'Rowing' inflatable dinghies
Jake
I work for a yachting magazine as well as being a keen but leisurely
open water rower (I row to work most days for example). We have just
been enjoying last week's fabulous weather out on the river Hamble
group testing 16 inflatable tenders (The small dinghies that yachtsmen
use to get to and from their boats when at anchor somewhere).
So poorly do the vast majority of these boats row, I'm working myself
up to a rant about it in the magazine. I feel quite strongly that
rowing performance is more important than the makers of these dinghies
understand. Many is the time I have had to row an inflatable dinghy
quickly to get up river to the pub against a strong ebb tide, and not
all of us want to spoil the idyll of a quiet anchorage with a
screaming small outboard motor.
For a start none of them have oars anywhere near long enough. Even
worse, many of these boats recently have started sporting high plank
type thwarts mounted on the tubes- so at the same height as the
oarlocks. This means they don't have clearance for decent length oars
so they get round this bodge by the further bodge of reducing oar
inboard to in some cases less than a foot, so the whole stroke takes
place with the hands out by the sides of the body... Horrible. And
very slow, which in these already inefficient boats often means the
difference between stemming a tide and going backwards in tidal
situations.
What annoys me most of all about it is that from my rowing background
I know that humanity worked out the basics of fixed seat rowing
ergonomics literally hundreds of years ago, and that the old Avons and
Zodiacs we used to have 15 years ago all rowed acceptably. These new
boats are much stiffer with a vee bottom now though, so if the
ergonomics were sorted should row better than the old saggy flat
bottomed craft. The truth is, the expectation is that everyone will
motor them everywhere so the makers don't really care about how they
row any more... which I find sad.
I've read in various books over the years the basic rules of arranging
a fixed seat rowing craft, but I can't remember where. I'd like to
point these errant manufacturers towards a seminal text that will
explain how to arrange their boats in a fashion that will make them
remotely rowable.
Something along the lines of the following parameters:
"The oarlocks should be xxx-xx cm above the level of the seat. The
seat should be xx-xx cm towards the bow from the oarlocks. The oars
should be at least xx cm long. The oar's outboard length should be
(roughly) x times the oar's inboard length. The oarlocks should be
situated (roughly) xx % from the bow of the boat and xx% from the
stern."
Anyone got any idea where I'd find such basic rule of thumb numbers
for slow speed fixed seat boats?
Jake Frith
Editor, Sailing Today Magazine
http://www.sailingtoday.co.uk
Swanwick Marina
Lower Swanwick
Southampton
SO31 1ZL
01489585213
Roger
>
> Swanwick Marina
> Lower Swanwick
> Southampton
> SO31 1ZL
> 01489585213
Hey Jake,
I guess we need some input from some racing fix seat scullers. What
about the skiff rowers up on the Thames. Mr Biddolph may be able to
help.
Roger
Rio De Janierio
Brazil
Kit
>
> Swanwick Marina
> Lower Swanwick
> Southampton
> SO31 1ZL
> 01489585213
Minor quibble:
> humanity worked out the basics of fixed seat rowing
> ergonomics literally hundreds of years ago,
"hundreds" = "thousands".
;)
Kit
Roger
>
> - Show quoted text -
Come to think of it another group to talk to about this would be the
adaptive athletes, some of them race fix seat and as an olympic event
some effort has gone into how best to set up rigging for them. Not
quite the same hull shape but between then and the skiff racers you
should have a pretty good idea of what will work and what wont.
Andy McKenzie
>
> - Show quoted text -
From an 1861 book - Athletic sports and recreations for boys!
The fittings of sea-going boats are usually very bad; the thwarts are
too high and too near the rowlocks, the oars are badly balanced, and
there is no stretcher. If there is much sea, it is not possible to
pull a long stroke or to feather quickly. This and the general defects
in the fittings render the rowing of sailors almost always very bad
and utterly unfit for imitation; but the good oarsman should always
row as well as the boat will admit: the back may always be kept flat,
the shoulders down, and the stroke pulled through.
Andy
Carl Douglas
<snip>
> Something along the lines of the following parameters:
> "The oarlocks should be xxx-xx cm above the level of the seat. The
> seat should be xx-xx cm towards the bow from the oarlocks. The oars
> should be at least xx cm long. The oar's outboard length should be
> (roughly) x times the oar's inboard length. The oarlocks should be
> situated (roughly) xx % from the bow of the boat and xx% from the
> stern."
> Anyone got any idea where I'd find such basic rule of thumb numbers
> for slow speed fixed seat boats?
>
> Jake Frith
Hi Jake -
It's simple geometry.
Say you want to draw your hands in at ~30cm/12" above the thwart, maybe
higher in a seaway, & you need to get the blade in up to its neck. You
know the ratio of distance from hand to oarlock (A) & from oarlock to
neck of blade (B) - which will depend on oar length to neck (A+B) & how
far the builder has stuck the pin from the boat's centreline (C) - & A
must be consistent with being able to row that oar in that position
without excessive overlap or separation of hands. And you know the
distance of thwart above water (D)?
In that case the required height of the oarlock above water, E, is given by:
E = B * (30 + D)/(A + B) cm
Obviously that's approximate, but you have to start somewhere.
Typically a fixed seat is ahead of the pin. Often the stern edge of the
thwart, which might be 9"/23cm wide, will be in line with the pin.
Where the thwart is in the boat is, one hopes, where having you sat on
it keeps the boat in a decent fore-aft trim - therefore very
shape-dependent. If the bow is waving in the breeze, that'll make life
tough. But life is always tough if you're trying to get any kind of
performance out of something never designed to perform under oars.
HTH -
Carl
--
Carl Douglas Racing Shells -
Fine Small-Boats/AeRoWing Low-drag Riggers/Advanced Accessories
Write: Harris Boatyard, Laleham Reach, Chertsey KT16 8RP, UK
Find: http://tinyurl.com/2tqujf
Email: ca...@carldouglas.co.uk Tel: +44(0)1932-570946 Fax: -563682
URLs: www.carldouglas.co.uk (boats) & www.aerowing.co.uk (riggers)
Henry Law
> In that case the required height of the oarlock above water, E, is given
> by:
> E = B * (30 + D)/(A + B) cm
Now, for the "A" level course, would you turn your mind to the coracle?
http://www.youtube.com/watch?v=JJgMnq0NVW0
--
Henry Law Manchester, England
Carl Douglas
> On 15/04/11 14:07, Carl Douglas wrote:
>> In that case the required height of the oarlock above water, E, is given
>> by:
>> E = B * (30 + D)/(A + B) cm
>
> Now, for the "A" level course, would you turn your mind to the coracle?
>
> http://www.youtube.com/watch?v=JJgMnq0NVW0
>
You'll get a better idea here:
http://www.youtube.com/watch?v=SxSWmWq4-M8&NR=1&feature=fvwp
Cheers -