David wrote:

I would also cut away the radii in the corners. If the corners are square, it will be easier to bond on pieces of hardwood trim to cover the messy edge.

I will plan to do this as well. I found my tiny hack saw. I think it should work for squaring up the corners.

I started working on getting the core out with a chisel. Balsa is more difficult to break apart than I expected. I am happy it is not plywood.

Do you have a recommendation for a hard wood to use? My first thought was oak. Then I read on the West System website that oak should never be used with epoxy. I can't seem to find any ash boards. Poplar looked good, but then I found people online saying it is no good for boats due to poor water resistance.

The price of maple terrifies me. Hickory I have only found as flooring sold by the case.

At the moment I think Douglas Fir seems like the best option for 'hardwood strips' even if it is not really hardwood. 

David T wrote: I would rather chisel out the core to a depth of 1 1/2" all the way around, bond in hardwood strips in to fill that cavity, then bond and bolt the plywood on top. Having done that, an extra two squares of thick plywood of smaller size, surrounding the tabernacle, will transfer the load satisfactorily, to the larger square.

Thank you. This seems to be a very good plan. Hopefully after I chisel out 1.5" I will have solid dry core all around.

Your help is very much appreciated.

Scott

David T wrote:

I think we need more information and pictures to be of specific help to you, Scott.

Hi David,

Thank you for taking the time to respond. I will attach all the photos I took when I was at the boat. 

I am not sure what information to provide. The tabernacle will be buried in the deck approximately 890mm. For selecting a mast I came up with a target yield strength of 1753 kpm. I would like to determine what sort of deck structure I need to ensure that the deck will not crush or collapse if and when the mast really sees that 1753 kpm load.

If I understand all those numbers correctly then I think the deck will need to withstand a force equivalent to 1970 kg applied sideways. I am not sure where to go from there.

I need some advice on mast partners.

I do not remember any specific scantlings from PJR. I would appreciate any opinion.

I removed the hatch on my S2 yesterday. Unfortunately there is rot in some of the balsa. Fortunately it is not in ALL the balsa. I will be sure to repair any damaged core.

Beyond repair I am not sure what I should do. 

Including the gelcoat but not the headliner the deck is about 18mm thick. About 12mm is balsa. It is about 2.5mm of polyester and fiberglass on each side and just about 1mm of gelcoat. I attached a photo.

Is it enough to fill in the hatch area with a similar layup? Or does it need to be double this much all the way out to the hull side in each direction? 

David Tyler’s thinking around using glass sheathing makes sense to me.

I have used glass sheathing on two wooden masts, mainly to get a good protection against abrasion. The first mast was Malena’s hollow mast (1995). The (West epoxy) glassing was then given seven coats of two-pot polyurethane varnish, over twice the recommended. Still, after around 13 - 14 years, the glassing showed signs of coming apart on the sunny side. Since the owner didn’t take action, water ingress led to rot, and in 2011 the mast was scrapped. To me it looked as if the varnish held, but even on 59°N, it let through enough UV radiation to destroy the epoxy underneath.

The second wooden mast, the one for Johanna (2002), was given the same glassing, but this time the coating was white, two-pot polyurethane paint. I hope that this will hold better. It looked good when I sold Johanna in 2014.

The two wooden topmasts of my hybrid masts (2013 and 2016) have only been painted with many coats of polyurethane paint, without any glassing. So far, they look good.

What I want to try is to use polyurethane varnish as resin when glassing. If the stuff penetrates and saturates the glass nicely, then one can have a very strong and long-lasting surface. Since the glass will be invisible on more than 50cm distance, one could  have a nice clear-varnish finish (as on Malena’s mast), which will last ‘forever’.
I will try this on a piece of plywood, once the temperatures rise again...

Arne