GRP sheathing

[HunterWanderer]

Has anyone got a good experience of GRP sheathing and how did they complete it?
I've got a 27ft broads sailing cruiser built in 1948 by Herbert Woods. Its carvel construction of pine on oak. Its had lots of new planking over the years and the bilge is now almost dry. Ive sprayed the inside with clear cuprinol preservative and now get little deterioration. However I do get a little water in when Its heeled over and the wood at the bottom of the tabernacle gets wet again and I would hate to see wet rot in it as thats a really big job to replace.
The hull planks have been caulked with putty originally but since ive had her any new planks i've treated with cuprinol , primed with primacon and sealed with sikkaflex.
Now its in good condition I'm thinking of grp sheathing below the boot top to reduce the amount of work in the future as I'm getting older and dont want to be clambering about under an old wooden boat. So after the sheathing with 4 layers of 300 gsm I would coat with west epoxy and apply an antifoul.
I've been coating the hull with bitumen up to now so all that would need to be stripped off.

 

[PCUK]

Forget the csm and use biaxial cloth and epoxy. Good piece in PBO on using that stuff.

 

[William_H]

I would caution against sheathing. Firstly obviously it will not be authentic wooden boat. You can keep an eye on the wood and do maintenance on it. However sheathing on wood might seem really good but thin sheathing tends to move with wood swelling and delaminates really easily allowing water to be trapped under the sheath. Now many might disagree here and they may be right. However I think the only way to do it is with really thick GRP such that you really have a GRP hull which used a wood male mould which is left in place. Bu this will make a really heavy hull. olewill

 

[Iliade]

What about popping a load of rock salt on the beam shelf? Was an old trick to deal with just this sort of thing.

 

[Daydream believer]

Yes been there done it , had the T shirt & it worked great. I did it on a clinker Stella No 103 which was a virtual wreck.
The boat had sprung planks, was rove sick ( I could push some fasteners back & forth with my fingers) decks were rotten in several places & there was rot in transom knees. the chainplates were hanging loose. It had 12 broken ribs
First I made a steel frame to hold the boat in its correct shape.& stored it in a building.
I stripped everything out of the boat down to a bare hull & removed the deck and bulkheads.
Then I had it sand blasted inside & out. This blew holes in it where the rot was & also removed the previous owners attempts at repair with pitch !!.. Some of the planks were half inch clear at the bow & he had just filled the gap with pitch.
This removed most of the paint & I only had to chip the paint from behind the ribs where they crossed the lands & that took about 6 hours & was easy as it just poked out.
The 12 ribs were repaired in one saturday afternoon on my own using the west system ( I have a joinery works & all equipment & English oak to hand)
I repaired all the rotten areas & the ribs. & re fastened the planks at the bow.
Then I grouved the gap between the lands 6mm * 6mm & filled using west epoxy & filler. This should have been enough on its own but there were so many worm holes that I went further.
I coated the iside with a very thin resin supplied by wessex resins. To apply this I needed an air assisted mask due to the fumes. It applied like cuprinol but had the seeking properties of antifreeze. ie it found every single hole in the wood & highlighted lots of worm holes that I had not seen. It also worked its way around all the loose roves. I had tried re tightening these without success.. I coated the entire inside which was unlike a normal epoxy finish as it soaked right into the wood rather than sat on the surface. It gave the surface a crystalline sort of finish.
Then, under the supervision of the Wessex rep I covered the hull & the new ply deck with 300grm woven matt laid diagonally in 1 metre squares. For a carvel hull one can do bigger pieces but with clinker it is very difficult to work around the curves. The trick is to lay the matt diagonally.. First apply resin to the hull, then soak the matt & roll it out then apply matt to the hull..It only needs one layer plus an extra triangular layer at stress areas such as chain plates
During the whole operation the boat had the moisture content lowered to about 10% and I had fans blowing though it and monitored the % carefully.
The rep from Wessex was always on hand to give advice & visited several times.
If i did it again I would turn the boat upside down & it would be so much easier as all the resin would run into the lands & onto the surfaces & not into my hair.

I took the boat to Burnham yacht harbour where it was launched & left the keys with the manager so he could pump out each day. After a week I went back to the boat & received a cheer as I walked into the office, I asked why & they said that it was the first Stella they had put back that had never leaked a drop. There was still dust in the bilges.
When I went on the Wessex stand at LIBS the rep let me into a secret- It was the first clinker hull that they had seen successfully sheathed. They had seen carvel done but most could not successfully sheath clinker.
I spoke to the current owner 17 years later & the boat is still Ok. Do not take any notice of those who say that it cannot be done. Provided it is done properly it will work . Only half done bodges fail. Looking at the boat one would not know that it had been done as it is painted & looks just like my first Stella did ( No 104)
The boat cost £ 2200-00( inc a good engine) the final cost all in was £14500-00 inc new sails, rig, paint etc ( inc 3500-00 for west system bought trade) I did not cost a lot of the material that came out of my joinery shop such as oak & mahogany & fastenings etc. I sold it 3 years later for £ 9000-00. But I really enjoyed the build so did not mind the loss.

 

[Cockaigne]

Plenty of information on the WEST Epoxy website.

 

[tillergirl]

I have no experience of doing it (fortunately never needed that) but over the years I have read quite a few contrasting opinions. My conclusion is that both opinions such as William H and Daydream are worth and worthy of attention. I would also suggest that you seek an opinion on the Wooden Boat Forum (http://forum.woodenboat.com/forumdisplay.php?1-Building-Repair). It's an American site and has a lot of experience of sheathing and huge experience of epoxy. Generally the American's don't speak English 100%: for example most do not recognise the term 'wet rot' but you will value the comments. Opinions for and against will be well argued.

I regret you have used Sikaflex - depending on the version. As a Broads sailing boat she will be lighter built and will have naturally flexed: Sikaflex will not to the same extent. Of course, others will have a different opinion.

Good luck. She deserves your work.

 

[lw395]

Yes been there done it , had the T shirt & it worked great......

How much glass did you put on?

I think sheathing has got a bad reputation due to early efforts with polyester resin, on boats that could have been saved with a bit of woodwork, instead they rotted in the sheathing. Some quite good old boats were destroyed like this.
I have seen others which were pretty much beyond repair by woodwork, sometimes sheathing got a few years extra use out of them. Sometimes it was just a waste of resin.