hull integrity question

[Rickmerrill]

Without access I don't think they can. Looking at a rotten stringer can fool you, thumping can fool you (it will tell you if it's delaminated) but drilling holes and looking at what comes out, that works.

 

[vinnie1234]

unfortunately the floor rot seems to be above the deepest part of the hull. coincidence? I think not. are the stringers not completely encased in glass? I will try and drill what I can access. I am pretty sure things are solid at the stern. Had the engine mount out to repair the trim motor. all seems pretty solid.
Am I correct in assuming that because it is a sterndrive I can be a little less worried about transom issues? There doesn't seem to be a lot of reinforcement there.
As for the rotten floor section. I have to wonder if I can pull it out in such a way that I can put it back easily. Perhaps I can just cut a strip with a circular saw and then screw it back in afterwards?

 

[jigngrub]

The stringers may or may not be completely glassed in, but you can be assured the workmanship will be sloppy because once the deck goes in no one will ever see them.

The transom should be checked while you're at it, transoms are a concern on any kind of boat.

As for the rotten floor section. I have to wonder if I can pull it out in such a way that I can put it back easily. Perhaps I can just cut a strip with a circular saw and then screw it back in afterwards?

Picture yourself in a boat on a river
With tangerine trees and marmalade skies...

... now that we've gotten that nice little dream out of the way, the rot you can feel on the top side of the deck is just a fraction of the rot on the bottom side. Think of a funnel shape turned upside down. There will more than likely be wet foam that spreads out further than the rot... the section of decking you will end up removing will be large, if not all of the decking.

 

[vinnie1234]

Well, jigngrub, I sincerely hope you are wrong, however there is nothing wrong with diligence. My first priority is to assess the safety of the boat. I don't have time for a rebuild now, so if the boat proves to be unsafe, then I will have to park it for the rest of the season. I will do all of the tests that are suggested here and see how it goes.
In my logic, the issue of a rotten stringer has to be related to handling, as it is related to structure, and maneuvers on the water are forces applied to the water, which means forces applied to the hull, from the water.
I have been doing some research into the design of fibreglass boat hulls. As I understand it, the stringers, crossbeams and bulkheads all act together with the decking and hull to create a monocoque frame system. The stringer portion is designed primarily to prevent longitudinal flex of the hull, whereas the crossbeams and bulkheads (including transom) are designed to prevent torsional flex.

If I understand it correctly, the stringers are glued directly to the hull, and should be straight with no bends, (or if bends then additional reinforcement req'd). The crossbeams are laminated to the top of the stringers and the sides of the hull, and then to the deck, where the deck is laminated to the hull at the edges.

When going head on into chop, the stress on the hull would be primarily on the stringers, however the up/down flex of the hull would also cause the sides at the apex to apply force to crossbeams and decking, as the hull would try to move out and in at the sides as a result of the applied forces.

In a turn on flat water, there would be more torsional force on the boat, as the sterndrive pushes to the side and causes the boat to pitch into the turn. In addition, because the prop is moving the boat forward, the prop would want to run under the boat, but in stead would pull down on the rear engine mount and up on the front one. Since the mounts are on the stringers, this would introduce longitudinal flex.

Torsional flex would be highest at the widest and deepest point of the hull, and longitudinal flex would be more sternward, depending on the amount of force being applied to the stringer through the engine mounts.

In a turn on choppy water, there would be a more varied distribution of force, due to dynamic and uneven loading, but it would all compound with the primary loads introduced by a powered turn.

Looking at my boat (again if I understand this correctly) with the boat being a bowrider, (and with evidence of some rot in the floor slightly in front of the helm) the weakest point would be near the helm. The clearing for the walkway to the bow would be able to flex easier as there is nothing joining the hull laterally at this point.

Where I am going with all of this is back to my earlier post where I made an observation about "fishtailing" or drifing in a turn. I was on choppy water, going 30 to 40 km/h and in a fairly hard turn (20 to 25 degree pitch).

I am experiencing a moment of clarity here. It would make sense to me logically, that the crossbraces and decking are poor, not only from looking at the decking, but also from the drive. That fishtail could have very easily been caused by torsional flex in the hull. I can confirm this by looking under this part of the boat.

The stringers I am thinking are probably okay (but will drill to be sure). The reason I am saying this is that when hammering waves straight on, or under acceleration the bow maintains a very straight attitude. Also when trailering the boat seems to be very rigid when on the winch.

I should be able to measure between the two sides of the walk way (perhaps a dial guage) and measure lateral and torsional flex on the boat in various situations. If it is all consistently put together, I should be able to get similar readings for deflection in a straight line under acceleration (when the bow comes up), or in a turn. A greater amount of deflection under one of these situations would indicate loading differences in the hull, and making measurements while anchored and observing the guage when waves rock the boat etc can give me a better picture of how the hull behaves.

Don't get me wrong, I will not be using these techniques to determine if the boat is safe, but I think it will be interesting to see how effective this is in assessing the condition of the boats structure. Next season after a rebuild I can repeat the process and see how differently it behaves.

This all makes sense to me, but I have only a limited (and new) knowledge of boats. If you can poke some holes in this, or tell me where I've got it wrong, please let me know. Just tossin around ideas.

 

[jigngrub]

You can't really tell how bad of shape your boat is in by the performance... until after you restore it, then you'll probably notice quite a difference... most people do.

Whether you continue to use your boat or not is your choice, I'm sure there are people out running around on the water in boats in worse shape than yours and most of them always seem to make it back to the dock.

The rot on the deck is telling you it's time to do something, it's your decision on when to do it.

There's a saying in the dry dock here "Hope for the best, but be prepared for the worst" when you start digging into a boat... and there's a reason for that.

When you do decide to dig into her we'll be here for technical and moral support, post lots of pics and ask any questions.

 

[sheboyganjohn]

I was thinking about using that epoxy chip garage floor stuff as a floor topper in stead of carpet,

Better look closely at the labels. I used that stuff for the closed in bilge on my dory and not on the deck because it does not have UV inhibitors in it and will break down in the sun. If you are using poly resin you would be better off with gelcoat. I build the dory with epoxy so that limited my choices.

 

[vinnie1234]

Good point about the UV Sheboyganjohn! Thanks for the tip.

Jigngrub, If I put a dial guage on the hull and only get a few fractions of an inch, and I drill my stringers to find dry wood, should that not at least be sufficient knowledge to tell me I can use the boat? In lieu of what has been discussed here, I will reserve service for calm waters, however I would expect that significant rot would yield significant flex in the hull.
Is this logic not sound?
I figure, that without hull flex, then stress cracking or hull failure would not occur.
Of course, if I rip into this boat and find rotten stringers it will be a different story......

And don't think me as trying to be a know it all here either. Just the opposite - I am here to learn, but I am also trying to approach this as a technician. Understand the dynamics of the problem and symptoms and confirm the diagnosis and repairs.
Perhaps the measuring technique will prove useless, but if it doesn't wouldn't it be great to know another diagnostic technique?

 

[Browndog10]

I thought my boat had some rot also. I learned very quickly that it was just the tip of the iceberg. Everything, I mean everything had to go. So instead of fishing with it this year, I have been restoring.

 

[jbcurt00]

Boat & boat resto safely

ANY pix at this point would be better then none...

A question that should help clarify the situation as I see it:

I have a 1978 Chevy Cavalier 4cyl 4dr, it makes a strange knocking noise, possibly under the hood, from just off idle until I take my foot off the gas. My neighbor works on his own vehicles and he said it was safe to drive for the rest of the summer. In the fall when he's not as busy, he'll help me fix it. When I open the hood & look around, I don't see anything out of the ordinary or damaged. If I put gas in it, and turn the key, it starts and stays running. Since it's the only car I have, it runs & drives and the tires hold air, I intend to keep driving it.

As an auto mechanic, remotely via the internet, w/ no pix of my car, nor audio of the noise, do YOU think it's safe for me to continue driving it?

In this ^^^ example safe is defined as not blowing up my motor or shredding my transmission. I have no idea if Chevy even made a Cavalier in 1978, but it's for reference only anyway.....

Even if you find another 1978 Crestliner Crusader that looks like it's in the exact same condition as yours, the below deck structure could be in drastically different condition. 1 boat serviceable for the rest of this season, the other not.

Is your boat's soft deck a symptom, a cause or a result of another larger problem?

 

[jigngrub]

Jigngrub, If I put a dial guage on the hull and only get a few fractions of an inch, and I drill my stringers to find dry wood, should that not at least be sufficient knowledge to tell me I can use the boat?

Even if you do find rot in the stringers, your boat isn't going to be any different than all the other times you've had it out this year. The only difference is you know a little more about what's going on with it than you did before. Using it in calmer water and not hot dogging it would probably be a good idea.

I doubt your boat is going to break in half or suffer any more structural problems than it already has if you continue to use it this season. My biggest concern would actually be sinking if swamped, that wet floatation foam and the weight it adds to your boat will take it right to the bottom... but that probably won't happen either, maybe.

I personally wouldn't be using the boat... because I'd be too busy digging into it. I'm the kind of person that wouldn't be able to stand not knowing just what exactly was going on under that damn deck and I would have to tear into it to find out. I do have a real good idea of what evils lurk below the decking and I believe that would fuel my curiosity even more. You too could get a better insight as to what awaits you if you'll read the different fiberglass restorations in this forum... but for most people in your shoes they only bring gloom, despair, agony, and depression instead of curiosity.

 

[vinnie1234]

No doubt the deck rot is the result of something underneath. How could it be anything else? I am also in agreement that there will be a great deal more rot than I can see with my eye. Where is it though?

With respect to the instance of the car, certainly I couldn't tell someone it is safe without looking at it. I could however instruct them as to how to check the problems to verify it's safety. (This does require a certain degree of competence and experience of course).

Although it would have been great if someone said "oh those crestliners never rot - you're fine" that isn't really what I am interested in.
I am interested in correctly assessing the problems I have and prioritizing the timing of repairs. I know that I could very easily answer all of my questions by ripping into the boat and looking at it. If I choose that route, then I wont know until February whether or not I even made the right decision.
The purpose of this thread for me, was to see if there are some ways that I can determine whether or not I have a death trap or just an old boat that needs some work.
If a massive hull failure and sinking are in the cards, I must park it. If not, then I will leave it until the winter. In both cases, the boat is going to get ripped apart and properly fixed. I just don't want to put myself or my family in jeopardy.

 

[jigngrub]

No doubt the deck rot is the result of something underneath. How could it be anything else? I am also in agreement that there will be a great deal more rot than I can see with my eye. Where is it though?

With respect to the instance of the car, certainly I couldn't tell someone it is safe without looking at it. I could however instruct them as to how to check the problems to verify it's safety. (This does require a certain degree of competence and experience of course).

Although it would have been great if someone said "oh those crestliners never rot - you're fine" that isn't really what I am interested in.
I am interested in correctly assessing the problems I have and prioritizing the timing of repairs. I know that I could very easily answer all of my questions by ripping into the boat and looking at it. If I choose that route, then I wont know until February whether or not I even made the right decision.
The purpose of this thread for me, was to see if there are some ways that I can determine whether or not I have a death trap or just an old boat that needs some work.
If a massive hull failure and sinking are in the cards, I must park it. If not, then I will leave it until the winter. In both cases, the boat is going to get ripped apart and properly fixed. I just don't want to put myself or my family in jeopardy.

I like your attitude.

If you're going to drill the stringers, drill them as close to the soft spot as you can... but they may still be decent from the middle to the top and totally rotten from the middle to the bottom. Drilling is like taking a biopsy for cancer, if you don't hit the cancerous spot you don't know.

Another way to find out what you may have is to drill holes through your decking in and around the soft spot. Use a 1/4" bit and then insert wooden dowels like bamboo shish kabob skewers down into the foam until they bottom out, leave them in for a few hours and pull them out. If they come out wet you have saturation and water intrusion problems = rot.

Boat rot is boat cancer and the very best way to find out just how bad it is, is to do exploratory surgery and remove the decking and start digging out foam.

 

[vinnie1234]

I wont be going on the water tonight, but I will be going home with a drill, a hammer and a borescope. I will drill the stringers (if I can get that sealant today) tap test the hull, stringers and transom and poke my camera around and see if I can get a better idea what I am in for.

Unless the wifey sideswipes my plans tonight.... I will let you know what I figure out. As far as time in the water this year, I figure I have had about 50km of travel total. Most in very small waves. Enough that I had to trim out some porpoising when on plane. You are probably right in that if it was rotted all to hell I would have already had to rent a barge.

I have always wanted a boat since I was a kid, and this one was pretty much given to me. My wife is nervous about boats too, so I am being ultra cautious about everything that I can think of to ensure that the experience is good for all of us. I am probably being over cautious, if there is such a thing. Having said that the waters of Georgian bay are cold, deep and tempermental. I don't need to go for a swim.

 

[jigngrub]

I doubt you'll see much with the bore scope, all the black juicy stuff will be hidden behind floatation foam... but try it anyway.

I know exactly where Georgian Bay is and how the water is there, with the winds and the outcroppings of that Canadian shield rock I wouldn't want my boat in anything but tip-top shape out there... and I'd probably be trying to molest a Musky.

 

[IUPapabear]

Has anyone used alternate materials to wood for stringer repair?

I am no expert by any means, but one piece of advice that I have gotten here was to "Don't get into information overload." Advise I listened to, but with the way my brain is I am always thinking and trying to come at a situation from all angles. Just my nature and a product of my career. I am a Theatre Technical Director, which is a fancy title for "I build set pieces for live plays/musicals." In this business we are always trying to "Create" the look of something, without actually building it. Inherent with this process I always try to find the best materials for the job that tries to stay on budget.

With my boat, I have had plenty of time to think and research, little time to actually work on it lately. I was like you, and many others, in the fact, if wood rots, why not use something else?? I am sure there are arguments for all options. For me, my boat is 35 years old. It's probably been longer, but lets just assume the wood has been rotting for the last 10 years. That means that for 25 years of who knows what kind of preventive maintenance, the boat was good.

I researched all kinds of materials to replace the stringers/deck/transom with. Honeycomb, composite, wood of all types, etc. and I finally came to the conclusion, as most do, I will be taking 100 times better care of this boat when I am finished. In a poorly maintained boat the wood lasted +/- 25 years. IT WILL LAST LONGER when I am done!!!! Not to mention, I am 50 y/o, my grandson is 1 y/o, if we can get 20-25 years of fishing out of it, it will be worth it !!!!

It will have to be in better shape than me. lol I just turned 50 in Feb., had my 25th anniversary yesterday, I have a TKR in my left knee, a bad back, and I get kidney stones on a regular basis. So another 25 years sounds great on many ways, and scary as hell on many others.

Good luck with your boat and keep us informed!!!

 

[vinnie1234]

Well, good news, bad news - it's all the same. came home and took an impact socket all around the exterior of the hull. Both port and starboard were consistent with bright sounding taps all around the boat. No dull thuds. Good news, sort of. I then went into a bunch of holes in the bow and stern and fuel tank area and it looks dry. Floatation foam looks dry. Under the decking seems dry too. BUT! In the area where the floor is rotten I can see moisture underneath. Also, i drilled the stringer at the stern and it is wet. Not rotten. Wet. Which is the same thing in my books. This all sucks big time.

 

[jigngrub]

Sorry to hear that Vin, but hey... it's a '78 and it sounds like it's in a lot better shape than the vast majority of '78s, even if she does need work.

 

[vinnie1234]

Yes. This sucks not because I have a to do the work, but because now I have to decide what to do about the boating season. I think a day in calm water with a dial Guage will either make me feel better or scare the crap out of me.

 

[jigngrub]

Whenever I'm in Canada some of that black label Barcardi rum made in Cuba always makes me feel better!

 

[jbcurt00]

Unless you constantly monitor gauges across a multitude of measurement points, you'll just be collecting data of nil value. But set up a dial gauge if you feel it'll give you info you need.........

Just because you put in during exceptionally calm seas, doesn't mean it'll be that way the whole time you're out.