32' cruising design from scratch. Few basic questions...

I'm planing to go to the IYRS in Newport, hopefully starting next year. I'd like to have a good bit of design work finished on a 32' cruising design so I could build it after finishing this school.

I want it to be a moderate displacement cruising boat, built in the strip-plank/fiberglass composite method.

LOD: 32'
Beam: 10'
Draft: no more than 4'6"
Headroom: 6'6" (my brother is tall and I want him to be able to stand up when he visits!)
Displacement: I was thinking 10,000lbs?
Sail Area: 500-600 sq.ft.

I was thinking something along the lines of a cross between a Watkins 32 (interior), a Southern Cross 31 (hull shape), and perhaps a Herreshoff Cat Ketch (rig).

I'm not entirely set on the Cat Ketch rig or the Full-Keeled hull. However I want a plumb bow and stern for the longest possible waterline, and I want the rudder either keel or skeg-mounted to keep the transom clean for a windvane. Attached is a .DXF file that I did in HULLs. I know it's a 5-chine design, but I'd be building in round-chine construction.

 

Displacement: I was thinking 10,000lbs?

This will be hard to do as very lightweight construction is difficult , and must be maintained for the life of the vessel. Will you be having guests aboard and requiring them to only bring toothpaste that is 9/10 gone?

A stern mounted rudder gives the best shot at having a self steering that actuates a trim tab on the rudder, and is easiest to unship & repair.

A trim tab can be activated by the cheapest ram autopilot and the electric bill is minor as the force to move the tab is tiny.
You can also hook a small tiller to the trim tab for "power steering" at times when you are overpowered , but enjoyoing the extra speed.

FAST FRED

 

The Watkins 32 is considered a heavily-built cruising boat with a 50% ballast-to-displacement ratio, 10,800#s of displacement and 470sq.ft. of sail area on a sloop rig.

I figured 10,000lbs displacement because:
1) I'll have a 6" deeper draft, and likewise the ballast will be located that much lower. I *might* even go with some form of external ballast if it shows an advantage.
2) With a Cat Ketch rig I'll have less weight aloft and a lower center of gravity.
3) With a plumb bow and stern I should have a longer waterline without much more weight.

I could go for 1000-2000lbs more displacement, but I wouldn't want to go any more than that. I'm designing it around cruising 1-2 with any more guests/charters staying no longer than 1 week.

For self-steering, I want to use the Cape Horn system. This is easier to install with a clear transom, though it can be rigged off-center to clear transom-hung rudders.

Mostly, I just like the look of a clean transom. A nice big place to paint a mural or something....

The "power steering" idea is slick, I've never heard of that before

 

What is the displacement of the hull you have drawn?
To me it looks like the midship area is approx 1m2 (0.96m2)
The length is close to 10m (9.76m?)
So with a Cp of 0.54 the displacement is 5 tons (or slightly more in salt water). That is if the waterline is right under the stem.
10000lbs is 4.5 tons.

 

10,000 lbs on a (say) 30-ft waterline is a DLR of about 165 - hardly "very lightweight". I don't really see "ultralight" as starting until a DLR of about 100. 50 is superlight.
So, where's the beef? If cruising "needs" are kept to a minimum, air-conditioning is forbidden, and teak is banned from the boat, there should be no problem building this beast to the weight desired.
Steve "my 2 cents"

 

The .dxf hull has a displacement of 10,000lbs in seawater.
It has a maximum length of 32', maximum beam of 10', and maxiumum draft of 49" (basically 4'). I have some more work to do in order to get the 4'6" draft, but that is basically just a longer keel. Also, with he limited number of bulkheads I can't get anything but a full-keel shape from the Hulls Program. I may decide on a keel similar to the Watkins 32... or not.

I bought an easel and a large pad of graph paper with 1" squares. I'm going to see what I come up with going at it by hand, then try to build a multi-chine model. I should probably look into taking a CAD course at the local college...

 

I think drawing on paper is easiest for initial design.

 

However I have no clue how to figure out displacement when drawing on paper. It's not like I'm designing with mathematical formulas spelling out the underwater profiles.
I only got a C in calculus, and that was years ago
So I do preliminary work in Hulls to give me the rough idea of what the shape can do, then I'll fine-tune what I want it to look like on paper, then I'll have someone who actually knows what they're doing have a look at it :idea:

Maybe I should break out the graphing calculator and my old calculus book and do some learnin'...

 

If you have a target displacement and a waterline length you can start by drawing a curve of areas. The area under the curve is equal to the displacement and you know the midship area to get the Cp you want.

Then you know the area for each section

 

Get a copy of Skenes Eliments of Yacht Design , the tried and true pencil methods (no Calc required) still produce fine vessels.

With the limitations built into computer modeling , the pencil drawn boats look better too!

FAST FRED

 

I Agre, Fred, and if you can't draw a boat by hand, how woudl you use the software?

 

I'm going ot take exception to that one, FRed - I've not drawn on paper these last 15 years...
Steve

 

Steve and Fred, I think everyone should start with pencil and paper when the want to learn about hull design. Make a small boat with a given displacement (approx) for example.