Engine mounts and stringers

[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]

Originally Posted by 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]

Originally Posted by 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.

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