designing a fast rowboat

Hi BNT

Thank your for your compliment, and for your thoughts to my boat as well. The current weight is a bit more than 30 kgs without rig, but it could be built lighter for sure. As this boat is a prototype developed from scratch low weight was not of man concern. I used 6 mm sapeli plywood for the internal structure (some stations within the cockpit, and one flat panel on each side) carrying the rails for the rigger chariot, for and the two bulkheads fore and aft of the cockpit as well. One could replace this material without any problems e.g. by superlight sandwich panels made from e.g. aramid wave or foam covered with glass or carbon. And one could use thinner strips than the 6mm strips I used, and 120g/m2 glass instead of 160g/m2 to cover the hull and the deck as well. And the chariot for the wing I use now is a rather heavy one I used for first function /measurement tests with a simple stand-alone box during the build of the boat.
But first of all I'm testing the use under different conditions, and with some good rowers as well. After this I will know more for sure what and how to change whatever is needed to improve the overall use, and to reduce weight as well.
And then I'll come back to tell all interested in the subject about it.

Hi BNT

first of all thank you for the flowers - they are highly appreciated.

Weight:
To my shame I must say that I haven't weighed the boat so far ... but will do this soon.
As this boat is a prototype, weight was not of main concern.
I can imagine that it can be built somehow lighter by using thinner wood strips, lighter cloth for sheating the deck, honeycomb panels instead of plywood for the knees and the bulkheads, replacing the fully adjustable seat support by something way simpler, creating a super lightweight cart (honeycomb panels) ... The wing rigger is made by tiny wood strips, it is hollow and rather light - not much potential to make it lighter with reasonable costs.
And with the bicycle trailer I've built too I'm able to handle it alone.


Sliding rigger, linear guides and cart:
After gathering some experience I decided to change my system for the rigger cart. First I used linear guides made by IGUS (Drylin W series). It worked for about three weeks very well, then it started to show some slight jams, not really serious, but I didn't liked it anyway. I tried to fix the problem, and I got very good help from IGUS (including a personal visit of an IGUS employeed in my worksop). But the main problem with intermittent light jams could not be solved.
The IGUS system has to few play to handle the tiny size chenges one has in a wooden boat - and it requires horizontally perfect parallel mounts tha must be on the same horizontel plane too for the rail mounts.
And even the tiniest distortions of the rails themselves create jams. I made and tested several different installations according to the hints I got from IGUS, but with not great success.

So I decided to use oval aluminum tubes as rail, and nylon rolls on these tubes for the cart. I had to change (cut off) some parts inside of the boat, and to create and to mount some new ones to make this work.
And I built a new cart too, that weighs about one third of the old (prototype) cart I used before. I've tested this system now several times, and it works very well.
I've atttached a file showing the new installation. And as soon as time allows I'll update my build process documentation.
Ruderboot Biber JS1 Sliding Rigger - Holzleisten https://oeko-travel.org/de/home_made/product/rowboat_biber_js1_sliding_rigger_wood_strip.php



And I've built two new sculling oars (wood shaft and honeycomb blade). One of them weighs about 1.7 kgs.
Erzeugnisse – Biber Boote Schweiz https://biber-boote.ch/?page_id=628#Skull_Ruder_leicht_8211_Sculling_Oar_Lightweight
Build Plan and Instruction are available here (free)
Anleitungen – Biber Boote Schweiz https://biber-boote.ch/?page_id=1950#Lightweight_Laminated_Spoon_Blade_Sculling_Oars


Speed:
I can reach a max speed around 5.5 knots or a tiny bit more. I'm not a good rowers, and I'm more than 70 years old. I can imagine that a younger and good rower is able to reach a higher speed.

Plans:
From time to time I'm working on the creation of plans for the boat that can be used by others - but this will last some time.
All the drawings and plans I've made and used so far need some rework and some changes as well.

All the best, and have a great time
Beaver

Nice job Beaver!

Impressive.

If you wanted to lighten the knees and bulkheads, you could use thinner plywood with a thicker piece of wood capping it, to form an I-beam.

BlueBell said:

Nice job Beaver!

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thank you, and have a nice day

rnlock said:

Impressive.

If you wanted to lighten the knees and bulkheads, you could use thinner plywood with a thicker piece of wood capping it, to form an I-beam.

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Thank you for your tip. I'll have a look on this too. As the boat shown here is a prototype lightweight was not my primary concern.
There are several options for saving weight available.
I tend to use a sandwich construction - Glass/Epoxy/Honeycomb or Foam - instead of plywood for the bulkheads, the knees, the supports for cart rails and the seat, the seat itself, and for the cart as well.
I've some experience with this by making sculling oar blades already, and my second cart is a sandwich construction too. I like this kind of construction because of its low weight, and its form stability (less tendency for warping than plywood).
To keep the "wood view" for the interior I'll probably use thin plywood to cover the honeycomb.
But I'm always open for new ideas .
The wooden wing rigger is hollow, and it is rather light and stiff.
I made it with 4x4 mm wood strips, and it's covered with glass and epoxy. I used unidirectional and woven cloth depending on the stress in this part.

Now I'm drawing some construction plans and a bild instruction for sale that could be of use to somebody else (hull, interior, wing, cart, parts and so on).
And it could be that I'll build another (hopefully better and lighter) Biber Vajra one day based on my experinces with the first build. We'll see . . .

As I recall, fiberglass stretches a lot more than wood does before breaking. At least along the grain. So the wood would break before the full strength of the glass is used. As I recall, e-glass has an elastic modulus of 6 mpsi or so, and its yeild strength is in the hundreds of thousands. Say, for example, 400,000 psi. That gives an elongation at yield of around 7 percent. A real layup would be less, even if unidirectional, but I suspect it would still be quite stretchy. Numbers for wood are all over the place, but I seem to recall 2 mpsi and 6,000 psi are not unusual. That would be a third of one percent. Some carbon fiber has an elastic modulus of 33mpsi and yield of around 500,000 psi. That would be 1.5 percent. Again, a real layup would be less. But I think it's clear that more of the strength would be used before the wood broke. Soller Composites is currently selling one type of carbon tow at $18 (US) per lb.

Hi rnlock
I'm a little bit puzzled about what you mean. But I assume you're addressing the construction of the wing. Right?

beaver said:

Hi rnlock
I'm a little bit puzzled about what you mean. But I assume you're addressing the construction of the wing. Right?

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I'm addressing the use of fiberglass vs carbon fiber when reinforcing wood. I guess in this case that's the wing.

fine, thanx.