Question about transverse planking

[Rush Wingate]

Hello all. Im Thinking of building a 20 foot punt based off this design. It calls for transverse planking on the bottom.

Two questions.
1. Are 1x6 boards good enough for a boat bottom like this? It will be used in light, protected waters, with a 40-50 hp outboard.
2. Is it ok to use fiberglass cloth over this planking, and if yes, is there anything i deed to put between each board? Or will the fiberglass cloth take care of it?
Thank in advance.

 

[BlueBell]

Good question but you should ask the designer.

 

[wet feet]

That is a huge punt according to the dimensions.Will it spend it's life afloat or on a trailer?

 

[Rush Wingate]

That is a huge punt according to the dimensions.Will it spend it's life afloat or on a trailer?

The plans in the pic have it at 26 foot. Its an Aussie style oystering punt. I plan to shorten it to 20'. I live on canal that feeds into the James river, and then to the Chesapeake Bay. It will spend its life on a boat lift when not being used in the water.

 

[Rush Wingate]

Good question but you should ask the designer.

Well thats an issue. The drawing is from an Australian maritime museum. There is no designer for me to contact.

 

[rwatson]

1 inch planks are 25 mm. Based on similar size boats, that's very, very strong for a 20 footer, and if you are going to fibreglass it, its going to be thick enough.
Most plywood boats that size use 16mm plywood, which is more structurally homogenous, but if you are going to glue the planks, as well as glass the outside, its going to be plenty strong enough.

Here is a link to a very similar deign, and it only uses 12mm play on its flat base.
https://boatbuildercentral.com/StudyPlans/HB20_STUDY.pdf

 

[jehardiman]

Yeah, what rwatson said. Even better if you spline the bottom planks together. Oyster skiffs/punts take a hell of a beating. Bottom planking is therefore comparatively thick because of the known wastage.

 

[Tops]

If you chase this link down to the larger images
https://forum.woodenboat.com/forum/designs-plans/9003422-sharptown-barges-built-in-sharptown-md
The material list would indicate find #6 as 7/8".
I am not an expert, just saw it and thought of this thread , to be used as a data point.
Boat is 22' LOA but narrow beam less than 5'

 

[rangebowdrie]

In a boat like that, (really a barge with one end sloped,) transverse bottom planking would be used as a means of reducing the number of frames, (or even eliminating most of them,) in favor of some longitudinal stringers.
The bottom planks would be vertical grain to prevent "cupping" and well caulked.
The boat WILL get wet on the inside.
Wet/Dry cycles WILL cause swelling/shrinking of the boards, and a layer of Fiberglas cloth will not prevent that.
Over some time, the cloth will split at the seams.
You'd be better served with plywood, (even more than one layer if needed,) that is glassed outside and WELL coated with epoxy inside.
Yes, planked hulls have been successfully "glassed over", but it take a LOT more than a layer of cloth.

 

[Dave G 9N]

Hello all. Im Thinking of building a 20 foot punt based off this design. It calls for transverse planking on the bottom.

Two questions.
1. Are 1x6 boards good enough for a boat bottom like this? It will be used in light, protected waters, with a 40-50 hp outboard.
2. Is it ok to use fiberglass cloth over this planking, and if yes, is there anything i deed to put between each board? Or will the fiberglass cloth take care of it?
Thank in advance.

1. Yes, on the 1x6, no idea about horsepower. The answer might involve how well you secured the planks.

2. No, a cross planked bottom does not lend itself well to fiberglass due to the way wood swells and shrinks.

A plywood bottom would be better. The cross plies do a lot to reduce shrinkage, so the glass can work a lot better on the more stable surface.

Longleaf yellow pine for example, which is available in VA as one of the various species sold as yellow pine: Shrinkage:Radial: 5.1%, Tangential: 7.5%, Volumetric: 12.2%, T/R Ratio: 1.5. Glass does not like to stretch, and the wood will generate a lot of force. If you only do one side of a cross planked bottom, it will try to curl right up.

Hampton has a good maritime museum if I remember correctly, so there might be someone there who can help. There are people familiar with this construction at CBMM in St. Michaels MD. They build boats like this and know more that I ever will. It will take lots of glass on both sides of the planks to overcome the swelling. File bottoms should live on the water because they are only watertight after they swell up and close the gaps. After one dries out, it opens up and leaks. This is normal. When you build one, you tie it up in shallow water and let it sink and swell until the seams come together. I have seen this done at CBMM.