my new boat

The Didi 950 projects of Fred Grimminck in Australia and Mike Vermeersch in USA continue in parallel. Fred's build is from plans only and Mike's is from a kit that was cut by CNC router. Both have completed the flat sheet panels of the sides and bottom and are now skinning the radiused parts of their hulls. This is the stage that the hull shape really starts to show.

Some of the photos that I show of these two projects show minor differences, due to building from a pre-cut kit or with the builder cutting all components. Both produce the same boat at the end of the process but they may look a little different at times while being built.

Side and bottom panels all completed, ready for radius to start.

The photo above is of Mike's kit boat, with neat edges at the sheer (where hull and deck will meet). The photo below is of Fred's boat with irregular edges at the sheer. This is because the kit panels are supplied with a uniform strip of waste to be trimmed off to the final line after turning the hull over, while the boat built without a kit has the panels inividually cut by the builder and the waste width may vary.

Same stage, Fred's boat. Backbone still to be trimmed at forefoot.

The radius is skinned in two layers, made with narrow transverse strips. The first layer lies on the stringers and the doublers of the tangent stringers, fitted between the edges of the side and bottom panels. These edges have rebates pre-cut into them and onto which the second layer will be laid.

First layer of radius being fitted to Mike's boat.

The rebate along the edge of the side panel can be seen in this photo.

Final hull shape starting to become clear.

Construction of the boat in Latvia has now started and the boat in Greece will soon follow. To see more of this design and others in our stock design range, please visit http://dixdesign.com.

There appears to be considerable interest in my posts about the boats being built to our Didi 950 design. This is a radius chine plywood design with hard chine in the topsides, designed to fit into the Classe 950 box rule. In the past few days I have received a bunch of new photos that show the build process clearly, as well as some updated progress photos.

Before going into the new photos, you might like to read the article that I posted today on my Boatbuilder Tips for Amateurs blog about how to construct building stocks or beds, the foundation off which the skeleton of a wooden boat is built. It is illustrated with photos of the Didi 950 that is being built by Fred Grimminck in Australia. The photos below are mostly of that same project, being built from scratch without a kit.

The photo below shows the various backbone components, all of which slot eggcrate-fashion into the bulkheads. The slots help to locate the bulkheads and backbones correctly relative to each other. The bow and stern have single backbone on centreline and the mid-part of the hull as two backbones that run down each side of the keel support box. The two shorter pieces on the right are the paired double-backbone parts. Next toward the left is the aft backbone, which turns up at the far end to support the transom. Extreme left is the bow backbone, which turns up at the far end to form the stem and supports a bow bulkhead into which the forward ends of the stringers are located.

Didi 950 backbone components. Click on all photos to enlarge.

The photos below show a few of the forward bulkheads with the bow backbone dry-fitted in place. The backbone has doublers just below deck level for through-bolting the bow chainplate. The doublers can be seen at the forward lower end of the backbone.

Didi 950 bow backbone and forward bulkheads

Didi 950 bulkheads and backbones

In this next photo, the transom doubler has been set up as a doubler and the stringers etc run through, then are trimmed flush. When the transom is glued over the doubler the end-grain of the longitudinals will be covered and protected. Look through the 4th cutout from left through the doubler to see how the aft end of the aft backbone turns up against the inside face of the doubler. The backbone has locating tabs that slot through the doubler, seen as light-coloured marks on centreline of the doubler. In the lower photo the transom is being glued over the outside of the doubler.

Didi 950 transom doubler

Didi 950 transom being glued over doubler.

The sheer clamps on this design sit diagonally across the corner at the intersection between hull sides and decks. They are screwed and glued to cleats on the faces of all bulkheads. In this photo the sheer clamp is clamped to those cleats. You can also see how the stringers are slotted through the bulkheads. Once the hull skin has been glued on, these junctions become very strong and rigid

Didi 950 sheer clamp

Looking forward along the hull just prior to fitting the bottom skin. The wide stringers on both sides are the tangent stringers, with doublers to back up the joint between flat bottom panels and radius skin panels at the turn of the bilge.  The single aft backbone can be seen running through to the 3rd bulkhead from the bottom of the photo. The double backbone runs forward from the 2nd bulkhead from the bottom of the photo, then changes back to a single backbone further forward, also visible.

Didi 950 bottom stringers and backbones

Stringers in the forward part of the hull, mainly showing the radius area. The two broad stringers are at the tangents, joining the flat and radiused skins together. Between them are three radius stringers, over which the double-skin radius will be formed. Below the lower of the two tangent stringers are the stringers for the side skin panels.

Didi 950 stringers

This last photo shows Mike Vermeesch's boat, being built from a kit in Ohio. Mike has the side panels all dry-fitted to check for fit ahead of gluing in place. Looks like a nice fit. The bow will be capped with solid wood, which will cover and protect the end-grain of the stringers.

Didi 950 hull side panels

Thank you to both Fred Grimminck and Mike Vermeersch for taking the trouble to send me these photos and allowing their use.

To see our other designs, please visit http://dixdesign.com/ .

Fred Grimminck in Queensland, Australia, has previously built a boat to our Didi Mini design. Now he is building a Didi 950. In contrast to the boat of Mike Vermeersch that I showed yesterday, Fred is building his boat from scratch, marking and cutting the plywood panels himself from our drawings.

Today I have received photos from Fred of his project. He is at the same stage as Mike but the different perspective of his photos shows the details from different angles to help visualise how it all goes together. Click on the photos to enlarge.

Bottom panels fitted, bow view

In this photo you can see how the bottom panels are slightly Veed aft but the V increases toward the bow and the flat panels become very fine, both features to soften the ride when the boat is planing fast in lumpy water and slamming over short waves can become uncomfortable. The edges of the panels land on the doublers of the tangent stringers at the intersections of flat and radiused skin panels. The edges are rebated to half-thickness, with the first layer of radius plywood landing on the doubler and the second layer landing on the rebate, forming a Z-shape joint detail.

Ready for side panels to start

 In the photo above, the doubler at the upper tangent is in place and part of the lower side panel is clamped in place, seen at bottom right. The left edge of this panel has been planed to form the sloping surface for the scarph joint to the next piece, the main difference from the jigsaw joints of Mike's kit. Also visible in this photo, are scarph joints in some of the stringers. These appear to have been glued in place on the hull. The alternative is to pre-glue them into long lengths before installing in the boat.

Interior view of transom and cockpit area

The photo above shows some of the interior detail. The transom is 9mm plywood but has doublers to strengthen it around the perimeter, at the backbone and at the rudder hardware. You can see the plywood backbone passing through the bulkhead ahead of the transom. These intersections are self-locating egg-crate detailing to assist with accuracy during setting up the skeleton. The backbone is on centreline in bow and stern but changes to a pair of backbones offset from centreline from forward of the mast through to the cockpit.

A major difference between the two boats of Mike and Fred is in the keel detailing. Mikes boat has a fixed bulb keel that hangs from an internal support box that is bolted between the two components of the double backbone. The support box also holds the engine beds and bearers, sited directly over the keel. Fred's boat will have a lifting keel. It will be housed in a modified keel support box of identical footprint but with integrated casing for the lifting keel and without the engine beds. Fred's engine will be a saildrive unit located under the companionway and front of the cockpit.

There are also boats to the Didi 950 design beign built in Greece and Latvia. Watch this blog for news on all of them.

Go to http://dixdesign.com/ to see our full range of designs.

Mike Vermeersch's amateur boatbuilding project of a Didi 950 is moving on to the next stage, with bottom panels fitted and work starting on the side panels. Mike is building from a plywood kit that we supplied to him and reports that the fit is good. The kit has jigsaw joints on all large panels, making them easy to assemble either on the floor or on the boat.

Didi 950 with all stringers installed.

Two of the stringers each side, at the junctions between flat and radiused skin areas, have plywood doublers attached to serve as backing pads to the joint. I call these the tangent stringers. The doubler on the upper tangent stringer is in process of being fitted and can be seen running forward from the transom through to the third bulkhead from aft.

In the photo below, the transom has been fitted, followed by the bottom panels. These panels each have two transverse jigsaw joints and join each other at a centreline butt joint over the plywood backbone. In the photo the jigsaw joints have temporary battens over them to secure them while the glue is setting.

Bottom panels fitted.

Mike has also started to dry-fit the side panels ahead of gluing in place. At the right of the photo the forward lower panel can be seen and which will continue through to the transom. The lower edge, as seen upside-down like this, forms one half of the chine. The other half of the chine will be formed by the upper side panel.

Today Mike's 300lb brother decided to test the hull stiffness of this partially-built Didi 950 . He climbed onto the bottom of the boat and jumped on the bottom panels. They passed his improvised test but I think that I would have recommended that he wait until the whole hull was skinned before doing such a test.

Mike's 300lb brother tests the Didi 950 hull stiffness.

The broad stringer that shows on this photo is the upper tangent that will join the lower side panel to the radius.

To see our other designs, visit http://dixdesign.com/ .

John Gilbert asked a question in response to my recent post, Stability with Water Ballast.

I do not get why the red and blue curves do not meet up at 180 degrees. Inverted the boat has no windward side as you point out, so you have water ballast on one side and none on the other side. As you have drawn the curves you have powerful stability in the  inverted position with the water on one side (red), but actually a righting moment if you have water on the other side(blue). What is the difference?

To help with understanding this I thought it better to write a new post that expands on the dynamics of stability than to try to answer it in the comments section after that post.

This will be more easily understood by seeing a diagram showing the stability graph expanded through a full 360 degrees rather than all conditions overlaid on top of each other in a 0-180 degree range. This is exactly the same stability info for the Didi 950 as shown in the graph of my earlier post but shown in a different manner.

Diagram of Stability through 360 Degrees

I will start with the green curve. This shows the stability without water ballast. The centre of gravity (CG) is on centreline. The stability curve intersects with the horizontal grid line at 0 degrees heel and increases identically both to left and right of the 0 degree line, so the boat will float without any heel to either side when right way up. The boat will stay that way in the absence of any wind, wave action or crew movement on the boat.

Follow the green curve until it comes down past 130 degrees to again intersect with the horizontal line at the Angle of Vanishing Stability (AVS). Then it enters a range of negative stability where it will proceed toward upside-down. At 170 degrees it crosses to above the horizontal line again. This indicates that the superstructure volume is trying to turn it back upright and doesn't want the boat to lie totally inverted. It will easily flop back and forth between the 170 and 190 degree points. The boat can return to upright along either green curve.

This all depends on a totally waterproof superstructure, of course. In practice water is likely to enter the boat at a rate that depends on what is open at the time, which will affect the inverted stability. 

Moving on to the stability with water ballast, in my earlier post I said that the boat will capsize along the red curve and recover along the blue curve. I explained the relationship between the two curves but that relationship is not easy to visualise if only seen across the 180 degree range.

In the diagram above you can see that the red and blue curves only meet in two places and both are on the horizontal line. These are the two points at which the boat will rest when there are no outside influences from wind, waves or crew movement.

The boat cannot rest totally upright nor totally upside-down because the weight of the water to one side is heeling it toward that side. It will rest at approximately -5 degrees heel instead of upright and at 200 degrees instead of upside-down when inverted.

Bearing in mind that the areas of the curves below the horizontal line indicate how much energy it needs for the boat to get past the AVS points so that it can right itself when in that 200 degree situation, it is now easy to see that it will take a large amount of wave energy to get past the AVS of the red curve but a very small amount of wave action to get past the AVS of the blue curve.

This graphic shows that if a water ballasted boat capsizes it will do so along the red curve but it is very unlikely to return along that same path, nor is it likely to stay capsized for long. Once past the AVS of the red curve the negative stability will push it to 20 degrees past upside-down. After that the blue curve will take over and almost guarantee that the boat returns to right-way-up pronto.

It's My Boat Radio is a weekly online radio program that runs on Blog Talk Radio. Hosts are Barbara Jean Walsh and Ann Avary. They do interviews with people who are experienced boaters or in the boating industry, on a broadening range of subjects.

This week I was invited to participate, on the subject of kit boats. You can listen in to the program by clicking on the link below. It is about 30 minutes and you can listen while doing other stuff. Unlike live radio, if you think that you missed something then you can go back to whatever part you missed and listen again, or go back to the start and listen to the whole program again.

Kit Boats and More! online radio program

Small selection of our plywood kit designs

Plywood kits for our designs

To see our full range of designs, go to http://dixdesign.com/