Any Creative Ways to Check for Dry Rot in Stringers & Bulkheads ???

[tpenfield]

Hi Folks:

I am in the process of checking the structure of my boat for dry rot (or wet rot) as I have an opportunity to fix things before the boating season arrives in the northeast.

Long story made short . . .

(1) Last year I was doing some R&R on the engine mounts and as I tightened the starboard mount (thru-bolted not lagged), I heard a 'crack' sound. I discovered that the stringer was basically hollow and it appeared that the wood core had rotted away, but was not wet (so dry rot ???). See attached pictures #1 & #2 . . .

I repaired the stringer by filling it from the top with polyester resin to make it solid. The port side seemed to be OK, so I left it alone.

(2) I removed the engine last Fall to do some engine work and re-finished the bilge while the engine was out. As I was prepping the bilge, I noticed that the bulkhead was not properly glassed in and had rotted (this area looked more like wet rot).

I also repaired this area and added 3 layers of fiberglass mat. See attached picture #3 . . .

Everything is now solid from the outside, no soft spots or anything like that; the transom seems to be solid as well. HOWEVER, I am thinking that there are other areas that have either dry or wet rot beyond the 2 areas that I fixed. Before I put the engine back in I am wondering if there is a creative way to determine if other areas of the stringers & bulkheads are hollow on the inside. I tried a stud finder to see if I can determine solid versus hollow areas, but I'm not sure it is really telling me much.

My Question/Challenge . . .

Other than getting some fancy (expensive) infrared equipment, are there some other creative (i.e. economical) ways to check for hollowed (i.e. rotted) areas? As I said, everything is solid on the outside, but possibly hollow on the inside.

I was thinking that I could drill some test holes in various places in the stringers and bulkheads to see what it looks like on the inside. I'm just wondering if there are any 'clever' ways of checking without drilling.

Sorry for the long story, I hope that you did not fall asleep reading this. T.I.A

Pictures below:

 

[ondarvr]

Re: Any Creative Ways to Check for Dry Rot in Stringers & Bulkheads ???

drilling is about the only method.

 

[Friscoboater]

Re: Any Creative Ways to Check for Dry Rot in Stringers & Bulkheads ???

Yep, drilling is the only sure. way. Tapping sometimes works, but if there is an air bubble between the glass on the wood, it can give you a sound like rot, when it is not.

If you found that you have a hollow stringer, you need to get that fixed asap.

 

[Yacht Dr.]

Re: Any Creative Ways to Check for Dry Rot in Stringers & Bulkheads ???

Yea.. um.. remove and rebed the motor mount L brackets.

Get a small screwdriver or ice pic in the holes that mount the alum brackets.

Good start.

YD.

 

[tpenfield]

Re: Any Creative Ways to Check for Dry Rot in Stringers & Bulkheads ???

I did some more inspecting and poking around today . . . it looks like I have another project to add to the list.

I think both stringers have dry rot going on in the area of the engine compartment. The dry rot looks like it is starting to extend itself more forward on the port side. The starboard side looks and feels OK.


Fortunately, the boat has a large hatch ( 2ft x 6 ft) in the cockpit floor that is there in case the fuel tank ever needs to come out, etc. So, I can gain access by removing the hatch assembly. I am wondering if I should remove the fuel tank as well . . . .

This should be *fun* . . . of course I won't start for another month or so, as the weather is too cold for fiberglass work.

I suppose I should post some pictures as I go . . .

 

[eclipse196]

Re: Any Creative Ways to Check for Dry Rot in Stringers & Bulkheads ???

I am new to this forum and relatively new to boat building. My son has a sailboat that he has reworked and is part of the boating community here in New Orleans. What I am being told concerning stringers is that it does not matter the condition of the interior of the stringers as long as the fiberglass is solid. It is the fiberglass that gives the strength. The only place that the inside matters is where you are doing thru bolting. I am in the process of rebuilding a boat right now. I will be starting a string as soon as I get the down time to do so. I am being told by the boat builders to make hollow stringers using plywood or foam board for the mold. Do the layup then remove from the form and install in the boat with the proper tabbing. Just what I am being told to do by those that do this for a profession.

 

[Yacht Dr.]

Re: Any Creative Ways to Check for Dry Rot in Stringers & Bulkheads ???

I am new to this forum and relatively new to boat building. My son has a sailboat that he has reworked and is part of the boating community here in New Orleans. What I am being told concerning stringers is that it does not matter the condition of the interior of the stringers as long as the fiberglass is solid. It is the fiberglass that gives the strength. The only place that the inside matters is where you are doing thru bolting. I am in the process of rebuilding a boat right now. I will be starting a string as soon as I get the down time to do so. I am being told by the boat builders to make hollow stringers using plywood or foam board for the mold. Do the layup then remove from the form and install in the boat with the proper tabbing. Just what I am being told to do by those that do this for a profession.

Welcome to Iboats ..

Um..I just had to log in to tell you that Im sure your son and his blow boat does not have a 350 or 454 mounted to his stringers.

Sailboats and powerboats are 2 totally different builds man.

Your 'professionals' are completely Wrong !! and yes .. WE here do this for a living.

Some molded stringer systems are designed to take the torque and stress for an I/O .. but trust me .. the Research to get those systems to pass CGR is very expansive and extensive. Even to Repair such a stringer system should only be done by True professionals and NOT for the DIY'ers !!

Please do not pass on information that you do not Completely understand Yourself..it could be dangerous to other members that might take kindly to your advise.

Peace.

YD.

 

[tpenfield]

Re: Any Creative Ways to Check for Dry Rot in Stringers & Bulkheads ???

Yup, I'm sure we are going to have a lot of discussion about stringers and strength of materials, etc.

The strength of a stringer really depends on how much wood versus how much fiberglass. A layer or two, just to encapsulate the wood really needs the wood. If the fiberglass around the wood is fairly thick 3-4 layers or more . . . then the wood is acting more like a core material.

I got some stringer areas where it definitely is relying on the wood and other areas where the fiberglass covering can hold its own.

I'm not sure how long the stringer situation in my boat has been playing out; the boat is 21 years old. It does have a 454 engine and the stringers, even hollowed out, have held up to the engine forces . . . but I would not want to let it go like that for too long.

Anyway, this should be a fun (?) project fixing my boat, and I'm sure I'll get lots of advice along the way, for which I am thankful

 

[ondarvr]

Re: Any Creative Ways to Check for Dry Rot in Stringers & Bulkheads ???

I am new to this forum and relatively new to boat building. My son has a sailboat that he has reworked and is part of the boating community here in New Orleans. What I am being told concerning stringers is that it does not matter the condition of the interior of the stringers as long as the fiberglass is solid. It is the fiberglass that gives the strength. The only place that the inside matters is where you are doing thru bolting. I am in the process of rebuilding a boat right now. I will be starting a string as soon as I get the down time to do so. I am being told by the boat builders to make hollow stringers using plywood or foam board for the mold. Do the layup then remove from the form and install in the boat with the proper tabbing. Just what I am being told to do by those that do this for a profession.

This only works if the stringer was engineered to take all of the stress without factoring in the strength of the wood inside. Plus, not only does the strength of the wood come into play, but so does the added strength needed when having a hollow (no) core. Without a core that can withstand the crushing effect of the stringer changing shape while being flexed and stressed the stringer needs to be built stronger and heavier.

So while it sounds good, many things need to factored in to determine whether it will work.

 

[BillP]

Re: Any Creative Ways to Check for Dry Rot in Stringers & Bulkheads ???

In this rare moment ondarvr and I actually agree. There are many boats plying the waters with foam/glass stringers under the motors. The only reason wood is used is because its faster, cheaper and easier. This isn't rocket science and any DYI can do it so don't get wacked out about it being only for "experts".

There are many ways to check and repair your situation...but have you considered the "dry rot" may actually be old foam? Core drilling is the easiest way to sample. Grinding or cutting (sawzall) off the top of the stringer is an option. A few layers of heavy glass over the old stringer will restore strength without a total stringer replacement too. You can cut out the motor area, set in new wood and glass it back together if you don't want to use glass for the entire buildup. Many ways to make this work successfully.

bp

 

[tpenfield]

Re: Any Creative Ways to Check for Dry Rot in Stringers & Bulkheads ???

I'm thinking of several techniques for restoration and will probably use a combination of all of them, based on the situation that I find once I 'open' things up to take a look. My thoughts so far . . .

- I need to see how far back the rot goes and do whatever I can to protect migration into the transom.
- the engine compartment stringers should have a solid fill because of the through bolted engine mounts. If I can easily suck out the remaining debris, then I will probably fill these stringer areas will polyester resin to get back to a solid structure for the engine mounts.
- the bulkhead at the front of the engine compartment and the rest of the stringers leading forward will be interesting. I will have to see what the situation is once I get in there for a closer look. I want to avoid major surgery and perhaps add strength by adding fiberglass.

We shall see . . .

BTW: There have been a few posts recently over on offshoreonly.com about rot in this vintage Formula boats (late 1980's - early 1990's). So, I can also see what these guys did to fix their boats.

 

[ondarvr]

Re: Any Creative Ways to Check for Dry Rot in Stringers & Bulkheads ???

My thoughts so far . . .


- the engine compartment stringers should have a solid fill because of the through bolted engine mounts. If I can easily suck out the remaining debris, then I will probably fill these stringer areas will polyester resin to get back to a solid structure for the engine mounts.


We shall see . . .

BTW: There have been a few posts recently over on offshoreonly.com about rot in this vintage Formula boats (late 1980's - early 1990's). So, I can also see what these guys did to fix their boats.

There are hundreds of stringer and transom replacement threads on this site, do a search and you will be reading for weeks.

Filling anything with polyester resin is of little value, while possibly better than wood pulp, the resin by itself is weak and brittle, it needs glass to have any strength.

 

[eclipse196]

Re: Any Creative Ways to Check for Dry Rot in Stringers & Bulkheads ???

Thanks for the welcome YachtDr. I was not really speaking with any authority or implying people on here did not know what they were talking about. I was just sharing what I am being told. I am still researching and reading through all these threads to get the true skinny on what I need to be doing with this restore I am doing. Sometimes it is difficult to reflect true intent in an email or post. I have seen several different approaches and want to make sure I do mine the right way without doing more work or spending more money than is necessary.

 

[oops!]

Re: Any Creative Ways to Check for Dry Rot in Stringers & Bulkheads ???

hi eclipse/

welcome aboard....

start a thread on your restoration.....lets see what you have got going on....

as yd suggested......a motor boat and a sail boat are two totally different things.

some of the guys that have responded to this thread are some of the top professionals in north america.....chance are that your boat building buddies use their services !

since there is no formal school for fiberglass boat building or re building............iboats has the largest library assembled on the subject.
we call it boat university.

so what ever your situation you are in with your, and your sons boat, we can help !

cheers
oops

 

[tpenfield]

Re: Any Creative Ways to Check for Dry Rot in Stringers & Bulkheads ???

There are hundreds of stringer and transom replacement threads on this site, do a search and you will be reading for weeks.

Yup, lots and lots of stringer threads here and elsewhere . . .

The only thing is that I guess OMC made an engine called the "stringer" ??? lots of those threads come up in the search as well.

I only mention the OSO site because there are a bunch of Formula owners over there, so the discussion (and pictures) are more specific to my boat. I actually found a thread from a guy that had to do the same sort of thing on his Formula 302 (30 foot GFBL).

Anyway, lots to read in lots of places. I figure that I have about a month to research and plan out the work. Of course, once I uncover the boat and start working on it, watch it snow a foot or two !!!

 

[tpenfield]

Re: Any Creative Ways to Check for Dry Rot in Stringers & Bulkheads ???

A Quick UPDATE . . .

I sent an email to Formula to gain some insight to how the boat was constructed and get some advice on the repair work.

So, Scott Smith of their techncial staff replied today with some advice . . . and it sounds like a fair amount of rot has occurred. They would normally use wood for the reapir, but also said that a synthetic board could also be used, if I chose to do so.

They also described their technique in removing the fuel tank, which should be a great help.

So, as soon as it stops snowing and the snow melts a bit, I think that I will remove the fuel tank for a better look at things. I'll probably start a project thread at that time and also post stuff to my web site.