Lapstrake lap width

[timo4352]

How wide would you want the lap width to be using 3/8" or 9mm ply for a hull like my Ninigret? Hard chine. Lapstrake sides only --- the bottom is sheet plywood.
The frames all run straight from the chine to the sheer, so kind of slab sided, I guess.
I'm thinking one inch would be good...or is that too much?
Planning on using 5 planks.

Ninigret-3.jpg

[Rich Jones]

On my glued lap boats, I've used 1/2" laps. But, these are small human powered boats not subjected to the stress of power. I wouldn't go any smaller then 3/4". One inch should be plenty.

[Timo_N62.9_E27.7]

My boat http://forum.woodenboat.com/showthre...screte-ST-quot
has 25mm laps. Remains to be seen whether that is sufficient, the boat was in the water for the first time today

[DoctorB]

I recall my Atkin skiff was 1" - a nice easy number. That was riveted cedar though.

[Thad]

The only rule I know says double plank thickness, 3/4 inch in your case. With glued lap construction I would imagine 3/8 is really enough but that little more might be a good idea to make sure you have enough lap.

[Peerie Maa]

The only rule I know says double plank thickness, 3/4 inch in your case. With glued lap construction I would imagine 3/8 is really enough but that little more might be a good idea to make sure you have enough lap.

^This. 3/4 inch.

[Ian McColgin]

Why?

Why lapstrake?

Why such a drastic reduction in plank thickness?

[Max F]

I learned in the boatbuilding school that the traditional lap was to be 2.5 times the thickness of the planking stock.
I know some folks do less lap when gluing with epoxy, but I like this rule and had all my boats build with this rule.

[timo4352]

Why?

Why lapstrake?

Why such a drastic reduction in plank thickness?

The plans call for 3/8" lapstrake planking for the topsides.

[Ian McColgin]

I misread the remarks on the Atkin site. 3/8" it is.

I wonder if the hard chine does the job or if a lifting strake is needed. And could it be that shifting to lapstrake for the topsides will somewhat take the place of a lifting strake?

So many choices. It will be interesting to see how you interpret this nice little boat.

[Peerie Maa]

I misread the remarks on the Atkin site. 3/8" it is.

I wonder if the hard chine does the job or if a lifting strake is needed.

Yes, if your lifting strake causes the flow to separate from a round bilge hull.

And could it be that shifting to lapstrake for the topsides will somewhat take the place of a lifting strake?

No they are not deep enough to have any hydrodynamic effect. They will substitute for longitudinal stiffening battens through as well as looking better than boring flat panels. There is a batten on the bottom for stiffening as well, I notice.
Lapstrake topsides may make skinning the boat easier if there would be double curvature in a single panel.

So many choices. It will be interesting to see how you interpret this nice little boat.

[timo4352]

... They will substitute for longitudinal stiffening battens through as well as looking better than boring flat panels. There is a batten on the bottom for stiffening as well, I notice.
Lapstrake topsides may make skinning the boat easier if there would be double curvature in a single panel.

I'm thinking the laps forming battens will stiffen the sides, kind of forming a grid with the frames...
Possibly the sides are not developable and need to be done lapstrake..?
It looks good in any case.
2.5 times the planking thickness gives me 15/16" laps, so one inch would be easier to deal with, I guess.

[Canoeyawl]

^^^
One inch is easy, and I think you are correct, the lap forms a structural batten or beam.

[pvg]

Rule of thumb, as Thad said in post #5 above, is twice the plank thickness; however Iain Oughtred calls for 1" lap for the 9mm (3/8") planking on the PennyFee.
pvg

[nedL]

I’m not sure I can agree with some of these “rules of thumb” (i.e. 2x or 2.5x planking thickness)... my planking is 7/8 cedar and I know the laps aren’t 1 3/4. Maybe it works for thin planking/small boats, not su much as they grow.

[Thad]

Probably. Rules are made to be broken. Good sense rules.

[Canoeyawl]

Maybe a new rule? It is more about the fasteners than anything else.
Say ten times the fastener diameter, or maybe 3x the rove dia. ?

[Peerie Maa]

Maybe a new rule? It is more about the fasteners than anything else.
Say ten times the fastener diameter, or maybe 3x the rove dia. ?

Nope. It is about the wood. The same dia fastener will split the wood near the end of a plank when it will be OK away from the end. Eric McKee drew an excellent diagram illustrating the issue.
Scan_20191020.jpg

[pvg]

I’m not sure I can agree with some of these “rules of thumb” (i.e. 2x or 2.5x planking thickness)... my planking is 7/8 cedar and I know the laps aren’t 1 3/4. Maybe it works for thin planking/small boats, not su much as they grow.

I thought it was understood that "rule of thumb" is kind of a suggested starting point; not a hard and fast rule. Again, I like Thad's remark in post #16, "Good sense rules"
regards
pvg