kayak hull material

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overland
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kayak hull material

Post by overland »

I'm trying to decide on a hull material for Klepper kayak skin that I'm rebuilding. (The old canvas deck is still pretty good, and I'm going to reuse it.) One is 22 oz PVC sold by Mauritzon in Chicago. They also sell an 18 oz version, which is what I think Tom Yost used on his kayaks. This is the stuff Pakboats uses on its kayaks, although I think it uses a heavier weight on the bottoms.
The other choice is 38 oz. CSM (Hypalon), also from Mauritzon. I don't know how this weight compares to the original Hypalon fabric used in Kleppers. Does anyone know? As far as I can tell, it's the same weight as Pennel Orca 828, which I think is used for inflatables. It's much more expensive than PVC, of course--$40 a yard--although they have a "B" grade material, they said, for $12 a yard. They also have a 16 oz. CSM. I'm in Chicago, so this stuff is easy for me to pick up.
Any thoughts?

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chrstjrn
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Re: kayak hull material

Post by chrstjrn »

I would go with PVC. Lighter, cheaper, much easier to work with, and some would even say that it is stronger.
Chris T.
~'91 Klepper A2 w/ BSD schooner rig.
'64 Klepper Passat/Tradewind and T12 restoration projects.
Non-folding: Early '90s Old Town Canoe.
Previously owned '04 Pakboat Puffin II and '05 Swift (prototype), as well as an '84 Hobie 16.

overland
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Re: kayak hull material

Post by overland »

Is 22 oz pvc a good weight? I notice it's also available in a 32 oz. version.
By the way, Alv at Pakboats suggested putting a thin 1/4" foam pad between the frame and the skin--as Pakboats have--to reduce abrasion.

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chrstjrn
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Re: kayak hull material

Post by chrstjrn »

I would definitely take Alv's advice on the padding, and also ask him what he recommends for fabric weight.
Chris T.
~'91 Klepper A2 w/ BSD schooner rig.
'64 Klepper Passat/Tradewind and T12 restoration projects.
Non-folding: Early '90s Old Town Canoe.
Previously owned '04 Pakboat Puffin II and '05 Swift (prototype), as well as an '84 Hobie 16.

overland
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Re: kayak hull material

Post by overland »

Alv says they use 18 oz. PVC fabric on the sides and heavier stuff on the bottom--he didn't say how heavy, but judging from some patch material I have it's about 28 or 30 oz. But he adds that applying keel strips might be good enough in place of heavier bottom material. Of course I could also buy heavier material for the bottom and glue it to some 18 oz material on the sides. I should get out my Pakcanoe and see how they do it. I remember Alv saying in a conversation I had with him over the phone that he didn't understand why boat manufacturers used heavy material for the whole hull, when it was really only needed on the bottom.
Last edited by overland on Thu Apr 27, 2017 3:28 pm, edited 2 times in total.

RainerM
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Re: kayak hull material

Post by RainerM »

Another alternative:

http://www.extremtextil.de/catalog/Nylo ... ::773.html

No matter whitch material is taken, a keel-seam must be sewn so that the hull is wrinkle-free

R.

overland
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Re: kayak hull material

Post by overland »

That's interesting. That fabric is about 18 oz. per square yard and about .028 inches thick. I have some hypalon patch material that's about .025 inches thick and 26 oz. per square yard. And I can buy cheap hypalon (CSM) that's either 16 oz or 38 oz., with a nylon weave (I don't know the thickness). I think the hypalon on my old hull is about 45 oz per yd.
There are a lot of choices. I need to go look at the hypalon. I wonder if the 16 oz. stuff would work with strips everywhere where wood meets the hull? I would save a lot of weight.
By keel seam you mean the seam at either end of the hull?

RainerM
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Re: kayak hull material

Post by RainerM »

overland wrote: By keel seam you mean the seam at either end of the hull?
Yes and no:

long keel seam:
http://www.heise-faltboote.de/dia/photos/bild45.jpg

Material must be cut out in the area of the keel.
Depending on the boat's shape and stretchability of the material more or less. In an extreme case, the shell consists of two parts
R,
430SL1.jpg
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430SL3.jpg
430SL3.jpg (92.45 KiB) Viewed 243 times
430SL2.jpg
430SL2.jpg (89.46 KiB) Viewed 243 times

overland
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Re: kayak hull material

Post by overland »

Hmm. My old Aeruis hull has seams only at the ends--as you show in the third photo--and nothing like in the first photo.
You did a great job with that seam, by the way. How did you do it? What's the material? I'm intending to use the old hull as a pattern. The marks that go across the seam were to keep it lined up? Did you sew the deck on before or after closing up the ends?

arcprof
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Re: kayak hull material

Post by arcprof »

A word of caution when using the old hull as a pattern. Old hulls shrink and your new hull will probably need to be a few cm longer than the old one. What I suggest is to use the old hull as a pattern for the width and the shape of the ends but make your new hull a bit longer. Sew one end to form the toe then try it on your frame. Pull the edges together on the unsewen end and see how much shorter you need it make it to fit with a little stretching that comes with the pushing down of the frame ladders. Ideally you want the length snug with the ladder halves just short of locked down. Sew the other end and re-check using the frame.

The next important step is to match the old deck with the new hull. Measure the length of the stitch seam along the deck end to end. Now measure the length of the edge of your hull at say 10mm in from the edge. Compare this measurement to your deck seam length. The two MUST be the same. If your hull seam length is too long, you will need to move your intended seam further away from the edge. If your hull seam length is too short you will need to move your intended deck seam in further than the original.

Before sewing the deck to the hull you need to do any remedial work on the deck. I'd recommend overstitching all the original seams then look at possibly reinforcing the rear corners of the cockpit (end of boomerang) and around the front grommet where the coaming tee piece protrudes. Check all your other grommets and the beading that inserts into the coaming slot. How is the sponson tube condition and its stitching to the deck. Paddle bungees? Sailng D rings? It is MUCH easier to deal with these before the deck is sewn to the hull. Remove the sponsons.

When you are ready. Staple the upside down deck to the inside out hull. Position the staples exactly where you stitch line is. If you got your measurements right the two should line up nicely with no excess material. Now sew a seam outside the staples to hold it all together. Remove the staples and sew the final seam. Turn the hull inside out from how you sewed it to get it the correct way round and test fit it on your frame. Be prepared for some unpicking and re-sewing.
Folbot:Super, Sporty, Greenland II, Klepper:1960's AE2, 1970's AE2, 1990's AE2000

overland
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Re: kayak hull material

Post by overland »

Excellent advice. Thank you. Have you used Hypalon here, or something else? Also, how did you sew the end seam? It looks extremely well done?

Alv
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Re: kayak hull material

Post by Alv »

Since I have been mentioned a couple of times in this discussion, I will include some comments. It seems to be assumed that nylon is the substrate material to use. We tried nylon in a few of our early boats because we thought its ability to stretch would be an asset in shaping the boat skin to the frame. It turned out that the lack of dimensional stability just caused problems. Polyester is much more stable, yet stretchy enough. Nylon is popular in inflatables, and that makes sense. There is no frame that needs to fit. Folding and inflatable boats have different fabric requirements.

A foam pad between skin and frame improves abrasion resistance - a lot. We cover the bottom in all our canoes with a 1/4" pad. PakCanoes are used on remote wilderness rivers and carry heavy loads, and the foam makes a big difference. We don't use foam in our kayaks, mostly because foam is bulky and does not pack very well. Also, abrasion is generally much less of an issue in kayaks.

We like PVC as a coating because it is easy to work with, and it works well. Is is also readily available in various weights. It makes sense to me to use relatively light material in the sides and heavier for the bottom. But there is a catch. Light should not mean a flimsy substrate. The substrate is what gives you the tear- and tensile strength. It also provides the dimensional stability. The coating is what keeps the water out, and it provides the abrasion resistance. Get fabric with unbalanced coating if you can (most of the coating on one side), and put the "heavy side" on the outside. There is very little abrasion on the inside of the boat, and excess coating there just adds weight and cost.

I can see some comments coming my way. Yes, we use polyurethane on our kayak skins. That is mostly driven by a desire to be "greener", and we now have kayak materials that we are very happy with. Unfortunately, we'd have to be a much larger company to be able to offer polyurethane in several colors. The minimum production runs are simply too large.

Keel strips should be film - not reinforced fabric unless you use a keel strip to reinforce a keel seam. On our boats, keel strips only reinforce against abrasion. Abrasion is concentrated where the skin rests against the frame, and that is where reinforcement is needed. Ideally, keel strips should be the same material as the coating on the bottom fabric. You can use different materials, but if you do, you should make sure your adhesive is compatible with both the keel strip and the fabric coating.

arcprof
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Re: kayak hull material

Post by arcprof »

I think you have confused my reply with Rainer's. His photos show the seam joining the two sides of the bow and stern ends. That is how I did my last two Klepper re-builds. Rainer talks of a centre line seam the whole length of the frame but the original Klepper Aerius 2 hulls I have replaced, were made of one piece of rubber material. My last project was an Aerius 2000 (tramp) and this did have a centre seam but I think it was straight and I figured they did it that way to optimise material that came in a certain width. Probably depends on the amount of rocker. For a kayak with a bit of rocker a centerline seam will be necessary to remove the excess material formed by the curve but the Aerius has a flat rocker so short seams on the ends are all that is needed. I followed the way the original ends were formed. Use a ZZ stitch 6mm is better than 4mm. You just butt join the edges with the ZZ stitch. This is not a water proof join but holds the pieces together so you can glue strips over the seam to seal and protect the join.
Cheers Jim
Folbot:Super, Sporty, Greenland II, Klepper:1960's AE2, 1970's AE2, 1990's AE2000

RainerM
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Re: kayak hull material

Post by RainerM »

The center seam is necessary for materials which have low tensile stretch fabric. Old Klepper have a stretched canvas carrier fabric with natural rubber coating, The "better" Klepper (not Blauwal 4) from the 1970s partly canvas carrier fabric, partly "Trevira" carrier fabric (very badly stretchable) with Hypalon coating.
Look at the original hull of my Aerius single (approx. 1977): synthetic fiber carrier fabric, middle seam and Hypalon coating. The material width was until 1980 1 Meter. Therefore, the old Aerius-double have laterally placed skin strips in the middle right and left.

Crucial is the "keel jump" (Kiel jump ?, Rocker?). Old Klepper from the 1950's like T65, T66, T6 and T9 (also old Pionier like 450Wa, 430SL, not 450S or 450SS!) have a continuous middle/center seam. The hull consists of two parts. 10-12mm ZZ stitch is best. This is how the professionals work. My sewing machine has only max. 4mm ZZ stitch...

First it is best to try with cheap PVC tarpaulin or order a new skin according to your wishes. Ask e.g. Markus Heise: http://www.heise-Faltboote.de
Because: The first self-made hull is usually so bad that you will throw it into the trash can :(

At the Aerius single I replaced the gray hull against a used black one from an Aerius-Expedition, in which the deck was rotten. Too much work for a too much heavy and much too slow boat!

R.
(The pictures in my other post show the hull of a Pionier 430 Slalom: old used PVC-hull in very good condition from a Pouch E65 with canvas fabric, very stretchy. A photo of the boat with new skin I also attach below)
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AEI_Inkontinent1.jpg
AEI_Inkontinent1.jpg (61.94 KiB) Viewed 214 times
AEI_new_hull.jpg
AEI_new_hull.jpg (63.13 KiB) Viewed 214 times

overland
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Re: kayak hull material

Post by overland »

Can the material above be sewn on a home sewing machine, or is an industrial sized machine necessary?
In any case, the contributors here have offered as authoritative an account of how to re-hull a boat as I've ever seen. There's an incredible amount of knowledge and experience here.

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