Changing The design of a Kingfisher rowing shell to strip consruction

[Brian75137]

Has anyone taken the plans for a Kingfisher rowing shell and redesigned it for strip consruction. I want to build my kingfisher using stip construction, and the plans call for using okume plywood (stitch & glue) I want to use 4 different colored woods and create a geometeric design on both fore and aft decks. I'm a rank amateur at this and could really use some help with the design and layout of each bulkhead so the boat is fair.
Brian75137

 

[messabout]

Brian, that is going to be problematic. It is do able but it will have some disadvantages. If the design is for S&G then that implies flat panels and hard intersections, not the most appropriate for strip building.

Plans for S&G usually show the layout of the panels and not much detail about the station shapes. The location and dimensions of stripper mould frames may be difficult to determine from such a set of plans.

One possibility is to build the stitch and glue boat in rough form and then use it as a male mold to build the stripper. Or build it in smooth form and then cover the exterior with thin strips that will be strictly for cosmetic purposes.

The other option is to get the plans for a similar boat that is designed for Clinker, carvel, or strip. In that way you will get a table of offsets that let you do the section molds with some degree of certainty.

 

[rwatson]

I think its Texas River rat who builds develop-able panels out of wood strips, so that his ' S&G ' designs look like strip plank/

It looks really good, and with the right timbers, may even be better than plywood.

 

[Skyak]

Has anyone taken the plans for a Kingfisher rowing shell and redesigned it for strip consruction. I want to build my kingfisher using stip construction, and the plans call for using okume plywood (stitch & glue) I want to use 4 different colored woods and create a geometeric design on both fore and aft decks. I'm a rank amateur at this and could really use some help with the design and layout of each bulkhead so the boat is fair.
Brian75137

Brian, there is such a thing as a hybrid that only has a strip deck on a S&G hull. This would be easy to just round the S&G deck. Strippers are usually continuous curves so it will always be an interpretation. When I design strip kayaks I use 'kayak foundry' -works great.

 

[JerryD]

Changing The design of a Kingfisher rowing shell to strip construction

Brian

I'm currently building a Kingfisher. Like you, I wanted to build with strips instead of plywood and before I started I talked with two guys. One previously owned a Kingfisher and one who had built one of Graeme King's racing shells - strip planked. They both recommended that I contact Graeme King. Graeme had two recommendations; first, use strips to build flat panels, and second be as accurate as I could be. I took his advice. I built my panels from 1/8" western red cedar that I resawed from 2x10s so my panels are full width from a single piece of cedar except for the scarphs. The inside of the panels are glassed with type 106 fiberglass cloth. The outside will be glassed with 2oz or possibly a little heavier to get a little more abrasion resistance. If you want to talk further send me a PM.

JD

 

[Brian75137]

Strip built rowing shell

Brian, there is such a thing as a hybrid that only has a strip deck on a S&G hull. This would be easy to just round the S&G deck. Strippers are usually continuous curves so it will always be an interpretation. When I design strip kayaks I use 'kayak foundry' -works great.

Skyak: I understand that strippers are continuous curves. I wanted to get away from flat sides - to me curves are more pleasing to the eye. Could you please give me some more information on "kayak foundry". Have you ever built a rowing shell using strips? Is it really necessary to have hard chines for a rowing shell? Is there some computer program which would assist in the conversion from flat sides (S&G) to rounded sides (strippers) while retaining essentially the same "seaworthiness". Would I need to build a S&G shell and get a table of offsets this way, then use them to create my stripper? Any help you could provide would be very much appreciated.
Brian

 

[bregalad]

There is a previous thread that addressed this issue. You might want to try to contact one or more of those folks. See post #18
http://forum.woodenboat.com/showthread.php?137091-Strip-Built-Rowing-Shell

 

[Skyak]

Skyak: I understand that strippers are continuous curves. I wanted to get away from flat sides - to me curves are more pleasing to the eye. Could you please give me some more information on "kayak foundry". Have you ever built a rowing shell using strips? Is it really necessary to have hard chines for a rowing shell? Is there some computer program which would assist in the conversion from flat sides (S&G) to rounded sides (strippers) while retaining essentially the same "seaworthiness". Would I need to build a S&G shell and get a table of offsets this way, then use them to create my stripper? Any help you could provide would be very much appreciated.
Brian

Brian,
I have not built a stripper rowing shell. I just wanted to point out Kayak foundry software because it is so useful designing and making stripper hulls. You can get it here:

http://www.blueheronkayaks.com/kayak/software/software.htm

The software allows you to adjust the stations or smooth the hull directly. You don't need to make the chine model first, you can just use the dimensions to make the center mold, then the quarters, then the eighths, then smooth the hull. The software calculates properties for you. In order of importance they are waterline length, wetted surface area, waterline beam, prismatic coef... If you match up the properties your rounded hull should be equivalent to your target but with less wetted surface it will be faster. When you have something you like post it to the rower forums for comment -they might have some good tweeks.

About chines and "seaworthyness" chines cause water to slow or separate when it flows in any direction across them except along their length. The resulting vortex is taking energy from the movement. The only positive to taking energy away is damping motion. Some big heavy boats might want some damping but to my knowledge rowing boats don't. Further my opinion is that chines forward of max beam of a displacement hull are always a negative for hull drag, and aft it takes some very clever design to make a chine that is net positive. Most of what you consider "seaworthyness" is stability and kayak foundry will give you the stability and buoyancy curves you need for comparison (you will have to adjust for seat position).

 

[ancient kayaker]

The construction of Graeme King's Kingfisher is ply (3 mm?) over a frame of stringers and bulkheads, not S&G. Its design has to accommodate the inability of plywood to curve in two directions at once, but it is a fine boat with near-competition performance. Its design pays more attention to ease of building and safety in the water than typical rowing shell designs. Kingfisher's hull is not glassed ASFAIK but the deck is reinforced with some fabric. The building of Kingfisher is described in issues 61, 62 & 63 of wooden Boat magazine; pdf copies are available from their web site - considerably cheaper than the plan set and adequate to get a feel for the process. Of course if you go ahead then get the plans which include full size templates.

The rounded hull of a strip-built boat helps to improve the limited strength of strips, but strippers are almost always glassed inside and out for proper strength, which adds significant weight, not to mention rigging. I built a partially-stripped canoe with laminated ribs and a ply bottom that is not glassed, so it can be done; it is exceedingly light, but demands careful handling.

Since the construction is ply over stringers the panels would be cut to fit, so I don't expect the plank developments (needed for S&G) are provided in the plan set. I don't think it would be a big deal to add another stringer partway up the sheer planks to introduce more shape to the topsides. It would have a slight effect on behaviour in the water but not much, you could offset that by moving the chine stringers inboard by enough to keep the waterline beam the same. A simple way to judge the effect on appearance would be to make a model.

 

[rwatson]

The rowing shells I used when I was young, were made of plywood.

Its true that plywood resists bending in two directions, but the little it can be made to is enough.

The build technique relies more on variable radius along the hull more than for after bending, as the shells have more or less parallel sides for a good proportion of their length.

To get the bow and stern built, is more of a sharper angle at the keel, and less curve in the panel.

The Tornado catamaran uses similar technique.

I would be keen to try 5mm foam and inner/outer glass. The little bit of experimentation I have done with it seems to indicate real strength/lightness benefits.

Some hints at the design process at
http://www.multihulldesigns.com/pdf/cm33.pdf

 

[ancient kayaker]

Ray, this is the guy's first build - might be best to keep it simple eh?

 

[rwatson]

Yes, but its not that difficult,

Remember when you built your first corrugated iron canoe ?

You create a half round stern, and get the wide beam, then you tie the two other ends together to make the bow.

Two of those makes a canoe sterned rowing shell.