Thread: Beth Sailing Canoe(materials) - few questions

Howdy Robert,

With Beth - keep everything as light as possible - that is a very large part of the secret of the boat's performance and handling.


Beth Reefed in South OZ

I wouldn't go any heavier than spruce for spars - that is what I used on mine - cost a fortune in Australia - and the quality was terrible - the timber was so bendy and kept changing shape because it wasn't properly dried.

Spruce would be a good substitute for the Fir/Oregon parts of the boat too - an excellent choice.

To substitute the cedar it would be nice to find something lighter than spruce - but if spruce is the lightest timber you can get without excessive expense - then that is a good choice.

For the ply - the lowest density plywood you can get - of good quality.

Epoxy - you will need around 9 litres - but if it is economical to do so get some extra - for example if the manufacturer does a 12 litre - that will prove useful for all the other projects you and Maria do too.



If you can't get well known brands like WEST or System 3 in Poland you might have to source something else - here are some things to look out for.

• Don't buy prethickened epoxy glues - they work really well on low strength items like furniture - but on boats they are not strong enough. Thinner epoxies that you add powder to to thicken them into a glue are better.
• Epoxy should not be a 1:1 mix - the chemistry doesn't allow that easily - so compromises have to be made. 2:1, and higher are fine.
• Smell the epoxy - there should be no solvent smell. If it has a solvent smell avoid it too. A slight ammonia smell is fine.

Gluing Powder - maybe around 2kg I think this will be too much, so don't get more.

HOpe this helps
Michael Storer

Michael,

Thanks a lot for reply!

9 (12) litres of epoxy... and 2 kg of powder ...not cheap ...

Lightest Polish wood is a spruce (European spruce Picea abies syn. Picea excelsia) - circa 450 kg/m3 when dry I expect not good quality of it. Pine (Pinus sylvestris) is a bit heavier (up to 500 kg/m3) but I can find excellent quality of it.

OK! I will to look for good quality of spruce.

Marine plywood available in Poland:
okoume - circa 460 kg/m3 ....but expensive but look there:
http://www.sklejka-pisz.com.pl/144 (550-700 kg/m3!!!)
spruce/pine (marine plywood) - circa 550-620 kg/m3
alder (marine plywood) - circa 580 kg/m3
beech (marine plywood) - circa 720 - 800 kg/m3
oak (marine plywood) - circa 720 - 800 kg/m3 (to haevy... but excellent quality!)

OK, I will consider to buy okoume ply.

Merry Christmas !!!

Robert,

I've done a little chart comparing the weights of timbers commonly available here for the Rowboat.

I still have to check my maths, but I think I've calculated the cubic metres correctly, it's an interesting comparison, and if you have the scantlings schedule it wouldn't be too hard to work out. If only you get something like Western Red Cedar!



Cheers,

P

Hi bitingmidge,

Thanks, but all wood species which you comparing are not European species. They are not available in my country.
You can see: Paulownia is lighter two times almost than European spruce which is similar to a hoop pine in Basic Density.

My boat will be haevier than designed

Sadly, I do realise what you are up against!

As many of the scantlings in Mik's boats are really gluing cleats rather than beams, I wonder if you could heavily chamfer the non-structural ones, to make them almost triangular in section. That would perhaps remove a third of the weight, and save a kilo or two?

Many wouldn't go to that trouble, but I suspect you are a little like myself!

Cheers,

P

Originally Posted by bitingmidge

Sadly, I do realise what you are up against!

As many of the scantlings in Mik's boats are really gluing cleats rather than beams, I wonder if you could heavily chamfer the non-structural ones, to make them almost triangular in section. That would perhaps remove a third of the weight, and save a kilo or two?

Yes - making cleats lighter I can save a kilo or two

Many wouldn't go to that trouble, but I suspect you are a little like myself!

Probably ...yes

Originally Posted by bitingmidge

Sadly, I do realise what you are up against!

As many of the scantlings in Mik's boats are really gluing cleats rather than beams, I wonder if you could heavily chamfer the non-structural ones, to make them almost triangular in section. That would perhaps remove a third of the weight, and save a kilo or two?

Many wouldn't go to that trouble, but I suspect you are a little like myself!

Cheers,

P

this is an excellent alternative strategy for cleating (joining two pieces of plywood at an angle! Good idea Midge.

Spruce as the solid timber would be OK anyhow - any parts used as beams could be reduced in width - NOT DEPTH - by the density of the density of the timber relative to the cedar.

So if you used Spruce for the beam or longitudinal centre stringers to support the deck then the width of the spruce could be
Original width (19mm) x (density of Cedar / density of Spruce)

This would be for slightly stronger results than the cedar as spruce has straighter grain.

I think you are heading toward meeting the same weight as the standard Beth.

With the bottom plywood of the boat ... If you can't get Gaboon ... I would probably suggest making the bottom of 6mm plywood rather than the 9mm mentioned and increasing the depth of the longitudinal pieces of wood on the outside of the bottom. A couple of millimetres of extra depth will make a huge difference in stiffness.

Michael Storer

Hi Michael,

Thanks for advice!
Spruce beams in width will be circa 15 mm

an excellent alternative strategy for cleating (joining two pieces of plywood at an angle!

I don't understand that idea could you clear? Cross section of cleat with triangle shape???

Probably yes...

Originally Posted by robhosailor

Hi Michael,

Thanks for advice!
Spruce beams in width will be circa 15 mm

I don't understand that idea could you clear? Cross section of cleat with triangle shape???

Probably yes...

Howdy Robert,

The cleats/chine logs etc that are used to join plywood panels at 90 degrees are generally glued to the plywood on only two faces. The other two faces are doing nothing - so you could plane them down to create a hypotenuse (as in Pythagoras the Greek Mathematician). So long as the gluing faces are not changed the rest will be OK.

With the epoxy - it will save you so much money in paint and varnish (not to mention work) over the next dozen years that it is well worth the investment.

You could see how you go with 6 litres and if precoating do the inside surfaces only. Leave the outside surfaces until the end - and you will know what you have left.

To save a bit of epoxy you can roll or sqeegee it out quite thin for each of the successive wet on wet coats - it is still best to use 3 coats. Don't thin them with solvents though!!!

Best wishes
Michael

Originally Posted by Boatmik

The cleats/chine logs etc that are used to join plywood panels at 90 degrees are generally glued to the plywood on only two faces. The other two faces are doing nothing - so you could plane them down to create a hypotenuse (as in Pythagoras the Greek Mathematician). So long as the gluing faces are not changed the rest will be OK.

Michael,
Thanks a lot. I understand.
As an attachement is part of your drawing from plans with shown triangle cleat (red triangle is a new shape of cleat).

Really can I use triangle cross section for chine logs and sheerclamps when spruce/pine?

I can see one problem - clamping triangle cleat to knee etc. Clamping square cleat is so simple (so easy) but triangle is more difficult to placing without sliding tendences. Better probably trapezoid shape of cross section is. See another attached picture. Yellow shape of cleat's cross section will be better for clamping it to knee I think so ...but it save less of weight

About epoxy: I will check out available packages and I will choose beter in economics solution

About plywood for bottom: My friend and boat designer who have his great www page with great free plans of dinghies ( http://www.dinghy.pl/ ) use thick (8-12 mm) plywood for bottom. I think 8 mm alder plywood will be enought, but I want to check out 6 mm plywood for it (lighter then 8 mm) and I can use two additional buttstrapes if nesessery.

Howdy Robert.

The triangle idea is correct - but as it is a weight saving maybe you only need to go part that way and leave a little flat area for clamping

Or use the drywall/plasterboard screws - assemble first square then remove and plane down before gluing.

Or possibly you could use a router after glueing to take the excess material off.

Regarding the bottom Ply - the original Beth was only 6mm - which was adequate, but a little flexible. A more dense plywood will be stiffer of course.

The only time I would go to a 12mm bottom would be either in a very high speed boat or a cabin sailing boat larger than 8metres. It is amazing what can be accomplished with a little bit of framing. I am sure the 8mm will be more than enough.

Best wishes
Michael

Thanks Michael,

I can see use removable drywall/plasterboard screws as a best method of cleat glueing for me.

About bottom plywood again: I want to use 6 mm plywood as designed!!! (My another friend, well known boat designer and architect T.Piasecki, said: "Use all parts stronger than designed - for your satisfaction" but I prefer lightness and performance!!!) I like Beth as designed!

Originally Posted by robhosailor

Thanks Michael,

About bottom plywood again: I want to use 6 mm plywood as designed!!! (My another friend, well known boat designer and architect T.Piasecki, said: "Use all parts stronger than designed - for your satisfaction" but I prefer lightness and performance!!!) I like Beth as designed!

Howdy Robert,

This was my rationale around the 9mm bottom in the plans vs the 6mm bottom of the original boat.

The original boat I used 6mm Keruing - a tropical hardwood ply of poor quality. It is twice the weight of Gaboon. The bottom was a little bit too flexible occasionally bowing in when going over waves. So I added the second plywood bottom thickener - like a second butt strap in the cockpit area. This resolved most of the problem.

So when it came time to draw up the plans - gaboon was readily available - so 9mm gaboon would be much stiffer and LIGHTER than the 6mm Keruing. So that is what I specify in the plan.

However as you can't get the 9mm Gaboon, I would suggest going with a 6mm ply and I will suggest some small dimensioned longitudinal pieces of timber on the outside of the hull over the length of the cockpit area.

MIK

Originally Posted by Boatmik

This was my rationale around the 9mm bottom in the plans vs the 6mm bottom of the original boat.
/.../
So when it came time to draw up the plans - gaboon was readily available - so 9mm gaboon would be much stiffer and LIGHTER than the 6mm Keruing. So that is what I specify in the plan.

However as you can't get the 9mm Gaboon, I would suggest going with a 6mm ply and I will suggest some small dimensioned longitudinal pieces of timber on the outside of the hull over the length of the cockpit area.

Michael,

It was missunderstanding probably: I can see sheet of plans of Beth with panels layout - there are shown five (5) panels of plywood

1. three (3) panels of 4 mm plywood for side panels, deck and centercase sides
2. two (2) panels of 6 mm plywood for bottom panels, 4 bulkhaeds, knees, 2 bottom buttstraps and deck camber template.

In manual on MATERIALS chapter (page no 8) you have written: "It is envisaged that Beth will be build of 6mm (1/4 inch) five ply and 4mm (5/32") three ply Gaboon (Okoume) Ply." So: that is designed I think so
So I understand it:

1. If I use Gabon (Okoume) Ply 6mm for bottom it will be ok,
2. If I need to use plywood of worse quality (less density etc.) I need use 8-9 mm plywood for it.

Sorry for missunderstanding

I can ask my local supplier of marine plywood available in my area. If 4 and 6 mm Gabon (Okoume) Plywood is available I will use it.

"small dimensioned longitudinal pieces of timber on the outside of the hull over the length of the cockpit" are great idea! They are excellent as stiffeners and they are great for protection of bottom ...and they are taking part similar to centreboard, keel, leeboards and chine runners (bilge runners). Efficiency in sailing with half rised daggerboard (centre board) will be better thankful of those "small dimensioned..." I think so ...

Sounds well...???