Hi Johannes,

I have a lot of experience with light builds….most of the boats I have built in the last several years are 30 lbs or less and my lightest boats are all strip builds.   Fwiw, its hard to get superlight with okoume as it is just a very heavy (and strong) starting point. 

For the shearwater hybrid sport I would focus on the following in terms of opportunities for saving:

• 3 mm okoume for the hull
• 3/16 cedar for the deck (you can run the ¼ inch strips through a thickness planer)
• One layer of 4 oz s glass on the outside (hull and deck)
• One layer of 4 oz s glass inside the hull and very small/well sculpted fillets – no need to fill the weave on the inside except in the cockpit area.  You could go 2 oz glass outside of the cockpit area.
• One layer of 4 oz s glass underneath the deck – no need to fill the weave
• End pours that are built prior to assembly using a paste of epoxy and micro balloons – only as big as needed so that if you drill a hole for the toggle – that it doesn’t create an opening into the boat.
• Bungee rigging with no screws – drill a 5/16 hole in the deck – fill with epoxy  - drill it out to 3/16 ….then pull bungee through it and tie it underneath – save the weight of screws
• 3 coats only of varnish – varnish only the outside and inside around the seat where the sun shines.   varnish actually adds a lot of weight – so no more than you neeed. (you could also consider painting the hull – in which case you could do the fill coat with microballoons – and pick a paint that covers well)
• Careful epoxy work throughout.
• Lightweight toggles or just loops of rope (vs handles and rope).

On some of the points you mentioned:

• I would not not glass the interior – just don’t add extra epoxy to fill the weave.  Or as mentioned above, consider 2 oz glass.  You just tend to be much more susceptable to water intrusion with no glass.
• Definitiely on any strip work – you need to glass both sides, in my view.  It is pretty weak unless you have the full composite effect – but as mentioned – you can go with 3/16 cedar and not fill the weave under the deck.

When building light, I like to substitute s glass for e-glass – its much stronger and does not pay a weight penalty and helps compensate for the thinner wood elements.

for all my builds the i am trying to build light,  i develop a bill of material with weights from the manufacturer as you cannot build a light boat of a certain weight unless you actually have a recipe that supports your approach.   i don't have one for a boat with okoume....but see the picture below for what i mean - the figures for okoume should be easy to get.....and you can experiment prior to building with your weight.

hope this helps.

h

Hi Johannes, 

i wanted to add some additional thoughts that might be useful:

1. as a historical note (i have been hanging out on this site for ~ 30 years now), CLC used to offer a light build option on a lot of their kits so you could make a special request to have your stitch and glue cut with 3 mm okoume.  there are other stittch and glue boats routinely built with 3 mm and the weight is really cut down.
2. you do need to be sensitive to ensuring strength around the cockpit and while these boats are sturdy, there are certain manuevers, that even a normal build, should be sensitive to - particularly point loads like banging into a rock or getting into the boat with a paddle brace onto the back of the coaming or deck.
3. fwiw, having a target and building that little bill of material spreadsheet with weights i found very useful for experimenting with trade-offs.   your boat, even at their design weight of 48 lbs are still lighter than most production boats....but if you can get into the 30 lbs zone you will find an amazing difference in terms of it just being easy to move around....which leads to more use.  the boat i have that gets the most use, fwiw, is my slightly below 30 lbs modfiied petrel play......
   hope that is helpful
4. h

   Hello h,

thank you very much for your detailed reply, I appreciate it! I've read multiple of your past posts and your results with the Frej 90 impressed me very much, and actually it started my ambition to build a lighter-than-standard Shearwater Sport Hybrid.

I ran some ballpark figures, based on the Fyne Boat Kits information on the weight, which they mention as 18.5 kg, or 41 lbs. That is also closer to the SW 14 Hybrid, which is 39 lbs while having the same length and being at bit more narrow. The 48 lbs mentioned here at CLC matches the sectional all-plywood SW Sport, so I assume it's a mistake. 

Using 3mm plywood instead of 4mm may already shave off 6 lbs, and partially using 2 oz glas (below deck, inside the cockpit) may save an additional 1.3 lbs. That would result in 33.7 lbs, or 15.2 kg. Using microballons for hull fill coats and maybe some other small items may bring it just below 15 kg or 33 lbs, which is now my goal.

I'm buying my kit from CLC's partner in Germany, and already sent him an E-Mail about the 3mm plywood. 

Thinking about building and using such a light boat is quite exiting, can't wait to get started.

Thank you very much, again!

BR, Johannes

Hi johannes, 

glad you noticed the 48 lbs thing....i ran some figures as well (happened to have a spreadsheet in front of me) and could not sort out how they got 48 lbs...so i was wondering if it was a mistake.....so yes 41 as baseline sounds about right.

and like you, when i ran it with some of the ideas we came up with (3mm okoume, etc)  i came in the low 30 lbs range

  :)

h