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DIY Hull Replacement (Klepper but applic to other folders)

Posted: Sun Apr 26, 2015 6:12 am
by arcprof
I have replaced the hulls on three Kleppers now. My last project was a AE2000, one of the smaller singles. I have been using this boat a lot and after a good seasons use can now report on how well this repair method has held up.
The deck was sound but the black PU hull has cracking up and delaminating off the supporting cloth weave. The method I developed for this repair was to replace the hull with clear unsupported PVC. My experience with this material as used in windsurfer sails has shown it to be extremely durable. I like the fact that it is homogeneous with no tendency for the outer layers to peel off the core. One problem is the tendency for stitches to pull through the seam edge so I decided to sew a thin strip of supported PVC to the canvas deck on the same seam line as the old hull and then to glue the clear PVC onto the strip. The following photo shows the strip sewn to the deck with the clear PVC hull glued to it.
This kayak has proven to be extremely durable and has received a lot of admiring glances. There is something about a clear bottomed boat that appeals to the masses but with all the frame in the way and the distortion caused by the unavoidable curvature in the skin between longerons, the benefit of being able to see out through the hull is minimal. However, one big advantage is the ability to see where everything is and to be able to see all the frame pieces from outside the hull. The next photo shows what I mean.
Here is a view of the complete kayak. The hull/deck is free of any unsightly ripples in the materials and is very tidy looking. It is a lot lighter than the original although I haven't got an actual weight. The PVC is about 0.7mm thick. It does get quite soft and pliable when heated by the sun but seems to retain its shape well and once in the water the hull is cooled by the water but I would not recommend use in geothermally heated lakes!
I will describe the process I used to glue the hull to the deck strip and other details in later posts if there is any interest. Sewing the narrow strip to the deck is easily done with a domestic sewing machine so this method does not need any specialised equipment with the use of a heat curing PVC glue making life a lot easier for the amateur repair person.


Re: DIY Hull Replacement (Klepper but applic to other folder

Posted: Sun Apr 26, 2015 10:16 am
by chrstjrn
I'm very interested in learning more. I have to replace the hull (and the deck) on my T12, and also to do some repairs on the Passat hull. Both are 1960s/old school, i.e. natural rubber with a cotton core. I'm not aware of any Klepper having used polyurethene at any point-- it was rubber up until some time in the 70s (or maybe 80s?) and then hypalon for a long time. In the last few years they have gone to PVC. I know that Pakboats and others have gone from PVC to PU for environmental reasons (and maybe encouragement from some distributors).

Re: DIY Hull Replacement (Klepper but applic to other folder

Posted: Sun Apr 26, 2015 6:42 pm
by arcprof
Hi Chris,
I figured my original hull material was TPU as the Klepper site states this is the current material they use on their Tramp/Scout which is the new name for my AE2000. I didn't think it was hypalon as it was in a bad way after only 20 years service. The bow and stern caps are rubber and the hull was made in two halves sewn together down the middle with rubber strips glued over the seam.

Here is the overall sequence to replacing the hull.

1. Pull off bow and stern caps and undo rudder mount (10mm socket from inside hull).
2. Turn hull and deck inside out.
3. Remove sponsons.
4. Rip stitching between hull and deck with seam ripper. Note if deck is to be re-used leave the trim beading stitched to the canvas in place.
5. Pull deck away from hull.
6. If re-using deck, closely inspect seams and if in doubt re-stitch. Look for any weak points like around mast opening and the rear corners at the ends of the boomerang. I had to reinforce the grommet penetrations. Making a new deck is not too hard. I have made one using the old deck for a pattern but this is not the subject of this post.
7. Flatten out the old hull by pulling off the strips covering the stitching where the hull ends are sewn to force shape into the ends. You can use this old hull as a pattern for cutting out the new hull. Be aware that old rubber hulls do shrink with age so if you were having difficulty forcing down the keel ladders in your old hull you will have to make the new one a little longer. One advantage of using the clear PVC is that it will stretch but there are limits.

8. Lay the old hull on top of the new clear PVC.

Note that this material is available in different thicknesses. I used a 0.7mm sheet. I wouldn't go any thinner. 1mm is probably about right. As you need a a width of just over 1m for a klepper and standard roll widths are over 2m you can cut the roll down the middle and glue two strips together to get the required length. This way you only need to buy a length just over half as long as your kayak. I did it this way and made a 50mm overlap join that runs across the hull that has given no problems. Make sure the overlap is done so the top edge of the join (outside the hull) is facing to the rear. I used a heat curing PVC glue called Unigrip 999 made by Bostik. I'm in New Zealand so you may have to find an equivalent. It is used in the shoe industry. It's major advantage over non heat curing contact glue is you can place the parts together and re-adjust their positions before using a a heat gun to get the glue to take. I added a catylist to improve the strength of the glue.

9. Mark out the new hull shape and cut out the new hull. Scissors work fine on this material.

10. Hand tack a few stitches in the bow and stern ends to form the ends. Assemble the frame and test the hull fits snugly. If you had doubts the old hull was the correct length and were using the join two sheets together method you could form the ends in the two sheets before gluing them together and then you could adjust the overall length to get a good fit. I only thought of this now as I did not have a problem with my length.

11. Once happy with the length, machine sew the "horns" of the ends together by butting the edges together and using a wide ZZ stitch. I did this on a domestic machine. Note a roller foot helps the feed. You can see the stitching in this photo.

To be continued.....

Re: DIY Hull Replacement (Klepper but applic to other folder

Posted: Sun Apr 26, 2015 6:48 pm
by arcprof
12. Glue cover strips of clear PVC over the stitching on both sides to make the join waterproof. You can use the wooden frame ends to support the hull as you force the strips over the curve. These strips only need to be wide enough to seal the join as the wider they are the more difficult it is to avoid wrinkles. Finally glue on a wider strip to protect the end from damage when hitting the shore. Clear PVC is very pliable when warm so when heated up with a heat gun and stretched it is possible to get a good looking end to your hull. I remember clamping one end of the strip to the hull with the bow or stern piece inside and stretching the strip while heating it with the heatgun as it is pulled round the curve of the end to get a wrinkle free join.

13. The hull is now ready to be glued to the deck.

14. Sew a 30mm wide strip of supported PVC fabric to the deck where the original hull was attached. This seam needs to be strong. I use three rows of stitching using a sailmakers thread Serabond 40. Using supported PVC gives a much stronger join than using the clear PVC material. Be aware old decks can shrink so drape your deck over the assembled frame and check its length. If it is short, you can stretch it to make it fit BEFORE the PVC strip is sewn to it. If yours is like this then tack the strip in place with the deck stretched on the frame (clamp at each end). A paper stapler will work to make temporary tacks, just staple on the inside of where the stitches will go so there are no holes in the strip where it shows on the outside of the hull. Now sew the strip to the deck and stretch the deck while it is going through the machine. Test the fit on the frame. If the deck is too short you will have to unpick the strip and try again.

To be continued....

Re: DIY Hull Replacement (Klepper but applic to other folder

Posted: Mon Apr 27, 2015 6:31 am
by chrstjrn
Excellent write-up. Very helpful. Thank you very much. Looking forward to the final installment.

Re: DIY Hull Replacement (Klepper but applic to other folder

Posted: Mon Apr 27, 2015 6:02 pm
by arcprof
15. I glued the hull to the deck with the hull turned inside out just as you would if you were sewing it. I seem to remember propping the assembled frame upside down on the ground with the right way up deck underneath. I then drapped the inside out hull over the frame and used clothes pegs to temporary hold the join together to see how they matched for length. In my case the deck was a little short and I had to try and force more hull length into the join to get them to match. This meant cutting little "V" notches in the outer edge of the hull but it was not that successful and I ended up with an inch or so of excess hull edge towards the stern on one side which I had to cut out by putting a big "V" in the hull so that it showed well below the PVC strip and was below the waterline but was easily covered with a clear patch and doesn't look too bad. Obviously, it is best if you can avoid this by ensuring the lengths of the deck strip and the outer hull edge are equal before glueing. That is why I mentioned earlier that you have to make sure the deck length matches the frame length before sewing on the PVC strip. If the hull edge is too long and the deck length is fine then you could consider trimming an inch or so off the entire hull edge to reduce its length as it does follow a curve. You get these same problems when you try and sew a deck to a hull as in the original construction method used by Klepper but in our case things have shrunk (your old deck and/or the old hull you used as a pattern) so you need to adjust for these changes before joining the two together.

16. Once you are happy the two edges to be glued are the same length down both sides, then start at the bow and press the surfaces together with heat to get them to bond. Work your way down till you reach the stern and now you have a complete hull.

17. Turn the inside out hull inside out again to get it the way round you will be using it. Once you are happy the glue has reached full strength try inserting the frame and admire your work.

18. Glue on small pieces of PVC fabric to the top of the bow and stern caps to cover the extreme tip of the deck and seal the pointy bit on each end.

19. If your rudder stern piece has a finger that slips under a strap on the stern capping, make up a strip of PVC to go over the cap and sew on a strap that forms a saddle to take the end of the rudder piece. My AE2000 originally did not have such a finger but I added one (white piece in photo) as it strengthens the whole rudder mount and I wanted a strong rudder as I intended to sail my AE2000. Check out the closeup photo to see how I did this.
20. Install the rudder mount and insert the sponsons.

21. Add keelstrips (4) to protect the hull where it touches the longeron rods and outer edge of the keel boards. I always do this on an assembled boat with the sponsons inflated. Make sure the hull is centered before marking where the strips go.

22. More photos.
Hope this post will inspire others to make their own hulls. Even if you do not fancy the clear PVC, this method will work for other PVC materials and avoids a difficult sewing job. Believe me, I have sewn entire hulls to decks and it ain't easy.


P.S. It was a year ago when I made my new hull so there could be some errors in my summary. Please feel free to ask if something does not make sense.

I should point out that gluing PVC to PVC does require some preparation using solvents and keeping things clean but I was impressed with how well the heat curing glue worked.

Re: DIY Hull Replacement (Klepper but applic to other folder

Posted: Mon Apr 27, 2015 6:13 pm
by chrstjrn
Wonderful, Jim! Thank you very much!

Re: DIY Hull Replacement (Klepper but applic to other folder

Posted: Tue May 05, 2015 8:02 pm
by mje
VERY impressive! That's pro quality work.

Re: DIY Hull Replacement (Klepper but applic to other folder

Posted: Sun Jun 14, 2015 9:00 am
by DLee
I agree with Michael. Amazing work.

So it still comes apart and you pack it up the usual way etc. etc. etc.?

Any difference in the overall weight in the end?

Thanks, this is very cool.


Re: DIY Hull Replacement (Klepper but applic to other folder

Posted: Fri Jun 26, 2015 8:53 am
by arcprof
Boat assembly is identical to original hull. I used clear pvc at 0.7mm and the boat is definitely lighter but I don't know by how much.