Paulownia or balsa?

Hi all,

Returning to kayak building after a long hiatus.

One of the builds I am planning is a Guillemot 'Yukon' for flatwater fitness paddling and racing. I want to build as light as possible, so the obvious choice is paulownia. However, I'm interested in thoughts on balsa for the core?

It will be glassed in and out, and I may use carbon fibre on the underside and inside for strength, but will have the top clear-coated...may even use some RWC for feature strips on the top.

Whilst paulownia has a weight of 280kg/m3 and WRC is 370kg/m3, balsa is 150kg/m3. But crushing strength is 50% of paulownia and 30% of WRC. No surprises. I'm assuming lateral strength is a lot less too.

I remember seeing a canoe or two built out of balsa ages ago here, and it's used for surfboard blanks so I figure it's do-able.

Would the trade-off in strength/hardness be worth it for the weight saving? Or would I need to increase the strip size (thickness) to complensate, and therefore lose any weight advantage? Quite happy to use paulownia, but keeping weight down is key...but I'd hate to hole it or have it snap in half! I will be paddling in rivers so liely to encounter a submerged log or two, so need some strength on the bottom (maybe thicker glass?)

Hoping some of the more knowledgeable members can help me decide :) I've only done ply S&G previously so still learning the properties of strip woods.

Thanks,
Darren

The balsa canoe was done by BoatMik (moderator of this forum) some time ago and there is a page about it on the Storer Boat Plans site :
http://www.storerboatplans.com/Balsa...alsacanoe.html

Some thoughts:
Given the susceptibility to punctures perhaps a composite of Paulownia hull and balsa deck/bulkheads might work. Might need some extra reinforcing around the coaming though.

A few of us on here have used 84gsm glass rather than the 4 or 6oz favoured in the USA and found it to be quite acceptable. You could consider using this outside and an even lighter glass inside. From what I have seen some of the lighter glass is more expensive but if you are talking carbon fibre then I gather that a bit of extra cost is worth it to you to reduce the weight.

Thinner than standard strips is another idea that has been used successfully but for a first build I think you would need to be careful with this. I'm not suggesting you don't do it but taking a bit of extra care would make the build a bit longer.

My latest kayak is a K1, so it is 5.2 metres long. It is made from 3.5mm Paulownia with 85gsm glass inside and out. Until I put a big slab of polystyrene foam in the back for floatation, it was just under the 8kg minimum weight for a marathon K1.

If Paulownia and glass can get the weight that low, I really can't see that the extra expense of basla and carbon fibre is worth it.

Hi,

Thanks both. Looks like paulownia is the way to go. Good tip on the glass, I used 84gsm on my SUP and it's strong enough so will look at that (and maybe lighter on top or inside). Balsa will cost more but if I'm as careful as Anewhouse I should keep the weight down :-) Pretty confident I can do thin strips (I build model ships so kayak strips are huge!). May do paulownia on the bottom and some balsa on top.

Once I've made the building space I'll get into it and do a build log. So some time to ponder it all before then.

Thanks,
Darren

If bashability is a concern with the softer woods consider using Sglass. It's big plus is high compression strength as apposed to tensile strength like carbon/kevlar.

Quote:

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Originally Posted by anewhouse

My latest kayak is a K1, so it is 5.2 metres long. It is made from 3.5mm Paulownia with 85gsm glass inside and out. Until I put a big slab of polystyrene foam in the back for floatation, it was just under the 8kg minimum weight for a marathon K1.

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Just out of interest, how fragile is that? Is it a case of don't touch anything solid, or will it bounce?

How strong is it? I guess the only answer that really matters is that it is plenty strong enough for flatwater marathon racing.

I don't believe that I have to treat it any more carefully than the fibreglass, kevlar or carbon fibre K1s that I compete against. I have seen the occasional one of them crack along the seam when people tie them down a bit tight on their roof racks. I have seen them with cracks in the gel coat because they flexed when people put a bit too much weight on the deck behind the cockpit. Mine hasn't had those problems.

I have bumped sticks in the water a few times and slid over logs a couple of times with no sign of damage. I have no doubt that a sharp object would leave a dent, but that happens with some of the new lightweight foam core sea kayaks and skis. If they sit on a pebble on a sandy beach, it can leave a dent in the outer layer.

I am sure that being swept sideways onto a rock could puncture the hull, just as it would puncture most K1s. However, K1s are rarely put in that position.

I have no concerns about its strength.

Thanks. That gives me a pretty good idea. Always interesting to see what other people can get away with.

I am quite new to canoe building, but have built many Alaias out of paulownia. These are 19mm thick by 6ft long boards that are surfed standing up. No glass, no resin, nothing. They flex beautifully into the face of the wave with excellent memory/elasticity. I have surfed them in double overhead waves and never broken one. Good quality Paulownia is very strong even without glass or resin. The reason we use it for Alaias is that it resist salt water penetration better an any other timber we know of. This means that it simply needs a bit of linseed oil every couple of weeks to keep it protected.

I would strongly recommend it as a strong and lightweight timber for your craft. Shame you'd have to glass and gunk it up though.

Ill be be making my first canoe paddles from some slabs I have left over to see how it fairs in that context. No ply, glass, resin or varnishes. Just timber and oil.

Regards,
Dave

I've just been thinking about oars. It occurred to me that a paulownia core with hoop pine (or similar) laminate on the front and back faces would give an oar that was as stiff as a normal one, but with a substantial reduction in weight. I think I'm going to have to try that.

Hi Andrew, I'm looking to build a K1 myself, yours sounds great at only 8kgs !. Did you have a plan? or did you design it yourself? I'm having difficulties finding any K1 plans. Regards

Mark R

Hey Mark welcome to the forum. I presume that you are asking about Alan Newhouse's K1. I'm sure he would reply if he had seen your question but until he comes along here is a link to his design thread on the Blue Heron Kayaks forum.
Blue Heron Kayaks • View topic - K1 for old paddlers

Alan was generous enough to post his design file in that thread so anyone else can use it. To look at his design you will need to download and install the KayakFoundry software - don't worry, it's not only free but also easy to use. To convert a design into plans you just print the forms. These can then be glued to ply or other board to make the forms.

I've oversimplified things a bit but it really is easy - and there is a wealth of advice available on either the Blue Heron forum or here.

hi
can i just ask
what design is your K1 as am having problems interpreting david paynes K1 plans, just need some advice on building instruction
regards
glenn

Anyone building a strip canoe in Tassie? Would love to have a look

This is the boards I've made in the past. Haven't made any for sometime. Take a look at: Dorff Boards