Got an oar problem. A dilemma really.

[John B]

about a year or so ago I was in this second hand boat bit place and found a pair of short nicely shaped tender oars. 5 ft long. professionally made by the looks and spruce by the feel( and look) either that or exceptionally light Oregon. So I bought them thinking yep, that'll do the next kids dinghy. they're too long for the dinghy I just built but the handle is formed, the loom is tapered and the fact is the blade surface area is too big for the wee boat anyway.
I've just about resolved to take the saw to the blade and just lop off some length there but before I do I'd like some opinions on the correct length.


throw some inboard/ outboard ratios or beam x factor = oar length at me will you. someone who knows a parameter to work within.
the boat is 33 inches beam. ( I converted it, aren't I good) 840mm.

Tell you a funny story while I'm at it.
I made the oars for the last kids boat I built en forum in 2001 and was carrying them around in the boot of my car. Some scumbag stole the damn car!! so I made those oars twice!! :mad:

[wyhjr]

Shaw & Tenney's oar length formula:

(1/2 span + 2)/7 x 25 = oar length

where span = distance between oar locks

your oar would be:

(33/2 + 2)/7 x 25 = 66 approx.

[Paul Scheuer]

Since the future skipper probably doesn't conform to normal ergonomics, I'd mock up somethng quick with plywood and broom sticks, and do a shakedown cruise. You could "U" bolt the blades for adjustability.

It looks like the formula above gets you to 5-1/2 feet.

[John B]

I was thinking that the oars were too long. That formula says they're too short at 5ft so I'll just leave them as they are length wise and take some meat off the loom end of the blades to lessen weight and blade area. thanks for the info.

[Bruce Hooke]

Remember, for easiest use, the oars should be just slightly blade heavy, in other words the balance point should be just a little bit outside the oarlocks. Most oars are too heavy in the blades and too light in the inboard section of the loom.

If the blade area is too big I would take the area down but reducing the WIDTH of the blade. Narrow oars are easier to row with because you don't have to lift the blade as much to clear the water.

[mower]

The first oars I built to the Shaw and Tinney formula seemed too long to me when they were completed. However, upon using them I came to realize that I had probably never rowed a boat with the correct size oars. I'll bet the majority of row boats out there are using oars that are too short. Boy, what a difference it makes when you use oars that are long enough to really do something.

[John B]

Bruce, That's a good point and exactly what I'm concerned about. They ARE too blade heavy. I'll reduce blade length ( off the loom end as I said, they're made for an adult sized tender of some sort) but I'll narrow them and shave a bit of meat out of the thickness as well.
Mower, yes that's the other concern and I agree with you 100 %. I've always thought I made the oars too long for these Kids boats but they grow into them ( the longer oars)in no time.

[Jon Etheredge]

The Shaw & Tenney formula is great but keep in mind that it assumes that the rower wants the oar handles to overlap by 2 inches when the oars are horizontal. BTW, the amount of handle overlap is also dependent on the height of the oarlocks above the water. In a boat with lots of freeboard you may only have overlap on the recovery part of the stroke while a very low sided boat may have overlap on both the power and recovery parts of the stroke.

Having the handles overlap is the norm in rowing shells (sculls) because it allows you to use a longer oar while maintaining a reasonable leverage. But overlapping handles require the rower to pass one hand over the other at midstroke rather than passing them side by side. Sculls are usually set up with the handles overlapping by about 5 inches and are often the source of skinned knuckles when scullers first start learning.

Overlapping handles contribute to rowing efficiency but you may want clearance between the handles under some circumstances. For example, oars for a dinghy that is used to come alongside larger boats might be easier to manage with clearance between the handles so your hands don't accidentally hit at an inopportune time. Or it may be that you just prefer to have clearance between your hands.

If you are of the school of rowers who prefer to have an inch or so clearance between the handles when the oars are at the midstroke you can use the following formula:

(1/2 span + overlap) / 7 x 25 = oar length

so if we want 1" clearance between the handles:

(1/2 span - 0.5) / 7 x 25 = oar length

or

[(33/2) - 0.5] / 7 x 25 = 57 inches approx.

This maintains the 7:18 inboard to outboard ratio, or "gear ratio", of the Shaw & Tenney formula. The 7:18 ratio is certainly a good starting point but need not be considered an absolute requirement. It may be appropriate to use a slightly lower ratio for children.

There are many variables involved in oar length selection. The Shaw & Tenney formula is a terrific starting point but in the end it all comes down to personal preference.

My apologies if this is waaay more than anyone wanted to hear about oar length smile.gif

[John B]

More good points Thankyou Jon.. It occurred to me that there should possibly be an overlap. He's 8, He's been rowing since he was 2, he could probably handle it. I could certainly sell the idea by telling him he'll go faster.. LOL.
The 57 inches you've worked out.. that's where my eyechrometer had put the sawcut( but you can see I'm reluctant to do it). I'll keep the length, shave some weight off the blades and see if he wants the overlap. The worst that will happen is that I have to shift the collar.

[ 12-09-2003, 06:21 PM: Message edited by: John B ]

[John B]

and I'm going to hollow out one face too. That teaches them something and it helps the balance problem as well.

[Peter Malcolm Jardine]

Dare I tongue.gif ? here goes

Sorry to hear your first pair went oar-ry

and of course you could get definitive advice
from an oar nose and throat specialist tongue.gif

[John B]

ar ar arr ar. :D
It's Ok Peter. It was 2 years ago. the second pair are better than the oregonal ones anyway.
I'm not pining for them anymore.
I'll just spruce up these new( second hand) ones and we'll be going along just swimmingly thanks.

[Bruce Hooke]

Yup, most commercially produced oars have blades that are much thicker than necessary. However, in this case it is worth remembering that children can be hard on oars through using them to push off the bottom, push off rocks, etc. so some extra thickness in the blades is not such a bad idea...

[jwaldin]

A tip about oars. Never coat the hand grip part of the oar with anything. Leave that part unfinished and you will never get blisters from rowing. Ask any labourer who works with a shovel all day. It's the friction caused by the varnish varathen or what ever that causes blisters. When I see a set of oars where the ends are unfinished I think "there's a real waterman".
I recently made a new pair of one piece red cedar oars. I'll post a pic on jws pics soon of them.

[Murray Campbell]

fwiw...i found rowing with hands overlapping a bit awkward for a few days, but i love it now...it's really helpful for getting reasonable oar length packed in those darn dinghys which are always a bit too small

[Paul Reagan]

I'm coming into this late, but I'd like to point out that the Shaw & tenney formula does not promote any overlap. The formula calls for a span measurement which is parallel to the water, but the oars are not used parallel to the water, they are used at an angle. In other words, 1/2 the span is the base of a triangle, but the inboard oar length is the hypotenuse of the triangle. The two inches which are added are to compensate for the height of the triangle.

[John B]

I meant to say thanks for the help on this. I was close to taking some of the length off those oars but in fact , by the formula, they are a bit short anyway. In reality the boat goes relly well and the gear ratio seems right. he's taking quite slow strokes and going fast .

Test row.
http://www.imagestation.com/picture/sraid93/p3372042b83c838fda7fbb9539ce5fc71/fa509c89.jpg
I've had fun doing this . :D