Lofting the Brewer catboat

[Mrleft8]

I assume that you'll be laminating your mast... I'll keep an eye out at my local yard for nice Black Spruce stock if you'd like...How much will you need?

[Jim Ledger]

Not laminating, Lefty. Birds mouth, maybe, but not laminating. If you could ask around about a suitable tree I'd appreciate it. I see Ken Hutchens used a nice Black Spruce for his mast. That would be best, unless an unusually large (for these parts) piece of Douglas fir should turn up. Thanks.

Here's a link to the "Silent Maid" build with some nice shots of the keel structure. Again, the CB slot looks about 2" wide. Silent Maid is about 30' with about a 900 sq. ft. sail, and so is considerably larger than the design in question.

http://www.woodboatbuilder.com/pages/maidhome.html

[merlinron]

there is a way to do a reliable, easily done "bicycle brake cable" style pendant attatchment on a wood board of about 1/12 inches or more thick and include a radiused track for the cable to travel on without derailing when slack. it doesn't involve any expensive machine shop time, either, just a couple of suitable sized plates, a short length of bronze or stainless 1/2+/- in rod, some bronze or stainless flathead machine screws of 1/4, 5/16 or 3/8 diameter as long as the board is thick and some simple hole to drill. screw and pin sizes will depend on weight and size of the board.
i am not a whizz on this computer thing and don't have or know how to draw on it, but i can try to explain it....

from the top edge of the board, where the pendant would attatch, lay out a radius that suitably follows the path that the forward edge of the pendant needs to take from the winch to the board when down to eliminate any hard spots. this radius is drawn down into the board so that it's upper end is at the top edge of the board and aimed at the winch, just as the pendant would lie when the board is fully down and extended into the board about 8 inches or so.
next, layout a line that follows the pendant's aft edge from the board to the winch. lay this line si ther is about an inch between the forward radius line and the aft line at whatever depth into the board you chose to stop the forward radius line.
next, lay out a circle, square area at the bottom od these two lines that will be large enough to contain whatever method of pedant attatchment you want to use. a rigging toggle would work great here.
now, cut this layed out shape out of the board.
next, figure out how big a plate you need to cover the hole you just cut out and overlap the hole by 1-1/2 inches at the top fore and aft and at the bottom of the hole. lay out the plates on both sides of the board, and let these plates into the board so they are flush to the sides. when you are satisfied with thier fit in the board, clamp them in place and drill through both plates and the board with a tap size drill for whatever size flathead machine screws you chose. tap threads in one plate and drill the other out for the screw size. counter sink the holes in the drilled out plate to recieve the screw heads fully flush. make sure the head of the screws are good and flush, even sunk into the plate just a bit. you should now be able to clamp the two plates in thier mortices with the screws.
now, on the inside surface of the plates, lay out a center for the pin where it will be located at the bottom of the cut out and positioned to be in the center of the one inch gap between the forward radius and aft pendant lines. this is the pivot pin for your toggle that is contained in the space at the bottom of the cut out. drill a small pilot hole here, throught both plates. then take a drill bit that will be a loose fit on the pin and counterbore the inside of the plates, just stopping before the drill breaks through the out side of the plates, making shoulders to contain the pin betweem the plates. size the pin length to fit snug in the hole, between the plates clamped in the board.
by this time, the rest is pretty obvious..........
if you would like a drawing of this, pm me your adress and i'll draw something up.

[Ian McColgin]

I'd ask Brewer about converting to a wood board.

I think it would be too big to just widen the keel slot without adding a lot of structure down there, which in turn would obstruct the flow fore and aft in the two bilges. Unless you have enough water to overtop the floor boards, there's no way for water to get from one side to the other, so plan on two pumps. Add a pile of stuff on either side of the keel and you have to add a couple of pumps forward.

It could be that off-setting a wooden board would work with some accomodation changes. You could get a nice double berth next to the board, maybe even going out under the bridge deck a little, more the companion a bit more on center and make an actually pleasant head at the foot of the companion. Or, much like the current layout but swap head and galley with the head access from forward.

One advantage/disadvantage of the heavy metal board is that as it drags on the bottom it slows you down. Nice if you're inattentivly heading toward the hard brown stuff around the edges as it stops you while you're still floating, often. But not so good if you're bouncing a shoal you know you'll get over.

I cannot imagine that the shere weight of the metal board adds to stability, but it may slice the water more nicely than a thick board and the weight might damp the roll a bit. Brewer thought about all this and if he thinks it a wretched idea, won't charge (I imagine) for calling you and your pals on WBF fools. If he thinks it possible, I bet the fee for him engineering it right would be more than worth the cost.

G'luck

[holzbt]

The centerboard on the Modesty (36') is 1 3/4" thick. Red oak drifted with galv. steel. Seems to have lasted okay for the last 28 years and hoisted by a simple tackle on the cabin top.

[Jim Ledger]

Thanks for that, Merlinron. I had to read through a couple of times to get the gist but it seems like a good method.

Of course, your right, Ian, asking Mr.Brewers opinion of the wood board is the thing to do. Going the whole route and asking for a design with construction details scares me a bit though. Asking architects how something should be done is often something I regret, wishing I'd kept my mouth shut. I mean, a solid wood board, even a triangular one, shouldn't be a difficult piece of work. Nor should a through-bolted case instead of a plywood one. The only difference would be the increase of an inch or so of width to the board, slot and case. Not much really.

As for widening the keel, the design calls for cheek pieces to be screwed to the sides of the keel to increase the back rabbet. Widening the keel would incorporate these cheek pieces into the keel itself, leaving the bilge architecture pretty much the same.

Now, how about boxing the heels of the frames? I want to but the design calls for frames stopping short of the keel, bolted to the floors. Very good for drainage and easy to build but..

..a catboat endures a tremendous amount of torque. That big, unstayed rig up forward, working against that beamy hull puts a hellacious amount of twist on things. Sea Rover has frames 1 3/4" by 2 1/2" half dovetailed 2" deep into the keel with wedges that locked everything in place. Crosbys did this and it's not an uncommon detail in many older boats. Seems better, somehow.

You see, I'm not experienced with working from designers plans and I'm not sure how much is written in stone and what's intended to be left to the builders discretion. The shape of the hull, the rig details and general layout are what I want from the plans. When it come to the joinery, I'm kind of opinionated and don't take instruction well, unless I happen to agree, of course.

Here's a small bit of progress. the grid is laid out and the profile is drawn. This is the profile of the tumblehome stem.

[Jim Ledger]

The centerboard on the Modesty (36') is 1 3/4" thick. Red oak drifted with galv. steel. Seems to have lasted okay for the last 28 years and hoisted by a simple tackle on the cabin top.

Maybe we can take a look during the boat show at the Museum in July.

http://www.limaritime.org/boatshowpage.html

[holzbt]

[holzbt]

[holzbt]

[Ian McColgin]

Here's why Jim will get Brewer to at least approve if not engineer any change to an off-set board and/or wooden board. The stresses on a little barely one ton boat and a boat that displaces five or six tons are huge.

[paladin]

Jim...early next week maybe the pony express will bring you some drawings by Charles Wittholz, similar sized boat for comparison....

[Ian McColgin]

Chuck, is the Wittholz as hefty? I always think of his work as less mass-intensive but I only know of, not viewed, his (what is it?) twenty five footer.

Jim, don't you just love that stem. And that's only one of the incredible curves. The whole boat is such a riot of shape it's for Brewer what Bounty was for LFF. Like LFH stems, that's an easy one to get wrong. In life it makes the boat float above the water.

I want, project #7,458 when I have the $$$$, to put in a controlable pitch prop. Probably Sabb since Hundestead doesn't make anything small enough. Especially for a catboat, where motor loads vary hugely depending on whether you're flogging into wind and sea, cruising across a plate of glass, or using the mill to keep her speed up around five on a beat with a deadline, the ability to match seems a good thing. The Autoprop, nifty as the concept is, has an interesting wear problem I'd want to know more about before going that route.

I saw pix of a glass Chappy 25 that had a hefty outboard set in a well under the cockpit sole. I don't see how this idea could work in wood but it does raise the notion, why not gain some real sail efficiency by off-setting the shaft and prop? Given the hull shape, I'd expect her to pull hard on the prop side in reverse but otherwise, the extra efficiency under sail might be nice. Sorta. As drawn, the Chappy is really docile under power, very easy to bring into the dock at a crowded resteraunt-bar and look like you know what you're doing - Anyone know Baxters?

[Jim Ledger]

Roger, thanks for the various offset trunk details but I'm not ready to re-think things to that extent. Still like to have a look a Modesty's trunk, though.

Chuck, thanks, what can I say? I'll be looking forward to seeing the Wittholz plans. A comparison will be very informative and no doubt provide a lot of new ideas.

Ian, That stem profile is almost too much. In a good way, of course. No one will ever call it understated. Sheer's nice, too. They look so good on the flat I can't wait to see them in three dimensions. The numbers are working out really well, so far, nothing more than a sixteenth off the batten, which I call dead-on.

A word about the Sabb adjustable pitch propeller. Sea Rover has a Sabb G-10. One of the last. A great engine and particularly suited to a catboat. You have to account for the slow acceleration of the single cylinder with the heavy flywheel while maneuvering in close but it has plenty of power. I've always used it with full pitch an all conditions, so far.
I'm not sure that the propeller could be used without the engine, as they're designed as a unit. I'll explain more if you're interested.

.

[Joe (SoCal)]

What no photos?

Even still I'm sitting here with a Homer Drool

[norseman]

Sounds like an interesting project. As to propeller systems, as far as I know almost any combination is possible. Depending on your budget..
http://www.westmekan.com/index.php?o...d=29&Itemid=29

[Jim Ledger]

What no photos?

It's difficult to get interesting lofting pictures. Although the process is fascinating, it doesn't translate well into pictures. So, to play it up for the camera, here's the rudder. The BARN DOOR rudder.

[Jim Ledger]

Picture of the day.

The half-breadth of the sheer.

[paladin]

Jim.....I made some drafting "ducks" about three times the normal weight for such things.....then used a lot of salvaged diving weights in place of the ice picks....saved the "drafting table"....helps you develop the strong forearms for operating the tiller later......

[Jim Ledger]

Good idea, Chuck. A little more exercise at the end of the day might be a good thing.


Larry, 6-0-0+, station 4.

[Jim Ledger]

Here you go, Larry, the midship section. At this point it needs a little tweaking but you get the picture.

The pattern seems to be...get a curve down, play around with it, then leave it overnight. Go read Chappele, Vaitses or a something Fenwick Williams wrote about catboat design, "Design Elements of the Catboat". I find these books very difficult to study without actually lofting a boat. Once immersed in the process, however, they suddenly become extremely relevant and useful. The logic and sequence to take is not immediately apparent and I'm content to take things slowly, enjoying the lines as they emerge, hopefully there won't be too much backtracking. Maybe it's the white paint but these lines are a bitch to erase.

[JimD]

you mean overall beam is 12'.. Wow.... a big 'un

Twelve feet and an eighth of an inch.

[Jim Ledger]

Twelve feet and an eighth of an inch.

Plus rub rails.

[Joe (SoCal)]

This is gonna be my favorite thread to watch.

I just had a dream that I won the lottery just as "The Legand" was finishing up this boat and I handed him a big bag of $$$$$ and sailed off into the sunset in a cabinet maker grade liveaboard catboat.

Given Jim "The Legand" Ledger level of skill and artistic eye this is going to be one of the great catboats of all time, so says I, one for the books.

[Jim Ledger]

Thanks, I may will look up for those books mentioned..

What are you using for drawing/lofting your lines with? Is its chalk?

No, pencil, carpenters and regular #2 and yesterday I picked up a box of colored pencils so thing don't get too confusing.

There's a lot of good reading out there about catboats, Larry. "The Catboat Book" for starters. The Catboat Association (http://www.catboats.org/) prints a great little booklet called "The Catboat and How to Sail Her" with lots of rigging tips. Stan Grayson wrote two books about cats, "Catboats" and "Cape Cod Catboats". "The Making of Tom Cat" is a good read, especially if you're building Bill Gardens Tom Cat design. Mystic Seaport has a nice little book called "The Building of Frances" about the recent building of a Crosby design that's a part of the museum exhibits.

And Joe, if you must, "legend" is spelled with an "e". You've got a pretty critical eye when it comes to catboats, as I recall. I've got some ideas I want to run by you next time we meet.

[Mrleft8]

I did that colored pencil thing when I did the lines for the Marjie B. It really does help a LOT.

[Russ Manheimer]

Jim,

Thanks for taking the time to let us watch over your shoulder. Some firm bilge there. What do you use for battens?

Russ

[P.L.Lenihan]

And Joe, if you must, "legend" is spelled with an "e". .

You'd think a guy posting from an 8GB iphone would at least have spell check and the Merriam-Webster on the darned thing.....

But no matter how you spell it,the spirit is right and many look forward to this long treat of a thread!

Peter

[Jim Ledger]

Jim,

What do you use for battens?

Russ

Hi, Russ.

I've been putting aside suitable rippings for some time and have a nice selection. The batten shown outlining the sheer is glued up from three lengths of clear cedar. It's good for long, fairly easy curves and measures about 3/4" x 1 1/4" x 36'. Getting it home was fun. For the body plan sections, as shown, I'm using some red oak about 1/4" x1" which can be sprung in one, two, three or four layers depending on the curve. The oak takes a tighter bend than cedar or fir without breaking. As needs arise, I'll rip whatever sizes and species works in a particular situation.

[Joe (SoCal)]

Love the strategicly placed Catboat Assoc. coffee mug

[Robmill0605]

I'm really enjoying this thread, I like the use of the icepicks instead of nails. I'm making some lofting whales to try out like Chuck has.
Looking like a terrific start. Thanks for the pics! More!

[Jim Ledger]

I like the use of the icepicks instead of nails.!

The icepicks are an idea out of Alan Vaitses book "Lofting", a book which I'm finding a great help. The icepicks are quick and easy to use single handed, but they do get in the way a bit sighting down the battens.

Getting into the thick of it a bit more now, the body plan. Things aren't lining up as nicely as in the beginning, lines are shorter and more quickly curved with the marks more closely spaced.

Let me try to explain what's going on for those who might be interested. Many here have been through this and already know, but there might be some with a desire to give it a try. For them, I recommend reading up on it and starting with something simple. My observations are those of someone with limited knowledge of the subject and should be regarded as such. However, I have no doubt that the results will be satisfactory.

The first things to draw are the lines on the boat that will be unchanging. By this I mean, that once plotted and drawn will not be subject to modification. These lines include the sheerline, outline of the keel and stem and the rabbet line. These are drawn in profile and plan view and provide a framework on which to work out the lines of the body of the hull itself.

Next, the body plan is plotted. It's shown in this picture, ten athwartships sections of the hull centered on that #5 line. You can't see them very well, though, because they're penciled in red, very finely. The reason for this is that they'll likely be changed somewhat as things progress.

The forward section is shown with the battens sprung around. Notice the nice bit of tumblehome in the bow.

After each section is plotted, its measurements are transferred to a stick, shown here. one side of the stick records the heights and the other side is used for the widths involved.

[Jim Ledger]

So, there are the ten stations, each one with a stick full of marks, carefully measured and noted. Here, each stick is placed on its corresponding station on the profile. Heights will be measured, referenced off the waterline. The waterline mark on each stick is lined up with the waterline on the drawing, then the rest of the heights can be ticked off, no measuring needed and so, less chance of error.

[Jim Ledger]

After the marks are transferred to the profile, the long lines can be plotted. These shown are the after portions of the buttock lines. They look neat, however they needed considerable tweaking to lie near their marks. Some of the marks couldn't be hit without bending the battens out of a fair curve. Hence the light pencil marks on the body plan. Things will have to be erased and redrawn until the views agree.

I should mention that at this point the table of offsets has been put aside except for reference. From this point on, the battens will determine the final curves.

[Ian McColgin]

I'd double check the off-sets. They should give a fair curve, even if it's fair in a way the batten does not like. A set of fair sections will not necessarily yield a fair hull.

Anyway, incredible job. Yesterday I painted Marmalade and plan to get her off the railway today. (That's why I'm up so early - crashed about 2000.) Painting is a wonderful way to really feel the riot of curves in this hull and there's really nothing like easing my arthritic back into the moaning chair with a glass of the good and the sunset giving harmony to the white topsides and red bottom.