How many layers?

[Manipulator]

Stringer repair. Plan on using 4 layers of fiberglass mat. Will it hold?

 

[Robj]

Re: How many layers?

What type of boat is it? How was it installed originally? Mine used only matt when installed at the factory. I used three layers of matt, then added a layer of WR around the engine mounts and about half way up the hull until the stringer starts to curve upwards. I had a post a few weeks back asking the same question, you should check it out. Pictures would also help others to see what you are dealing with.

Have a great day,

Rob.

 

[Manipulator]

Re: How many layers?

Thanks Rob. I have a Sea Ray, 1983. Heres the situation. The boat is a OMC stringer, with time the front hydralic rams started to leak. The oil got in and around the motor mounts and on top of the the front stringers. The front stringers look fine, oil didn't penetrate them. The rams/motor mounts have 4 holes to mount to the stringer. Sea Ray only used 3 of the holes. Two holes were in the stringer, then next to the stringer was a 6 inch piece of wood butted up to the stringer and epoxy/fiberglassed in and onto the side of the stringer. This small piece of wood had a hole drilled into it for one of the lag bolts. The oil got under the fiberglass that encapsulated this and the whole thing popped right off the stringer. It looks like they used 1-2 layers of mat and that was about it. I plan on grinding the glass on the stringer, installing this small piece of wood, epoxy it and use stainless screws or small lags to attach it to the stringer. Then epoxy and fiberglass it all in. There are so many types of mat out there along with the WR.This is the first time I have done this type of work and I am mechanically inclined enough to tackle this. Looks aren't my concern, strength is. Here are some pics to give you a better idea of what I am dealing with. Thanks for your help.

 

[Manipulator]

Re: How many layers?

Just looked, there is some rot in the stringer where the lags went in. It isn't wet just dry rot and I did some core samples around it and it was fine. What do you think about injecting epoxy in these holes then redrilling?

 

[Solittle]

Re: How many layers?

I'll leave comment on what to do to others.

Just got to say that I wish all posters would do the fine job you did with both the pictures and explanation.

 

[Manipulator]

Re: How many layers?

Thanks! As they say a "picture is worth a thousand words".

 

[Old Salt Oz]

Re: How many layers?

Standard resins are not that good at keeping water out of timber, add to this the fact the the timber used would have had some moisture of it's own when glassed as well as some natural oils. The bottom line here is that standard resin and Chopped Strand Mat (CSM) will not stick to timber in the long term.

Epoxy resins do stick very well to timber and go a long way to reducing water ingress.

Any and all holes drilled into the timber should be drilled at least 12 mm (Half an inch) oversize, then filled with Microfibers and epoxy resin, then re drilled to the required size after curing, this is also required when fixing through bolts for transom mounted drives.

New or replacement engine mount blocks (or other timber items) should be coated with an epoxy resin prior to glassing, to ensure good penetration the epoxy can be thinned using up to 40% by volume of methylated spirits mixed with the resin after the hardener has been mixed in, apply several coats, you will see when it's saturated, it stops sucking it up, apply extra coats on any end grain. Let it cure and sand off any high gloss areas with a 200 grit, just enough to remove the shine; let this cure and sand as above before glassing.

Any Stringers and blocks should have all corners well rounded to help the cloth follow the profile, also ensure the block to point of fixing has a good size well rounded fillet to run the cloth down.

When laying up ensure each layer is wider / longer than the last, this ensures the load and flexing is spread over a larger area and prevents 'hard spots'.

For most stringers 2 layers of 300 gram bidirectional or crows foot cloth will be fine, engine mount blocks will need an extra 2 or even three strips between block and hull applied like a flashing.
It's a good idea to add a layer of light rovings over the job after the last layer has been applied; this helps cover and prickly ends and heps in providing a smoother finish as well a good final rolling surface to remove any excess resin, most important when using an epoxy.

I hope this helps.

Avagoodweekend......