Catboat offsets and bread and butter conversion🥴

[Sunkenpunt]

Hello again! I had (and still have) plans for making a skin-on-frame canoe. Moving and lack of time/facilities, though, has halted plans so far.

So. I've since scaled down my plans. I hope I'm not insulting anyone's intelligence/skills for real boat building with this inquiry. But I want to make a model of a 20-ish ft "catboat" for a friend(that's the kind he likes). Maybe around 20". From what I've seen bread and butter construction is my best shot given my set of tools and brains. But anyway, I have three questions.

What are the characteristics of a catboat?
Does anyone know of offsets or plans that can be used for a model?
Does anyone know how to convert regular boat plans to bread and butter cutlines?

Let me know if those questions need to be clarified.
Thanks all in advance.
SP

[wizbang 13]

Whutz “bread and butter “?

[Landrith]

Many half models and model boats are made from the plans in books like American Small Sailing Craft: Their Design, Development and Construction by Howard I. Chapelle. The Lines plans dictate form the flats that can be glued together in a finished solid hull.

The study plan of Chapelle’s 1888 Martha’s Vineyard Cat from American Small Sailing Craft with offsets is in this blog by David Churbuck :

https://churbuck.com/2021/09/28/half-a-catboat/

[Sunkenpunt]

Many half models and model boats are made from the plans in books like American Small Sailing Craft: Their Design, Development and Construction by Howard I. Chapelle. The Lines plans dictate form the flats that can be glued together in a finished solid hull.

The study plan of Chapelle’s 1888 Martha’s Vineyard Cat from American Small Sailing Craft with offsets is in this blog by David Churbuck :

https://churbuck.com/2021/09/28/half-a-catboat/

Wow, that's great! I think that's exactly what I'm looking for. Even the right sail, a gaff rig. Thanks. I'm probably gonna have more questions down the road, like how to understand those offsets. But that's a great start. Thanks

[Peerie Maa]

Wow, that's great! I think that's exactly what I'm looking for. Even the right sail, a gaff rig. Thanks. I'm probably gonna have more questions down the road, like how to understand those offsets. But that's a great start. Thanks

Use the offsets of the stem plotted on suitable graph paper at the correct scale to make a profile of the stem and stem rebate.
Then plot the waterline half breadths You might want to take off the half thickness of the stem and keel.
Plane your stock to the scale spacing of the waterlines. Cut a profile to the outside of the stem and keel from stock of half the thickness of the stem/keel assembly and set it aside.
Saw out your stack of slabs to the shapes of the waterlines and if there is tumble home make sure that you have enough width in those slabs.
If you want accuracy, rather than just a representative model, plot and make templates of the sections, to use when cutting away the waste.

This is a long vid, but takes you through the process

[Canoeyawl]

0C4511E1-4415-4824-AC62-4FA3621936CC.jpeg

[Sunkenpunt]

Very cool. That should be very helpful. Thanks

Wood is awesome, isn't it?

[Sunkenpunt]

Many half models and model boats are made from the plans in books like American Small Sailing Craft: Their Design, Development and Construction by Howard I. Chapelle. The Lines plans dictate form the flats that can be glued together in a finished solid hull.

The study plan of Chapelle’s 1888 Martha’s Vineyard Cat from American Small Sailing Craft with offsets is in this blog by David Churbuck :

https://churbuck.com/2021/09/28/half-a-catboat/

I'm ready to start start plotting. I decided to go the Autocad route. But I can't read any of the numbers on that table of offsets. It's alot worse than I remember. Am I missing something? Any help appreciated. Thanks

[Sunkenpunt]

Since Landrith OP'd those catboat offsets maybe he can chime in. Unless someone else is able to provide some input. Thanks for any help you can provide.

[Peerie Maa]

I'm ready to start start plotting. I decided to go the Autocad route. But I can't read any of the numbers on that table of offsets. It's alot worse than I remember. Am I missing something? Any help appreciated. Thanks

Is it these that you are having difficulty with?


They seem OK to me. AS the text states, the half breadths are feet. inches. 1/8ths. The baseline might be to the underside of the salient keel

[Jim Ledger]

"Design Elements of the Catboat", by Fenwick Williams. Available in paperback from the Catboat Association.


https://www.catboats.org/store/viewp...spx?id=3728391

[Sunkenpunt]

Peerie maa. I was ok reading that chart. But it's mostly this one that's very fuzzy for me. I obviously don't know what I'm doing, so is the chart you posted the only one I need?MVCATCHAPELLE.jpg

[Peerie Maa]

Peerie maa. I was ok reading that chart. But it's mostly this one that's very fuzzy for me. I obviously don't know what I'm doing, so is the chart you posted the only one I need?MVCATCHAPELLE.jpg

No, I believe that they are different boats.
I am away from home, returning tomorrow. I'll dig out my copy and see if it is legible. If it is, I'll scan and post a better copy.

[Sunkenpunt]

Thanks! That is very generous. I wish I were able to contribute to the brains here. But I don't have much of that to offer in the boat category. Unless your boat has an engine! That's a different story.

[Peerie Maa]

Try this. It might not be much better. I recommend that you lay out and loft by hand, that will soon sort out any errors.
Scan_20230509 (2).jpg
Print it off as big as you can.

[Sunkenpunt]

Thanks alot for doing that. I really hate to say this again, but I can't see a thing. No matter how big I make it, or how I open it. I can't read anything. Could someone else please look at it and see if it comes out legible at all?

Alternatively, does anyone know of other offsets for a catboat? Or something similar. Thank you

[Peerie Maa]

Thanks alot for doing that. I really hate to say this again, but I can't see a thing. No matter how big I make it, or how I open it. I can't read anything. Could someone else please look at it and see if it comes out legible at all?

Alternatively, does anyone know of other offsets for a catboat? Or something similar. Thank you

MVCATCHAPELLE.jpg
Plan B
Blow the lines up with a photocopier or photo editing software so that you can trace the curves onto the wood without any need for lofting. You will need a calculator to work out the % scaling and a stock of paper, but it is a system that works.

[Sunkenpunt]

Ohhhhh. Interesting. I will try that. Thanks for your patience and help. I'll go with that and might be back with questions

[mick allen]

this is fairly legible:

[Sunkenpunt]

Oh man! That sure is legible. I'm excited to try plotting one out. I like to use autocad, so this will give me an excuse. I'm going to trace like Peerie Maa advised. But I want to try my hand at understanding offsets. Thanks