Real basic material question

[Duane Brown]

For a small'ish 15'-16' lapstrake boat, what is your choice for the station molds? MDF? OSB? Ply? Don't want to build them with dimensional lumber I want to use some form of sheet material. Thanks.

[David G]

Lacking any further detail, I can only say: whatever the designer specifies... or, barring that, whatever is cheapest.

[J.Madison]

I did a 16' lapstrake boat with molds of OSB. It was $6 a sheet. I did it because I didn't know any better and it worked just fine. A couple 1x2s screwed onto the panel, horizontal on one side and vertical on the other would help prevent any warping if you are worried about that. I didn't add any reinforcement and was no worse off for it.

[TerryLL]

For a small'ish 15'-16' lapstrake boat, what is your choice for the station molds? MDF? OSB? Ply? Don't want to build them with dimensional lumber I want to use some form of sheet material. Thanks.

Any of the above will do the job, but using a decent quality plywood has a few advantages. The ply will hold its edges better than the OSB, and take screws better than the MDF. However, using sheet stock for the molds will require clamping blocks screwed onto the molds. I definitely prefer open molds made from dimensional lumber for the ease of clamping.

[Sayla]

For a small'ish 15'-16' lapstrake boat, what is your choice for the station molds? MDF? OSB? Ply? Don't want to build them with dimensional lumber I want to use some form of sheet material. Thanks.

Ply for re-use, but mdf is much easier to draw on, and cut. I have a lapstrake dinghy set up currently with ply, but I reckon I would choose mdf next time; as a one-off it's strong enough, and easier to draw on, and cut - there's a lot of angled cross grain cutting in it - some mdf is wayy cheap as well.

sayla

[Eric Hvalsoe]

My recent small boat molds have been of reasonable quality 3/4 inch ply, for some of the reasons stated above, stability, fastening etc. Strictly for a one off I can see an argument for less expensive sheet material. Pine lumber is the most pleasant to work but considerably more time consuming to piece together.

[JimConlin]

I've never built the same boat twice, so re-use hasn't been an issue.
My work space is subject to variations in humidity and some plywood curls.
1/2" MDF is my current preference.

[Bob Cleek]

My vote would be for natural "real" wood and not a sheet product. 1) It's cheaper. You will go through a fair number of 4x8' sheets if you cut your molds out of sheet stock and that adds up. One can generally find scrap pine, fir, or whatever (even busted up old pallets, if you don't mind pulling the nails) for very little money. You only need short lengths and there's much less waste. You don't have to worry about knots and such, low quality wood will do fine. If you have a dump that recycles old construction materials, you're set. 2) It's easier to work. If you are using the usual "nail heads on the line" method of pickinng up the lines from the lofting, real wood (especially the softer white woods) is much better because the nail heads will dent it much more readily. (It's sometimes nearly impossible to get a register mark from a nail head with chip board or oriented strand board because it's so hard.) Open centered molds are nearly a necessity for clamping, or else you are going to be forever screwing on clamping blocks, at which point you might as well have used real wood to begin with. There's no point in cutting the insides out of sheet stock molds when you can cobb together short lengths of lumber with drywall screws. Planing the edges of grown wood is far easier than manufactured sheet stock. Handling grown wood frames is easier. It's a lot lighter. You don't have to wrestle 4x8' sheets of the stuff on the bandsaw table or whatever. Frame removal when they've done their job is often much easier if you can disassemble a made up mold instead of pulling a whole sheet mold out in one piece, if that's even possible. Screwing ribbands to real wood frames is much easier than screwing into the edge of plywood and sometimes you can't get screws to hold in the edges of composition sheet stock at all. (The bending forces when fastening a ribband to the edge of 3/4" chipboard can easily bust the screw right out of chip board.)

[Duane Brown]

OK, thanks for all of the advice.. Specifics: The boat is Walter Simmons Ducktrap wherry, 16' glued lap ply. I already have all of the mold stations (station molds) cut out on mylar pattern stock. So what I was planning to do is use the edge of the mylar as the baseline which is how I layed them out. Lay the individual patterns out on the sheet goods and arrange them in a way that hopefully allows me to get good usage from each sheet.
I have been planning to start this boat since last year when I gott the plans but then I was the victim of a really really nasty hand injury to my right hand, I'm right handed, and now with only one surgery remaining (feb 14) and maybe two or three more months of physical therapy, I should be able to start building. I can use my hand somewhat normally right now and was hoping to sqeeze in some set up before my hopefully last surgery which will put me out of commision until about April or May. This sucks! I was just wanting to get the strongback set up with the stations, transom and stem and the keel member on. It doesn't appear that that is going to happen either as life, it seems, is going to prevent me from doing even that before my surgery.
I sort figured that using the sheet stock for the stations with the mylar patterns would reduce the chance of error in getting both sides the same. I don't have the same skill level and resulting confidence level as you more experienced folks.
I've been following Jim's Matinicus build and now I'm not sure that I don't want to build that instead. Oh the choices. It appears that I have a few more months to think about it now.
One or the other is going to get built though and my plans will be the same for either so this question applies to either.
Walt, by the way, uses boards for his molds but say that any other material connot be used.
By the way Bob, a very good reply. All very good points and they are well taken. I may just try them that way first and see how I do with that type of construction. I just figured it would be easier with the sheet stuff.

[Thad Van Gilder]

I like to use whatever mixed hardwoods are available at the local sawmill. 50 cent a bf is much cheaper than 3/4" ply and easier to work with as well.

-Thad