20 ft Offshore Model - Bow and Keel Repair Questions

[Alan Sturgess]

I am back to working on my 1962 20 ft Thompson Offshore. I have it all stripped down and have finally started the restoration phase rather than the removal of parts stage.

I noticed that several ribs in the forward section had pulled away 1/2"” to 3/4” from the inner keel stem so that you could see the nails that had been driven in to hold the ends of the ribs outside oak stem from the bow down to where it is horizontal where a vertical bolt goes through to hold it up through the keel. I could then see light through the slot on both sides of the inner keel/stem.

On the web page listed below I have a series of photos inside and outside of the boat showing the condition of the ribs and hull.

www.accentart.ca/boat2.html

The reddish coloured glue/caulking material used originally simply crumbled away when I removed the outer bow stem. It appears that the hull strakes were/are simply fastened to the inner bow stem with copper nails, (not ring type) after a good bead(s) of the red caulking was applied to the stem. It does not appear that any screws were used to actually fasten the strakes to the inner bow stem.

I will roll the boat over to do the following bottom up.

My plan is to gently pry up the strakes off the bow keel piece, clean and scrape out the old adhesive/slealant and refasten it with copper nails with a good beading of a Sikaflex sealant before nailing. Which Skiaflex is recommended? What suggestions do you have and what do I watch out for? As I remove the old nails holding the strakes to the stem the strakes are going to spring out. What sort of clamping or pressure devices has anyone used to hold the stakes tight against the stem when I start to refasten them?

Also I know I now need to lift both of the wide innermost strakes up off the keel right to the stern and clean it out as I am doing the bow strakes, and refasten it as well. This will give me a chance to CPES the bottom of the inside keel and the bottom of the inside ribs and seal them properly. Should I be nailing with “copper ring nails” or just straight copper nails as were used originally?

Any other input from those of you who have already done this would be appreciated.

Alan Sturgess

[a j r]

Hey Alan, Good luck with this project. Yup, you need to tighten everything up so there is no light passing thru the hull! Can you imagine how much water would pour thru that opening!

Your proceedures sound fine. Not sure how you are going to get teh ribs back tight against the keelson and stem. Make certain you have good bracing so that the boat does not loose her correct shape as you are taking things apart...

I would use ring shank or spiral shank nails and probably also some screws (silicon bronze).

Definately use a generous amount of flexible marine caulking (NOT adhesive) to bed everything after all the woodwork is completed. Life Caulk by Boat Life is one brand that comes to mind.

Sealing and prime painting before reattaching is also a good idea.

Andreas

[Rodney Syverson]

Alan: I was faced with a similiar dilema with my Sea Lancer. Mine was seperated in those same areas but my ribs were not pulled away from the stem any where near as much as your photos show yours. I am puzzled why yours are so far from the stem. I can't believe your stem has shrunk that much nor your ribs have shrunk that much. Irregardless I think it would be a good idea to try to tie the frames as well as you can to the stem. I had my cutwater piece (outside of and forward of the stem) off just like you and I was able to draw the gar planks and strakes down tight by simply renailing. As I had replaced my frames which originally are secured to the stem and keelson I needed to tie those back together with a screw drilled and fastened through the garplank and frame and into the stem and cleats along side the keelson. I think this is important as this is primarily what holds the two hull halves together. Its also a spot that is prone to loosen and leak. I think what I would do is either replace the frames in that area or remove them and get them tight up to the stem after the garplank is secured by simply moving them down until they are tight to the stem. As you already have a lot of fasteners coming out the end of those frames in that area the end of the frame won't have much material to support any fastener such as a screw through the plank, frame and into the stem. That's why a new frame would be nice and those forward frames though they have an S-curve to them bend real easy. This frame tie might not be as critical, as getting the planks firmly secured to the stem. I am going to disagree with ajr on this one and recomend 5200 for bedding this area together. It is an area that is prone to seperate and leak and I think 5200 with its tremendous adhesive properties would help hold this area together. Rather than acting as a simple bedding compound it would contribute structurally by tieing all the components together. I would also bed the cutwater in 5200 as well, as that will also help tie the two halves together. 5200 in my estimation is very similiar if not identical to the urethanes we use to install windshields in cars and it has incredible adhesion and strength properties at the same time remain flexible unlike epoxies. Though difficult, it can be cut with sharp knives, razor blades or piano wire after it has cured should you ever want to disassemble in the future. I think the benefits of using it far outway the disadvantages.
If you find it is necessary to clamp the two halve together I would make some blocks that are cut at the correct angle and install on either side of the hull so that a large C-clamp or bar clamp could force both halves together. The blocks could be screwed but if you did not want to drill holes in the planks then glue them down with 5200, allow to cure then clamp and when done use piano wire to remove or chisel or whatever. Holes I drilled in my hull were filled by toothpicks glued in the hole and trimmed and sanded.
I used Silicon Bronze ring shanked nails for securing the planks to the stem and keelson. You must first drill a pilot hole as they are difficult to drive into solid oak. I ordered a pound and have most of them left. E mail me with an address and I will send you all you need.
Anyhow just some thoughts and hope this helps.
Rod

[Alan Sturgess]

Rod, Thanks for the great input. Interesting how the problems we find in upgrading these beasts are similar, but always with slight variations. Before I started this project I might wake up in the middle of the night and think about a problem at work, or some sales or marketing plan at work that needed tweaking. Now I find if I wake up it is much more productive working on a boat problem like this!

First like you Rod, I am not sure why the group of strakes on each side seemed to have split away from the oak stem so much. It is a 20 fter and is deeper than the 16 to 18 ft boats. I think that perhaps the fellow who attached them that day at the plant did not put enough nails, but who knows. Perhaps Thompson had those Friday and Monday production problems that the big three automakers had. I am confident I can get the bow and stem repaired back to better than the original factory installation and here is what I think I will try to do.

- cut the various nails flush at the bottom of the angle portion of the various ribs that have pulled away from the stem.
- With very small vice grips lever the nails that go into the oak stem out of the stem.
- I have found that by driving wood wedges into the opening outside the boat I can pry out the copper nails that were driven in to hold the strakes against the outside of the stem. I got them out with a long pair of needle nose pliers.
- I agree that with the right pressure, clamping and using the right adhesive that the strakes can been held tight against the stem, glued and well fastened with ring nails and perhaps a few screws. I would then leave it clamped for a week to ensure the 5200 has set and bonded well. I am siding with Rod on using 5200, the more permanent adhesive. The old Thiokol adhesive got the boat through 44 years and I am sure the 5200 will give it the same period and anyway I am not going to be around then to be blamed for any problems in taking it apart a second time!
- As for clamping I think I would like to try drilling about four to five 1/4 “ diameter holes through the stem and then by trial and error design a snug fitting vee clamp of wood or metal to bolt up through the stem and then be able to tighten a nut on the inside to snug the strakes in against the stem. These holes can be easily filled after the clamps are removed.
- I am sure that the lower ends of the angled ribs will pull in against the stem when the clamps are tightened. I have wondered about replacing those ribs and also thought that perhaps attaching a sister rib the full length or for 2 ft in the lower portion might work. As soon as I rig up my clamping system and do a dry clamp as a test I should know right away what might work.

Thanks for the input as I have been working on this problem in my mind for a few weeks now. I am just starting to renew all the rub strips after having redone the cockpit side deck beams, and refastened the angled aft deck beam that the steering consol fastens.

I am curious to know if others have redone the sheer the way I did. I laminated in place three strips running from the stern through to about 6” in front of the angled aft deck beam. They end up forming a considerable twist as they move forward into the front deck area. I felt gluing three strips in place was easier than steaming it and bending it in place.

The finished size was 2” x 7/8” and I then bolted it through the sheer strake and the rib. With a hand plane I was able to knock some off the top to level it with the deck beams in the forward area. I then made new shorter deck beams and fastened them with glue and screws to the new sheer clamp rather than simply with one screw from the outside of the hull. I then attached the inner cockpit combing to the new shorter deck beams. The end result seems to be a lot stronger and stiffer side deck. The old side decks were fasten at the transom with about 6 screws and about four at the front. Then the factory simply hammered a bunch of brass nails down into the rub strip and the inner cockpit combing. I plan to screw into the rub strip and the cockpit combing and then plug the holes. Again I think we have more time than they did at the factory and can now take the time to fasten the side decks better and end up with a stiffer boat.

Any lapstrake dinghy or boat normally has a sheer clamp, but material cost and labour dictated that they left this off these boats and simply drove a screw in from the outside to hold the side deck beam in place.

I am still open to thoughts and suggestions to the above repair method.


Alan

[txcaptdan]

Alan, As to why your stem ribs pulled away from keel, I would suspect ice damage. it is very believable that water trapped in bow froze - especially where you live - and forced open ribs and panels,
My boat from Wisconsin had been allowed to collect water then ice in keel and it seperated all three keel beams from each other and broke all horizontal and vertical bronze bolts. The ice forced outer keel beams about 3/4'' open from center beam.
There was no rot in any of these beams so I clamped, glued back together and replaced new hardware and new keel cap.
If you ribs and keel are in good shape then I suspect you can re clamp/ reattach ribs and you should be fine.

[Rodney Syverson]

Alan:
Your idea for clamping sounds like a slick idea. Keep us posted if it works and how well. Your laminated sheer idea sounds like a good idea as well but isn't there a vertical face that the rub rail attaches to. I think I am following you correctly and can see it would be a slick way of making that part other than planing a vertical outboard face on a glue joint. Unless your exterior laminate is large enough in dimension to allow planing without getting into the laminate joint.

The lengthy time necessary to complete a lot of these operations gives us ample opportunities to think about how to do it and ultimately come up with a procedure to make it work. I am not so sure if it is necessarily more productive than work but I know It comes with a whole lot less stress and greater satisfaction.

Rod

Dan: Never thought of your idea about water freezing and spreading the hull but it is a good possibility. What makes this site Great

[Alan Sturgess]

Thanks for the good comments.

I will take some photos and post the sheer strake improvement, but am away on business next week in Atlanta so will do it some time after the 11th. I will keep you posted on the clamping method. It would take someone from the south to clue me in on the freezing situation, but I am sure it happens quite often. If it happened several times I could see the gap progressively expanding.

Alan