NEW BOATER!! Repairing stringers

Bigreddon

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Hi guys!! I love this forum!! It has answered all my questions about my first boat..a 15' fiberform 1978 with a 90hp mercury I6. Got it in the water twice, and now time to winterize.

I decided to replace the carpet, and found, ou guessed it, rotted floor. The 'glass is shot that covers the wood, up to about within three inches I where the 'glass meets the hull. I think I know what to do as far as replacing the flooring itself, and glassing over that. I have a question regarding the stringers.

This boat has two, and the glass over the top of the stringers (between top of stringer and bottom of floor) has all come off, and the stringers are wet...not rotten...but I'm sure they are on their way. The bottom of the stringer where the glass meets the hill is quite solid. My question is: if it's possible, can I remove the wood from the glass stringer and replace with new wood? As I understand it, the wood is just a form for te stringer glass...(that is , it makes a box section of fiberglass to add ridgidity to the hull.) I read in the restoration section about this repair, but couldn't find anything about removing the wood, but leaving the glass in.

Also, if that is true, if the top of the stringer is missing(which it is) the strength of the stringer surely comes from the sides of the rectangular stringer box shape, correct?

Any experienced advice would be appreciated. I expect to have many more posts here!!!(commentary, and advice!)
 

tpenfield

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You really are not saving anything by trying to re-stuff the stringer with new wood. Best to cut it all out down to the hull surface and build up from there.

The strongest part of the stringer is the top part (not the side). The taller the stringer, the more stiff it is.
 

tpenfield

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BTW - Welcome to iBoats . . . it is a great place for restoration and other technical advice.

Tell us a bit more about your boat and post some pics when you can.
 

Bigreddon

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Well..for $1000 here is what got...it's a 1978 fiberform tri hull, trailer that needed a winch strap..mercury 90horse outboard, and was pretty quick on my maiden voyage(35 mph). I have since added a tach, replaced the water pump, fixed the ignition switch, bypassed the PTT Limit switch, remounted the PTT pump, rebuilt the carbs, lubed up and cleaned off all the 37 year old grease from the steering, mercontrol, and shift linkages. Ordered new shift and throttle cable. Fixed the broken bimini slider. Now...the floor!! That should be everything. (Not much left on this little boat!!
 

Bigreddon

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You really are not saving anything by trying to re-stuff the stringer with new wood. Best to cut it all out down to the hull surface and build up from there.

The strongest part of the stringer is the top part (not the side). The taller the stringer, the more stiff it is.

So my question would be..if the taller sides make the stringer stronger, how is it the top is the strongest part? Seems if you had a flat surface(top of stringer) versus the side of the stringer being taller , the top would have no strength gained. Taller sides would flex less right? Like the old plywood comparison...a life of ply flat on the ground is easy to bend up and down...but that same ply on its edge is impossible to bend...
 

tpenfield

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It is all about strength of materials and beam characteristics. The hull acts like the bottom of the beam . . . the stringer is the upright (depth) of the beam. The deck act like the top of the beam. The most stress is at the upper and lower most portions of the beam as it is caused to flex.


The center section of the beam does not do much as shown below, as an example of beam flexing . . .

2444_Determine%20the%20maximum%20bending%20stresses1.png


The fiberglass coating over the plywood adds some strength to the beam (stringer) but typically the wood is most of the strength, depending on how much fiberglass is at the top of the beam (stringer).
 
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alldodge

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:welcome: to iboats

Well tpenfield knows this stuff better then I but I'll comment; The stringer needs all parts, sides and top. The glass encapsulation provides additional strength but the wood is were the actual strength is. A thin layer of glass keeps moisture away from attacking the wood core. If you take the top off a 2x4 by and inch or so, your not going to be able to glue or screw a top back on it to make it as strong as the original 2x4. The lateral forces on the stringer by the engine is held from bending by the glass to the hull. The stringer does not come in direct contact with the transom, glass is used between the two surfaces. The glass is used to provide some flex though it be kind of small, it helps from having a hard spot. Hard spots are avoided because they can cause cracks in the outer hull
 

Rickmerrill

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BRD, since your stringer has wood in it I doubt it is just a form for a fiberglass stringer. By laminating the wood it makes for a much stronger stringer. How thick is the fiberglass on the side of your stringers? Better yet let us see what you are seeing.
 

Bigreddon

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Trying to Upload pictures from my phone but keep getting a.JPG error… i'll get some pictures. So as I understand the stringer works kind of as a lever to help keep the transom from flexing by placing the engine torque along the stringer to the base of the hull? The glass around the stringer it's sticker on the sides then along with the top. Actually most of the top glass is no longer there as it rotted away with the floor. The glass that went over the floor is pretty thick where it meets the hull, and becomes thinner towards the center of the floor. Suffice to say I should remove all of the old glass up to or very close to the hull so as not to damage the hull, remove the glass from around the wooden stringers and re-glass everything once I get my stringers installed? I LOVE THIS FORUM!!!
 

Bigreddon

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Also, I have read to avoid a solid wood as it expands more than the fiberglass should it get wet causing the fiberglass to stretch and break is this true.?
 

Rickmerrill

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They did an upgrade to iboats a few months back and the upload facilities haven't worked well since. Most of us upload to photobucket, free, and then copy the img file from there and then you can just paste the link right into your post.
 

alldodge

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Also, I have read to avoid a solid wood as it expands more than the fiberglass should it get wet causing the fiberglass to stretch and break is this true.?

Who or wear ever your reading that, you need to delete that link and try hard to erase that from your memory. You need solid wood and preferably kiln dried wood. Wood once encapsulated will not expand or contract due to moisture if it is dry. If the wood is wet or moist it will, and with all expansions and contractions, it will then delaminate from the glass. Glass will also not stick to damp wood
 

tpenfield

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I think the best bag for the buck on DIY restoration wood is good ol' Exterior Grade Plywood. Less $$$ than Marine grade, but pretty much the same characteristics . . . same glue.

If you can post your photos to a photobucket (or similar) account, then it is fairly easy to paste the image links into the the posts.

I will admit . . . I am more of a fan of using foam as a stringer core on a complete rebuild than wood. Either one can get you good results and we have seen plenty of good restorations here on iBoats. The only draw-back I see with wood is that it readily absorbs and retains water. Foam (closed cell) does not . . . The only problem is that the strength has to come more from the fiberglass than the foam. With wood as the 'skeleton', you can rely on the strength of it.
 
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Bigreddon

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Here's where I found about not using solid wood...ever...http://boatbuildercentral.com/howto/repair.php

I have manged to remove the foam and floor from the port side. As I stated, the glass has come off the stringer along the top, but near the helm te de lamination has stopped, and the wood floor is drier, and the foam is totally dry. This is as far as I can go. I dot have the means to have the helm/"dashboard" windows and walk through/seats of bow to be removed. I'm going to replace the floor as far forward as the helm, and the stringers from stern to helm. There is about 6 inches between the floor and hull at the stern, but less than 1/2 near the helm, where the foam is dry. Although not perfect, I would expect good results with new stringers running from stern to helm, and joining then up with what's near the helm.
 

Bigreddon

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Nov 21, 2014
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Here's pics. Port side floor and glass removed....viewed from transom..
 

Bigreddon

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tpenfield

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The pictures help visualize what you are doing. If you have good structure in the forward part of the boat (which is often the case) there is no crime in making an overlap joint up near the helm to bond the new structure to the existing structure.

"Woodonglass" (a forum member here) has a lot of illustrations and write-ups on stringer fabrication and bonding that you can take a look at by checking out some of his posts, etc.
 

Bigreddon

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Nov 21, 2014
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Thanks for the tips and encouragement . I will post more pics after the floor is gutted.
 

Watermann

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She's a little cuttie, I can see why you're wanting to make her new again :thumb:

You have the photo posting hard part done, when viewing your pics at PB, click in the field to the right that says IMG, it will auto copy and you then just have
to paste in it the message field here... like this.

Oh and I see that flag in the background... GO Cougs!

 
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Bigreddon

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Nov 21, 2014
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That's my neighbors house....he's the cougar fan!!! I'm a Duck fan. GO DUCKS!!!

I have the foam removed, and the stringers exposed. As I explained, the glass on the top of the stringers was all but gone. I have found the sides fairly intact, but they aren't adhered to the wood stringers. The glad is solid at the hull. Should the glass actually adhere to the wood? I find it odd that not one spot of glass was actually stuck to the stringer. In my pictures you can see the inboard side of the port stringer, and the glass I removed from it. Also, I have a picture of the inboard side of the starboard stringer with a pry bar between the glass and stringer to illustrate of what I speak. So...should the glass be adhered to the glass?
 
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