Thread: Sea going rowboat design considerations

Originally Posted by Daddles

No-one has tackled the oar question - traditional diamond cross section blades or curved blades, endurance vs power?

Richard

You didn't ask us.

Oars for sea have been traditionally symmetrical in all directions with long blades relative to the loom.

Oars with front and back convex and concave faces want to develop higher forces out of plane with the rowing action when the blade is less than perfectly placed in the water.

Longer blades are more likely to produce useful drive whether the end of the blade is immersed one or two feet.

Get the hull right and a nicely balanced moderately oar of any middle of the road blade design will be fine.

Use a performance rowing shape and it might get to be fun in rougher water - though many will use them for open water racing events.

MIK

Originally Posted by Boatmik

You didn't ask us.

Yes, I did, back in the first post (pokes out tongue)

Thanks for that.

I got the idea about effort from Jim Michalak's article on oar making. I have, in fact, made all my oars based on his pattern (just reproportioned to suit the three lengths I've made). I'll probably use that pattern again this time, though my methods have evolved a bit. Next pair will be for Sixpence

Richard

Michael has just mimicked comments that I made to him in an email.

Many pulling craft designs don't consider the comfort of the rower or the ease of penetration compared to the work effort.

By this I mean there is a delicate balance between initial stability, entry penetration in to a sea and the ability for the oarsman to comfortably pull through over long distances.

From a design stand point I look at the general speed that can be generated by a young healthy rower at a moderate pace, then shape the bottom and sides of the boat to this S/L target. This is one reason Bolger's boats perform so well and also why the Herreshoff is so well regarded. These boats don't try to move too much water around the hull (or too little) at the average general speeds they'll travel at.

Dragging a hole or lots of eddies along with you on each stroke, just limits the rowers endurance. This coupled with an uneasy feeling of a tender boat (like an under loaded dory for example) tends to keep the boat in the carport, not working it's way around the local puddles.

By their very nature a good pulling boat wants to be light and tender for best performance, with easy ends to part and permit the flow to rejoin with little fuss. For deeper water efforts, the designer likes to increase the freeboard, particularly at the bow, but I've found this isn't always necessary, when a removable canvas deck can be employed, stretched between the rails. It'll shed boarding water, but not let the boat get blown off because it has a deep water "proboscis". Traditional dories have this treatment and they're a pain in the butt to row in rough conditions as a result. This in addition to their equally proud stern height, causes them to be miserable beasts in any contrary winds.

The oar blade issue I think is a matter of user preference. I personally prefer a standard symmetrical blade, without "power cups" or other high pressure shapes. In a short duration race, sure these "fancy" blades can have an advantage, but for recreational rowing, I don't want to have to concentrate about blade position any more then what is comfortable.

Current SLSA surf boats are primarily open water racing sculls, with some ability to enter & exit via surf. They combines all the features Paul mentions except the long canvas fore-deck. Perhaps a scaled-down version of one of these, with a long water-shedding fore-deck would do the trick ? Added bonus of being locally "authentic".

Don't know where you'd get the plans though. SLSA competitions web sites talk of "standard" boats, so it must exist somewhere.

cheers
AJ

http://www.asrlsa.com.au/

I have been in many Irish Currachs over the years, they are still used by my brothers in laws to take sheep and crew back and forth from Innishkea Island to the mainland. The oars are long and narrow with attachments for the Thole pins. This is the business end of the blades.



The tholepin pieces (name?) are nailed on to the oar with Galvanised nails.




Going ashore on Innishkea North. 3 men,2 dogs and a shearing plant and generator.

Howdy AJ,

The lifeboats really are raceboats and have a number of extreme features now. For example the older boats had to be designed to keep the water out. The modern boats are evolving towards decked in boats with small cockpits for the crew and a high capacity pump going all the time.

A more serious problem is that if you scale a boat down stability disappears REALLY quickly. It varies with the 4th power (mathematically speaking)

So if the size of the boat is reduced by 15%, but the shape stays constant the stability will be equal to 0.75 to the 4th power = 32% of the original boat.

So if you take an somewhat unstable model like the OZ surfboat and reduce the size a bit ... big probs.

I did an article about this last year for AABB - someone shrunk one of my Goat Island Skiffs then found they couldn't keep it upright. I ended up drawing up some sail and spar mods that brought things back into proportion a bit more.

I know that sometimes on the net you can see people saying you can change the size of a boat by 10 or 15% and it will be OK - but like almost all rules of thumb and supposed ratios there are far more exceptions than there are situations where you can use the rule. Generally an increase in length is not too bad - but is best to talk to the designer

(AJ - this is a general diatribe - I know you know most of this).

Now to get back to the rowboat choice ...

PAR - I saw someone talking about one of your rowboats on the woodenboat or boatdesign forums ... are any of them suitable?

Best wishes
Michael

I was looking through Gardner's book today - the Herreshoft is in "More Building Classic Small Craft" which might be just a reprint of Vol. 2.

Anyways, that Herrshoft is 17 ft long

Yes, I know boats shrink on the water and that longer is better, but I've got grave doubts about the general maneagability of a boat that long when not in open water eg, on the bank or in a crowed creek. It's also a hell of a lot of timber which has to translate into weight (and expense). Still thinking about it though, it's just a hell of a bite to take.

The McInnes looked better but at 12'8", is it a bit too short, particularly seeing it's a double ender? I'm guessing here - part of the idea of this thread is to further my education.

Still, length is only relative and dependent on the situation. I guess I'm not likely to take the Herreshoft into a narrow creek to chase bream ... but then again, I would take the McInnes. Then again, I've got Redback for the cramped work but that assumes I'll always be able to have a fleet of boats stacked up in the back yard.

Come on lads, convince me that 17' is only scary because ... it's so damned frightening

What the modern versions of these boats and their derivatives?

Another question - where does 'better' become irrelevant?

Richard

And having just gone through PAR's original post for about the tenth time, why did it come as a surprise to find that the Herreshoff is 17 ft?

Don't be coy about suggesting your own designs either PAR, it's pretty obvious you're not here to spam us.

Richard

Hey Daddles, - I built one - it was the first boat I ever built.

It was light - out of 6mm ply with a 9mm bottom, no ribs spaced inwales and bow and stern knees.

Work on the lightness aspect and I'd be betting there would be very little weight difference between that and the McIness.

If you can build a Eureka at around 45lbs out of 6mm ply i'd be very surprised if you couldn't get the Herreshoff well under 90lbs with care - it won't be any heavier than my rowboat.

And length is the best thing in the world - for travelling, seaworthiness and also to help you get it on the car roof.

Michael

In other words, the length just sounds scary ... and won't fit in my shed - Sixpence fills it and she's on 14'.

It looks the goods though. Hell, I might even build it with the stupid ribs.

Richard

Hi,
I did a heap of research about the Cosine Wherry before buying the plans.
When I eventually build it ...it will be for lakes (ie Gippsland variety) and rivers.
I emailed the folks (in Canada?) who build these boats and they reckon that it handles a 5-foot chop and stays "dry".
They also use Spoon blade oars and reckon the boat reaches speed after about 5 strokes.
So that's one extreme. At the other end of the spectrum I believe it was designed by a naval architect using the slippery ( cosine curve) design used for Submarines ..
I hope this is not an Omen!! ( must fit some more flotation)

At 14 ft. and beamy.... it is set up as a fixed seat for one or two person rowing.

Do a Google search on Cosine Wherry and heaps of sites will appear.

Food for thought

Cheers
Bob

Richard

I think the type of boat you're looking for (coastal waters) is variuosly called a called a dory, fishing dory, or wherry.
try a google search

the light boat I really like is this one from Pygmy Boats http://www.pygmyboats.com/mall/WGWSPECS.asp



ian

Originally Posted by PAR

http://www.asrlsa.com.au/

[shakes head sadly]
went looking for something like this back in Feb/March.
Searched high & low at several SLSA state-level sites without success.
And a Floridan finds it at a Club site not 200 miles from me...
How embarrassment...