H28 Offsets

[suzyj]

Hi guys,

Am daydreaming a bit, thinking of what I could do after finishing Elena.

I'd like to knock together a sketch model of a H28 to continue the daydreaming process. Does anyone have a table of offsets?

[PeterSibley]

They're in ''Sensible Cruising Designs '' Suzy, I'd scan and post or email but my scanner died. Someone will have them for you.

A sweet, sweet design !

[MattSplatt]

I have a copy of that same book ordered and theoretically on the way, Suzy. I can send you the offsets once I have it.

[suzyj]

Thanks guys, that's really awesome.

[skaraborgcraft]

Building the H28 in a booklet form is availiable for a few bucks from D N Goodchild, if that helps.

[Jay Greer]

Here is the H28 model of our ketch "Bright Star" that my father in law made from Sensible Cruising designs. A copy of the book is certainly worth having and can be purchased on line from Amazon.com.
Jay

[Sayla]

Hi guys,

Am daydreaming a bit, thinking of what I could do after finishing Elena.

I'd like to knock together a sketch model of a H28 to continue the daydreaming process. Does anyone have a table of offsets?

I'll second getting a copy of the book, check for second hand online. There's a whole chapter on building the H-28, including drawings of fittings and all. Later in the day I'll email a link to offsets so you can start some drawing. If you get the book there's a whole world of daydreaming to be done I can assure you....so many nice designs in there, it's scary.
cheers
Darryl

[suzyj]

Just ordered a copy. Now for the wait. I want instant gratification, and I want it now!

[Jay Greer]

Good on ya Suzy!
Jay

[Sayla]

If you can get hold of it, "The View From Pluto" by Stuart Buchanan, is a pleasant story about sailing along our coast here, Queensland, in a H-28.

[Rik van der Vaart]

Suzy,
A model or the real thing?

[suzyj]

A sketchup model for starters. I have to build a decent shed before I could start building a boat of this size, so it's a very long term process. Hence just daydreaming at present.

[Rik van der Vaart]

I identify. My wishbuild has the same constraints. So I am going for a smaller similar design... Still JW.

[suzyj]

Thanks for the offsets guys! Another dumb question... How much headroom is there in the cabin? Enough to stand up without smacking our heads too much? We're both pretty tall, about 5'9 in the old measures...

[MattSplatt]

On your model? ;-) How big is the model going to be?

[suzyj]

1:1

[suzyj]

Answering my own question, sorta.

https://tinef.wordpress.com/2013/10/...ll-fitted-h28/

[Rik van der Vaart]

What is it going to be? Model or full scale?

[Jay Greer]

Thanks for the offsets guys! Another dumb question... How much headroom is there in the cabin? Enough to stand up without smacking our heads too much? We're both pretty tall, about 5'9 in the old measures...

Our H28 is about as close to the original design, other than the fact that the interior is a bit more fancy, as one might get. I am nearly six feet tall and have no problem finding comfort when below. With the main scuttle slid open it is simple to stand and work in the galley. The partial bulk heads have ample rounded caps on their edges that afford a good hand hold when moveing about when under way. The sides of the deck house have cupped caps that at the carlins that also give a good place to grab for support. The cabin space is comfortable and can seat four at the saloon table for having meals if desired. I do plan to build a collapsible dodger over the main scuttle to give protection in less than ideal conditions. The settee berths are comfortable and can be made into a king size bunk by adding an insert in the middle. All in all I find the cabin area of the H28 to be very comfortable as designed and would not change it as I see it as being perfect as it is.
Jay

[suzyj]

What is it going to be? Model or full scale?

A digital model, so can be scaled to whatever I like. Much like what I did with Elena.

[Rik van der Vaart]

Ohhh... Opening all the possibilities... Exciting future.

[suzyj]

Blimey, some of these offsets are miles out. Worst one so far is LWL-1 at station 22, which is out by a whole foot. The deck has two that appear out by about 4". Methinks typos.

[suzyj]

So here's some views of my model thus far. That's a really pretty hull.







Theres 1200mm from the lowest reasonable floor level to the deck, so if I wanted to stand up in the cabin, I'd need the roof to be some 550mm above the deck.

[skaraborgcraft]

I have always found the hull lines attractive, as i find they are similar to a Nordic Folkboat, but with the benefit of more space and less draft.

[MattSplatt]

Lovely.

I still don't quite follow how you are doing these in Sketchup. I tried to follow along from your instructions in the Elena thread. I probably need an actual project to work to, and follow the steps you described. :-)

[brucemoffatt]

Theres 1200mm from the lowest reasonable floor level to the deck, so if I wanted to stand up in the cabin, I'd need the roof to be some 550mm above the deck.

There's a nice design challenge for you! Make it worthy of the H28. I bet you can!

[suzyj]

There's a nice design challenge for you! Make it worthy of the H28. I bet you can!

It's very tempting to scale the whole thing vertically by 110%, then my 1200mm becomes 1320mm, and the cabin only needs to be 430mm from the deck...

[brucemoffatt]

Is that a function you can do easily in your software? If so, let's have a gander.

[suzyj]

Lovely.

I still don't quite follow how you are doing these in Sketchup. I tried to follow along from your instructions in the Elena thread. I probably need an actual project to work to, and follow the steps you described. :-)

It's just super tedious.

Here's a view of the working that I used to loft this design. I started by drawing the cross shaped former, which I put on it's own layer so I could easily turn it on and off. Then I made a moveable "frame former" on which I can draw frames. I have lines at the station points on the initial piece, and move it around to draw the various lines from the offsets. In each case I move the former so that either a horizontal or vertical surface is where I need it, and rule offsets onto that. Then I use the 3 point arc tool to connect offsets and make fair curves, effectively interpolating between the offsets. Some mucking about is needed to ensure everything is fair.



Once the specified lines are drawn, I then slide the frame former to various points and draw smooth frames, by selecting the points where the lines intersect my former, again using the 3 point arc tool to interpolate between lines.



The frame lines now give me more points so that I can interpolate more WL+n lines. I do this every 4", or 101.6mm.



Finally the really tedious bit is drawing a huge pile of triangles to sheet the hull. Once the lines are drawn, they get selected, then the properties changed to smooth the hull over them. You can see I started with a 101.6mm grid at the bow, but got sick of it about 1/3rd of the way along the hull and swapped to a 203.2mm grid.

[MattSplatt]

Ah. That makes more sense now. Thank you.

I'm not sure I'm patient enough to have a go at that. I might have a dig around the open source hull modelling packages first and see if there's a tool that can make offsets into a 3D mesh I can export to other programs. I am comfortable modelling in Sketchup, but it's much better with square things, as you know.

[suzyj]

Is that a function you can do easily in your software? If so, let's have a gander.

Yah, it's a doddle.





I put the floor 2.2 feet below the waterline. This is probably further down than it'd be really.

[brucemoffatt]

So now the sweep of the bow and rake of the transom need resetting.

[PeterSibley]

You're making me feel old Suzy! I can do that* on film with a pencil and splines but I have no idea at all of how to do it on CAD.

* but not those amazing projections !

[Jay Greer]

Don't feel like the Lone Ranger! I still design from half models and use splines and whale shaped weights.
And, this boat was done that way by the master himself. Some say it was inspired by the 12 1/2 designed by his father who also used half models and spline weights. Not that CAD is bad, I just like to feel the shape with my hands, eyes and mind rather than swimming in cyberspace.
Jay

[Peerie Maa]

Dunno whether it is a problem with the software's ability to render, but there is a wobble above the WL at the station through the heel of the sternpost.