Half hull model, need help with waterlines and boot stripe

[kanihoncho]

Hi all. I am building a half hull model and am creating the patterns for lifts from the plans.

The waterlines on this plan are 6 inches apart except for WL 24/LWL which is 6 and 3/4" apart. I want to add a 1/4" or so contrasting piece of wood for the boot stripe.

The extra 3/4" in the WL 24 is shown in green in the attached photo. The contrasting wood is represented in pink.

I plan to blow this plan up so that the lifts are all 3/4" wood. Why is the one lift a different size compared to the others and am I approaching this problem correctly?

Thanks, I'm sorry for the reduced size of the photo but those are the limits here.

1358

[Gerarddm]

Well, you may have to re-loft the plans yourself to get your equal lift thicknesses.

[gibetheridge]

It's hard to say why the person who drew the plans chose to put the waterlines where they are, but does it really matter? One of your lifts will have to be a little thicker than the others, and the next lift above will be 3/4 including the darker colored piece, no problem. You won't even have to do the math, just take it from the expanded drawing.

Maybe you will post pics as you go?

[Dave Lesser]

Welcome to the Forum, kanihoncho.

In some lines plans, the LWL is used as the basis, and the other waterlines are measured at fixed intervals above and below the LWL.

But for most plans, the basis is set at an arbitrary point, usually below the lowest point on the profile. The waterlines are then drawn at fixed intervals, and it would be strictly coincidence if the LWL fell exactly on one of those intervals. On your plan, since the LWL fell within 3/4" of the 30" interval waterline, the designer probably didn't want to clutter up the drawing with a separate line. Remember, the lines weren't drawn for the purpose of creating half-hull lifts of equal thickness. If you loft the plans you should be able to determine the shape of the lift at the 30" interval line.

If you want to add a contrasting boot top, it will look better if you add a little up-sweep at the fore and aft ends. The bottom edge of the boot top should be straight. Here is the lines plan for a half-hull model that I made:

http://farm6.static.flickr.com/5252/5472433289_56362a9915_z.jpg

The red lines are at the same thickness as the other lifts, but the boot top was made as a sandwich within the lift. This was done by cutting the sweep of the (walnut) boot top on a bandsaw, then cutting the upper part of the lift (pine) to match. These were glued together, then the flat bottom layer (mahogany) was glued on. The whole assembly was then run through the planer to get the right thickness of the lift before it was cut to shape.

http://farm6.static.flickr.com/5214/5472433341_8d36f26fc5_z.jpg

[CundysHarbor]

The way I do it, and I know that this is heracy to some, is to make section templates from light sheet metal and carve the hull from a solid block until the templates fit. If you glue in a contrasting clapboard shaped piece for the waterline, the top will be a nicely swept curve and the bottom level (with no fitting of curved surfaces needed). If the clapboard is twisted, the sweep can be made more pronounced forward than aft. This method was shown to me by Sturge Crocker with great enthusiasm. In reality, one cannnot glue six pieces of stock together and get six times the thickness of the individual layers. Once you see a half model done this way, the layered ones just don't look right. End of rant.
Dave

[kanihoncho]

Dave,

I'm not a purist so, though I want to be fairly accurate, I'm willing to learn as much as possible. Since you build from a solid block I assume you have a three piece block, to add the clapboard piece, to carve from? Do you find the time factor for carving that much longer? I can see where the band saw and the supporting cutouts would be much safer.

[kanihoncho]

Dave,

Great information. I am taking a lofting class next month to learn a bit more. I love the way you do the bootstripe, I haven't seen anyone do it that way in wood. I assume you are resawing the two pieces to form the boot lift? Are you that good with the band saw to get a perfect seam?

[Dave Lesser]

Are you that good with the band saw to get a perfect seam?

No, not at all. There is some shaping and sanding to do, but it is not very difficult to get a good fit, especially with the soft pine. I found that the trick was to get a good fit between the pieces before using the planer to set the final lift thickness.

This is a slight modification of the method that Eric Dow described. He wrote an excellent article that includes lots of illustrations in WoodenBoat #182, available as a digital download in .pdf format from our hosts for $3.50. It would be money well spent if you're interested in making half-hull models. Eric also teaches a course in half-hull modeling at the WoodenBoat School.

[kanihoncho]

I DL that and a couple of others last night and am reviewing today. Too bad this site doesn't have a dedicated thread for half hull building.

[CundysHarbor]

Yes, I use a three piece block; underwater, boottop and topsides. Does it take longer? I believe it probably does although I never worry about time spent in the shop. How you remove the excess stock has a big effect on time.
Dave