Scram Pram Progress

I have previously written about a Scram Pram which I am finishing off for a customer from Sydney. Scram Pram is a design from the board of Jim Michalak, and makes use of the so-called, "Birdwatcher" form of cabin. You can read some of what I have written previously in the post which you can find by clicking this link:-  http://rosslillistonewoodenboat.blogspot.com.au/2012/10/potpurrri.html

The Scram Pram which I am working on was started and taken to about two thirds completion by a builder in Sydney, but work commitments and lack of time prevented him from finishing the job. He asked me whether I would be prepared to finish off the boat, and I told him I would be very glad to do that as it would give me an opportunity to gain experience with the "Birdwatcher"-style of hull.

The boat is now nearing structural completion, and we hope that she will be in the water in a week or two. Internal painting will still need to be completed but we will have a good opportunity to test the boat on the local dam. Below are some photos which may be of interest.

Windows installed, but without bedding compound at this stage.

Windows installed, but without bedding compound at this stage.  The large decks forward and aft, are fitted to the hull using silicon-bronze screws, and set in bedding compound. This allows them to be removed periodically for internal inspection and maintenance. 

The large side windows are simply screwed to the internal faces of the hull-sides, with the screws passing through timber battens so as to cover the unsightly bedding compound, and to spread the point loads so as to help prevent cracking of the Perspex.

This is a view of the leeboard on the starboard side of the boat, looking aft. You can see the 1/2 inch pivot bolt with a very large washer, and at the top the uphaul and downhaul tackle. This is all very simple, although since this photograph was taken I have added a pulley block to the fairlead which you can see on the far right of the photo. This has reduced friction and made the uphaul easier to operate.

 Note the bronze plates which prevent wear on the timber surfaces.

 Note the bronze plates which prevent wear on the timber surfaces.

Scram Pram makes use of water ballast, with three tanks underneath the cabin floor. These are filled and emptied through drains in the bottom of the boat. This photo shows how I modified the brass tube and bung arrangement which was supplied so that the brass tube would not protrude beneath the bottom of the boat, and that water would drain right down to the level of the bottom. The brass tube was cut just long enough to fit the entire length of the bung, and holes drilled laterally level with the bottom of the boat. The block of timber I made to support the tube has been thoroughly sealed with many coats of epoxy, both inside and out.

Here are the same components, but with the bung fitted.

In this view you can see the wooden block, the brass tube, and the bung all fitted permanently to the inside-bottom of the boat. The photograph has been taken looking downwards through a screw-in hatch which is set into the cabin floor. In use, it is an easy matter to launch the boat, reach in through the hatches, and open the bung. When the tank has filled, just replace the bung and screw in the hatch. Emptying is carried out in the reverse manner once the boat has been hauled out onto a trailer.

This is the mast partner which is bolted and glued to the forward bulkhead slightly to port of the centre line. The plan called for either steel or aluminium alloy for the closure plate, but specified half inch thickness. I have taken the liberty of using 8mm aluminium alloy, and set-up the closure plate as a pivoting gate. Time will tell whether this will be strong enough, and also whether it should simply be a plate with two holes and held on by butterfly nuts.

The owner of this boat asked me to modify the design of the rudder so that it did not protrude below the depth of the skeg. In order to do this I designed a shallow rudder with roughly the same area as that shown on the design, but I then added substantial endplates. Testing will prove whether this is adequate.

The rudder is very robust, and the endplate is glued on with epoxy and is supported by a substantial epoxy fillet reinforced by 450GSM woven glass. This should be strong enough to act as a step to assist people re-entering from the water.

I also shaped the upper edge of the rudder so that a foot can be placed on it without sliding off. The combination of the endplate, top of the rudder, and the outboard motor well should make for a serviceable ladder.

This shows the tiller position looking aft towards the rear bulkhead.

Here you can see the leather chaffing guard sewn around the mast where it enters the partner.

This is leathering on the yard at the point where the halyard is attached. The lump in the middle is the leather sewn around a commercial fairlead.

Here you can see leather glued to the started side of the boom, which in this view is upside down. The downhaul is attached through the black cleat and pulls downwards when the boat is rigged.

This is a pulley block with beckett attached to a pad eye which has been very securely screwed to the masthead. The mast is square sectioned and solid Hoop Pine.

Once the boat has been launched and initial test sailing has been conducted, I will publish another post.

Water Rat in 4mm Plywood - Sailing Version?

Water Rat is a 3 foot wide plywood kayak which can be built with a length of either 9' or 10'10". This boat has an unusual, but attractive shape, and has proved to be quite popular. She was initially drawn by my friend Doug Laver back in the days when we were working at my workshop in Brisbane, and we had started experimenting with Gregg Carlson's Hull Designer program.The plans that Doug and I used originally were very difficult to interpret when it came to the shape of the developed panel sections, and I subsequently redrew them in a CAD program, incorporating a few variations and conventional dimensioning. You can read about the boat in a previous post here:-    http://rosslillistonewoodenboat.blogspot.com.au/2011/11/water-rat-developments.html

Doug's original Water Rat with my son, Steven, showing off the boat's stability. Steve was about 12 then, and I haven't seen this activity performed by an adult - but for a canoe she is a very stable boat.

Ross Trinder, from Toowoomba in Queensland, Australia, has built a number of boats recently including a Green Island 15, one of my First Mates, and a Water Rat. My good friend Al Burke also built a Water Rat, but used 4mm plywood instead of the 6mm plywood specified. Al applied some strategic stiffening materials and as you can see in the comments, his boat weighed in at 17 kg.

Ross Trinder is now building a second Water Rat, and this time he also is using 4 mm ply. Another variation on the theme being experimented with by Geoff Leedham in his boatbuilding program at a school in Alice Springs, Outback Australia, is to use 4 mm plywood for the entire boat with the exception of the bottom panel, which is made from 6 mm plywood.

This boat is a very simple project which involves very little time and very little money. However, it represents a great way to gain experience in the use of  epoxy and plywood, and the resulting boat is great fun to use, is very stable, and is surprisingly seaworthy in protected waters.

Ross Trinder has asked me whether it would be practical to fit Water Rat with a sailing rig. Given that she is 3 feet wide and carries her breadth out into the bow and the stern, I think that she would be able to carry sail reasonably well, and the only real challenge is to decide how best to give her some lateral plane. My first reaction is to make use of the leeboard, but I'm beginning to think that an off centre dagger board would suit the boat very well. I will be doing some preliminary drawings shortly, and will post them here.

In the meantime, here are some photographs of the early stages of construction of Ross Trinder's 4 mm Water Rat. You can also see Al Burke's finished 4 mm version via the link at the end of the first paragraph.

In this photograph the panels and bulkheads have been cut out accurately, have had holes drilled along the edges of the panels, and the boat assembled using plastic cable ties. After having ensured that there is no twist in the boat, Ross has placed a series of short tabs of thickened epoxy between the cable ties in the forward and middle sections of the boat.

Here you can see how the "tack-welds"of thickened epoxy remain clear of the cable ties, and are very small in cross-section. After the epoxy has cured, the cable ties will be removed and a larger fillets of thickened epoxy will be applied in a continuous run over the top of the "tack-welds" and have glass tapes laid over them while still wet.

Note how the bow and stern transoms, and the bulkheads, have centrelines marked. These are lined up with the centreline on the bottom panel, and as long as there is no twist allowed, the boat must come out the correct shape - even though there is no strong-back or mold.

Here you can get a good idea of the shape of the boat, and as long as the panels are cut out accurately, the shape of the boat is smooth and fair. This particular boat goes together very easily, and it may be possible to get away with as few as half of the cable ties you see in the photo.

Voice recognition software

I am writing this short post in order to test the voice recognition software embedded in Windows 7. It is my hope that I can write posts more frequently in this way and also answer my backlog of emails.

My primary work is boatbuilding and design and I am finding it difficult to keep up with the administrative work which articles, emails, and the blog entail.

At the moment I am teaching the software how to recognise my Australian accent, and it seems to be having great difficulty!

There will soon be posts about a Water Rat being built from 4 mm plywood which is coming along very nicely indeed, and I will be posting some photographs of the Scram Pram which is almost completed. The windows are in and we hope to have the boat in the water within a few weeks for trials.

The voice recognition software seems to be working, but please be tolerant of my mistakes!

Ross Trinder's beautifully built 4mm Water Rat

Scram Pram with her windows dry-fitted, and the decks screwed down on bedding compound

Now, doing all of that with voice-recognition software was VERY time consuming, but stand-by for an improved service!

Whimbrel Developments

My plans for Whimbrel have been sitting 90% finished for a long time. The drawings which have been finished are nicely detailed, and I really like the boat. But for some reason the final step of completing the plans for publication has been very difficult to complete.

Outboard Profile of Whimbrel, showing her with the original balance lug rig and free-standing mast. Note how the heel of the mast has to swing down and up through the foredack. This arrangement is catered for by the installation of a slot-type box - similar to a centreboard case, but upside-down.

Whimbrel was designed with a balance lug mainsail, and to capitalise on some of the advantages of this rig (no headsails, no sail-track or lacing, self-vanging boom, simple and effective reefing) the design was drawn with free-standing masts. An important component of the rig was to be a main-mast set in a tabernacle, so as to allow quick and easy rigging and un-rigging for trailer transport, and for reducing windage when on a mooring in bad weather. You can see the lowered mast position in dotted lines on the drawing above.

Tabernacles can be bulky affairs, and I dislike having a tabernacle which extends a long way above the deck line. However, a free-standing mast benefits from substantial "bury" of the mast within an arrangement of mast step and mast partners, or, as in this case, within a tabernacle. My approach was to have the base of the mast swing up and down through a slot in the foredeck, with sides to the box which extend all the way to the level of the mast step. That way, water can drain down the mast, or come on deck as spray, and it simply runs down to the bottom on the mast case and is then drained over the sides through scuppers - making the mast case self-draining.

The design of the slot and case was fairly straight forward, and I was very pleased with how the structural members support each other and go together in a logical fashion. The trouble is that although the mast case (i.e. a structure similar to an upside-down centreboard case) is simple to construct, it was and is very difficult for me to explain on paper. The drawings of all the components are complete in a 2D form, but I do not have the skills to operate the 3D CAD program I have on hand (TurboCAD 17). I do all of my CAD work in an AutoCAD 2D program (AutoSketch 9).

Several times I've tried to do a simple diagram as an "exploded" isometric drawing, but nothing satisfying has eventuated. I thought that the simplest thing would be to build a prototype, and photograph the case construction in detail, as I was/am sure that as soon as people see it, they will appreciate the simplicity and structural elegance.

In the meantime, one of my sons has been experimenting with a tiny jib (set flying) on a small clinker/lapstrake dinghy he built years ago. The small jib has boosted the windward performance of the boat enormously, even though the sail area of the jib is only 11sq. ft (from memory). This boat sailed quite badly with the free-standing rig as originally built, using a carbon windsurfer mast. The mast was just too soft, even with the addition of substantial alloy sleeve at the lower end.

Here you can see Dave's boat sailing with the original free-standing mast. She had initially sailed with the sail made according to the sail-plan on the plans, but that sail had been awful. Perhaps it would have been ok on a stiffer mast instead of the windsurfer stick. We then changed to an old Laser sail as shown in the pictures, but the mast was still far too soft, and the boat was a very poor performer to windward.

I've told this story before on the blog, but I suggested to Dave that we put some stays on the rig, with the point of attachment (hounds) being just a fraction over halfway up from the deck to the masthead. He was reluctant, but I eventually convinced him to give it a go and we made up a forestay and two shrouds using Dyneema/Spectra. This also allowed us to set an old jib, as a "flying jib" i.e. a jib with is not attached to the forestay with hanks.

The performance of the boat was dramatically transformed for the better, and the boat is giving great service.

My point in re-telling parts of the rig story is to illustrate that sometimes a very modest increase in complication can result in huge gains in performance. Now, back to Whimbrel....

The revelations about performance brought about by the addition of the jib to Dave's boat got me thinking a little outside the box I normally occupy. I tend to be a bit obsessive when it come to rig simplicity, because I hate clutter in a boat when rigging and un-rigging at the boat ramp. Our experiments with the dinghy rig above have brought me to the point where I'm considering some different rigging arrangements for Whimbrel, and the design evolution continues - perhaps it was fortunate that I hung off from completing the original drawings.

In the above drawing you can see the proposed new rig for Whimbrel. The hull is unchanged, as is the mizzen, but the main part of the rig is now a lightly stayed, gaff-headed mainsail with a staysail set on the forestay. The staysail can either be hanked onto the forestay, or could be permanently attached to the forestay with a simple roller-furling tackle set at the tack.

Because the mainmast is now supported by stays in the form of a forestay and two shrouds, the mast no longer requires the support of a tabernacle which runs deeply into the hull. In this case the tabernacle is short and extends only to the level of the deck, and the foredeck is no longer cut up by a mast case and slot. So the mast is significantly shorter at the foot, and the diameter of the mast is reduced from 92mm (3-5/8") to 65mm (2-9/16").

Whimbrel set up for the night with a boom tent rigged and the mizzen sheeted flat to hold he head -to-wind.  I can't see the anchor rode - it must be some of that invisible rope I sometimes use!

I'm continuing to consider some options for the cockpit, and will up-date soon.

Current jobs in the workshop include a Jim Michalak-designed Scram Pram I'm finishing off for a customer who has done a lot of work on the job already, but whose work commitments have prevented him from carrying out the final few jobs. See my previous post for photos. I have to say that this boat is very exciting and I look forward to the test sailing so that I can gain first-hand experience of the "Bird Watcher"concept.

Ian Hamilton's First Mate is nearing completion finally. The interior has been painted using a water-reducible linear polyurethane paint, and despite the difficulty in applying this sort of paint in very hot conditions (over the last month or so, the temperature inside my shed during the day has reached 43C/109.4F on many occasions), the end result has been very satisfactory. Properly applied, the paint ends up being as tough as the conventional two-pack polyurethanes, but has a pleasing subdued gloss which is appropriate for wooden boats, and the paint can be applied with much less concern about the dangers of VOCs (Volitile Organic Compounds). Brushes wash out in water, and as they say, you can drink the thinners (water!). I've used this sort of paint on many occasions in the past, and I can tell you that it is not easy to apply unless the conditions are perfect. However, if you follow the manufacturer's instructions to the letter, the end result is worth the effort.

Three Brothers. Ian's version will have the layout shown in the upper profile

As soon as either the Scram Pram or the First Mate has left the workshop, I'll be making a start on Three Brothers - this is also for Ian Hamilton. It is Ian's intention to use this boat on an extended journey along the Kimberley coast of Western Australia.

The intention with Three Brothers is to produce a boat which is simple and quick to build using the 'stitch-and-glue' construction method, and which will operate effectively in the semi-displacement mode. My aim was to get efficient running at a speed/length ratio of 2.2 which in the case of this boat means 10.5 knots or 12.1 mph. According to my calculations, with a reasonable load, this speed could be achieved with 15.6hp.

My performance predictions with 288kg (634lbs) passenger weight and 85kg (187lbs) for engine and fuel are as follows: -

·         Assume displacement of 820kg (1804 lbs) NOTE: This is for the performance calculations only. Displacement as shown in the drawings is 1191kg (2620 lbs) so the boat is capable of carrying significantly more than the 288kg (634lb) passenger load.

·         Salt water
·         LWL 22.6 ft
·         Power to achieve 10kts                                                           -           13.9hp
·         Power to achieve optimum SL ratio 2.2                              -           15.6hp
·         Speed with 30hp (Crouch’s Planing Speed Formula)             -           19.3kts
·         Speed with 40hp (Crouch’s Planing Speed Formula)             -           22.3kts
·         Speed with 50hp (Crouch’s Planing Speed Formula)             -           25kts

My choice of motor would be either:

·         18hp four-cycle outboard, giving a full-throttle fuel consumption of approximately 5.7 lt/hr (1.5 gal/hr);

·         30hp four-cycle outboard, giving a full-throttle fuel consumption of approximately 9.8 lt/hr (2.6 gal/hr);

·         30hp two-cycle outboard, giving a full-throttle fuel consumption of approximately 13.0 lt/hr ( 3.4 gal/hr), but with a weight and cost advantage.

      Due to the initial load that Ian thinks he will have to carry, he intends equipping his boat with a 50hp outboard, although this is still open to discussion.

      The construction of  Three Brothers will take place over about two years, as Ian needs to earn money to feed into the project, and I will only be able to devote a limited number of hours eack week due to other jobs.

      In addition to the building jobs mentioned, I have another First Mate to finish off, and three sets of plans to complete for publication.  The First Mate has been brought to a structurally complete hull stage by her owner, but changes to his work space mean that he must reluctantly pass the boat on to me for completion. However, he will do some work on her whenever he is able to get to my place.

      Plans for Whimbrel, Little Egret, and Fleet are all very close to publication stage, and in fact boats could be build using what is already available. However, I need to finish off some detail drawings and instructions before letting them loose.

Whimbrel

      

Little Egret

Fleet

     More information soon.

Workshop News

It is about time I said a little bit about what is going on in the workshop. Being a one-man-band is very satisfying, but it means that just a few concurrent jobs take up all of my time. I like writing and designing, but at the moment I'm definitely burning the candle at both ends!

Annapolis Wherry Tandem

In late 2012 I reported on the construction of a CLC Annapolis Wherry Tandem in this post  and showed some photos of the finished boat in this one. After completion the Annapolis Wherry Tandem sat for a number of months under shelter beside my workshop because the owner was overseas doing post-graduate studies. 

Well, the day finally came for a test row and the boat went very well indeed. The only problem was a slight bow-down trim, but that was sorted out on the second outing, and turned out to have simply been caused by having the foot stretcher set too far forward. With that adjusted the trim is now perfect. The following photos were taken on the initial outing, so you may just detect the trim I mentioned. Despite that the boat went fine, and on the second outing a few weeks later she was perfect.

That is the owner, Dr McArthur, looking on as I make preparations for the initial launching.  Dr McArthur is a very experienced oarsman, having rowed for 55 years of his long life.

Just getting the feel of the boat about two minutes after the launching.  You can see how we have the excellent  Piantedosi Row Wing adjusted for a "left-over-right" rigging.

A "turtle's eye view" as Dr McArthur  becomes more familiar with the boat. 

Even though we had the foot stretcher too far forward, the boat is still trimmed  reasonably, and she certainly ran nicely, with excellent directional stability.

The boat proved to be stable and fast. Subsequent outings have been  longer, and we've  explored more of the performance envelope. She is a practical and enjoyable package.

Jim Michalak Scram Pram

In this post I mentioned that I had been given the job of finishing off the construction of a Jim Michalak Scram Pram. 

My part in the project is nearing completion, with just some detail work around the hull, initial coating work on the spars, and setting up the running rigging and sail to go. The owner will pick-up the boat and do the remainder of the painting and varnishing. However, I hope that he and I will be able to fit in a day or two of sea-trials prior to her departure (by road) for her home waters. Here are just a few pictures: -

View from the helmsman's position, port side, looking forward. You can see what an enormously roomy vessel she is for a light fifteen footer. It is easy to see that if the boat suffered a knock-down, the windows (not yet installed) and the raised deck on either side of the centre walkway would keep the boat dry and buoyant.

Forward/port window dry-installed with Pencil Cedar surrounds.  Window and internal framing held in with silicon bronze screws throughout. See the aft/port window loosely fitted and waiting for the surrounds to be fabricated.

Close-up of internal framing showing how I have stamped markings at the top/right to identify the components after disassembly. The window installation was a much more difficult and time-consuming process that I had anticipated, as each window is  slightly different from its fellows, and there were a number of lurking "tricks for young players".

Windows from the outside. The protective film and paper will be left in place as long as possible. Fore and aft decks will be screwed down onto flexible bedding compount to allow future removal for maintenance. When I did it, it took 93  #8 x 1-1/4" silicon bronze screws! However, it is a very good idea.

Filling/draining bungs for the three water ballast tanks were sourced from Duckworks. They come as a brass tube (see longest tube in the photo) and an expanding rubber or plastic plug. When the lever is pushed down the plug expands and grips the inside of the tube. My problem was that the bottom of the boat is only 9mm/3/8" thick and the tube would protrude. I worked out the shortest length that the tube could be and still allow the plug a full-depth grip, and cut the tube (see cut tube in foreground). I then fabricated some blocks so that the tube protruded only 9mm/3/8" below the block. When set in the tanks on the bottom of the hull, the brass tube and plug fit neatly without extending past the outer surface of the hull. Note how I cut holes in the blocks and the brass tube to allow water to drain right down to the bottom of the tank.

Bung set into the bottom of the tank, positioned below the inspection port to allow opening and closing.  The block was very thoroughly sealed with about four full coats of epoxy prior to installation, and the tube and block were set in polyurethane bedding compound during installation. This was done so that the expansion and contraction of the brass would be taken up by the bedding compound - an epoxy joint would surely show hair-line cracks before long.

Mast partner is held to the forward bulkhead by four 5/16" bolts - two of them are silicon bronze and two (which you can see) extend through the aft face of the partner and act also as attachment and pivot for the mast gate, which I made from 8mm alloy plate. These two bolts are from 316 stainless steel, and if I can locate the required plate, I may replace the alloy with 316 stainless.

1-1/2" thick laminated mast step sitting upside-down on the bench prior to installation in the hull. Note the groove to act as a drain to prevent water accumulating in the step, and also the very thorough sealing of the internal surfaces with epoxy. This was done ahead of installation because access is difficult after. The rounded-over edge at the rear of the step (as it sits in the photo) is to allow it to sit neatly against the glass fillet between the forward bulkhead and the floor of the cabin (which is also the top of one of the water-ballast tanks).

More about jobs, both in the workshop and coming up, and also some progress reports on stock designs such as Whimbrel and Fleet in a day or so. I need to go to bed!