Dealing with some cracked frames

[tillergirl]

Views on the following would be appreciated please.

I have a couple of cracked frames on either side at the tuck of the stern. They are relatively stable in the sense that some epoxy putty put in the cracks last winter shows no sign of movement and the seams adjacent are tight. However, this year is the time to do something about them. And here is the subject of choice.

I do not really want to take the cockpit apart as that would be major reconstruction so the issue is what can I achieve with the access I've got. That is access through the cockpit floor and through the cockpit lockers, the floors of which are removable. Against this is a very substantial bilge stringer under which the replacement frame would have to be wiggled.

This photo taken 16 years ago on re-engining shows the extent of the curve into the bilge. Obviously there is a reverse curve for the topsides. The stringer is just out of sight. The cracked frames are level with the stuffing box.

Choices seem to be:

1. Steam complete new frames - but the frames will each be nearly 2 metres in length and 25mm x 32mm section. The restricted access and the bilge stringer is going to make it really difficult - if not doubtful - to get the frame in. Best option but also the most difficult?
2. Laminate complete new frames - but with that tuck at the turn of the bilge, steaming is still going to be necessary and then there is the problem of gluing wet timber
3. Steam new frames in two pieces with a long scarf about mid section either above or below the bilge stringer - this would enable each half to be bent in the available space. There might be an issue in keeping the half that does not tuck under the stringer in place during the fitting and the scarf would have to accomodate some of the curve.
4. Cut out the cracked part of the frames (the bottom bits) and steam the replacement and scarf this to the part of the old frame left in situ.
5. Is there another alternative?

Any comments or suggestions. I would really like to do option 1 but I fear there is just not enough access.

 

[jstarboat]

Hi Roger,
As a wooden boat builder I would take them out and renew in a whole bit, but as you say that would involve removing a great deal of woodwork and that you wish to avoid this if possible. Where is the break and would just streaming a double piece do the job. As you have stated it as not moved since you put epoxy putty in the area and there as not been any movement then other alternative is to leave well alone.

Regards

 

[cliffordpope]

How would you rivit the lower bit anyway, with that massive shaft log in the way of the hammer? Or can you get a copper equivalent of pop rivits, tightened from the outside?

What is the risk - that they might suddenly snap, cause some more adjacent frames to break, and let in a gush of water through a long gap between the planks?
I'd be tempted just to make up a big wedge of the right size and knock it down the side of the log, to brace the sharp turn, and secure it with a nail.

 

[tillergirl]

Simon

I was thinking of doubling. The cracks are about in line with the prop shaft. I think if I am honest there has been movement since this photo - not significant movement but some nontheless. I am really loathe to remove the cockpit having done significant work over the years to get it watertight! Do I understand you right that you would go for option 3?

Clifford

The difficult to get at nail ends are just turned over - that was how she was originally made with roves obviously the moment there is room to swing the tapper. So I would copy that. Risk? Well in 1994 there was only one cracked and that I suspect was from new (1964). That was port side in line with the stuffing box - you can just see the unkind curve where it is. My fear is that the frame in front of this old crack has gone exactly in line and there is a couple now the other side. I'm thinking, TG is 46 yrs old, I am 62, best do this now; its only going to get worse. I actually think the frames would not snap; the crack actually eases pressure on the frame and none are completely through.

I just think it is possible that more might crack. I am not sure I want to go for the 'big wedge' option - bit ineligant.

 

[old_salt]

Looking at it there is some turn of the quarter miss shape there but if it's set and secure I would not recommend trying to alter it in any way.
I also think you are referring to the ribs rather then the frames.
Are the cracks/brakes along the grain or across it less of a danger if along the grain.
Again looking I suspect he brakes to be across the grain of the ribs.
So I would leave the broken/cracked ribs in place if they are secure and tight fitting.
Why not make up a proper 3ins or so wide oak floor and fit it in next to the broken rib fixing it to the stern/transom knee. Don't be spartan with you sizing it is there to do a job and prevent any further cracking up of you ribs.
There is some for and against fixing floors to posts or knees but if not actually fastened then a good close fit should be fine, leaving limber clearance at the hog to allow drainage.
Be easer to do a a cardboard/ hardboard joggled templed, lots of chalk to make sure you have a good bed/fit then a good mastic bedding and bronze screws from the out side.
And the job should be a goodun.


Photos of my re-build.
As you can see I had a lot of broken ribs and very cutaway floors that where not intended for an engine installation so they had to be beefed up considerably.
Most of what you can see in the second photo is new only the hull planks and stringers are original.
I did have the advantage of stripping the top off to get at the hull.
With some luck seanick will spot your post and add some useful information.

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[tillergirl]

Yes across the grain. And ribs if you prefer. Certainly not sawn frames. The misshape is certainly more noticeable on the inside than outside. I have no intention of trying to alter the shape.

That's an interesting idea. While looking at it this morning, I did silently think about a sawn frame strategically placed but your idea of a floor gets round my worry about a sawn frame. One potential problem is that the two cracked frames - sorry ribs - are staggered by one either side. Putting it by the 'common' rib would put it too close to the stuffing box. Moving it forward one rib would be fine starboard side but potentially a little far from the rearmost cracked portside one - if you follow me. But bearing in mind that there is just such a floor as part of the original construction four ribs further aft it may be paranoia to worry. I am attracted to the idea. Thanks.

 

[DoubleEnder]

Laminate sisters?

You could possibly use thin veneers epoxied or resorcinol glued together to build up a sister frame alongside each of the offending ribs. By using very thin veneers, and perhaps plastic staples, you should be able to build up a nicely fitting rib which can then be screw fastened from outside. It might get a bit messy with the glue but the thin veneers should be easy enough to handle and to bend.
FWIW

Graham

 

[tillergirl]

I was thinking that the trouble with this appoach is that the veneers would have to be pretty thin to bend without steaming - and indeed I concluded looking at it this morning that I would be lucky to get dry veneers bending that much without steaming which then of course brings a gluing problem.

How thin were you thinking the veneer would have to be?

 

[tonijon]

Hi Roger got the same problem with Toni only got 11 of them to do!
what our surveyor has recommended us to do is what you are proposing as option 4 (as we would have to remove her side decks) but make sure that there are fastenings going though the scarfs Are you over wintering Tillergirl in the basin this year?

 

[tillergirl]

Yes, I'm in Adrian's yard

 

[Keith 66]

Steamed timers often break in this area, doubling alongside is in my book poor practice as you double the strength ofthe rib except at the original break, this creates a hard spot in the new doubler & it will certainly snap again eventually.
I would cut the roves of each side of the break drive out the fastenings & cut a scarph on the timber, in the tuck like this you would only need to lay a steel rule alongside the timber & scribe under it, then plant a new piece of oak on top & glue it on with epoxy,it would not need to be steamed. Fair it in to the original shape of the rib & refasten, a good repair that will look identical to the old timber.

 

[tillergirl]

Umm, interesting. There wouldn't be much length to the scarf although I'll measure up to check. I do appreciate the 'hard spot' argument though.

 

[old_salt]

Mum, interesting. There wouldn't be much length to the scarf although I'll measure up to check. I do appreciate the 'hard spot' argument though.

This would be a good solution, the length of the scarf needs to be as long as you can possibly make it even longer to get the best result.
A semi prepared rib steamed on a jig setup would maybe work,
I would suggest making up the new rib piece offering it in place then marking out the old rib remove the necessary nails cut away the old rib and fit again use chalk as an indicator to get a good bedding fit.
Glue and rivet or use long waxed 6 BA screws with large washers to set in place then nail and rivet up.
As for glue Balcotan is an excellent glue.
link:-http://freespace.virgin.net/melco/about.htm

Instling a full floor would go along way to resolving the recurrence of any further cracked ribs as the broken ribs are showing there is a vulnerable area of the hull where some working is taking place.

 

[oldfrank]

Personally, I hate sistered timbers - they're just an invitation to rot and don't look very nice either. You don't have a structural problem with just a couple of timbers gone like that. I might be tempted just to leave it to see if the nearest timbers crack in a similar position. Once they do, you'll have to replace or you'll soon have a nice row of cracks. Doesn't have to be this year's job - although the bilges do look nice and clean. I don't think I'd laminate more than a couple in a row. It's not everyone's idea of perfection but it's also possible with modern glues, to laminate new ends on to existing timbers. Many yards now do this due to the cost of refinishing the brightwook after replacing timbers. Again, not too many in a line.

 

[Keith 66]

The worst doubling job i ever saw was on a blackwater sloop, it had a complete line of breaks on the turn of the bilge along the same seam both sides. It had been completely doubled from keel to sheer not once but twice. All the doublers were broken in the same place as well.
Effectively all that was holding the top half of the boat to the bottom was the stem & sternpost nothing else in the middle but habit.
I rest my case!

 

[cliffordpope]

Why not make up a proper 3ins or so wide oak floor and fit it in next to the broken rib ]

That's what I meant to say - close fitting oak floor = wedge

 

[tillergirl]

Thanks chaps - had to nip to France to earn some timber vouchers. Saturday armed with a print out of the thread I am going down to the yard to look at the problem again. I feel I should tackle it this year as back in 1991 there was only one frame cracked, now there are four, two either side. It's only going to get worse. I like the oak floor idea but it may be too close to the stuffing box.

 

[old_salt]

If it is just behind the stuffing box like mine that will give the hull planks the support they need. May be help to quell any vibration if you have any as a bonus.
If it is in front can you cut a large hole to give you access to the the gland and stuffing box.
Then as you say you have four cracked frames two 2" floors may be the answer maybe make the tops level and they could support a locker sole plate.
Another thing I did was to make up two long silicon bronze screws with turned wood screw threads 4" long with a 3/8" whit tread 1" long at the top they where screwed into pilot holes each side of the Stern tube in the stern post.
I have posted a photo of my old and new stern post, aft deadwood and horn timber so you can see what I had to work with.
The new one was beefed up as the original was never intended to have a prop shaft though it. it had over the years been patched on ether side with numerous bits of wood inside and out to strengthen it so we thought lets make a proper one to do the job.

 

[gavin_lacey]

A method I have used in the past. Grind away the old frame in a 10 or 12 to 1 scarf. An angle grinder fitted with a 40 grit sanding disc will go through wood and fastenings. You can mark the scarfs by using a rubber wedge of the right taper which bends round the hull shape. rebuild using thin veneers of matching wood with epoxy. Each veneer can be teporarily tacked in place. Dont use polyurethane adhesive as it expands and pushes the veneers apart. Make the scarfing piece out of veneers a bit wider than the original to allow for slight misalignment and final shaping. Re fasten alonside the original fastenings which are left in place but truncated. Slow job but invisible. Very strong but does not pull hull into shape if that is needed

 

[tillergirl]

Gavin, thanks.