beautiful skeleton

Just as a footnote to this thread, here's a couple of photos of my covered SOF rowing boat, taken before I added all the reinforcing tapes to the keel, stringers and gunwales today. I can still pick this 16ft boat up with one hand, so guess it probably weighs somewhere around 25lbs.


Jeremy

 

Damn I have become very interested in this way to build.
Looks very nice.

 

Thanks, this is the first boat I've ever designed and built, so it's been a bit of a learning experience. My background is aviation and I've built and designed light aircraft, so I just used construction techniques that I was familiar with.

This boat will take part in a "Cordless Challenge" where it will be powered by a cordless drill in a race in June (the prize is around $1800 worth of cordless tools..........), then I plan to row it around 50 odd miles down the River Thames, in company with a dozen or so assorted friends in their boats.

The basic design is open source, so will be published for free use by anyone daft enough to want to build another one, but it won't be a design supported by detailed build instructions - it'll just be the basics, so anyone wanting to build one will need to understand some of the basic stuff, like how to work with metal and aircraft-type fabric covering.

Jeremy

 

Mr harris- whats the beam and depth amidships of your boat? looks very nice - Justin

 

Nice work, JH! Of course, with it being that light you'll have to be careful that you don't blow away!

 

Jeremy,

Very nice boat.
Could you show some pictures of the stem and stern and at the gunwale to show what the joints look like in your covering?
As I remember this is an adaption of Gentry's Ruth, correct?
What is the function of the aluminum pan in the bottom, support for a sliding seat rig?

Thanks, Marc

 

It is a cookie sheet. Being a sharp cookie he doesn't want to pierce the hull.

 

Hoyt,

I had a couple of other suggestions but I continue to try and overcome my old Navy training and supress those non-PC ideas, at least in the company of others I don't really know.

Marc

 

It's cast iron and it's to stop it blowing away! All of us lightweight boat builders have these problems; you guys need to be more sensitive.

 

Phew, I didn't realise posting a couple of photos would cause such a flurry of interest - thanks folks. Answering the questions/observations in order:

1. The maximum beam is 890mm, depth amidships is 325mm (35" and 12.8" respectively for non-metric folk).

2. I'm working on the boat outside and do have to keep it tied down to the trestles else the wind does indeed try to blow it over!

3. The stem and transom are made from extruded polystyrene foam covered with epoxy glass, the same technique that Rutan uses to make the famous "eZee" series of composite aircraft. I've attached some photos of them. The alloy tubes are bonded and riveted into these parts with the tubes then faired to them so that the fabric lies smooth. I should have used wood for these parts - it'd have been a lot quicker and easier - but I set myself the challenge to build a wood-free boat (even the oars are alloy and composite).

4. The inspiration came from reading Dave Gentry's thread on Ruth on the Wooden Boat forum, but I don't have his plans etc, so started from scratch to design something similar but using aluminium alloy.

5. The aluminium pan is both floorboards and support for the seat and rigger arrangement, which will mount to the fore and aft rails. I may go to a sliding seat in future, but first I'm sticking with a fixed seat and forward facing rowing sytem I've designed. The alloy floor will be covered in some non-slip stuff.

6. Yup, the alloy sheet is there so I don't stand through the fabric bottom of the boat! It's only 18g sheet, but it's reinforced underneath with cross members that are connected to the inner keel section so that it can take the point loads of being stood on OK.

Jeremy
Jeremy

 

Thanks Jeremy,

BUT, you did it again.
Are you ready to share details of your forward facing rowing system?
While I enjoy rowing, in my modest manner, seeing where I am going would be a plus.

Did you ever consider using the Kevlar "fiber" 45 degree tapes like Platt Monfort did? I keep wondering what the effect is on the surface below the waterline.

Marc

 

Like you, I dislike facing backwards when rowing, plus I have some neck damage that makes turning around to see painful, hence the idea of making a forward rowing system. There are some commercial units available, but they are all in the US (high shipping cost for me!) and either look a bit Heath Robinson or are pretty expensive, so I decided to design and build my own version. The idea has been around at least since 1875, as that's the earliest patent I could find, so by now it's pretty much a public domain design I believe. I've attached a rough sketch of the forward rowing system, I can post some photos once I've assembled all the parts. There's a carbon fibre rigger that takes all the loads directly into the fore and aft floor rails and a fairly standard reversing linkage using stainless rose joints. The linkage is mounted on a plate that's free to pivot vertically, with a fore and aft pivot axis. The linkage is designed to have an acceleration factor, meaning that the oars will seem longer than they really are. This keeps the wrist angles on the handles relatively low, but still allows a good sweep and high blade speed.

I happen to think that Platt Montfort maybe making the skin of his boats more liable to puncture damage because of those Kevlar cords. Polyester aircraft fabric is very strong, but can be punctured fairly easily if it is restrained from being allowed to stetch. It can stretch a heck of a lot before it breaks, so allowing the fabric to dent when it hits something is a good thing. I think that the Kevlar cords limit this and remain unconvinced of their merit. We don't do things like this when covering aircraft, where strength is paramount, so I've stuck with what I know well and just used standard aircraft covering techniques.

The only thing I'm doing differently to covering an aircraft is using a more abrasion resistant coating for the fabric. I'm testing some samples now and think I'll end up using a water based flexible hard coat finish produced by Plastidip (this stuff: http://www.plastidip.co.uk/eStore/index.cfm?type=Domestic_Solutions/HCF&stage=1). So far it seems to bond very well to the fabric samples and remains very flexible when dry. I just need to see how well the samples cope with being abraded.

 

Frame

how did you arrive at the shape for your frame? Did you have plans and loft from them or did you build from your own plans. I'd also like to see the glue joints at bow and stern. Would it be a problem in a larger boat to add extra stringers? Last question, hnave you floated her, and how much does the fabric deflect?

 

Thanks for the interest. For background, my background is aircraft design and construction (as a hobby), so that's coloured my approach. I've never designed boat before, but did restore an old pitch pine on oak, gaff rigged, carvel built, yacht about 20 years ago.

The design is wholly mine, but was heavily influenced by Dave Gentry's "Ruth", as described on the Wooden Boat forum.

I set out to design a boat that met the rules for the Watercraft magazine "Cordless Canoe Challenge". This set the maximum LOA at 5m. I realised that low weight would be an advantage (lower wetted area) and then set about designing a hull that would be close to the lowest possible weight for a decent waterline length, whilst keeping the beam and cross section adequate for roll stability.

After starting the build the opportunity arose to join a group of like-minded folk on a 5 day trip down the river Thames. I then decided to adapt the design into a rowing boat.

Four stringers, plus the keel and gunwales, are fine for a longer boat, but I'd increase the number of frames. Having frames closer together at the stern, where the stringers are relatively straight and less able to resist fabric tension, would be a good idea. Had I not been so obsessed with saving weight I'd have increased the number of frames. On my boat they are at 800mm centres, and I think they'd have been better at 600mm centres.

She's not been in the water yet, but based on the high tension in the fabric I doubt very much that it will deflect much. It's as tight as a drum skin, as I used the maximum shrink temperature and pulled it as tight as I could when I ironed it.

It should hit the water in about three weeks time, if all goes well. I'll report back on how it turns out then.

Jeremy

 

Got a question for you, Jeremy. I'm interested in doing an SOF rowboat, but to my own design and with a timber frame. I am keen to incorporate bouyancy tanks in each end of the boat by bulkheading them off.
Now with ply or strip planking this is easy. I think (emphasis on think) that it should also be possible with SOF if there is sufficient bonding area and a decent adhesive, but obviously the wrap angle is zero.

Got any thoughts on how to do this easily and durably?