designing a fast rowboat

Yeah the holes make sense, just from the point of view of drainage. You could have a dish that was deep enough without a hole, but it'd collect water anyway (as well as being heavier).

 

FWIW, I love these products for the cush

http://www.gelsport.com/products.html

Not sure they are still in Biz. Based in TOtonto.

 

Yup, I saw you raving about how good they were on your blog. They're a bit pricey for my liking though. Plus I'm thinking it'd be kinda fun to build one of the sculling seats. Never made one before, and it's an interesting shape. I was even wondering if I could incorporate the principles into a thwart while making it look good.

 

I'll be getting more serious about training for racing soon, but I have to say that recently I've been reminded that one of the best things about having a fast rowboat is when you aren't bothering to row it fast.

Easy lines and low wetted surface just make the damned things glide so nicely. They just keep going and going and going. In perfect conditions mine will run twice its length for every relaxed heave on the oars if I'm just toddling along and enjoying the scenery. It won't be travelling fast, but it can be very relaxing and enjoyable.

 

The joy of the 'glide'. I often try to explain it to kayak (or any human powered boat) buyers. I know that they will not develop into enthusiasts if their boat does not reward effort and good form. Too often beginners opt for stability and low price -which are quickly outgrown. At the other extreme I need to explain that length does not equal efficiency or speed. I have a CLC Pax 20 and it feels like I am paddling in motor oil. The GPS shows the high speed but it doesn't 'glide' because it has so much surface area from the length. It's raison d'etre is going fast and if you are not making a great effort it's not the right boat.

What I always try to figure is how much thrust someone is likely to generate, then consider the whetted surface area vs the wavelength drags. We all seem to be obsessed with top speed when there is more value to the customer in a boat that best matches their needs. The crossover speed is likely more important than hull speed.

Beyond drag there are more factors to the glide sensation, being closer to the water, a smaller boat, and I think that a fixed seat and sliding rig have a greater glide sensation than sliding seat.

That's a beautiful boat you have there. It's almost a shame to stop building.

 

Yup.

Well any boat will glide less at high speeds than it does at low speeds, simply because the resistance is far greater at high speeds and increases faster than the momentum does. Greater decelerating force relative to momentum means less "glide" or, more accurately, faster deceleration on each return, plus the much greater resistance means you are working a lot harder. That's what makes the boat seem to "bog" when it's being pushed hard.

But sure, length alone doesn't equal efficiency. At the low speeds I was talking about, my boat is too long for lowest drag (and has too high a prismatic). It's still very nice to row, but if I was optimising for those speeds I'd build a different boat.

Yup. When I was drawing mine up I made several compromises. One was that I wanted to match the Herreshoff/Gardner boat for initial stability, with better reserve stability. If just designing for my own preferences I would have gone with less metacentric height (although I do have to say she is a very well-behaved boat as she is).

Another was that although I was prepared to take a resistance penalty at low speeds, to get an advantage at higher speeds, I did not want to have more resistance at moderate cruising speeds (ie: somewhere around 4.5 knots, which is fairly easy going for boats like this). IOW, reasonable crossover speed for general use. A higher prismatic would give a bit less resistance at high speeds, but would introduce a resistance hump at moderate speeds.

I hadn't thought about the last bit, but it makes sense. I have considered trying a sliding rigger setup in my boat at some point. She's long enough to make good use of one.

Well I haven't stopped building. Not really. I'm just taking a bit of a break.

 

Regarding a comfortable seat, you may find this document useful. It can certainly point you towards making your own custom fitment. I know this is for sliding seat rowing but the same basics apply to a large degree.


http://www.carldouglasrowing.com/sitedata/files/Customised_seat.pdf

 

Thanks for that. Sitting on something squashable was basically how I thought it'd be best to start. The principle seems straightforward: just create a shape that supports without creating pressure points, taking into account the base of the spine as well as the pelvis. Any tips would be appreciated though.

I was thinking that fixed seat ought to be easier to make comfortable, since you aren't doing the knees-up on the return.

 

I think you could create a one off seat pretty easily, though the commercial ones use a heated matched alloy tooling. If you get a really good seat or pattern, or even use a soft part crushable foam (a bit like the photo in the pdf), to get a basic form with the relief centres. Use something like plaster of Paris and polythene sheet to get one side of teh form. Smooth and then after a release layer - polythene say, take off the other side. Then laminate some veneers about 1-1.5mm. After they are glued up, trim and bore the hole centres approx 32-35mm and bevel with a sharp knife. For a foam to make a form from the cheap blue insulation foam would be OK as it works quite well. It's also strong enough to sit on so you can test it.

No reason for it not to end up very professional. You then have the support part to deal with but a pair of support 'rails' only require spokeshaving to fit to a well curved seat base, so don't worry there won't be any complex double curvature at the sides!. How yoy wish to fix the 'seat' to the thwart and arrange the geometry of the blades - up to you to optimise. Obviously like riggers etc this area becomes personal fitment and what works for you.

Be nice for you, to get your nice new boat to work even better for you.

 

I've only tried one pad from GelSport, a relatively thin one they sent to me for trials and its worked for years. Some think they are too thin. In response this is from from Colleen at GelSport in Toronto

"Thank you for recommending our pads. We actually make two different styles for rowers. There are many competitive/high mileage rowers that find our thinner rowing pad meets their needs. There are some folks, that row, who prefer a comfortable derriere; usually we recommend our Adventure Racing Gel Pad. This was designed for Transatlantic Race Rowers (4-6 weeks, 10-12 hours daily). It is perhaps a little overkill for a recreational rower.

There are a growing number of National level coaches that put their athletes on our Adventure Racing Gel Pads."

 

Hey just for something completely different, some stuff I saw on the river the other day.

Home-made bamboo raft (the local bamboo clumps can be up to fifty feet tall).




Two blokes in a tiny dinghy that was shorter than the blokes. They were having a bit of trouble staying upright, but were generally moving forwards.

 

Must have been too much XXXX.........

 

It seemed be more more a problem of not enough metacentric height, but beer may also have been involved.

It's funny how some people just don't get the concept of sitting in the middle, and sitting still.

 

Ok, I have come up with a solution that doesn't involve me spending time on fancy woodwork when I could be rowing, and doesn't involve going and finding expensive things and paying for them.

I had bits of old carpet and foam underlay that I've been using for padding cradles, etc, so I decided to to make myself a bum pad. After playing around with various ideas I came up with the thing in the pix.

Layer of carpet top and bottom, one continuous layer of foam underlay in the middle, and three extra strips of foam each side (75 mm , 50 mm and 25 mm wide) to make a nice cradle effect for the outer sides of said bum. It's stitched together along each end with a basic coarse running stitch, using nylon brickie's line.

This thing is really comfortable, as far as I can tell from testing it by sitting on a concrete slab. From thirty feet away it looks as flash as a custom professionally-made sheepskin cushion, and I'll be sitting on it rather than looking at it anyway. Will see how it goes in action tomorrow, but I figure it has to be a lot better than the status quo.

Total cost: nuffink. Total labour time: about an hour, including head scratching and making a cup of coffee.

 

Seats tailored exactly to an individuals posterior can be made using the method of race car seat builders. .......

Required material consists of a poly bag and some foam in place material. Pour the mixed foaming agent in the bag and sit on it for a few minutes. Initial sitting is slightly uncomfortable because of exotherm but not painful. You can use the formed foam, still in the bag, to make a mold for a FRP seat base or use it as a model from which you can extract the 3D lines. You can also use the foamed structure as it is for trials runs.