RMS Some More

What's the diff?

In the hull proper there isn't much difference. In the original version the bow transom was curved at the top and also curved athwartships. Working out the build for this little quirk was difficult and it may be beyond the experience of the typical backyard builder so I made the new transom flat.

In the original design the keel was a flat plate with a the keel  attached to it. This came out of a design I was toying with much earlier. Here is a picture of a model of that design. I have long since lost the actual drawings during several moves but the model remains. You can see in the picture of the bottom the space for the keel piece which is a tapered, curved and beveled 2x12. Again probably not the best design for a backyard builder. It took me quite a while to get the model right.

I am a great believer in models. When I did the design for the WoodenBoat competition I made a half model to make sure the design would come together off the paper.

In the next  picture you can see the keel piece.

The change to the keel, which adds a box to the keel was to get the flow right to the new motor which is electric versus gasoline and we'll delve further into that as we develop the design. I don't think that the box keel will be that difficult to build as long as the build method is ply or plank on frame versus stitch and glue.

My instructor at Westlawn commented that this would be a wet boat because the sides are almost up and down at the bow, he obviously hadn't spent any time looking at Phil Bolgers designs for small boats.

RMS

The First Sampan Skiff

In 1990 I was deeply involved in the Westlawn process and WoodenBoat, an excellent publication, ran a design contest for a 15' boat that would be equally at home being rowed, sailed or running under a small motor. As part of my course work I entered that contest Here is part of the lines drawing, I can't show you it all because it was all done by hand to a scale 1”=1'.

 The quality of the picture is very poor because it is a scan of a photocopy of a 16 year old drawing ( I never throw anything away). However I show it to you so you can see the detail that is required.

I have taken that design and redone it in my CAD programme, changed the hull a little bit and altered the lateral resistance quite a bit. Here are the new lines.

The original design had a fore and aft box seat for rowing with a hinged top into which you could stow the spars, sail, leeboard and oars. It had a small, 2hp, outboard that just cleared the tiller when tipped up, was clear of the keel but did not clear the water. I think you can all see the problems all this would create.

Over the next few weeks we'll look at the changes made and discuss why I made them and work this up to a completed design. I'm doing this is smaller chunks so that I can actually get a post out at more regular intervals.

Round Bottom Boats

Round Bottom Boats

In the last post I said that your client had changed his mind, what I intended to do was to modify the power dory to take an outboard. However whilst I have been taking a break from posting, primarily because I actually have to create the design from scratch, I was contacted by a follower who wanted more rounded boats, so here we go,

Several years ago I designed a rowing boat which I called Sally Blank, (white hall=salle blanche= Sally Blank, I told you I liked puns) she looked like this,

 I called her the poor man's Whitehall skiff. However she was hard chined, here are the lines.

So to satisfy the request for a round chined boat, I redesigned her. The process is much like that described here and here. However in order to create a fair hull more lines are needed. Here are the almost finished lines of the new Sally Blank.

You can see that there are far more defining lines than in the drawing of the hard chine version. In the first version you have only one waterline, which you don't even draw in, here you have four which must be drawn in. Those lines give you the hull shape looking at it from below.

Then you have buttock lines, those are the lines in the section drawing parallel to the centerline. When transferred to the profile they give the hull shape from the side.

There are some extraneous lines to be removed and a last set of lines drawn in.

If you carefully compare the hard chine version and the round chine version you'll notice that the chine line and the keel line from the hard chine version are shown in the new version, that's because I used those lines to establish the new hull shape and the location of the chine and curve of the bilge You'll also notice that the stem is still straight which it can't be in the new boat. So we'll remove the extraneous lines, alter the stem and draw in a keel.

You'll notice two new lines in the sections drawing, those are a diagonal which will give us an idea of the flow around the hull. If we've done this right that diagonal, which will show as red line on the profile, will also be a fair curve.

C'est bon, n'es pas (yes I know I fractured the language).

So there you have it from a hard chine row boat to a round chine skiff. The work is not difficult, just tedious however, as I said here, using a computer speeds up the process.

Maybe we'll start something more ambitious next time.