4,8m Skiff

Gents

I've changed the hull design to include a 15 degree rocker and raise the bow and stern with a radius on the keel of 75mm.

Any comments please?

Thanks

Graham

 

Looks like you are just trying to reinvent the wheel.

Check out
http://www.boatdesign.net/forums/sailboats/marketing-new-sailing-dinghy-brand-41242.html

 

You mentioned using a little outboard. What hp did you have in mind and what speed were you hoping for under power?

 

Phil

The motor is an old 2hp Seagull

Walking speed is fine. Say 3.5-4 knots.

I only want something to motor if there is no wind, get somewhere and then paddle about, maybe let the kids have a swim.

I also have a 6hp, but that may be too ambitious to use.

Graham

 

She looks lovely, but I can't afford a boat like that and I enjoy the fun of designing and building something myself.

I have an existing mast spars and sails which I can utilise for example.

Thanks for the idea

Graham

 

One thing you'll notice is that your design differs from all the others posted in that you show a much finer bow than others. The max beam, and more importantly, the fore-aft location with the greatest submerged cross section, is pushed far aft in your design. This isn't something that will work too well for you considering the other aspects of the build and the performance envelope. It is done in modern racing boats for some peculiar reasons that relate to racing rules, the overall size of the boats (bigger than yours, mostly), and extreme lightweight construction.

I'd rather see a pram bow like the Pelican, and the location of max area pushed forward close to the middle of the waterline. Pram bows just seem to be eminently practical on this size boat. The stern shouldn't drag at all in this boat with just one person aboard. It should probably just kiss the waterline at the center.

The boat you pictured could not be built out of sheet goods and follow the keel line, chine line, and sheer. The surfaces are not developable. In a file bottom boat, I find it best to choose the chine line first, then the midship cross section, and look at the options as far as how the displaced volume gets distributed along the length of the boat. The keel line just ends up where ever it does as a result of these considerations. Then you have to go back and use Rabl's method to figure out the actual shape of the midsection, because it won't be exactly what you assumed it to be. The frames won't have straight edges, they will be curved, and you should fiddle with the chine a bit to preserve the volume distribution that you originally strove for.

The sketch you drew shows the flare of the topsides getting small as you go forward. This is the opposite of what you want. A 15 degree flare for most of the topside is good for this type boat. It is economical as far as materials and effective as far as stability goes. (Most stability for a given girth.) But you should have at least that much forwards where waves are encountered. You show that area flattening out. The deadrise angle of the bottom panels looks pretty good to my eye. About 5-7 degrees at the midship and getting somewhat steeper forward to the extent the ply will take the bend. The stern can be flatter, no more that 5 degrees, and usually tortured into a bit more of a curve than what it wants to go. (The outboard corner can be pushed up about an inch from where the computer says it should lay.) If you are building purely stitch and glue, this doesn't work. You need a frame a couple feet forward of the transom to pull this off.

 

Phil

Many thanks I ill go and think how to improve along these lines

Graham

 

I used to take my two boys fishing in a Pram, similar to the one you have posted. My Pram was 8' (almost 3M) long. It fit in the Camper and in the Pickup bed.

I rowed though. Never put a motor on that little boat.
It's so easy to beach so the boys could explore.
We huddled under it during a Rain storm.
They both learned to Row in that pram too.
The Boys and I had fun in that little thing too.

 

simple rowing sailing skiff

http://www.sredmond.com/index_boat.htm

 

That's a good skiff if your gonna row long distances. I like the Jon boat front end better than that unstable pointy bow when your having kids and women out in the Boat. Far mor stable when going to the Beach.

Old folks need the stability of the flat bottom. Our balance seems to forget where it needs to be and when it needs to be there.
Kids don't seem to notice. They run around in a boat, not thinking the older folks are hanging on for dear life as the boat is maneuvered by those kids.

It's all fun of course. But, with kids and older folks you need the flat bottom.

 

Graham; Try to transfer some of your enthusiasm for self design into some other activity about which you are more expert. This is a common plea here on the forum. You are going to spend time and money with your build. It is almost always less costly to buy some insurance in the form of a set of professionally done plans for boats with an established history of good result.

This is not to question you intelligence or capacity for creativity. It is simply standard and thoroughly proven advice.

The Great Pelican is a fine and very capable boat. It may be bigger than you want. The smaller San Francisco Bay Pelican is also a very capable little boat.

Take a look at some of the Bolger designs. These designs are famously simple to build and use. Google Dynamite Payson to find small Bolger boats. His Gypsy is a tried and true design, stitch and glue, sails very well with only 5.5 Sq. Meters of sail. Rows decently too. It is about 4.7 meters long and much lighter than The Great Pelican. The last I knew, a set of complete plans and instructions were $75 US. There are plenty of good designs from others that will suit your purpose too. Most of them modestly priced.

 

Gee...nothing wrong with self design. Its a small craft and this is what small craft are all about.

The internet is full of inspirational small craft designs . Have a look and start designing !!!

 

To me this is part of the fun, creating the whole boat from almost nothing.

Graham

 

Gents

I've had a quick go at a pram, 4.25m long and 1.6m beam. Many of the changes proposed have been made.

The waterline is set to 150mm, but it could be less looking at the displacement.

I haven't run the Rabi calcs yet, so it's a quick idea rather than a full design.

Are the chines too high regarding the waterline?

Does it have adequate stability towards the bows?

With my previous pram the only real weakness was weight had to be kept aft for this reason.

From my feel of the linespan it looks dodgy. But I am no expert.

Any comments please before I go further?

Thanks,

Graham

 

Run a development check on this. The bow looks highly loaded and not plankable in sheet goods. Rather than waste time with pretty pictures, that you haven't a clue about hydrodynamiclly, let alone if they can physically be built, in the fashion you'd like, maybe some study is in order. Considering the little I know about your SOR, this is a flawed set of shapes (the latest posted drawing). This hunt and peck approach is surely going to take a long time. Establish your SOR, which refines the design, so you can develop a GA, then work around the volume you need, of course placed appropriately for the goals and targets of the SOR. The net result is a design well suited to your needs, the first time out of the box (okay, after a few rounds on the spiral).