Bolgeresque Noodle

Comments from the peanut gallery.

I'm afraid that you are starting to compromise some of the primary aspects of your original design. By going to so many angled surfaces, you are increasing the complexity of the build while not necessarily gaining that much from it.

By angling the topsides out, without increasing the BOA, you are loosing a lot of form stability. I suspect that your goal was a reduction in displacement. I think that you could still go vertical sides on both the topsides and the box-keel without that much of an increase in wetted surface.

IMHO I think that your original proposal has better keel design aspects. The box-keel stops short of the stern and the bow. Pros: reduced displacement, reduced surface area, more maneuverability, better propeller arrangement, inboard rudder(could solve your tiller placement problem with the yawl rig). Cons: reduced lateral area, loss of walk-way/stowage area. I could see stopping the box-keel short of the bow also with some sort of a "cut-water" to fill in the step between the forward hull bottom and the keel.

With vertical sides, the cabin/deckhouse structure will be easier to construct too. 1X (or even 2X) layed inside the sheer for the inwale with the cabin sides glued to the inside of the inwale. Lapjoints, parallel faying surfaces, glue and screw type stuff without a lot of fitting and trimming.

That's my two cents. It looks like a fun project.

 

"The box-keel stops short of the stern and the bow. Pros: reduced displacement, reduced surface area, more maneuverability, better propeller arrangement, inboard rudder(could solve your tiller placement problem with the yawl rig)."

The Atkin boats had the box start with the bow , but it ended 20% or so short aft . This gives space for the rudder and propulsion , and perhaps allows better steering.

FF

 

End of boxkeel 20% from aft

I agree with FF and would use a steerable thrust tube around the prop. This gives better efficiency, better straight forward motoring, manouvrability both fwd and reverse... but that is maybe more something for powerboats instead of sail...

 

I think your first drawings is the best. If you want to improve much on that you can just as well get rid of the chines and build a round bottom with a wide naca keel

Have you considered using a naca 0012 or 0015 for the box keel ?

 

A lot about this design reminds me of a St Pierre dory. It had a flat bottom and angled sides, but it used a centerboard. Not much volume because of the short waterline, but trailerable and about as seaworthy as any craft ever designed for its displacement. I've been noodling with a dory like that-- beachable, low conservative rig, leeboards, a kind of motorsailer concept.
I'd have a skeg, but it would follow the forward curvature of the bottom closely to allow beaching. Maybe 28 ft, 8 1/2 ft beam. Weight between 3000 and 5000#.
There's a simple boat to build. Could be simlar to this: http://www.nexusmarine.com/st_pierre.html


A,

 

...Or this one, which has a steel hull, but I don't like the cabin. Note the brick chimmney. http://www.boatsandoutboards.co.uk/view/F68698/

A.

 

I would have to look up the specs for those...not something that is at the top of my head.

Steve

 

I hope the heck those ain't shingles on that roof....

 

So say we put aside the latest stuff and go back to the original...or maybe the second iteration and massage the keel somewhat more. Can't do it this morning...am pooped. Maybe between jobs this evening.

Steve

 

Why not the original design of hull, with a much shallower box keel with a thick steel ballast/grounding plate designed to carry waterballast, fuel, batteries and a steel centreboard? The interior hull floor would be your cabin floor, and by keeping the rocker profile of the keel flatter than the hull rocker you could still put the propshaft and engine in there too. You could have a pop-top cabintop for headroom at rest and reduced windage at other times (make it strong and watertight) or a fixed second tier of cabin over the standing areas of the cabin only. I had similar ideas in mind after wondering how I might want a development of an AS29 to look.

Andy

 

I try not to get involved in these types of threads for the reasons Tom has hinted at. The low cost and free software available to assist the design process, isn't the blessing it first may appear. Wonderful, clever and intriguing shapes can be modeled, but the program doesn't tell you if it's a good shape for the design parameters.

When it comes to the box keel shapes, typically they are multi chine "V" shapes (sometimes flat bottom skiff shapes, but not often) for the first half of the hull, where a knuckle develops in the last half of the hull form. This knuckle permits the steep deadrise to continue toward the stern, usually terminating about 20% forward (of the LWL) of the stern post, and then blends the second chine into very flat aft sections. Some of these aft sections may has some reverse in the deadrise, but the later versions of the Atkins designs, resorted to using a hook and dead flat aft sections in this second strake. The hook was an easier to build concession, usually requiring only a gentle bump in the rabbit. This "bump" is critical to the boats abilities, with too little the bow rises sharply once the S/L tries to pass displacement speed, too much and a huge hole is dragged along with the boat, underway and getting to displacement speed is a challenge.

Bolger has used boxes to create headroom and reasonably stable platform, using unusually skinny hull forms, to provide some efficiency. His designs of this type also show considerable thought toward keeping them very lightly built, again to address the efficiency of a light, narrow hull form that has to drag along this burden of a box.

A well thought out box keel craft can achieve moderate plane speeds and remain efficient and economical when in displacement mode. It takes substantial understanding to assemble these attributes in this hull form, which software has yet to provide. These new software packages are little more then a electronic "T" square, ruling pen and built in calculator, nothing else.

 

I would think involvement in the thread is what is wanted, and then it becomes a learning experience for all involved. You seem to know quite a bit about boat design, and I read your comments with interest. I know far less, and I know it, and I can appreciate from recent experience that it's hard to know how much "help" someone's looking for.
I see it like this: Steve is putting this out for a reason, and it isn't to show off his software. You can really help him. I know I would welcome any criticism that took my own design parameters into account.
You're right on about CAD. CAD is a racing bike, and hand drawing is a Sears single speed with coaster brake. Both will get you there, but neither know where they're going. They both have to be steered and supplied with a destination.
Regarding the design here, I can see that headroom is what's wanted and I know I wouldn't build a 30 ft boat that required crouching. It's clear that the box keel, even if only 20 ft long, is pushing volume down low, and yet the boat will not stand up (beach) on it reliably. Neither will it make an aisle to walk in because to sink it without water ballast would require a displacement in excess of the desired trailering weight.
My own inclination would be to have a dory midsection and a low rig and twin bilge keels for lateral plane and to hang some ballast from (beachability). The dory is famous for its seakeeping qualities and its ease of construction. That long bolgeresque waterline with plumb ends is good for ultimate speed but it might use some rake to increase light air performance and reduce or rearrange its displacement without losing deckspace or upper cabin room. A 24 ft waterline would drop the displacement by 20%, and yet lose only 8/10 of a knot. Now the midship section can be larger at the same displacement. A 10 ft2 midesection on a 30 ft waterline makes about a 10,000 displacement. A 12 1/2 ft2 midsection on a 24 ft waterline also makes for a 10,000 displacement.
Now the waterline beam could be wider, and the cabin sole deeper, and the boat will stand up on a three foot wide bottom. If the galley were full height (6' 6"), by sacrificing a three by four foot long area of the box keel cavity, the loss of water ballastable space would amount to maybe 700 lbs, but maybe 1300 lbs of water would be left in the remaining box keel.
The the boat would weigh 8700 lbs on the trailer.

 

Here's what happened when I drew it...

 

Just doodling

 

Scheldeschouw

Hoi Lewis,

Found this thread very interesting, perhaps the lines of the 30ft steel Scheldeschouw can be of some inspiration to you.
Her speed often surprised me.

More pictures: http://www.bootaanbod.nl/01001362.htm (sales site link may become corrupt)

Design by L.A. Vermeulen Jr. about 196?