Construction Redux Anew

Construction Redux Anew

Way back here and here we talked about the construction plan and I suggested that you build a few boats to find out how they go together. When you are considering a design you should have some idea of the construction method you intend.

Let's look briefly at RMS, which is, as designed, a hard chine boat which lends itself to plywood and carvel construction.

 
You could do the sides in clinker (lapstrake) but that's a complicated joint at the chine. However there is a little twist. If we look at the lines plan,

You'll notice that the bottom of the boat is not altogether flat, and there is a little triangular section in way of the keel. 

There are several ways ways to do that and at least one of them should be shown in your construction plan. I'll show you one,

This diagram shows ply planking 1/4” for the sides and 3/8ths for the bottom, the chine and keel joint should be epoxied with fiberglas tape.

But should this boat be round bottom? Would that change the design significantly?

Here's the redesign,

It looks much the same as the picture at the top of the article but it is a very different boat. And we'll explore those differences anon.

Shrouds and stays

Shrouds and Stays – Yes/No

Here is the new interior arrangement in plan,

and profile

The bury, the distance from the deck mast hole to the mast step, is 20” and the foredeck is 32” wide in way of the mast. The mast is well supported by the foredeck and the mast support beam that I plan not to have a forestay or shrouds (stays go fore and aft, shrouds athwartships) which simplifies rigging.

In place of the rowing bench in the original I have gone with a fixed thwart and with the removal of the engine well we have enough room for sternsheets.

There is enough room between the sternsheets and the rowing thwart to sit in the bottom of the boat when sailing.

The pad eyes for the sheets are shown in the profile and plan but the location of the oarlock is not as that location depends very much on the rower, although generally speaking 12 to 14 inches forward of the thwart is usually right.

The standing lug employs two sheets which are led to the quarters, this allows for sail adjustment absent a boom. The biggest problem with this sail is the twist that develops at the head. That can be corrected with a yard vang, a line from the end of the yard to the quarters to adjust for twist, but that is overly complicated for this size of boat.

So there you have it, Row, Motor, Sail (RMS).

Next time we'll talk briefly about construction and would this be better as a round bottom boat.

Changes yet again

The Look Astern and Other Changes

The stern on the original design was also quite complicated. It had a motor well for the outboard which could be sealed off when the motor was not fitted by a plate which was held in place by a bungee cord attached top a removable curved piece that fit into two slots in the side of the well. The space on either side of the well was for storage and flotation.

So in the new version the transom is flat across and the well is eliminated. And an electric trolling motor is fitted through a PVC tube right aft of the dead wood. The original also had a leeboard which in the new version I've traded for a centreboard.

Because all the spars had to fit into the hull for rowing they were quite short which constricted the sail area. It was about 49 sqft, a boomless standing lug sail, with sheets led to each quarter. There were no permanent stays or shrouds.

This is the new design with the old rig.

The previous design was more row, motor, sail. In the new design I wanted more emphasis on the sail and less on the motor so I increased the sail area to 80 sqft keeping the the same foot and yard as in the old sail which means that the mast is now some 17 ft tall which might require stays and shrouds. So here we have the new rig. You'll notice that the centreboard is located in exactly the same place as with the old rig. But, because of the shifted centre of effort of the sail, it is deeper.

The sheets also had to be beefed up a bit given the increase in sail area.

We'll look at the interior arrangement next time and that will determine how we can lay out the shrouds and stays or even if we need to use them.

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.

The short strokes

Finishing up (this one)

I have been remiss, my other work has dragged me away from this and put me behind schedule however I'm back at it and so we'll finish up.

The last thing to be done with this design is to add the finishing touches, to add to each of the drawings those things which are present in other drawings and which are relevant to a particular drawing.

So on the inboard profile we drew in the engine bearers those need to be transferred to the construction profile and to the construction plan.

To the inboard plan I added chocks at the stern for berthing lines, those need to be shown in other drawings.

Lastly it is usual to draw one or two typical construction sections and in larger designs furniture detail in this case we'll just do the mid section

You can add specifications directly to the drawings or do as Bolger did, number all the parts and draw up a specification list.

When your drawings are done you can either put them all on one big sheet or do up separate drawing sheets for each of the views.

Here' the sheet for one of my designs, Vole.

In this case I wrote a build document that specified all the parts and sizes and the building process.

Next time we'll throw a spanner in the works and have the client change his mind about what he wants.