Engine mounts and stringers

[grady]

Deeper and deeper we go, After pulling the powerplant and sterndrive. And after pulling up the sections of cockpit sole, (access hatches) to gain access to the fuel tanks to ready them for removal. I noticed some small cracks around the stringer where the engine posts attach.


Let me better describe my boat. It's a 1986 24' grady white I/O it appears to have two stringers (at least aft of amid ships) of about 2"x4" in size.

In the engine compartment there are two post that rise in toward the centerline from the stringers. they are about 4"x6"x 12" tall. where my motor mounts sit on top.

The cracks are in the glass around the base of the post where they meet the stringers.


Now my question is this a sign that too much torque has been applied. Or just normal wear and tear.

Is this serious enough to grind down the area and reinforce the post then reglass.

Note: I repowered the boat twice in recent past with a 350 ci increasing both the hp and the torq of the original engine 230 omc. by about 20%.

So am I in trouble here? I'll try to post some pics tonite.

thanks guys

Grady

[TerryKing]

..(snip)...
In the engine compartment there are two post that rise in toward the centerline from the stringers. they are about 4"x6"x 12" tall. where my motor mounts sit on top. ... The cracks are in the glass around the base of the post where they meet the stringers.Grady

Grady I'm sure you'll get more answers from the group, but sounds like something you'll want to deal with! Are the 'cracks' just in the topmost layer of resin, or can you see any fibres??

4"x6"x 12" tall with a 500 Lb 350 weight on the top, in a roll, chop, slam etc. sounds like a lot of force, as least occasionally.

Does the engine have resilient mounts, I assume?? Are their any diagonal or cross braces on those pedestals? Is there stuff like plumbing and wiring in the area between the pedestals? Or could you add some bracing like 3/4" ply fore and aft of the pedestals/posts??

Anyone familiar with this particular boat??

[grady]

Here are those shots of the damaged areas

[charmc]

There will be better and more specific recommendations from others, I'm sure, but to me it looks like a serious problem. I see a void inside that last picture, i.e. a wide crack showing dry fiber inside, "dry" meaning no sign of resin ever being there. The fiber looks like coarse chopped fiber, rather than cloth or mat. If it is chopped fiber, then there might have been a bubble or similar defect in construction, creating a weak spot and leading to the crack. The cracks are big enough and deep enough that I would be concerned about moisture in the wood of the stringer. I would grind away all the loose material until you get down to solid glass resin, or to the wood stringers. Test the wood for soundness in several places. Any soft spots (rot), I would rip the stringer out. Whether you have to replace the stringer or not, build up with lots of resin on the stringer, then glass mat, then resin, for at least 3-4 layers. Using mat for the repair will make the area stronger than the original. You'll need the extra strength for your bigger engine, and to improve on the original construction, which doesn't look up to G-W's reputed quality.

[marshmat]

From the looks of the photos, the engine bearers simply aren't beefy enough and are built too weakly for a motor that size. I think you'll have to get all the broken material out and see what's left- I doubt much will have survived. You'll find out what the stringer's like in the process.
When you build the new engine bearers, use woven cloth. Production builders use the chopped fibre crap because they can spray-gun it in with minimal labour. The short random strands are not that effective at increasing strength though. Sheets of mat are fine for building up thickness but are not very strong- fibreglass gets its strength from the long, straight, continuous fibres of a woven cloth. Use cloth, lots of it, with little pieces of mat where you want more thickness.
If you intend to keep the boat a while, I'd suggest you consider a better way of mounting your engine; maybe through-bolted aluminum L-brackets, maybe a full cradle. Lag bolting the mounts directly to the engine bearers is common practice, yes, but there are stronger and more reliable ways of mounting a motor.

[grady]

Boy I've been considering the task of tearing those engine bearers and stringers out , daunting. But I guess if you just put your head down and have at it, it might move along alright.
My concerns are the mounting dimentions. So if I document the height I just may be able to improve on the design of the bearers with the help of near by bulkheads and alum braces then cap it with a piece of L stock weld it all up and down the road we go.
Next question. How does one go about tearing out this stringer? The bearers seam straight forward enough, but with the stringer glassed to the hull bottom, I'm a little apprehensive.
By the way is it possible that these stringers go only as far as the bulkhead that boarders the engine compartment?
I'll try to post more pics later today.

Thanks Grady

[charmc]

Next question. How does one go about tearing out this stringer? The bearers seam straight forward enough, but with the stringer glassed to the hull bottom, I'm a little apprehensive.
Thanks Grady

Grady,

Circular cutting wheel held parallel to the inside of the hull so it cuts only into the stringer should work without damaging the hull. If the stringer was resin bedded, you'll have to cut through it, then go back and grind away to good glass inside the hull. When you glass in your new stringers you'll be reinforcing the hull again. It's possible the engine stringers only go to the first bulkhead, only way to tell is to measure centers first. If they're different, obviously no problem. If they are on the same line, you could make a small cut at the bulkhead-stringer junction, which will tell you if it's one piece or two. If the original was one stringer going full hull length, I have some ideas on reinforcing a new stringer section, but I'll wait for someone with more experience redoing stringers; there might be a proven and generally accepted repair method that I don't know.

[grady]

The tank compartment forward of the bulkhead is inboard of the stringer centerline. With no access to view, at least by a full grown adult. My guess would be that these stringers go further than the next bulkhead.

I got in there and poked and proded some areas with much longer exposure than these cracks and found no soft wood.

This damage can only be one season (maybe two) old because I had the motor out twice in the the last 4 years and as recently as late in the season two seasons ago and noticed no damage. And I did exstensive work around and on these bearers 4years ago. So I am hopful that the damage is just to the glass and I will be able to grind away my problems and reglass the stingers. I am still considering replacing the engine bearers and assisting them with a alum cross brace and certainly capping with a large piece of L stock thru bolted to the bearers from the side. Then bolting to the alum without penetrating the bearer from the top


thanks Grady

[marshmat]

Hi Grady,
If you've been poking an awl into the stringers and finding no soft wood, that's a good sign. You'll find out for sure when the damaged glass is gone, of course....
If you want a longer-lived stringer this time around, I'd suggest you go easy on the chopped-mat crap and use a lot of layers of a flexible, easy-draping glass cloth. The extra labour will be well worth the vastly higher strength and integrity.
The aluminum engine bearing structure you describe sounds good, definitely better than lag-bolting the mounts directly into the bearers (which will lead to the exact same rot/deterioration problem all over again). Through-bolting an L-angle, with a big beefy backing plate on the other side, should be a fair bit more durable in the long term.

[grady]

Hey Matt, Yeah I've got my fingers crossed.

What material makes for the best engine bearers, I would think clear fir but I have litte or no knowledge on how various woods behave in this enviorment.
What with all the stress and potential exposure to moisture.

Thanks Grady

[PAR]

Those cracks are classic stress risers, which have delaminated the sheathing. You have no choice but to grind it all out of there and replace the laminate with new stuff (Matt's right, cloth is a much better product)

Once you've stripped the sheathing away, the stringer condition can be accessed. If they too, need replacement (you're probably okay given the short amount of time) then Douglas fur could be a good choice (SYP is another). Make sure the wood is straight grained, clear and dry. Scrub the surface with acetone and let dry, just prior to wetting out with unthickened epoxy, to remove the oils and resin seen in fur.

Removing the stringers isn't particularly pleasant, but you can hack at it with one of several tools. The stringers on your boat do pass through the bulkhead. Making the stringers thicker in the sided dimension wouldn't hurt and provides more "meat" for engine mounts.

[charmc]

Here is a good discussion of stringer repair/replacement, also transom and sole work: http://bateau2.com/content/view/144/28/

[grady]

WELL today was enlightening!!
I took a 4.5" angle grinder to the bearers and the stringers as well as the areas around the bearers on the hull bottom. some not all glass was adhered
to the wood. And where it wasn't there was some moisture, I can't tell to what extent the moisture has done damage. But It doesn't look bad at all.

What I was surprized to find are voids under the stringers on the inboard side
and void or bubbles on the hull bottom in the tabbing that brings the stringers and the bearers to the hull. Some of these had water not moisture in them.

I would have thought that the low side of the stringer would have been filled with epoxy or puddy or something.

Overall I was happy with the condition of the wood But disappointed with the quality of the workmenship.

any thoughts?

Grady

[charmc]

WELL today was enlightening!! ... Overall I was happy with the condition of the wood But disappointed with the quality of the workmenship. Grady

Grady,

I've ceased being surprised at the stuff that gets past "quality control" at boat and engine manufacturers. I once almost lost a transmission and got a bilge full of oil because a line running outside the bottom of the transmission housing of a 31' sportfisherman was made of steel tubing instead of brass, and rusted through. The boat and engine suppliers were both big names, known for quality.

Look like you'll be doing more work, but at least you'll know it's done right.

[PAR]

You're correct, there should have been a putty/grout mixture under the stringers. If you found pools of trapped water, then you've likely got some rot. A scratch awl can be a very handy tool to find "soft" spots. These isolated pockets of rot will need to be removed and repairs made to the stringer.

It may be easier to remove and replace wholesale sections of stringer(s), rather then little bits and pieces along its length. It's likely that there will be other air pockets and voids under the stringers, as well as failed sheathing bonds under the 'glass on the stringers and tabbing. Most times you can find larger sections of sheered or delaminated 'glass with a mallet (I use a home made leather one, but most use a deadblow or rubber hammer), using the sound as a key to yank out the grinder for a look see. This will not find voids under the stringers, so maybe it's better to just hack the skins off and have a look for yourself. A chisel you don't especially care for, is also a handy tool in this kind of work.

[grady]

Gee Par your were up late,
the water was found well away form the stringers. the wood looked pretty good

But if by chance I should decide to remove the stringers for a more complete and detailed job. How doe's one go about splicing the new section to the old with max strength as first prioritry?
Can the new section be wider and taller?
Also can you just tab the stringer to the transom? Or does it have to be mortised into the transom.
I was wondering if they would have used any means other than epoxy bedding and glass encapsulation of attaching the bearers to the stringers.
I figure if I spending all this time, energy and money on this project, I might as well go ahead and improve on the engineering and design.

Thanks everyone

Grady

[PAR]

You can scarf the stringers (8:1 minimum, 12:1 much more desirable), you can also lap them, but this is a weaker joint that is prone to stress risers. The stress riser issue can be eased some, if the 90 degree angles in the lap joint (the "hook") are radiused as much as the material will permit. This "softened" hook in the lap will decrease much of the point loading found in this type of joint.

If the sole (the thing you walk on) isn't lying on top of the stringers, then you can make them as big as you like.

Your boat would have been built of polyester, with no epoxy at all. The area under the stringers, should have had a healthy bed, of well saturated mat, which the stringer would have be mushed down into, prior to tabbing it in place to the bottom. The engine bearers would be attached the same way. The mat serves to "key" the piece's dissimilar mating surfaces and bond the two. The tabbing ties the element to the structure (hull shell in this case), reinforcing it by forming a flange in the area of contact, which spreads out loads, increases shell thickness locally (under the tabbing), makes the piece moisture resistant and turns the separate components into a single, homogenous unit (a single, giant polymer molecule actually). Unfortunately, the polyester resin used in your boat (now being phased out of the industry) doesn't stick to wood very well, isn't particularly strong, nor water proof without very careful application. Epoxy will be much stronger then the polyester, so strength issues will ease. Vinylester will also provide better properties then the polyester, but not as good as the epoxy.

Look, some times it's the Golf Channel or helping with boat stuff, that gets me sleepy enough to doze off. I'm dog sitting a Rotty pup, that's been barking its little ass off most of the evening. It's 2 pounds and my smallest dog is 15 times bigger, with my largest being 45 times it's weight. It has to be pretty intimating standing around with monsters that smell the part, but are just way to big fool with. I need it to be dark and noise free (reasonably) to fall asleep. This damn puppy seems to wait until I'm right there on the edge, then yelps out a half dozen retorts. I may have to get out the 5 minute epoxy and fix it for good . . .

[grady]

hey Par, thanks for the input. I've taken a day or two off from the project. But the new fuel tanks were delivered yesterday, So I beter get busy. I will post some more pics tonite some that we all can talk about the condition of the wood on both the stringers and the bearers. But it seems pretty clear that in order to gain access to 100% of the stringers the bearers have got to go.

The construction does appear to be as you describe, although I'm hoping to be able to strengthen the stringers rather than piece them out. Only time will tell, (all fingers are crossed.

Well just wanted to reply with a thanks, and i'll get back to it and post some more pics and up dates.


May the pup rest easy

Grady

[grady]

here are some progress pics, Poor quality on some.They are mostly close ups of the port stringer and bearer. the sun washed out a couple.

[grady]

Hey guys, from these photos I hope you can tell what condition these members are in. It's not quite certain, but things are looking good from my point of view.

thanks

Grady

[grady]

Well just steped out of the boat, and as always with a new round of questions.

It looks like the stringers are in fact in good condition, although this maybe a moot point. It is also quite clear that these members do not go thru the next bulkhead. So is it possible that these stringers are just part of the engine mounting system and that there are other stringers that run the length of the boat? I ask this because I'm thinking that if these are short weight and stress distributing, engine bearer stringers. That it would be 10X easier to remove them in order to properly prep the outboard side of the stingers and the glass mat that tabs them to the hull. And if I have got them out to work behind them I might as well replace them.
Does this make any sense? To anyone?

I did shoot a new series of photos today will post soon.


Thanks all

Grady

[grady]

here's some photos

[grady]

Going left to right and top to bottom, the picture descriptions are as follows.

1, portside stringer where it meets bulkhead. ( clearly ends 1/8" before contact )
2, starboard stringer where it meets bulkhead. ( again seems to stop just prior to contact ).
3,port stringer and hull bottom. ( note the gap under the stringer ).

second row
4,starboard stringer where it meets the transom. ( there was a 3/4" X 3" viod in the transom where it meets the hull bottom this void had water in it ).
5,full view of engine compartment with engine bearers removed. ( note some type of hard bed or pad that the bearers were sitting on.)
6,bearer sitting on deck

third row
7,bearer on deck rotated 180 degrees
8, shot of transom and hull bottom.

any comments?

Thanks for all the help.

Grady.

[marshmat]

I'm trying to figure this structure out, and it just doesn't make sense to me. In the engine bay, there are only two stringers (right?) and both end at the first bulkhead. What's providing the structure ahead of that bulkhead, or through it? There has to be something.
If it were my boat I would be looking around the next compartment forward of that bulkhead too. It would be good to know more about the structure of this boat as what you've shown us so far just doesn't look quite right.

[grady]

"Well just steped out of the boat, and as always with a new round of questions"

It looks like the stringers are in fact in good condition, although this maybe a moot point. It is also quite clear that these members do not go thru the next bulkhead. So is it possible that these stringers are just part of the engine mounting system and that there are other stringers that run the length of the boat? I ask this because I'm thinking that if these are short weight and stress distributing, engine bearer stringers. That it would be 10X easier to remove them in order to properly prep the outboard side of the stingers and the glass mat that tabs them to the hull. And if I have got them out to work behind them I might as well replace them.
Does this make any sense? To anyone?

"

Grady

Yeah Matt that is my question, I'm not sure if there is another set outboard of these two that run the whole length of the boat. Very limited access beyond this point. I might call the factory and review the prints with an engineer, there very good like that down there in the good ol'south.

I'll keep you posted.

thanks

Grady

[grady]

hey guys here's what the factory sent me, Please review and comment.

Looks to me like they use a wider, short section of stock aft of that last bulkhead.

So I would imagine I'm all clear to remove this stringer section and get back to grinding, my favorite part of this whole process.


Thanks

Grady

[ratrace2]

Those cracks are classic stress risers, which have delaminated the sheathing. You have no choice but to grind it all out of there and replace the laminate with new stuff (Matt's right, cloth is a much better product)

Once you've stripped the sheathing away, the stringer condition can be accessed. If they too, need replacement (you're probably okay given the short amount of time) then Douglas fur could be a good choice (SYP is another). Make sure the wood is straight grained, clear and dry. Scrub the surface with acetone and let dry, just prior to wetting out with unthickened epoxy, to remove the oils and resin seen in fur.

Removing the stringers isn't particularly pleasant, but you can hack at it with one of several tools. The stringers on your boat do pass through the bulkhead. Making the stringers thicker in the sided dimension wouldn't hurt and provides more "meat" for engine mounts.
I like Oak...nice wood..

[PAR]

The manufacture did as I would have and used "engine beds", which butt against the two stringers and have engine mount blocks attached to the sides of these.

Thin laminations of oak would work with careful prep, but not really necessary. You're on the right track Grady, enjoy your latest grinding session. I find with sufficient beer on hand, I can tolerate grinding much better then without.

[ratrace2]

Southern Yellow Pine, "Doug Fir"...Why this wood when ships have been built for hundreds of years from Oak?

[grady]

Hey guy's this was an older post. I ended up finding some old growth reclaimed pitch pine ( real nice tight grain) for the stringers and some reclaimed old growth white oak for the engine bearers. They have been cut to size and coated with epoxy ready to install I posted the link in the materials forum great source for old lumber.

He had 1000's of board feet of live oak left over from the SS old ironsides refit 20 years ago still in tree trunk form http://www.cataumetsawmill.com