rowing geometry

[Romeo]

Anyone got a good reference page for getting rowing geometry right? I am trying to rearrange a wee shetland boat a bit so that she can be rowed by two rowers with two oars each. As matters stand at the moment, the thwarts are a bit too close together, and I am going to have to move one or the other, and decide where to put the fittings for the crutches. Might also want to muck about a wee bit with the height of the thwarts. Although a bit of trial and error will be needed it would be good to find a bit of a guide from folk that have been there before, before I start.

 

[NormanS]

I would just make up an adjustable mock-up arrangement, so that you can get the ergonomics to suit you.

 

[Keith 66]

A good start would be thwarts 7" below the gunwale, rowlocks anywhere from 12 to 14" aft of rear edge of thwart. Oars 2 1/2 times the beam, if you like crossover on the handles one rowlock can be set a bit higher than the other. If setting up a new boat i like to clamp a block to the gunwale with a rowlock in it & move it till i feels right. A good foot stretcher & positioning is also important.

 

[Romeo]

A good start would be thwarts 7" below the gunwale, rowlocks anywhere from 12 to 14" aft of rear edge of thwart. Oars 2 1/2 times the beam, if you like crossover on the handles one rowlock can be set a bit higher than the other. If setting up a new boat i like to clamp a block to the gunwale with a rowlock in it & move it till i feels right. A good foot stretcher & positioning is also important.

What would be your view on minimum distance between thwarts for two sculling Keith? Seats will be high enough that feet can fit under the thwart in front, so that is not a limiting factor, but bumping into the stroke sculler at the catch will be! Boat is for small adventures and I am trying to work out whether I can rig it so that we can leave the mast up even with two rowing.

 

[Keith 66]

If your feet are under the thwart in front you will be too close to the rower in front of you & will hit him with your blade handles.
My new 16ft 6" pair sculling boat has thwarts 7" wide & there is 35" between them, her overall beam is 4ft 4".
Its a common fault for rowing boats to have poor geometry, The St Ayles Skiff is a great boat but the seats are too close together. Likewise the Harkers yard Gig.
Neither boat can get a decent long stroke & crews complain about hitting each other with oars!

 

[tobermoryphil]

3 feet thwart spacing, plus or minus an inch or two. Oar lengths twice the beam. Oar angles 17 to 25 degrees.
ETA: this is of course for two oared pulling, oars not crossed, and a skiff of normal width, i.e. no outriggers.

 

[Romeo]

The latest edition of Water Craft has and article on the topic. However it is from a river rower, and seems to be more about what he has found suits him rather than what the limits are are what is optimum.... and he says not to have your hands overlapping in the middle of the stroke, which is something that I think is essential if you are going to have a good stroke at catch and finish. Still looking for that definitive article (particularly if it is slightly biased towards sea rowing boats, with their greater freeboard.

 

[Keith 66]

Im, surprised that a river rower says dont overlap, in fine sliding boat rowing virtually all sculling boats have overlapping handles as a matter of course & far more training is devoted to technique than in fixed seat rowing. It might be worth while looking on British Rowing's website as they have plenty of advice on technique.
With Fixed seat boats there is so much variation in boat types that one size does not always fit all.
In the end a lot is down to who is going to row the boat, a good set up for a very tall bloke with long arms wont be any good for a short bloke!

 

[cliffordpope]

You might also want to consider flexibility so as to be able to use different rowing combinations, adjusting the position of the thwart(s) to maintain weight distribution.
I appreciate that fixed thwarts provide considerable structural strength, but if one of them could be moved to an alternative position you might find it useful.
It's miserable trying to row a boat with its trim upset because you can't adjust to number of rowers or number or weight/size of passengers.

 

[Romeo]

You might also want to consider flexibility so as to be able to use different rowing combinations, adjusting the position of the thwart(s) to maintain weight distribution.
I appreciate that fixed thwarts provide considerable structural strength, but if one of them could be moved to an alternative position you might find it useful.
It's miserable trying to row a boat with its trim upset because you can't adjust to number of rowers or number or weight/size of passengers.

Yup, plan is to have a removable thwart aft of the single rowers thwart, with some sort of stubby removable out riggers to maintain the distance between the crutches despite the reduction in beam. Bow rowers thwart will be fixed, and his feet will have to go under the fixed single rowers thwart. Hope I have explained that! I am trying to work out how far aft the removable thwart has to go, and how far forward the bow rowers thwart has to go in order to give him sufficient room. Former is constrained by the rapidly reducing beam on this double ender, former is restricted by the fact that the thwart currently supports the mast. (although I have some flexibility, to fix the mast to the after side of the support under the thwart, rather than going down a hole in the middle of the thwart which it currently does.

All a bit complicated for a relatively simple wee boat, and why I would rather be doing some sums in advance rather than just starting with tinkering about to see how it feels. (Although I have now had her on the water, mostly sailing but also rowing and shifting my crew about to see the effect on trim.

 

[lukedh]

Posted on the Wooden Boat Forum:

http://www.woodenboat.com/geometry-rowing-craft

It may interest someone, more information in Wooden Boat 240



edit, correct error.