Adding Stringers

[Josh viking]

Hi there everyone, with regards to stringers, I am in the process of redoing my 16.6 ski craft. To cut a long story short I've had to remove everything down to the Hull. For some odd reason this boat was never built with stringers. It relied on 6 foam filled strakes for strength which as I'm sure you can imagine have not held up too well. I have sanded the top off, removed the foam, On the inside of the hull and filled them with a fillet mix. I had to sand down the entire hull as the old patches over the years were not done right and had gotten moisture in between. I am going to add a entire layer of glass to the hull to thicken it up a bit and then install stringers. I am going to be using sealed plywood 18mm. I think that's about 3/4 if I'm not mistaken. This will be tabbed in and then glassed. Would it be better to have 4x 3/4 inch stringers or 2x 1,1/2 inch stringers. Basically laminating 2 of the 3/4 together and then installing them? As for the placement. Should I just go in the same position as what the strakes are, or choose a new position which suits my intended layout better. I will add some photos for a reference. Thanks in advance.

 

[Josh viking]

 

[Big Fish]

Just my opinion, I would go back with 3/4 stringers and put them back were they were. One in center and then two on each side. Your picture looks like there were 3 on each side of center stringer. That’s the way my boat is made and I figure it must give the strength to the whole hull.

 

[kapnD]

Just a word of caution, the amount of work and cost of materials involved for a dubious outcome often makes projects like this regrettable.
I’d be shopping for a similar used boat that’s in good condition.
If you’re dead set on proceeding, do a careful weight analysis before beginning, a small boat won’t perform well if it’s overloaded, and it sounds like you plan to build heavy.
Two 3/4” stringers and two bulkheads well bonded to the deck should do it, and I’d skip the extra layer of glass on the floor.
How’s the transom?

 

[Josh viking]

Hi KapnD thanks for that. I bought the boat as sea worthy with valid certificates and all. Turns out the guy who surveyed it is friends with the previous owner..... im sure you get the idea. So unfortunately there's no going back now as the deal is done.

I will try go as light as possible. Perhaps just do 2x single stringers. I would have loved to use composite foam for reduced weight. But it's extremely pricey. The transom has to be done too, but I will be saving some weight by doing the deck with honeycomb. Aka "nidaplast" I put in the extra layer of glass on the hull today. The reason for that was some areas being very thin after grinding out the old patches that people did over the years. When they glassed things in they never sanded properly, didn't do it in dry conditions etc. In some places I sanded off half an inch of resin that had pooled up. Really got ripped a new one on this deal, but I will make the best of it

 

[Josh viking]

 

[kapnD]

Transom is extremely thin to be supporting an outboard motor.
How big a motor will it need to carry?
This is where the sandwiched double plywood goes.

 

[Josh viking]

What you are seeing there is the outer layer of glass that is remaining after I removed the rotten wood. I have 2 pieces of 21mm ply that will be sandwiched in there. The boat has twin 50 yamahas

 

[Josh viking]

 

[Josh viking]

Just my opinion, I would go back with 3/4 stringers and put them back were they were. One in center and then two on each side. Your picture looks like there were 3 on each side of center stringer. That’s the way my boat is made and I figure it must give the strength to the whole hull.

Hi Bigfish. When you say that I should put stringers where they were, are you referring to where the foam filled strakes were, that area you see in the center of the hull close to the transom that looks like it had something glassed in there was the transom support. There was a piece of ply glassed in at a 45 degree joining the transom and the hull.

 

[Big Fish]

From your pictures , looks like there was one in deep v and then two on each side. That’s the way my boat was made so I’m going back the same way. Mine were 3/4 ply wood that were Tabbed in then two layers of glass on them. I am going back with plywood since that’s what was originally built with and Cosa board is so expensive.