There are many work-arounds for dealing with the frustrating and confusing pile of curves that end up on the lofting floor - the use of different colored pencils or inks for different views is a prime example. There are many more.

Please, please, please find a way that will work for you to have all three views available at the same time. You won't regret it. Going from long lines to body plan is where the rubber meets the road for hull shape, let alone picking up stem and keel rabbets.

Lofting is when you go from "crush" to "love." You get a true understanding of what makes any design what it is and how all of the giblets come together to make a boat worth building. If the concept of lofting is that daunting to you, then I suggest that you build a boat from plans that include patterns. There is no less honor in the process; it's just that someone else has done that part. There are many beautiful examples out there.

Lofting is not Santeria or Game Theory. It is a surprisingly simple and rewarding process. Don't muddle it by re-inventing the wheel. You'll love it. I swear.

Was that preachy enough?

Best of luck.

[jalmberg]

I agree all three views are necessary, but see no problem with using a separate board for body plan.

[J.Madison]

The separate board is not a problem but it sounds like you aren't planning on drawing the whole boat full size. YOU NEED TO DO THIS! It is the only way to get the right shape for the boat as others have said. Buy Greg Rossels book Building Small Boats. It has an excellent chapter on lofting and much more info that you will need. This is a very beautiful and complex hull and absolutely needs to be lofted in its entirety. This is because the molds won't be quite right as they are given in the offsets. You must fix them.

As to your original question, it is much better to only draw one half of the stations. Build two halves of each mold to those lines and then attach them into a whole. This assures symmetry. If you draw them as full stations there will inevitably be differences between the two halves.

[John How]

Thanks everyone, some interesting things being learned in this process, the first of which is in doing the lofting I have decided I don't want to build this boat after all and have decided on another. It is the Oughtred designed Fulmar and while it comes with full size patterns, I am in fact (or have in fact) lofted it in full size all three views, thanks to your encouragement. There is much to be gained in doing this I can see now and it will make forming parts much easier since I will be able to see the shape of many parts that will later need to be made even in the fitting out of the boat after the hull is completed. Thanks once again to the wisdom of the forum!!!

[Sayla]

I imagine that the plans have plank positions marked on the sections (?fullsize) but consider battening anyway, to get the curves really smooth

[potomac]

John- What happened to the Fulmar? New direction?

[John How]

John- What happened to the Fulmar? New direction?

Still Fulmar, yes! I was considering another boat earlier.