Thickness of hull planks ?

I am finished cutting all the Stringers, frames & keel of the plan below. The parts weigh about 100 pounds. Engine is a inboard 305 CI Chevy with dry exhausts for raceboat get togethers. No mufflers needed.

Sooo. How thin can the 3 to 4" wide planks be if NOT using Mahogny ? How about Sitka Spruce or other similar weight & strength.

The version I am doing only has the rear seat open. Fronts are decked over. Engine in about the same place. We will slide the engine around to get level.

I know very little on very light race boats planking woods. I will be gluing the planks edges with those " Biscuts " for rigidty.

Thanks

Re: Thickness of hull planks ?

Nice. I'd love to see some pics. That is a really neat classic design!

Have you considered using plywood? If you are planning on making it a go-fast boat, which it appears you are- it could offer you SIGNIFICANT advantages. You'd be able to fiberglass it, and bond it all with epoxy- which would give you tremendous strength. It would be a lot less work down the line, too...

If you are a 'stickler' for tradition, you could always plank the topsides- And no one would ever know

If you choose to plank it, I'd contact a naval architect or builder who builds similar boats before I messed with plank thickness too much, and get some advice from them... Bottom planking is about the LAST place you'd want to have a failure!

Re: Thickness of hull planks ?

Uhm, is there a reason you are looking to change from the original batten seam construction? Also, 'biscuts' have no place in boat construction, they will not add strength. When you say you will "slide the engine around to get level", that's something you really can't do to much. A couple of inches forward or aft could greatly affect the high speed performance, and will change your shaft angle and strut & stuffing box requirements. Are the plans you show the actual design you are building, or just something similar that has been designed with 200hp in mind? The original Chas Mower design you are showing looks like it was designed for about 75HP (looks like a flat head four in the plans), not a 200 HP 305CID Chevy. Given the overall investment you will be making it might be a good idea to consult a proper N.A. about your changes.

Re: Thickness of hull planks ?

All of the internal parts are marine ply for rigidty. The frames are on 12" centers to prevent twisting a 48" wide hull. The keel & engine stringers are full depth. The lower V hull is a constant 23 degrees to the transom. Below is a picture the interlocking framing method being used. We will add very light Pine 1" x 1" triangular gusset strips on all 4 edges at each intersection. The floor will lay on top of gusseted frames, stringer & keel.
the bottom of the V skins are Marine ply for stiffness & weight reasons.
My question about planking was about the planking from the chine upwards.
All the old woodies I have seen & rode in all have hair line movements & cracks along board seams. Most are developing the dark mold streaks at the surface of the seams.
I am on the fence about just having 3.... 8' marine plies ..scarfed.. at a yard professionally and let the bow, 2 engine area frames & the transom dictate the curves. Boats of that period were quite slab sided. 1 of the reasons I picked this boat.
If scarfed ply is done. I have a friend that is great at applying vacuum bagged veneers over anything.
As this is my 2nd DIY, I am asking for help about my weakest area of knowledge.

I have been told several times, that a boat with a constant 23 degree deadrise this long, is VERY draggy & will eat horsepower without any doubts. Never can have to much power if the driver has no Death Wish. I have towed boats & like a good margin of towing power.

High speed in this boat is 35 to a maximum of 40. With the constant 23 degrees of deadrise full length, the risk of bow hooking is eliminated, compared to the " Warped Bottom " hull of the plans. I DO know for a fact, Warped Bottom hulls do bow hook viscously in a chop if on a full plane.

Thanks for any help.

Re: Thickness of hull planks ?

Oh, ok now, it sounds like you have a good handle on things, I'll give your question some thought & see if I can add any constructive comments. - I'd be interested in seeing lines for what you are actually building.

Re: Thickness of hull planks ?

Here is the construction " interlocking " that we will use for for the hull up to the chine.