designing a fast rowboat

Rhino can import .dxf and .dwg files.

 

Oh cool. Hey if you wouldn't mind scanning the tables of offsets, I'd be happy to model those in Delftship for reference. Yes, the four longer boats would be the ones of interest.

One thought that did occur to me about all this. Clinton wants to beat guideboats just mainly because he doesn't really like guideboats all that much. It should be possible to do it too. What will probably happen, if he does it, is that someone else who really likes guideboats will decide that they want a guideboat that will beat his guideboat beater. The defntion of "guideboat" is pretty loose, and it would also be possible to build a boat that would pass the class specs for the guideboat races, but was noticeably quicker than Grant's Virginia.

 

RE: I am totally open to something that can meet these specs for the guideboat races.

You know, I am coming around on Guideboats. Some of them really are pretty. Some are..."exaggerated".

I could also become accustomed to 8' oars.

At this point I am up for anything.

If we try something that meets these GB race specs, let's make sure we hit the maximum beam and get the length max too. Narrow on the bottom board.

I just downloaded MICHLET and Delft. Will look at last files.

I think it would be cool to use this forum and see if we could come up with something stunning. I could be the Guinea Pig.

 

OK, I thought it started in the river! And I thought a bit over 5kts was the target!

Thanks.

Hey where is the Delftship file?

 

Personally, although I find guideboats interesting on a technical level, I'm not that fussed about building something that would be defined as a guideboat. Over here, they are about as relevant as a Shetland sixern. Nobody is obsessed with them as a traditional local type, and honestly I find the beam restriction rather pointless and counterproductive.*

However, if you do want to build something for guideboat races you'd have to be careful, because the class rules include a stipulation that the race committee can use its own subjective judgement in deciding whether your boat meets the spirit of the class.


*ETA: Well ok, it wasn't pointless and counterproductive in the original context, because they were trying everything to save ounces on long carries.

 

The Dellftship file is here: http://www.boatdesign.net/forums/at...signing-fast-rowboat-grant_virginia_basic.fbm

 

I need to be more specific....I like the idea of the guideboat from a functional standpoint...something that does well in sheltered water (lakes and rivers) and appears to do well in the ocean. I like that....but I should constrain my project to some dimensions. Do they need to meet the GB race spec rules....no I don't think so.

I also don't think my boat needs to have the characteristic hollow of a GB or the SLRS...unless it is deemed necessary...I notice your 18 footer and the Finnish boat do not have this hollow.

So I can view your Delft file. It sure looks like a Guideboat!

Here is an intriguing midship section. This is a 17' open water cruising rowboat by Gartside.


Section_gartside by Clint Chase Boatbuilder, on Flickr

http://store.gartsideboats.com/coll...pedal-boat/products/17-ft-coastal-rowboat-179

 

Yup, have seen that boat on Gartside's site. Honestly, it looks like a right pig of a thing to handle in waves. I know he thinks that section is "ideal for coastal cruising" but to me it looks like it would be bucking you all over the place. Would be fine in flat water but............*

Re hollow sections: a convex section will always have more area for a given perimeter, which translates into more displacement for the same wetted surface. So generally I would be avoiding significant hollows.

*ETA: come to think of it, would be ok in long waves. I can imagine a bit of a chop on the beam being a problem though. Also, wouldn't be good for general recreational use. I doubt it would float upright when empty.

 

I was just looking at the Savo 575 pics that the builder sent me when I was going to work on kits with him. I still may. But this is one thought: the Savo 575, reduce to 18' LOA, a touch of rocker to the keel, and maybe a little more rake and flare to the stern.


P1030150 by Clint Chase Boatbuilder, on Flickr

You can see in the blue boat that Ruud decided to do away with the outer keel to reduce wetted surface. He said there was little difference on the water.

Love this boat

The Savo 575 by Clint Chase Boatbuilder, on Flickr

Definitely not a Guideboat!

 

Oh, re Michlet output files: they're rather horrible. Leo is a thorough bloke and has included a lot of stuff for naval ships and the like. For the basic rowboat resistance stuff, scoot down to Line 1887. That's where the table of resistance values starts.

Resistance values are in kilonewtons, which is also horrible, but doesn't matter because it's only the value relative to another hull that we have to worry about. Speeds are in metres per second, and I usually do my files from 2 knots up to 7, in 0.1 knot intervals.

If you need kilonewtons to pounds conversion, multiply by 225.

ETA: And yes, the Savo's are very nice indeed.

 

That was my thought...the waves coming in and pushing up on that flare.

I also am concerned about the long straight keel of the Savo in the ocean....when the sea starts to make your boat go one way, I like a flick or two of the oars to be able to straighten things out.

Is this concern warranted regarding the straight Savo keel? Would a little rocker not hurt and a little more rake aft to help in a following sea?

 

You can go with some rocker if you think it'll help. I have run a few things through Godzilla (the "how to find new hulls" side of Michlet) and for the fairly low prismatics that seem about right, there doesn't seem to be any resistance penalty for a bit of rocker aft (AFAICT so far). All the hulls seem to come out with some rocker for'd too. So I'd start with what you think looks right for a keel line, and take it from there.

 

Blackburn = 19.6 statute miles

The Blackburn course is 19.6 statute miles as measured by GPS a few times.

 

Ok cool. Thanks for the tip.

That 17.2 nautical miles I got from a rough run around Google Earth translates to 19.8 statute miles (1% difference), so it looks like I have the right bridge this time.

If we go with 19.6 statute, that's exactly (or near as makes no difference) 17 nautical miles.

 

Thanks for the info Nick.

If you guys don't know Nick's work, you are missing out. Google him!

Delftship looks rather nice...the hydros are nice. Are they accurate?

I have a lot to think about with this next boat. The Savo is a little light...I'll need to make create some volume of displacement for me especially if it is 18' LOA. Seems like the flat plank keel would provide that extra space plus more of a convex. GB fanatics swear by the concave section. I must say, the elegance of the GB has grown on me.

I'd be interested to see what they look like in the 17-18' range.