Timber paddle

[labr@]

This is more of an accessory build than a boat build. In another section of the forum someone asked about how I joined my paddle blades to the shaft. Here is a short build log with extra pics of the joining process. There is a longer log in the Do It Yourself section on AKFF.
Blades were made by laminating sections of recycled timber blind slats and cutting out the shape.
http://img208.imageshack.us/img208/1600/laminated.jpg
http://img172.imageshack.us/img172/7181/markingout.jpg

Hollow shaft was made by routing out the back of lengths of quad and then gluing them together to form a tube.
http://img177.imageshack.us/img177/5138/hollowpieces.jpg
http://img246.imageshack.us/img246/4876/endviewglued.jpg


Ends of the shaft were cut diagonally and glued to the blades with a thick mix of epoxy and wood flour. This was reinforced with a glass patch. The ends of the blades stick out past the join to help keep water out of the kayak when paddling. This could be modified to have the shaft edge line up with the end of the blade and that would probably suit oarmaking more.

Test set up without glue. Note simple method of wedging blocks under blade to hold against shaft. Shaft must be held down of course:
http://img40.imageshack.us/img40/677/bladesetup2.jpg

Glue on blade:
http://img294.imageshack.us/img294/6774/bladegluing1.jpg

Clamped to a board and held up at an angle to help glue stay in area:
http://img55.imageshack.us/img55/4572/12gluesetting.jpg

Joint sanded:
http://img55.imageshack.us/img55/6749/13gluesanded.jpg

Fibreglass patch applied:
http://img55.imageshack.us/img55/930/15glasspatched.jpg

[Bill P]

Nice Bob,

Just wondering about the finished weight and how much flex in it?

Cheers Bill P

[labr@]

Thanks Bill,

Weight is 970g - will still be under 980 when varnished. This is mid range as far as I can tell. Web sites quote weights from around 740g for carbon fibre up to about 1130 for aluminium/plastic.

I still have not used it yet so don't know if the design is any good or not. That doesn't matter too much though because I can always cut and remodel it.
It does flex quite a bit when I put weight on it on a solid surface but I think it will be OK on water - for me at least, as I'm in the lower range of weight/strength.

A 'quick and dirty' paddle I built earlier had a 25mm diameter hollow shaft (this one is 30mm) but it was wrapped in glass for the full length and has proven quite strong enough.

[Bill P]

Hi Bob,

I would call that light weight. My usual commercial alum/glass paddle is about 1250g. Other ones I have are heavier.

I just made a Greenland style paddle from Douglas Fir and was hoping to get about 1200g, , but its about 1500g:~.

Do you reckon you could do chin ups with your paddle without it breaking?


Regards Bill P

[Arron]

Thanks. Still curious about how the curve was achieved in the blades - the curve is obvious in the first figure. Did you laminate multiple thicknesses of timber (ie multiple slats) around a form ?

thanks
Arron\

[labr@]

Do you reckon you could do chin ups with your paddle without it breaking?

Chin ups:o? Hey, I don't do whitewater!

That made me curious though so I put it across 2 saw horses - under the shaft as far apart as possible, NOT the blades - and it held my weight when pushing down at the points where my hands should be when paddling. I am sure that my full weight (80kg) in the centre or with supports under the blades would break it.

Arron,
You sure are a curious feller - are you certain you weren't a lab rat in a previous life?

Yes the blades are laminated. First layer was 4 widths edge glued on a flat surface then 1 side sanded (to become the concave side). Second layer had 1 piece split and the half widths put either side to stagger the joint lines. First layer was clamped over some suitable blocks onto a base of chipboard and fiddled with until the curve looked about right. The strips of the top layer were then glued on by removing clamps 1 at a time to get all the pieces clamped at 1 end first then repeating at the other end.
http://img26.imageshack.us/img26/2696/piecessmall.jpg

http://img26.imageshack.us/img26/1903/glueing1small.jpg

http://img188.imageshack.us/img188/5946/glueing2small.jpg

The convex side was sanded after the epoxy set.

[Bill P]

Hi Bob,

Thnaks for that.

Still a bit curious if the shaft construction method is worth it. I would expect such a tubular shaft to be as stiff as a solid one, since the bending force is a function of the diameter. (ps Chin ups is just an old rule of thumb for strength)

I would expect some additional stiffening due to the 4 longitudinal epoxy seams. Not sure how much though. interesting to think about.

Tas oak apparently has a density of ~680kg/ cu m. I would be interesred to learn the excavated volume of your shaft to calculate the weight saved vs solid shaft. Maybe if you could just approximate the inner diameter i can work it out .

I like tubular structures. How thin do you reckon you could you route the quad before it fails?

Bill P

[labr@]

I actually weighed 1 of the pieces of quad after each pass to see how much weight was being taken out but forgot to write anything down:~. From memory the piece went from around 210 g down to about 110 - 120. This would give the tube weight at 480ish before cutting to length.

Taking some measurement from the pic below gives a mean wall thickness of around 4.5mm. I went through the maths and came up with a shaft weight of 392g finished and 762 before routing. This was using your specific gravity figure of 0.68 and it all seems to tie up reasonably well.

http://img10.imageshack.us/img10/871/endviewglued2.jpg

I believe (firmly) that the epoxy would add practically nothing to the stiffness. I agree that the core of a tube has much less effect on stiffness than the skin - that's why I went down this path.

Not sure how thin you could go but if you went below 4mm I think you would need to use a cutter that would give a thin wall in the middle of each piece and leave the mating faces a bit larger. In mine I did not have a suitable cutter available so did passes from each end with a slightly offset 6.5mm one, leaving a slightly scalloped internal shape. Not ideal but it worked.

[Arron]

Thanks for doing that. Some interesting ideas there.

Arron

[Bill P]

Thats Great Bob.

I've done some quick weight calcs and the numbers look great. Tas Oak would be unfeasible as a solid shaft but its a ripper the way you've done it.

I intend to copy your shaft construction method. I note from the other forum you say :

...The inside surfaces were thoroughly coated with epoxy and then the pieces were put together on supports with sides. Two plastic irrigation joiners were put in the ends to help stop the pieces collapsing while numerous cable ties were applied. The lesson from the Mk1 was that lots of control is needed to obtain a round, ridge free shaft. The cable ties were applied at wide intervals at first then the gaps filled in stages. ...

Was there any drama in getting the shaft layup straight & true? Did you use straight unthickened epoxy? Any other tips for the novice?

Bill P

[labr@]

Tips FOR the novice?:o

Mate, I AM the novice :hahaha:

If you've read the AKFF thread and everything here I don't think there's much to add.
I can confirm that the gluing was done with unthickened epoxy and while this would be weaker in a gap filling situation the joints in the shaft are very tight so it should be fine.

The only other tip is to do a dry layup of the shaft using rubber bands or something similar to check for straightness. My Mk1 is a bit bent so I played with the pieces on the Mk3 (don't even mention the Mk2) and swapped them around until the curves acted against each other to give a straight shaft. You will notice on the end of the tube in the pic that each piece is marked with dots - once you start applying epoxy everything becomes a blur and all the pieces look the same so the marking will ensure a straight shaft.

Incidentally, the only reason I used Tas Oak is because it was all I could find in 15mm radius - think I got lucky though 'cos it's all good so far :cool:.

[b.o.a.t.]

G'day Bob
I take it you haven't tried ovalling the shafts where your hands grip it ?
cheers
AJ
(making slow progress with kayak - unless I test unpainted, it will likely be an August launch now.)

[labr@]

Hi AJ,

No, I thought that's something I can do later if needed. Have used ones like that but then it means you need to have the paddle around a particular way all the time. Clumsy beggars like me tend to hit themselves in the head when turning a paddle end for end so better to do without if possible.

Thanks for answering my unasked question - have been tempted to bump the Clayton Bay thread just to see where you were.
August though :cold: brrrr.......

[b.o.a.t.]

Hi AJ,
<snip>
then it means you need to have the paddle around a particular way all the time. ....

Not so !!
if the oval is not extreme, and is in line with both blades, the paddle is fully reversible,
and your hands can 'see' how to hold it, even upside-down in muddy water !! :o

[labr@]

Hhhhmmmmm.....trying to picture it but can't quite get there. I think you'll have to show me sometime.

Don't suppose it's 'cos I failed to show that my paddle is feathered - would that make a difference? The feather angle is about 80 degrees.:?

Which reminds me......

For those contemplating doing this, I recommend some research on feather angle. I always thought it had to be 90deg but that's not so. If you are a high angle paddler (like me) then the angle of your arm naturally twists the paddle a long way and this suits a large angle. For a low angle paddler you will need to use more wrist if you have a large feather angle so a low angle may be better. Also depends on blade shape/size and type of paddling eg whitewater, touring etc.

Also important for feathering: make sure you know which way to orientate the offset - if you are used to a right hand control and get it wrong you may have trouble with your new left hand control paddle:p.